Science.gov

Sample records for noise reduction efforts

  1. Preliminary noise reduction efforts in a medical intensive care unit.

    PubMed

    Nannapaneni, Srikant; Lee, Sarah J; Kashiouris, Markos; Elmer, Jennifer L; Thakur, Lokendra K; Nelson, Sarah B; Bowron, Catherine T; Danielson, Richard D; Surani, Salim; Ramar, Kannan

    2015-01-01

    Noise is a significant contributor to sleep disruption in the intensive care unit (ICU) that may result in increased patient morbidity such as delirium and prolonged length of stay in ICU. We conducted a pre-post intervention study in a 24-bed tertiary care academic medical ICU to reduce the mean noise levels. Baseline dosimeter recordings of ICU noise levels demonstrated a mean noise level of 54.2 A-weighted decibels (dBA) and peak noise levels of 109.9 dBA, well above the Environmental Protection Agency's recommended levels. There were 1735 episodes of "defects" (maximum noise levels > 60 dBA). Following implementation of multipronged interventions, although the mean noise levels did not change significantly between pre- and post-intervention (54.2 vs 53.8 dBA; p = 0.96), there was a significant reduction in the number of "defects" post-intervention (1735 vs 1289, p ≤ 0.000), and the providers felt that the patients were sleeping longer in the ICU post-intervention.

  2. Objective Measures of Listening Effort: Effects of Background Noise and Noise Reduction

    ERIC Educational Resources Information Center

    Sarampalis, Anastasios; Kalluri, Sridhar; Edwards, Brent; Hafter, Ervin

    2009-01-01

    Purpose: This work is aimed at addressing a seeming contradiction related to the use of noise-reduction (NR) algorithms in hearing aids. The problem is that although some listeners claim a subjective improvement from NR, it has not been shown to improve speech intelligibility, often even making it worse. Method: To address this, the hypothesis…

  3. Objective Measures of Listening Effort: Effects of Background Noise and Noise Reduction

    ERIC Educational Resources Information Center

    Sarampalis, Anastasios; Kalluri, Sridhar; Edwards, Brent; Hafter, Ervin

    2009-01-01

    Purpose: This work is aimed at addressing a seeming contradiction related to the use of noise-reduction (NR) algorithms in hearing aids. The problem is that although some listeners claim a subjective improvement from NR, it has not been shown to improve speech intelligibility, often even making it worse. Method: To address this, the hypothesis…

  4. Listening effort and perceived clarity for normal hearing children with the use of digital noise reduction

    PubMed Central

    Gustafson, Samantha; McCreery, Ryan; Hoover, Brenda; Kopun, Judy G; Stelmachowicz, Pat

    2013-01-01

    Objectives The goal of this study was to evaluate how digital noise reduction (DNR) impacts listening effort and judgment of sound clarity in children with normal hearing. It was hypothesized that, when two DNR algorithms differing in signal-to-noise ratio (SNR) output are compared, the algorithm which provides the greatest improvement in overall output SNR will reduce listening effort and receive a better clarity rating from child listeners. A secondary goal was to evaluate the relation between the inversion method measurements and listening effort with DNR processing. Design Twenty-four children with normal hearing (ages 7-12 years) participated in a speech recognition task in which consonant-vowel-consonant nonwords were presented in broadband background noise. Test stimuli were recorded through two hearing aids with DNR-off and DNR-on at 0 dB and +5 dB input SNR. Stimuli were presented to listeners and verbal response time (VRT) and phoneme recognition scores were measured. The underlying assumption was that an increase in VRT reflects an in increase in listening effort. Children rated the sound clarity for each condition. The two commercially available HAs were chosen based on: 1) an inversion technique which was used to quantify the magnitude of change in SNR with the activation of DNR, and 2) a measure of magnitude-squared coherence which was used to ensure that DNR in both devices preserved the spectrum. Results One device provided a greater improvement in overall output SNR than the other. Both DNR algorithms resulted in minimal spectral distortion as measured using coherence. For both devices, VRT decreased for the DNR-on condition suggesting that listening effort decreased with DNR in both devices. Clarity ratings were also better in the DNR-on condition for both devices. The device showing the greatest improvement in output SNR with DNR engaged improved phoneme recognition scores. The magnitude of this improved phoneme recognition was not accurately

  5. Effects of noise reduction on speech intelligibility, perceived listening effort, and personal preference in hearing-impaired listeners.

    PubMed

    Brons, Inge; Houben, Rolph; Dreschler, Wouter A

    2014-10-13

    This study evaluates the perceptual effects of single-microphone noise reduction in hearing aids. Twenty subjects with moderate sensorineural hearing loss listened to speech in babble noise processed via noise reduction from three different linearly fitted hearing aids. Subjects performed (a) speech-intelligibility tests, (b) listening-effort ratings, and (c) paired-comparison ratings on noise annoyance, speech naturalness, and overall preference. The perceptual effects of noise reduction differ between hearing aids. The results agree well with those of normal-hearing listeners in a previous study. None of the noise-reduction algorithms improved speech intelligibility, but all reduced the annoyance of noise. The noise reduction that scored best with respect to noise annoyance and preference had the worst intelligibility scores. The trade-off between intelligibility and listening comfort shows that preference measurements might be useful in addition to intelligibility measurements in the selection of noise reduction. Additionally, this trade-off should be taken into consideration to create realistic expectations in hearing-aid users.

  6. The Effects of Hearing Aid Directional Microphone and Noise Reduction Processing on Listening Effort in Older Adults with Hearing Loss.

    PubMed

    Desjardins, Jamie L

    2016-01-01

    Older listeners with hearing loss may exert more cognitive resources to maintain a level of listening performance similar to that of younger listeners with normal hearing. Unfortunately, this increase in cognitive load, which is often conceptualized as increased listening effort, may come at the cost of cognitive processing resources that might otherwise be available for other tasks. The purpose of this study was to evaluate the independent and combined effects of a hearing aid directional microphone and a noise reduction (NR) algorithm on reducing the listening effort older listeners with hearing loss expend on a speech-in-noise task. Participants were fitted with study worn commercially available behind-the-ear hearing aids. Listening effort on a sentence recognition in noise task was measured using an objective auditory-visual dual-task paradigm. The primary task required participants to repeat sentences presented in quiet and in a four-talker babble. The secondary task was a digital visual pursuit rotor-tracking test, for which participants were instructed to use a computer mouse to track a moving target around an ellipse that was displayed on a computer screen. Each of the two tasks was presented separately and concurrently at a fixed overall speech recognition performance level of 50% correct with and without the directional microphone and/or the NR algorithm activated in the hearing aids. In addition, participants reported how effortful it was to listen to the sentences in quiet and in background noise in the different hearing aid listening conditions. Fifteen older listeners with mild sloping to severe sensorineural hearing loss participated in this study. Listening effort in background noise was significantly reduced with the directional microphones activated in the hearing aids. However, there was no significant change in listening effort with the hearing aid NR algorithm compared to no noise processing. Correlation analysis between objective and self

  7. Core Noise Reduction

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.

    2011-01-01

    This presentation is a technical summary of and outlook for NASA-internal and NASA-sponsored external research on core (combustor and turbine) noise funded by the Fundamental Aeronautics Program Subsonic Fixed Wing (SFW) Project. Sections of the presentation cover: the SFW system-level noise metrics for the 2015, 2020, and 2025 timeframes; turbofan design trends and their aeroacoustic implications; the emerging importance of core noise and its relevance to the SFW Reduce-Perceived-Noise Technical Challenge; and the current research activities in the core noise area. Recent work1 on the turbine-transmission loss of combustor noise is briefly described, two2,3 new NRA efforts in the core-noise area are outlined, and an effort to develop CMC-based acoustic liners for broadband noise reduction suitable for turbofan-core application is delineated. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The reduction of aircraft noise is critical to enabling the anticipated large increase in future air traffic. The Subsonic Fixed Wing Project's Reduce-Perceived-Noise Technical Challenge aims to develop concepts and technologies to dramatically reduce the perceived aircraft noise outside of airport boundaries.

  8. Listening effort and perceived clarity for normal-hearing children with the use of digital noise reduction.

    PubMed

    Gustafson, Samantha; McCreery, Ryan; Hoover, Brenda; Kopun, Judy G; Stelmachowicz, Pat

    2014-01-01

    The goal of this study was to evaluate how digital noise reduction (DNR) impacts listening effort and judgment of sound clarity in children with normal hearing. It was hypothesized that when two DNR algorithms differing in signal-to-noise ratio (SNR) output are compared, the algorithm that provides the greatest improvement in overall output SNR will reduce listening effort and receive a better clarity rating from child listeners. A secondary goal was to evaluate the relation between the inversion method measurements and listening effort with DNR processing. Twenty-four children with normal hearing (ages 7 to 12 years) participated in a speech recognition task in which consonant-vowel-consonant nonwords were presented in broadband background noise. Test stimuli were recorded through two hearing aids with DNR off and DNR on at 0 dB and +5 dB input SNR. Stimuli were presented to listeners and verbal response time (VRT) and phoneme recognition scores were measured. The underlying assumption was that an increase in VRT reflects an increase in listening effort. Children rated the sound clarity for each condition. The two commercially available HAs were chosen based on: (1) an inversion technique, which was used to quantify the magnitude of change in SNR with the activation of DNR, and (2) a measure of magnitude-squared coherence, which was used to ensure that DNR in both devices preserved the spectrum. One device provided a greater improvement in overall output SNR than the other. Both DNR algorithms resulted in minimal spectral distortion as measured using coherence. For both devices, VRT decreased for the DNR-on condition, suggesting that listening effort decreased with DNR in both devices. Clarity ratings were also better in the DNR-on condition for both devices. The device showing the greatest improvement in output SNR with DNR engaged improved phoneme recognition scores. The magnitude of this improved phoneme recognition was not accurately predicted with

  9. Emerging Community Noise Reduction Approaches

    NASA Technical Reports Server (NTRS)

    Envia, Edmane

    2012-01-01

    An overview of the current NASA research portfolio in the area of aircraft noise reduction is presented. The emphasis of the research described herein is on meeting the aggressive near- and mid-term national goals for reducing aircraft noise emissions, which NASA internal studies have shown to be feasible using noise reduction technologies currently being developed in-house or in partnership with NASA s industry and academic partners. While NASA has an active research effort in airframe noise reduction, this overview focuses on propulsion noise reduction only.

  10. Television noise reduction device

    NASA Technical Reports Server (NTRS)

    Gordon, B. L.; Stamps, J. C. (Inventor)

    1975-01-01

    A noise reduction system that divides the color video signal into its luminance and chrominance components is reported. The luminance component of a given frame is summed with the luminance component of at least one preceding frame which was stored on a disc recorder. The summation is carried out so as to achieve a signal amplitude equivalent to that of the original signal. The averaged luminance signal is then recombined with the chrominance signal to achieve a noise-reduced television signal.

  11. Cochlear implant optimized noise reduction

    NASA Astrophysics Data System (ADS)

    Mauger, Stefan J.; Arora, Komal; Dawson, Pam W.

    2012-12-01

    Noise-reduction methods have provided significant improvements in speech perception for cochlear implant recipients, where only quality improvements have been found in hearing aid recipients. Recent psychoacoustic studies have suggested changes to noise-reduction techniques specifically for cochlear implants, due to differences between hearing aid recipient and cochlear implant recipient hearing. An optimized noise-reduction method was developed with significantly increased temporal smoothing of the signal-to-noise ratio estimate and a more aggressive gain function compared to current noise-reduction methods. This optimized noise-reduction algorithm was tested with 12 cochlear implant recipients over four test sessions. Speech perception was assessed through speech in noise tests with three noise types; speech-weighted noise, 20-talker babble and 4-talker babble. A significant speech perception improvement using optimized noise reduction over standard processing was found in babble noise and speech-weighted noise and over a current noise-reduction method in speech-weighted noise. Speech perception in quiet was not degraded. Listening quality testing for noise annoyance and overall preference found significant improvements over the standard processing and over a current noise-reduction method in speech-weighted and babble noise types. This optimized method has shown significant speech perception and quality improvements compared to the standard processing and a current noise-reduction method.

  12. Cochlear implant optimized noise reduction.

    PubMed

    Mauger, Stefan J; Arora, Komal; Dawson, Pam W

    2012-12-01

    Noise-reduction methods have provided significant improvements in speech perception for cochlear implant recipients, where only quality improvements have been found in hearing aid recipients. Recent psychoacoustic studies have suggested changes to noise-reduction techniques specifically for cochlear implants, due to differences between hearing aid recipient and cochlear implant recipient hearing. An optimized noise-reduction method was developed with significantly increased temporal smoothing of the signal-to-noise ratio estimate and a more aggressive gain function compared to current noise-reduction methods. This optimized noise-reduction algorithm was tested with 12 cochlear implant recipients over four test sessions. Speech perception was assessed through speech in noise tests with three noise types; speech-weighted noise, 20-talker babble and 4-talker babble. A significant speech perception improvement using optimized noise reduction over standard processing was found in babble noise and speech-weighted noise and over a current noise-reduction method in speech-weighted noise. Speech perception in quiet was not degraded. Listening quality testing for noise annoyance and overall preference found significant improvements over the standard processing and over a current noise-reduction method in speech-weighted and babble noise types. This optimized method has shown significant speech perception and quality improvements compared to the standard processing and a current noise-reduction method.

  13. Reduction of turbomachinery noise

    NASA Technical Reports Server (NTRS)

    Waitz, Ian A. (Inventor); Brookfield, John M. (Inventor); Sell, Julian (Inventor); Hayden, Belva J. (Inventor); Ingard, K. Uno (Inventor)

    1999-01-01

    In the invention, propagating broad band and tonal acoustic components of noise characteristic of interaction of a turbomachine blade wake, produced by a turbomachine blade as the blade rotates, with a turbomachine component downstream of the rotating blade, are reduced. This is accomplished by injection of fluid into the blade wake through a port in the rotor blade. The mass flow rate of the fluid injected into the blade wake is selected to reduce the momentum deficit of the wake to correspondingly increase the time-mean velocity of the wake and decrease the turbulent velocity fluctuations of the wake. With this fluid injection, reduction of both propagating broad band and tonal acoustic components of noise produced by interaction of the blade wake with a turbomachine component downstream of the rotating blade is achieved. In a further noise reduction technique, boundary layer fluid is suctioned into the turbomachine blade through a suction port on the side of the blade that is characterized as the relatively low-pressure blade side. As with the fluid injection technique, the mass flow rate of the fluid suctioned into the blade is here selected to reduce the momentum deficit of the wake to correspondingly increase the time-mean velocity of the wake and decrease the turbulent velocity fluctuations of the wake; reduction of both propagating broad band and tonal acoustic components of noise produced by interaction of the blade wake with a turbomachine component downstream of the rotating blade is achieved with this suction technique. Blowing and suction techniques are also provided in the invention for reducing noise associated with the wake produced by fluid flow around a stationary blade upstream of a rotating turbomachine.

  14. Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Kenny, Patrick

    2004-01-01

    The Acoustics Branch is responsible for reducing noise levels for jet and fan components on aircraft engines. To do this, data must be measured and calibrated accurately to ensure validity of test results. This noise reduction is accomplished by modifications to hardware such as jet nozzles, and by the use of other experimental hardware such as fluidic chevrons, elliptic cores, and fluidic shields. To insure validity of data calibration, a variety of software is used. This software adjusts the sound amplitude and frequency to be consistent with data taken on another day. Both the software and the hardware help make noise reduction possible. work properly. These software programs were designed to make corrections for atmosphere, shear, attenuation, electronic, and background noise. All data can be converted to a one-foot lossless condition, using the proper software corrections, making a reading independent of weather and distance. Also, data can be transformed from model scale to full scale for noise predictions of a real flight. Other programs included calculations of Over All Sound Pressure Level (OASPL), Effective Perceived Noise Level (EPNL). OASPL is the integration of sound with respect to frequency, and EPNL is weighted for a human s response to different sound frequencies and integrated with respect to time. With the proper software correction, data taken in the NATR are useful in determining ways to reduce noise. display any difference between two or more data files. Using this program and graphs of the data, the actual and predicted data can be compared. This software was tested on data collected at the Aero Acoustic Propulsion Laboratory (AAPL) using a variety of window types and overlaps. Similarly, short scripts were written to test each individual program in the software suite for verification. Each graph displays both the original points and the adjusted points connected with lines. During this summer, data points were taken during a live experiment

  15. Active noise reduction

    NASA Astrophysics Data System (ADS)

    Geyer, Carolyn R.

    Active noise reduction (ANR) techniques are described with reference to their application to crewmembers during aircraft operation to enhance productivity and safety. ANR concepts and theory are explained, and the development of protective ANR systems for direct implementation are described. Sound attenuation testing was conducted to study the feasibility of aircraft-powered ANR systems, and the positive results spurred their development for compatibility with flight helmets. The Helmets Limited ANR system uses a bypass mode at times of limited available power and complements the use of passive sound attenuation. Subjective testing results show that the device is effective, and a planned program of intensive evaluation is discussed. The aircraft that require an ANR system are listed, and key areas of implementation include battery power and the combination of ANR circuitry and helmet oxygen masks. It is suggested that ANR techniques can positively impact the efficiency and performance of crewmembers in high-noise-level aircraft.

  16. NASA's Subsonic Jet Transport Noise Reduction Research

    NASA Technical Reports Server (NTRS)

    Powell, Clemans A.; Preisser, John S.

    2000-01-01

    Although new jet transport airplanes in today s fleet are considerably quieter than the first jet transports introduced about 40 years ago, airport community noise continues to be an important environmental issue. NASA s Advanced Subsonic Transport (AST) Noise Reduction program was begun in 1994 as a seven-year effort to develop technology to reduce jet transport noise 10 dB relative to 1992 technology. This program provides for reductions in engine source noise, improvements in nacelle acoustic treatments, reductions in the noise generated by the airframe, and improvements in the way airplanes are operated in the airport environs. These noise reduction efforts will terminate at the end of 2001 and it appears that the objective will be met. However, because of an anticipated 3-8% growth in passenger and cargo operations well into the 21st Century and the slow introduction of new the noise reduction technology into the fleet, world aircraft noise impact will remain essentially constant until about 2020 to 2030 and thereafter begin to rise. Therefore NASA has begun planning with the Federal Aviation Administration, industry, universities and environmental interest groups in the USA for a new noise reduction initiative to provide technology for significant further reductions.

  17. Aircraft Noise Reduction Subproject Overview

    NASA Technical Reports Server (NTRS)

    Fernandez, Hamilton; Nark, Douglas M.; Van Zante, Dale E.

    2016-01-01

    The material presents highlights of propulsion and airframe noise research being completed for the Advanced Air Transport Technology Project. The basis of noise reduction plans along with representative work for the airframe, propulsion, and propulsion-airframe integration is discussed for the Aircraft Noise reduction Subproject.

  18. Fan Noise Reduction: An Overview

    NASA Technical Reports Server (NTRS)

    Envia, Edmane

    2001-01-01

    Fan noise reduction technologies developed as part of the engine noise reduction element of the Advanced Subsonic Technology Program are reviewed. Developments in low-noise fan stage design, swept and leaned outlet guide vanes, active noise control, fan flow management, and scarfed inlet are discussed. In each case, a description of the method is presented and, where available, representative results and general conclusions are discussed. The review concludes with a summary of the accomplishments of the AST-sponsored fan noise reduction research and a few thoughts on future work.

  19. Noise Reduction Techniques

    NASA Astrophysics Data System (ADS)

    Hallas, Tony

    There are two distinct kinds of noise - structural and color. Each requires a specific method of attack to minimize. The great challenge is to reduce the noise without reducing the faint and delicate detail in the image. My most-used and favorite noise suppression is found in Photoshop CS 5 Camera Raw. If I cannot get the desired results with the first choice, I will use Noise Ninja, which has certain advantages in some situations that we will cover.

  20. Technologies for Turbofan Noise Reduction

    NASA Technical Reports Server (NTRS)

    Huff, Dennis

    2005-01-01

    An overview presentation of NASA's engine noise research since 1992 is given for subsonic commercial aircraft applications. Highlights are included from the Advanced Subsonic Technology (AST) Noise Reduction Program and the Quiet Aircraft Technology (QAT) project with emphasis on engine source noise reduction. Noise reduction goals for 10 EPNdB by 207 and 20 EPNdB by 2022 are reviewed. Fan and jet noise technologies are highlighted from the AST program including higher bypass ratio propulsion, scarf inlets, forward-swept fans, swept/leaned stators, chevron nozzles, noise prediction methods, and active noise control for fans. Source diagnostic tests for fans and jets that have been completed over the past few years are presented showing how new flow measurement methods such as Particle Image Velocimetry (PIV) have played a key role in understanding turbulence, the noise generation process, and how to improve noise prediction methods. Tests focused on source decomposition have helped identify which engine components need further noise reduction. The role of Computational AeroAcoustics (CAA) for fan noise prediction is presented. Advanced noise reduction methods such as Hershel-Quincke tubes and trailing edge blowing for fan noise that are currently being pursued n the QAT program are also presented. Highlights are shown form engine validation and flight demonstrations that were done in the late 1990's with Pratt & Whitney on their PW4098 engine and Honeywell on their TFE-731-60 engine. Finally, future propulsion configurations currently being studied that show promise towards meeting NASA's long term goal of 20 dB noise reduction are shown including a Dual Fan Engine concept on a Blended Wing Body aircraft.

  1. Noise Reduction by Signal Accumulation

    ERIC Educational Resources Information Center

    Kraftmakher, Yaakov

    2006-01-01

    The aim of this paper is to show how the noise reduction by signal accumulation can be accomplished with a data acquisition system. This topic can be used for student projects. In many cases, the noise reduction is an unavoidable part of experimentation. Several techniques are known for this purpose, and among them the signal accumulation is the…

  2. Noise Reduction by Signal Accumulation

    ERIC Educational Resources Information Center

    Kraftmakher, Yaakov

    2006-01-01

    The aim of this paper is to show how the noise reduction by signal accumulation can be accomplished with a data acquisition system. This topic can be used for student projects. In many cases, the noise reduction is an unavoidable part of experimentation. Several techniques are known for this purpose, and among them the signal accumulation is the…

  3. Technologies for Aircraft Noise Reduction

    NASA Technical Reports Server (NTRS)

    Huff, Dennis L.

    2006-01-01

    Technologies for aircraft noise reduction have been developed by NASA over the past 15 years through the Advanced Subsonic Technology (AST) Noise Reduction Program and the Quiet Aircraft Technology (QAT) project. This presentation summarizes highlights from these programs and anticipated noise reduction benefits for communities surrounding airports. Historical progress in noise reduction and technologies available for future aircraft/engine development are identified. Technologies address aircraft/engine components including fans, exhaust nozzles, landing gear, and flap systems. New "chevron" nozzles have been developed and implemented on several aircraft in production today that provide significant jet noise reduction. New engines using Ultra-High Bypass (UHB) ratios are projected to provide about 10 EPNdB (Effective Perceived Noise Level in decibels) engine noise reduction relative to the average fleet that was flying in 1997. Audio files are embedded in the presentation that estimate the sound levels for a 35,000 pound thrust engine for takeoff and approach power conditions. The predictions are based on actual model scale data that was obtained by NASA. Finally, conceptual pictures are shown that look toward future aircraft/propulsion systems that might be used to obtain further noise reduction.

  4. The Airframe Noise Reduction Challenge

    NASA Technical Reports Server (NTRS)

    Lockard, David P.; Lilley, Geoffrey M.

    2004-01-01

    The NASA goal of reducing external aircraft noise by 10 dB in the near-term presents the acoustics community with an enormous challenge. This report identifies technologies with the greatest potential to reduce airframe noise. Acoustic and aerodynamic effects will be discussed, along with the likelihood of industry accepting and implementing the different technologies. We investigate the lower bound, defined as noise generated by an aircraft modified with a virtual retrofit capable of eliminating all noise associated with the high lift system and landing gear. However, the airframe noise of an aircraft in this 'clean' configuration would only be about 8 dB quieter on approach than current civil transports. To achieve the NASA goal of 10 dB noise reduction will require that additional noise sources be addressed. Research shows that energy in the turbulent boundary layer of a wing is scattered as it crosses trailing edge. Noise generated by scattering is the dominant noise mechanism on an aircraft flying in the clean configuration. Eliminating scattering would require changes to much of the aircraft, and practical reduction devices have yet to receive serious attention. Evidence suggests that to meet NASA goals in civil aviation noise reduction, we need to employ emerging technologies and improve landing procedures; modified landing patterns and zoning restrictions could help alleviate aircraft noise in communities close to airports.

  5. Video noise reduction

    NASA Astrophysics Data System (ADS)

    Drewery, J. O.; Storey, R.; Tanton, N. E.

    1984-07-01

    A video noise and film grain reducer is described which is based on a first-order recursive temporal filter. Filtering of moving detail is avoided by inhibiting recursion in response to the amount of motion in a picture. Motion detection is based on the point-by-point power of the picture difference signal coupled with a knowledge of the noise statistics. A control system measures the noise power and adjusts the working point of the motion detector accordingly. A field trial of a manual version of the equipment at Television Center indicated that a worthwhile improvement in the quality of noisy or grainy pictures received by the viewer could be obtained. Subsequent trials of the automated version confirmed that the improvement could be maintained. Commercial equipment based on the design is being manufactured and marketed by Pye T.V.T. under license. It is in regular use on both the BBC1 and BBC2 networks.

  6. Noise reduction for vocal pathologies.

    PubMed

    Matassini, L; Manfredi, C

    2002-01-01

    A noise reduction scheme, particularly suited for the correction of vocal pathologies, is proposed. The filter makes use of concepts originated within the theory of dynamical systems and deterministic chaos. In particular, the idea of embedding scalar data in order to reconstruct a phase space is of fundamental importance here. Furthermore, the concept of an attractor as a result of dynamical constraints is exploited. In order to perform noise reduction one needs redundancy and the human voice provides it even within a phoneme, namely the smallest structural unit of speech. Due to several repetitions of a pattern called pitch inside a phoneme, separation between the pure voice signal and the noise is possible, provided the latter is uncorrelated with the former. With a proper parameter tuning, different kinds of noise can be removed. We describe the idea behind the noise reduction algorithm and present applications to vocal pathologies.

  7. Jet Engine Noise Reduction

    DTIC Science & Technology

    2009-04-01

    factors include: – Maceration of the thin skin of the ear canal leading to pain/and or infection. – Ear canal infection (external otitis ...145 – 150 dB) around jet aircraft. The magnitude and impact of noise transmitted via bone and other media such as fluid is largely unknown. The ear

  8. Noise reduction experience at Hughes Helicopter, Inc.

    NASA Technical Reports Server (NTRS)

    Janakiram, D. S.

    1982-01-01

    Noise reduction is mostly limited to light helicopters whose noise signature is dominated by their tail rotors. It is primarily hardware oriented. Well known noise reduction techniques such as reduction of rotor speeds with an accompanying increase in solidity to maintain performance, engine noise reduction with the use of exhaust mufflers, and acoustic blanketing of transmission and engine compartment are used. The concept of blade phasing as a means of reducing tail rotor noise is also used. Engine noise (exhaust noise), power train noise and airframe noise becomes important at low rotor tip speeds and means must be found to reduce these noise sources if further noise reductions are desired. The use of a special test rig aids in isolating the various noise sources and arriving at the penalties (performance or payload) involved in quieting them. Significant noise reduction are achieved for the light helicopter with minimum performance or weight penalties because of the dominance of a single noise source (the tail rotor).

  9. Noise reduction experience at Hughes Helicopter, Inc.

    NASA Technical Reports Server (NTRS)

    Janakiram, D. S.

    1982-01-01

    Noise reduction is mostly limited to light helicopters whose noise signature is dominated by their tail rotors. It is primarily hardware oriented. Well known noise reduction techniques such as reduction of rotor speeds with an accompanying increase in solidity to maintain performance, engine noise reduction with the use of exhaust mufflers, and acoustic blanketing of transmission and engine compartment are used. The concept of blade phasing as a means of reducing tail rotor noise is also used. Engine noise (exhaust noise), power train noise and airframe noise becomes important at low rotor tip speeds and means must be found to reduce these noise sources if further noise reductions are desired. The use of a special test rig aids in isolating the various noise sources and arriving at the penalties (performance or payload) involved in quieting them. Significant noise reduction are achieved for the light helicopter with minimum performance or weight penalties because of the dominance of a single noise source (the tail rotor).

  10. Recent Progress in Engine Noise Reduction for Commercial Aircraft Applications

    NASA Technical Reports Server (NTRS)

    Huff, Dennis L.

    2003-01-01

    Considerable progress has been made over the past ten years developing technologies for reducing aircraft noise. Engine noise continues to be a dominate source, particularly for aircraft departing from airports. Research efforts have concentrated on developing noise prediction methods, experimental validation, and developing noise reduction concepts that have been verified through model scale and static engine tests. Most of the work has concentrated on fan and jet components for commercial turbofan engines. In this seminar, an overview of the engine noise reduction work that was sponsored by NASA s Advanced Subsonic Technology Noise Reduction Program will be given, along with background information on turbofan noise sources and certification procedures. Concepts like "chevron" nozzles for jet noise reduction and swept stators for fan noise reduction will be highlighted. A preliminary assessment on how the new technologies will impact future engines will be given.

  11. Supersonic jet shock noise reduction

    NASA Technical Reports Server (NTRS)

    Stone, J. R.

    1984-01-01

    Shock-cell noise is identified to be a potentially significant problem for advanced supersonic aircraft at takeoff. Therefore NASA conducted fundamental studies of the phenomena involved and model-scale experiments aimed at developing means of noise reduction. The results of a series of studies conducted to determine means by which supersonic jet shock noise can be reduced to acceptable levels for advanced supersonic cruise aircraft are reviewed. Theoretical studies were conducted on the shock associated noise of supersonic jets from convergent-divergent (C-D) nozzles. Laboratory studies were conducted on the influence of narrowband shock screech on broadband noise and on means of screech reduction. The usefulness of C-D nozzle passages was investigated at model scale for single-stream and dual-stream nozzles. The effect of off-design pressure ratio was determined under static and simulated flight conditions for jet temperatures up to 960 K. Annular and coannular flow passages with center plugs and multi-element suppressor nozzles were evaluated, and the effect of plug tip geometry was established. In addition to the far-field acoustic data, mean and turbulent velocity distributions were measured with a laser velocimeter, and shadowgraph images of the flow field were obtained.

  12. Digital Noise Reduction: An Overview

    PubMed Central

    Bentler, Ruth; Chiou, Li-Kuei

    2006-01-01

    Digital noise reduction schemes are being used in most hearing aids currently marketed. Unlike the earlier analog schemes, these manufacturer-specific algorithms are developed to acoustically analyze the incoming signal and alter the gain/output characteristics according to their predetermined rules. Although most are modulation-based schemes (ie, differentiating speech from noise based on temporal characteristics), spectral subtraction techniques are being applied as well. The purpose of this article is to overview these schemes in terms of their differences and similarities. PMID:16959731

  13. Reduction of propeller noise by active noise control

    NASA Astrophysics Data System (ADS)

    Bschorr, O.; Kubanke, D.

    1992-04-01

    Active noise control, a method of cancelling noise by means of interference with a secondary anti-noise source, is now in full development. The first commercial application of this technique is in the case of active electronically controlled head sets. The next step will be the active noise cancellation in air ducts and in passenger cabins. The aim of this paper is to assess the possibilities of the anti-noise technique for reducing propeller noise. First, by a mathematical simulation the theoretical noise reduction on the ground was calculated and found to be promising for further investigations. In the case of the periodic engine and propeller noise, for example, with only a single anti-noise source, the noise foot prints of the lower propeller harmonics can be reduced by up to 10 dB. In laboratory tests the theoretical values will be confirmed experimentally. For cancellation of the periodic noise one can use synchronous anti-noise generators. Compared with the engine and propeller noise the reduction of jet noise by the anti-noise technique is much more difficult. Therefore a sensor and controlling unit are necessary because of the stochastic nature of jet noise. Since aircraft noise is a severe problem, all methods are to be considered.

  14. Train noise reduction scenarios for compliance with future noise legislation

    NASA Astrophysics Data System (ADS)

    Leth, S.

    2003-10-01

    The Technical Specification for Interoperability (TSI) for high-speed trains on the European market includes limits on noise emission. These and other future restrictions on exterior noise of high-speed and intercity trains will require that train manufacturers implement noise control measures early in the design phase. A fundamental problem faced by manufacturers during the design process is determining how much noise reduction is required for each of the various noise sources on the train in order to achieve an optimal balance. To illustrate this process, estimates are presented of the contributions from different sources on existing Bombardier trains, based on measured data, numerical calculations and empirical formulae. In addition, methods of achieving the required noise reductions for different sources are briefly discussed along with targets for future exterior noise emission. Measurement results presented demonstrate the importance of track quality in noise emission. Noise restrictions, including future legislation, must give proper recognition to this important parameter.

  15. 1/f noise and effort on implicit measures of bias.

    PubMed

    Correll, Joshua

    2008-01-01

    Phenomena that vary over time can often be represented as a complex waveform. Fourier analysis decomposes this complex wave into a set of sinusoidal component waves. In some phenomena, the amplitude of these waves varies in inverse relation to frequency. This pattern has been called 1/f noise and, unlike white noise, it reflects nonrandom variation. Latencies in simple computer tasks typically reveal 1/f noise, but the magnitude of the noise decreases as tasks become more challenging. The current work hypothesizes a correspondence between 1/f noise and effort, leading to the prediction that increasing effort will reduce 1/f noise. In 2 studies, the author examined the relationship between an individual's attempts to avoid bias (measured in Study 1, manipulated in Study 2) and 1/f noise in implicit measures of stereotyping and prejudice. In each study, participants who made an effort to modulate the use of racial information showed less 1/f noise than did participants who made less effort. The potential value of this analytic approach to social psychology is discussed.

  16. Noise Reduction of Aircraft Flap

    NASA Technical Reports Server (NTRS)

    Hutcheson, Florence V. (Inventor); Brooks, Thomas F. (Inventor)

    2009-01-01

    A reduction in noise radiating from a side of a deployed aircraft flap is achieved by locating a slot adjacent the side of the flap, and then forcing air out through the slot with a suitable mechanism. One, two or even three or more slots are possible, where the slot is located at one;or more locations selected from a group of locations comprising a top surface of the flap, a bottom surface of the flap, an intersection of the top and side surface of the flap, an intersection of the bottom and side surfaces of the flap, and a side surface of the flap. In at least one embodiment the slot is substantially rectangular. A device for adjusting a rate of the air forced out through the slot can also be provided.

  17. Airport noise impact reduction through operations

    NASA Technical Reports Server (NTRS)

    Deloach, R.

    1981-01-01

    The airport-noise levels and annoyance model (ALAMO) developed at NASA Langley Research Center is comprised of a system of computer programs which is capable of quantifying airport community noise impact in terms of noise level, population distribution, and human subjective response to noise. The ALAMO can be used to compare the noise impact of an airport's current operating scenario with the noise impact which would result from some proposed change in airport operations. The relative effectiveness of number of noise-impact reduction alternatives is assessed for a major midwest airport. Significant reductions in noise impact are predicted for certain noise abatement strategies while others are shown to result in relatively little noise relief.

  18. Engine Validation of Noise and Emission Reduction Technology Phase I

    NASA Technical Reports Server (NTRS)

    Weir, Don (Editor)

    2008-01-01

    This final report has been prepared by Honeywell Aerospace, Phoenix, Arizona, a unit of Honeywell International, Inc., documenting work performed during the period December 2004 through August 2007 for the NASA Glenn Research Center, Cleveland, Ohio, under the Revolutionary Aero-Space Engine Research (RASER) Program, Contract No. NAS3-01136, Task Order 8, Engine Validation of Noise and Emission Reduction Technology Phase I. The NASA Task Manager was Dr. Joe Grady of the NASA Glenn Research Center. The NASA Contract Officer was Mr. Albert Spence of the NASA Glenn Research Center. This report is for a test program in which NASA funded engine validations of integrated technologies that reduce aircraft engine noise. These technologies address the reduction of engine fan and jet noise, and noise associated with propulsion/airframe integration. The results of these tests will be used by NASA to identify the engineering tradeoffs associated with the technologies that are needed to enable advanced engine systems to meet stringent goals for the reduction of noise. The objectives of this program are to (1) conduct system engineering and integration efforts to define the engine test-bed configuration; (2) develop selected noise reduction technologies to a technical maturity sufficient to enable engine testing and validation of those technologies in the FY06-07 time frame; (3) conduct engine tests designed to gain insight into the sources, mechanisms and characteristics of noise in the engines; and (4) establish baseline engine noise measurements for subsequent use in the evaluation of noise reduction.

  19. Noise environment reduction foam spheres in space

    NASA Technical Reports Server (NTRS)

    Scharton, Terry; Kern, Dennis; Badilla, Gloria

    1989-01-01

    The advent of lightweight fairings for new spacecraft and the increased thrust of new launch vehicles have intensified the need for better techniques for predicting and for reducing the low frequency noise environment of spacecraft at liftoff. This paper presents a VAPEPS (VibroAcoustic Payload Environment Prediction System) parametrical analysis of the noise reduction of spacecraft fairings and explores a novel technique for increasing the low frequency noise reduction of lightweight fairing by approximately 10 dB.

  20. Television noise-reduction device

    NASA Technical Reports Server (NTRS)

    Stamps, J. C.; Gordon, B. L.

    1973-01-01

    System greatly improves signal-to-noise ratio with little or no loss in picture resolution. By storage of luminance component, which is summed with chrominance component, system performs mathematical integration of basically-repetitive television signals. Integration of signals over interval of their repetition causes little change in original signals and eliminates random noise.

  1. Sodium intake reduction efforts in Lebanon

    PubMed Central

    Almedawar, Mohamad M.; Nasreddine, Lara; Olabi, Ammar; Hamade, Haya; Awad, Elie; Toufeili, Imad; Arnaout, Samir

    2015-01-01

    Sodium intake reduction efforts in Lebanon are quite recent and have just started to take effect on the national level. Starting out from an academic institution, the Lebanese Action on Sodium and Health (LASH) campaign was established to counter the increasing prevalence of hypertension and associated adverse health effects. The campaign’s strategy was based on four pillars: research, health communication, advocacy, and monitoring. The LASH group set out with determining: baseline sodium intake of the population, main sources of sodium intake, and the knowledge, attitudes, and behaviors (KAB) of the population as a situation analysis that prompts for action. This gave LASH tangible evidence of the magnitude of the problem and the need for the government, the food industry, and the consumers, to be mobilized to take part in devising a solution. Currently, Lebanon is at a stage of technically working to reduce the sodium content in the major sources of sodium, namely local bread and bread-like products. The next steps will include implementation of a plan for monitoring industry compliance, while studying other food targets, including dairy products and processed meat. Meanwhile, the health communication plan is ongoing and the Salt Awareness Week is celebrated every year with media appearances of LASH researchers to raise the issue to the public eye. PMID:26090328

  2. Helicopter Flight Procedures for Community Noise Reduction

    NASA Technical Reports Server (NTRS)

    Greenwood, Eric

    2017-01-01

    A computationally efficient, semiempirical noise model suitable for maneuvering flight noise prediction is used to evaluate the community noise impact of practical variations on several helicopter flight procedures typical of normal operations. Turns, "quick-stops," approaches, climbs, and combinations of these maneuvers are assessed. Relatively small variations in flight procedures are shown to cause significant changes to Sound Exposure Levels over a wide area. Guidelines are developed for helicopter pilots intended to provide effective strategies for reducing the negative effects of helicopter noise on the community. Finally, direct optimization of flight trajectories is conducted to identify low noise optimal flight procedures and quantify the magnitude of community noise reductions that can be obtained through tailored helicopter flight procedures. Physically realizable optimal turns and approaches are identified that achieve global noise reductions of as much as 10 dBA Sound Exposure Level.

  3. Noise Reduction Technologies for Turbofan Engines

    NASA Technical Reports Server (NTRS)

    Huff, Dennis L.

    2007-01-01

    Significant progress continues to be made with noise reduction for turbofan engines. NASA has conducted and sponsored research aimed at reducing noise from commercial aircraft. Since it takes many years for technologies to be developed and implemented, it is important to have aggressive technology goals that lead the target entry into service dates. Engine noise is one of the major contributors to the overall sound levels as aircraft operate near airports. Turbofan engines are commonly used on commercial transports due to their advantage for higher performance and lower noise. The noise reduction comes from combinations of changes to the engine cycle parameters and low noise design features. In this paper, an overview of major accomplishments from recent NASA research programs for engine noise will be given.

  4. UHB Engine Fan Broadband Noise Reduction Study

    NASA Technical Reports Server (NTRS)

    Gliebe, Philip R.; Ho, Patrick Y.; Mani, Ramani

    1995-01-01

    A study has been completed to quantify the contribution of fan broadband noise to advanced high bypass turbofan engine system noise levels. The result suggests that reducing fan broadband noise can produce 3 to 4 EPNdB in engine system noise reduction, once the fan tones are eliminated. Further, in conjunction with the elimination of fan tones and an increase in bypass ratio, a potential reduction of 7 to 10 EPNdB in system noise can be achieved. In addition, an initial assessment of engine broadband noise source mechanisms has been made, concluding that the dominant source of fan broadband noise is the interaction of incident inlet boundary layer turbulence with the fan rotor. This source has two contributors, i.e., unsteady life dipole response and steady loading quadrupole response. The quadrupole contribution was found to be the most important component, suggesting that broadband noise reduction can be achieved by the reduction of steady loading field-turbulence field quadrupole interaction. Finally, for a controlled experimental quantification and verification, the study recommends that further broadband noise tests be done on a simulated engine rig, such as the GE Aircraft Engine Universal Propulsion Simulator, rather than testing on an engine statically in an outdoor arena The rig should be capable of generating forward and aft propagating fan noise, and it needs to be tested in a large freejet or a wind tunnel.

  5. Active Chevrons for Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Depuru-Mohan, N. K.; Doty, M. J.

    2017-01-01

    Jet noise is often a dominant component of aircraft noise, particularly at takeoff. To meet the stringent noise regulations, the aircraft industry is in a pressing need of advanced noise reduction concepts. In the present study, the potential of piezoelectrically-activated chevrons for jet noise reduction was experimentally investigated. The perturbations near the nozzle exit caused by piezoelectrically-activated chevrons could be used to modify the growth rate of the mixing layer and thereby potentially reduce jet noise. These perturbations are believed to increase the production of small-scale disturbances at the expense of large-scale turbulent structures. These large-scale turbulent structures are responsible for the dominant portion of the jet mixing noise, particularly low-frequency noise. Therefore, by exciting the static chevron geometry through piezoelectric actuators, an additional acoustic benefit could possibly be achieved. To aid in the initial implementation of this concept, several flat-faced faceted nozzles (four, six, and eight facets) were investigated. Among the faceted nozzles, it was found that the eight-faceted nozzle behaves very similarly to the round nozzle. Furthermore, among the faceted nozzles with static chevrons, the four-faceted nozzle with static chevrons was found to be most effective in terms of jet noise reduction. The piezoelectrically-activated chevrons reduced jet noise up to 2 dB compared to the same nozzle geometry without excitation. This benefit was observed over a wide range of excitation frequencies by applying very low voltages to the piezoelectric actuators.

  6. Fluidic Injection for Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda

    2010-01-01

    Investigations into fluidic injection for jet noise reduction began over 50 years ago. Studies have included water and air injection for the reduction of noise in scale model jets and jet engines and water injection for the reduction of excess overpressures on the Space Shuttle at lift-off. Injection systems have included high pressure microjets as well as larger scale injectors operating at pressures that can be achieved in real jet engines. An historical perspective highlighting noise reduction potential is presented for injection concepts investigated over the last 50 years. Results from recent investigations conducted at NASA are presented for supersonic and subsonic dual-stream jets. The noise reduction benefits achieved through fluidic contouring using an azimuthally controlled nozzle will be discussed.

  7. Propulsion Noise Reduction Research in the NASA Advanced Air Transport Technology Project

    NASA Technical Reports Server (NTRS)

    Van Zante, Dale; Nark, Douglas; Fernandez, Hamilton

    2017-01-01

    The Aircraft Noise Reduction (ANR) sub-project is focused on the generation, development, and testing of component noise reduction technologies progressing toward the NASA far term noise goals while providing associated near and mid-term benefits. The ANR sub-project has efforts in airframe noise reduction, propulsion (including fan and core) noise reduction, acoustic liner technology, and propulsion airframe aeroacoustics for candidate conventional and unconventional aircraft configurations. The current suite of propulsion specific noise research areas is reviewed along with emerging facility and measurement capabilities. In the longer term, the changes in engine and aircraft configuration will influence the suite of technologies necessary to reduce noise in next generation systems.

  8. Noise reduction in OCT skin images

    NASA Astrophysics Data System (ADS)

    Turani, Zahra; Fatemizadeh, Emad; Adabi, Saba; Mehregan, Darius; Daveluy, Steven; Nasiriavanaki, Mohammadreza

    2017-03-01

    OCT skin images suffer from artifacts. Speckle is the main artifact while the other one is called background noise. In this study, we propose an algorithm that significantly reduces the background noise before applying a speckle reduction method. The results show that the diagnostically relevant features in the images become clearer after applying the proposed method. We used sub-pixel weighted median filtering for speckle reduction. The results from background noise removal in combination with the proposed speckle reduction algorithm show a significant improvement in the clarity of diagnostically relevant features in in-vivo human skin images.

  9. Recent Progress in Engine Noise Reduction Technologies

    NASA Technical Reports Server (NTRS)

    Huff, Dennis; Gliebe, Philip

    2003-01-01

    Highlights from NASA-funded research over the past ten years for aircraft engine noise reduction are presented showing overall technical plans, accomplishments, and selected applications to turbofan engines. The work was sponsored by NASA's Advanced Subsonic Technology (AST) Noise Reduction Program. Emphasis is given to only the engine noise reduction research and significant accomplishments that were investigated at Technology Readiness Levels ranging from 4 to 6. The Engine Noise Reduction sub-element was divided into four work areas: source noise prediction, model scale tests, engine validation, and active noise control. Highlights from each area include technologies for higher bypass ratio turbofans, scarf inlets, forward-swept fans, swept and leaned stators, chevron/tabbed nozzles, advanced noise prediction analyses, and active noise control for fans. Finally, an industry perspective is given from General Electric Aircraft Engines showing how these technologies are being applied to commercial products. This publication contains only presentation vu-graphs from an invited lecture given at the 41st AIAA Aerospace Sciences Meeting, January 6-9, 2003.

  10. Airframe Noise Reduction Studies and Clean-Airframe Noise Investigation

    NASA Technical Reports Server (NTRS)

    Fink, M. R.; Bailey, D. A.

    1980-01-01

    Acoustic wind tunnel tests were conducted of a wing model with modified leading edge slat and trailing edge flap. The modifications were intended to reduce the surface pressure response to convected turbulence and thereby reduce the airframe noise without changing the lift at constant incidence. Tests were conducted at 70.7 and 100 m/sec airspeeds, with Reynolds numbers 1.5 x 10 to the 6th power and 2.1 x 10 to the 6th power. Considerable reduction of noise radiation from the side edges of a 40 deflection single slotted flap was achieved by modification to the side edge regions or the leading edge region of the flap panel. Total far field noise was reduced 2 to 3 dB over several octaves of frequency. When these panels were installed as the aft panel of a 40 deg deflection double slotted flap, 2 dB noise reduction was achieved.

  11. Noise Reduction Through Circulation Control

    NASA Technical Reports Server (NTRS)

    Munro, Scott E.; Ahuja, K. K.; Englar, Robert J.

    2005-01-01

    Circulation control technology uses tangential blowing around a rounded trailing edge or a leading edge to change the force and moment characteristics of an aerodynamic body. This technology has been applied to circular cylinders, wings, helicopter rotors, and even to automobiles for improved aerodynamic performance. Only limited research has been conducted on the acoustic of this technology. Since wing flaps contribute to the environmental noise of an aircraft, an alternate blown high lift system without complex mechanical flaps could prove beneficial in reducing the noise of an approaching aircraft. Thus, in this study, a direct comparison of the acoustic characteristics of high lift systems employing a circulation control wing configuration and a conventional wing flapped configuration has been made. These results indicate that acoustically, a circulation control wing high lift system could be considerably more acceptable than a wing with conventional mechanical flaps.

  12. Flap Edge Noise Reduction Fins

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R. (Inventor); Choudhan, Meelan M. (Inventor)

    2015-01-01

    A flap of the type that is movably connected to an aircraft wing to provide control of an aircraft in flight includes opposite ends, wherein at least a first opposite end includes a plurality of substantially rigid, laterally extending protrusions that are spaced apart to form a plurality of fluidly interconnected passageways. The passageways have openings adjacent to upper and lower sides of the flap, and the passageways include a plurality of bends such that high pressure fluid flows from a high pressure region to a low pressure region to provide a boundary condition that inhibits noise resulting from airflow around the end of the flap.

  13. Principal Components as a Data Reduction and Noise Reduction Technique

    NASA Technical Reports Server (NTRS)

    Imhoff, M. L.; Campbell, W. J.

    1982-01-01

    The potential of principal components as a pipeline data reduction technique for thematic mapper data was assessed and principal components analysis and its transformation as a noise reduction technique was examined. Two primary factors were considered: (1) how might data reduction and noise reduction using the principal components transformation affect the extraction of accurate spectral classifications; and (2) what are the real savings in terms of computer processing and storage costs of using reduced data over the full 7-band TM complement. An area in central Pennsylvania was chosen for a study area. The image data for the project were collected using the Earth Resources Laboratory's thematic mapper simulator (TMS) instrument.

  14. Hearing through the noise: Biologically inspired noise reduction

    NASA Astrophysics Data System (ADS)

    Lee, Tyler Paul

    Vocal communication in the natural world demands that a listener perform a remarkably complicated task in real-time. Vocalizations mix with all other sounds in the environment as they travel to the listener, arriving as a jumbled low-dimensional signal. A listener must then use this signal to extract the structure corresponding to individual sound sources. How this computation is implemented in the brain remains poorly understood, yet an accurate description of such mechanisms would impact a variety of medical and technological applications of sound processing. In this thesis, I describe initial work on how neurons in the secondary auditory cortex of the Zebra Finch extract song from naturalistic background noise. I then build on our understanding of the function of these neurons by creating an algorithm that extracts speech from natural background noise using spectrotemporal modulations. The algorithm, implemented as an artificial neural network, can be flexibly applied to any class of signal or noise and performs better than an optimal frequency-based noise reduction algorithm for a variety of background noises and signal-to-noise ratios. One potential drawback to using spectrotemporal modulations for noise reduction, though, is that analyzing the modulations present in an ongoing sound requires a latency set by the slowest temporal modulation computed. The algorithm avoids this problem by reducing noise predictively, taking advantage of the large amount of temporal structure present in natural sounds. This predictive denoising has ties to recent work suggesting that the auditory system uses attention to focus on predicted regions of spectrotemporal space when performing auditory scene analysis.

  15. Feedback Control for Noise Reduction Program

    NASA Astrophysics Data System (ADS)

    Tucker, Jerry H.

    2002-12-01

    As part of Langley Research Center's continuing noise reduction program, an active noise control system (ANC) is being developed to suppress noise inside an aircraft cabin. This interior noise reduction system consists of the following major components: 1. Several accelerometers. 2. An input amplifier. 3. A digital signal processor (DSP) system that includes an analog to digital converter (ADC) and a digital to analog converter (DAC). 4. A high voltage power amplifier. 5. PZT actuators. 6. Power supply and distribution. The accelerometers detect interior panel vibrations. The accelerometer signals are fed to the input amplifier where they are conditioned prior to being sent to the ADC. The DSP receives the digitized signals form the ADC, processes these signals, and sends the result to the DAC. The DAC's analog output is used as input to the high voltage power amplifier. The power amplifier drives the PZT actuators to cancel noise form 50 to 1,300 Hz. The specific area of concern for this work was development of a DSP system that could be used for an actual flight demonstration. It was decided to base the system on a commercially available DSP board, the Spectrum Digital eZdsp. This was complicated by the fact that the ADC and DAC capabilities available on the eZdsp board were not sufficient to meet the system specification. Designing and fabricating a special ADC and DAC daughter card for the eZdsp circumvented this problem. The DSP system hardware has been successfully tested and is currently being integrated into the complete noise reduction system. This work has been completed in collaboration with another ASEE Fellow, Dr.William Edmonson from Hampton University and was conducted under the direction of the principle investigator, Dr. Qamar A. Shams of the Instrumentation Systems Development Branch, as part of a continuing noise reduction program.

  16. Azimuthally Varying Noise Reduction Techniques Applied to Supersonic Jets

    NASA Astrophysics Data System (ADS)

    Heeb, Nicholas S.

    An experimental investigation into the effect of azimuthal variance of chevrons and fluidically enhanced chevrons applied to supersonic jets is presented. Flow field measurements of streamwise and cross-stream particle imaging velocimetry were employed to determine the causes of noise reduction, which was demonstrated through acoustic measurements. Results were obtained in the over- and under- expanded regimes, and at the design condition, though emphasis was placed on the overexpanded regime due to practical application. Surveys of chevron geometry, number, and arrangement were undertaken in an effort to reduce noise and/or incurred performance penalties. Penetration was found to be positively correlated with noise reduction in the overexpanded regime, and negatively correlated in underexpanded operation due to increased effective penetration and high frequency penalty, respectively. The effect of arrangement indicated the beveled configuration achieved optimal abatement in the ideally and underexpanded regimes due to superior BSAN reduction. The symmetric configuration achieved optimal overexpanded noise reduction due to LSS suppression from improved vortex persistence. Increases in chevron number generally improved reduction of all noise components for lower penetration configurations. Higher penetration configurations reached levels of saturation in the four chevron range, with the potential to introduce secondary shock structures and generate additional noise with higher number. Alternation of penetration generated limited benefit, with slight reduction of the high frequency penalty caused by increased shock spacing. The combination of alternating penetration with beveled and clustered configurations achieved comparable noise reduction to the standard counterparts. Analysis of the entire data set indicated initial improvements with projected area that saturated after a given level and either plateaued or degraded with additional increases. Optimal reductions

  17. Prediction of Landing Gear Noise Reduction and Comparison to Measurements

    NASA Technical Reports Server (NTRS)

    Lopes, Leonard V.

    2010-01-01

    Noise continues to be an ongoing problem for existing aircraft in flight and is projected to be a concern for next generation designs. During landing, when the engines are operating at reduced power, the noise from the airframe, of which landing gear noise is an important part, is equal to the engine noise. There are several methods of predicting landing gear noise, but none have been applied to predict the change in noise due to a change in landing gear design. The current effort uses the Landing Gear Model and Acoustic Prediction (LGMAP) code, developed at The Pennsylvania State University to predict the noise from landing gear. These predictions include the influence of noise reduction concepts on the landing gear noise. LGMAP is compared to wind tunnel experiments of a 6.3%-scale Boeing 777 main gear performed in the Quiet Flow Facility (QFF) at NASA Langley. The geometries tested in the QFF include the landing gear with and without a toboggan fairing and the door. It is shown that LGMAP is able to predict the noise directives and spectra from the model-scale test for the baseline configuration as accurately as current gear prediction methods. However, LGMAP is also able to predict the difference in noise caused by the toboggan fairing and by removing the landing gear door. LGMAP is also compared to far-field ground-based flush-mounted microphone measurements from the 2005 Quiet Technology Demonstrator 2 (QTD 2) flight test. These comparisons include a Boeing 777-300ER with and without a toboggan fairing that demonstrate that LGMAP can be applied to full-scale flyover measurements. LGMAP predictions of the noise generated by the nose gear on the main gear measurements are also shown.

  18. Airport noise impact reduction through operations

    NASA Technical Reports Server (NTRS)

    Deloach, R.

    1981-01-01

    The effects of various aeronautical, operational, and land-use noise impact reduction alternatives are assessed for a major midwestern airport. Specifically, the relative effectiveness of adding sound absorbing material to aircraft engines, imposing curfews, and treating houses with acoustic insulation are examined.

  19. Noise reduction of diesel engine for heavy duty vehicles

    SciTech Connect

    Miura, Y.; Arai, S.

    1989-01-01

    Noise reduction of diesel engines installed in heavy duty vehicles is one of the highest priorities from the viewpoints of meeting the regulations for urban traffic noise abatement and noise reduction in the cabin for lightening fatigue with comfortable long driving. It is necessary that noise reduction measures then be applied to those causes. All noise reduction measures for the diesel engine researched for the purpose of practical use are described in this paper.

  20. Fluidic Chevrons for Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Kinzie, Kevin; Henderson, Brenda; Whitmire, Julia

    2004-01-01

    Chevron mixing devices are used to reduce noise from commercial separate-flow turbofan engines. Mechanical chevron serrations at the nozzle trailing edge generate axial vorticity that enhances jet plume mixing and consequently reduces far-field noise. Fluidic chevrons generated with air injected near the nozzle trailing edge create a vorticity field similar to that of the mechanical chevrons and allow more flexibility in controlling acoustic and thrust performance than a passive mechanical design. In addition, the design of such a system has the future potential for actively controlling jet noise by pulsing or otherwise optimally distributing the injected air. Scale model jet noise experiments have been performed in the NASA Langley Low Speed Aeroacoustic Wind Tunnel to investigate the fluidic chevron concept. Acoustic data from different fluidic chevron designs are shown. Varying degrees of noise reduction are achieved depending on the injection pattern and injection flow conditions. CFD results were used to select design concepts that displayed axial vorticity growth similar to that associated with mechanical chevrons and qualitatively describe the air injection flow and the impact on acoustic performance.

  1. Heuristics Made Easy: An Effort-Reduction Framework

    ERIC Educational Resources Information Center

    Shah, Anuj K.; Oppenheimer, Daniel M.

    2008-01-01

    In this article, the authors propose a new framework for understanding and studying heuristics. The authors posit that heuristics primarily serve the purpose of reducing the effort associated with a task. As such, the authors propose that heuristics can be classified according to a small set of effort-reduction principles. The authors use this…

  2. Heuristics Made Easy: An Effort-Reduction Framework

    ERIC Educational Resources Information Center

    Shah, Anuj K.; Oppenheimer, Daniel M.

    2008-01-01

    In this article, the authors propose a new framework for understanding and studying heuristics. The authors posit that heuristics primarily serve the purpose of reducing the effort associated with a task. As such, the authors propose that heuristics can be classified according to a small set of effort-reduction principles. The authors use this…

  3. Distributed Exhaust Nozzles for Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Gaeta, R. J.; Hellman, B.; Schein, D. B.; Solomon, W. D., Jr.; Huff, Dennis (Technical Monitor)

    2001-01-01

    The main objective of this study is to validate the jet noise reduction potential of a concept associated with distributed exhaust nozzles. Under this concept the propulsive thrust is generated by a larger number of discrete plumes issuing from an array of small or mini-nozzles. The potential of noise reduction of this concept stems from the fact that a large number of small jets will produce very high frequency noise and also, if spaced suitably, they will coalesce at a smaller velocity to produce low amplitude, low frequency noise. This is accomplished through detailed acoustic and fluid measurements along with a Computational Fluidic Dynamic (CFD) solution of the mean (DE) Distributed Exhaust nozzle flowfield performed by Northrop-Grumman. The acoustic performance is quantified in an anechoic chamber. Farfield acoustic data is acquired for a DE nozzle as well as a round nozzle of the same area. Both these types of nozzles are assessed numerically using Computational Fluid Dynamic (CFD) techniques. The CFD analysis ensures that both nozzles issued the same amount of airflow for a given nozzle pressure ratio. Data at a variety of nozzle pressure ratios are acquired at a range of polar and azimuthal angles. Flow visualization of the DE nozzle is used to assess the fluid dynamics of the small jet interactions. Results show that at high subsonic jet velocities, the DE nozzle shifts its frequency of peak amplitude to a higher frequency relative to a round nozzle of equivalent area (from a S(sub tD) = 0.24 to 1. 3). Furthermore, the DE nozzle shows reduced sound pressure levels (as much as 4 - 8 dB) in the low frequency part of the spectrum (less than S(sub tD) = 0.24 ) compared to the round nozzle. At supersonic jet velocities, the DE nozzle does not exhibit the jet screech and the shock-associated broadband noise is reduced by as much as 12 dB.

  4. Reduction of noise of large amplitude through adaptive neighborhoods.

    PubMed

    Mera, M Eugenia; Morán, Manuel

    2009-07-01

    We propose a noise reduction algorithm based on adaptive neighborhood selection that is able to obtain high levels of noise reduction for chaotic vector time series corrupted by observational noises with a noise-to-signal ratio of up to 300%.

  5. Gas turbine exhaust nozzle. [for noise reduction

    NASA Technical Reports Server (NTRS)

    Straight, D. M. (Inventor)

    1973-01-01

    An elongated hollow string is disposed in an exhaust nozzle combustion chamber and communicates with an air source through hollow struts at one end. The other end of the string is bell-mouth shaped and extends over the front portion of a nozzle plug. The bell-mouth may be formed by pivotally mounted flaps or leaves which are used to vary the exhaust throat area and the area between the plug and the leaves. Air from the engine inlet flows into the string and also between the combustion chamber and a housing disposed around the chamber. The air cools the plug and serves as a low velocity inner core of secondary gas to provide noise reduction for the primary exhaust gas while the other air, when it exits from the nozzle, forms an outer low velocity layer to further reduce noise. The structure produces increased thrust in a turbojet or turbofan engine.

  6. Wing Leading Edge Concepts for Noise Reduction

    NASA Technical Reports Server (NTRS)

    Shmilovich, Arvin; Yadlin, Yoram; Pitera, David M.

    2010-01-01

    This study focuses on the development of wing leading edge concepts for noise reduction during high-lift operations, without compromising landing stall speeds, stall characteristics or cruise performance. High-lift geometries, which can be obtained by conventional mechanical systems or morphing structures have been considered. A systematic aerodynamic analysis procedure was used to arrive at several promising configurations. The aerodynamic design of new wing leading edge shapes is obtained from a robust Computational Fluid Dynamics procedure. Acoustic benefits are qualitatively established through the evaluation of the computed flow fields.

  7. Twin jet shielding. [for aircraft noise reduction

    NASA Technical Reports Server (NTRS)

    Parthasarathy, S. P.; Cuffel, R. F.; Massier, P. F.

    1979-01-01

    For an over-the-wing/under-the-wing engine configuration on an airplane, the noise produced by the upper jet flow is partially reflected by the lower jet. An analysis has been performed which can be used to predict the distribution of perceived noise levels along the ground plane at take-off for an airplane which is designed to take advantage of the over/under shielding concept. Typical contours of PNL, the shielding benefit in the shadow zone, and the EPNL values at 3.5 nautical miles from brake release as well as EPNL values at sideline at 0.35 nautical miles have been calculated. This has been done for a range of flow parameters characteristic of engines producing inverted velocity profile jets suitable for use in a supersonic cruise vehicle. Reductions up to 6.0 EPNdB in community noise levels can be realized when the over engines are operated at higher thrust and the lower engines simultaneously operated with reduced thrust keeping the total thrust constant.

  8. Twin jet shielding. [for aircraft noise reduction

    NASA Technical Reports Server (NTRS)

    Parthasarathy, S. P.; Cuffel, R. F.; Massier, P. F.

    1979-01-01

    For an over-the-wing/under-the-wing engine configuration on an airplane, the noise produced by the upper jet flow is partially reflected by the lower jet. An analysis has been performed which can be used to predict the distribution of perceived noise levels along the ground plane at take-off for an airplane which is designed to take advantage of the over/under shielding concept. Typical contours of PNL, the shielding benefit in the shadow zone, and the EPNL values at 3.5 nautical miles from brake release as well as EPNL values at sideline at 0.35 nautical miles have been calculated. This has been done for a range of flow parameters characteristic of engines producing inverted velocity profile jets suitable for use in a supersonic cruise vehicle. Reductions up to 6.0 EPNdB in community noise levels can be realized when the over engines are operated at higher thrust and the lower engines simultaneously operated with reduced thrust keeping the total thrust constant.

  9. High-Speed Jet Noise Reduction NASA Perspective

    NASA Technical Reports Server (NTRS)

    Huff, Dennis L.; Handy, J. (Technical Monitor)

    2001-01-01

    History shows that the problem of high-speed jet noise reduction is difficult to solve. the good news is that high performance military aircraft noise is dominated by a single source called 'jet noise' (commercial aircraft have several sources). The bad news is that this source has been the subject of research for the past 50 years and progress has been incremental. Major jet noise reduction has been achieved through changing the cycle of the engine to reduce the jet exit velocity. Smaller reductions have been achieved using suppression devices like mixing enhancement and acoustic liners. Significant jet noise reduction without any performance loss is probably not possible! Recent NASA Noise Reduction Research Programs include the High Speed Research Program, Advanced Subsonic Technology Noise Reduction Program, Aerospace Propulsion and Power Program - Fundamental Noise, and Quiet Aircraft Technology Program.

  10. Innovative speckle noise reduction procedure in optical encryption

    NASA Astrophysics Data System (ADS)

    Vélez Zea, Alejandro; Fredy Barrera, John; Torroba, Roberto

    2017-05-01

    Encrypting techniques are currently of interest in the optical domain. A common issue when using coherent techniques is speckle noise which influences the final results. Most efforts to solve this issue were directed towards processing the output of the systems. Instead, we present an alternative approach where we seek to control the input to enhance the performance of these techniques. In particular, we analyze an encoding procedure with a joint transform correlator architecture as a case study. We first demonstrate the dependence of the output noise on the spatial distribution of the input, showing the existence of a neglected random correlation noise which contributes to the degradation of the output. We then propose a rearrangement of the input that results in a reduction of the noise level in the outcome. This rearrangement consists of separating the pixels of the input by introducing black pixels between them, keeping the usual remaining procedure unaltered. Our experimental approach opens up new possibilities for the applications of optical security techniques beyond the limitations imposed by noise.

  11. Summary of noise reduction characteristics of typical general aviation materials

    NASA Technical Reports Server (NTRS)

    Roskam, J.; Grosveld, F.; Van Aken, J.

    1979-01-01

    The paper presents the results of a large number of systematic tests to determine noise reduction characteristics of general aviation materials. Effects of material type (metallic and composite), thickness, panel stiffening, vibration damping materials, sound absorption materials and pressurization on noise reduction are included. Several promising methods for reducing cabin interior noise in light airplanes are discussed based on the results.

  12. Reductions in Multi-Component Jet Noise by Water Injection

    NASA Technical Reports Server (NTRS)

    Norum, Thomas D.

    2004-01-01

    An experimental investigation was performed in the NASA Langley Low Speed Aeroacoustics Wind Tunnel to determine the extent of jet exhaust noise reduction that can be obtained using water injection in a hot jet environment. The effects of water parameters such as mass flow rate, injection location, and spray patterns on suppression of dominant noise sources in both subsonic and supersonic jets were determined, and extrapolations to full-scale engine noise reduction were made. Water jets and sprays were injected in to the shear layers of cold and hot circular jets operating at both subsonic and supersonic exhaust conditions. Use of convergent-divergent and convergent nozzles (2.7in. D) allowed for simulations of all major jet noise sources. The experimental results show that water injection clearly disrupts shock noise sources within the jet plume, with large reductions in radiated shock noise. There are smaller reductions in jet mixing noise, resulting in only a small decrease in effective perceived noise level when projections are made to full scale. The fact that the measured noise reduction in the direction upstream of the nozzle was consistently larger than in the noisier downstream direction contributed to keeping effective perceived noise reductions small. Variations in the operation of the water injection system clearly show that injection at the nozzle exit rather than further downstream is required for the largest noise reduction. Noise reduction increased with water pressure as well as with its mass flow, although the type of injector had little effect.

  13. An active noise reduction system for aircrew helmets

    NASA Technical Reports Server (NTRS)

    Wheeler, P. D.; Rawlinson, D.; Pelc, S. F.; Dorey, T. P.

    1978-01-01

    An active noise reduction system was developed for use in aircrew flying helmets in which the acoustic noise field inside the ear defender is detected using a miniature microphone and an antiphase signal is fed back to a communications telephone within the ear defender. Performance of the active noise reduction system in a laboratory trial simulating flight conditions is shown to be satisfactory.

  14. Evaluation of the Advanced Subsonic Technology Program Noise Reduction Benefits

    NASA Technical Reports Server (NTRS)

    Golub, Robert A.; Rawls, John W., Jr.; Russell, James W.

    2005-01-01

    This report presents a detailed evaluation of the aircraft noise reduction technology concepts developed during the course of the NASA/FAA Advanced Subsonic Technology (AST) Noise Reduction Program. In 1992, NASA and the FAA initiated a cosponsored, multi-year program with the U.S. aircraft industry focused on achieving significant advances in aircraft noise reduction. The program achieved success through a systematic development and validation of noise reduction technology. Using the NASA Aircraft Noise Prediction Program, the noise reduction benefit of the technologies that reached a NASA technology readiness level of 5 or 6 were applied to each of four classes of aircraft which included a large four engine aircraft, a large twin engine aircraft, a small twin engine aircraft and a business jet. Total aircraft noise reductions resulting from the implementation of the appropriate technologies for each class of aircraft are presented and compared to the AST program goals.

  15. Application of Circulation Control Technology to Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Sankar, L. N.; Englar, R. J.; Munro, Scott E.; Li, Yi; Gaeta, R. J.

    2003-01-01

    This report is a summary of the work performed by Georgia Tech Research Institute (GTRI) under NASA Langley Grant NAG-1-2146, which was awarded as a part of NASA's Breakthrough Innovative Technologies (BIT) initiative. This was a three-year program, with a one-year no-cost extension. Each year's study has been an integrated effort consisting of computational fluid dynamics, experimental aerodynamics, and detailed noise and flow measurements. Year I effort examined the feasibility of reducing airframe noise by replacing the conventional wing systems with a Circulation Control Wing (CCW), where steady blowing was used through the trailing edge of the wing over a Coanda surface. It was shown that the wing lift increases with CCW blowing and indeed for the same lift, a CCW wing was shown to produce less noise. Year 2 effort dealt with a similar study on the role of pulsed blowing on airframe noise. The main objective of this portion of the study was to assess whether pulse blowing from the trailing edge of a CCW resulted in more, less, or the same amount of radiated noise to the farfield. Results show that a reduction in farfield noise of up to 5 dB is measured when pulse flow is compared with steady flow for an equivalent lift configuration. This reduction is in the spectral region associated with the trailing edge jet noise. This result is due to the unique advantage that pulsed flow has over steady flow. For a range of frequencies, more lift is experienced with the same mass flow as the steady case. Thus, for an equivalent lift and slot height, the pulsed system can operate at lower jet velocities, and hence lower jet noise. The computational analysis showed that for a given time-averaged mass flow rate, pulsed jets give a higher value of C(sub l) and a higher L/D than equivalent steady jets. This benefit is attributable to higher instantaneous jet velocities, and higher instantaneous C(sub mu) values for the pulsed jet. Pulsed jet benefits increase at higher

  16. Identification of Noise Sources and Design of Noise Reduction Measures for a Pneumatic Nail Gun.

    PubMed

    Jayakumar, Vignesh; Kim, Jay; Zechmann, Edward

    An experimental-analytical procedure was implemented to reduce the operating noise level of a nail gun, a commonly found power tool in a construction site. The procedure is comprised of preliminary measurements, identification and ranking of major noise sources and application of noise controls. Preliminary measurements show that the impact noise transmitted through the structure and the exhaust related noise were found to be the first and second major contributors. Applying a noise absorbing foam on the outside of the nail gun body was found to be an effective noise reduction technique. One and two-volume small mufflers were designed and applied to the exhaust side of the nail gun which reduced not only the exhaust noise but also the impact noise. It was shown that the overall noise level could be reduced by as much as 3.5 dB, suggesting that significant noise reduction is possible in construction power tools without any significant increase of the cost.

  17. Noise Reduction with Microphone Arrays for Speaker Identification

    SciTech Connect

    Cohen, Z

    2011-12-22

    Reducing acoustic noise in audio recordings is an ongoing problem that plagues many applications. This noise is hard to reduce because of interfering sources and non-stationary behavior of the overall background noise. Many single channel noise reduction algorithms exist but are limited in that the more the noise is reduced; the more the signal of interest is distorted due to the fact that the signal and noise overlap in frequency. Specifically acoustic background noise causes problems in the area of speaker identification. Recording a speaker in the presence of acoustic noise ultimately limits the performance and confidence of speaker identification algorithms. In situations where it is impossible to control the environment where the speech sample is taken, noise reduction filtering algorithms need to be developed to clean the recorded speech of background noise. Because single channel noise reduction algorithms would distort the speech signal, the overall challenge of this project was to see if spatial information provided by microphone arrays could be exploited to aid in speaker identification. The goals are: (1) Test the feasibility of using microphone arrays to reduce background noise in speech recordings; (2) Characterize and compare different multichannel noise reduction algorithms; (3) Provide recommendations for using these multichannel algorithms; and (4) Ultimately answer the question - Can the use of microphone arrays aid in speaker identification?

  18. Noise Reduction in an Undergraduate Library.

    ERIC Educational Resources Information Center

    Bird, Charles P.; Puglisi, Dawn D.

    1984-01-01

    Reports on program initiated to reduce noise in undergraduate library through combination of space reallocation, rule changes, and staff monitoring of noise. Objective and subjective measures of noise (sound-level readings, preintervention and postintervention questionnaires) and results of intervention program are discussed. Memo distributed on…

  19. Prediction and reduction of rotor broadband noise

    NASA Technical Reports Server (NTRS)

    Hayden, R. E.; Aravamudan, K. S.

    1978-01-01

    Prediction techniques which can be or have been applied to subsonic rotors, and methods for designing helicopter rotors for reduced broadband noise generation are summarized. It is shown how detailed physical models of the noise source can be used to identify approaches to noise control.

  20. Circular cylinders with soft porous cover for flow noise reduction

    NASA Astrophysics Data System (ADS)

    Geyer, Thomas F.; Sarradj, Ennes

    2016-03-01

    The use of porous materials is one of several approaches to passively control or minimize the generation of flow noise. In order to investigate the possible reduction of noise from struts and other protruding parts (for example components of the landing gear or pantographs), acoustic measurements were taken in a small aeroacoustic wind tunnel on a set of circular cylinders with a soft porous cover. The aim of this study was to identify those materials that result in the best noise reduction, which refers to both tonal noise and broadband noise. The porous covers were characterized by their air flow resistivity, a parameter describing the permeability of an open-porous material. The results show that materials with low air flow resistivities lead to a noticeable flow noise reduction. Thereby, the main effect of the porous cylinder covers is that the spectral peak of the aeolian tone due to vortex shedding appears much narrower, but is not suppressed completely. Based on the measurement results, a basic model for the estimation of the total peak level of the aeolian tone was derived. In addition to the minimization of the vortex shedding noise, a reduction of broadband noise can be observed, especially at higher Reynolds numbers. The noise reduction increases with decreasing air flow resistivity of the porous covers, which means that materials that are highly permeable to air result in the best noise reduction.

  1. Meeting 2006, outdoor noise directive (OND) noise levels for a diesel engine driven air compressor: A case study in noise reduction

    NASA Astrophysics Data System (ADS)

    Rowe, David F.

    2005-09-01

    In January 2006, the noise limits for many products in the European Union will drop by 2-3 dBA, as directed by 2000/14/EC ``Noise Emission in the Environment by Equipment Used Outdoors,'' commonly called the ``Outdoor Noise Directive,'' or ``OND.'' Air compressors are among the products addressed by this directive. At Ingersoll-Rand, significant effort has been directed at meeting the challenge of reducing noise on a variety of diesel engine driven air compressor platforms, ranging from 15 to 350 kW diesel engine power ratings. This paper presents a case study of the noise reduction on a 750 cfm (21 m3/min) air compressor operating at 300 psig (21 bar), to meet the 2006 OND noise limit of 100 LwA.

  2. Subjective ratings of noise-reduction hearing aids.

    PubMed

    Kuk, F K; Tyler, R S; Mims, L

    1990-01-01

    The effectiveness of seven commercially available noise-reduction hearing aids was evaluated using subjective ratings of continuous discourse. Subjective scales of listening comfort, speech quality, speech understanding, noise interference, and overall liking were used. Fifteen experienced hearing-aid users participated. Two hearing aids that used amplitude compression (Audiotone A-54 and Telex 363C), two hearing aids that used the Zeta Noise Blocker (two versions of a Maico SP147), and three hearing aids that proportionally attenuated the low-frequencies (Rion HB-69AS, Richards ASE-B, and Siemens 283 ASP) were evaluated. None of the noise-reduction hearing aids significantly altered group performance on any subjective scale. Individually, however, subjects responded differently to different noise-reduction hearing aids, indicating that some noise-reduction hearing aids may help some hearing-impaired individuals.

  3. Phase Noise Reduction of Laser Diode

    NASA Technical Reports Server (NTRS)

    Zhang, T. C.; Poizat, J.-Ph.; Grelu, P.; Roch, J.-F.; Grangier, P.; Marin, F.; Bramati, A.; Jost, V.; Levenson, M. D.; Giacobino, E.

    1996-01-01

    Phase noise of single mode laser diodes, either free-running or using line narrowing technique at room temperature, namely injection-locking, has been investigated. It is shown that free-running diodes exhibit very large excess phase noise, typically more than 80 dB above shot-noise at 10 MHz, which can be significantly reduced by the above-mentioned technique.

  4. Broadband Shock Noise Reduction in Turbulent Jets by Water Injection

    NASA Technical Reports Server (NTRS)

    Kandula, Max

    2008-01-01

    The concept of effective jet properties introduced by the author (AIAA-2007-3 645) has been extended to the estimation of broadband shock noise reduction by water injection in supersonic jets. Comparison of the predictions with the test data for cold underexpanded supersonic nozzles shows a satisfactory agreement. The results also reveal the range of water mass flow rates over which saturation of mixing noise reduction and existence of parasitic noise are manifest.

  5. Study results on combat aircraft source noise reduction

    NASA Astrophysics Data System (ADS)

    Borchers, I. U.; Hackstein, H. J.; Bartels, P.

    1992-04-01

    For use in combat aircraft noise control, important results of extensive studies on jet noise reduction are presented. The studies covered low-noise nozzle designs such as linear arrays of circular nozzles, inverted profile jets as well as special shape mixing nozzles and coaxial bypass flow configurations. In addition interesting results of systematic research on special acoustic absorbers for propulsion system internal noise reduction and of initial theoretical and experimental studies on promising ejector flow systems are reported. The results of the different investigations are explained and discussed. Furthermore, practical applications, including examples of performed and possible future integrations of the considered noise control measures into aircraft, are presented. It is noted that the implementation of these methods could significantly reduce combat aircraft engine noise. For substantial noise reductions, of the order of 20 dB or more as obtained for civil jet transport aircraft, the integration of advanced ejector flow systems is suggested which are capable of effectively lowering the jet exhaust speed as required and with this strongly reduce the jet noise generation. It is concluded that extensive information and an advanced technology basis for jet engine noise reduction exist. Applying this, by giving the needed noise control equal importance and priority as other critical aircraft aspects, may help resolve the related noise problem.

  6. New circuit theory of multiconductor transmission lines resulting from a new practice of noise reduction.

    PubMed

    Toki, Hiroshi; Sato, Kenji

    2014-01-01

    In modern life, we are surrounded by and filled with electromagnetic noise caused by the dominant use of energy in the form of electricity. This situation is brought about by the fact that the noise is not understood theoretically. A new practice of noise reduction was introduced for the construction of Heavy Ion Medical Accelerator in Chiba (HIMAC). The key concept is a symmetric three-line circuit that arranges power supplies, noise filters and magnets around a third central ground line. A continuous theoretical effort forced us to find a new circuit theory involving a multiconductor transmission-line system starting from Maxwell's equations without any approximation. We discuss the essence of all of these experimental and theoretical developments with the hope to remove unnecessary electromagnetic noise not only from power supplies, but also from all electric devices. The newly derived circuit theory of multiconductor transmission lines is universal, and establishes the validity of the practice of noise reduction.

  7. Noise reduction in supersonic jets by nozzle fluidic inserts

    NASA Astrophysics Data System (ADS)

    Morris, Philip J.; McLaughlin, Dennis K.; Kuo, Ching-Wen

    2013-08-01

    Professor Philip Doak spent a very productive time as a consultant to the Lockheed-Georgia Company in the early 1970s. The focus of the overall research project was the prediction and reduction of noise from supersonic jets. Now, 40 years on, the present paper describes an innovative methodology and device for the reduction of supersonic jet noise. The goal is the development of a practical active noise reduction technique for low bypass ratio turbofan engines. This method introduces fluidic inserts installed in the divergent wall of a CD nozzle to replace hard-wall corrugation seals, which have been demonstrated to be effective by Seiner (2005) [1]. By altering the configuration and operating conditions of the fluidic inserts, active noise reduction for both mixing and shock noise has been obtained. Substantial noise reductions have been achieved for mixing noise in the maximum noise emission direction and in the forward arc for broadband shock-associated noise. To achieve these reductions (on the order of greater than 4 and 2 dB for the two main components respectively), practically achievable levels of injection mass flow rates have been used. The total injected mass flow rates are less than 4% of the core mass flow rate and the effective operating injection pressure ratio has been maintained at or below the same level as the nozzle pressure ratio of the core flow.

  8. Perceptually optimized gain function for cochlear implant signal-to-noise ratio based noise reduction.

    PubMed

    Mauger, Stefan J; Dawson, Pam W; Hersbach, Adam A

    2012-01-01

    Noise reduction in cochlear implants has achieved significant speech perception improvements through spectral subtraction and signal-to-noise ratio based noise reduction techniques. Current methods use gain functions derived through mathematical optimization or motivated by normal listening psychoacoustic experiments. Although these gain functions have been able to improve speech perception, recent studies have indicated that they are not optimal for cochlear implant noise reduction. This study systematically investigates cochlear implant recipients' speech perception and listening preference of noise reduction with a range of gain functions. Results suggest an advantageous gain function and show that gain functions currently used for noise reduction are not optimal for cochlear implant recipients. Using the cochlear implant optimised gain function, a 27% improvement over the current advanced combination encoder (ACE) stimulation strategy in speech weighted noise and a 7% improvement over current noise reduction strategies were observed in babble noise conditions. The optimized gain function was also most preferred by cochlear implant recipients. The CI specific gain function derived from this study can be easily incorporated into existing noise reduction strategies, to further improve listening performance for CI recipients in challenging environments.

  9. Compression station upgrades include advanced noise reduction

    SciTech Connect

    Dunning, V.R.; Sherikar, S.

    1998-10-01

    Since its inception in the mid-`80s, AlintaGas` Dampier to Bunbury natural gas pipeline has been constantly undergoing a series of upgrades to boost capacity and meet other needs. Extending northward about 850 miles from near Perth to the northwest shelf, the 26-inch line was originally served by five compressor stations. In the 1989-91 period, three new compressor stations were added to increase capacity and a ninth station was added in 1997. Instead of using noise-path-treatment mufflers to reduce existing noise, it was decided to use noise-source-treatment technology to prevent noise creation in the first place. In the field, operation of these new noise-source treatment attenuators has been very quiet. If there was any thought earlier of guaranteed noise-level verification, it is not considered a priority now. It`s also anticipated that as AlintaGas proceeds with its pipeline and compressor station upgrade program, similar noise-source treatment equipment will be employed and retrofitted into older stations where the need to reduce noise and potential radiant-heat exposure is indicated.

  10. State space forecasting and noise reduction

    SciTech Connect

    Eubank, S.; Casdagli, M.; Farmer, J.D.; Gibson, J.

    1990-01-01

    We discuss the effects of nonlinearity and noise on the problem of finding states and dynamics. We point out problems which arise in the construction of state space models for scalar time series. We describe solutions for the case when error due to noise dominates parameter estimation error and outline a framework for the general case.

  11. How hearing aids, background noise, and visual cues influence objective listening effort.

    PubMed

    Picou, Erin M; Ricketts, Todd A; Hornsby, Benjamin W Y

    2013-09-01

    The purpose of this article was to evaluate factors that influence the listening effort experienced when processing speech for people with hearing loss. Specifically, the change in listening effort resulting from introducing hearing aids, visual cues, and background noise was evaluated. An additional exploratory aim was to investigate the possible relationships between the magnitude of listening effort change and individual listeners' working memory capacity, verbal processing speed, or lipreading skill. Twenty-seven participants with bilateral sensorineural hearing loss were fitted with linear behind-the-ear hearing aids and tested using a dual-task paradigm designed to evaluate listening effort. The primary task was monosyllable word recognition and the secondary task was a visual reaction time task. The test conditions varied by hearing aids (unaided, aided), visual cues (auditory-only, auditory-visual), and background noise (present, absent). For all participants, the signal to noise ratio was set individually so that speech recognition performance in noise was approximately 60% in both the auditory-only and auditory-visual conditions. In addition to measures of listening effort, working memory capacity, verbal processing speed, and lipreading ability were measured using the Automated Operational Span Task, a Lexical Decision Task, and the Revised Shortened Utley Lipreading Test, respectively. In general, the effects measured using the objective measure of listening effort were small (~10 msec). Results indicated that background noise increased listening effort, and hearing aids reduced listening effort, while visual cues did not influence listening effort. With regard to the individual variables, verbal processing speed was negatively correlated with hearing aid benefit for listening effort; faster processors were less likely to derive benefit. Working memory capacity, verbal processing speed, and lipreading ability were related to benefit from visual cues. No

  12. Musical noise reduction using an adaptive filter

    NASA Astrophysics Data System (ADS)

    Hanada, Takeshi; Murakami, Takahiro; Ishida, Yoshihisa; Hoya, Tetsuya

    2003-10-01

    This paper presents a method for reducing a particular noise (musical noise). The musical noise is artificially produced by Spectral Subtraction (SS), which is one of the most conventional methods for speech enhancement. The musical noise is the tin-like sound and annoying in human auditory. We know that the duration of the musical noise is considerably short in comparison with that of speech, and that the frequency components of the musical noise are random and isolated. In the ordinary SS-based methods, the musical noise is removed by the post-processing. However, the output of the ordinary post-processing is delayed since the post-processing uses the succeeding frames. In order to improve this problem, we propose a novel method using an adaptive filter. In the proposed system, the observed noisy signal is used as the input signal to the adaptive filter and the output of SS is used as the reference signal. In this paper we exploit the normalized LMS (Least Mean Square) algorithm for the adaptive filter. Simulation results show that the proposed method has improved the intelligibility of the enhanced speech in comparison with the conventional method.

  13. The challenges of lawnmower noise reduction

    NASA Astrophysics Data System (ADS)

    Drutowski, Carol J.; Fetzer, Keith

    2005-09-01

    The European Noise Directive (2000/14/EC) became effective in the year 2000, limiting the allowable noise level for lawnmowers sold in the European Union. Noise level limits are based on cutting width. The Directive requires that manufacturers meet these limits and include statistical uncertainties, then declare their noise levels and have these results certified by an independent third party agency. There are two major challenges with this Directive. First by taking statistical uncertainties into account, this creates a limit lower than the published limit. Second is to lower the sound power level while still maintaining acceptable performance. The physical phenomena that generate the unwanted noise of a lawnmower are also used to perform work. For rotary lawnmowers, a dominant noise source is the cutting deck assembly, which is required to lift and cut grass, then dispose of the clippings. To cut grass with a good quality of cut appearance, the blades are required to turn at a very high tip speed to generate the necessary airflow. For lawnmowers, noise levels and unit performance are intrinsically linked. This has frustrated our industry for over 20 years.

  14. An assessment of propeller aircraft noise reduction technology

    NASA Technical Reports Server (NTRS)

    Metzger, F. Bruce

    1995-01-01

    This report is a review of the literature regarding propeller airplane far-field noise reduction. Near-field and cabin noise reduction are not specifically addressed. However, some of the approaches used to reduce far-field noise produce beneficial effects in the near-field and in the cabin. The emphasis is on propeller noise reduction but engine exhaust noise reduction by muffling is also addressed since the engine noise becomes a significant part of the aircraft noise signature when propeller noise is reduced. It is concluded that there is a substantial body of information available that can be used as the basis to reduce propeller airplane noise. The reason that this information is not often used in airplane design is the associated weight, cost, and performance penalties. It is recommended that the highest priority be given to research for reducing the penalties associated with lower operating RPM and propeller diameter while increasing the number of blades. Research to reduce engine noise and explore innovative propeller concepts is also recommended.

  15. A novel PACU design for noise reduction.

    PubMed

    Smykowski, Lenore

    2008-08-01

    As redesign and renovation of patient care units occur, health care providers are looking to the literature and finding evidence for the importance of lowering environmental stressors. In the PACU at Memorial Sloan Kettering Cancer Center, patients historically expressed dissatisfaction with excessive noise levels and frequently cited overhearing staff conversations as most troubling. Nurses found the noise stressful and wearing. When the time approached to design the new PACU, we took the opportunity to explore a unique floor plan to minimize noise and improve privacy.

  16. Nordic Standards for measurement of aircraft noise immission in residential areas and noise reduction of dwellings

    NASA Astrophysics Data System (ADS)

    Svane, Christian; Plovsing, Birger

    Quantification by measurement of aircraft noise in residential areas and air traffic noise reduction of dwellings suffer from sensibility to the measurement technique used. Around the Copenhagen Airport (200.000 opr./year) 3.500 families have been granted from 50% to 90% of sound insulation costs by the Danish Government. Based on experience from evaluation measurements carried out by the Danish Acoustical Institute, the authors have proposed standardized measurement methods for the outdoor aircraft noise in residential areas and for the noise reduction of dwellings. In 1989 both noise measurement methods were accepted as Nordic Standards (NORDTEST ACOU 074 and 075) by Denmark, Finland, Iceland, Norway and Sweden.

  17. Development and Evaluation of Single-Microphone Noise Reduction Algorithms for Digital Hearing Aids

    NASA Astrophysics Data System (ADS)

    Marzinzik, Mark; Kollmeier, Birger

    In this study single-microphone noise reduction procedures were investigated for use in digital hearing aids. One widely reported artifact of most noise suppression systems, the musical noise phenomenon, can partly be overcome by the Ephraim-Malah noise suppression algorithms [1,2]. Based on these algorithms, three different versions have been implemented together with a procedure for automatically updating the noise-spectrum estimate. To evaluate the algorithms, different tests have been performed with six normal-hearing and six hearing-impaired subjects. With `standard' measurement methods no increase in speech intelligibility was found compared to the unprocessed signal. However, benefits with respect to reductions in listener fatigue and in the mental effort needed to listen to speech in noise over longer periods of time were found in this study by use of a newly developed ease-of-listening test. Subsequent paired comparison tests also revealed a clear preference of the hearing-impaired subjects for the noise-reduced signals in situations with rather stationary noise. In the case of strongly fluctuating noise at low SNR, however, the subjects preferred the unprocessed signal due to speech distortions caused by the noise reduction algorithms.

  18. Critical Low-Noise Technologies Being Developed for Engine Noise Reduction Systems Subproject

    NASA Technical Reports Server (NTRS)

    Grady, Joseph E.; Civinskas, Kestutis C.

    2004-01-01

    NASA's previous Advanced Subsonic Technology (AST) Noise Reduction Program delivered the initial technologies for meeting a 10-year goal of a 10-dB reduction in total aircraft system noise. Technology Readiness Levels achieved for the engine-noise-reduction technologies ranged from 4 (rig scale) to 6 (engine demonstration). The current Quiet Aircraft Technology (QAT) project is building on those AST accomplishments to achieve the additional noise reduction needed to meet the Aerospace Technology Enterprise's 10-year goal, again validated through a combination of laboratory rig and engine demonstration tests. In order to meet the Aerospace Technology Enterprise goal for future aircraft of a 50- reduction in the perceived noise level, reductions of 4 dB are needed in both fan and jet noise. The primary objectives of the Engine Noise Reduction Systems (ENRS) subproject are, therefore, to develop technologies to reduce both fan and jet noise by 4 dB, to demonstrate these technologies in engine tests, and to develop and experimentally validate Computational Aero Acoustics (CAA) computer codes that will improve our ability to predict engine noise.

  19. Source Noise Modeling Efforts for Fan Noise in NASA Research Programs

    NASA Technical Reports Server (NTRS)

    Huff, Dennis L.

    2006-01-01

    There has been considerable progress made in fan noise prediction over the past 15 years. NASA has conducted and sponsored research that has improved both tone and broadband fan noise prediction methods. This presentation highlights progress in these areas with emphasis on rotor/stator interaction noise sources. Tone noise predictions are presented for an advanced prediction code called "LINFLUX". Comparisons with data are" included for individual fan duct modes. There has also been considerable work developing new fan broadband noise prediction codes and validation data from wind tunnel model tests. Results from several code validation exercises are presented that show improvement of predicted sound power levels. A summary is included with recommendations for future work.

  20. Seismic exploration noise reduction in the Marginal Ice Zone.

    PubMed

    Tollefsen, Dag; Sagen, Hanne

    2014-07-01

    A sonobuoy field was deployed in the Marginal Ice Zone of the Fram Strait in June 2011 to study the spatial variability of ambient noise. High noise levels observed at 10-200 Hz are attributed to distant (1400 km range) seismic exploration. The noise levels decreased with range into the ice cover; the reduction is fitted by a spreading loss model with a frequency-dependent attenuation factor less than for under-ice interior Arctic propagation. Numerical modeling predicts transmission loss of the same order as the observed noise level reduction and indicates a significant loss contribution from under-ice interaction.

  1. Subspace algorithms for noise reduction in cochlear implants

    NASA Astrophysics Data System (ADS)

    Loizou, Philipos C.; Lobo, Arthur; Hu, Yi

    2005-11-01

    A single-channel algorithm is proposed for noise reduction in cochlear implants. The proposed algorithm is based on subspace principles and projects the noisy speech vector onto ``signal'' and ``noise'' subspaces. An estimate of the clean signal is made by retaining only the components in the signal subspace. The performance of the subspace reduction algorithm is evaluated using 14 subjects wearing the Clarion device. Results indicated that the subspace algorithm produced significant improvements in sentence recognition scores compared to the subjects' daily strategy, at least in stationary noise. Further work is needed to extend the subspace algorithm to nonstationary noise environments.

  2. Department of Navy Jet Noise Reduction Project Overview

    DTIC Science & Technology

    2010-12-01

    Leadership direction, the Office of Naval Research initiated the Jet Noise Reduction (JNR) Project as part of the Noise-Induced Hearing Loss ( NIHL ) Program...Naval Research initiated the Jet Noise Reduction (JNR) Project as part of the Noise-Induced Hearing Loss ( NIHL ) Program. The JNR Project’s over...ONR Code 342 5 2007: ASN(RD&A) request to address hearing loss prevention 2008: ASN(RD&A), ASN(I&E), CNR approval of FY09-17 NIHL roadmap NIHL /JNR

  3. Simple noise-reduction method based on nonlinear forecasting.

    PubMed

    Tan, James P L

    2017-03-01

    Nonparametric detrending or noise reduction methods are often employed to separate trends from noisy time series when no satisfactory models exist to fit the data. However, conventional noise reduction methods depend on subjective choices of smoothing parameters. Here we present a simple multivariate noise reduction method based on available nonlinear forecasting techniques. These are in turn based on state-space reconstruction for which a strong theoretical justification exists for their use in nonparametric forecasting. The noise reduction method presented here is conceptually similar to Schreiber's noise reduction method using state-space reconstruction. However, we show that Schreiber's method has a minor flaw that can be overcome with forecasting. Furthermore, our method contains a simple but nontrivial extension to multivariate time series. We apply the method to multivariate time series generated from the Van der Pol oscillator, the Lorenz equations, the Hindmarsh-Rose model of neuronal spiking activity, and to two other univariate real-world data sets. It is demonstrated that noise reduction heuristics can be objectively optimized with in-sample forecasting errors that correlate well with actual noise reduction errors.

  4. Simple noise-reduction method based on nonlinear forecasting

    NASA Astrophysics Data System (ADS)

    Tan, James P. L.

    2017-03-01

    Nonparametric detrending or noise reduction methods are often employed to separate trends from noisy time series when no satisfactory models exist to fit the data. However, conventional noise reduction methods depend on subjective choices of smoothing parameters. Here we present a simple multivariate noise reduction method based on available nonlinear forecasting techniques. These are in turn based on state-space reconstruction for which a strong theoretical justification exists for their use in nonparametric forecasting. The noise reduction method presented here is conceptually similar to Schreiber's noise reduction method using state-space reconstruction. However, we show that Schreiber's method has a minor flaw that can be overcome with forecasting. Furthermore, our method contains a simple but nontrivial extension to multivariate time series. We apply the method to multivariate time series generated from the Van der Pol oscillator, the Lorenz equations, the Hindmarsh-Rose model of neuronal spiking activity, and to two other univariate real-world data sets. It is demonstrated that noise reduction heuristics can be objectively optimized with in-sample forecasting errors that correlate well with actual noise reduction errors.

  5. Recent Developments in U.S. Engine Noise Reduction Research

    NASA Technical Reports Server (NTRS)

    Bridges, James; Envia, Edmane; Huff, Dennis

    2001-01-01

    Aircraft engine noise research in the United States has made considerable progress over the past 10 years for both subsonic and supersonic flight applications. The Advanced Subsonic Technology (AST) Noise Reduction Program started in 1994 and will be completed in 2001 without major changes to program plans and funding levels. As a result, significant progress has been made toward the goal of reducing engine source noise by 6 EPNdB (Effective Perceived Noise level in decibels). This paper will summarize some of the significant accomplishments from the subsonic engine noise research performed over the past 10 years. The review is by no means comprehensive and only represents a sample of major accomplishments.

  6. Definition of 1992 Technology Aircraft Noise Levels and the Methodology for Assessing Airplane Noise Impact of Component Noise Reduction Concepts

    NASA Technical Reports Server (NTRS)

    Kumasaka, Henry A.; Martinez, Michael M.; Weir, Donald S.

    1996-01-01

    This report describes the methodology for assessing the impact of component noise reduction on total airplane system noise. The methodology is intended to be applied to the results of individual study elements of the NASA-Advanced Subsonic Technology (AST) Noise Reduction Program, which will address the development of noise reduction concepts for specific components. Program progress will be assessed in terms of noise reduction achieved, relative to baseline levels representative of 1992 technology airplane/engine design and performance. In this report, the 1992 technology reference levels are defined for assessment models based on four airplane sizes - an average business jet and three commercial transports: a small twin, a medium sized twin, and a large quad. Study results indicate that component changes defined as program final goals for nacelle treatment and engine/airframe source noise reduction would achieve from 6-7 EPNdB reduction of total airplane noise at FAR 36 Stage 3 noise certification conditions for all of the airplane noise assessment models.

  7. The effects of noise and reverberation on listening effort for adults with normal hearing

    PubMed Central

    Picou, Erin M.; Gordon, Julia; Ricketts, Todd A.

    2015-01-01

    Objectives The purpose of this study was to investigate the effects of background noise and reverberation on listening effort. Four specific research questions were addressed related to listening effort. These questions were: A) with comparable word recognition performance across levels of reverberation, what are the effects of noise and reverberation on listening effort? (B) what is the effect of background noise when reverberation time is constant? (C) what is the effect of increasing reverberation from low to moderate when signal-to-noise ratio is constant? (D) what is the effect of increasing reverberation from moderate to high when signal-to-noise ratio is constant? Design Eighteen young adults (mean age 24.8 years) with normal hearing participated. A dual-task paradigm was used to simultaneously assess word recognition and listening effort. The primary task was monosyllable word recognition and the secondary task was word categorization (press a button if the word heard was judged to be a noun). Participants were tested in quiet and in background noise in three levels of reverberation (T30 < 100 ms, T30 = 475 ms, and T30 = 834 ms). Signal-to-noise ratios used were chosen individually for each participant and varied by reverberation to address the specific research questions. Results As expected, word recognition performance was negatively affected by both background noise and by increases in reverberation. Furthermore, analysis of mean response times revealed that background noise increased listening effort, regardless of degree of reverberation. Conversely, reverberation did not affect listening effort, regardless of whether word recognition performance was comparable or signal-to-noise ratio was constant. Conclusions The finding that reverberation did not affect listening effort, even when word recognition performance was degraded, is inconsistent with current models of listening effort. The reasons for this surprising finding are unclear and warrant

  8. Wind fence enclosures for infrasonic wind noise reduction.

    PubMed

    Abbott, JohnPaul; Raspet, Richard; Webster, Jeremy

    2015-03-01

    A large porous wind fence enclosure has been built and tested to optimize wind noise reduction at infrasonic frequencies between 0.01 and 10 Hz to develop a technology that is simple and cost effective and improves upon the limitations of spatial filter arrays for detecting nuclear explosions, wind turbine infrasound, and other sources of infrasound. Wind noise is reduced by minimizing the sum of the wind noise generated by the turbulence and velocity gradients inside the fence and by the area-averaging the decorrelated pressure fluctuations generated at the surface of the fence. The effects of varying the enclosure porosity, top condition, bottom gap, height, and diameter and adding a secondary windscreen were investigated. The wind fence enclosure achieved best reductions when the surface porosity was between 40% and 55% and was supplemented by a secondary windscreen. The most effective wind fence enclosure tested in this study achieved wind noise reductions of 20-27 dB over the 2-4 Hz frequency band, a minimum of 5 dB noise reduction for frequencies from 0.1 to 20 Hz, constant 3-6 dB noise reduction for frequencies with turbulence wavelengths larger than the fence, and sufficient wind noise reduction at high wind speeds (3-6 m/s) to detect microbaroms.

  9. Wind Noise Reduction in a Non-Porous Subsurface Windscreen

    NASA Technical Reports Server (NTRS)

    Zuckerwar, Allan J.; Shams, Qamar A.; Knight, H. Keith

    2012-01-01

    Measurements of wind noise reduction were conducted on a box-shaped, subsurface windscreen made of closed cell polyurethane foam. The windscreen was installed in the ground with the lid flush with the ground surface. The wind was generated by means of a fan, situated on the ground, and the wind speed was measured at the center of the windscreen lid with an ultrasonic anemometer. The wind speed was controlled by moving the fan to selected distances from the windscreen. The wind noise was measured on a PCB Piezotronics 3†electret microphone. Wind noise spectra were measured with the microphone exposed directly to the wind (atop the windscreen lid) and with the microphone installed inside the windscreen. The difference between the two spectra comprises the wind noise reduction. At wind speeds of 3, 5, and 7 m/s, the wind noise reduction is typically 15 dB over the frequency range of 0.1-20 Hz.

  10. Perceptual effects of noise reduction by time-frequency masking of noisy speech.

    PubMed

    Brons, Inge; Houben, Rolph; Dreschler, Wouter A

    2012-10-01

    Time-frequency masking is a method for noise reduction that is based on the time-frequency representation of a speech in noise signal. Depending on the estimated signal-to-noise ratio (SNR), each time-frequency unit is either attenuated or not. A special type of a time-frequency mask is the ideal binary mask (IBM), which has access to the real SNR (ideal). The IBM either retains or removes each time-frequency unit (binary mask). The IBM provides large improvements in speech intelligibility and is a valuable tool for investigating how different factors influence intelligibility. This study extends the standard outcome measure (speech intelligibility) with additional perceptual measures relevant for noise reduction: listening effort, noise annoyance, speech naturalness, and overall preference. Four types of time-frequency masking were evaluated: the original IBM, a tempered version of the IBM (called ITM) which applies limited and non-binary attenuation, and non-ideal masking (also tempered) with two different types of noise-estimation algorithms. The results from ideal masking imply that there is a trade-off between intelligibility and sound quality, which depends on the attenuation strength. Additionally, the results for non-ideal masking suggest that subjective measures can show effects of noise reduction even if noise reduction does not lead to differences in intelligibility.

  11. Experimental Quiet Sprocket Design and Noise Reduction in Tracked Vehicles

    DTIC Science & Technology

    1981-04-01

    Track and Suspension Noise Reduction Statistical Energy Analysis Mechanical Impedance Measurement Finite Element Modal Analysis\\Noise Sources 2...shape and idler attachment are different. These differen- ces were investigated using the concepts of statistical energy analysis for hull generated noise...element r,’calculated from Statistical Energy Analysis . Such an approach will be valid within reasonable limits for frequencies of about 200 Hz and

  12. External Acoustic Liners for Multi-Functional Aircraft Noise Reduction

    NASA Technical Reports Server (NTRS)

    Jones, Michael G. (Inventor); Thomas, Russell H. (Inventor); Nark, Douglas M. (Inventor); Howerton, Brian M. (Inventor); Czech, Michael J. (Inventor)

    2017-01-01

    Acoustic liners for aircraft noise reduction include one or more chambers that are configured to provide a pressure-release surface such that the engine noise generation process is inhibited and/or absorb sound by converting the sound into heat energy. The size and shape of the chambers can be selected to inhibit the noise generation process and/or absorb sound at selected frequencies.

  13. Intelligibility in noise of three LPC (Linear Predictive Coders) voice channels with active noise reduction headsets

    NASA Astrophysics Data System (ADS)

    Nixon, Charles W.; McKinley, Richard L.

    1988-11-01

    Voice communications processed by Linear Predictive Coders (LPC) are vulnerable to degradation by noise. An earlier study demonstrated that the major effect occurs at the listener. Possible mechanisms for this effect range from poor LPC speech quality to the apparent ease of masking LPC speech by noise. The intelligibility of analog systems is increased with improved signal-to-noise ratios at the ear of the listener. The previous study used state-of-the-art communications headsets with passive sound attenuation. The amount of attenuation provided by these headsets has reached a practical limit, consequently the speech-to-noise ratio cannot be increased for wearable devices. Improvements in speech intelligibility provided by the enhanced and high quality LPC vocoders have not eliminated the problem. A prototype Active Noise Reduction (ANR) headset used with the LPC vocoder systems provided active sound attenuation in addition to the passive attenuation of the headset and resulted in reduced noise at the ear. This reduction improved the speech-to-noise ratio which led to improved intelligibility. Current versions of active noise reduction systems have a high potential for markedly reducing the noise masking problem with the vocoders. State-of-the-art active noise reduction has been proven in laboratory and flight tests. This technology should be applied to these vocoder systems and verified in flight demonstrations in the future.

  14. Noise Reduction Methods for Weighing Lysimeters

    USDA-ARS?s Scientific Manuscript database

    Mechanical vibration of the grass and crop weighing lysimeters, located at the University of California West Side Field Research and Extension Station at Five Points, CA generated noise in lysimeter mass measurements and reduced the quality of evapotranspiration (ET) data. Two filtering methods for ...

  15. Stretchable Mesh for Cavity Noise Reduction

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R. (Inventor)

    2017-01-01

    A stretchable mesh material extends across the opening of a cavity of the landing gear of an aircraft when the landing gear is in the deployed position. The mesh material alters the flow of air across the opening of the landing gear cavity and significantly reduces the amount of noise produced by the wheel well at low-to-mid frequencies.

  16. Adaptive noise reduction circuit for a sound reproduction system

    NASA Technical Reports Server (NTRS)

    Engebretson, A. Maynard (Inventor); O'Connell, Michael P. (Inventor)

    1995-01-01

    A noise reduction circuit for a hearing aid having an adaptive filter for producing a signal which estimates the noise components present in an input signal. The circuit includes a second filter for receiving the noise-estimating signal and modifying it as a function of a user's preference or as a function of an expected noise environment. The circuit also includes a gain control for adjusting the magnitude of the modified noise-estimating signal, thereby allowing for the adjustment of the magnitude of the circuit response. The circuit also includes a signal combiner for combining the input signal with the adjusted noise-estimating signal to produce a noise reduced output signal.

  17. Supersonic Jet Noise Reductions Predicted With Increased Jet Spreading Rate

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Morris, Philip J.

    1998-01-01

    In this paper, predictions are made of noise radiation from single, supersonic, axisymmetric jets. We examine the effects of changes in operating conditions and the effects of simulated enhanced mixing that would increase the spreading rate of jet shear layer on radiated noise levels. The radiated noise in the downstream direction is dominated by mixing noise and, at higher speeds, it is well described by the instability wave noise radiation model. Further analysis with the model shows a relationship between changes in spreading rate due to enhanced mixing and changes in the far field radiated peak noise levels. The calculations predict that enhanced jet spreading results in a reduction of the radiated peak noise level.

  18. Supersonic jet noise reductions predicted with increased jet spreading rate

    NASA Astrophysics Data System (ADS)

    Dahl, Milo D.; Morris, Philip J.

    1995-03-01

    In this paper, predictions are made of noise radiation from single, supersonic, axisymmetric jets. We examine the effects of changes in operating conditions and the effects of simulated enhanced mixing that would increase the spreading rate of the jet shear layer on radiated noise levels. The radiated noise in the downstream direction is dominated by mixing noise and it is well described by the instability wave noise radiation analysis. A numerical prediction scheme is used for the mean flow providing an efficient method to obtain the mean flow development for various operating conditions and to simulate the enhanced mixing. Using far field radiated noise measurements as a reference, the calculations predict that enhanced jet spreading results in a reduction of radiated noise.

  19. Supersonic Jet Noise Reductions Predicted with Increased Jet Spreading Rate

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Morris, Philip J.

    1995-01-01

    In this paper, predictions are made of noise radiation from single, supersonic, axisymmetric jets. We examine the effects of changes in operating conditions and the effects of simulated enhanced mixing that would increase the spreading rate of the jet shear layer on radiated noise levels. The radiated noise in the downstream direction is dominated by mixing noise and it is well described by the instability wave noise radiation analysis. A numerical prediction scheme is used for the mean flow providing an efficient method to obtain the mean flow development for various operating conditions and to simulate the enhanced mixing. Using far field radiated noise measurements as a reference, the calculations predict that enhanced jet spreading results in a reduction of radiated noise.

  20. Electromagnetic films as lightweight actuators for active noise reduction

    NASA Astrophysics Data System (ADS)

    Sachau, Delf; Kletschkowski, Thomas

    2006-03-01

    The increasing industrialization and markets across the globe do result in noise pollution that affects humans. In order to reduce the sound pressure level (SPL) of disturbing noise active noise control (also known as noise cancellation, active noise reduction (ANR) or anti-noise) is a good option. Herewith unwanted noise from a primary sound source can be reduced significantly by anti-noise generated from a secondary source: At present commercial active noise reduction systems are using moving-coil loudspeakers as actuators. These actuators need a quite large built-in volume and they are not lightweight. Therefore the industrial application of ANR in vehicles is limited. To reduce these difficulties the use of flat loudspeakers made of electromagnetic films seems to be a promising approach. It is a precondition for the use of such new technologies within an ANR- system to have a basic understanding of the dynamic systems behaviour and the sound transmission behaviour of such a lightweight active component: This paper describes the investigation of a flat panel speaker which is based on electrostatic loudspeaker technology. First of all the passive transmission properties have been measured in a test bed. The passive acoustic insulation has been analyzed and weak spots in the frequency response were discovered. Afterwards the flat panel speaker has been used as actuator in an ANR-System to support insulation at those frequencies. An adaptive filter (FxLMS) was adjusted to the panel and the reduction capabilities of a single-output system have been determined.

  1. Revolutionary Concepts for Helicopter Noise Reduction: SILENT Program

    NASA Technical Reports Server (NTRS)

    Edwards, Bryan; Cox, Charles; Booth, Earl R., Jr. (Technical Monitor)

    2002-01-01

    As part of a NASA initiative to reduce helicopter main rotor noise, a Phase 1 study has been performed of candidate noise reduction concepts. Both conventional and novel design technologies have been analyzed that reduce the community impact of helicopter operations. In this study the noise reduction potential and design implications are assessed for conventional means of noise reduction, e.g., tip speed reduction, tip shapes and airfoil tailoring, and for two innovative design concepts: modulated blade spacing and x-force control. Main rotor designs that incorporate modulated blade spacing are shown to have reduced peak noise levels in most flight operations. X-force control alters the helicopter's force balance whereby the miss distance between main rotor blades and shed vortices can be controlled. This control provides a high potential to mitigate BVI noise radiation. Each concept is evaluated using best practice design and analysis methods, achieving the study's aim to significantly reduce noise with minimal performance degradation and no vibration increase. It is concluded that a SILENT main rotor design, incorporating the modulated blade spacing concept, offers significantly reduced noise levels and the potential of a breakthrough in how a helicopter's sound is perceived and judged. The SILENT rotor represents a definite advancement in the state-of-the-art and is selected as the design concept for demonstration in Phase 2. A Phase 2 Implementation Plan is developed for whirl cage and wind tunnel evaluations of a scaled model SILENT rotor.

  2. Jet Noise Reduction by Microjets - A Parametric Study

    NASA Technical Reports Server (NTRS)

    Zaman, K. B. M. Q.

    2010-01-01

    The effect of injecting tiny secondary jets (microjets ) on the radiated noise from a subsonic primary jet is studied experimentally. The microjets are injected on to the primary jet near the nozzle exit with variable port geometry, working fluid and driving pressure. A clear noise reduction is observed that improves with increasing jet pressure. It is found that smaller diameter ports with higher driving pressure, but involving less thrust and mass fraction, can produce better noise reduction. A collection of data from the present as well as past experiments is examined in an attempt to correlate the noise reduction with the operating parameters. The results indicate that turbulent mixing noise reduction, as monitored by OASPL at a shallow angle, correlates with the ratio of jet to primary jet driving pressures normalized by the ratio of corresponding diameters (p d /pjD). With gaseous injection, the spectral amplitudes decrease at lower frequencies while an increase is noted at higher frequencies. It is apparent that this amplitude crossover is at least partly due to shock-associated noise from the underexpanded jets themselves. Such crossover is not seen with water injection since the flow in that case is incompressible and there is no shock-associated noise. Centerline velocity data show that larger noise reduction is accompanied by faster jet decay as well as significant reduction in turbulence intensities. While a physical understanding of the dependence of noise reduction on p d /pjD remains unclear, given this correlation, an analysis explains the observed dependence of the effect on various other parameters.

  3. Sampling, noise-reduction and amplitude estimation issues in surface electromyography.

    PubMed

    Clancy, E A; Morin, E L; Merletti, R

    2002-02-01

    This paper reviews data acquisition and signal processing issues relative to producing an amplitude estimate of surface EMG. The paper covers two principle areas. First, methods for reducing noise, artefact and interference in recorded EMG are described. Wherever possible noise should be reduced at the source via appropriate skin preparation, and the use of well designed active electrodes and signal recording instrumentation. Despite these efforts, some noise will always accompany the desired signal, thus signal processing techniques for noise reduction (e.g. band-pass filtering, adaptive noise cancellation filters and filters based on the wavelet transform) are discussed. Second, methods for estimating the amplitude of the EMG are reviewed. Most advanced, high-fidelity methods consist of six sequential stages: noise rejection/filtering, whitening, multiple-channel combination, amplitude demodulation, smoothing and relinearization. Theoretical and experimental research related to each of the above topics is reviewed and the current recommended practices are described.

  4. Smooth local subspace projection for nonlinear noise reduction

    SciTech Connect

    Chelidze, David

    2014-03-15

    Many nonlinear or chaotic time series exhibit an innate broad spectrum, which makes noise reduction difficult. Local projective noise reduction is one of the most effective tools. It is based on proper orthogonal decomposition (POD) and works for both map-like and continuously sampled time series. However, POD only looks at geometrical or topological properties of data and does not take into account the temporal characteristics of time series. Here, we present a new smooth projective noise reduction method. It uses smooth orthogonal decomposition (SOD) of bundles of reconstructed short-time trajectory strands to identify smooth local subspaces. Restricting trajectories to these subspaces imposes temporal smoothness on the filtered time series. It is shown that SOD-based noise reduction significantly outperforms the POD-based method for continuously sampled noisy time series.

  5. Evaluation of noise reduction techniques for digital hearing aids

    NASA Astrophysics Data System (ADS)

    Parsa, Vijay; Umapathy, Karthikeyan

    2003-10-01

    Individuals with sensorineural hearing loss have increased difficulty in understanding speech in noisy backgrounds. To combat this issue, there has been a major thrust in recent years toward the development of noise reduction algorithms. The goals of this paper are to quantify the relative benefits of different single-microphone noise reduction algorithms, and to investigate the interaction between the noise reduction and dynamic range compression algorithms. Noise reduction techniques evaluated in this paper include spectral subtraction-based techniques, a wavelet-packet-based technique and a matching pursuit-based technique. All algorithms were tested with HINT signals with SNR levels ranging from -5 to 15 dB, and two different noise types viz. the speech-shaped noise and multi-talker babble. Performance was quantified using the ITU standardized PESQ measure which computes the perceptual similarity between the enhanced signal and the original signal. Initial PESQ results showed that the spectral subtraction-based techniques perform superior to that of the wavelet-packet and matching pursuit-based approaches and that the compression time constants have an impact on the overall performance. Perceptual data collected from hearing impaired listeners on sound quality and noise reduction performance will be presented and their correlation with the objective measurements will be discussed.

  6. The Reduction of Advanced Military Aircraft Noise

    DTIC Science & Technology

    2011-12-01

    agreement is obtained between the baseline nozzle measurements at both facilities. This establishes both the noise scaling methodology as well as...c hevron configuration, was run, as well as a twelve chevron designs with different length and penetration parameters. Table 1 shows t he...ratio (NPR) of 2.5 and a n ozzle area ratio (AR) of 1.295. T he GE data and lower array NASA data compare fairly well . NASA’s upper array is

  7. Review of Aircraft Engine Fan Noise Reduction

    NASA Technical Reports Server (NTRS)

    VanZante, Dale

    2008-01-01

    Aircraft turbofan engines incorporate multiple technologies to enhance performance and durability while reducing noise emissions. Both careful aerodynamic design of the fan and proper installation of the fan into the system are requirements for achieving the performance and acoustic objectives. The design and installation characteristics of high performance aircraft engine fans will be discussed along with some lessons learned that may be applicable to spaceflight fan applications.

  8. Experimental Study of Wake / Flap Interaction Noise and the Reduction of Flap Side Edge Noise

    NASA Technical Reports Server (NTRS)

    Hutcheson, Florence V.; Stead, Daniel J.; Plassman, Gerald E.

    2016-01-01

    The effects of the interaction of a wake with a half-span flap on radiated noise are examined. The incident wake is generated by bars of various widths and lengths or by a simplified landing gear model. Single microphone and phased array measurements are used to isolate the effects of the wake interaction on the noise radiating from the flap side edge and flap cove regions. The effects on noise of the wake generator's geometry and relative placement with respect to the flap are assessed. Placement of the wake generators upstream of the flap side edge is shown to lead to the reduction of flap side edge noise by introducing a velocity deficit and likely altering the instabilities in the flap side edge vortex system. Significant reduction in flap side edge noise is achieved with a bar positioned directly upstream of the flap side edge. The noise reduction benefit is seen to improve with increased bar width, length and proximity to the flap edge. Positioning of the landing gear model upstream of the flap side edge also leads to decreased flap side edge noise. In addition, flap cove noise levels are significantly lower than when the landing gear is positioned upstream of the flap mid-span. The impact of the local flow velocity on the noise radiating directly from the landing gear is discussed. The effects of the landing gear side-braces on flap side edge, flap cove and landing gear noise are shown.

  9. Noise reduction by recycling dynamically coupled time series.

    PubMed

    Mera, M Eugenia; Morán, Manuel

    2011-12-01

    We say that several scalar time series are dynamically coupled if they record the values of measurements of the state variables of the same smooth dynamical system. We show that much of the information lost due to measurement noise in a target time series can be recovered with a noise reduction algorithm by crossing the time series with another time series with which it is dynamically coupled. The method is particularly useful for reduction of measurement noise in short length time series with high uncertainties.

  10. Single and Multiple Microphone Noise Reduction Strategies in Cochlear Implants

    PubMed Central

    Azimi, Behnam; Hu, Yi; Friedland, David R.

    2012-01-01

    To restore hearing sensation, cochlear implants deliver electrical pulses to the auditory nerve by relying on sophisticated signal processing algorithms that convert acoustic inputs to electrical stimuli. Although individuals fitted with cochlear implants perform well in quiet, in the presence of background noise, the speech intelligibility of cochlear implant listeners is more susceptible to background noise than that of normal hearing listeners. Traditionally, to increase performance in noise, single-microphone noise reduction strategies have been used. More recently, a number of approaches have suggested that speech intelligibility in noise can be improved further by making use of two or more microphones, instead. Processing strategies based on multiple microphones can better exploit the spatial diversity of speech and noise because such strategies rely mostly on spatial information about the relative position of competing sound sources. In this article, we identify and elucidate the most significant theoretical aspects that underpin single- and multi-microphone noise reduction strategies for cochlear implants. More analytically, we focus on strategies of both types that have been shown to be promising for use in current-generation implant devices. We present data from past and more recent studies, and furthermore we outline the direction that future research in the area of noise reduction for cochlear implants could follow. PMID:22923425

  11. Potential for Landing Gear Noise Reduction on Advanced Aircraft Configurations

    NASA Technical Reports Server (NTRS)

    Thomas, Russell H.; Nickol, Craig L.; Burley, Casey L.; Guo, Yueping

    2016-01-01

    The potential of significantly reducing aircraft landing gear noise is explored for aircraft configurations with engines installed above the wings or the fuselage. An innovative concept is studied that does not alter the main gear assembly itself but does shorten the main strut and integrates the gear in pods whose interior surfaces are treated with acoustic liner. The concept is meant to achieve maximum noise reduction so that main landing gears can be eliminated as a major source of airframe noise. By applying this concept to an aircraft configuration with 2025 entry-into-service technology levels, it is shown that compared to noise levels of current technology, the main gear noise can be reduced by 10 EPNL dB, bringing the main gear noise close to a floor established by other components such as the nose gear. The assessment of the noise reduction potential accounts for design features for the advanced aircraft configuration and includes the effects of local flow velocity in and around the pods, gear noise reflection from the airframe, and reflection and attenuation from acoustic liner treatment on pod surfaces and doors. A technical roadmap for maturing this concept is discussed, and the possible drag increase at cruise due to the addition of the pods is identified as a challenge, which needs to be quantified and minimized possibly with the combination of detailed design and application of drag reduction technologies.

  12. NASA Noise Reduction Program for Advanced Subsonic Transports

    NASA Technical Reports Server (NTRS)

    Stephens, David G.; Cazier, F. W., Jr.

    1995-01-01

    Aircraft noise is an important byproduct of the world's air transportation system. Because of growing public interest and sensitivity to noise, noise reduction technology is becoming increasingly important to the unconstrained growth and utilization of the air transportation system. Unless noise technology keeps pace with public demands, noise restrictions at the international, national and/or local levels may unduly constrain the growth and capacity of the system to serve the public. In recognition of the importance of noise technology to the future of air transportation as well as the viability and competitiveness of the aircraft that operate within the system, NASA, the FAA and the industry have developed noise reduction technology programs having application to virtually all classes of subsonic and supersonic aircraft envisioned to operate far into the 21st century. The purpose of this paper is to describe the scope and focus of the Advanced Subsonic Technology Noise Reduction program with emphasis on the advanced technologies that form the foundation of the program.

  13. Single and multiple microphone noise reduction strategies in cochlear implants.

    PubMed

    Kokkinakis, Kostas; Azimi, Behnam; Hu, Yi; Friedland, David R

    2012-06-01

    To restore hearing sensation, cochlear implants deliver electrical pulses to the auditory nerve by relying on sophisticated signal processing algorithms that convert acoustic inputs to electrical stimuli. Although individuals fitted with cochlear implants perform well in quiet, in the presence of background noise, the speech intelligibility of cochlear implant listeners is more susceptible to background noise than that of normal hearing listeners. Traditionally, to increase performance in noise, single-microphone noise reduction strategies have been used. More recently, a number of approaches have suggested that speech intelligibility in noise can be improved further by making use of two or more microphones, instead. Processing strategies based on multiple microphones can better exploit the spatial diversity of speech and noise because such strategies rely mostly on spatial information about the relative position of competing sound sources. In this article, we identify and elucidate the most significant theoretical aspects that underpin single- and multi-microphone noise reduction strategies for cochlear implants. More analytically, we focus on strategies of both types that have been shown to be promising for use in current-generation implant devices. We present data from past and more recent studies, and furthermore we outline the direction that future research in the area of noise reduction for cochlear implants could follow.

  14. Listening effort and speech intelligibility in listening situations affected by noise and reverberation.

    PubMed

    Rennies, Jan; Schepker, Henning; Holube, Inga; Kollmeier, Birger

    2014-11-01

    This study compared the combined effect of noise and reverberation on listening effort and speech intelligibility to predictions of the speech transmission index (STI). Listening effort was measured in normal-hearing subjects using a scaling procedure. Speech intelligibility scores were measured in the same subjects and conditions: (a) Speech-shaped noise as the only interfering factor, (b) + (c) fixed signal-to-noise ratios (SNRs) of 0 or 7 dB and reverberation as detrimental factors, and (d) reverberation as the only detrimental factor. In each condition, SNR and reverberation were combined to produce STI values of 0.17, 0.30, 0.43, 0.57, and 0.70, respectively. Listening effort always decreased with increasing STI, thus enabling a rough prediction, but a significant bias was observed indicating that listening effort was lower in reverberation only than in noise only at the same STI for one type of impulse responses. Accordingly, speech intelligibility increased with increasing STI and was significantly better in reverberation only than in noise only at the same STI. Further analyses showed that the broadband reverberation time is not always a good estimate of speech degradation in reverberation and that different speech materials may differ in their robustness toward detrimental effects of reverberation.

  15. Noise reduction by dynamic signal preemphasis

    NASA Astrophysics Data System (ADS)

    Takeda, Kazuyuki; Takegoshi, K.

    2011-02-01

    In this work we propose an approach to reduce the digitization noise for a given dynamic range, i.e., the number of bits, of an analog to digital converter used in an NMR receiver. In this approach, the receiver gain is dynamically increased so that the free induction decay is recorded in such an emphasized way that the decaying signal is digitized using as many number of bits as possible, and at the stage of data processing, the original signal profile is restored by applying the apodization that compensates the effect of the preemphasis. This approach, which we call APodization after Receiver gain InCrement during Ongoing sequence with Time (APRICOT), is performed in a solid-state system containing a pair of 13C spins, one of which is fully isotopically labeled and the other is naturally abundant. It is demonstrated that the exceedingly smaller peak buried in the digitization noise in the conventional approach can be revealed by employing APRICOT.

  16. Noise reduction by dynamic signal preemphasis.

    PubMed

    Takeda, Kazuyuki; Takegoshi, K

    2011-02-01

    In this work we propose an approach to reduce the digitization noise for a given dynamic range, i.e., the number of bits, of an analog to digital converter used in an NMR receiver. In this approach, the receiver gain is dynamically increased so that the free induction decay is recorded in such an emphasized way that the decaying signal is digitized using as many number of bits as possible, and at the stage of data processing, the original signal profile is restored by applying the apodization that compensates the effect of the preemphasis. This approach, which we call APodization after Receiver gain InCrement during Ongoing sequence with Time (APRICOT), is performed in a solid-state system containing a pair of (13)C spins, one of which is fully isotopically labeled and the other is naturally abundant. It is demonstrated that the exceedingly smaller peak buried in the digitization noise in the conventional approach can be revealed by employing APRICOT. Copyright © 2010 Elsevier Inc. All rights reserved.

  17. Fifty Years of Fluidic Injection for Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda

    2010-01-01

    The paper reviews 50 years of research investigating jet noise reduction through fluidic injection. Both aqueous and gaseous injection concepts for supersonic and subsonic jet exhausts are discussed. Aqueous injection reduces jet noise by reducing main jet temperature through evaporation and main jet velocity through momentum transfer between water droplets and the main jet. In the launch vehicle environment where large quantities of fluid do not have to be carried with the vehicle, water injection is very effective at reducing excess overpressures. For in-flight use, aqueous injection is problematic as most studies show that either large quantities of water or high injection pressures are required to achieve noise reduction. The most effective noise reduction injection systems require water pressures above 2000 kPa (290 psi) and water-to-mainjet mass flow rates above 10% to achieve overall sound pressure level reductions of roughly 6 dB in the peak jet noise direction. Injection at lower pressure (roughly 1034 kPa or 150 psi) has resulted in a 1.6 EPNdb reduction in effective perceived noise level. Gaseous injection reduces noise through jet plume modifications resulting from the introduction of streamwise vorticity in the main jet. In subsonic single-stream jets, air injection usually produces the largest overall sound pressure level reductions (roughly 2 dB) in the peak jet noise direction. In dual-stream jets, properly designed injection systems can reduce overall sound pressure levels and effective perceived noise levels but care must be taken to choose injector designs that limit sound pressure level increases at high frequencies. A reduction of 1.0 EPNdB has been achieved with injection into the fan and core streams. However, air injection into dual-stream subsonic jets has received little attention and the potential for noise reduction is uncertain at this time. For dual-stream supersonic jets, additional research needs to be conducted to determine if

  18. Reduction of Wake-Stator Interaction Noise Using Passive Porosity

    NASA Technical Reports Server (NTRS)

    Tinetti, Ana F.; Kelly, Jeffrey J.; Thomas, Russell H.; Bauer, Steven X. S.

    2002-01-01

    The present study was conducted to assess the potential of Passive Porosity Technology as a mechanism to reduce interaction noise in turbomachinery by reducing the fluctuating forces acting on the vane surfaces. To do so, a typical fan stator airfoil was subjected to the effects of a transversely moving wake; time histories of the primitive aerodynamic variables, obtained from Computational Fluid Dynamics (CFD) solutions, were then input into an acoustic prediction code. This procedure was performed on the solid airfoil to obtain a baseline, and on a series of porous configurations in order to isolate those that yield maximum noise reductions without compromising the aerodynamic performance of the stator. It was found that communication between regions of high pressure differential - made possible by the use of passive porosity - is necessary to significantly alter the noise radiation pattern of the stator airfoil. In general, noise reductions were obtained for those configurations incorporating passive porosity in the region between x/c is approximately 0.15 on the suction side of the airfoil and x/c is approximately 0.20 on the pressure side. Reductions in overall radiated noise of approximately 1.0 dB were obtained. The noise benefit increased to about 2.5 dB when the effects of loading noise alone were considered.

  19. Subjective Listening Effort and Electrodermal Activity in Listening Situations with Reverberation and Noise

    PubMed Central

    Haeder, Kristina; Imbery, Christina; Weber, Reinhard

    2016-01-01

    Disturbing factors like reverberation or ambient noise can impair speech recognition and raise the listening effort needed for successful communication in daily life. Situations with high listening effort are thought to result in increased stress for the listener. The aim of this study was to explore possible measures to determine listening effort in situations with varying background noise and reverberation. For this purpose, subjective ratings of listening effort, speech recognition, and stress level, together with the electrodermal activity as a measure of the autonomic stress reaction, were investigated. It was expected that the electrodermal activity would show different stress levels in different acoustic situations and might serve as an alternative to subjective ratings. Ten young normal-hearing and 17 elderly hearing-impaired subjects listened to sentences from the Oldenburg sentence test either with stationary background noise or with reverberation. Four listening situations were generated, an easy and a hard one for each of the two disturbing factors, which were related to each other by the Speech Transmission Index. The easy situation resulted in 100% and the hard situation resulted in 30 to 80% speech recognition. The results of the subjective ratings showed significant differences between the easy and the hard listening situations in both subject groups. Two methods of analyzing the electrodermal activity values revealed similar, but nonsignificant trends. Significant correlations between subjective ratings and physiological electrodermal activity data were observed for normal-hearing subjects in the noise situation. PMID:27698257

  20. Combined effect of noise and room acoustics on vocal effort in simulated classrooms.

    PubMed

    Cipriano, Marcella; Astolfi, Arianna; Pelegrín-García, David

    2017-01-01

    This work investigated the relationships between room acoustics, background noise level, and vocal effort of a speaker in simulated classrooms of various volumes. Under simulated acoustic environments, talkers adjusted their vocal effort linearly with the voice support, i.e., the degree of amplification offered by the room to the voice of a speaker, at his own ears. The slope of this relationship, called the room effect, of -0.24 dB/dB was significant only in the case of the highest noise levels of 62 dB. The vocal comfort for the speaker, however, was found to be more closely related to noise annoyance than to room reverberance.

  1. EBF noise reduction through nozzle/flap positioning

    NASA Technical Reports Server (NTRS)

    Kadman, Y.; Chandiramani, K. L.

    1976-01-01

    Results are presented of an experimental and analytical study of the dependence of externally blown flap (EBF) noise on the relative position and shape of engine exhaust nozzle. Tests, conducted on a 1/15 scale model of a triple-slotted EBF system, indicate that a significant reduction (of up to 10 to 15 db for no forward speed case and of up to 5 to 10 db for forward speed case) is possible in the low frequency (around 63 Hz) region of the noise spectrum of the full scale device for small nozzle/flap separation distances. The overall acoustic performance, measured in PNdb, does not exhibit significant reductions. The analysis of the EBF noise is carried out for two limiting airfoil in a free jet. The analytical results also suggest that low frequency noise can be reduced by placing the nozzle close to the flow turning elements.

  2. Reduction of internal noise in auditory perceptual learning.

    PubMed

    Jones, Pete R; Moore, David R; Amitay, Sygal; Shub, Daniel E

    2013-02-01

    This paper examines what mechanisms underlie auditory perceptual learning. Fifteen normal hearing adults performed two-alternative, forced choice, pure tone frequency discrimination for four sessions. External variability was introduced by adding a zero-mean Gaussian random variable to the frequency of each tone. Measures of internal noise, encoding efficiency, bias, and inattentiveness were derived using four methods (model fit, classification boundary, psychometric function, and double-pass consistency). The four methods gave convergent estimates of internal noise, which was found to decrease from 4.52 to 2.93 Hz with practice. No group-mean changes in encoding efficiency, bias, or inattentiveness were observed. It is concluded that learned improvements in frequency discrimination primarily reflect a reduction in internal noise. Data from highly experienced listeners and neural networks performing the same task are also reported. These results also indicated that auditory learning represents internal noise reduction, potentially through the re-weighting of frequency-specific channels.

  3. Low-frequency noise reduction of lightweight airframe structures

    NASA Technical Reports Server (NTRS)

    Getline, G. L.

    1976-01-01

    The results of an experimental study to determine the noise attenuation characteristics of aircraft type fuselage structural panels were presented. Of particular interest was noise attenuation at low frequencies, below the fundamental resonances of the panels. All panels were flightweight structures for transport type aircraft in the 34,050 to 45,400 kg (75,000 to 100,000 pounds) gross weight range. Test data include the results of vibration and acoustic transmission loss tests on seven types of isotropic and orthotropically stiffened, flat and curved panels. The results show that stiffness controlled acoustically integrated structures can provide very high noise reductions at low frequencies without significantly affecting their high frequency noise reduction capabilities.

  4. The relation between psychoacoustical factors and annoyance under different noise reduction conditions for railway noise.

    PubMed

    Kasess, Christian H; Maly, Thomas; Majdak, Piotr; Waubke, Holger

    2017-05-01

    The A-weighted sound pressure level (SPL) is commonly used to assess the effect of noise reduction measures on noise-induced annoyance. While for road traffic noise loudness seems to be a better descriptor of annoyance, for railway noise a systematic investigation seems to be lacking. Thus, in this study, the relation between annoyance and perceptually motivated descriptors was investigated for various conditions of binaural recordings of pass-bys of cargo and passenger trains. The conditions included free field and spectral mitigations caused by a 4 m high noise barrier, a 1 m high noise barrier close to the track, and rail dampers. Forty listeners performed a free magnitude estimation of annoyance for different presentation levels and the ratings were fit to various models. Further, level changes required to evoke a noticeable change in annoyance (annoyance thresholds) were acquired. The models based on the A-weighted SPL explained the ratings and thresholds better when the reduction measure was explicitly provided as a parameter. However, the optimal models were loudness-level-based models, which were able to better describe the annoyance, even independently of the reduction measure. Both experiments underline the effectiveness of loudness when describing the annoyance in the area of railway noise reduction.

  5. Future developments in transport aircraft noise reduction technology

    SciTech Connect

    Pendley, R.E.

    1982-01-01

    During the past 13 years, important advances in the technology of aircraft noise control have resulted from industry and government research programs. Quieter commercial transport airplanes have entered the fleet and additional new designs now committed to production will begin service in a few years. This paper indicates the noise reductions that will be achieved by the quieter transports that will replace the older designs and remarks on the outlook for still quieter designs.

  6. Noise reduction and signal-to-noise ratio improvement of atomic magnetometers with optical gradiometer configurations.

    PubMed

    Kamada, Keigo; Ito, Yosuke; Ichihara, Sunao; Mizutani, Natsuhiko; Kobayashi, Tetsuo

    2015-03-09

    In the field of biomagnetic measurement, optically-pumped atomic magnetometers (OPAMs) have attracted significant attention. With the improvement of signal response and the reduction of sensor noise, the sensitivity of OPAMs is limited mainly by environmental magnetic noise. To reduce this magnetic noise, we developed the optical gradiometer, in which the differential output of two distinct measurement areas inside a glass cell was obtained directly via the magneto-optical rotation of one probe beam. When operating in appropriate conditions, the sensitivity was improved by the differential measurement of the optical gradiometer. In addition, measurements of the pseudo-magnetic noise and signal showed the improvement of the signal-to-noise ratio. These results demonstrate the feasibility of our optical gradiometer as an efficient method for reducing the magnetic noise.

  7. Arrhythmia ECG Noise Reduction by Ensemble Empirical Mode Decomposition

    PubMed Central

    Chang, Kang-Ming

    2010-01-01

    A novel noise filtering algorithm based on ensemble empirical mode decomposition (EEMD) is proposed to remove artifacts in electrocardiogram (ECG) traces. Three noise patterns with different power—50 Hz, EMG, and base line wander – were embedded into simulated and real ECG signals. Traditional IIR filter, Wiener filter, empirical mode decomposition (EMD) and EEMD were used to compare filtering performance. Mean square error between clean and filtered ECGs was used as filtering performance indexes. Results showed that high noise reduction is the major advantage of the EEMD based filter, especially on arrhythmia ECGs. PMID:22219702

  8. Re-engining - The sound case for aircraft noise reduction

    NASA Astrophysics Data System (ADS)

    Goddard, K.

    1991-06-01

    The paper reviews the history of legislation to reduce jet-powered aircraft noise, particularly in the U.S.A. Recently introduced legislation is discussed and the paper goes on to explain the fundamental advantage of re-engining as a means of reducing aircraft noise. Th Rolls-Royce Tay engine is introduced and the two re-engine programs already launched are described. The expected large reductions in noise level which result from re-engining are illustrated. The paper concludes with a discussion on new programs, on the current airline business scene and on some aspects of the economics of re-engining.

  9. Survey of inlet noise reduction concepts for gas turbine engines

    NASA Technical Reports Server (NTRS)

    Lansing, D. L.; Chestnutt, D.

    1976-01-01

    An overview is given of advanced concepts for the suppression of noise in the inlets of gas turbine engines. Inlet geometric and operating parameters are presented and design criteria for suppression methods are discussed. Noise suppression concepts are described, the directions of current research are reviewed. Problem areas requiring further work are indicated. Well established approaches to inlet noise reduction - namely, acoustic liners and high subsonic Mach number inlets which are the focus of considerable current research activity are considered along with the acoustic absorption and watet vapor injection.

  10. Noise exposure reduction of advanced high-lift systems

    NASA Technical Reports Server (NTRS)

    Haffner, Stephen W.

    1995-01-01

    The purpose of NASA Contract NAS1-20090 Task 3 was to investigate the potential for noise reduction that would result from improving the high-lift performance of conventional subsonic transports. The study showed that an increase in lift-to-drag ratio of 15 percent would reduce certification noise levels by about 2 EPNdB on approach, 1.5 EPNdB on cutback, and zero EPNdB on sideline. In most cases, noise contour areas would be reduced by 10 to 20 percent.

  11. Amplitude Noise Reduction of Ion Lasers with Optical Feedback

    NASA Technical Reports Server (NTRS)

    Herring, Gregory C.

    2011-01-01

    A reduction in amplitude noise on the output of a multi-mode continuous-wave Ar-ion laser was previously demonstrated when a fraction of the output power was retroreflected back into the laser cavity. This result was reproduced in the present work and a Fabry-Perot etalon was used to monitor the longitudinal mode structure of the laser. A decrease in the number of operating longitudinal cavity modes was observed simultaneously with the introduction of the optical feedback and the onset of the amplitude noise reduction. The noise reduction is a result of a reduced number of lasing modes, resulting in less mode beating and amplitude fluctuations of the laser output power.

  12. A Landing Gear Noise Reduction Study Based on Computational Simulations

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Lockard, David P.

    2006-01-01

    Landing gear is one of the more prominent airframe noise sources. Techniques that diminish gear noise and suppress its radiation to the ground are highly desirable. Using a hybrid computational approach, this paper investigates the noise reduction potential of devices added to a simplified main landing gear model without small scale geometric details. The Ffowcs Williams and Hawkings equation is used to predict the noise at far-field observer locations from surface pressure data provided by unsteady CFD calculations. Because of the simplified nature of the model, most of the flow unsteadiness is restricted to low frequencies. The wheels, gear boxes, and oleo appear to be the primary sources of unsteadiness at these frequencies. The addition of fairings around the gear boxes and wheels, and the attachment of a splitter plate on the downstream side of the oleo significantly reduces the noise over a wide range of frequencies, but a dramatic increase in noise is observed at one frequency. The increased flow velocities, a consequence of the more streamlined bodies, appear to generate extra unsteadiness around other parts giving rise to the additional noise. Nonetheless, the calculations demonstrate the capability of the devices to improve overall landing gear noise.

  13. Michelson Interferometer characterisation of noise reduction in DFB fibre lasers

    NASA Astrophysics Data System (ADS)

    Canagasabey, Albert; Jones, David; Mann, David; Canning, John; Fleming, Simon; Holdsworth, John

    2012-02-01

    A comparison is made between unpackaged and packaged distributed feedback (DFB) fibre lasers using the Michelson interferometer configuration for delayed self-heterodyne interferometery (MIDSHI) to ascertain the improvements to the external environmental noise, quantified by reductions in the Gaussian linewidth. Voigt fitting is used to extract and separate out the Lorentzian and Gaussian linewidth contributions and therefore the associated sources of noise. Significant improvements in the Gaussian linewidth were achieved as a result of significant reductions in the sensitivity of the DFB laser to external perturbations using packaging. However, a broadening of the laser Lorentzian linewidth was observed.

  14. Newly-Developed Adaptive Noise Absorption Control Technology for High Speed Fan Noise Reduction

    NASA Astrophysics Data System (ADS)

    Kobayashi, Hiroshi; Koh, Masaharu; Ozaki, Shunichi; Yokochi, Makoto; Sato, Takuo

    The paper describes about a newly-developed adaptive noise absorption control (AAC) technology I for fan noise reduction and about proof test results of the technology. The AAC technology adaptively controls the reactance part of acoustic impedance of duct liners with mobile reflective plates and large acoustic chambers, absorbs fan tones and broadband noise together, and achieves larger overall fan noise reduction over a wide fan speed range. For actual proof of the technology, adaptive duct liner I was made on trial basis and was examined. The test result clarifies that the duct liner I could reduce fan noise larger than O.A. SPL 10dB (A) at max fan speed of 6000rpm, including reduction of low frequency noise and fundamental BPF tone and harmonics of 18dB at maximum. In response to fan speed change, the reflective plate movement control could achieve the large peak frequency shift and peak level increase in the acoustic absorption spectra, and could reduce fan noise larger than O.A. SPL 9dB (A) over the fan speed range from 1000 to 6000rpm.

  15. Broadband Noise Reduction of a Low-Speed Fan Noise Using Trailing Edge Blowing

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.

    2005-01-01

    An experimental proof-of-concept test was conducted to demonstrate reduction of rotor-stator interaction noise through the use of rotor-trailing edge blowing. The velocity deficit from the viscous wake of the rotor blades was reduced by injecting air into the wake from a continuous trailing edge slot. Hollow blades with interior guide vanes create flow channels through which externally supplied air flows from the blade root to the trailing edge. A previous paper documented the substantial tonal reductions of this Trailing Edge Rotor Blowing (TERB) fan. This report documents the broadband characteristics of TERB. The Active Noise Control Fan (ANCF), located at the NASA Glenn Research Center, was used as the proof-of-concept test bed. Two-component hotwire data behind the rotor, unsteady surface pressures on the stator vane, and farfield directivity acoustic data were acquired at blowing rates of 1.1, 1.5, and 1.8 percent of the total fan mass flow. The results indicate a substantial reduction in the rotor wake turbulent velocity and in the stator vane unsteady surface pressures. Based on the physics of the noise generation, these indirect measurements indicate the prospect of broadband noise reduction. However, since the broadband noise generated by the ANCF is rotor-dominated, any change in the rotor-stator interaction broadband noise levels is barely distinguishable in the farfield measurements.

  16. F‐GHG Emissions Reduction Efforts: FY2015 Supplier Profiles

    EPA Pesticide Factsheets

    The Supplier Profiles outlined in this document detail the efforts of large‐area flat panel suppliers to reduce their F‐GHG emissions in manufacturing facilities that make today’s large‐area panels used for products such as TVs and computer monitors.

  17. Reduction of voluntary dehydration during effort in hot environments

    NASA Technical Reports Server (NTRS)

    Sohar, E.; Adar, R.; Gilat, T.; Tennenbaum, J.; Nir, M.

    1982-01-01

    During an experimental marching trip the daily positive fluid balance was preserved by providing a wide choice of beverages during the hours of the day. It was found that the beverage most suitable for drinking in large quantities during periods of effort was a cold drink with sweetened (citrus) fruit taste. Carbonated drinks, including beer, but milk also, were found unsuitable for this purpose.

  18. An assessment of psychological noise reduction by landscape plants.

    PubMed

    Yang, Fan; Bao, Zhi Yi; Zhu, Zhu Jun

    2011-04-01

    The emphasis in the term 'Green Transportation' is on the word 'green'. Green transportation focuses on the construction of a slow transport system with a visually pleasing, easy and secure trip environment composed of urban parks, green roadside spaces and some other space that is full of landscape plants. This trip environment encourages residents to make trip choices that reduce fuel consumption and pollution and is one of the most important ways of popularizing green transportation. To study the psychological benefits provided by urban parks and other landscape environments, we combined a subjective approach (a questionnaire) with an objective quantitative approach (emotional tests using an electroencephalogram; EEG). Using a questionnaire survey, we found that 90% of the subjects believed that landscape plants contribute to noise reduction and that 55% overrated the plants' actual ability to attenuate noise. Two videos (showing a traffic scene and a plant scene) were shown to 40 participants on video glasses. We detected and recorded EEG values with a portable electroencephalograph, and a comparison between the results of the two groups revealed that there was a highly significant asymmetry between the EEG activity of the vegetation scene and traffic scene groups. The results suggest that the emotions aroused by noise and visual stimuli are manifested in the synchronization of beta frequency band and the desynchronization of alpha frequency band, indicating that landscape plants can moderate or buffer the effects of noise. These findings indicate that landscape plants provide excess noise attenuating effects through subjects' emotional processing, which we term 'psychological noise reduction'.

  19. Computational Evaluation of Airframe Noise Reduction Concepts at Full Scale

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Duda, Benjamin; Hazir, Andreas; Fares, Ehab

    2016-01-01

    High-fidelity simulations focused on full-scale evaluation of new technologies for mitigating flap and landing gear noise are presented. These noise reduction concepts were selected because of their superior acoustic performance, as demonstrated during NASA wind tunnel tests of an 18%-scale, semi-span model of a Gulfstream aircraft. The full-scale, full-aircraft, time-accurate simulations were performed with the lattice Boltzmann PowerFLOW(Registered Trademark) solver for free air at a Mach number of 0.2. Three aircraft configurations (flaps deflected at 39? without and with main gear deployed, and 0? flaps with main gear extended) were used to determine the aero-acoustic performance of the concepts on component-level (individually) and system-level (concurrent applica-tion) bases. Farfield noise spectra were obtained using a Ffowcs-Williams and Hawkings acoustic analogy approach. Comparison of the predicted spectra without (baseline) and with the noise treatments applied showed that noise reduction benefits between 2-3 dB for the flap and 1.3-1.7 dB for the main landing gear are obtained. It was also found that the full extent of the benefits is being masked by the noise generated from the flap brackets and main gear cavities, which act as prominent secondary sources.

  20. Supersonic jet noise reduction by coaxial rectangular nozzles

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Manes, J. P.; Massey, K. C.

    1992-01-01

    A physical understanding of noise reduction mechanisms in supersonic, single, and coaxial rectangular jets is quantified and obtained, with emphasis on shock noise reduction. For all conditions, corresponding acoustic measurements for an equivalent round jet are also obtained so that the noise characteristics of the two types of jets can be compared directly to quantify the noise reductions. Comparisons are thus provided for a single rectangular nozzle vs a single equivalent round nozzle, and a coaxial rectangular nozzle vs an equivalent round nozzle. It is shown that different operating conditions and nozzle arrangements for the same thrust, total exit area, and mass flow rate can produce different noise levels. With at least one stream operated supersonically, the coaxial rectangular nozzle operated in the inverted-velocity profile is always quieter than in the normal velocity profile mode for the same thrust, exit area, and mass flow rate. In general, the coaxial rectangular nozzle is shown to be quieter than an equivalent circular nozzle only for those conditions for which both nozzles are operated supersonically.

  1. Supersonic jet noise reduction by coaxial rectangular nozzles

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Manes, J. P.; Massey, K. C.

    1992-01-01

    A physical understanding of noise reduction mechanisms in supersonic, single, and coaxial rectangular jets is quantified and obtained, with emphasis on shock noise reduction. For all conditions, corresponding acoustic measurements for an equivalent round jet are also obtained so that the noise characteristics of the two types of jets can be compared directly to quantify the noise reductions. Comparisons are thus provided for a single rectangular nozzle vs a single equivalent round nozzle, and a coaxial rectangular nozzle vs an equivalent round nozzle. It is shown that different operating conditions and nozzle arrangements for the same thrust, total exit area, and mass flow rate can produce different noise levels. With at least one stream operated supersonically, the coaxial rectangular nozzle operated in the inverted-velocity profile is always quieter than in the normal velocity profile mode for the same thrust, exit area, and mass flow rate. In general, the coaxial rectangular nozzle is shown to be quieter than an equivalent circular nozzle only for those conditions for which both nozzles are operated supersonically.

  2. Sound quality measures for speech in noise through a commercial hearing aid implementing digital noise reduction.

    PubMed

    Ricketts, Todd A; Hornsby, Benjamin W Y

    2005-05-01

    This brief report discusses the affect of digital noise reduction (DNR) processing on aided speech recognition and sound quality measures in 14 adults fitted with a commercial hearing aid. Measures of speech recognition and sound quality were obtained in two different speech-in-noise conditions (71 dBA speech, +6 dB SNR and 75 dBA speech, +1 dB SNR). The results revealed that the presence or absence of DNR processing did not impact speech recognition in noise (either positively or negatively). Paired comparisons of sound quality for the same speech in noise signals, however, revealed a strong preference for DNR processing. These data suggest that at least one implementation of DNR processing is capable of providing improved sound quality, for speech in noise, in the absence of improved speech recognition.

  3. Airframe self-noise: Four years of research. [aircraft noise reduction for commercial aircraft

    NASA Technical Reports Server (NTRS)

    Hardin, J. C.

    1976-01-01

    A critical assessment of the state of the art in airframe self-noise is presented. Full-scale data on the intensity, spectra and directivity of this noise source are evaluated in the light of the comprehensive theory developed by Ffowcs-Williams and Hawkins. Vibration of panels on commercial aircraft is identified as a possible additional source of airframe noise. The present understanding and methods for prediction of other component sources - airfoils, struts, and cavities - are discussed, and areas for further research as well as potential methods for airframe noise reduction are identified. Finally, the various experimental methods which have been developed for airframe noise research are discussed and sample results are presented.

  4. Aircraft interior noise reduction by alternate resonance tuning

    NASA Technical Reports Server (NTRS)

    Bliss, Donald B.; Gottwald, James A.; Srinivasan, Ramakrishna; Gustaveson, Mark B.

    1990-01-01

    Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at lower frequencies, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is being studied which considers aircraft fuselage lined with panels alternately tuned to frequencies above and below the frequency that must be attenuated. Adjacent panels would oscillate at equal amplitude, to give equal source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to become cutoff, and therefore be non-propagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is currently being investigated both theoretically and experimentally. This new concept has potential application to reducing interior noise due to the propellers in advanced turboprop aircraft as well as for existing aircraft configurations.

  5. Prediction of Turbulent Jet Mixing Noise Reduction by Water Injection

    NASA Technical Reports Server (NTRS)

    Kandula, Max

    2008-01-01

    A one-dimensional control volume formulation is developed for the determination of jet mixing noise reduction due to water injection. The analysis starts from the conservation of mass, momentum and energy for the confrol volume, and introduces the concept of effective jet parameters (jet temperature, jet velocity and jet Mach number). It is shown that the water to jet mass flow rate ratio is an important parameter characterizing the jet noise reduction on account of gas-to-droplet momentum and heat transfer. Two independent dimensionless invariant groups are postulated, and provide the necessary relations for the droplet size and droplet Reynolds number. Results are presented illustrating the effect of mass flow rate ratio on the jet mixing noise reduction for a range of jet Mach number and jet Reynolds number. Predictions from the model show satisfactory comparison with available test data on perfectly expanded hot supersonic jets. The results suggest that significant noise reductions can be achieved at increased flow rate ratios.

  6. 4-D noise-based seismology at volcanoes: Ongoing efforts and perspectives

    NASA Astrophysics Data System (ADS)

    Brenguier, Florent; Rivet, Diane; Obermann, Anne; Nakata, Nori; Boué, Pierre; Lecocq, Thomas; Campillo, Michel; Shapiro, Nikolai

    2016-07-01

    Monitoring magma pressure buildup at depth and transport to surface is a key point for improving volcanic eruption prediction. Seismic waves, through their velocity dependence to stress perturbations, can provide crucial information on the temporal evolution of the mechanical properties of volcanic edifices. In this article, we review past and ongoing efforts for extracting accurate information of temporal changes of seismic velocities at volcanoes continuously in time using records of ambient seismic noise. We will first introduce the general methodology for retrieving accurate seismic velocity changes from seismic noise records and discuss the origin of seismic velocity temporal changes in rocks. We will then discuss in a second part how noise-based monitoring can improve our knowledge about magmatic activity at a long (years) to a short (days) time scale taking example from Piton de la Fournaise volcano (La Réunion). We will also mention ongoing efforts for operational noise-based seismic monitoring on volcanoes. Further, we will discuss perspectives for improving the spatial localization of detected velocity changes at depth with a special focus on the use of dense seismic arrays. In the last part, we will finally explore the complex response of volcanic regions to seismic shaking with an example from Japan and show how imaging seismic velocity susceptibility allows characterizing the state of pressurized fluids in volcanic regions.

  7. Development of Novel Methods for the Reduction of Noise and Weight in Helicopter Transmissions

    NASA Astrophysics Data System (ADS)

    Dimofte, Florin; Keith, Theo G., Jr.

    2003-01-01

    Over the 70-year evolution of the helicopter, man's understanding of vibration control has greatly increased. However, in spite of the increased performance, the extent of helicopter vibration problems has not significantly diminished. Crew vibration and noise remains important factors in the design of all current helicopters. With more complex and critical demands being placed on aircrews, it is essential that vibration and noise not impair their performance. A major source of helicopter cabin noise (which has been measured at a sound pressure level of over 100 dB) is the gearbox. Reduction of this noise has been a goal of NASA and the U.S. Army. Gear mesh noise is typically in the frequency range of 1000 to 3000 Hz, a range important for speech. A requirement for U.S. Army/NASA Advanced Rotorcraft Transmission project has been a 10-dB reduction compared to current designs. A combined analytical/experimental effort has been underway, since the end of the 80's, to study effects of design parameters on noise production. The noise generated by the gear mesh can be transmitted to the surrounding media through the bearings that support the gear shaft. Therefore, the use of fluid film bearings instead of rolling element bearings could reduce the transmission noise by 10 dB. In addition, the fluid film bearings that support the gear shaft can change the dynamics of the gear assembly by providing damping to the system and by being softer than rolling element bearings. Wave bearings can attenuate, and filter, the noise generated by a machine component due to the dynamic stiffness and damping coefficients. The attenuation ratio could be as large as 35-40 dB. The noise components at higher frequencies than a synchronous frequency can be almost eliminated.

  8. Development of Novel Methods for the Reduction of Noise and Weight in Helicopter Transmissions

    NASA Technical Reports Server (NTRS)

    Dimofte, Florin; Keith, Theo G., Jr.

    2003-01-01

    Over the 70-year evolution of the helicopter, man's understanding of vibration control has greatly increased. However, in spite of the increased performance, the extent of helicopter vibration problems has not significantly diminished. Crew vibration and noise remains important factors in the design of all current helicopters. With more complex and critical demands being placed on aircrews, it is essential that vibration and noise not impair their performance. A major source of helicopter cabin noise (which has been measured at a sound pressure level of over 100 dB) is the gearbox. Reduction of this noise has been a goal of NASA and the U.S. Army. Gear mesh noise is typically in the frequency range of 1000 to 3000 Hz, a range important for speech. A requirement for U.S. Army/NASA Advanced Rotorcraft Transmission project has been a 10-dB reduction compared to current designs. A combined analytical/experimental effort has been underway, since the end of the 80's, to study effects of design parameters on noise production. The noise generated by the gear mesh can be transmitted to the surrounding media through the bearings that support the gear shaft. Therefore, the use of fluid film bearings instead of rolling element bearings could reduce the transmission noise by 10 dB. In addition, the fluid film bearings that support the gear shaft can change the dynamics of the gear assembly by providing damping to the system and by being softer than rolling element bearings. Wave bearings can attenuate, and filter, the noise generated by a machine component due to the dynamic stiffness and damping coefficients. The attenuation ratio could be as large as 35-40 dB. The noise components at higher frequencies than a synchronous frequency can be almost eliminated.

  9. A Background Noise Reduction Technique Using Adaptive Noise Cancellation for Microphone Arrays

    NASA Technical Reports Server (NTRS)

    Spalt, Taylor B.; Fuller, Christopher R.; Brooks, Thomas F.; Humphreys, William M., Jr.; Brooks, Thomas F.

    2011-01-01

    Background noise in wind tunnel environments poses a challenge to acoustic measurements due to possible low or negative Signal to Noise Ratios (SNRs) present in the testing environment. This paper overviews the application of time domain Adaptive Noise Cancellation (ANC) to microphone array signals with an intended application of background noise reduction in wind tunnels. An experiment was conducted to simulate background noise from a wind tunnel circuit measured by an out-of-flow microphone array in the tunnel test section. A reference microphone was used to acquire a background noise signal which interfered with the desired primary noise source signal at the array. The technique s efficacy was investigated using frequency spectra from the array microphones, array beamforming of the point source region, and subsequent deconvolution using the Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) algorithm. Comparisons were made with the conventional techniques for improving SNR of spectral and Cross-Spectral Matrix subtraction. The method was seen to recover the primary signal level in SNRs as low as -29 dB and outperform the conventional methods. A second processing approach using the center array microphone as the noise reference was investigated for more general applicability of the ANC technique. It outperformed the conventional methods at the -29 dB SNR but yielded less accurate results when coherence over the array dropped. This approach could possibly improve conventional testing methodology but must be investigated further under more realistic testing conditions.

  10. Trailing edge noise reduction in a backward-curved impeller

    NASA Astrophysics Data System (ADS)

    Lauchle, Gerald C.

    2002-05-01

    Motorized impellers are used in many air-moving applications including room circulation, duct flow, roof and wall exhaust, and cooling of electronic components in cabinets. These fans are backward-curved centrifugal blowers that operate with no volute casing. These fans radiate broadband noise due to turbulence ingestion and trailing edge (TE) noise generating mechanisms. Considered here are trailing edge noise generation and its reduction in a typical motorized impeller. The sound power of the subject fans is measured in an acoustically transparent test plenum according to ANSI Standard S12.11-1987. Two different serrated TE treatments are designed. The designs assume that a turbulent boundary layer exists at the blade TE, but the actual fan Reynolds number based on chord length is transitional. Therefore, to assure that a turbulent boundary layer exists at the TE, two different inlet turbulators are implemented. These trip the blade boundary layer to a turbulent state. Reported are the effects of the TE serrations and turbulators acting individually on the fan noise, along with the synergistic effects of using them in combinations. Up to 6 dBA of noise reduction is observed when the two are used together. [Work supported by Nortel Networks.

  11. A novel approach to fast noise reduction of infrared image

    NASA Astrophysics Data System (ADS)

    Lin, Chih-Lung; Kuo, Chih-Wei; Lai, Chih-Chin; Tsai, Ming-Dar; Chang, Yuan-Chang; Cheng, Hsu-Yung

    2011-01-01

    The goal of this paper is to develop a fast noise reduction (FNR) approach to infrared (IR) images. The IR images usually have noise, edges, text information and small objects of interest. The well known standard median filter (MF) is not suitable to process these IR images. The main characteristics of the proposed approach are that no prior knowledge about the IR image noise is necessary and no parameters must be preset. It is developed based on IR imaging mechanism to detect the noisy pixels and on modified median-based filter to remove the noisy pixels in IR images. The FSN approach has the advantage of low computation load. In addition, it can retain reasonably good edges, details and texture information even if the size of the filter window increases. The goal of the proposed approach is feasible for an effective process for reducing noise of IR images, regardless of the filter windows' and objects' sizes. It also significantly speeds up the noise reduction process and can apply to real-time video processing. FNR approach will extend the IR image applications of medicine.

  12. Propeller noise reduction by means of unsymmetrical blade-spacing

    NASA Astrophysics Data System (ADS)

    Dobrzynski, W.

    1993-05-01

    The noise reduction potential of propellers with circumferentially unsymmetrical blade-spacing is predicted on theoretical grounds and substantiated through both aerodynamic and aeroacoustic full scale wind tunnel experiments. To avoid potential balancing problems such propellers have two (or several) pairs of opposite blades, each such pair constituting a symmetrical two-blade propeller. Spacing angles between these individual blade pairs are optimized towards achieving minimum A-weighted noise radiation in the plane of rotation. The result is then compared with the corresponding noise level from a symmetrical reference propeller with the same total number of geometrically identical blades. The study reveals that the value of the optimum spacing angle depends almost entirely on the operational helical blade-tip Mach number, assuming values of about 40 deg at a Mach number of O.5 and decreasing to 15 deg at a Mach number of 0.8. The noise reduction to be achieved from such unsymmetrical blade-spacing is limited to about 4 dB(A) in the direction of maximum noise radiation since the related acoustic effect is due to interference between the sound pressure signatures of the individual blades. It is found that both the harmonic sound pressure level spectrum and the acoustic directivity pattern is affected.

  13. Aeroacoustic Evaluation of Flap and Landing Gear Noise Reduction Concepts

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Humphreys, William M., Jr.; Lockard, David P.; Ravetta, Patricio A.

    2014-01-01

    Aeroacoustic measurements for a semi-span, 18% scale, high-fidelity Gulfstream aircraft model are presented. The model was used as a test bed to conduct detailed studies of flap and main landing gear noise sources and to determine the effectiveness of numerous noise mitigation concepts. Using a traversing microphone array in the flyover direction, an extensive set of acoustic data was obtained in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the information was acquired with the model in a landing configuration with the flap deflected 39 deg and the main landing gear alternately installed and removed. Data were obtained at Mach numbers of 0.16, 0.20, and 0.24 over directivity angles between 56 deg and 116 deg, with 90 deg representing the overhead direction. Measured acoustic spectra showed that several of the tested flap noise reduction concepts decrease the sound pressure levels by 2 - 4 dB over the entire frequency range at all directivity angles. Slightly lower levels of noise reduction from the main landing gear were obtained through the simultaneous application of various gear devices. Measured aerodynamic forces indicated that the tested gear/flap noise abatement technologies have a negligible impact on the aerodynamic performance of the aircraft model.

  14. A beamformer post-filter for cochlear implant noise reduction.

    PubMed

    Hersbach, Adam A; Grayden, David B; Fallon, James B; McDermott, Hugh J

    2013-04-01

    Cochlear implant users have limited ability to understand speech in noisy conditions. Signal processing methods to address this issue that use multiple microphones typically use beamforming to perform noise reduction. However, the effectiveness of the beamformer is diminished as the number of interfering noises increases and the acoustic environment becomes more diffuse. A multi-microphone noise reduction algorithm that aims to address this issue is presented in this study. The algorithm uses spatial filtering to estimate the signal-to-noise ratio (SNR) and attenuates time-frequency elements that have poor SNR. The algorithm was evaluated by measuring intelligibility of speech embedded in 4-talker babble where the interfering talkers were spatially separated and changed location during the test. Twelve cochlear implant users took part in the evaluation, which demonstrated a significant mean improvement of 4.6 dB (standard error 0.4, P < 0.001) in speech reception threshold compared to an adaptive beamformer. The results suggest that a substantial improvement in performance can be gained for cochlear implant users in noisy environments where the noise is spatially separated from the target speech.

  15. Benefits of Swept and Leaned Stators for Fan Noise Reduction

    NASA Technical Reports Server (NTRS)

    Woodward, Richard P.; Elliott, David M.; Hughes, Christopher E.; Berton, Jeffrey J.

    1998-01-01

    An advanced high bypass ratio fan model was tested in the NASA Lewis Research Center 9 x 15-Foot Low Speed Wind Tunnel. The primary focus of this test was to quantify the acoustic benefits and aerodynamic performance of sweep and lean in stator vane design. Three stator sets were used for this test series. A conventional radial stator was tested at two rotor-stator axial spacings. Additional stator sets incorporating sweep + lean, and sweep only were also tested. The hub axial location for the swept + lean, and sweep only stators corresponded to the location of the radial stator at the upstream rotor-stator spacing, while the tip axial location of these modified stators corresponded to the radial stator axial position at the downstream position. The acoustic results show significant reductions in both rotor-stator interaction noise and broadband noise beyond what could be achieved through increased axial spacing of the conventional, radial stator. Theoretical application of these results to acoustically quantify a fictitious 2-engine aircraft and flight path suggested that about 3 Effective Perceived Noise (EPN) dB could be achieved through incorporation of these modified stators. This reduction would represent a significant portion of the 6 EPNdB noise goal of the current NASA Advanced Subsonic Technology (AST) initiative relative to that of 1992 technology levels. A secondary result of this fan test was to demonstrate the ability of an acoustic barrier wall to block aft-radiated fan noise in the wind tunnel, thus revealing the acoustic structure of the residual inlet-radiated noise. This technology should prove valuable toward better understanding inlet liner design, or wherever it is desirable to eliminate aft-radiated noise from the fan acoustic signature.

  16. Prediction and Reduction of Noise in Pneumatic Bleed Valves

    NASA Astrophysics Data System (ADS)

    Taghavi Nezhad, Shervin

    This study investigates numerically the fluid mechanics and acoustics of pneumatic bleed valves used in turbofan engines. The goal is to characterized the fundamental processes of noise generation and devise strategies for noise reduction. Three different methods are employed for both analysis and redesign of the bleed valve to reduce noise. The bleed valve noise problem is carefully divided into multiple smaller problems. For large separations and tonal noises, the unsteady Reynolds-Averaged Navier-Stokes (URANS) method is utilized. This method is also applied in the re-designing of the bleed valve geometry. For the bleed valve muffler, which is comprised of perforated plates and a honeycomb, a Reynolds-Averaged Navier-Stokes (RANS) method combined with a simplified acoustic analogy is used. The original muffler design is modified to improve noise attenuation. Finally, for sound scattering through perforated plates, a fully implicit linearized Euler solver is developed. The problem of sound interaction with perforated plates is studied from two perspectives. In the first study the effect of high--speed mean flow is considered and it is shown that at Strouhal numbers of around 0.2-0.25 there is an increase in transmitted incident sound. In the second part, the interaction of holes in two--dimensional perforated plates is investigated using three different configurations. The study demonstrates that the hole interaction has a significant impact on sound attenuation, especially at high frequencies.

  17. Zwicker Tone Illusion and Noise Reduction in the Auditory System

    NASA Astrophysics Data System (ADS)

    Franosch, Jan-Moritz P.; Kempter, Richard; Fastl, Hugo; van Hemmen, J. Leo

    2003-05-01

    The Zwicker tone is an auditory aftereffect. For instance, after switching off a broadband noise with a spectral gap, one perceives it as a lingering pure tone with the pitch in the gap. It is a unique illusion in that it cannot be explained by known properties of the auditory periphery alone. Here we introduce a neuronal model explaining the Zwicker tone. We show that a neuronal noise-reduction mechanism in conjunction with dominantly unilateral inhibition explains the effect. A pure tone’s “hole burning” in noisy surroundings is given as an illustration.

  18. An aeroacoustic study of micro-tab on airframe noise reduction

    NASA Astrophysics Data System (ADS)

    Kuo, Chiawei B.

    Aircraft high-lift devices such as leading-edge slats and trailing-edge flaps generate noise when extended, causing significant contributions to overall aircraft sound pressure levels, in particular in approach to land phase. It is shown by previous research efforts that noise generated by the high-lift devices increases with their deployment angles. Hence it is possible to mitigate such high-lift noise by using reduced settings without sacrificing the aerodynamic performance, particularly lift. In this dissertation research, micro-tab device attached at the pressure side of the flap surface near its trailing-edge is envisioned as the way to compensate the lift loss due to reduced high-lift device settings. Hybrid numerical method, which combines computational fluid dynamics and acoustics analogy, was adopted to predict the farfield noise spectrum. It is the goal of this research project to illustrate that noise level increase due to micro-tab deployment is smaller than that from the prescribed slat and flap setting increases, so that an overall airframe noise reduction can be achieved. Two-dimensional computational simulations and three-dimensional computational simulations were performed progressively. Results indicated that the proposed reduced high-lift settings with micro-tab application achieved noise reduction, particularly in the mid-frequency range where human hearing is most sensitive to. Parametric studies involving geometry and size effects of the micro-tab configurations were conducted using two-dimensional and three-dimensional models. Results showed that considerable noise reduction was obtained if slit micro-tab was used. An airworthiness study regarding applying micro-tab device onto existing commercial airliners as retrofit to lower noise emission in approach was also investigated and compliance strategy was provided. In the last part of this research, a different approach from aviation policy was taken as the airport noise compatibility planning

  19. New circuit theory of multiconductor transmission lines resulting from a new practice of noise reduction

    PubMed Central

    TOKI, Hiroshi; SATO, Kenji

    2014-01-01

    In modern life, we are surrounded by and filled with electromagnetic noise caused by the dominant use of energy in the form of electricity. This situation is brought about by the fact that the noise is not understood theoretically. A new practice of noise reduction was introduced for the construction of Heavy Ion Medical Accelerator in Chiba (HIMAC). The key concept is a symmetric three-line circuit that arranges power supplies, noise filters and magnets around a third central ground line. A continuous theoretical effort forced us to find a new circuit theory involving a multiconductor transmission-line system starting from Maxwell’s equations without any approximation. We discuss the essence of all of these experimental and theoretical developments with the hope to remove unnecessary electromagnetic noise not only from power supplies, but also from all electric devices. The newly derived circuit theory of multiconductor transmission lines is universal, and establishes the validity of the practice of noise reduction. PMID:24522153

  20. Combustion generated noise in gas turbine combustors. [engine noise/noise reduction

    NASA Technical Reports Server (NTRS)

    Strahle, W. C.; Shivashankara, B. N.

    1974-01-01

    Experiments were conducted to determine the noise power and spectra emitted from a gas turbine combustor can exhausting to the atmosphere. Limited hot wire measurements were made of the cold flow turbulence level and spectra within the can. The fuels used were JP-4, acetone and methyl alcohol burning with air at atmospheric pressure. The experimental results show that for a fixed fuel the noise output is dominated by the airflow rate and not the fuel/air ratio. The spectra are dominated by the spectra of the cold flow turbulence spectra which were invariant with airflow rate in the experiments. The effect of fuel type on the noise power output was primarily through the heat of combustion and not the reactivity. A theory of combustion noise based upon the flame radiating to open surroundings is able to reasonably explain the observed results. A thermoacoustic efficiency for noise radiation as high as .00003 was observed in this program for JP-4 fuel. Scaling rules are presented for installed configurations.

  1. Image noise reduction algorithm for digital subtraction angiography: clinical results.

    PubMed

    Söderman, Michael; Holmin, Staffan; Andersson, Tommy; Palmgren, Charlotta; Babic, Draženko; Hoornaert, Bart

    2013-11-01

    To test the hypothesis that an image noise reduction algorithm designed for digital subtraction angiography (DSA) in interventional neuroradiology enables a reduction in the patient entrance dose by a factor of 4 while maintaining image quality. This clinical prospective study was approved by the local ethics committee, and all 20 adult patients provided informed consent. DSA was performed with the default reference DSA program, a quarter-dose DSA program with modified acquisition parameters (to reduce patient radiation dose exposure), and a real-time noise-reduction algorithm. Two consecutive biplane DSA data sets were acquired in each patient. The dose-area product (DAP) was calculated for each image and compared. A randomized, blinded, offline reading study was conducted to show noninferiority of the quarter-dose image sets. Overall, 40 samples per treatment group were necessary to acquire 80% power, which was calculated by using a one-sided α level of 2.5%. The mean DAP with the quarter-dose program was 25.3% ± 0.8 of that with the reference program. The median overall image quality scores with the reference program were 9, 13, and 12 for readers 1, 2, and 3, respectively. These scores increased slightly to 12, 15, and 12, respectively, with the quarter-dose program imaging chain. In DSA, a change in technique factors combined with a real-time noise-reduction algorithm will reduce the patient entrance dose by 75%, without a loss of image quality. RSNA, 2013

  2. Noise Reduction Of Air Blower Casing Using Composites

    NASA Astrophysics Data System (ADS)

    Kolla*, S.; Kumar, Y. Anil; Rajesh, S.

    Sound subjectively, what is heard by the ear; objectively, is a mecha nical disturbance from equilibrium in an elastic medium. The noise produced by a rotating component has two main components, the broadband noise and the discrete frequency noise. The broadband noise from a rotor is due to random loading forces on the blades, which are induced by the absorption of atmospheric turbulence. The discrete frequency noise is due to periodic interaction of incoming air with the blades of the rotor. At present the centrifugal blowers, in Naval defense application which is made of steel is generating a noise of 86dB, which causes mental imbalance to the people working near the blower on ship. Therefore in Naval defense applications the reduction of sound level from a source is very important and critical task. Hence the objective of this paper is to reduce the noise level produced by the metal air blower. The noise radiated by the casing of a centrifugal blower can be effectively reduced by the use of (1) Composite Materials, (2) Visco-Elastic material treatment and (3) Stiffness addition. In this paper it is proposed to carry out a study to evaluate the effectiveness of composites in reducing noise levels of the casing. Composite materials are those containing more than one bonded material, each with different struc tural properties. The advantage of composite materials is the potential for a high ratio of stiffness to weight. In order to evaluate the effectiveness of composites over metals, modal analysis (Eigen value analysis) and Static analysis was performed on both composite and metal blowers using FEA package (ANSYS). Modal analysis is performed on both metals (Alluminium and Composite) blower casing to find out the first ten natural frequencies and static analysis is performed for a pressure of 1570 Pa. This paper also describes the experimental setup of the centrifugal blower, the values of the sound levels for both metal and FRP blowers are taken at a distance of

  3. Background Elimination and Noise Reduction by Mechanical Modulation Raman Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hinko, Kathleen; Ibeneche, Chieze; Keidel, Andrea; Bartsch, Tobias; Florin, Ernst-Ludwig

    2011-03-01

    Raman spectroscopy is widely used by biophysicists for the molecular identification of cellular substructures. However, there are high levels of background and noise associated with Raman spectra from other molecules in the microscopic detection volume. We present two methods of mechanical modulation for background subtraction and noise reduction in a Raman microscope: (1) a three-axis stage modulation for fixed objects and (2) a separate optical trap modulation for objects in solution. With our technique, we completely eliminate the background in our spectra and improve the signal-to-noise ratio by two orders of magnitude. We applied this technique to lipid vesicles and fission yeast cells in solution. Additionally, we obtained mechanical modulation Raman spectra of fission yeast in three dimensions and observed spatial differences in the molecular composition for different metabolic states of a single yeast cell.

  4. The NIRS Analysis Package: noise reduction and statistical inference.

    PubMed

    Fekete, Tomer; Rubin, Denis; Carlson, Joshua M; Mujica-Parodi, Lilianne R

    2011-01-01

    Near infrared spectroscopy (NIRS) is a non-invasive optical imaging technique that can be used to measure cortical hemodynamic responses to specific stimuli or tasks. While analyses of NIRS data are normally adapted from established fMRI techniques, there are nevertheless substantial differences between the two modalities. Here, we investigate the impact of NIRS-specific noise; e.g., systemic (physiological), motion-related artifacts, and serial autocorrelations, upon the validity of statistical inference within the framework of the general linear model. We present a comprehensive framework for noise reduction and statistical inference, which is custom-tailored to the noise characteristics of NIRS. These methods have been implemented in a public domain Matlab toolbox, the NIRS Analysis Package (NAP). Finally, we validate NAP using both simulated and actual data, showing marked improvement in the detection power and reliability of NIRS.

  5. A hybrid algorithm for speckle noise reduction of ultrasound images.

    PubMed

    Singh, Karamjeet; Ranade, Sukhjeet Kaur; Singh, Chandan

    2017-09-01

    Medical images are contaminated by multiplicative speckle noise which significantly reduce the contrast of ultrasound images and creates a negative effect on various image interpretation tasks. In this paper, we proposed a hybrid denoising approach which collaborate the both local and nonlocal information in an efficient manner. The proposed hybrid algorithm consist of three stages in which at first stage the use of local statistics in the form of guided filter is used to reduce the effect of speckle noise initially. Then, an improved speckle reducing bilateral filter (SRBF) is developed to further reduce the speckle noise from the medical images. Finally, to reconstruct the diffused edges we have used the efficient post-processing technique which jointly considered the advantages of both bilateral and nonlocal mean (NLM) filter for the attenuation of speckle noise efficiently. The performance of proposed hybrid algorithm is evaluated on synthetic, simulated and real ultrasound images. The experiments conducted on various test images demonstrate that our proposed hybrid approach outperforms the various traditional speckle reduction approaches included recently proposed NLM and optimized Bayesian-based NLM. The results of various quantitative, qualitative measures and by visual inspection of denoise synthetic and real ultrasound images demonstrate that the proposed hybrid algorithm have strong denoising capability and able to preserve the fine image details such as edge of a lesion better than previously developed methods for speckle noise reduction. The denoising and edge preserving capability of hybrid algorithm is far better than existing traditional and recently proposed speckle reduction (SR) filters. The success of proposed algorithm would help in building the lay foundation for inventing the hybrid algorithms for denoising of ultrasound images. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Speech Perception in Noise and Listening Effort of Older Adults With Nonlinear Frequency Compression Hearing Aids.

    PubMed

    Shehorn, James; Marrone, Nicole; Muller, Thomas

    2017-08-10

    The purpose of this laboratory-based study was to compare the efficacy of two hearing aid fittings with and without nonlinear frequency compression, implemented within commercially available hearing aids. Previous research regarding the utility of nonlinear frequency compression has revealed conflicting results for speech recognition, marked by high individual variability. Individual differences in auditory function and cognitive abilities, specifically hearing loss slope and working memory, may contribute to aided performance. The first aim of the study was to determine the effect of nonlinear frequency compression on aided speech recognition in noise and listening effort using a dual-task test paradigm. The hypothesis, based on the Ease of Language Understanding model, was that nonlinear frequency compression would improve speech recognition in noise and decrease listening effort. The second aim of the study was to determine if listener variables of hearing loss slope, working memory capacity, and age would predict performance with nonlinear frequency compression. A total of 17 adults (age, 57-85 years) with symmetrical sensorineural hearing loss were tested in the sound field using hearing aids fit to target (NAL-NL2). Participants were recruited with a range of hearing loss severities and slopes. A within-subjects, single-blinded design was used to compare performance with and without nonlinear frequency compression. Speech recognition in noise and listening effort were measured by adapting the Revised Speech in Noise Test into a dual-task paradigm. Participants were required trial-by-trial to repeat the last word of each sentence presented in speech babble and then recall the sentence-ending words after every block of six sentences. Half of the sentences were rich in context for the recognition of the final word of each sentence, and half were neutral in context. Extrinsic factors of sentence context and nonlinear frequency compression were manipulated, and

  7. Reduction of Altitude Diffuser Jet Noise Using Water Injection

    NASA Technical Reports Server (NTRS)

    Allgood, Daniel C.; Saunders, Grady P.; Langford, Lester A.

    2011-01-01

    A feasibility study on the effects of injecting water into the exhaust plume of an altitude rocket diffuser for the purpose of reducing the far-field acoustic noise has been performed. Water injection design parameters such as axial placement, angle of injection, diameter of injectors, and mass flow rate of water have been systematically varied during the operation of a subscale altitude test facility. The changes in acoustic far-field noise were measured with an array of free-field microphones in order to quantify the effects of the water injection on overall sound pressure level spectra and directivity. The results showed significant reductions in noise levels were possible with optimum conditions corresponding to water injection at or just upstream of the exit plane of the diffuser. Increasing the angle and mass flow rate of water injection also showed improvements in noise reduction. However, a limit on the maximum water flow rate existed as too large of flow rate could result in un-starting the supersonic diffuser.

  8. Reduction of Altitude Diffuser Jet Noise Using Water Injection

    NASA Technical Reports Server (NTRS)

    Allgood, Daniel C.; Saunders, Grady P.; Langford, Lester A.

    2014-01-01

    A feasibility study on the effects of injecting water into the exhaust plume of an altitude rocket diffuser for the purpose of reducing the far-field acoustic noise has been performed. Water injection design parameters such as axial placement, angle of injection, diameter of injectors, and mass flow rate of water have been systematically varied during the operation of a subscale altitude test facility. The changes in acoustic far-field noise were measured with an array of free-field microphones in order to quantify the effects of the water injection on overall sound pressure level spectra and directivity. The results showed significant reductions in noise levels were possible with optimum conditions corresponding to water injection at or just upstream of the exit plane of the diffuser. Increasing the angle and mass flow rate of water injection also showed improvements in noise reduction. However, a limit on the maximum water flow rate existed as too large of flow rate could result in un-starting the supersonic diffuser.

  9. Gene regulation and noise reduction by coupling of stochastic processes

    NASA Astrophysics Data System (ADS)

    Ramos, Alexandre F.; Hornos, José Eduardo M.; Reinitz, John

    2015-02-01

    Here we characterize the low-noise regime of a stochastic model for a negative self-regulating binary gene. The model has two stochastic variables, the protein number and the state of the gene. Each state of the gene behaves as a protein source governed by a Poisson process. The coupling between the two gene states depends on protein number. This fact has a very important implication: There exist protein production regimes characterized by sub-Poissonian noise because of negative covariance between the two stochastic variables of the model. Hence the protein numbers obey a probability distribution that has a peak that is sharper than those of the two coupled Poisson processes that are combined to produce it. Biochemically, the noise reduction in protein number occurs when the switching of the genetic state is more rapid than protein synthesis or degradation. We consider the chemical reaction rates necessary for Poisson and sub-Poisson processes in prokaryotes and eucaryotes. Our results suggest that the coupling of multiple stochastic processes in a negative covariance regime might be a widespread mechanism for noise reduction.

  10. Gene regulation and noise reduction by coupling of stochastic processes

    PubMed Central

    Hornos, José Eduardo M.; Reinitz, John

    2015-01-01

    Here we characterize the low noise regime of a stochastic model for a negative self-regulating binary gene. The model has two stochastic variables, the protein number and the state of the gene. Each state of the gene behaves as a protein source governed by a Poisson process. The coupling between the the two gene states depends on protein number. This fact has a very important implication: there exist protein production regimes characterized by sub-Poissonian noise because of negative covariance between the two stochastic variables of the model. Hence the protein numbers obey a probability distribution that has a peak that is sharper than those of the two coupled Poisson processes that are combined to produce it. Biochemically, the noise reduction in protein number occurs when the switching of genetic state is more rapid than protein synthesis or degradation. We consider the chemical reaction rates necessary for Poisson and sub-Poisson processes in prokaryotes and eucaryotes. Our results suggest that the coupling of multiple stochastic processes in a negative covariance regime might be a widespread mechanism for noise reduction. PMID:25768447

  11. Gene regulation and noise reduction by coupling of stochastic processes.

    PubMed

    Ramos, Alexandre F; Hornos, José Eduardo M; Reinitz, John

    2015-02-01

    Here we characterize the low-noise regime of a stochastic model for a negative self-regulating binary gene. The model has two stochastic variables, the protein number and the state of the gene. Each state of the gene behaves as a protein source governed by a Poisson process. The coupling between the two gene states depends on protein number. This fact has a very important implication: There exist protein production regimes characterized by sub-Poissonian noise because of negative covariance between the two stochastic variables of the model. Hence the protein numbers obey a probability distribution that has a peak that is sharper than those of the two coupled Poisson processes that are combined to produce it. Biochemically, the noise reduction in protein number occurs when the switching of the genetic state is more rapid than protein synthesis or degradation. We consider the chemical reaction rates necessary for Poisson and sub-Poisson processes in prokaryotes and eucaryotes. Our results suggest that the coupling of multiple stochastic processes in a negative covariance regime might be a widespread mechanism for noise reduction.

  12. Noise Reduction for a MEMS-Gyroscope-Based Head Mouse.

    PubMed

    Du, Jiaying; Gerdtman, Christer; Lindén, Maria

    2015-01-01

    In this paper, four different signal processing algorithms which can be applied to reduce the noise from a MEMS-gyroscope-based computer head mouse are presented. MEMS-gyroscopes are small, light, cheap and widely used in many electrical products. MultiPos, a MEMS-gyroscope-based computer head mouse system was designed for persons with movement disorders. Noise such as physiological tremor and electrical noise is a common problem for the MultiPos system. In this study four different signal processing algorithms were applied and evaluated by simulation in MATLAB and implementation in a dsPIC, with aim to minimize the noise in MultiPos. The algorithms were low-pass filter, Least Mean Square (LMS) algorithm, Kalman filter and Weighted Fourier Linear Combiner (WFLC) algorithm. Comparisons and system tests show that these signal processing algorithms can be used to improve the MultiPos system. The WFLC algorithm was found the best method for noise reduction in the application of a MEMS-gyroscope-based head mouse.

  13. A new noise reduction method for airborne gravity gradient data

    NASA Astrophysics Data System (ADS)

    Jirigalatu; Ebbing, Jörg; Sebera, Josef

    2016-09-01

    Airborne gravity gradient (AGG) measurements offer an increased resolution and accuracy compared to terrestrial measurements. But interpretation and processing of AGG data are often challenging as levelling errors and survey noise affect the data, and these effects are not easily recognised in the gradient components. We adopted the classic method of upward continuation in the noise reduction using the noise level estimates by the AGG system. By iteratively projecting the survey data to a lower level and upward continuing the data back to the survey height, parts of the high-frequency signal are suppressed. The filter, which is defined by this approach, is directly dependent on the noise level of the AGG data, the maximum number of iterations and the iterative step. We demonstrate the method by applying it to both synthetic data and real AGG data over Karasjok, Norway, and compare the results to the directional filtering method. The results show that the iterative filter can effectively reduce high-frequency noise in the data.

  14. Recruitment-of-loudness effects of attenuative noise reduction algorithms

    NASA Astrophysics Data System (ADS)

    Whitmal, Nathaniel; Vosoughi, Azadeh

    2002-05-01

    Hearing-impaired listeners have greater difficulty understanding speech in noise than normal-hearing listeners do. As a result, hearing aid users are often challenged by the inability of their hearing aids to improve intelligibility in noise. Several investigators have addressed this problem by using well-known signal processing methods (e.g., spectral subtraction, Wiener filtering) to enhance noise-corrupted speech. Unfortunately, these methods have failed to provide significant improvements in intelligibility. One possible explanation is the level-dependent nature of the attenuation that the algorithms impose on the speech. In the cases described above, this attenuation resembles the piecewise-linear input-output characteristic observed in certain recruitment-of-loudness simulators. The purpose of this study was to compare the intelligibility of processed speech with that expected for recruitment-of-loudness simulation. Trials of the CUNY Nonsense Syllable Test were conducted with 12 normal-hearing listeners, using syllables that were mixed with additive noise at SNRs of 6, 12, and 18 dB. Input-output characteristics for the signals were measured and used to determine the effective threshold shift imposed by the algorithms. Comparisons of measured intelligibility scores with articulation index-based intelligibility predictions indicate that the behavior of such noise reduction algorithms can be successfully modeled as a form of mild sensorineural hearing loss.

  15. Noise reduction in ultrasonic NDT using undecimated wavelet transforms.

    PubMed

    Pardo, E; San Emeterio, J L; Rodriguez, M A; Ramos, A

    2006-12-22

    Translation-invariant wavelet processing is applied to grain noise reduction in ultrasonic non-destructive testing of materials. In particular, the undecimated wavelet transform (UWT), which is essentially a discrete wavelet transform (DWT) that avoids decimation, is used. Two different UWT processors have been specifically developed for that purpose, based on two UWT implementation schemes: the "à trous" algorithm and the cycle-spinning scheme. The performance of these two UWT processors is compared with that of a classical DWT processor, by using synthetic grain noise registers and experimental pulse-echo NDT traces. The synthetic ultrasonic traces have been generated by an own-developed frequency-domain model that includes frequency dependence in both material attenuation and scattering. The experimental ultrasonic traces have been obtained by inspecting a piece of carbon-fiber reinforced plastic composite in which we have mechanized artificial flaws. Decomposition level-dependent thresholds, which are suitable for correlated noise, are specifically determined in all cases. Soft thresholding, Daubechies db6 mother wavelet and the three well-known threshold selection rules, Universal, Minimax and SURE, are applied to the different decomposition levels. The performance of the different de-noising procedures for single echo detection has been comparatively evaluated in terms of signal-to-noise ratio enhancement.

  16. USB noise reduction by nozzle and flap modifications

    NASA Technical Reports Server (NTRS)

    Hayden, R. E.

    1976-01-01

    The development of concepts for reducing upper surface blown flap noise at the source through flap modifications and special nozzles is reviewed. In particular, recent results obtained on the aerodynamic and acoustic performance of flaps with porous surfaces near the trailing edge and multi-slotted nozzles are reviewed. Considerable reduction (6-10 db) of the characteristic low frequency peak is shown. The aerodynamic performance is compared with conventional systems, and prospects for future improvements are discussed.

  17. Improvement of speech recognition by nonlinear noise reduction

    NASA Astrophysics Data System (ADS)

    Urbanowicz, Krzysztof; Kantz, Holger

    2007-06-01

    The success of nonlinear noise reduction applied to a single channel recording of human voice is measured in terms of the recognition rate of a commercial speech recognition program in comparison to the optimal linear filter. The overall performance of the nonlinear method is shown to be superior. We hence demonstrate that an algorithm that has its roots in the theory of nonlinear deterministic dynamics possesses a large potential in a realistic application.

  18. Improvement of speech recognition by nonlinear noise reduction.

    PubMed

    Urbanowicz, Krzysztof; Kantz, Holger

    2007-06-01

    The success of nonlinear noise reduction applied to a single channel recording of human voice is measured in terms of the recognition rate of a commercial speech recognition program in comparison to the optimal linear filter. The overall performance of the nonlinear method is shown to be superior. We hence demonstrate that an algorithm that has its roots in the theory of nonlinear deterministic dynamics possesses a large potential in a realistic application.

  19. Aircraft noise reduction technology. [to show impact on individuals and communities, component noise sources, and operational procedures to reduce impact

    NASA Technical Reports Server (NTRS)

    1973-01-01

    Aircraft and airport noise reduction technology programs conducted by NASA are presented. The subjects discussed are: (1) effects of aircraft noise on individuals and communities, (2) status of aircraft source noise technology, (3) operational procedures to reduce the impact of aircraft noise, and (4) NASA relations with military services in aircraft noise problems. References to more detailed technical literature on the subjects discussed are included.

  20. Study of noise reduction characteristics of double-wall panels

    NASA Technical Reports Server (NTRS)

    Navaneethan, R.; Quayle, B.; Stevenson, S.; Graham, M.

    1983-01-01

    The noise reduction characteristics of general aviation type, flat, double-wall structures were investigated. The experimental study was carried out on 20-by-20 inch panels with an exposed area of 18 by 18 inches. A frequency range from 20 to 5000 Hz was covered. The experimental results, in general, follow the expected trends. At low frequencies the double-wall structures are no better than the single-wall structures. However, for depths normally used in the general aviation industry, the double-wall panels are very attractive. The graphite-spoxy skin panels have higher noise reduction at very low frequencies ( 100 Hz) than the Kevlar skin panels. But the aluminum panels have higher noise reduction in the high frequency region, due to their greater mass. Use of fiberglass insulation is not effective in the low frequency region, and at times it is even negative. But the insulation is effective in the high-frequency region. The theoretical model for predicting the transmission loss of these multilayered panels is also discussed.

  1. Single-channel noise reduction using optimal rectangular filtering matrices.

    PubMed

    Long, Tao; Chen, Jingdong; Benesty, Jacob; Zhang, Zhenxi

    2013-02-01

    This paper studies the problem of single-channel noise reduction in the time domain and presents a block-based approach where a vector of the desired speech signal is recovered by filtering a frame of the noisy signal with a rectangular filtering matrix. With this formulation, the noise reduction problem becomes one of estimating an optimal filtering matrix. To achieve such estimation, a method is introduced to decompose a frame of the clean speech signal into two orthogonal components: One correlated and the other uncorrelated with the current desired speech vector to be estimated. Different optimization cost functions are then formulated from which non-causal optimal filtering matrices are derived. The relationships among these optimal filtering matrices are discussed. In comparison with the classical sample-based technique that uses only forward prediction, the block-based method presented in this paper exploits both the forward and backward prediction as well as the temporal interpolation and, therefore, can improve the noise reduction performance by fully taking advantage of the speech property of self correlation. There is also a side advantage of this block-based method as compared to the sample-based technique, i.e., it is computationally more efficient and, as a result, more suitable for practical implementation.

  2. Voice communications in the cockpit noise environment: The role of active noise reduction

    NASA Astrophysics Data System (ADS)

    Wheeler, Peter David

    The topic of voice communications in the cockpit noise environment of modern fast-jet aircraft and helicopters is addressed, and in particular, research undertaken in support of the development of a system for reducing the noise level at the operators' ear is described by acoustic cancellation within the ear defender, known as active noise reduction (ANR). The internal noise spectra of today's high performance fast-jet aircraft and military helicopters is described, and the complex interaction of acoustic noise transmission, speech, and microphone noise pick-up, which produces the total acoustic environment at the aircrews' ears, is discussed. Means of mathematically modelling the audio channel, quantifying the components identified above, and identifying areas of shortfall in performance are derived, leading to a procedure for the development of attenuation requirements, described as the communications audit. A model of the electroacoustic characteristics of the ANR ear defender assembly is presented and the sound field distribution within the ear defender/ear cavity, and its effect upon cancellation performance, is discussed. The extensive laboratory and flight testing of the ANR system that was undertaken is reviewed, paying particular attention to the measurement and analysis techniques employed in such testing. Finally, the performance characteristics of ANR are discussed and compared with the requirements previously established. Design limitations placed upon the system by the constraints of its area of application are described, and the scope for future improvements is considered.

  3. Numerical Prediction of Chevron Nozzle Noise Reduction using Wind-MGBK Methodology

    NASA Technical Reports Server (NTRS)

    Engblom, W.A.; Bridges, J.; Khavarant, A.

    2005-01-01

    Numerical predictions for single-stream chevron nozzle flow performance and farfield noise production are presented. Reynolds Averaged Navier Stokes (RANS) solutions, produced via the WIND flow solver, are provided as input to the MGBK code for prediction of farfield noise distributions. This methodology is applied to a set of sensitivity cases involving varying degrees of chevron inward bend angle relative to the core flow, for both cold and hot exhaust conditions. The sensitivity study results illustrate the effect of increased chevron bend angle and exhaust temperature on enhancement of fine-scale mixing, initiation of core breakdown, nozzle performance, and noise reduction. Direct comparisons with experimental data, including stagnation pressure and temperature rake data, PIV turbulent kinetic energy fields, and 90 degree observer farfield microphone data are provided. Although some deficiencies in the numerical predictions are evident, the correct farfield noise spectra trends are captured by the WIND-MGBK method, including the noise reduction benefit of chevrons. Implications of these results to future chevron design efforts are addressed.

  4. An Assessment of Psychological Noise Reduction by Landscape Plants

    PubMed Central

    Yang, Fan; Bao, Zhi Yi; Zhu, Zhu Jun

    2011-01-01

    The emphasis in the term ‘Green Transportation’ is on the word ‘green’. Green transportation focuses on the construction of a slow transport system with a visually pleasing, easy and secure trip environment composed of urban parks, green roadside spaces and some other space that is full of landscape plants. This trip environment encourages residents to make trip choices that reduce fuel consumption and pollution and is one of the most important ways of popularizing green transportation. To study the psychological benefits provided by urban parks and other landscape environments, we combined a subjective approach (a questionnaire) with an objective quantitative approach (emotional tests using an electroencephalogram; EEG). Using a questionnaire survey, we found that 90% of the subjects believed that landscape plants contribute to noise reduction and that 55% overrated the plants’ actual ability to attenuate noise. Two videos (showing a traffic scene and a plant scene) were shown to 40 participants on video glasses. We detected and recorded EEG values with a portable electroencephalograph, and a comparison between the results of the two groups revealed that there was a highly significant asymmetry between the EEG activity of the vegetation scene and traffic scene groups. The results suggest that the emotions aroused by noise and visual stimuli are manifested in the synchronization of beta frequency band and the desynchronization of alpha frequency band, indicating that landscape plants can moderate or buffer the effects of noise. These findings indicate that landscape plants provide excess noise attenuating effects through subjects’ emotional processing, which we term ‘psychological noise reduction’. PMID:21695027

  5. Minimizing noise in fiberglass aquaculture tanks: Noise reduction potential of various retrofits

    USGS Publications Warehouse

    Davidson, J.; Frankel, A.S.; Ellison, W.T.; Summerfelt, S.; Popper, A.N.; Mazik, P.; Bebak, J.

    2007-01-01

    Equipment used in intensive aquaculture systems, such as pumps and blowers can produce underwater sound levels and frequencies within the range of fish hearing. The impacts of underwater noise on fish are not well known, but limited research suggests that subjecting fish to noise could result in impairment of the auditory system, reduced growth rates, and increased stress. Consequently, reducing sound in fish tanks could result in advantages for cultured species and increased productivity for the aquaculture industry. The objective of this study was to evaluate the noise reduction potential of various retrofits to fiberglass fish culture tanks. The following structural changes were applied to tanks to reduce underwater noise: (1) inlet piping was suspended to avoid contact with the tank, (2) effluent piping was disconnected from a common drain line, (3) effluent piping was insulated beneath tanks, and (4) tanks were elevated on cement blocks and seated on insulated padding. Four combinations of the aforementioned structural changes were evaluated in duplicate and two tanks were left unchanged as controls. Control tanks had sound levels of 120.6 dB re 1 ??Pa. Each retrofit contributed to a reduction of underwater sound. As structural changes were combined, a cumulative reduction in sound level was observed. Tanks designed with a combination of retrofits had sound levels of 108.6 dB re 1 ??Pa, a four-fold reduction in sound pressure level. Sound frequency spectra indicated that the greatest sound reductions occurred between 2 and 100 Hz and demonstrated that nearby pumps and blowers created tonal frequencies that were transmitted into the tanks. The tank modifications used during this study were simple and inexpensive and could be applied to existing systems or considered when designing aquaculture facilities. ?? 2007 Elsevier B.V. All rights reserved.

  6. 40 CFR 211.207 - Computation of the noise -reduction rating (NRR).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 24 2010-07-01 2010-07-01 false Computation of the noise -reduction... (CONTINUED) NOISE ABATEMENT PROGRAMS PRODUCT NOISE LABELING Hearing Protective Devices § 211.207 Computation of the noise -reduction rating (NRR). Calculate the NRR for hearing protective devices by...

  7. Tanlock loop noise reduction using an optimised phase detector

    NASA Astrophysics Data System (ADS)

    Al-kharji Al-Ali, Omar; Anani, Nader; Al-Qutayri, Mahmoud; Al-Araji, Saleh

    2013-06-01

    This article proposes a time-delay digital tanlock loop (TDTL), which uses a new phase detector (PD) design that is optimised for noise reduction making it amenable for applications that require wide lock range without sacrificing the level of noise immunity. The proposed system uses an improved phase detector design which uses two phase detectors; one PD is used to optimise the noise immunity whilst the other is used to control the acquisition time of the TDTL system. Using the modified phase detector it is possible to reduce the second- and higher-order harmonics by at least 50% compared with the conventional TDTL system. The proposed system was simulated and tested using MATLAB/Simulink using frequency step inputs and inputs corrupted with varying levels of harmonic distortion. A hardware prototype of the system was implemented using a field programmable gate array (FPGA). The practical and simulation results indicate considerable improvement in the noise performance of the proposed system over the conventional TDTL architecture.

  8. Supersonic Jet Noise Reduction Using Flapping Injection and Pulsed Injection

    NASA Astrophysics Data System (ADS)

    Hafsteinsson, Haukur; Eriksson, Lars-Erik; Cuppoletti, Daniel; Gutmark, Ephraim; Department of Applied Mechanics, Chalmers University of Technology Team; Department of Aerospace Engineering, University of Cincinatti Team; Swedish Defence Material Administration, Sweden Team

    2013-11-01

    Aircraft are in general noisy and there is a high demand for reducing their noise levels. The jet exhaust is in most cases the main noise source of the aircraft, especially for low bypass ratio jet engines. Fluidic injection affecting the shear layer close to the nozzle exit is a promising noise reduction technique as it can be turned of while not needed and thus the negative effect on the engine performance will be minimized. In the presented work, LES is used to compare steady-state mass flow injection with steady-state mass flow flapping jet injection. The work is a direct continuation of a previous LES study on pulsed injection which showed that the pulsed injection induced pressure pulses in the jet which caused increased tonal noise in the downstream directions. The injection system considered in the presented work consists of eight evenly distributed injectors at the nozzle exit plane with a 90° injection angle relative to the flow direction. Flapping jet injection is believed to minimize the creation of these pressure pulses since it provides steady-state mass flow. This work is funded by Swedish Defense Material Administration (FMV).

  9. A dual-cable noise reduction method for Langmuir probes

    NASA Astrophysics Data System (ADS)

    Yang, T. F.; Zu, Q. X.; Liu, Ping

    1995-07-01

    To obtain fast time response plasma properties, electron density and electron temperature, with a Langmuir probe, the applied probe voltage has to be swept at high frequency. Due to the RC characteristics of coaxial cables, an induced noise of a square-wave form will appear when a sawtooth voltage is applied to the probe. Such a noise is very annoying and difficult to remove, particularly when the probe signal is weak. This paper discusses a noise reduction method using a dual-cable circuit. One of the cables is active and the other is a dummy. Both of them are of equal length and are laid parallel to each other. The active cable carries the applied probe voltage and the probe current signal. The dummy one is not connected to the probe. After being carefully tuned, the induced noises from both cables are nearly identical and therefore can be effectively eliminated with the use of a differential amplifier. A clean I-V characteristic curve can thus be obtained. This greatly improves the accuracy and the time resolution of the values of ne and Te.

  10. Serration Design Methodology for Wind Turbine Noise Reduction

    NASA Astrophysics Data System (ADS)

    Mathew, J.; Singh, A.; Madsen, J.; Arce León, C.

    2016-09-01

    Trailing edge serrations are today an established method to reduce the aeroacoustic noise from wind turbine blades. In this paper, a brief introduction to the aerodynamic and acoustic design procedure used at LM Wind Power is given. Early field tests on serrations, retrofitted to the turbine blades, gave preliminary indication of their noise reduction potential. However, a multitude of challenges stand in the way of any proof of concept and a viable commercial product. LM undertook a methodical test and validation procedure to understand the impact of design parameters on serration performance, and quantify the uncertainties associated with the proposed designs. Aerodynamic and acoustic validation tests were carried out in number of wind tunnel facilities. Models were written to predict the aerodynamic, acoustic and structural performance of the serrations. LM serration designs have evolved over the period of time to address constraints imposed by aero performance, structural reliability, manufacturing and installation. The latest LM serration offering was tested in the field on three different wind turbines. A consistent noise reduction in excess of 1.5 dB was achieved in the field for all three turbines.

  11. Aircraft interior noise reduction by alternate resonance tuning

    NASA Technical Reports Server (NTRS)

    Gottwald, James A.; Bliss, Donald B.

    1990-01-01

    The focus is on a noise control method which considers aircraft fuselages lined with panels alternately tuned to frequencies above and below the frequency that must be attenuated. An interior noise reduction called alternate resonance tuning (ART) is described both theoretically and experimentally. Problems dealing with tuning single paneled wall structures for optimum noise reduction using the ART methodology are presented, and three theoretical problems are analyzed. The first analysis is a three dimensional, full acoustic solution for tuning a panel wall composed of repeating sections with four different panel tunings within that section, where the panels are modeled as idealized spring-mass-damper systems. The second analysis is a two dimensional, full acoustic solution for a panel geometry influenced by the effect of a propagating external pressure field such as that which might be associated with propeller passage by a fuselage. To reduce the analysis complexity, idealized spring-mass-damper panels are again employed. The final theoretical analysis presents the general four panel problem with real panel sections, where the effect of higher structural modes is discussed. Results from an experimental program highlight real applications of the ART concept and show the effectiveness of the tuning on real structures.

  12. Aircraft interior noise reduction by alternate resonance tuning

    NASA Technical Reports Server (NTRS)

    Bliss, Donald B.; Gottwald, James A.; Gustaveson, Mark B.; Burton, James R., III; Castellino, Craig

    1989-01-01

    Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at lower, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is being studied which considers aircraft fuselages lines with panels alternately tuned to frequencies above and below the frequency to be attenuated. Adjacent panels would oscillate at equal amplitude, to give equal source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to become cut off and therefore be non-propagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is currently being investigated both theoretically and experimentally. This new concept has potential application to reducing interior noise due to the propellers in advanced turboprop aircraft as well as for existing aircraft configurations. This program summarizes the work carried out at Duke University during the third semester of a contract supported by the Structural Acoustics Branch at NASA Langley Research Center.

  13. Noise reduction by magnetostatic coupling in geomagnetic-field sensors

    NASA Astrophysics Data System (ADS)

    Zhao, Chong-Jun; Li, Min; Li, Jian-Wei; Ding, Lei; Teng, Jiao; Yu, Guang-Hua

    2014-11-01

    A new magnetoresistive (MR) thin film with a structure of “antiferromagnetic layer/pinned soft magnetic layer/non-magnetic MgO spacer layer/sensitive NiFe layer” was designed. The barber-pole MR elements with a Wheatstone bridge circuit were fabricated using photolithographic methods. The testing results show that, in comparison to the element with a typical structure of Ta/NiFe/Ta, the fabricated MR element shows significant reduction in the Barkhausen noise and the 1/f noise and good magnetic stability while maintaining high magnetic field sensitivity. This element with improved signals can be attributed to the magnetostatic coupling between the pinned soft magnetic layer and the sensitive NiFe layer, which can act as a small stabilizing field, leading to the coherent rotation of magnetic moment in the sensitive NiFe layer.

  14. Noise reduction techniques for the restoration of musical recordings

    NASA Astrophysics Data System (ADS)

    Cappe, Olivier

    The evaluation of short time spectral attenuation techniques using a simplified model of standard noise suppression rules and with elementary test signals is assessed. Signal distortions induced by the restoration process are evaluated analytically, and their audibility is addressed by use of classic psychoacoustics results. Phenomena observed experimentally in previous studies, such as the modification of timbre, the appearance of modulations, and the spreading of transients, are brought to light. Drawing from these results, a noise reduction technique intended for enhancing musical signals is described. In the first step, the noisy signal is analyzed by use of a medium frequency resolution short time transform. The restoration then takes place in each subband in two different ways according to the nature of the subband signal: the processing is carried out block by block when steady signal components are detected, or locally otherwise. This approach was successfully applied to several musical recordings yielding promising results.

  15. Jet-noise reduction through liquid-base foam injection.

    NASA Technical Reports Server (NTRS)

    Manson, L.; Burge, H. L.

    1971-01-01

    An experimental investigation has been made of the sound-absorbing properties of liquid-base foams and of their ability to reduce jet noise. Protein, detergent, and polymer foaming agents were used in water solutions. A method of foam generation was developed to permit systematic variation of the foam density. The investigation included measurements of sound-absorption coefficents for both plane normal incidence waves and diffuse sound fields. The intrinsic acoustic properties of foam, e.g., the characteristic impedance and the propagation constant, were also determined. The sound emitted by a 1-in.-diam cold nitrogen jet was measured for subsonic (300 m/sec) and supersonic (422 m/sec) jets, with and without foam injection. Noise reductions up to 10 PNdB were measured.

  16. Jet-noise reduction through liquid-base foam injection.

    NASA Technical Reports Server (NTRS)

    Manson, L.; Burge, H. L.

    1971-01-01

    An experimental investigation has been made of the sound-absorbing properties of liquid-base foams and of their ability to reduce jet noise. Protein, detergent, and polymer foaming agents were used in water solutions. A method of foam generation was developed to permit systematic variation of the foam density. The investigation included measurements of sound-absorption coefficents for both plane normal incidence waves and diffuse sound fields. The intrinsic acoustic properties of foam, e.g., the characteristic impedance and the propagation constant, were also determined. The sound emitted by a 1-in.-diam cold nitrogen jet was measured for subsonic (300 m/sec) and supersonic (422 m/sec) jets, with and without foam injection. Noise reductions up to 10 PNdB were measured.

  17. Noise and vibration reduction technology in aircraft internal cabin

    NASA Astrophysics Data System (ADS)

    Takahashi, Kosaku; Monzen, Hirotaka; Yamaoka, Toshihiro; Kusumoto, Koji; Bansaku, Kazuhiro; Kimoto, Junichi; Isoe, Akira; Hirose, Yasuo; Sanda, Tomio; Matsuzaki, Yuji

    2003-08-01

    The study to reduce noise and vibration in aircraft cabin through PZT was implemented, using a semi-monocoque structure, 1.5m in diameter and 3.0m long with 2.3mm skin, which stimulates an aircraft body. We utilized PZT of 480 pieces bonded on inner surface of the structure as sensor and actuator. We applied random noise of low frequency range between 0~500Hz to the test model. We tried to reduce the vibration level of structure and internal air due to the external load by controlling the PZTs. Two control methods, gain control and feed-forward control, were tried. We measured internal sound pressure on 150 spots and compared overall values of sound pressure with gain control to them without control and evaluated its reduction capability. The tests showed 4.0dB O.A. reduction at maximum in gain control and 3.5dB O.A. reduction at maximum in feed forward control.

  18. Feasibility of noise reduction by a modification in ICU environment.

    PubMed

    Luetz, A; Weiss, B; Penzel, T; Fietze, I; Glos, M; Wernecke, K D; Bluemke, B; Dehn, A M; Willemeit, T; Finke, A; Spies, C

    2016-07-01

    Noise is a proven cause of wakefulness and qualitative sleep disturbance in critically ill patients. A sound pressure level reduction can improve sleep quality, but there are no studies showing the feasibility of such a noise reduction in the intensive care unit (ICU) setting. Considering all available evidence, we redesigned two ICU rooms with the aim of investigating the physiological and clinical impact of a healing environment, including a noise reduction and day-night variations of sound level. Within an experimental design, we recorded 96 h of sound-pressure levels in standard ICU rooms and the modified ICU rooms. In addition, we performed a sound source observation by human observers. Our results show that we reduced A-weighted equivalent sound pressure levels and maximum sound pressure levels with our architectural interventions. During night-time, the modification led to a significant decrease in 50 dB threshold overruns from 65.5% to 39.9% (door side) and from 50% to 10.5% (window side). Sound peaks of more than 60 decibels were significantly reduced from 62.0% to 26.7% (door side) and 59.3% to 30.3% (window side). Time-series analysis of linear trends revealed a significantly more distinct day-night pattern in the modified rooms with lower sound levels during night-times. Observed sound sources during night revealed four times as many talking events in the standard room compared to the modified room. In summary, we show that it is feasible to reduce sound pressure levels using architectural modifications.

  19. Critical Propulsion and Noise reduction Technologies for Future Commercial Subsonic Engines. Area of Interest 14.3: Separate Flow Exhaust System Noise

    NASA Technical Reports Server (NTRS)

    Janardan, B. A.; Hoff, G. E.; Barter, J. W.; Brausch, J. F.; Gliebe, P. R.; Coffin, R. S.; Martens, S.; Delaney, B. R.; Dalton, W. N.; Mengle, V. G.

    2000-01-01

    This presentation discusses: Project Objectives, Approach and Goal; Baseline Nozzles and Test Cycle Definition; Repeatability and Baseline Nozzle Results; Noise Reduction Concepts; Noise Reduction Tests Configurations of BPR=5 Internal Plug Nozzle adn Acoustic Results; Noise Reduction Test Configurations of BPR=5 External Plug Nozzle and Acoustic Results; and Noise Reduction Tests Configurations of BPR=8 External Plug Nozzle and Acoustic Results.

  20. A research program to reduce interior noise in general aviation airplanes: Noise reduction through a cavity-backed flexible plate

    NASA Technical Reports Server (NTRS)

    Roskam, J.; Vandam, C. P. G.

    1978-01-01

    A prediction method is reported for noise reduction through a cavity-backed panel. The analysis takes into account only cavity modes in one direction. The results of this analysis were to find the effect of acoustic stiffness of a backing cavity on the panel behavior. The resulting changes in the noise reduction through the panel are significant.

  1. Government-Backed Salt Reduction Efforts Could Deliver Big Health Pay Day

    MedlinePlus

    ... medlineplus.gov/news/fullstory_162976.html Government-Backed Salt Reduction Efforts Could Deliver Big Health Pay Day Researchers estimate a 10 percent cut in salt could save millions worldwide from heart disease To ...

  2. Wind noise in hearing aids: I. Effect of wide dynamic range compression and modulation-based noise reduction.

    PubMed

    Chung, King

    2012-01-01

    The objectives of this study were: (1) to examine the effect of wide dynamic range compression (WDRC) and modulation-based noise reduction (NR) algorithms on wind noise levels at the hearing aid output; and (2) to derive effective strategies for clinicians and engineers to reduce wind noise in hearing aids. Three digital hearing aids were fitted to KEMAR. The noise output was recorded at flow velocities of 0, 4.5, 9.0, and 13.5 m/s in a wind tunnel as the KEMAR head was turned from 0° to 360°. Flow noise levels were compared between the 1:1 linear and 3:1 WDRC conditions, and between NR-activated and NR-deactivated conditions when the hearing aid was programmed to the directional and omnidirectional modes. The results showed that: (1) WDRC increased low-level noise and reduced high-level noise; and (2) different noise reduction algorithms provided different amounts of wind noise reduction in different microphone modes, frequency regions, flow velocities, and head angles. Wind noise can be reduced by decreasing the gain for low-level inputs, increasing the compression ratio for high-level inputs, and activating modulation-based noise reduction algorithms.

  3. Reduction of airfoil trailing edge noise by trailing edge blowing

    NASA Astrophysics Data System (ADS)

    Gerhard, T.; Erbslöh, S.; Carolus, T.

    2014-06-01

    The paper deals with airfoil trailing edge noise and its reduction by trailing edge blowing. A Somers S834 airfoil section which originally was designed for small wind turbines is investigated. To mimic realistic Reynolds numbers the boundary layer is tripped on pressure and suction side. The chordwise position of the blowing slot is varied. The acoustic sources, i.e. the unsteady flow quantities in the turbulent boundary layer in the vicinity of the trailing edge, are quantified for the airfoil without and with trailing edge blowing by means of a large eddy simulation and complementary measurements. Eventually the far field airfoil noise is measured by a two-microphone filtering and correlation and a 40 microphone array technique. Both, LES-prediction and measurements showed that a suitable blowing jet on the airfoil suction side is able to reduce significantly the turbulence intensity and the induced surface pressure fluctuations in the trailing edge region. As a consequence, trailing edge noise associated with a spectral hump around 500 Hz could be reduced by 3 dB. For that a jet velocity of 50% of the free field velocity was sufficient. The most favourable slot position was at 90% chord length.

  4. In situ evaluation of aircraft interior noise reduction technologies

    NASA Astrophysics Data System (ADS)

    Klos, Jacob; Palumbo, Daniel L.

    2003-10-01

    In order to quantify the performance of interior noise treatments under flight conditions, it is desirable to evaluate the noise reduction due to treatment of a limited portion of an aircraft fuselage. However, radiation from the untreated areas of the fuselage can corrupt an intensity measurement in front of the treated area. In the past, this problem of corrupting noise has been solved by acoustically isolating the treated area from the rest of the fuselage. In this presentation, a method to evaluate the performance of an acoustic treatment applied to an aircraft fuselage in situ using correlation analysis is documented. The insertion loss of the acoustic treatments is estimated from the ratio of the intensity, correlated to reference transducers, measured with and without the treatment applied. The formulation is presented for both single and multiple reference transducers. Several experimental studies and numerical simulations have been conducted, and the results are documented. Through these case studies, it is demonstrated that this method can be used to evaluate the insertion loss of fuselage treatments without having to acoustically isolate the treated area.

  5. Speckle noise reduction of 1-look SAR imagery

    NASA Technical Reports Server (NTRS)

    Nathan, Krishna S.; Curlander, John C.

    1987-01-01

    Speckle noise is inherent to synthetic aperture radar (SAR) imagery. Since the degradation of the image due to this noise results in uncertainties in the interpretation of the scene and in a loss of apparent resolution, it is desirable to filter the image to reduce this noise. In this paper, an adaptive algorithm based on the calculation of the local statistics around a pixel is applied to 1-look SAR imagery. The filter adapts to the nonstationarity of the image statistics since the size of the blocks is very small compared to that of the image. The performance of the filter is measured in terms of the equivalent number of looks (ENL) of the filtered image and the resulting resolution degradation. The results are compared to those obtained from different techniques applied to similar data. The local adaptive filter (LAF) significantly increases the ENL of the final image. The associated loss of resolution is also lower than that for other commonly used speckle reduction techniques.

  6. Speckle noise reduction of 1-look SAR imagery

    NASA Astrophysics Data System (ADS)

    Nathan, Krishna S.; Curlander, John C.

    Speckle noise is inherent to synthetic aperture radar (SAR) imagery. Since the degradation of the image due to this noise results in uncertainties in the interpretation of the scene and in a loss of apparent resolution, it is desirable to filter the image to reduce this noise. In this paper, an adaptive algorithm based on the calculation of the local statistics around a pixel is applied to 1-look SAR imagery. The filter adapts to the nonstationarity of the image statistics since the size of the blocks is very small compared to that of the image. The performance of the filter is measured in terms of the equivalent number of looks (ENL) of the filtered image and the resulting resolution degradation. The results are compared to those obtained from different techniques applied to similar data. The local adaptive filter (LAF) significantly increases the ENL of the final image. The associated loss of resolution is also lower than that for other commonly used speckle reduction techniques.

  7. Low Delay Noise Reduction and Dereverberation for Hearing Aids

    NASA Astrophysics Data System (ADS)

    Löllmann (Eurasip Member), Heinrich W.; Vary, Peter

    2009-12-01

    A new system for single-channel speech enhancement is proposed which achieves a joint suppression of late reverberant speech and background noise with a low signal delay and low computational complexity. It is based on a generalized spectral subtraction rule which depends on the variances of the late reverberant speech and background noise. The calculation of the spectral variances of the late reverberant speech requires an estimate of the reverberation time (RT) which is accomplished by a maximum likelihood (ML) approach. The enhancement with this blind RT estimation achieves almost the same speech quality as by using the actual RT. In comparison to commonly used post-filters in hearing aids which only perform a noise reduction, a significantly better objective and subjective speech quality is achieved. The proposed system performs time-domain filtering with coefficients adapted in the non-uniform (Bark-scaled) frequency-domain. This allows to achieve a high speech quality with low signal delay which is important for speech enhancement in hearing aids or related applications such as hands-free communication systems.

  8. Edge Preserved Speckle Noise Reduction Using Integrated Fuzzy Filters.

    PubMed

    Biradar, Nagashettappa; Dewal, M L; Rohit, Manoj Kumar

    2014-01-01

    Echocardiographic images are inherent with speckle noise which makes visual reading and analysis quite difficult. The multiplicative speckle noise masks finer details, necessary for diagnosis of abnormalities. A novel speckle reduction technique based on integration of geometric, wiener, and fuzzy filters is proposed and analyzed in this paper. The denoising applications of fuzzy filters are studied and analyzed along with 26 denoising techniques. It is observed that geometric filter retains noise and, to address this issue, wiener filter is embedded into the geometric filter during iteration process. The performance of geometric-wiener filter is further enhanced using fuzzy filters and the proposed despeckling techniques are called integrated fuzzy filters. Fuzzy filters based on moving average and median value are employed in the integrated fuzzy filters. The performances of integrated fuzzy filters are tested on echocardiographic images and synthetic images in terms of image quality metrics. It is observed that the performance parameters are highest in case of integrated fuzzy filters in comparison to fuzzy and geometric-fuzzy filters. The clinical validation reveals that the output images obtained using geometric-wiener, integrated fuzzy, nonlocal means, and details preserving anisotropic diffusion filters are acceptable. The necessary finer details are retained in the denoised echocardiographic images.

  9. Edge Preserved Speckle Noise Reduction Using Integrated Fuzzy Filters

    PubMed Central

    Dewal, M. L.; Rohit, Manoj Kumar

    2014-01-01

    Echocardiographic images are inherent with speckle noise which makes visual reading and analysis quite difficult. The multiplicative speckle noise masks finer details, necessary for diagnosis of abnormalities. A novel speckle reduction technique based on integration of geometric, wiener, and fuzzy filters is proposed and analyzed in this paper. The denoising applications of fuzzy filters are studied and analyzed along with 26 denoising techniques. It is observed that geometric filter retains noise and, to address this issue, wiener filter is embedded into the geometric filter during iteration process. The performance of geometric-wiener filter is further enhanced using fuzzy filters and the proposed despeckling techniques are called integrated fuzzy filters. Fuzzy filters based on moving average and median value are employed in the integrated fuzzy filters. The performances of integrated fuzzy filters are tested on echocardiographic images and synthetic images in terms of image quality metrics. It is observed that the performance parameters are highest in case of integrated fuzzy filters in comparison to fuzzy and geometric-fuzzy filters. The clinical validation reveals that the output images obtained using geometric-wiener, integrated fuzzy, nonlocal means, and details preserving anisotropic diffusion filters are acceptable. The necessary finer details are retained in the denoised echocardiographic images. PMID:27437499

  10. Supersonic impinging jet noise reduction using a hybrid control technique

    NASA Astrophysics Data System (ADS)

    Wiley, Alex; Kumar, Rajan

    2015-07-01

    Control of the highly resonant flowfield associated with supersonic impinging jet has been experimentally investigated. Measurements were made in the supersonic impinging jet facility at the Florida State University for a Mach 1.5 ideally expanded jet. Measurements included unsteady pressures on a surface plate near the nozzle exit, acoustics in the nearfield and beneath the impingement plane, and velocity field using particle image velocimetry. Both passive control using porous surface and active control with high momentum microjet injection are effective in reducing nearfield noise and flow unsteadiness over a range of geometrical parameters; however, the type of noise reduction achieved by the two techniques is different. The passive control reduces broadband noise whereas microjet injection attenuates high amplitude impinging tones. The hybrid control, a combination of two control methods, reduces both broadband and high amplitude impinging tones and surprisingly its effectiveness is more that the additive effect of the two control techniques. The flow field measurements show that with hybrid control the impinging jet is stabilized and the turbulence quantities such as streamwise turbulence intensity, transverse turbulence intensity and turbulent shear stress are significantly reduced.

  11. Programmable noise bandwidth reduction by means of digital averaging

    NASA Technical Reports Server (NTRS)

    Poklemba, John J. (Inventor)

    1993-01-01

    Predetection noise bandwidth reduction is effected by a pre-averager capable of digitally averaging the samples of an input data signal over two or more symbols, the averaging interval being defined by the input sampling rate divided by the output sampling rate. As the averaged sample is clocked to a suitable detector at a much slower rate than the input signal sampling rate the noise bandwidth at the input to the detector is reduced, the input to the detector having an improved signal to noise ratio as a result of the averaging process, and the rate at which such subsequent processing must operate is correspondingly reduced. The pre-averager forms a data filter having an output sampling rate of one sample per symbol of received data. More specifically, selected ones of a plurality of samples accumulated over two or more symbol intervals are output in response to clock signals at a rate of one sample per symbol interval. The pre-averager includes circuitry for weighting digitized signal samples using stored finite impulse response (FIR) filter coefficients. A method according to the present invention is also disclosed.

  12. Filter for speckle noise reduction based on compressive sensing

    NASA Astrophysics Data System (ADS)

    Leportier, Thibault; Park, Min-Chul

    2016-12-01

    In holographic reconstruction, speckle noise is a serious factor that may degrade the image quality greatly. Several methods have been proposed, so far, to filter speckle from hologram reconstruction. The first approach is based on averaging several speckle patterns. The second solution is to apply a filter on the reconstructed image. In the first case, several holograms should be acquired, while compromise between speckle reduction and edge preservation is usually a challenge in the case of digital filtering. We propose a method to filter speckle noise based on compressive sensing (CS). CS is a method that has been demonstrated recently to reconstruct images with a sampling inferior to the Nyquist rate. By applying several times the CS algorithm on the hologram reconstruction with different initial downsampling, several versions of the same images can be reconstructed with slightly different speckle patterns. Then, speckle noise can be greatly decreased while preserving sharpness of the image. We demonstrate the effectiveness of our proposed method with simulations as well as with holograms acquired by phase-shifting method.

  13. Evaluation of a Noise Reduction Procedure for Chest Radiography

    PubMed Central

    Fukui, Ryohei; Ishii, Rie; Kodani, Kazuhiko; Kanasaki, Yoshiko; Suyama, Hisashi; Watanabe, Masanari; Nakamoto, Masaki; Fukuoka, Yasushi

    2013-01-01

    Background The aim of this study was to evaluate the usefulness of noise reduction procedure (NRP), a function in the new image processing for chest radiography. Methods A CXDI-50G Portable Digital Radiography System (Canon) was used for X-ray detection. Image noise was analyzed with a noise power spectrum (NPS) and a burger phantom was used for evaluation of density resolution. The usefulness of NRP was evaluated by chest phantom images and clinical chest radiography. We employed the Bureau of Radiological Health Method for scoring chest images while carrying out our observations. Results NPS through the use of NRP was improved compared with conventional image processing (CIP). The results in image quality showed high-density resolution through the use of NRP, so that chest radiography examination can be performed with a low dose of radiation. Scores were significantly higher than for CIP. Conclusion In this study, use of NRP led to a high evaluation in these so we are able to confirm the usefulness of NRP for clinical chest radiography. PMID:24574577

  14. Application of variational mode decomposition to seismic random noise reduction

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Cao, Siyuan; Wang, Zhiming

    2017-08-01

    We have proposed a new denoising method for the simultaneous noise reduction and preservation of seismic signals based on variational mode decomposition (VMD). VMD is a recently developed adaptive signal decomposition method and an advance in non-stationary signal analysis. It solves the mode-mixing and non-optimal reconstruction performance problems of empirical mode decomposition that have existed for a long time. By using VMD, a multi-component signal can be non-recursively decomposed into a series of quasi-orthogonal intrinsic mode functions (IMFs), each of which has a relatively local frequency range. Meanwhile, the signal will focus on a smaller number of obtained IMFs after decomposition, and thus the denoised result is able to be obtained by reconstructing these signal-dominant IMFs. Synthetic examples are given to demonstrate the effectiveness of the proposed approach and comparison is made with the complete ensemble empirical mode decomposition, which demonstrates that the VMD algorithm has lower computational cost and better random noise elimination performance. The application of on field seismic data further illustrates the superior performance of our method in both random noise attenuation and the recovery of seismic events.

  15. Noise reduction studies for the U-10 airplane

    NASA Technical Reports Server (NTRS)

    Hilton, D. A.; Connor, A. B.; Hubbard, H. H.; Dingeldein, R. C.

    1975-01-01

    A study was undertaken by the NASA Langley Research Center to determine the noise reduction potential of the U-10 airplane in order to reduce its aural detection distance. Static and flyover noise measurements were made to document the basic airplane noise signature. Two modifications to the airplane configuration are suggested as having the best potential for substantially reducing aural detection distance with small penalty to airplane performance or stability and control. These modifications include changing the present 3-blade propeller to a 5-blade propeller, changing the propeller diameter, and changing the propeller gear ratio, along with the use of an engine exhaust muffler. The aural detection distance corresponding to normal cruising flight at an altitude of 1,000 ft over grassy terrain is reduced from 28,000 ft (5.3 miles) to about 50 percent of that value for modification 1, and to about 25 percent for modification 2. For the aircraft operating at an altitude of 300 ft, the analysis indicates that relatively straightforward modifications could reduce the aural detection distance to approximately 0.9 mile. Operation of the aircraft at greatly reduced engine speed (1650 rpm) with a 1.3-cu-ft muffler provides aural detection distances slightly lower than modification 1.

  16. The cost of applying current helicopter external noise reduction methods while maintaining realistic vehicle performance

    NASA Technical Reports Server (NTRS)

    Bowes, M. A.

    1978-01-01

    Analytical methods were developed and/or adopted for calculating helicopter component noise, and these methods were incorporated into a unified total vehicle noise calculation model. Analytical methods were also developed for calculating the effects of noise reduction methodology on helicopter design, performance, and cost. These methods were used to calculate changes in noise, design, performance, and cost due to the incorporation of engine and main rotor noise reduction methods. All noise reduction techniques were evaluated in the context of an established mission performance criterion which included consideration of hovering ceiling, forward flight range/speed/payload, and rotor stall margin. The results indicate that small, but meaningful, reductions in helicopter noise can be obtained by treating the turbine engine exhaust duct. Furthermore, these reductions do not result in excessive life cycle cost penalties. Currently available main rotor noise reduction methodology, however, is shown to be inadequate and excessively costly.

  17. Hydrofoil vibration and noise reduction with leading edge isolation

    NASA Astrophysics Data System (ADS)

    Brungart, Timothy A.; Myer, Eric C.; Capone, Dean E.; Campbell, Robert L.

    2005-09-01

    A technique for reducing the vibration and noise from hydrofoils subject to unsteady hydrodynamic loads was demonstrated experimentally. Unsteady loads are generated when hydrofoils interact with approach-flow disturbances such as hull boundary layer turbulence or wakes from upstream rotors. Since the unsteady loads are known to be concentrated in the vicinity of the leading edge, a single stage vibration isolation mount was incorporated into a hydrofoil at its 20% chord location to inhibit the leading edge-generated unsteady loads from being transmitted to the remainder of the foil and any structures coupled to it. The hydrofoil was tested in a water tunnel facility with a wake generator placed upstream to produce the approach-flow disturbances. The reduction in the loading on the portion of the hydrofoil isolated from the leading edge was inferred from vibration measurements. Reductions of 5 to 10 dB were demonstrated.

  18. Comparison of single-microphone noise reduction schemes: can hearing impaired listeners tell the difference?

    PubMed

    Huber, Rainer; Bisitz, Thomas; Gerkmann, Timo; Kiessling, Jürgen; Meister, Hartmut; Kollmeier, Birger

    2017-01-23

    The perceived qualities of nine different single-microphone noise reduction (SMNR) algorithms were to be evaluated and compared in subjective listening tests with normal hearing and hearing impaired (HI) listeners. Speech samples added with traffic noise or with party noise were processed by the SMNR algorithms. Subjects rated the amount of speech distortions, intrusiveness of background noise, listening effort and overall quality, using a simplified MUSHRA (ITU-R, 2003 ) assessment method. 18 normal hearing and 18 moderately HI subjects participated in the study. Significant differences between the rating behaviours of the two subject groups were observed: While normal hearing subjects clearly differentiated between different SMNR algorithms, HI subjects rated all processed signals very similarly. Moreover, HI subjects rated speech distortions of the unprocessed, noisier signals as being more severe than the distortions of the processed signals, in contrast to normal hearing subjects. It seems harder for HI listeners to distinguish between additive noise and speech distortions or/and they might have a different understanding of the term "speech distortion" than normal hearing listeners have. The findings confirm that the evaluation of SMNR schemes for hearing aids should always involve HI listeners.

  19. Effects of noise reduction on AM and FM perception.

    PubMed

    Ives, D Timothy; Calcus, Axelle; Kalluri, Sridhar; Strelcyk, Olaf; Sheft, Stanley; Lorenzi, Christian

    2013-02-01

    The goal of noise reduction (NR) algorithms in digital hearing aid devices is to reduce background noise whilst preserving as much of the original signal as possible. These algorithms may increase the signal-to-noise ratio (SNR) in an ideal case, but they generally fail to improve speech intelligibility. However, due to the complex nature of speech, it is difficult to disentangle the numerous low- and high-level effects of NR that may underlie the lack of speech perception benefits. The goal of this study was to better understand why NR algorithms do not improve speech intelligibility by investigating the effects of NR on the ability to discriminate two basic acoustic features, namely amplitude modulation (AM) and frequency modulation (FM) cues, known to be crucial for speech identification in quiet and in noise. Here, discrimination of complex, non-linguistic AM and FM patterns was measured for normal hearing listeners using a same/different task. The stimuli were generated by modulating 1-kHz pure tones by either a two-component AM or FM modulator with patterns changed by manipulating component phases. Modulation rates were centered on 3 Hz. Discrimination of AM and FM patterns was measured in quiet and in the presence of a white noise that had been passed through a gammatone filter centered on 1 kHz. The noise was presented at SNRs ranging from -6 to +12 dB. Stimuli were left as such or processed via an NR algorithm based on the spectral subtraction method. NR was found to yield small but systematic improvements in discrimination for the AM conditions at favorable SNRs but had little effect, if any, on FM discrimination. A computational model of early auditory processing was developed to quantify the fidelity of AM and FM transmission. The model captured the improvement in discrimination performance for AM stimuli at high SNRs with NR. However, the model also predicted a relatively small detrimental effect of NR for FM stimuli in contrast with the average

  20. Digital Image Processing for Noise Reduction in Medical Ultrasonics

    NASA Astrophysics Data System (ADS)

    Loupas, Thanasis

    Available from UMI in association with The British Library. Requires signed TDF. The purpose of this project was to investigate the application of digital image processing techniques as a means of reducing noise in medical ultrasonic imaging. Ultrasonic images suffer primarily from a type of acoustic noise, known as speckle, which is generally regarded as a major source of image quality degradation. The origin of speckle, its statistical properties as well as methods suggested to eliminate this artifact were reviewed. A simple model which can characterize the statistics of speckle on displays was also developed. A large number of digital noise reduction techniques was investigated. These include frame averaging techniques performed by commercially available devices and spatial filters implemented in software. Among the latter, some filters have been proposed in the scientific literature for ultrasonic, laser and microwave speckle or general noise suppression and the rest are original, developed specifically to suppress ultrasonic speckle. Particular emphasis was placed on adaptive techniques which adjust the processing performed at each point according to the local image content. In this way, they manage to suppress speckle with negligible loss of genuine image detail. Apart from preserving the diagnostically significant features of a scan another requirement a technique must satisfy before it is accepted in routine clinical practice is real-time operation. A spatial filter capable of satisfying both these requirements was designed and built in hardware using low-cost and readily available components. The possibility of incorporating all the necessary filter circuitry into a single VLSI chip was also investigated. In order to establish the effectiveness and usefulness of speckle suppression, a representative sample from the techniques examined here was applied to a large number of abdominal scans and their effect on image quality was evaluated. Finally, further

  1. Bio-inspired canopies for the reduction of roughness noise

    NASA Astrophysics Data System (ADS)

    Clark, Ian A.; Daly, Conor A.; Devenport, William; Alexander, W. Nathan; Peake, Nigel; Jaworski, Justin W.; Glegg, Stewart

    2016-12-01

    This work takes inspiration from the structure of the down covering the flight feathers of larger species of owls, which contributes to their ability to fly almost silently at frequencies above 1.6 kHz. Microscope photographs of the down show that it consists of hairs that form a structure similar to that of a forest. The hairs initially rise almost perpendicular to the feather surface but then bend over in the flow direction to form a canopy with an open area ratio of about 70 percent. Experiments have been performed to examine the noise radiated by a large open area ratio canopy suspended above a surface. The canopy is found to dramatically reduce pressure fluctuations on the underlying surface. While the canopy can produce its own sound, particularly at high frequencies, the reduction in surface pressure fluctuations can reduce the noise scattered from an underlying rough surface at lower frequencies. A theoretical model is developed which characterizes the mechanism of surface pressure reduction as a result of the mixing layer instability of flow over forest canopies.

  2. NASA/AHS rotorcraft noise reduction program - NASA Langley Acoustics Division contributions

    NASA Technical Reports Server (NTRS)

    Martin, Ruth M.

    1989-01-01

    An account is given of the contributions made by NASA-Langley's rotorcraft noise research programs over the last five years. Attention has been given to the broadband and blade-vortex interaction noise sources; both analytical and empirical noise-prediction codes have been developed and validated for several rotor noise sources, and the 'Rotonet' comprehensive system-noise prediction capability has been instituted. Among the technologies explored for helicopter noise reduction have been higher harmonic control and active vibration-suppression.

  3. Low-Speed Fan Noise Reduction With Trailing Edge Blowing

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.; Tweedt, Daniel L.; Fite, E. Brian; Envia, Edmane

    2002-01-01

    An experimental proof-of-concept test was conducted to demonstrate reduction of rotor-stator interaction noise through rotor-trailing edge blowing. The velocity deficit from the viscous wake of the rotor blades was reduced by injecting air into the wake from a trailing edge slot. Composite hollow rotor blades with internal flow passages were designed based on analytical codes modeling the internal flow. The hollow blade with interior guide vanes creates flow channels through which externally supplied air flows from the root of the blade to the trailing edge. The impact of the rotor wake-stator interaction on the acoustics was also predicted analytically. The Active Noise Control Fan, located at the NASA Glenn Research Center, was used as the proof- of-concept test bed. In-duct mode and farfield directivity acoustic data were acquired at blowing rates (defined as mass supplied to trailing edge blowing system divided by fan mass flow) ranging from 0.5 to 2.0 percent. The first three blade passing frequency harmonics at fan rotational speeds of 1700 to 1900 rpm were analyzed. The acoustic tone power levels (PWL) in the inlet and exhaust were reduced 11.5 and -0.1, 7.2 and 11.4, 11.8 and 19.4 PWL dB, respectively. The farfield tone power levels at the first three harmonics were reduced 5.4, 10.6, and 12.4 dB PWL. At selected conditions, two-component hotwire and stator vane unsteady surface pressures were acquired. These measurements illustrate the physics behind the noise reduction.

  4. Evaluation of the noise reduction system in a commercial digital hearing aid.

    PubMed

    Alcántara, José L; Moore, Brian C J; Kühnel, Volker; Launer, Stefan

    2003-01-01

    We evaluated the effectiveness of a noise reduction system implemented in a commercial digital multichannel compression hearing aid. Eight experienced hearing aid wearers with moderate sensorineural hearing loss were fitted bilaterally according to the manufacturer's fitting guidelines. After a 3-month period of regular use of two programs, one with and one without the noise reduction system, speech recognition thresholds (SRTs) were measured in four types of background noise, including steady noise, and noises with spectral and/or temporal dips. SRTs were very similar with and without the noise reduction system; in both cases, SRTs were markedly lower than for unaided listening. SRTs were lower for the noises with dips than for the steady noise, especially for the aided conditions, indicating that amplification can help to 'listen in the dips'. Ratings of sound quality and listening comfort in the aided conditions were uniformly high and very similar with and without the noise reduction system.

  5. Noise reduction technologies implemented in head-worn preprocessors for improving cochlear implant performance in reverberant noise fields.

    PubMed

    Chung, King; Nelson, Lance; Teske, Melissa

    2012-09-01

    The purpose of this study was to investigate whether a multichannel adaptive directional microphone and a modulation-based noise reduction algorithm could enhance cochlear implant performance in reverberant noise fields. A hearing aid was modified to output electrical signals (ePreprocessor) and a cochlear implant speech processor was modified to receive electrical signals (eProcessor). The ePreprocessor was programmed to flat frequency response and linear amplification. Cochlear implant listeners wore the ePreprocessor-eProcessor system in three reverberant noise fields: 1) one noise source with variable locations; 2) three noise sources with variable locations; and 3) eight evenly spaced noise sources from 0° to 360°. Listeners' speech recognition scores were tested when the ePreprocessor was programmed to omnidirectional microphone (OMNI), omnidirectional microphone plus noise reduction algorithm (OMNI + NR), and adaptive directional microphone plus noise reduction algorithm (ADM + NR). They were also tested with their own cochlear implant speech processor (CI_OMNI) in the three noise fields. Additionally, listeners rated overall sound quality preferences on recordings made in the noise fields. Results indicated that ADM+NR produced the highest speech recognition scores and the most preferable rating in all noise fields. Factors requiring attention in the hearing aid-cochlear implant integration process are discussed.

  6. CMOS image sensor noise reduction method for image signal processor in digital cameras and camera phones

    NASA Astrophysics Data System (ADS)

    Yoo, Youngjin; Lee, SeongDeok; Choe, Wonhee; Kim, Chang-Yong

    2007-02-01

    Digital images captured from CMOS image sensors suffer Gaussian noise and impulsive noise. To efficiently reduce the noise in Image Signal Processor (ISP), we analyze noise feature for imaging pipeline of ISP where noise reduction algorithm is performed. The Gaussian noise reduction and impulsive noise reduction method are proposed for proper ISP implementation in Bayer domain. The proposed method takes advantage of the analyzed noise feature to calculate noise reduction filter coefficients. Thus, noise is adaptively reduced according to the scene environment. Since noise is amplified and characteristic of noise varies while the image sensor signal undergoes several image processing steps, it is better to remove noise in earlier stage on imaging pipeline of ISP. Thus, noise reduction is carried out in Bayer domain on imaging pipeline of ISP. The method is tested on imaging pipeline of ISP and images captured from Samsung 2M CMOS image sensor test module. The experimental results show that the proposed method removes noise while effectively preserves edges.

  7. Evaluating the effectiveness of active noise reduction in flight helmets

    NASA Astrophysics Data System (ADS)

    Forshaw, S. E.; Rylands, J. M.; Crabtree, R. B.

    1988-08-01

    The advent of high powered fixed- and rotary-wing aircraft and tracked armoured fighting vehicles has increased the level of noise to which crews are exposed. Active noise reduction (ANR) offers a means of increasing the attenuation at low and mid frequencies. It relies on sensing the sound inside a circumaural device and cancelling it by means of negative feedback through a miniature speaker inside the enclosed volume. This study was carried out to investigate laboratory procedures appropriate for measuring the effectiveness of ANR devices. The procedures were: ear-canal measurements using an acoustic test fixture (an objective procedure), and masked threshold and loudness balance tests (psycho-physical procedures). In addition, the effect of ANR on signal detection and speech reception was investigated. The results do not clearly permit one procedure to be recommended for the evaluation of ANR systems. Signal detection performance and speech intelligibility may be used, but the results are specific to the acoustic environment of the listener and the detection task or speech-system parameters of the evaluation. When the attenuation of the ANR system is measured objectively with a transducer inside the earmuff/ear-canal volume, the location of the transducer affects the observed ANR attenuations.

  8. Tip Fence for Reduction of Lift-Generated Airframe Noise

    NASA Technical Reports Server (NTRS)

    Ross, James C. (Inventor); Storms, Bruce L. (Inventor)

    1998-01-01

    The present invention is directed toward a unique lift-generated noise reduction apparatus. This apparatus includes a plurality of tip fences that are secured to the trailing and leading assemblies of the high-lift system, as close as possible to the discontinuities where the vortices are most likely to form. In one embodiment, these tip fences are secured to some or all of the outboard and inboard tips of the wing slats and flaps. The tip fence includes a generally flat, or an aerodynamically shaped plate or device that could be formed of almost any rigid material, such as metal, wood, plastic, fiber glass, aluminum, etc. In a preferred embodiment, the tip fences extend below and perpendicularly to flaps and the slats to which they are attached, such that these tip fences are aligned with the nominal free stream velocity of the aircraft. In addition to reducing airframe noise, the tip fence tends to decrease drag and to increase lift, thus improving the overall aerodynamic performance of the aircraft. Another advantage presented by the tip fence lies in the simplicity of its design, its elegance, and its ready ability to fit on the wing components, such as the flaps and the slats. Furthermore, it does not require non-standard materials or fabrication techniques, and it can be readily, easily and inexpensively retrofited on most of the existing aircraft, with minimal design changes.

  9. Emergent Adaptive Noise Reduction from Communal Cooperation of Sensor Grid

    NASA Technical Reports Server (NTRS)

    Jones, Kennie H.; Jones, Michael G.; Nark, Douglas M.; Lodding, Kenneth N.

    2010-01-01

    In the last decade, the realization of small, inexpensive, and powerful devices with sensors, computers, and wireless communication has promised the development of massive sized sensor networks with dense deployments over large areas capable of high fidelity situational assessments. However, most management models have been based on centralized control and research has concentrated on methods for passing data from sensor devices to the central controller. Most implementations have been small but, as it is not scalable, this methodology is insufficient for massive deployments. Here, a specific application of a large sensor network for adaptive noise reduction demonstrates a new paradigm where communities of sensor/computer devices assess local conditions and make local decisions from which emerges a global behaviour. This approach obviates many of the problems of centralized control as it is not prone to single point of failure and is more scalable, efficient, robust, and fault tolerant

  10. Computational Analyses of Offset Stream Nozzles for Noise Reduction

    NASA Technical Reports Server (NTRS)

    Dippold, Vance, III; Foster, Lancert; Wiese,Michael

    2007-01-01

    The Wind computational fluid dynamics code was used to perform a series of simulations on two offset stream nozzle concepts for jet noise reduction. The first concept used an S-duct to direct the secondary stream to the lower side of the nozzle. The second concept used vanes to turn the secondary flow downward. The analyses were completed in preparation of tests conducted in the NASA Glenn Research Center Aeroacoustic Propulsion Laboratory. The offset stream nozzles demonstrated good performance and reduced the amount of turbulence on the lower side of the jet plume. The computer analyses proved instrumental in guiding the development of the final test configurations and giving insight into the flow mechanics of offset stream nozzles. The computational predictions were compared with flowfield results from the jet rig testing and showed excellent agreement.

  11. Experimental and Numerical Analysis of Structural Acousticcontrol Interior Noise Reduction

    NASA Technical Reports Server (NTRS)

    Mei, Chuh; Bevan, Jeffrey S.

    1999-01-01

    The research results contained in this technical report were performed under the NASA grant entitled "Experimental and Numerical Structural Acoustic Control for Interior Noise Reduction". The report is based essentially on partial progress of the Ph.D. dissertation prepared by Jeffrey S. Bevan under direct guidance of Dr. Chuh Mei. The document presents a finite element formulation and control of sound radiated from cylindrical panels embedded with piezoceramic actuators. The extended MIN6 shallow shell element is fully electrical-structural coupled. A piezoelectric modal actuator participation (PMAP) is defined which indicates the actuator performance to each of the offending modes. Genetic algorithm is also employed to validate the sensor and actuator locations determined by the PMAP criteria. The work was conducted at the Department of Aerospace Engineering, Old Dominion University. Mr. Travis L. Turner, Structural Acoustics Branch, NASA Langley Research Center is the technical monitor.

  12. Reducing Centroid Error Through Model-Based Noise Reduction

    NASA Technical Reports Server (NTRS)

    Lee, Shinhak

    2006-01-01

    A method of processing the digitized output of a charge-coupled device (CCD) image detector has been devised to enable reduction of the error in computed centroid of the image of a point source of light. The method involves model-based estimation of, and correction for, the contributions of bias and noise to the image data. The method could be used to advantage in any of a variety of applications in which there are requirements for measuring precise locations of, and/or precisely aiming optical instruments toward, point light sources. In the present method, prior to normal operations of the CCD, one measures the point-spread function (PSF) of the telescope or other optical system used to project images on the CCD. The PSF is used to construct a database of spot models representing the nominal CCD pixel outputs for a point light source projected onto the CCD at various positions incremented by small fractions of a pixel.

  13. Phonon squeezed states: quantum noise reduction in solids

    NASA Astrophysics Data System (ADS)

    Hu, Xuedong; Nori, Franco

    1999-03-01

    This article discusses quantum fluctuation properties of a crystal lattice, and in particular, phonon squeezed states. Squeezed states of phonons allow a reduction in the quantum fluctuations of the atomic displacements to below the zero-point quantum noise level of coherent phonon states. Here we discuss our studies of both continuous-wave and impulsive second-order Raman scattering mechanisms. The later approach was used to experimentally suppress (by one part in a million) fluctuations in phonons. We calculate the expectation values and fluctuations of both the atomic displacement and the lattice amplitude operators, as well as the effects of the phonon squeezed states on macroscopically measurable quantities, such as changes in the dielectric constant. These results are compared with recent experiments. Further information, including preprints and animations, are available in http://www-personal.engin.umich.edu/∼nori/squeezed.html.

  14. Wake Management Strategies for Reduction of Turbomachinery Fan Noise

    NASA Technical Reports Server (NTRS)

    Waitz, Ian A.

    1998-01-01

    The primary objective of our work was to evaluate and test several wake management schemes for the reduction of turbomachinery fan noise. Throughout the course of this work we relied on several tools. These include 1) Two-dimensional steady boundary-layer and wake analyses using MISES (a thin-shear layer Navier-Stokes code), 2) Two-dimensional unsteady wake-stator interaction simulations using UNSFLO, 3) Three-dimensional, steady Navier-Stokes rotor simulations using NEWT, 4) Internal blade passage design using quasi-one-dimensional passage flow models developed at MIT, 5) Acoustic modeling using LINSUB, 6) Acoustic modeling using VO72, 7) Experiments in a low-speed cascade wind-tunnel, and 8) ADP fan rig tests in the MIT Blowdown Compressor.

  15. The Automatic Assessment and Reduction of Noise Using Edge Pattern Analysis in Nonlinear Image Enhancement

    NASA Technical Reports Server (NTRS)

    Jobson, Daniel J.; Rahman, Zia-ur; Woodells, Glenn A.; Hines, Glenn D.

    2004-01-01

    Noise is the primary visibility limit in the process of non-linear image enhancement, and is no longer a statistically stable additive noise in the post-enhancement image. Therefore novel approaches are needed to both assess and reduce spatially variable noise at this stage in overall image processing. Here we will examine the use of edge pattern analysis both for automatic assessment of spatially variable noise and as a foundation for new noise reduction methods.

  16. Automatic Assessment and Reduction of Noise using Edge Pattern Analysis in Non-Linear Image Enhancement

    NASA Technical Reports Server (NTRS)

    Jobson, Daniel J.; Rahman, Zia-Ur; Woodell, Glenn A.; Hines, Glenn D.

    2004-01-01

    Noise is the primary visibility limit in the process of non-linear image enhancement, and is no longer a statistically stable additive noise in the post-enhancement image. Therefore novel approaches are needed to both assess and reduce spatially variable noise at this stage in overall image processing. Here we will examine the use of edge pattern analysis both for automatic assessment of spatially variable noise and as a foundation for new noise reduction methods.

  17. High-Temperature Smart Structures for Engine Noise Reduction and Performance Enhancement

    NASA Technical Reports Server (NTRS)

    Quackenbush, Todd R.; McKillip, Robert M., Jr.

    2011-01-01

    One of key NASA goals is to develop and integrate noise reduction technology to enable unrestricted air transportation service to all communities. One of the technical priorities of this activity has been to account for and reduce noise via propulsion/airframe interactions, identifying advanced concepts to be integrated with the airframe to mitigate these noise-producing mechanisms. An adaptive geometry chevron using embedded smart structures technology offers the possibility of maximizing engine performance while retaining and possibly enhancing the favorable noise characteristics of current designs. New high-temperature shape memory alloy (HTSMA) materials technology enables the devices to operate in both low-temperature (fan) and high-temperature (core) exhaust flows. Chevron-equipped engines have demonstrated reduced noise in testing and operational use. It is desirable to have the noise benefits of chevrons in takeoff/landing conditions, but have them deployed into a minimum drag position for cruise flight. The central feature of the innovation was building on rapidly maturing HTSMA technology to implement a next-generation aircraft noise mitigation system centered on adaptive chevron flow control surfaces. In general, SMA-actuated devices have the potential to enhance the demonstrated noise reduction effectiveness of chevron systems while eliminating the associated performance penalty. The use of structurally integrated smart devices will minimize the mechanical and subsystem complexity of this implementation. The central innovations of the effort entail the modification of prior chevron designs to include a small cut that relaxes structural stiffness without compromising the desired flow characteristics over the surface; the reorientation of SMA actuation devices to apply forces to deflect the chevron tip, exploiting this relaxed stiffness; and the use of high-temperature SMA (HTSMA) materials to enable operation in the demanding core chevron environment

  18. Noise Reduction Effect of Multiple-Sampling-Based Signal-Readout Circuits for Ultra-Low Noise CMOS Image Sensors

    PubMed Central

    Kawahito, Shoji; Seo, Min-Woong

    2016-01-01

    This paper discusses the noise reduction effect of multiple-sampling-based signal readout circuits for implementing ultra-low-noise image sensors. The correlated multiple sampling (CMS) technique has recently become an important technology for high-gain column readout circuits in low-noise CMOS image sensors (CISs). This paper reveals how the column CMS circuits, together with a pixel having a high-conversion-gain charge detector and low-noise transistor, realizes deep sub-electron read noise levels based on the analysis of noise components in the signal readout chain from a pixel to the column analog-to-digital converter (ADC). The noise measurement results of experimental CISs are compared with the noise analysis and the effect of noise reduction to the sampling number is discussed at the deep sub-electron level. Images taken with three CMS gains of two, 16, and 128 show distinct advantage of image contrast for the gain of 128 (noise(median): 0.29 e−rms) when compared with the CMS gain of two (2.4 e−rms), or 16 (1.1 e−rms). PMID:27827972

  19. Noise Reduction Effect of Multiple-Sampling-Based Signal-Readout Circuits for Ultra-Low Noise CMOS Image Sensors.

    PubMed

    Kawahito, Shoji; Seo, Min-Woong

    2016-11-06

    This paper discusses the noise reduction effect of multiple-sampling-based signal readout circuits for implementing ultra-low-noise image sensors. The correlated multiple sampling (CMS) technique has recently become an important technology for high-gain column readout circuits in low-noise CMOS image sensors (CISs). This paper reveals how the column CMS circuits, together with a pixel having a high-conversion-gain charge detector and low-noise transistor, realizes deep sub-electron read noise levels based on the analysis of noise components in the signal readout chain from a pixel to the column analog-to-digital converter (ADC). The noise measurement results of experimental CISs are compared with the noise analysis and the effect of noise reduction to the sampling number is discussed at the deep sub-electron level. Images taken with three CMS gains of two, 16, and 128 show distinct advantage of image contrast for the gain of 128 (noise(median): 0.29 e(-)rms) when compared with the CMS gain of two (2.4 e(-)rms), or 16 (1.1 e(-)rms).

  20. Noise Reduction using Frequency Sub-Band Adaptive Spectral Subtraction

    NASA Technical Reports Server (NTRS)

    Kozel, David

    2000-01-01

    A frequency sub-band based adaptive spectral subtraction algorithm is developed to remove noise from noise-corrupted speech signals. A single microphone is used to obtain both the noise-corrupted speech and the estimate of the statistics of the noise. The statistics of the noise are estimated during time frames that do not contain speech. These statistics are used to determine if future time frames contain speech. During speech time frames, the algorithm determines which frequency sub-bands contain useful speech information and which frequency sub-bands contain only noise. The frequency sub-bands, which contain only noise, are subtracted off at a larger proportion so the noise does not compete with the speech information. Simulation results are presented.

  1. Design and optimization of a noise reduction system for infrasonic measurements using elements with low acoustic impedance.

    PubMed

    Alcoverro, Benoit; Le Pichon, Alexis

    2005-04-01

    The implementation of the infrasound network of the International Monitoring System (IMS) for the enforcement of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) increases the effort in the design of suitable noise reducer systems. In this paper we present a new design consisting of low impedance elements. The dimensioning and the optimization of this discrete mechanical system are based on numerical simulations, including a complete electroacoustical modeling and a realistic wind-noise model. The frequency response and the noise reduction obtained for a given wind speed are compared to statistical noise measurements in the [0.02-4] Hz frequency band. The effects of the constructive parameters-the length of the pipes, inner diameters, summing volume, and number of air inlets-are investigated through a parametric study. The studied system consists of 32 air inlets distributed along an overall diameter of 16 m. Its frequency response is flat up to 4 Hz. For a 2 m/s wind speed, the maximal noise reduction obtained is 15 dB between 0.5 and 4 Hz. At lower frequencies, the noise reduction is improved by the use of a system of larger diameter. The main drawback is the high-frequency limitation introduced by acoustical resonances inside the pipes.

  2. Noise reduction combining time-frequency epsilon-filter and M-transform.

    PubMed

    Abe, Tomomi; Matsumoto, Mitsuharu; Hashimoto, Shuji

    2008-08-01

    This paper introduces noise reduction combining time-frequency epsilon-filter (TF epsilon-filter) and time-frequency M-transform (TF M-transform). Musical noise is an offensive noise generated due to noise reduction in the time-frequency domain such as spectral subtraction and TF epsilon-filter. It has a deleterious effect on speech recognition. To solve the problem, M-transform is introduced. M-transform is a linear transform based on M-sequence. The method combining the time-domain epsilon-filter (TD epsilon-filter) and time-domain M-transform (TD M-transform) can reduce not only white noise but also impulse noise. Musical noise is isolated in the time-frequency domain, which is similar to impulse noise in the time domain. On these prospects, this paper aims to reduce musical noise by improving M-transform for the time-frequency domain. Noise reduction by using TD M-transform and the TD epsilon-filter is first explained to clarify its features. Then, an improved method applying M-transform to the time-frequency domain, namely TF M-transform, is described. Noise reduction combining the TF epsilon-filter and TF M-transform is also proposed. The proposed method can reduce not only high-level nonstationary noise but also musical noise. Experimental results are also given to demonstrate the performance of the proposed method.

  3. Flap Side Edge Liners for Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Jones, Michael G. (Inventor); Khorrami, Mehdi R. (Inventor); Choudhari, Meelan M. (Inventor); Howerton, Brian M. (Inventor)

    2014-01-01

    One or more acoustic liners comprising internal chambers or passageways that absorb energy from a noise source on the aircraft are disclosed. The acoustic liners may be positioned at the ends of flaps of an aircraft wing to provide broadband noise absorption and/or dampen the noise producing unsteady flow features, and to reduce the amount of noise generated due to unsteady flow at the inboard and/or outboard end edges of a flap.

  4. Acoustical and Perceptual Comparison of Noise Reduction and Compression in Hearing Aids.

    PubMed

    Brons, Inge; Houben, Rolph; Dreschler, Wouter A

    2015-08-01

    Noise reduction and dynamic-range compression are generally applied together in hearing aids but may have opposite effects on amplification. This study evaluated the acoustical and perceptual effects of separate and combined processing of noise reduction and compression. Recordings of the output of 4 hearing aids for speech in babble noise at +4 dB signal-to-noise ratio were used in 3 experiments: (a) acoustical measurements to determine the influence of processing on speech and noise levels; (b) perceptual measurements to determine the detectability of processing differences for 16 listeners with hearing impairment; and (c) perceptual measurements to determine the effect of processing on speech intelligibility, noise annoyance, speech naturalness, and overall preference. Noise reduction and compression processing differed between hearing aids. The combined processing (noise reduction with compression) most strongly reduced noise and speech levels. The combined processing was detectably different between hearing aids, but compression processing alone was not. The combined processing did not influence speech intelligibility. Preference for combined processing was lower than previously observed for noise reduction without compression. Differences in processing between hearing aids are perceptually salient. The effect of compression should be taken into account during the development and evaluation of hearing aid noise reduction.

  5. Experimental study of noise reduction for an unstiffened cylindrical model of an airplane fuselage

    NASA Astrophysics Data System (ADS)

    Willis, C. M.; Daniels, E. F.

    1981-12-01

    Noise reduction measurements were made for a simplified model of an airplane fuselage consisting of an unstiffened aluminum cylinder 0.5 m in diameter by 1.2 m long with a 1.6-mm-thick wall. Noise reduction was first measured with a reverberant field pink-noise load on the cylinder exterior. Next, noise reduction was measured by using a propeller to provide a more realistic noise load on the cylinder. Structural resonance frequencies and acoustic reverberation times for the cylinder interior volume were also measured. Comparison of data from the relatively simple test using reverberant-field noise with data from the more complex propeller-noise tests indicates some similarity in both the overall noise reduction and the spectral distribution. However, all of the test parameters investigated (propeller speed, blade pitch, and tip clearance) had some effect on the noise-reduction spectra. Thus, the amount of noise reduction achieved appears to be somewhat dependent upon the spectral and spatial characteristics of the flight conditions. Information is also presented on cyclinder resonance frequencies, damping, and characteristics of propeller-noise loads.

  6. Experimental study of noise reduction for an unstiffened cylindrical model of an airplane fuselage

    NASA Technical Reports Server (NTRS)

    Willis, C. M.; Daniels, E. F.

    1981-01-01

    Noise reduction measurements were made for a simplified model of an airplane fuselage consisting of an unstiffened aluminum cylinder 0.5 m in diameter by 1.2 m long with a 1.6-mm-thick wall. Noise reduction was first measured with a reverberant field pink-noise load on the cylinder exterior. Next, noise reduction was measured by using a propeller to provide a more realistic noise load on the cylinder. Structural resonance frequencies and acoustic reverberation times for the cylinder interior volume were also measured. Comparison of data from the relatively simple test using reverberant-field noise with data from the more complex propeller-noise tests indicates some similarity in both the overall noise reduction and the spectral distribution. However, all of the test parameters investigated (propeller speed, blade pitch, and tip clearance) had some effect on the noise-reduction spectra. Thus, the amount of noise reduction achieved appears to be somewhat dependent upon the spectral and spatial characteristics of the flight conditions. Information is also presented on cyclinder resonance frequencies, damping, and characteristics of propeller-noise loads.

  7. SU-C-207B-02: Maximal Noise Reduction Filter with Anatomical Structures Preservation

    SciTech Connect

    Maitree, R; Guzman, G; Chundury, A; Roach, M; Yang, D

    2016-06-15

    Purpose: All medical images contain noise, which can result in an undesirable appearance and can reduce the visibility of anatomical details. There are varieties of techniques utilized to reduce noise such as increasing the image acquisition time and using post-processing noise reduction algorithms. However, these techniques are increasing the imaging time and cost or reducing tissue contrast and effective spatial resolution which are useful diagnosis information. The three main focuses in this study are: 1) to develop a novel approach that can adaptively and maximally reduce noise while preserving valuable details of anatomical structures, 2) to evaluate the effectiveness of available noise reduction algorithms in comparison to the proposed algorithm, and 3) to demonstrate that the proposed noise reduction approach can be used clinically. Methods: To achieve a maximal noise reduction without destroying the anatomical details, the proposed approach automatically estimated the local image noise strength levels and detected the anatomical structures, i.e. tissue boundaries. Such information was used to adaptively adjust strength of the noise reduction filter. The proposed algorithm was tested on 34 repeating swine head datasets and 54 patients MRI and CT images. The performance was quantitatively evaluated by image quality metrics and manually validated for clinical usages by two radiation oncologists and one radiologist. Results: Qualitative measurements on repeated swine head images demonstrated that the proposed algorithm efficiently removed noise while preserving the structures and tissues boundaries. In comparisons, the proposed algorithm obtained competitive noise reduction performance and outperformed other filters in preserving anatomical structures. Assessments from the manual validation indicate that the proposed noise reduction algorithm is quite adequate for some clinical usages. Conclusion: According to both clinical evaluation (human expert ranking) and

  8. Background Noise Reduction Using Adaptive Noise Cancellation Determined by the Cross-Correlation

    NASA Technical Reports Server (NTRS)

    Spalt, Taylor B.; Brooks, Thomas F.; Fuller, Christopher R.

    2012-01-01

    Background noise due to flow in wind tunnels contaminates desired data by decreasing the Signal-to-Noise Ratio. The use of Adaptive Noise Cancellation to remove background noise at measurement microphones is compromised when the reference sensor measures both background and desired noise. The technique proposed modifies the classical processing configuration based on the cross-correlation between the reference and primary microphone. Background noise attenuation is achieved using a cross-correlation sample width that encompasses only the background noise and a matched delay for the adaptive processing. A present limitation of the method is that a minimum time delay between the background noise and desired signal must exist in order for the correlated parts of the desired signal to be separated from the background noise in the crosscorrelation. A simulation yields primary signal recovery which can be predicted from the coherence of the background noise between the channels. Results are compared with two existing methods.

  9. Reduction of sawing noise through constrained layer damping

    SciTech Connect

    Caldwell, D.B.

    1982-01-01

    Understanding the need for noise control in sawing operations is intuitive in people who have heard the characteristic high pitched scream at the lumber yard, in their own workshop, or at a construction site. Saw noise is a distinctive sound that we remember even from long ago boyhood days. So it was no surprise when, in the USA, the Occupational Health and Safety Act included sawing noise among industrial noises that had to be controlled. This paper describes and discusses our experiments and results. Noise emanating from a cut was accumulated then reduced to an average.

  10. National Oceanic and Atmospheric Administration's Cetacean and Sound Mapping Effort: Continuing Forward with an Integrated Ocean Noise Strategy.

    PubMed

    Harrison, Jolie; Ferguson, Megan; Gedamke, Jason; Hatch, Leila; Southall, Brandon; Van Parijs, Sofie

    2016-01-01

    To help manage chronic and cumulative impacts of human activities on marine mammals, the National Oceanic and Atmospheric Administration (NOAA) convened two working groups, the Underwater Sound Field Mapping Working Group (SoundMap) and the Cetacean Density and Distribution Mapping Working Group (CetMap), with overarching effort of both groups referred to as CetSound, which (1) mapped the predicted contribution of human sound sources to ocean noise and (2) provided region/time/species-specific cetacean density and distribution maps. Mapping products were presented at a symposium where future priorities were identified, including institutionalization/integration of the CetSound effort within NOAA-wide goals and programs, creation of forums and mechanisms for external input and funding, and expanded outreach/education. NOAA is subsequently developing an ocean noise strategy to articulate noise conservation goals and further identify science and management actions needed to support them.

  11. Statistical Analysis of speckle noise reduction techniques for echocardiographic Images

    NASA Astrophysics Data System (ADS)

    Saini, Kalpana; Dewal, M. L.; Rohit, Manojkumar

    2011-12-01

    Echocardiography is the safe, easy and fast technology for diagnosing the cardiac diseases. As in other ultrasound images these images also contain speckle noise. In some cases this speckle noise is useful such as in motion detection. But in general noise removal is required for better analysis of the image and proper diagnosis. Different Adaptive and anisotropic filters are included for statistical analysis. Statistical parameters such as Signal-to-Noise Ratio (SNR), Peak Signal-to-Noise Ratio (PSNR), and Root Mean Square Error (RMSE) calculated for performance measurement. One more important aspect that there may be blurring during speckle noise removal. So it is prefered that filter should be able to enhance edges during noise removal.

  12. Jet Noise Reduction Potential From Emerging Variable Cycle Technologies

    NASA Technical Reports Server (NTRS)

    2012-01-01

    Acoustic and flow-field experiments were conducted on exhaust concepts for the next generation supersonic, commercial aircraft. The concepts were developed by Lockheed Martin (LM), Rolls-Royce Liberty Works (RRLW), and General Electric Global Research (GEGR) as part of an N+2 (next generation forward) aircraft system study initiated by the Supersonics Project in NASA s Fundamental Aeronautics Program. The experiments were conducted in the Aero-Acoustic Propulsion Laboratory at the NASA Glenn Research Center. The exhaust concepts utilized ejectors, inverted velocity profiles, and fluidic shields. One of the ejector concepts was found to produce stagnant flow within the ejector and the other ejector concept produced discrete-frequency tones that degraded the acoustic performance of the model. The concept incorporating an inverted velocity profile and fluid shield produced overall-sound-pressure-level reductions of 6 dB relative to a single stream nozzle at the peak jet noise angle for some nozzle pressure ratios. Flow separations in the nozzle degraded the acoustic performance of the inverted velocity profile model at low nozzle pressure ratios.

  13. Jet Noise Reduction Potential from Emerging Variable Cycle Technologies

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda; Bridges, James; Wernet, Mark

    2012-01-01

    Acoustic and flow-field experiments were conducted on exhaust concepts for the next generation supersonic, commercial aircraft. The concepts were developed by Lockheed Martin (LM), Rolls-Royce Liberty Works (RRLW), and General Electric Global Research (GEGR) as part of an N+2 (next generation forward) aircraft system study initiated by the Supersonics Project in NASA s Fundamental Aeronautics Program. The experiments were conducted in the Aero-Acoustic Propulsion Laboratory at the NASA Glenn Research Center. The exhaust concepts utilized ejectors, inverted velocity profiles, and fluidic shields. One of the ejector concepts was found to produce stagnant flow within the ejector and the other ejector concept produced discrete-frequency tones that degraded the acoustic performance of the model. The concept incorporating an inverted velocity profile and fluid shield produced overall-sound-pressure-level reductions of 6 dB relative to a single stream nozzle at the peak jet noise angle for some nozzle pressure ratios. Flow separations in the nozzle degraded the acoustic performance of the inverted velocity profile model at low nozzle pressure ratios.

  14. Workshop on Jet Exhaust Noise Reduction for Tactical Aircraft - NASA Perspective

    NASA Technical Reports Server (NTRS)

    Huff, Dennis L.; Henderson, Brenda S.

    2007-01-01

    Jet noise from supersonic, high performance aircraft is a significant problem for takeoff and landing operations near air bases and aircraft carriers. As newer aircraft with higher thrust and performance are introduced, the noise tends to increase due to higher jet exhaust velocities. Jet noise has been a subject of research for over 55 years. Commercial subsonic aircraft benefit from changes to the engine cycle that reduce the exhaust velocities and result in significant noise reduction. Most of the research programs over the past few decades have concentrated on commercial aircraft. Progress has been made by introducing new engines with design features that reduce the noise. NASA has recently started a new program called "Fundamental Aeronautics" where three projects (subsonic fixed wing, subsonic rotary wing, and supersonics) address aircraft noise. For the supersonics project, a primary goal is to understand the underlying physics associated with jet noise so that improved noise prediction tools and noise reduction methods can be developed for a wide range of applications. Highlights from the supersonics project are presented including prediction methods for broadband shock noise, flow measurement methods, and noise reduction methods. Realistic expectations are presented based on past history that indicates significant jet noise reduction cannot be achieved without major changes to the engine cycle. NASA s past experience shows a few EPNdB (effective perceived noise level in decibels) can be achieved using low noise design features such as chevron nozzles. Minimal thrust loss can be expected with these nozzles (< 0.5%) and they may be retrofitted on existing engines. In the long term, it is desirable to use variable cycle engines that can be optimized for lower jet noise during takeoff operations and higher thrust for operational performance. It is also suggested that noise experts be included early in the design process for engine nozzle systems to participate

  15. Noise-reduction measurements of stiffened and unstiffened cylindrical models of an airplane fuselage

    NASA Technical Reports Server (NTRS)

    Willis, C. M.; Mayes, W. H.

    1984-01-01

    Noise-reduction measurements are presented for a stiffened and an unstiffened model of an airplane fuselage. The cylindrical models were tested in a reverberant-field noise environment over a frequency range from 20 Hz to 6 kHz. An unstiffened metal fuselage provided more noise reduction than a fuselage having the same sidewall weight divided between skin and stiffening stringers and ring frames. The addition of acoustic insulation to the models tended to smooth out the interior-noise spectrum by reducing or masking the noise associated with the structural response at some of the resonant frequencies.

  16. Noise correlation in CBCT projection data and its application for noise reduction in low-dose CBCT

    SciTech Connect

    Zhang, Hua; Ouyang, Luo; Wang, Jing E-mail: jing.wang@utsouthwestern.edu; Ma, Jianhua E-mail: jing.wang@utsouthwestern.edu; Huang, Jing; Chen, Wufan

    2014-03-15

    Purpose: To study the noise correlation properties of cone-beam CT (CBCT) projection data and to incorporate the noise correlation information to a statistics-based projection restoration algorithm for noise reduction in low-dose CBCT. Methods: In this study, the authors systematically investigated the noise correlation properties among detector bins of CBCT projection data by analyzing repeated projection measurements. The measurements were performed on a TrueBeam onboard CBCT imaging system with a 4030CB flat panel detector. An anthropomorphic male pelvis phantom was used to acquire 500 repeated projection data at six different dose levels from 0.1 to 1.6 mAs per projection at three fixed angles. To minimize the influence of the lag effect, lag correction was performed on the consecutively acquired projection data. The noise correlation coefficient between detector bin pairs was calculated from the corrected projection data. The noise correlation among CBCT projection data was then incorporated into the covariance matrix of the penalized weighted least-squares (PWLS) criterion for noise reduction of low-dose CBCT. Results: The analyses of the repeated measurements show that noise correlation coefficients are nonzero between the nearest neighboring bins of CBCT projection data. The average noise correlation coefficients for the first- and second-order neighbors are 0.20 and 0.06, respectively. The noise correlation coefficients are independent of the dose level. Reconstruction of the pelvis phantom shows that the PWLS criterion with consideration of noise correlation (PWLS-Cor) results in a lower noise level as compared to the PWLS criterion without considering the noise correlation (PWLS-Dia) at the matched resolution. At the 2.0 mm resolution level in the axial-plane noise resolution tradeoff analysis, the noise level of the PWLS-Cor reconstruction is 6.3% lower than that of the PWLS-Dia reconstruction. Conclusions: Noise is correlated among nearest neighboring

  17. Reduction of Helicopter BVI Noise, Vibration, and Power Consumption Through Individual Blade Control

    NASA Technical Reports Server (NTRS)

    Jacklin, Stephen A.; Blaas, Achim; Teves, Dietrich; Kube, Roland; Warmbrodt, William (Technical Monitor)

    1994-01-01

    A wind tunnel test was conducted with a full-scale BO 105 helicopter rotor to evaluate the potential of open-loop individual blade control (IBC) to improve rotor performance, to reduce blade vortex interaction (BVI) noise, and to alleviate helicopter vibrations. The wind tunnel test was an international collaborative effort between NASA/U.S. Army AFDD, ZF Luftfahrttechnik, Eurocopter Deutschland, and the German Aerospace Laboratory (DLR) and was conducted under the auspices of the U.S./German MOU on Rotorcraft Aeromechanics. In this test the normal blade pitch links of the rotor were replaced by servo-actuators so that the pitch of each blade could be controlled independently of the other blades. The specially designed servoactuators and IBC control system were designed and manufactured by ZF Luftfahrttechnik, GmbH. The wind tunnel test was conducted in the 40- by 80-Foot Wind Tunnel at the NASA Ames Research Center. An extensive amount of measurement information was acquired for each IBC data point. These data include rotor performance, static and dynamic hub forces and moments, rotor loads, control loads, inboard and outboard blade pitch motion, and BVI noise data. The data indicated very significant (80 percent) simultaneous reductions in both BVI noise and hub vibrations could be obtained using multi-harmonic input at the critical descent (terminal approach) condition. The data also showed that performance improvements of up to 7 percent could be obtained using 2P input at high-speed forward flight conditions.

  18. Reduction of Helicopter BVI Noise, Vibration, and Power Consumption Through Individual Blade Control

    NASA Technical Reports Server (NTRS)

    Jacklin, Stephen A.; Blaas, Achim; Teves, Dietrich; Kube, Roland; Warmbrodt, William (Technical Monitor)

    1994-01-01

    A wind tunnel test was conducted with a full-scale BO 105 helicopter rotor to evaluate the potential of open-loop individual blade control (IBC) to improve rotor performance, to reduce blade vortex interaction (BVI) noise, and to alleviate helicopter vibrations. The wind tunnel test was an international collaborative effort between NASA/U.S. Army AFDD, ZF Luftfahrttechnik, Eurocopter Deutschland, and the German Aerospace Laboratory (DLR) and was conducted under the auspices of the U.S./German MOU on Rotorcraft Aeromechanics. In this test the normal blade pitch links of the rotor were replaced by servo-actuators so that the pitch of each blade could be controlled independently of the other blades. The specially designed servoactuators and IBC control system were designed and manufactured by ZF Luftfahrttechnik, GmbH. The wind tunnel test was conducted in the 40- by 80-Foot Wind Tunnel at the NASA Ames Research Center. An extensive amount of measurement information was acquired for each IBC data point. These data include rotor performance, static and dynamic hub forces and moments, rotor loads, control loads, inboard and outboard blade pitch motion, and BVI noise data. The data indicated very significant (80 percent) simultaneous reductions in both BVI noise and hub vibrations could be obtained using multi-harmonic input at the critical descent (terminal approach) condition. The data also showed that performance improvements of up to 7 percent could be obtained using 2P input at high-speed forward flight conditions.

  19. Radially leaned outlet guide vanes for fan source noise reduction

    NASA Technical Reports Server (NTRS)

    Kazin, S. B.

    1973-01-01

    Two quiet engine program half scale fans one with a subsonic and the other with a supersonic fan tip speed at takeoff were run with 30 degree leaned and radial outlet guide vanes. Acoustic data at takeoff fan speed on the subsonic tip speed fan showed decreases in 200-foot sideline noise of from 1 to 2 PNdb. The supersonic tip speed fan a takeoff fan speed, however, showed noise increases of up 3 PNdb and a decrease in fan efficiency. At approach fan speed, the subsonic tip speed fan showed a noise decrease of 2.3 PNdb at the 200-foot sideline maximum angle and an increase in efficiency. The supersonic tip speed fan showed noise increase of 3.5 PNdb and no change in efficiency. The decrease in fan efficiency and the nature of the noise increase largely high frequency broadband noise lead to the speculation that an aerodynamic problem occurred.

  20. Laser Phase Noise Reduction for Industrial Interferometric Applications

    NASA Astrophysics Data System (ADS)

    Dubois, Marc; Burr, Kent C.; Drake, Thomas E.

    2004-08-01

    Laser ultrasound is a technique used for the ultrasonic inspection of composites during manufacturing of advanced jet fighters. With this technique laser interferometry is used to detect ultrasonic displacements generated by a laser. In theory, the signal-to-noise ratio is proportional to the square root of the collected detection light. In practice, laser phase noise limits the signal-to-noise ratio above a certain collected light level. Two techniques are presented to decrease effects due to laser noise. In one technique the dual-cavity Fabry-Perot currently used is replaced by an interferometer based on a photorefractive crystal. The other technique has a high-finesse Sagnac cavity that filters the phase noise from the detection laser. Experimental results demonstrate that these two techniques significantly reduce limitations due to laser noise.

  1. Supersonic Transport Noise Reduction Technology Program - Phase 2. Volume 1

    DTIC Science & Technology

    1975-09-01

    transport aircraft . In addition, PNL and EPNL con- tributions made by each major engine component ( jet , turbine , combustor and compressor) were... Turbine noise was studied using a J85 engine with massive Inlet suppressor and open nozzle to unmask the turbine . Second-stage turbine blade /nozzle...17. Kty Words (Suggnted by Author(tl) Jet Noise, High Velocity Suppression, Aircraft Engine Suppression, Turbomachlnery Noise, Hybrid Inlet

  2. Noise Reduction Stethoscope for United States Navy Application

    DTIC Science & Technology

    2007-11-02

    The first design shifted the frequency of Korotkoff sounds and eliminated acoustic coupling between pickup and earpieces . The second stethoscope...and minimal instrument manipulation artifact noise. The earpieces or sound transducers should be comfortable, adjustable, and provide excellent...bypassing the stethoscope. Noise N s 2 acts on the stethoscope itself, from the contact point with the patient, to the medic�s earpieces . This noise

  3. Reduction of classroom noise levels using group contingencies.

    PubMed

    Ring, Brandon M; Sigurdsson, Sigurdur O; Eubanks, Sean L; Silverman, Kenneth

    2014-01-01

    The therapeutic workplace is an employment-based abstinence reinforcement intervention for unemployed drug users where trainees receive on-the-job employment skills training in a classroom setting. The study is an extension of prior therapeutic workplace research, which suggested that trainees frequently violated noise standards. Participants received real-time graphed feedback of noise levels and had the opportunity to earn monetary group reinforcement for maintaining a low number of noise violations. Results suggested that feedback and monetary reinforcement reduced the number of noise violations.

  4. Acoustical and Perceptual Comparison of Noise Reduction and Compression in Hearing Aids

    ERIC Educational Resources Information Center

    Brons, Inge; Houben, Rolph; Dreschler, Wouter A.

    2015-01-01

    Purpose: Noise reduction and dynamic-range compression are generally applied together in hearing aids but may have opposite effects on amplification. This study evaluated the acoustical and perceptual effects of separate and combined processing of noise reduction and compression. Design: Recordings of the output of 4 hearing aids for speech in…

  5. Acoustical and Perceptual Comparison of Noise Reduction and Compression in Hearing Aids

    ERIC Educational Resources Information Center

    Brons, Inge; Houben, Rolph; Dreschler, Wouter A.

    2015-01-01

    Purpose: Noise reduction and dynamic-range compression are generally applied together in hearing aids but may have opposite effects on amplification. This study evaluated the acoustical and perceptual effects of separate and combined processing of noise reduction and compression. Design: Recordings of the output of 4 hearing aids for speech in…

  6. Estimation of Broadband Shock Noise Reduction in Turbulent Jets by Water Injection

    NASA Technical Reports Server (NTRS)

    Kandula, Max; Lonerjan, Michael J.

    2008-01-01

    The concept of effective jet properties introduced by the authors (AIAA-2007-3645) has been extended to the estimation of broadband shock noise reduction by water injection in supersonic jets. Comparison of the predictions with the test data for cold underexpanded supersonic nozzles shows a satisfactory agreement. The results also reveal the range of water mass flow rates over which saturation of mixing noise reduction and existence of parasitic noise are manifest.

  7. Boeing's variable geometry chevron: morphing aerospace structures for jet noise reduction

    NASA Astrophysics Data System (ADS)

    Calkins, Frederick T.; Mabe, James H.; Butler, George W.

    2006-03-01

    Boeing is applying cutting edge smart material actuators to the next generation morphing technologies for aircraft. This effort has led to the Variable Geometry Chevrons (VGC), which utilize compact, light weight, and robust shape memory alloy (SMA) actuators. These actuators morph the shape of chevrons on the trailing edge of a jet engine in order to optimize acoustic and performance objectives at multiple flight conditions. We have demonstrated a technical readiness level of 7 by successfully flight testing the VGCs on a Boeing 777-300ER with GE-115B engines. In this paper we describe the VGC design, development and performance during flight test. Autonomous operation of the VGCs, which did not require a control system or aircraft power, was demonstrated. A parametric study was conducted showing the influence of VGC configurations on shockcell generated cabin noise reduction during cruise. The VGC system provided a robust test vehicle to explore chevron configurations for community and shockcell noise reduction. Most importantly, the VGC concept demonstrated an exciting capability to optimize jet nozzle performance at multiple flight conditions.

  8. Structural parameters that influence the noise reduction characteristics of typical general aviation materials

    NASA Technical Reports Server (NTRS)

    Roskam, J.; Grosveld, F.

    1980-01-01

    Effect of panel curvature and oblique angle of sound incidence on noise reduction characteristics of an aluminum panel are experimentally investigated. Panel curvature results show significant increase in stiffness with comparable decrease of sound transmission through the panel in the frequency region below the panel/cavity resonance frequency. Noise reduction data have been achieved for aluminum panels with clamped, bonded and riveted edge conditions. These edge conditions are shown to influence noise reduction characteristics of aluminum panels. Experimentally measured noise reduction characteristics of flat aluminum panels with uniaxial and biaxial in-plane stresses are presented and discussed. Results indicate important improvement in noise reduction of these panels in the frequency range below the fundamental panel/cavity resonance frequency.

  9. Comparative intelligibility investigation of single-channel noise-reduction algorithms for Chinese, Japanese, and Englisha

    PubMed Central

    Li, Junfeng; Yang, Lin; Zhang, Jianping; Yan, Yonghong; Hu, Yi; Akagi, Masato; Loizou, Philipos C.

    2011-01-01

    A large number of single-channel noise-reduction algorithms have been proposed based largely on mathematical principles. Most of these algorithms, however, have been evaluated with English speech. Given the different perceptual cues used by native listeners of different languages including tonal languages, it is of interest to examine whether there are any language effects when the same noise-reduction algorithm is used to process noisy speech in different languages. A comparative evaluation and investigation is taken in this study of various single-channel noise-reduction algorithms applied to noisy speech taken from three languages: Chinese, Japanese, and English. Clean speech signals (Chinese words and Japanese words) were first corrupted by three types of noise at two signal-to-noise ratios and then processed by five single-channel noise-reduction algorithms. The processed signals were finally presented to normal-hearing listeners for recognition. Intelligibility evaluation showed that the majority of noise-reduction algorithms did not improve speech intelligibility. Consistent with a previous study with the English language, the Wiener filtering algorithm produced small, but statistically significant, improvements in intelligibility for car and white noise conditions. Significant differences between the performances of noise-reduction algorithms across the three languages were observed. PMID:21568430

  10. Comparative intelligibility investigation of single-channel noise-reduction algorithms for Chinese, Japanese, and English.

    PubMed

    Li, Junfeng; Yang, Lin; Zhang, Jianping; Yan, Yonghong; Hu, Yi; Akagi, Masato; Loizou, Philipos C

    2011-05-01

    A large number of single-channel noise-reduction algorithms have been proposed based largely on mathematical principles. Most of these algorithms, however, have been evaluated with English speech. Given the different perceptual cues used by native listeners of different languages including tonal languages, it is of interest to examine whether there are any language effects when the same noise-reduction algorithm is used to process noisy speech in different languages. A comparative evaluation and investigation is taken in this study of various single-channel noise-reduction algorithms applied to noisy speech taken from three languages: Chinese, Japanese, and English. Clean speech signals (Chinese words and Japanese words) were first corrupted by three types of noise at two signal-to-noise ratios and then processed by five single-channel noise-reduction algorithms. The processed signals were finally presented to normal-hearing listeners for recognition. Intelligibility evaluation showed that the majority of noise-reduction algorithms did not improve speech intelligibility. Consistent with a previous study with the English language, the Wiener filtering algorithm produced small, but statistically significant, improvements in intelligibility for car and white noise conditions. Significant differences between the performances of noise-reduction algorithms across the three languages were observed.

  11. An MDOE Investigation of Chevrons for Supersonic Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda; Bridges, James

    2010-01-01

    The impact of chevron design on the noise radiated from heated, overexpanded, supersonic jets is presented. The experiments used faceted bi-conic convergent-divergent nozzles with design Mach numbers equal to 1.51 and 1.65. The purpose of the facets was to simulate divergent seals on a military style nozzle. The nozzle throat diameter was equal to 4.5 inches. Modern Design of Experiment (MDOE) techniques were used to investigate the impact of chevron penetration, length, and width on the resulting acoustic radiation. All chevron configurations used 12 chevrons to match the number of facets in the nozzle. Most chevron designs resulted in increased broadband shock noise relative to the baseline nozzle. In the peak jet noise direction, the optimum chevron design reduced peak sound pressure levels by 4 dB relative to the baseline nozzle. The penetration was the parameter having the greatest impact on radiated noise at all observation angles. While increasing chevron penetration decreased acoustic radiation in the peak jet noise direction, broadband shock noise was adversely impacted. Decreasing chevron length increased noise at most observation angles. The impact of chevron width on radiated noise depended on frequency and observation angle.

  12. Quantum issues in optical communication. [noise reduction in signal reception

    NASA Technical Reports Server (NTRS)

    Kennedy, R. S.

    1973-01-01

    Various approaches to the problem of controlling quantum noise, the dominant noise in an optical communications system, are discussed. It is shown that, no matter which way the problem is approached, there always remain uncertainties. These uncertainties exist because, to date, only very few communication problems have been solved in their full quantum form.

  13. The Effects of Noise Reduction on Social Behaviors.

    ERIC Educational Resources Information Center

    Carbone, Vincent J.; Duncan, Phillip K.

    1986-01-01

    The study found no relationship between improved social behavior in a group of juveniles residing at a county shelter care facility and decreased frequency and duration of disruptions above 85 decibels. Subjects did reduce noise levels when stereo listening was made contingent on reduced noise. (Author/DB)

  14. Noise Level Reduction of .50 Caliber Gunfire by Terrain Shielding

    DTIC Science & Technology

    1994-07-01

    estimate or any other aspect of this ocal on of Wingntno including esetiggloris tor reducng this burden, to Washington Headquarter Services. Directorate...shock exists. The noise event of primary interest in the present experiment was the muzzle blast noise, since it is usually the greatest offender and

  15. Experimental evaluation of leaky least-mean-square algorithms for active noise reduction in communication headsets.

    PubMed

    Cartes, David A; Ray, Laura R; Collier, Robert D

    2002-04-01

    An adaptive leaky normalized least-mean-square (NLMS) algorithm has been developed to optimize stability and performance of active noise cancellation systems. The research addresses LMS filter performance issues related to insufficient excitation, nonstationary noise fields, and time-varying signal-to-noise ratio. The adaptive leaky NLMS algorithm is based on a Lyapunov tuning approach in which three candidate algorithms, each of which is a function of the instantaneous measured reference input, measurement noise variance, and filter length, are shown to provide varying degrees of tradeoff between stability and noise reduction performance. Each algorithm is evaluated experimentally for reduction of low frequency noise in communication headsets, and stability and noise reduction performance are compared with that of traditional NLMS and fixed-leakage NLMS algorithms. Acoustic measurements are made in a specially designed acoustic test cell which is based on the original work of Ryan et al. ["Enclosure for low frequency assessment of active noise reducing circumaural headsets and hearing protection," Can. Acoust. 21, 19-20 (1993)] and which provides a highly controlled and uniform acoustic environment. The stability and performance of the active noise reduction system, including a prototype communication headset, are investigated for a variety of noise sources ranging from stationary tonal noise to highly nonstationary measured F-16 aircraft noise over a 20 dB dynamic range. Results demonstrate significant improvements in stability of Lyapunov-tuned LMS algorithms over traditional leaky or nonleaky normalized algorithms, while providing noise reduction performance equivalent to that of the NLMS algorithm for idealized noise fields.

  16. Clinical review: The impact of noise on patients' sleep and the effectiveness of noise reduction strategies in intensive care units

    PubMed Central

    Xie, Hui; Kang, Jian; Mills, Gary H

    2009-01-01

    Excessive noise is becoming a significant problem for intensive care units (ICUs). This paper first reviews the impact of noise on patients' sleep in ICUs. Five previous studies have demonstrated such impacts, whereas six other studies have shown other factors to be more important. Staff conversation and alarms are generally regarded as the most disturbing noises for patients' sleep in ICUs. Most research in this area has focused purely on noise level, but work has been very limited on the relationships between sleep quality and other acoustic parameters, including spectrum and reverberation time. Sound-absorbing treatment is a relatively effective noise reduction strategy, whereas sound masking appears to be the most effective technique for improving sleep. For future research, there should be close collaboration between medical researchers and acousticians. PMID:19344486

  17. Science Policy Conference Speakers Examine Megadisasters and Call for Risk Reduction Efforts

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2013-07-01

    How well is the United States prepared for a megadisaster, such as a solar storm that knocks out the power grid for months, a large asteroid impact, a giant tsunami, or a rainstorm that lasts for weeks and leads to widespread flooding? Moreover, how can risk reduction efforts be made more effective? These were two topics addressed during two of the hazards sessions at the 2013 AGU Science Policy Conference on 25 and 26 June.

  18. Noise and Fuel Burn Reduction Potential of an Innovative Subsonic Transport Configuration

    NASA Technical Reports Server (NTRS)

    Guo, Yueping; Nickol, Craig L.; Thomas, Russell H.

    2014-01-01

    A study is presented for the noise and fuel burn reduction potential of an innovative double deck concept aircraft with two three-shaft direct-drive turbofan engines. The engines are mounted from the fuselage so that the engine inlet is over the main wing. It is shown that such an aircraft can achieve a cumulative Effective Perceived Noise Level (EPNL) about 28 dB below the current aircraft noise regulations of Stage 4. The combination of high bypass ratio engines and advanced wing design with laminar flow control technologies provide fuel burn reduction and low noise levels simultaneously. For example, the fuselage mounted engine position provides more than 4 EPNLdB of noise reduction by shielding the inlet radiated noise. To identify the potential effect of noise reduction technologies on this concept, parametric studies are presented to reveal the system level benefits of various emerging noise reduction concepts, for both engine and airframe noise reduction. These concepts are discussed both individually to show their respective incremental noise reduction potential and collectively to assess their aggregate effects on the total noise. Through these concepts approximately about 8 dB of additional noise reduction is possible, bringing the cumulative noise level of this aircraft to 36 EPNLdB below Stage 4, if the entire suite of noise reduction technologies would mature to practical application. In a final step, an estimate is made for this same aircraft concept but with higher bypass ratio, geared, turbofan engines. With this geared turbofan propulsion system, the noise is estimated to reach as low as 40-42 dB below Stage 4 with a fuel burn reduction of 43-47% below the 2005 best-in-class aircraft baseline. While just short of the NASA N+2 goals of 42 dB and 50% fuel burn reduction, for a 2025 in service timeframe, this assessment shows that this innovative concept warrants refined study. Furthermore, this design appears to be a viable potential future passenger

  19. Methods for clinical evaluation of noise reduction techniques in abdominopelvic CT.

    PubMed

    Ehman, Eric C; Yu, Lifeng; Manduca, Armando; Hara, Amy K; Shiung, Maria M; Jondal, Dayna; Lake, David S; Paden, Robert G; Blezek, Daniel J; Bruesewitz, Michael R; McCollough, Cynthia H; Hough, David M; Fletcher, Joel G

    2014-01-01

    Most noise reduction methods involve nonlinear processes, and objective evaluation of image quality can be challenging, since image noise cannot be fully characterized on the sole basis of the noise level at computed tomography (CT). Noise spatial correlation (or noise texture) is closely related to the detection and characterization of low-contrast objects and may be quantified by analyzing the noise power spectrum. High-contrast spatial resolution can be measured using the modulation transfer function and section sensitivity profile and is generally unaffected by noise reduction. Detectability of low-contrast lesions can be evaluated subjectively at varying dose levels using phantoms containing low-contrast objects. Clinical applications with inherent high-contrast abnormalities (eg, CT for renal calculi, CT enterography) permit larger dose reductions with denoising techniques. In low-contrast tasks such as detection of metastases in solid organs, dose reduction is substantially more limited by loss of lesion conspicuity due to loss of low-contrast spatial resolution and coarsening of noise texture. Existing noise reduction strategies for dose reduction have a substantial impact on lowering the radiation dose at CT. To preserve the diagnostic benefit of CT examination, thoughtful utilization of these strategies must be based on the inherent lesion-to-background contrast and the anatomy of interest. The authors provide an overview of existing noise reduction strategies for low-dose abdominopelvic CT, including analytic reconstruction, image and projection space denoising, and iterative reconstruction; review qualitative and quantitative tools for evaluating these strategies; and discuss the strengths and limitations of individual noise reduction methods.

  20. Speech recognition in noise using bilateral open-fit hearing aids: the limited benefit of directional microphones and noise reduction.

    PubMed

    Magnusson, Lennart; Claesson, Ann; Persson, Maria; Tengstrand, Tomas

    2013-01-01

    To investigate speech recognition performance in noise with bilateral open-fit hearing aids and as reference also with closed earmolds, in omnidirectional mode, directional mode, and directional mode in conjunction with noise reduction. A within-subject design with repeated measures across conditions was used. Speech recognition thresholds in noise were obtained for the different conditions. Twenty adults without prior experience with hearing aids. All had symmetric sensorineural mild hearing loss in the lower frequencies and moderate to severe hearing loss in the higher frequencies. Speech recognition performance in noise was not significantly better with an omnidirectional microphone compared to unaided, whereas performance was significantly better with a directional microphone (1.6 dB with open fitting and 4.4 dB with closed earmold) compared to unaided. With open fitting, no significant additional advantage was obtained by combining the directional microphone with a noise reduction algorithm, but with closed earmolds a significant additional advantage of 0.8 dB was obtained. The significant, though limited, advantage of directional microphones and the absence of additional significant improvement by a noise reduction algorithm should be considered when fitting open-fit hearing aids.

  1. Challenges and Recent Developments in Hearing Aids: Part I. Speech Understanding in Noise, Microphone Technologies and Noise Reduction Algorithms

    PubMed Central

    Chung, King

    2004-01-01

    This review discusses the challenges in hearing aid design and fitting and the recent developments in advanced signal processing technologies to meet these challenges. The first part of the review discusses the basic concepts and the building blocks of digital signal processing algorithms, namely, the signal detection and analysis unit, the decision rules, and the time constants involved in the execution of the decision. In addition, mechanisms and the differences in the implementation of various strategies used to reduce the negative effects of noise are discussed. These technologies include the microphone technologies that take advantage of the spatial differences between speech and noise and the noise reduction algorithms that take advantage of the spectral difference and temporal separation between speech and noise. The specific technologies discussed in this paper include first-order directional microphones, adaptive directional microphones, second-order directional microphones, microphone matching algorithms, array microphones, multichannel adaptive noise reduction algorithms, and synchrony detection noise reduction algorithms. Verification data for these technologies, if available, are also summarized. PMID:15678225

  2. Challenges and recent developments in hearing aids. Part I. Speech understanding in noise, microphone technologies and noise reduction algorithms.

    PubMed

    Chung, King

    2004-01-01

    This review discusses the challenges in hearing aid design and fitting and the recent developments in advanced signal processing technologies to meet these challenges. The first part of the review discusses the basic concepts and the building blocks of digital signal processing algorithms, namely, the signal detection and analysis unit, the decision rules, and the time constants involved in the execution of the decision. In addition, mechanisms and the differences in the implementation of various strategies used to reduce the negative effects of noise are discussed. These technologies include the microphone technologies that take advantage of the spatial differences between speech and noise and the noise reduction algorithms that take advantage of the spectral difference and temporal separation between speech and noise. The specific technologies discussed in this paper include first-order directional microphones, adaptive directional microphones, second-order directional microphones, microphone matching algorithms, array microphones, multichannel adaptive noise reduction algorithms, and synchrony detection noise reduction algorithms. Verification data for these technologies, if available, are also summarized.

  3. Effects of background noise on audiometric thresholds during positron emission tomography: passive and active noise-reduction.

    PubMed

    Kim, K; Burkard, R F; Lockwood, A H; Salvi, R J

    2000-01-01

    Position emission tomography (PET) is used to assess the functional activity of the human auditory brain; however, the activity detected by PET could be affected by ambient acoustic noise from the PET equipment. To evaluate these effects, we compared behavioural thresholds in the PET camera with those measured in an audiometric sound booth. Thresholds were measured with: (i) ER2 earphones, (ii) ER2 earphones + Cabot earmuffs, (iii) ER2 earphones + Bose Series II Aviation Headset with active noise-reduction off, and (iv) ER2 earphones + Bose Series II Aviation Headset with active noise-reduction on. Overall ambient noise level in the camera was 73 dB SPL and the maximum octave-band SPL was 68 dB SPL at 250 Hz. Threshold elevations in the PET camera were greatest with ER2 (17 dB, 125 Hz) earphones and lowest with ER2 earphones + Bose Series II Aviation Headset (8 dB at 250 Hz) with active noise-reduction. Thus, PET scanner noise had little or no effect on threshold when stimuli were presented through ER2 earphones covered with an activated Bose Series II Aviation Headset.

  4. Quantitative appraisal for noise reduction in digital holographic phase imaging.

    PubMed

    Montresor, Silvio; Picart, Pascal

    2016-06-27

    This paper discusses on a quantitative comparison of the performances of different advanced algorithms for phase data de-noising. In order to quantify the performances, several criteria are proposed: the gain in the signal-to-noise ratio, the Q index, the standard deviation of the phase error, and the signal to distortion ratio. The proposed methodology to investigate de-noising algorithms is based on the use of a realistic simulation of noise-corrupted phase data. A database including 25 fringe patterns divided into 5 patterns and 5 different signal-to-noise ratios was generated to evaluate the selected de-noising algorithms. A total of 34 algorithms divided into different families were evaluated. Quantitative appraisal leads to ranking within the considered criteria. A fairly good correlation between the signal-to-noise ratio gain and the quality index has been observed. There exists an anti-correlation between the phase error and the quality index which indicates that the phase errors are mainly structural distortions in the fringe pattern. Experimental results are thoroughly discussed in the paper.

  5. Survey of techniques for reduction of wind turbine blade trailing edge noise.

    SciTech Connect

    Barone, Matthew Franklin

    2011-08-01

    Aerodynamic noise from wind turbine rotors leads to constraints in both rotor design and turbine siting. The primary source of aerodynamic noise on wind turbine rotors is the interaction of turbulent boundary layers on the blades with the blade trailing edges. This report surveys concepts that have been proposed for trailing edge noise reduction, with emphasis on concepts that have been tested at either sub-scale or full-scale. These concepts include trailing edge serrations, low-noise airfoil designs, trailing edge brushes, and porous trailing edges. The demonstrated noise reductions of these concepts are cited, along with their impacts on aerodynamic performance. An assessment is made of future research opportunities in trailing edge noise reduction for wind turbine rotors.

  6. Flight-test measurement of the noise reduction of a jet transport delayed flap approach procedure

    NASA Technical Reports Server (NTRS)

    Foster, J. D.; Lasagna, P. L.

    1976-01-01

    A delayed flap approach procedure was flight tested using the NASA CV-990 airplane to measure and analyze the noise produced beneath the flight path. Three other types of landing approaches were also flight tested to provide a comparison of the noise reduction benefits to the delayed flap approach. The conventional type of approach was used as a baseline to compare the effectiveness of the other approaches. The decelerating approach is a variation of the delayed flap approach. A detailed comparison of the ground perceived noise generated during the approaches is presented. For this comparison, the measured noise data were normalized to compensate for variations in aircraft weight and winds that occurred during the flight tests. The data show that the reduced flap approach offers some noise reduction, while the delayed flap and decelerating approaches offer significant noise reductions over the conventional approach.

  7. Two Methods of Mechanical Noise Reduction of Recorded Speech During Phonation in an MRI device

    NASA Astrophysics Data System (ADS)

    Přibil, J.; Horáček, J.; Horák, P.

    2011-01-01

    The paper presents two methods of noise reduction of speech signal recorded in an MRI device during phonation for the human vocal tract modelling. The applied approach of noise speech signal cleaning is based on cepstral speech analysis and synthesis because the noise is mainly produced by gradient coils, has a mechanical character, and can be processed in spectral domain. Our first noise reduction method is using real cepstrum limitation and clipping the "peaks" corresponding to the harmonic frequencies of mechanical noise. The second method is coming out from substation of the short-time spectra of two signals recorded withal: the first includes speech and noise, and the second consists of noise only. The resulting speech quality was compared by spectrogram and mean periodogram methods.

  8. A simulation study of harmonics regeneration in noise reduction for electric and acoustic stimulation

    PubMed Central

    Hu, Yi

    2010-01-01

    Recent research results show that combined electric and acoustic stimulation (EAS) significantly improves speech recognition in noise, and it is generally established that access to the improved F0 representation of target speech, along with the glimpse cues, provide the EAS benefits. Under noisy listening conditions, noise signals degrade these important cues by introducing undesired temporal-frequency components and corrupting harmonics structure. In this study, the potential of combining noise reduction and harmonics regeneration techniques was investigated to further improve speech intelligibility in noise by providing improved beneficial cues for EAS. Three hypotheses were tested: (1) noise reduction methods can improve speech intelligibility in noise for EAS; (2) harmonics regeneration after noise reduction can further improve speech intelligibility in noise for EAS; and (3) harmonics sideband constraints in frequency domain (or equivalently, amplitude modulation in temporal domain), even deterministic ones, can provide additional benefits. Test results demonstrate that combining noise reduction and harmonics regeneration can significantly improve speech recognition in noise for EAS, and it is also beneficial to preserve the harmonics sidebands under adverse listening conditions. This finding warrants further work into the development of algorithms that regenerate harmonics and the related sidebands for EAS processing under noisy conditions. PMID:21117763

  9. A simulation study of harmonics regeneration in noise reduction for electric and acoustic stimulation.

    PubMed

    Hu, Yi

    2010-05-01

    Recent research results show that combined electric and acoustic stimulation (EAS) significantly improves speech recognition in noise, and it is generally established that access to the improved F0 representation of target speech, along with the glimpse cues, provide the EAS benefits. Under noisy listening conditions, noise signals degrade these important cues by introducing undesired temporal-frequency components and corrupting harmonics structure. In this study, the potential of combining noise reduction and harmonics regeneration techniques was investigated to further improve speech intelligibility in noise by providing improved beneficial cues for EAS. Three hypotheses were tested: (1) noise reduction methods can improve speech intelligibility in noise for EAS; (2) harmonics regeneration after noise reduction can further improve speech intelligibility in noise for EAS; and (3) harmonics sideband constraints in frequency domain (or equivalently, amplitude modulation in temporal domain), even deterministic ones, can provide additional benefits. Test results demonstrate that combining noise reduction and harmonics regeneration can significantly improve speech recognition in noise for EAS, and it is also beneficial to preserve the harmonics sidebands under adverse listening conditions. This finding warrants further work into the development of algorithms that regenerate harmonics and the related sidebands for EAS processing under noisy conditions.

  10. Column-Parallel Correlated Multiple Sampling Circuits for CMOS Image Sensors and Their Noise Reduction Effects

    PubMed Central

    Suh, Sungho; Itoh, Shinya; Aoyama, Satoshi; Kawahito, Shoji

    2010-01-01

    For low-noise complementary metal-oxide-semiconductor (CMOS) image sensors, the reduction of pixel source follower noises is becoming very important. Column-parallel high-gain readout circuits are useful for low-noise CMOS image sensors. This paper presents column-parallel high-gain signal readout circuits, correlated multiple sampling (CMS) circuits and their noise reduction effects. In the CMS, the gain of the noise cancelling is controlled by the number of samplings. It has a similar effect to that of an amplified CDS for the thermal noise but is a little more effective for 1/f and RTS noises. Two types of the CMS with simple integration and folding integration are proposed. In the folding integration, the output signal swing is suppressed by a negative feedback using a comparator and one-bit D-to-A converter. The CMS circuit using the folding integration technique allows to realize a very low-noise level while maintaining a wide dynamic range. The noise reduction effects of their circuits have been investigated with a noise analysis and an implementation of a 1Mpixel pinned photodiode CMOS image sensor. Using 16 samplings, dynamic range of 59.4 dB and noise level of 1.9 e− for the simple integration CMS and 75 dB and 2.2 e− for the folding integration CMS, respectively, are obtained. PMID:22163400

  11. Column-parallel correlated multiple sampling circuits for CMOS image sensors and their noise reduction effects.

    PubMed

    Suh, Sungho; Itoh, Shinya; Aoyama, Satoshi; Kawahito, Shoji

    2010-01-01

    For low-noise complementary metal-oxide-semiconductor (CMOS) image sensors, the reduction of pixel source follower noises is becoming very important. Column-parallel high-gain readout circuits are useful for low-noise CMOS image sensors. This paper presents column-parallel high-gain signal readout circuits, correlated multiple sampling (CMS) circuits and their noise reduction effects. In the CMS, the gain of the noise cancelling is controlled by the number of samplings. It has a similar effect to that of an amplified CDS for the thermal noise but is a little more effective for 1/f and RTS noises. Two types of the CMS with simple integration and folding integration are proposed. In the folding integration, the output signal swing is suppressed by a negative feedback using a comparator and one-bit D-to-A converter. The CMS circuit using the folding integration technique allows to realize a very low-noise level while maintaining a wide dynamic range. The noise reduction effects of their circuits have been investigated with a noise analysis and an implementation of a 1Mpixel pinned photodiode CMOS image sensor. Using 16 samplings, dynamic range of 59.4 dB and noise level of 1.9 e(-) for the simple integration CMS and 75 dB and 2.2 e(-) for the folding integration CMS, respectively, are obtained.

  12. X-/Ka-band dichroic plate noise temperature reduction

    NASA Technical Reports Server (NTRS)

    Veruttipong, W.; Lee, P.

    1994-01-01

    The X-/Ka-band (8.4 GHz/32.0 GHz) dichroic plate installed as DSS 13 contributes an estimated 3 K to the system noise temperature at 32.0 GHz. Approximately 1 percent of the Ka-band incident field is reflected by the plate into the 300-K environment of the DSS-13 pedestal room. A low-cost, easily implemented method of reducing the noise temperature is presented. Using a curved reflector, the reflected field can be re-focused into an 80-K cold load, reducing the noise temperature contribution of the dichroic plate by about 2 K.

  13. X-/Ka-Band Dichroic Plate Noise Temperature Reduction

    NASA Astrophysics Data System (ADS)

    Veruttipong, W.; Lee, P.

    1994-07-01

    The X-/Ka-band (8.4-GHz/32.0-GHz) dichroic plate installed at DSS 13 contributes an estimated 3 K to the system noise temperature at 32.0 GHz. Approximately 1 percent of the Ka-band incident field is reflected by the plate into the 300-K environment of the DSS-13 pedestal room. A low-cost, easily implemented method of reducing the noise temperature is presented. Using a curved reflector, the reflected field can be refocused into an 80-K cold load, reducing the noise temperature contribution of the dichroic plate by about 2 K.

  14. X-/Ka-band dichroic plate noise temperature reduction

    NASA Astrophysics Data System (ADS)

    Veruttipong, W.; Lee, P.

    1994-11-01

    The X-/Ka-band (8.4 GHz/32.0 GHz) dichroic plate installed as DSS 13 contributes an estimated 3 K to the system noise temperature at 32.0 GHz. Approximately 1 percent of the Ka-band incident field is reflected by the plate into the 300-K environment of the DSS-13 pedestal room. A low-cost, easily implemented method of reducing the noise temperature is presented. Using a curved reflector, the reflected field can be re-focused into an 80-K cold load, reducing the noise temperature contribution of the dichroic plate by about 2 K.

  15. Effects of directional microphone and adaptive multichannel noise reduction algorithm on cochlear implant performance.

    PubMed

    Chung, King; Zeng, Fan-Gang; Acker, Kyle N

    2006-10-01

    Although cochlear implant (CI) users have enjoyed good speech recognition in quiet, they still have difficulties understanding speech in noise. We conducted three experiments to determine whether a directional microphone and an adaptive multichannel noise reduction algorithm could enhance CI performance in noise and whether Speech Transmission Index (STI) can be used to predict CI performance in various acoustic and signal processing conditions. In Experiment I, CI users listened to speech in noise processed by 4 hearing aid settings: omni-directional microphone, omni-directional microphone plus noise reduction, directional microphone, and directional microphone plus noise reduction. The directional microphone significantly improved speech recognition in noise. Both directional microphone and noise reduction algorithm improved overall preference. In Experiment II, normal hearing individuals listened to the recorded speech produced by 4- or 8-channel CI simulations. The 8-channel simulation yielded similar speech recognition results as in Experiment I, whereas the 4-channel simulation produced no significant difference among the 4 settings. In Experiment III, we examined the relationship between STIs and speech recognition. The results suggested that STI could predict actual and simulated CI speech intelligibility with acoustic degradation and the directional microphone, but not the noise reduction algorithm. Implications for intelligibility enhancement are discussed.

  16. Reduction of Classical Measurement Noise via Quantum-Dense Metrology

    NASA Astrophysics Data System (ADS)

    Ast, Melanie; Steinlechner, Sebastian; Schnabel, Roman

    2016-10-01

    Quantum-dense metrology constitutes a special case of quantum metrology in which two orthogonal phase space projections of a signal are simultaneously sensed beyond the shot-noise limit. Previously, it was shown that the additional sensing channel that is provided by quantum-dense metrology contains information that can be used to identify and to discard corrupted segments from the measurement data. Here, we propose and demonstrate a new method in which this information is used for improving the sensitivity without discarding any measurement segments. Our measurement reached sub-shot-noise performance, although initially strong classical noise polluted the data. The new method has high potential for improving the noise spectral density of gravitational-wave detectors at signal frequencies of high astrophysical relevance.

  17. Noise Reduction in High-Throughput Gene Perturbation Screens

    USDA-ARS?s Scientific Manuscript database

    Motivation: Accurate interpretation of perturbation screens is essential for a successful functional investigation. However, the screened phenotypes are often distorted by noise, and their analysis requires specialized statistical analysis tools. The number and scope of statistical methods available...

  18. Reduction of Classical Measurement Noise via Quantum-Dense Metrology.

    PubMed

    Ast, Melanie; Steinlechner, Sebastian; Schnabel, Roman

    2016-10-28

    Quantum-dense metrology constitutes a special case of quantum metrology in which two orthogonal phase space projections of a signal are simultaneously sensed beyond the shot-noise limit. Previously, it was shown that the additional sensing channel that is provided by quantum-dense metrology contains information that can be used to identify and to discard corrupted segments from the measurement data. Here, we propose and demonstrate a new method in which this information is used for improving the sensitivity without discarding any measurement segments. Our measurement reached sub-shot-noise performance, although initially strong classical noise polluted the data. The new method has high potential for improving the noise spectral density of gravitational-wave detectors at signal frequencies of high astrophysical relevance.

  19. The cost of noise reduction in commercial tilt rotor aircraft

    NASA Technical Reports Server (NTRS)

    Faulkner, H. B.

    1974-01-01

    The relationship between direct operating cost (DOC) and departure noise annoyance was developed for commercial tilt rotor aircraft. This was accomplished by generating a series of tilt rotor aircraft designs to meet various noise goals at minimum DOC. These vehicles were spaced across the spectrum of possible noise levels from completely unconstrained to the quietest vehicle that could be designed within the study ground rules. A group of optimization parameters were varied to find the minimum DOC while other inputs were held constant and some external constraints were met. This basic variation was then extended to different aircraft sizes and technology time frames. It was concluded that reducing noise annoyance by designing for lower rotor tip speeds is a very promising avenue for future research and development. It appears that the cost of halving the annoyance compared to an unconstrained design is insignificant and the cost of halving the annoyance again is small.

  20. Noise and its reduction in graphene based nanopore devices.

    PubMed

    Kumar, Ashvani; Park, Kyeong-Beom; Kim, Hyun-Mi; Kim, Ki-Bum

    2013-12-13

    Ionic current fluctuations in graphene nanopore devices are a ubiquitous phenomenon and are responsible for degraded spatial and temporal resolution. Here, we descriptively investigate the impact of different substrate materials (Si and quartz) and membrane thicknesses on noise characteristics of graphene nanopore devices. To mitigate the membrane fluctuations and pin-hole defects, a SiNx membrane is transferred onto the substrate and a pore of approximately 70 nm in diameter is perforated prior to the graphene transfer. Comprehensive noise study reveals that the few layer graphene transferred onto the quartz substrate possesses low noise level and higher signal to noise ratio as compared to single layer graphene, without deteriorating the spatial resolution. The findings here point to improvement of graphene based nanopore devices for exciting opportunities in future single-molecule genomic screening devices.

  1. Noise reduction by continuous addition of subchannel holograms.

    PubMed

    Som, S C; Budhiraja, C J

    1975-07-01

    A new and convenient technique for reducing both speckle and coherent noise in holographic imagery is described with supporting experimental results. Its advantages and disadvantages have been mentioned in the context of other known techniques.

  2. Active-passive gradient shielding for MRI acoustic noise reduction.

    PubMed

    Edelstein, William A; Kidane, Tesfaye K; Taracila, Victor; Baig, Tanvir N; Eagan, Timothy P; Cheng, Yu-Chung N; Brown, Robert W; Mallick, John A

    2005-05-01

    An important source of MRI acoustic noise-magnet cryostat warm-bore vibrations caused by eddy-current-induced forces-can be mitigated by a passive metal shield mounted on the outside of a vibration-isolated, vacuum-enclosed shielded gradient set. Finite-element (FE) calculations for a z-gradient indicate that a 2-mm-thick Cu layer wrapped on the gradient assembly can decrease mechanical power deposition in the warm bore and reduce warm-bore acoustic noise production by about 25 dB. Eliminating the conducting warm bore and other magnet parts as significant acoustic noise sources could lead to the development of truly quiet, fully functioning MRI systems with noise levels below 70 dB.

  3. Acoustic noise reduction in a 4 T MRI scanner.

    PubMed

    Mechefske, Chris K; Geris, Ryan; Gati, Joseph S; Rutt, Brian K

    2002-01-01

    High-field, high-speed magnetic resonance imaging (MRI) can generate high levels of noise. There is ongoing concern in the medical and imaging research communities regarding the detrimental effects of high acoustic levels on auditory function, patient anxiety, verbal communication between patients and health care workers and ultimately MR image quality. In order to effectively suppress the noise levels inside MRI scanners, the sound field needs to be accurately measured and characterized. This paper presents the results of measurements of the sound radiation from a gradient coil cylinder within a 4 T MRI scanner under a variety of conditions. These measurement results show: (1) that noise levels can be significantly reduced through the use of an appropriately designed passive acoustic liner; and (2) the true noise levels that are experienced by patients during echo planar imaging.

  4. The Structure and Noise Reduction Capacity of Owl Down

    NASA Astrophysics Data System (ADS)

    Jaworski, Justin; Clark, Ian; Alexander, Nathan; Devenport, William; Daly, Conor; Peake, Nigel; Glegg, Stewart

    2014-11-01

    Many species of owl rely on specialized plumage to reduce their self-noise levels and enable hunting in acoustic stealth. In contrast to the leading-edge comb and compliant trailing-edge fringe attributes of owls, the aeroacoustic impact of the fluffy down material on the upper wing surface remains largely speculative as a means to eliminate aerodynamic noise across a broad range of frequencies. Photographic analysis of the owl down reveals a unique forest-like structure, whereby the down fibers rise straight up from the wing surface and then bend into the flow direction to form a porous canopy, with an open area fraction of approximately 70%. Experimental measurements demonstrate that the canopy feature reduces dramatically the turbulent pressure levels on the wing surface by up to 30dB, which affects the roughness noise characteristic of the down in a manner consistent with the theory of flows over and through vegetation. Mathematical models developed for the turbulence noise generation by the down fibers and for the mixing-layer instability above the porous canopy furnish a theoretical basis to understand the influence of the down geometric structure on its self-noise signature and noise suppression characteristics.

  5. Noise reduction in solid-state lasers using a SHG-based buffer reservoir.

    PubMed

    El Amili, Abdelkrim; Alouini, Mehdi

    2015-04-01

    The cancellation of resonant intensity noise, from a few kHz up to several GHz, is reported using a second-harmonic generation (SHG) buffer reservoir in a Nd:YAG solid-state laser. This approach is shown to be well suited and easily optimizable for reducing the excess noise lying at the laser relaxation oscillations as well as that originating from the beating between the lasing mode and nonlasing adjacent longitudinal modes. A thorough analysis of noise spectra of both laser and SHG signals confirms definitely that noise reduction is a consequence of a deep laser dynamics modification rather than noise evacuation mechanism.

  6. Older Adults Expend More Listening Effort than Young Adults Recognizing Speech in Noise

    ERIC Educational Resources Information Center

    Gosselin, Penny Anderson; Gagne, Jean-Pierre

    2011-01-01

    Purpose: Listening in noisy situations is a challenging experience for many older adults. The authors hypothesized that older adults exert more listening effort compared with young adults. Listening effort involves the attention and cognitive resources required to understand speech. The purpose was (a) to quantify the amount of listening effort…

  7. Brain Regions Recruited for the Effortful Comprehension of Noise-Vocoded Words

    ERIC Educational Resources Information Center

    Hervais-Adelman, Alexis G.; Carlyon, Robert P.; Johnsrude, Ingrid S.; Davis, Matthew H.

    2012-01-01

    We used functional magnetic resonance imaging (fMRI) to investigate the neural basis of comprehension and perceptual learning of artificially degraded [noise vocoded (NV)] speech. Fifteen participants were scanned while listening to 6-channel vocoded words, which are difficult for naive listeners to comprehend, but can be readily learned with…

  8. Quantum noise reduction using squeezed states in LIGO

    NASA Astrophysics Data System (ADS)

    Dwyer, Sheila E.

    Direct detection of gravitational waves will require earth based detectors to measure strains of the order 10-21, at frequencies of 100Hz, a sensitivity that has been accomplished with the initial generation of LIGO interferometric gravitational wave detectors. A new generation of detectors currently under construction is designed improve on the sensitivity of the initial detectors by about a factor of 10. The quantum nature of light will limit the sensitivity of these Advanced LIGO interferometers at most frequencies; new approaches to reducing the quantum noise will be needed to improve the sensitivity further. This quantum noise originates from the vacuum fluctuations that enter the unused port of the interferometer and interfere with the laser light. Vacuum fluctuations have the minimum noise allowed by Heisenberg's uncertainty principle, DeltaX1 Delta X2 ≤ 1, where the two quadratures X 1 and X2 are non-commuting observables responsible for the two forms of quantum noise, shot noise and radiation pressure noise. By replacing the vacuum fluctuations entering the interferometer with squeezed states, which have lower noise in one quadrature than the vacuum state, we have reduced the shot noise of a LIGO interferometer. The sensitivity to gravitational waves measured during this experiment represents the best sensitivity achieved to date at frequencies above 200 Hz, and possibly the first time that squeezing has been measured in an interferometer at frequencies below 700 Hz. The possibility that injection of squeezed states could introduce environmental noise couplings that would degrade the crucial but fragile low frequency sensitivity of a LIGO interferometer has been a major concern in planning to implement squeezing as part of baseline interferometer operations. These results demonstrate that squeezing is compatible with the low frequency sensitivity of a full scale gravitational wave interferometer. We also investigated the limits to the level of squeezing

  9. Minimizing noise in fiberglass aquaculture tanks: Noise reduction potential of various retrofits

    USDA-ARS?s Scientific Manuscript database

    Equipment used in intensive aquaculture systems, such as pumps and blowers can produce underwater sound levels and frequencies within the range of fish hearing. The impacts of underwater noise on fish are not well known, but limited research suggests that subjecting fish to noise could result in imp...

  10. A note on the low-frequency noise reduction of cylindrical capsules (L).

    PubMed

    Ungar, Eric E

    2006-12-01

    The noise reductions provided by capsules consisting of uniform cylindrical shells whose two ends are closed off by like circular plates are analyzed for the low-frequency regime in which a capsule acts quasi-statically, much like a pressure vessel. The change in the confined volume is determined from the structural deflections produced by a net pressure difference, taking account of the interactions of the shell and end plates. Expressions for the noise reduction of a single capsule and of two nested capsules are derived. Some insights into the noise reduction effects of interaction between the shell and end plates are discussed, as are the contributions of these components.

  11. Advanced supersonic propulsion study. [with emphasis on noise level reduction

    NASA Technical Reports Server (NTRS)

    Sabatella, J. A. (Editor)

    1974-01-01

    A study was conducted to determine the promising propulsion systems for advanced supersonic transport application, and to identify the critical propulsion technology requirements. It is shown that noise constraints have a major effect on the selection of the various engine types and cycle parameters. Several promising advanced propulsion systems were identified which show the potential of achieving lower levels of sideline jet noise than the first generation supersonic transport systems. The non-afterburning turbojet engine, utilizing a very high level of jet suppression, shows the potential to achieve FAR 36 noise level. The duct-heating turbofan with a low level of jet suppression is the most attractive engine for noise levels from FAR 36 to FAR 36 minus 5 EPNdb, and some series/parallel variable cycle engines show the potential of achieving noise levels down to FAR 36 minus 10 EPNdb with moderate additional penalty. The study also shows that an advanced supersonic commercial transport would benefit appreciably from advanced propulsion technology. The critical propulsion technology needed for a viable supersonic propulsion system, and the required specific propulsion technology programs are outlined.

  12. Study of active rotor control for in-plane rotor noise reduction

    NASA Astrophysics Data System (ADS)

    Yang, Tianxiao

    This research consists of two parts: the main part of this research is the study of active rotor control for in-plane rotor noise reduction. The objective of this part of the research is to develop a methodology to find a loading solution that results in noise reduction at a single observer or over an area (at multiple observers), and propose potential active devices that may realize the loading solution to reduce in-plane noise. Another part of the research is the study of thickness noise prediction method, which aims to develop a new thickness noise prediction method able to provide fast and relatively accurate thickness noise prediction. In this research, a new thickness noise prediction method, called dual compact thickness noise model is developed. In this dual compact model, at each radial location, the airfoil is divided into two parts and the uniform pressure distribution is integrated on the front and rear part respectively. This generates two loading lines acting at different chordwise locations, and the loading noise generated by these two loading lines reproduces the acoustic signal of the normal thickness noise. The positions of the two loading lines are determined to be .... = 0.133 and .... = 0.867 in a baseline case by matching normal thickness noise and the dual compact result at an in-plane observer directly ahead of the rotor. The dual compact thickness noise model is validated through thickness noise computation for a wide variety of cases, in which different airfoils, blade planforms, and tip Mach numbers, are considered. The dual compact thickness noise result is in good agreement with normal thickness noise for each case. Additionally, the locations of the two loading lines are kept unchanged for all the cases. The computation time is significantly reduced by using the dual compact thickness noise model as compared to the normal thickness noise computation (typically 25 times faster). Finally, the accuracy of dual compact thickness noise

  13. An MDOE Assessment of Nozzle Vanes for High Bypass Ratio Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda; Norum, Thomas; Bridges, James

    2006-01-01

    The effect of airfoil-shaped vanes placed in the fan stream of a BPR 8 coannular nozzle model system on the resulting jet noise was investigated. The experiments used a Modern Design of Experiments approach to investigate the impact of a range of vane parameters on the noise reduction achieved at representative takeoff conditions. The experimental results showed that the installation of the vanes decreased low frequency noise radiation in the downstream peak-noise direction and increased high frequency noise in the upstream direction. Results also showed that improper selection of the vane configuration resulted in increased low frequency noise radiation in the upstream direction. Large angles of attack are shown to reduce noise near the peak jet noise angle and increase noise in the upstream direction. The MDOE analysis yields an optimum design that minimizes perceived noise levels. Limited data taken with a BPR 5 nozzle system showed that the vanes result in better effective perceived noise reduction for lower bypass ratio nozzles than for the BPR 8 model.

  14. Innovative Use of the Electronic Health Record to Support Harm Reduction Efforts.

    PubMed

    Hyman, Daniel; Neiman, Jenae; Rannie, Michael; Allen, Renee; Swietlik, Marguerite; Balzer, Andrea

    2017-05-01

    Awareness of the impact of preventable harm on patients and families has resulted in extensive efforts to make our health care systems safer. We determined that, in our hospital, patients experienced 1 of 9 types of preventable harm approximately every other day. In an effort to expedite early identification of patients at risk and provide timely intervention, we used the electronic health record's (EHR) documentation to enable decision support, data capture, and auditing and implemented reporting tools to reduce rates of harm. Harm reduction strategies included aggregating data to generate a risk profile for hospital-acquired conditions (HACs) for all inpatients. The profile includes links to prevention bundles and available care guidelines. Additionally, lists of patients at risk for HACs autopopulate electronic audit tools contained within Research Electronic Data Capture, and data from observational audits and EHR documentation populate real-time dashboards of bundle compliance. Patient population summary reports promote the discussion of relevant HAC prevention measures during patient care and unit leadership rounds. The hospital has sustained a >30% reduction in harm for 9 types of HAC since 2012. In 2014, the number of HACs with >80% bundle adherence doubled coincident with the progressive rollout of these EHR-based interventions. Existing EHR documentation and reporting tools may be effective adjuncts to harm reduction initiatives. Additional study should include an evaluation of scalability across organizations, ongoing bundle adherence, and individual tests of change to isolate interventions with the highest impact on our results. Copyright © 2017 by the American Academy of Pediatrics.

  15. Fan noise reduction achieved by removing tip flow irregularities behind the rotor - forward arc test configurations

    NASA Technical Reports Server (NTRS)

    Dittmar, J. H.; Woodward, R. P.; Mackinnon, M. J.

    1984-01-01

    The noise source caused by the interaction of the rotor tip flow irregularities (vortices and velocity defects) with the downstream stator vanes was studied. Fan flow was removed behind a 0.508 meter (20 in.) diameter model turbofan through an outer wall slot between the rotor and stator. Noise measurements were made with far-field microphones positioned in an arc about the fan inlet and with a pressure transducer in the duct behind the stator. Little tone noise reduction was observed in the forward arc during flow removal; possibly because the rotor-stator interaction noise did not propagate upstream through the rotor. Noise reductions were maded in the duct behind the stator and the largest decrease occurred with the first increment of flow removal. This result indicates that the rotor tip flow irregularity-stator interaction is as important a noise producing mechanism as the normally considered rotor wake-stator interaction.

  16. Noise Reduction Analysis on Inverter Driven Two-Cylinder Rotary Compressor

    NASA Astrophysics Data System (ADS)

    Nonaka, Ryutaro; Suda, Akihiro; Matumoto, Kenzou

    Two-cylinder rotary compressor is dynamically balanced well because two rollers in each cylinder chamber are located in opposite sides. Thus, it helps to reduce the circumferential vibration based on the tracking torque ripple for gas compression. This concept has been recently applied to room airconditioners (RACs) for the purpose of reducing vibration and noise of the unit. However, it consequently requires the compressor, which is one of the main noise factors, extremely low noise to reduce RAC noise. This paper describes generating mechanisms of the compressor noise established by analysis using signal processing and computer aided engineering. In addition, concrete countermeasures are presented for the noise reduction of the two-cylinder rotary compressor. In conclusion, Countermeasures for resonance in cavities were achieved by reducing 630Hz∼1KHz levels and the effect of muffler in the chamber contributed to the reduction of 3KHz∼6KHz levels.

  17. Noise reduction in adaptive-optics imagery with the use of support constraints

    NASA Astrophysics Data System (ADS)

    Matson, Charles L.; Roggemann, Michael C.

    1995-02-01

    The use of support constraints for noise reduction in images obtained with telescopes that use adaptive optics for atmospheric correction is discussed. Noise covariances are derived for these type of data, including the effects of photon noise and CCD read noise. The effectiveness of support constraints in achieving noise reduction is discussed in terms of these noise properties and in terms of the types of algorithms used to enforce the support constraint. Both a convex-projections and a cost-function minimization algorithm are used to enforce the support constraints, and it is shown with the use of computer simulations and field data that the cost-function algorithm results in artifacts in the reconstructions. The convex-projections algorithms produced mean-square-error decreases in the image domain of approximately 10% for high light levels but essentially no error decreases for low light levels. We emphasize images that are well resolved by the telescope and adaptive-optics system.

  18. Experiments to Determine Neighborhood Reactions to Light Airplanes With and Without External Noise Reduction

    NASA Technical Reports Server (NTRS)

    Elwell, Fred S

    1953-01-01

    The work reported was part of a program of experimentation with external noise reduction on light airplanes. This particular study was in effect a byproduct survey conceived to utilize already available equipment and personnel to further the findings of the original research and to determine reactions in populated neighborhoods to light aircraft with and without noise-reduction equipment. The findings indicate that at the 10 sites within and about metropolitan Boston the degree of noise reduction previously found to be aerodynamically and structurally feasible did eliminate substantially all neighborhood objections to noise per se. The evidence clearly suggests that, when the noise nuisance is minimized to the extent found feasible, the number and severity of other objections also diminish -- evidently because the flight operations are noticed less when heard less.

  19. Noise reduction of a composite cylinder subjected to random acoustic excitation

    NASA Technical Reports Server (NTRS)

    Grosveld, Ferdinand W.; Beyer, T.

    1989-01-01

    Interior and exterior noise measurements were conducted on a stiffened composite floor-equipped cylinder, with and without an interior trim installed. Noise reduction was obtained for the case of random acoustic excitation in a diffuse field; the frequency range of interest was 100-800-Hz one-third octave bands. The measured data were compared with noise reduction predictions from the Propeller Aircraft Interior Noise (PAIN) program and from a statistical energy analysis. Structural model parameters were not predicted well by the PAIN program for the given input parameters; this resulted in incorrect noise reduction predictions for the lower one-third octave bands where the power flow into the interior of the cylinder was predicted on a mode-per-mode basis.

  20. Reduction of double Rayleigh scattering noise in distributed Raman amplifiers employing higher-order pumping.

    PubMed

    Bolognini, Gabriele; Bononi, Alberto

    2009-04-27

    We present a theoretical study of the performance of distributed Raman amplifiers with higher order pumping schemes, focusing in particular on double Rayleigh scattering (DRS) noise. Results show an unexpected significant DRS noise reduction for pumping order higher than third, allowing for an overall performance improvement of carefully designed distributed amplifiers, ensuring a large optical signal-to-noise ratio improvement together with reduced DRS-induced penalties.

  1. The Reduction of Ducted Fan Engine Noise Via a Boundary Integral Equation Method

    NASA Technical Reports Server (NTRS)

    Tweed, John

    2000-01-01

    Engineering studies for reducing ducted fan engine noise were conducted using the noise prediction code TBIEM3D. To conduct parametric noise reduction calculations, it was necessary to advance certain theoretical and computational aspects of the boundary integral equation method (BIEM) described in and implemented in TBIEM3D. Also, enhancements and upgrades to TBIEM3D were made for facilitating the code's use in this research and by the aeroacoustics engineering community.

  2. Research on noise and vibration reduction at DB to improve the environmental friendliness of railway traffic

    NASA Astrophysics Data System (ADS)

    Schulte-Werning, B.; Beier, M.; Degen, K. G.; Stiebel, D.

    2006-06-01

    One of the most prominent keywords relating to the environmental friendliness of railway traffic is noise reduction. Thus, the research and development programme "Low Noise Railway" of Deutsche Bahn (DB) is under way to treat the noise of the vehicles and infrastructure. The noise reduction of the trains and the rail/wheel system are being tackled within several projects. The direct noise experienced by railway-lineside residents due to train movements on the track can be reduced by minimising the sound radiation directly at the source. This is the first-choice solution, as it proves to be the most effective countermeasure regarding a cost-benefit relation. The limit values for the noise emission as specified in the technical specification for interoperability are an essential criterion to be confirmed during the procurement process of railway vehicles. A recently developed acoustical quality management scheme establishes systematic noise management to complete the vehicle procurement process in the phases of concept, design, construction and manufacturing. In freight traffic quiet railway wheels for block brake operation will play an important role in the future to meet the goal of a low-noise railway system. A first attempt to realise successfully the low-noise potential of such optimised wheels was performed, even if with mixed results. To show ways of reducing the noise of the cooling ventilation in locomotives, DB is a partner in a development project led by Siemens. A notable 8 dB(A) noise reduction was measured. Concerning bridge noise, a project was started based on an effective and cost-efficient combination of experiments and simulations in order to develop specifications for the construction of generic low-noise bridges.

  3. Recent efforts to validate EOS observations: hyperspectral data noise characterization using PCA: application to AIRS

    NASA Astrophysics Data System (ADS)

    Tobin, David; Revercomb, Henry; Antonelli, Paolo; Vinson, Kenneth; Dutcher, Steven; Knuteson, Robert; Taylor, Joseph; Best, Fred; Moeller, Chris; Gunshor, Mathew

    2006-08-01

    Exploiting the redundancy in high spectral resolution observations, dependent set Principle Component Analysis (PCA) is a simple yet very powerful tool not only for noise filtering and lossy compression, but also for the characterization of sensor noise and other variable artifacts using Earth scene data. Our approach for dependent set PCA of AIRS Earth scene data is presented. Aspects of the analyses include 1) estimation of NEDT using PCA and comparisons to values derived from on-board blackbodies, 2) estimation of the scene dependence of NEDN, 3) estimation of the spectrally correlated component of NEDT and comparison to pre-launch analyses using blackbody views, 4) investigation of non- Gaussian noise behavior, and 5) inspection of individual PCs. The results of the PCA analyses are generally consistent with results obtained pre-launch and on-orbit using blackbody and/or space view data. Specific findings include: 1) PCA estimates of AIRS spectrally random and spectrally correlated NEDN compare well with estimates computed from on-board blackbody and space views, 2) the signal dependence of AIRS NEDN is accurately parameterized in terms of the scene radiance, 3) examination of the reconstruction error allows non-Gaussian phenomenon such as popping to be characterized, and 4) inspection of the PCs and individual PC filtered radiance spectra is a powerful technique for diagnosing low level artifacts in hyperspectral data.

  4. Reduction of Classroom Noise Levels Using Group Contingencies

    ERIC Educational Resources Information Center

    Ring, Brandon M.; Sigurdsson, Sigurdur O.; Eubanks, Sean L.; Silverman, Kenneth

    2014-01-01

    The therapeutic workplace is an employment-based abstinence reinforcement intervention for unemployed drug users where trainees receive on-the-job employment skills training in a classroom setting. The study is an extension of prior therapeutic workplace research, which suggested that trainees frequently violated noise standards. Participants…

  5. Reduction of PMT Signal-Induced Noise in Lidar Receivers

    NASA Technical Reports Server (NTRS)

    Williamson, Cynthia K.; DeYoung, Russell J.

    1998-01-01

    Signal-induced noise is generated when a photomultiplier tube (PMT) is subjected to an intense light pulse. The PMT signal does not return to the dark current level after the signal is removed, but decays slowly (i.e., signal-induced noise). This is of practical significance for DIAL (Differential Absorption lidar) measurements where signal-induced noise decays are superimposed on the on-line (absorption) and off-line signals. Errors in the ozone density calculation result for stratosphere measurements. Other researchers have implemented mechanical choppers that block the intense pulse which may be from near field return scattering or scattering from a cloud. This configuration cannot be implemented for the DIAL system employed for aircraft measurements since the on-line and off-line pulses are 300 microseconds apart. A scheme has been developed in this study to electronically attenuate the signal induced noise. A ring electrode, external to the PMT photocathode, is utilized to perturb the electron trajectories between the photocathode and the first dynode. This effect has been used for position sensitive PMTs and suggested for gating PMTS.

  6. Reduction of Classroom Noise Levels Using Group Contingencies

    ERIC Educational Resources Information Center

    Ring, Brandon M.; Sigurdsson, Sigurdur O.; Eubanks, Sean L.; Silverman, Kenneth

    2014-01-01

    The therapeutic workplace is an employment-based abstinence reinforcement intervention for unemployed drug users where trainees receive on-the-job employment skills training in a classroom setting. The study is an extension of prior therapeutic workplace research, which suggested that trainees frequently violated noise standards. Participants…

  7. Reduction of Vane Noise in Wind-Tunnel Nozzles

    NASA Technical Reports Server (NTRS)

    Martin, R. M.; Brooks, T. F.; Hoad, D. R.

    1986-01-01

    Vane-induced noise reduced by adhering thin layer of porous material such as foam to downwind surface of vanes, particularly near sharp trailing edges, to prevent occurrence of edge tones. Other modifications made to aerodynamically streamline vane structure were rounding leading edges and smoothly fairing trailing edges. Boundary layer trip applied to leading edge to prevent laminar tone shedding from trailing edge.

  8. Slice Encoding for Metal Artifact Correction with Noise Reduction

    PubMed Central

    Lu, Wenmiao; Pauly, Kim B.; Gold, Garry E.; Pauly, John M.; Hargreaves, Brian A.

    2011-01-01

    Magnetic resonance imaging (MRI) near metallic implants is often hampered by severe metal artifacts. To obtain distortion-free MR images near metallic implants, SEMAC (Slice Encoding for Metal Artifact Correction) corrects metal artifacts via robust encoding of excited slices against metal-induced field inhomogeneities, followed by combining the data resolved from multiple SEMAC-encoded slices. However, as many of the resolved data elements only contain noise, SEMAC-corrected images can suffer from relatively low signal-to-noise ratio (SNR). Improving the SNR of SEMAC-corrected images is essential to enable SEMAC in routine clinical studies. In this work, a new reconstruction procedure is proposed to reduce noise in SEMAC-corrected images. A singular value decomposition (SVD) denoising step is first applied to suppress quadrature noise in multi-coil SEMAC-encoded slices. Subsequently, the SVD-denoised data are selectively included in the correction of through-plane distortions. The experimental results demonstrate that the proposed reconstruction procedure significantly improves the SNR without compromising the correction of metal artifacts. PMID:21287596

  9. Adaptive anisotropic diffusion for noise reduction of phase images in Fourier domain Doppler optical coherence tomography.

    PubMed

    Xia, Shaoyan; Huang, Yong; Peng, Shizhao; Wu, Yanfeng; Tan, Xiaodi

    2016-08-01

    Phase image in Fourier domain Doppler optical coherence tomography offers additional flow information of investigated samples, which provides valuable evidence towards accurate medical diagnosis. High quality phase images are thus desirable. We propose a noise reduction method for phase images by combining a synthetic noise estimation criteria based on local noise estimator (LNE) and distance median value (DMV) with anisotropic diffusion model. By identifying noise and signal pixels accurately and diffusing them with different coefficients respectively and adaptive iteration steps, we demonstrated the effectiveness of our proposed method in both phantom and mouse artery images. Comparison with other methods such as filtering method (mean, median filtering), wavelet method, probabilistic method and partial differential equation based methods in terms of peak signal-to-noise ratio (PSNR), equivalent number of looks (ENL) and contrast-to-noise ratio (CNR) showed the advantages of our method in reserving image energy and removing noise.

  10. Adaptive anisotropic diffusion for noise reduction of phase images in Fourier domain Doppler optical coherence tomography

    PubMed Central

    Xia, Shaoyan; Huang, Yong; Peng, Shizhao; Wu, Yanfeng; Tan, Xiaodi

    2016-01-01

    Phase image in Fourier domain Doppler optical coherence tomography offers additional flow information of investigated samples, which provides valuable evidence towards accurate medical diagnosis. High quality phase images are thus desirable. We propose a noise reduction method for phase images by combining a synthetic noise estimation criteria based on local noise estimator (LNE) and distance median value (DMV) with anisotropic diffusion model. By identifying noise and signal pixels accurately and diffusing them with different coefficients respectively and adaptive iteration steps, we demonstrated the effectiveness of our proposed method in both phantom and mouse artery images. Comparison with other methods such as filtering method (mean, median filtering), wavelet method, probabilistic method and partial differential equation based methods in terms of peak signal-to-noise ratio (PSNR), equivalent number of looks (ENL) and contrast-to-noise ratio (CNR) showed the advantages of our method in reserving image energy and removing noise. PMID:27570687

  11. Adaptive mean filtering for noise reduction in CT polymer gel dosimetry

    SciTech Connect

    Hilts, Michelle; Jirasek, Andrew

    2008-01-15

    X-ray computed tomography (CT) as a method of extracting 3D dose information from irradiated polymer gel dosimeters is showing potential as a practical means to implement gel dosimetry in a radiation therapy clinic. However, the response of CT contrast to dose is weak and noise reduction is critical in order to achieve adequate dose resolutions with this method. Phantom design and CT imaging technique have both been shown to decrease image noise. In addition, image postprocessing using noise reduction filtering techniques have been proposed. This work evaluates in detail the use of the adaptive mean filter for reducing noise in CT gel dosimetry. Filter performance is systematically tested using both synthetic patterns mimicking a range of clinical dose distribution features as well as actual clinical dose distributions. Both low and high signal-to-noise ratio (SNR) situations are examined. For all cases, the effects of filter kernel size and the number of iterations are investigated. Results indicate that adaptive mean filtering is a highly effective tool for noise reduction CT gel dosimetry. The optimum filtering strategy depends on characteristics of the dose distributions and image noise level. For low noise images (SNR {approx}20), the filtered results are excellent and use of adaptive mean filtering is recommended as a standard processing tool. For high noise images (SNR {approx}5) adaptive mean filtering can also produce excellent results, but filtering must be approached with more caution as spatial and dose distortions of the original dose distribution can occur.

  12. Fluorescence microscopy image noise reduction using a stochastically-connected random field model

    PubMed Central

    Haider, S. A.; Cameron, A.; Siva, P.; Lui, D.; Shafiee, M. J.; Boroomand, A.; Haider, N.; Wong, A.

    2016-01-01

    Fluorescence microscopy is an essential part of a biologist’s toolkit, allowing assaying of many parameters like subcellular localization of proteins, changes in cytoskeletal dynamics, protein-protein interactions, and the concentration of specific cellular ions. A fundamental challenge with using fluorescence microscopy is the presence of noise. This study introduces a novel approach to reducing noise in fluorescence microscopy images. The noise reduction problem is posed as a Maximum A Posteriori estimation problem, and solved using a novel random field model called stochastically-connected random field (SRF), which combines random graph and field theory. Experimental results using synthetic and real fluorescence microscopy data show the proposed approach achieving strong noise reduction performance when compared to several other noise reduction algorithms, using quantitative metrics. The proposed SRF approach was able to achieve strong performance in terms of signal-to-noise ratio in the synthetic results, high signal to noise ratio and contrast to noise ratio in the real fluorescence microscopy data results, and was able to maintain cell structure and subtle details while reducing background and intra-cellular noise. PMID:26884148

  13. Time-domain noise reduction based on an orthogonal decomposition for desired signal extraction.

    PubMed

    Benesty, Jacob; Chen, Jingdong; Arden Huang, Yiteng; Gaensler, Tomas

    2012-07-01

    This paper addresses the problem of noise reduction in the time domain where the clean speech sample at every time instant is estimated by filtering a vector of the noisy speech signal. Such a clean speech estimate consists of both the filtered speech and residual noise (filtered noise) as the noisy vector is the sum of the clean speech and noise vectors. Traditionally, the filtered speech is treated as the desired signal after noise reduction. This paper proposes to decompose the clean speech vector into two orthogonal components: one is correlated and the other is uncorrelated with the current clean speech sample. While the correlated component helps estimate the clean speech, it is shown that the uncorrelated component interferes with the estimation, just as the additive noise. Based on this orthogonal decomposition, the paper presents a way to define the error signal and cost functions and addresses the issue of how to design different optimal noise reduction filters by optimizing these cost functions. Specifically, it discusses how to design the maximum SNR filter, the Wiener filter, the minimum variance distortionless response (MVDR) filter, the tradeoff filter, and the linearly constrained minimum variance (LCMV) filter. It demonstrates that the maximum SNR, Wiener, MVDR, and tradeoff filters are identical up to a scaling factor. It also shows from the orthogonal decomposition that many performance measures can be defined, which seem to be more appropriate than the traditional ones for the evaluation of the noise reduction filters.

  14. A Wavelet-Based Noise Reduction Algorithm and Its Clinical Evaluation in Cochlear Implants

    PubMed Central

    Ye, Hua; Deng, Guang; Mauger, Stefan J.; Hersbach, Adam A.; Dawson, Pam W.; Heasman, John M.

    2013-01-01

    Noise reduction is often essential for cochlear implant (CI) recipients to achieve acceptable speech perception in noisy environments. Most noise reduction algorithms applied to audio signals are based on time-frequency representations of the input, such as the Fourier transform. Algorithms based on other representations may also be able to provide comparable or improved speech perception and listening quality improvements. In this paper, a noise reduction algorithm for CI sound processing is proposed based on the wavelet transform. The algorithm uses a dual-tree complex discrete wavelet transform followed by shrinkage of the wavelet coefficients based on a statistical estimation of the variance of the noise. The proposed noise reduction algorithm was evaluated by comparing its performance to those of many existing wavelet-based algorithms. The speech transmission index (STI) of the proposed algorithm is significantly better than other tested algorithms for the speech-weighted noise of different levels of signal to noise ratio. The effectiveness of the proposed system was clinically evaluated with CI recipients. A significant improvement in speech perception of 1.9 dB was found on average in speech weighted noise. PMID:24086605

  15. Acoustic and Laser Doppler Anemometer Results for Confluent, 22-Lobed, and Unique-Lobed Mixer Exhaust Systems for Subsonic Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Salikuddin, M.; Martens, S.; Shin, H.; Majjigi, R. K.; Krejsa, Gene (Technical Monitor)

    2002-01-01

    The objective of this task was to develop a design methodology and noise reduction concepts for high bypass exhaust systems which could be applied to both existing production and new advanced engine designs. Special emphasis was given to engine cycles with bypass ratios in the range of 4:1 to 7:1, where jet mixing noise was a primary noise source at full power takeoff conditions. The goal of this effort was to develop the design methodology for mixed-flow exhaust systems and other novel noise reduction concepts that would yield 3 EPNdB noise reduction relative to 1992 baseline technology. Two multi-lobed mixers, a 22-lobed axisymmetric and a 21-lobed with a unique lobe, were designed. These mixers along with a confluent mixer were tested with several fan nozzles of different lengths with and without acoustic treatment in GEAE's Cell 41 under the current subtask (Subtask C). In addition to the acoustic and LDA tests for the model mixer exhaust systems, a semi-empirical noise prediction method for mixer exhaust system is developed. Effort was also made to implement flowfield data for noise prediction by utilizing MGB code. In general, this study established an aero and acoustic diagnostic database to calibrate and refine current aero and acoustic prediction tools.

  16. Effective Jet Properties for the Prediction of Turbulent Mixing Noise Reduction by Water Injection

    NASA Technical Reports Server (NTRS)

    Kandula, Max; Lonergan, Michael J.

    2007-01-01

    A one-dimensional control volume formulation is developed for the determination of jet mixing noise reduction due to water injection. The analysis starts from the conservation of mass, momentum and energy for the control volume, and introduces the concept of effective jet parameters (jet temperature, jet velocity and jet Mach number). It is shown that the water to jet mass flow rate ratio is an important parameter characterizing the jet noise reduction on account of gas-to-droplet momentum and heat transfer. Two independent dimensionless invariant groups are postulated, and provide the necessary relations for the droplet size and droplet Reynolds number. Results are presented illustrating the effect of mass flow rate ratio on the jet mixing noise reduction for a range of jet Mach number and jet Reynolds number. Predictions from the model show satisfactory comparison with available test data on supersonic jets. The results suggest that significant noise reductions can be achieved at increased flow rate ratios.

  17. Transient noise reduction in speech signal with a modified long-term predictor

    NASA Astrophysics Data System (ADS)

    Choi, Min-Seok; Kang, Hong-Goo

    2011-12-01

    This article proposes an efficient median filter based algorithm to remove transient noise in a speech signal. The proposed algorithm adopts a modified long-term predictor (LTP) as the pre-processor of the noise reduction process to reduce speech distortion caused by the nonlinear nature of the median filter. This article shows that the LTP analysis does not modify to the characteristic of transient noise during the speech modeling process. Oppositely, if a short-term linear prediction (STP) filter is employed as a pre-processor, the enhanced output includes residual noise because the STP analysis and synthesis process keeps and restores transient noise components. To minimize residual noise and speech distortion after the transient noise reduction, a modified LTP method is proposed which estimates the characteristic of speech more accurately. By ignoring transient noise presence regions in the pitch lag detection step, the modified LTP successfully avoids being affected by transient noise. A backward pitch prediction algorithm is also adopted to reduce speech distortion in the onset regions. Experimental results verify that the proposed system efficiently eliminates transient noise while preserving desired speech signal.

  18. Evaluation of an independent linear model for acoustic noise on a conventional MRI scanner and implications for acoustic noise reduction.

    PubMed

    Wu, Ziyue; Kim, Yoon-Chul; Khoo, Michael C K; Nayak, Krishna S

    2014-04-01

    To evaluate an independent linear model for gradient acoustic noise on a conventional MRI scanner, and to explore implications for acoustic noise reduction in routine imaging. Acoustic noise generated from each physical gradient axis was modeled as the prescribed gradient waveform passed through a linear time-invariant system. Homogeneity and superposition properties were experimentally determined. We also developed a new method to correct relative time shifts between the measured impulse responses for different physical gradient axes. Model accuracy was determined by comparing predicted and measured sound using normalized energy difference. Transfer functions were also measured in subjects with different body habitus and at multiple microphone locations. Both superposition and homogeneity held for each physical gradient axis with errors less than 3%. When all gradients were on simultaneous sound prediction, error was reduced from 32% to 4% after time-shift correction. Transfer functions also showed high sensitivity to body habitus and microphone location. The independent linear model predicts MRI acoustic noise with less than 4% error. Acoustic transfer functions are highly sensitive to body habitus and position within the bore, making it challenging to produce a general approach to acoustic noise reduction based on avoiding system resonance peaks. Copyright © 2013 Wiley Periodicals, Inc.

  19. AST Critical Propulsion and Noise Reduction Technologies for Future Commercial Subsonic Engines: Separate-Flow Exhaust System Noise Reduction Concept Evaluation

    NASA Technical Reports Server (NTRS)

    Janardan, B. A.; Hoff, G. E.; Barter, J. W.; Martens, S.; Gliebe, P. R.; Mengle, V.; Dalton, W. N.; Saiyed, Naseem (Technical Monitor)

    2000-01-01

    This report describes the work performed by General Electric Aircraft Engines (GEAE) and Allison Engine Company (AEC) on NASA Contract NAS3-27720 AoI 14.3. The objective of this contract was to generate quality jet noise acoustic data for separate-flow nozzle models and to design and verify new jet-noise-reduction concepts over a range of simulated engine cycles and flight conditions. Five baseline axisymmetric separate-flow nozzle models having bypass ratios of five and eight with internal and external plugs and 11 different mixing-enhancer model nozzles (including chevrons, vortex-generator doublets, and a tongue mixer) were designed and tested in model scale. Using available core and fan nozzle hardware in various combinations, 28 GEAE/AEC separate-flow nozzle/mixing-enhancer configurations were acoustically evaluated in the NASA Glenn Research Center Aeroacoustic and Propulsion Laboratory. This report describes model nozzle features, facility and data acquisition/reduction procedures, the test matrix, and measured acoustic data analyses. A number of tested core and fan mixing enhancer devices and combinations of devices gave significant jet noise reduction relative to separate-flow baseline nozzles. Inward-flip and alternating-flip core chevrons combined with a straight-chevron fan nozzle exceeded the NASA stretch goal of 3 EPNdB jet noise reduction at typical sideline certification conditions.

  20. Noise Reduction to Reduce Patient Anxiety During Cast Removal: Can We Decrease Patient Anxiety With Cast Removal by Wearing Noise Reduction Headphones During Cast Saw Use?

    PubMed

    Mahan, Susan T; Harris, Marie S; Lierhaus, Anneliese M; Miller, Patricia E; DiFazio, Rachel L

    Noise reduction headphones decrease the sound during cast removal. Their effectiveness in decreasing anxiety has not been studied. Compare pediatric patients' anxiety levels during cast removal with and without utilization of noise reduction headphones combined with use of a personal electronic device. Quality improvement project. Patients randomly assigned to noise reduction headphone group or standard care group during cast removal. Faces, Legs, Activity, Cry, and Consolability Scale and heart rate were evaluated prior to, during, and after cast removal. Data were compared across groups. Fifty patients were included; 25 per group. No difference detected between the 2 groups in Faces, Legs, Activity, Cry, and Consolability Scale score prior to (p = .05) or after cast removal (p = .30). During cast removal, the headphone group had lower FLACC Scale scores (p = .03). Baseline heart rate was lower in the headphone group prior to (p = .02) and after (p = .005) cast removal with no difference during cast removal (p = .24). Utilizing noise reduction headphones and a personal electronic device during the cast removal process decreases patient anxiety.

  1. Evaluation of the sparse coding shrinkage noise reduction algorithm in normal hearing and hearing impaired listeners.

    PubMed

    Sang, Jinqiu; Hu, Hongmei; Zheng, Chengshi; Li, Guoping; Lutman, Mark E; Bleeck, Stefan

    2014-04-01

    Although there are numerous single-channel noise reduction strategies to improve speech perception in noise, most of them improve speech quality but do not improve speech intelligibility, in circumstances where the noise and speech have similar frequency spectra. Current exceptions that may improve speech intelligibility are those that require a priori knowledge of the speech or noise statistics, which limits practical application. Hearing impaired (HI) listeners suffer more in speech intelligibility than normal hearing listeners (NH) in the same noisy environment, so developing better single-channel noise reduction algorithms for HI listeners is justified. Our model-based "sparse coding shrinkage" (SCS) algorithm extracts key speech information in noisy speech. We evaluate it by comparison with a state-of-the-art Wiener filtering approach using speech intelligibility tests with NH and HI listeners. The model-based SCS algorithm relies only on statistical signal information without prior information. Results show that the SCS algorithm improves speech intelligibility in stationary noise and is comparable to the Wiener filtering algorithm. Both algorithms improve intelligibility for HI listeners but not for NH listeners. Improvement is less in fluctuating (babble) noise than in stationary noise. Both noise reduction algorithms perform better at higher input signal-to-noise ratios (SNR) where HI listeners can benefit but where NH listeners have already reached ceiling performance. The difference between NH and HI subjects in intelligibility gain depends fundamentally on the input SNR rather than the hearing loss level. We conclude that HI listeners need different signal processing algorithms from NH subjects and that the SCS algorithm offers a promising alternative to Wiener filtering. Performance of all noise reduction algorithms is likely to vary according to extent of hearing loss and algorithms that show little benefit for listeners with moderate hearing loss may

  2. Long-term effects of noise reduction measures on noise annoyance and sleep disturbance: the Norwegian facade insulation study.

    PubMed

    Amundsen, Astrid H; Klæboe, Ronny; Aasvang, Gunn Marit

    2013-06-01

    The Norwegian facade insulation study includes one pre-intervention and two post-intervention surveys. The facade-insulating measures reduced indoor noise levels by 7 dB on average. Before the intervention, 43% of the respondents were highly annoyed by noise. Half a year after the intervention, the proportion of respondents who were highly annoyed by road traffic noise had been significantly reduced to 15%. The second post-intervention study (2 yr after the first post-intervention study) showed that the proportion of highly annoyed respondents had not changed since the first post-intervention study. The reduction in the respondents' self-reported sleep disturbances (due to traffic noise) also remained relatively stable from the first to the second post-intervention study. In the control group, there were no statistically significant differences in annoyance between the pre-intervention and the two post-intervention studies. Previous studies of traffic changes have reported that people "overreact" to noise changes. This study indicated that when considering a receiver measure, such as facade insulation, the effect of reducing indoor noise levels could be predicted from exposure-response curves based on previous studies. Thus no evidence of an "overreaction" was found.

  3. Improving word recognition in noise among hearing-impaired subjects with a single-channel cochlear noise-reduction algorithm.

    PubMed

    Fink, Nir; Furst, Miriam; Muchnik, Chava

    2012-09-01

    A common complaint of the hearing impaired is the inability to understand speech in noisy environments even with their hearing assistive devices. Only a few single-channel algorithms have significantly improved speech intelligibility in noise for hearing-impaired listeners. The current study introduces a cochlear noise reduction algorithm. It is based on a cochlear representation of acoustic signals and real-time derivation of a binary speech mask. The contribution of the algorithm for enhancing word recognition in noise was evaluated on a group of 42 normal-hearing subjects, 35 hearing-aid users, 8 cochlear implant recipients, and 14 participants with bimodal devices. Recognition scores of Hebrew monosyllabic words embedded in Gaussian noise at several signal-to-noise ratios (SNRs) were obtained with processed and unprocessed signals. The algorithm was not effective among the normal-hearing participants. However, it yielded a significant improvement in some of the hearing-impaired subjects under different listening conditions. Its most impressive benefit appeared among cochlear implant recipients. More than 20% improvement in recognition score of noisy words was obtained by 12, 16, and 26 hearing-impaired at SNR of 30, 24, and 18 dB, respectively. The algorithm has a potential to improve speech intelligibility in background noise, yet further research is required to improve its performances.

  4. Development of an acoustic actuator for launch vehicle noise reduction.

    PubMed

    Henderson, Benjamin K; Lane, Steven A; Gussy, Joel; Griffin, Steve; Farinholt, Kevin M

    2002-01-01

    In many active noise control applications, it is necessary that acoustic actuators be mounted in small enclosures due to volume constraints and in order to remain unobtrusive. However, the air spring of the enclosure is detrimental to the low-frequency performance of the actuator. For launch vehicle noise control applications, mass and volume constraints are very limiting, but the low-frequency performance of the actuator is critical. This work presents a novel approach that uses a nonlinear buckling suspension system and partial evacuation of the air within the enclosure to yield a compact, sealed acoustic driver that exhibits a very low natural frequency. Linear models of the device are presented and numerical simulations are given to illustrate the advantages of this design concept. An experimental prototype was built and measurements indicate that this design can significantly improve the low-frequency response of compact acoustic actuators.

  5. Blade vortex interaction noise reduction techniques for a rotorcraft

    NASA Technical Reports Server (NTRS)

    Charles, Bruce D. (Inventor); Hassan, Ahmed A. (Inventor); Tadghighi, Hormoz (Inventor); JanakiRam, Ram D. (Inventor); Sankar, Lakshmi N. (Inventor)

    1996-01-01

    An active control device for reducing blade-vortex interactions (BVI) noise generated by a rotorcraft, such as a helicopter, comprises a trailing edge flap located near the tip of each of the rotorcraft's rotor blades. The flap may be actuated in any conventional way, and is scheduled to be actuated to a deflected position during rotation of the rotor blade through predetermined regions of the rotor azimuth, and is further scheduled to be actuated to a retracted position through the remaining regions of the rotor azimuth. Through the careful azimuth-dependent deployment and retraction of the flap over the rotor disk, blade tip vortices which are the primary source for BVI noise are (a) made weaker and (b) pushed farther away from the rotor disk (that is, larger blade-vortex separation distances are achieved).

  6. Blade vortex interaction noise reduction techniques for a rotorcraft

    NASA Technical Reports Server (NTRS)

    Charles, Bruce D. (Inventor); Hassan, Ahmed A. (Inventor); Tadghighi, Hormoz (Inventor); JanakiRam, Ram D. (Inventor); Sankar, Lakshmi N. (Inventor)

    1998-01-01

    An active control device for reducing blade-vortex interactions (BVI) noise generated by a rotorcraft, such as a helicopter, comprises a trailing edge flap located near the tip of each of the rotorcraft's rotor blades. The flap may be actuated in any conventional way, and is scheduled to be actuated to a deflected position during rotation of the rotor blade through predetermined regions of the rotor azimuth, and is further scheduled to be actuated to a retracted position through the remaining regions of the rotor azimuth. Through the careful azimuth-dependent deployment and retraction of the flap over the rotor disk, blade tip vortices which are the primary source for BVI noise are (a) made weaker and (b) pushed farther away from the rotor disk (that is, larger blade-vortex separation distances are achieved).

  7. Power Mapping and Noise Reduction for Financial Correlations

    NASA Astrophysics Data System (ADS)

    Andersson, P.-J.; Oeberg, A.; Guhr, T.

    2005-09-01

    The spectral properties of financial correlation matrices can show features known from completely random matrices. A major reason is noise originating from the finite lengths of the financial time series used to compute the correlation matrix elements. In recent years, various methods have been proposed to reduce this noise, i.e. to clean the correlation matrices. This is of direct practical relevance for risk management in portfolio optimization. In this contribution, we discuss in detail the power mapping, a new shrinkage method. We show that the relevant parameter is, to a certain extent, self-determined. Due to the ``chirality'' and the normalization of the correlation matrix, the optimal shrinkage parameter is fixed. We apply the power mapping and the well-known filtering method to market data and compare them by optimizing stock portfolios. We address the rôle of constraints by excluding short selling in the optimization.

  8. Reduction of Flap Side Edge Noise - the Blowing Flap

    NASA Technical Reports Server (NTRS)

    Hutcheson, Florence V.; Brooks, THomas F.

    2005-01-01

    A technique to reduce the noise radiating from a wing-flap side edge is being developed. As an airplane wing with an extended flap is exposed to a subsonic airflow, air is blown outward through thin rectangular chord-wise slots at various locations along the side edges and side surface of the flap to weaken and push away the vortices that originate in that region of the flap and are responsible for important noise emissions. Air is blown through the slots at up to twice the local flow velocity. The blowing is done using one or multiple slots, where a slot is located along the top, bottom or side surface of the flap along the side edge, or also along the intersection of the bottom (or top) and side surfaces.

  9. Noise reduction in tunnels by hard rough surfaces.

    PubMed

    Law, Ming Kan; Li, Kai Ming; Leung, Chun Wah

    2008-08-01

    This paper examines the feasibility of using two-dimensional hard rough surfaces to reduce noise levels in traffic tunnels with perfectly reflecting boundaries. First, the Twersky boss model is used to estimate the acoustic impedance of a hard rough surface. Second, an image source model is then used to compute the propagation of sound in a long rectangular enclosure with finite impedance. The total sound fields are calculated by summing the contributions from all image sources coherently. Two model tunnels are built to validate the proposed model experimentally. Finally, a case study for a realistic geometrical configuration is presented to explore the use of hard rough surfaces for reducing traffic noise in a tunnel which is constructed with hard boundaries.

  10. Noise Reduction Design of the Volute for a Centrifugal Compressor

    NASA Astrophysics Data System (ADS)

    Song, Zhen; Wen, Huabing; Hong, Liangxing; Jin, Yudong

    2017-08-01

    In order to effectively control the aerodynamic noise of a compressor, this paper takes into consideration a marine exhaust turbocharger compressor as a research object. According to the different design concept of volute section, tongue and exit cone, six different volute models were established. The finite volume method is used to calculate the flow field, whiles the finite element method is used for the acoustic calculation. Comparison and analysis of different structure designs from three aspects: noise level, isentropic efficiency and Static pressure recovery coefficient. The results showed that under the concept of volute section model 1 yielded the best result, under the concept of tongue analysis model 3 yielded the best result and finally under exit cone analysis model 6 yielded the best results.

  11. Landing Gear Door Liners for Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Jones, Michael G. (Inventor); Howerton, Brian M. (Inventor); Van De Ven, Thomas (Inventor)

    2014-01-01

    A landing gear door for retractable landing gear of aircraft includes an acoustic liner. The acoustic liner includes one or more internal cavities or chambers having one or more openings that inhibit the generation of sound at the surface and/or absorb sound generated during operation of the aircraft. The landing gear door may include a plurality of internal chambers having different geometries to thereby absorb broadband noise.

  12. High-frequency jet nozzle actuators for noise reduction

    NASA Astrophysics Data System (ADS)

    Davis, Christopher L.; Calkins, Frederick T.; Butler, George W.

    2003-08-01

    Rules governing airport noise levels are becoming more restrictive and will soon affect the operation of commercial air traffic. Sound produced by jet engine exhaust, particularly during takeoff, is a major contributor to the community noise problem. The noise spectrum is broadband in character and is produced by turbulent mixing of primary, secondary, and ambient streams of the jet engine exhaust. As a potential approach to controlling the noise levels, piezoelectric bimorph actuators have been tailored to enhance the mixing of a single jet with its quiescent environment. The actuators are located at the edge of the nozzle and protrude into the exhaust stream. Several actuator configurations were considered to target two excitation frequencies, 250 Hz and 900 Hz, closely coupled to the naturally unstable frequencies of the mixing process. The piezoelectric actuators were constructed of 10 mil thick d31 poled wafer PZT-5A material bonded to either 10 or 20 mil thick spring steel substrates. Linear analytical beam models and NASTRAN finite element models were used to predict and assess the dynamic performance of the actuators. Experimental mechanical and electrical performance measurements were used to validate the models. A 3 inch diameter nozzle was fitted with actuators and tested in the Boeing Quiet Air Facility with the jet velocity varied from 50 to 1000 ft/s. Performance was evaluated using near-field and far-field acoustic data, flow visualization, and actuator health data. The overall sound pressure level produced from the 3 inch diameter jet illustrates the effect of both static and active actuators.

  13. Algorithm for image registration and clutter and jitter noise reduction

    SciTech Connect

    Brower, K.L.

    1997-02-01

    This paper presents an analytical, computational method whereby two-dimensional images of an optical source represented in terms of a set of detector array signals can be registered with respect to a reference set of detector array signals. The detector image is recovered from the detector array signals and represented over a local region by a fourth order, two-dimensional taylor series. This local detector image can then be registered by a general linear transformation with respect to a reference detector image. The detector signal in the reference frame is reconstructed by integrating this detector image over the respective reference pixel. For cases in which the general linear transformation is uncertain by up to plus-or-minus two pixels, the general linear transformation can be determined by least squares fitting the detector image to the reference detector image. This registration process reduces clutter and jitter noise to a level comparable to the electronic noise level of the detector system. Test results with and without electronic noise using an analytical test function are presented.

  14. JT8D-100 turbofan engine, phase 1. [noise reduction

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The JT8D turbofan engine, widely used in short and medium range transport aircraft, contributes substantially to airport community noise. The jet noise is predominant in the JT8D engine and may be reduced in a modified engine, without loss of thrust, by increasing the airflow to reduce jet velocity. A configuration study evaluated the effects of fan airflow, fan pressure ratio, and bypass ratio on noise, thrust, and fuel comsumption. The cycle selected for the modified engine was based upon an increased diameter, single-stage fan and two additional core engine compressor stages, which replace the existing two-stage fan. Modifications were also made to the low pressure turbine to provide the increased torque required by the larger diameter fan. The resultant JT8D-100 engine models have the following characteristics at take-off thrust, compared to the current JT8D engine: Airflow and bypass ratio are increased, and fan pressure ratio and engine speed are reduced. The resultant engine is also longer, larger in diameter, and heavier than the JT8D base model, but these latter changes are compensated by the increased thrust and decreased fuel comsumption of the modified engine, thus providing the capability for maintaining the performance of the current JT8D-powered aircraft.

  15. Patient radiation dose reduction using an X-ray imaging noise reduction technology for cardiac angiography and intervention.

    PubMed

    Nakamura, Shigeru; Kobayashi, Tomoko; Funatsu, Atsushi; Okada, Tadahisa; Mauti, Maria; Waizumi, Yuki; Yamada, Shinichi

    2016-05-01

    Coronary angiography and intervention can expose patients to high radiation dose. This retrospective study quantifies the patient dose reduction due to the introduction of a novel X-ray imaging noise reduction technology using advanced real-time image noise reduction algorithms and optimized acquisition chain for fluoroscopy and exposure in interventional cardiology. Patient, procedure and radiation dose data were retrospectively collected in the period August 2012-August 2013 for 883 patients treated with the image noise reduction technology (referred as "new system"). The same data were collected for 1083 patients in the period April 2011-July 2012 with a system using state-of-the-art image processing and reference acquisition chain (referred as "reference system"). Procedures were divided into diagnostic (CAG) and intervention (PCI). Acquisition parameters such as fluoroscopy time, volume of contrast medium, number of exposure images and number of stored fluoroscopy images were collected to classify procedure complexity. The procedural dose reduction was investigated separately for three main cardiologists. The new system provides significant dose reduction compared to the reference system. Median DAP values decreased for all procedures (p < 0.0001) from 172.7 to 59.4 Gy cm(2), for CAG from 155.1 to 52.0 Gy cm(2) and for PCI from 229.0 to 85.8 Gy cm(2) with reduction quantified at 66, 66 and 63 %, respectively. Based on median values, the dose reduction for all procedures was 68, 60 and 67 % for cardiologists 1, 2 and 3, respectively. The X-ray imaging technology combining advanced real-time image noise reduction algorithms and anatomy-specific optimized fluoroscopy and cine acquisition chain provides 66 % patient dose reduction in interventional cardiology.

  16. ASSESSING THE ROLE OF EFFORT REDUCTION IN THE REINFORCING EFFICACY OF TIMEOUT FROM AVOIDANCE

    PubMed Central

    Galuska, Chad M.; Mikorski, Jeff; Perone, Michael

    2012-01-01

    Rats responded on concurrent schedules of shock-postponement or deletion (avoidance) and timeout from avoidance. In Experiment 1, 3 rats' responses on one lever postponed shocks for 20 s and responses on a second lever produced a 1-min timeout according to a variable-interval 45-s schedule. Across conditions, a warning signal (white noise) was presented 19.5 s, 16 s, 12 s, 8 s, or 4 s before an impending shock. Raising the duration of the warning signal increased both avoidance and timeout response rates. Timeout responding, although positively correlated with avoidance responding, was not correlated with the prevailing shock rate. In Experiment 2, 3 rats' responses on one lever deleted scheduled shocks according to a variable-cycle 30-s schedule and responses on a second lever produced a 2-min timeout as described above. After this baseline condition, the avoidance lever was removed and noncontingent shocks were delivered at intervals yoked to the receipt of shocks in the baseline sessions. Timeout responding decreased when the avoidance lever was removed, even though the shock-frequency reduction afforded by the timeout remained constant. These results suggest that a key factor in the reinforcing efficacy of timeout is suspension of the requirement to work to avoid shock, rather than the reduction in shock frequency associated with timeout. PMID:23144504

  17. Reduction of CMOS Image Sensor Read Noise to Enable Photon Counting

    PubMed Central

    Guidash, Michael; Ma, Jiaju; Vogelsang, Thomas; Endsley, Jay

    2016-01-01

    Recent activity in photon counting CMOS image sensors (CIS) has been directed to reduction of read noise. Many approaches and methods have been reported. This work is focused on providing sub 1 e− read noise by design and operation of the binary and small signal readout of photon counting CIS. Compensation of transfer gate feed-through was used to provide substantially reduced CDS time and source follower (SF) bandwidth. SF read noise was reduced by a factor of 3 with this method. This method can be applied broadly to CIS devices to reduce the read noise for small signals to enable use as a photon counting sensor. PMID:27070625

  18. Photorefractive two-beam coupling optimal thresholding filter for additive signal-dependent noise reduction

    NASA Astrophysics Data System (ADS)

    Fu, Jack; Khoury, Jehad; Cronin-Golomb, Mark; Woods, Charles L.

    1995-01-01

    Computer simulations of photorefractive thresholding filters for the reduction of artifact or dust noise demonstrate an increase in signal-to-noise ratio (SNR) of 70% to 95%, respectively, of that provided by the Wiener filter for inputs with a SNR of approximately 3. These simple, nearly optimal filters use a spectral thresholding profile that is proportional to the envelope of the noise spectrum. Alternative nonlinear filters with either 1/ nu or constant thresholding profiles increase the SNR almost as much as the noise-envelope thresholding filter.

  19. Reduction of CMOS Image Sensor Read Noise to Enable Photon Counting.

    PubMed

    Guidash, Michael; Ma, Jiaju; Vogelsang, Thomas; Endsley, Jay

    2016-04-09

    Recent activity in photon counting CMOS image sensors (CIS) has been directed to reduction of read noise. Many approaches and methods have been reported. This work is focused on providing sub 1 e(-) read noise by design and operation of the binary and small signal readout of photon counting CIS. Compensation of transfer gate feed-through was used to provide substantially reduced CDS time and source follower (SF) bandwidth. SF read noise was reduced by a factor of 3 with this method. This method can be applied broadly to CIS devices to reduce the read noise for small signals to enable use as a photon counting sensor.

  20. [Noise in intensive care units. Noise reduction by modification of gas humidification].

    PubMed

    Berg, P W; Stuttmann, R; Doehn, M

    1997-10-01

    Today, noise pollution is an evident and ubiquitous problem even in intensive care units. Noise can disturb the physiological and psychological balance in patients and staff. Especially intubated patients and those breathing spontaneously through a T-piece are exposed to the noise emitted by the nebuliser used to humidity the respiratory gas. This may make patients feel uncomfortable. To reduce noise pollution in the ICU a modified T-piece has been developed and investigated. In order to heat and humidity the respiratory gas a Conchaterm III unit (Kendall company) and a thermo flow cylinder (De Vilbiss company) is necessary. While respiratory gas is flowing, water is sucked out of the heated thermoflow cylinder and nebulised according to the Venturi-Bernoulli principle. To adjust the oxygen concentration of the respiratory gas a plastic ring must be turned to either close (98% oxygen) or open a valve allowing room air to mix (40% oxygen). Noise pollution of the unit varies with admixture of room air. With a new device--a special oxygen-air mixing chamber--the oxygen concentration of the respiratory gas can be adjusted outside the thermoflow cylinder, hardly producing any noise pollution. Therefore the principle of nebulisation could be changed to humidification. A thermoflow cylinder without the nebulisation unit allows the respiratory gas to flow through the thermoflow cylinder over heated and evaporating water, hardly causing any noise pollution. In both types of T-pieces the temperature of the respiratory gas is controlled and corrected by the Conchaterm unit. As the result of these modifications, noise pollution has been reduced from 70 dB(A) to 55 dB(A). In the modified T-piece, the quality of humidification has been evaluated with a fresh gas flow of 22 l/min and at a gas temperature of 37 degrees C, not only collecting condensed water but also lost water. The modified T-piece allows a physiological humidification of the respiratory gas. The modified T

  1. Study of noise reduction characteristics of multilayered panels and dual pane windows with Helmholtz resonators

    NASA Technical Reports Server (NTRS)

    Navaneethan, R.

    1981-01-01

    The experimental noise attenuation characteristics of flat, general aviation type, multilayered panels are discussed. Experimental results of stiffened panels, damping tape, honeycomb materials and sound absorption materials are presented. Single degree of freedom theoretical models were developed for sandwich type panels with both shear resistant and non-shear resistant core material. The concept of Helmholtz resonators used in conjunction with dual panel windows in increasing the noise reduction around a small range of frequency was tested. It is concluded that the stiffening of the panels either by stiffeners or by sandwich construction increases the low frequency noise reduction.

  2. Quantitative evaluation of noise reduction strategies in dual-energy imaging.

    PubMed

    Warp, Richard J; Dobbins, James T

    2003-02-01

    In this paper we describe a quantitative evaluation of the performance of three dual-energy noise reduction algorithms: Kalender's correlated noise reduction (KCNR), noise clipping (NOC), and edge-predictive adaptive smoothing (EPAS). These algorithms were compared to a simple smoothing filter approach, using the variance and noise power spectrum measurements of the residual noise in dual-energy images acquired with an a-Si TFT flat-panel x-ray detector. An estimate of the true noise was made through a new method with subpixel accuracy by subtracting an individual image from an ensemble average image. The results indicate that in the lung regions of the tissue image, all three algorithms reduced the noise by similar percentages at high spatial frequencies (KCNR=88%, NOC=88%, EPAS=84%, NOC/KCNR=88%) and somewhat less at low spatial frequencies (KCNR=45%, NOC=54%, EPAS=52%, NOC/KCNR=55%). At low frequencies, the presence of edge artifacts from KCNR made the performance worse, thus NOC or NOC combined with KCNR performed best. At high frequencies, KCNR performed best in the bone image, yet NOC performed best in the tissue image. Noise reduction strategies in dual-energy imaging can be effective and should focus on blending various algorithms depending on anatomical locations.

  3. Research on Noise Reduction of Reed Valves of a Hermetic Refrigerator Compressor

    NASA Astrophysics Data System (ADS)

    He, Zhilong; Chen, Qian; Li, Dantong; Wang, Ju; Xia, Pu; Wang, Tao

    2017-08-01

    The noise level of the refrigerator compressor has received more and more attention in recent years. As the key component of a compressor, reed valve is its main noise source. In this paper, a new noise reduction technology of coating on reed valve surface is proposed and verified by experiments. Firstly, the reed valves were coated, and their surface characteristics were checked. Then, the refrigerator compressor p-V diagram test was carried out to investigate the influence of doped diamond-like carbon (DLC) coating on power consumption. Finally, the noise test rig for the refrigerator compressor was set up. Based on the standard test method, noise spectrum was measured in a semi-anechoic room under standard working condition. Research results showed that the compressor noise was significantly reduced by 1.8dB (A) after coating. Moreover, the effect of aerodynamic noise reduction at suction side is better than that at discharge side. However, the influence of the film thickness on noise reduction value is little. The COP was reduced by 0.6% as compared to the compressor with uncoated reed valves.

  4. Reduction of Helicopter Blade-Vortex Interaction Noise by Active Rotor Control Technology

    NASA Technical Reports Server (NTRS)

    Yu, Yung H.; Gmelin, Bernd; Splettstoesser, Wolf; Brooks, Thomas F.; Philippe, Jean J.; Prieur, Jean

    1997-01-01

    Helicopter blade-vortex interaction noise is one of the most severe noise sources and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor blade-vortex interaction noise and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor blade vortex interaction noise reduction, including higher harmonic pitch control, individual blade control, and on-blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of noise reduction mechanism and controlling aerodynamic or structural parameters of a blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations, Published by Elsevier Science Ltd.

  5. Lead-Lag Control for Helicopter Vibration and Noise Reduction

    NASA Technical Reports Server (NTRS)

    Gandhi, Farhan

    1995-01-01

    , meant to achieve lag motion amplitudes up to 45 degrees. In order to reduce the required actuation force, the blade hinges were moved to 40% of the blade radius to increase the rotating lag frequency to approximately 1/rev. The blade hinges were redesigned to produce a flap-lag coupling so the large flapwise aerodynamic loads could be exploited to actuate the blades in the lag direction. A wind tunnel test of this rotor concept revealed actuation and blade motion scheduling problems. The project was eventually discontinued due to these problems and high blade stresses. Around the same time, at Boelkow in Germany, a similar lead-lag rotor program was conducted under the leadership of Hans Derschmidt. Here, too, the blade hinges were moved outboard to 34% radius to reduce the actuation loads. The main difference between this and the United Aircraft program was the use of a mechanical actuation scheme with maximum lead-lag motions of 400. This program was also discontinued for unclear reasons. The present study is directed toward conducting a comprehensive analytical examination to evaluate the effectiveness of controlled lead-lag motions in reducing vibratory hub loads and increasing maximum flight speed. Since both previous studies on this subject were purely experimental, only a limited data set and physical understanding of the problem was obtained. With the currently available analytical models and computational resources, the present effort is geared toward developing an in-depth physical understanding of the precise underlying mechanisms by which vibration reduction may be achieved. Additionally, in recognition of the fact that large amplitude lead-lag motions would - (i) be difficult to implement, and (ii) produce very large blade stresses; the present study examines the potential of only moderate-to-small lead-lag motions for reduction of vibratory hub loads. Using such an approach, the emphasis is not on eliminating the periodic variations in tangential velocity

  6. In situ calibration of atmospheric-infrasound sensors including the effects of wind-noise-reduction pipe systems.

    PubMed

    Gabrielson, Thomas B

    2011-09-01

    A worldwide network of more than 40 infrasound monitoring stations has been established as part of the effort to ensure compliance with the Comprehensive Nuclear Test Ban Treaty. Each station has four to eight individual infrasound elements in a kilometer-scale array for detection and bearing determination of acoustic events. The frequency range of interest covers a three-decade range-roughly from 0.01 to 10 Hz. A typical infrasound array element consists of a receiving transducer connected to a multiple-inlet pipe network to average spatially over the short-wavelength turbulence-associated "wind noise." Although the frequency response of the transducer itself may be known, the wind-noise reduction system modifies that response. In order to understand the system's impact on detection and identification of acoustical events, the overall frequency response must be determined. This paper describes a technique for measuring the absolute magnitude and phase of the frequency response of an infrasound element including the wind-noise-reduction piping by comparison calibration using ambient noise and a reference-microphone system. Measured coherence between the reference and the infrasound element and the consistency between the magnitude and the phase provide quality checks on the process.

  7. Speech intelligibility and protective effectiveness of selected active noise reduction and conventional communications headsets.

    PubMed

    Gower, D W; Casali, J G

    1994-06-01

    An experiment was conducted to compare both speech intelligibility and noise attenuation of a conventional passive headset (David Clark H10-76) and an electronic Active Noise Reduction (ANR) headset (Bose Aviation) operated with and without its ANR feature. Modified Rhyme Tests were conducted in pink and tank noise, and with and without bilateral phase reversal between earphones. The Bose ANR unit required a significantly higher speech-to-noise (S/N) ratio in both noise environments than the two passive headset systems to maintain equal intelligibility, in part because of its stronger noise reduction and higher required signal level. Articulation Index calculations corroborated the empirical result that the David Clark afforded comparable intelligibility to the Bose ANR device. Bilateral phase reversal proved to be of no benefit, and pink noise proved to be the harsher environment for speech intelligibility. On a speech intelligibility basis alone, the results do not justify the additional cost of the ANR headset; however, when severe noise exposure is at issue, a properly functioning ANR unit may afford more protection than a similar passive headset without electronics, especially in low-frequency noise spectra.

  8. Blade-Mounted Flap Control for BVI Noise Reduction Proof-of-Concept Test

    NASA Technical Reports Server (NTRS)

    Dawson, Seth; Hassan, Ahmed; Straub, Friedrich; Tadghighi, Hormoz

    1995-01-01

    This report describes a wind tunnel test of the McDonnell Douglas Helicopter Systems (MDHS) Active Flap Model Rotor at the NASA Langley 14- by 22-Foot Subsonic Tunnel. The test demonstrated that BVI noise reductions and vibration reductions were possible with the use of an active flap. Aerodynamic results supported the acoustic data trends, showing a reduction in the strength of the tip vortex with the deflection of the flap. Acoustic results showed that the flap deployment, depending on the peak deflection angle and azimuthal shift in its deployment schedule, can produce BVI noise reductions as much as 6 dB on the advancing and retreating sides. The noise reduction was accompanied by an increase in low frequency harmonic noise and high frequency broadband noise. A brief assessment of the effect of the flap on vibration showed that significant reductions were possible. The greatest vibration reductions (as much as 76%) were found in the four per rev pitching moment at the hub. Performance improvement cam results were inconclusive, as the improvements were predicted to be smaller than the resolution of the rotor balance.

  9. Prediction and reduction of aircraft noise in outdoor environments

    NASA Astrophysics Data System (ADS)

    Tong, Bao N.

    This dissertation investigates the noise due to an en-route aircraft cruising at high altitudes. It offers an improved understanding into the combined effects of atmospheric propagation, ground reflection, and source motion on the impact of en-route aircraft noise. A numerical model has been developed to compute pressure time-histories due to a uniformly moving source above a flat ground surface in the presence of a horizontally stratified atmosphere. For a moving source at high elevations, contributions from a direct and specularly reflected wave are sufficient in predicting the sound field close to the ground. In the absence of wind effects, the predicted sound field from a single overhead flight trajectory can be used to interpolate pressure time histories at all other receiver locations via a simplified ray model for the incoherent sound field. This approach provides an efficient method for generating pressure time histories in a three-dimensional space for noise impact studies. A variety of different noise propagation methods are adapted to a uniformly moving source to evaluate the accuracy and efficiency of their predictions. The techniques include: analytical methods, the Fast Field Program (FFP), and asymptotic analysis methods (e.g., ray tracing and more advanced formulations). Source motion effects are introduced via either a retarded time analysis or a Lorentz transform approach depending on the complexity of the problem. The noise spectrum from a single emission frequency, moving source has broadband characteristics. This is a consequence of the Doppler shift which continuously modifies the perceived frequency of the source as it moves relative to a stationary observer on the ground. Thus, the instantaneous wavefronts must be considered in both the frequency dependent ground impedance model and the atmospheric absorption model. It can be shown that the Doppler factor is invariant along each ray path. This gives rise to a path dependent atmospheric

  10. Civil helicopter noise assessment study Boeing-Vertol model 347. [recommendations for reduction of helicopter noise levels

    NASA Technical Reports Server (NTRS)

    Hinterkeuser, E. G.; Sternfeld, H., Jr.

    1974-01-01

    A study was conducted to forecast the noise restrictions which may be imposed on civil transport helicopters in the 1975-1985 time period. Certification and community acceptance criteria were predicted. A 50 passenger tandem rotor helicopter based on the Boeing-Vertol Model 347 was studied to determine the noise reductions required, and the means of achieving them. Some of the important study recommendations are: (1) certification limits should be equivalent to 95 EPNdb at data points located at 500 feet to each side of the touchdown/takeoff point, and 1000 feet from this point directly under the approach and departure flight path. (2) community acceptance should be measured as Equivalent Noise Level (Leq), based on dBA, with separate limits for day and night operations, and (3) in order to comply with the above guidelines, the Model 347 helicopter will require studies and tests leading to several modifications.

  11. A simple noniterative principal component technique for rapid noise reduction in parallel MR images.

    PubMed

    Patel, Anand S; Duan, Qi; Robson, Philip M; McKenzie, Charles A; Sodickson, Daniel K

    2012-01-01

    The utilization of parallel imaging permits increased MR acquisition speed and efficiency; however, parallel MRI usually leads to a deterioration in the signal-to-noise ratio when compared with otherwise equivalent unaccelerated acquisitions. At high accelerations, the parallel image reconstruction matrix tends to become dominated by one principal component. This has been utilized to enable substantial reductions in g-factor-related noise. A previously published technique achieved noise reductions via a computationally intensive search for multiples of the dominant singular vector which, when subtracted from the image, minimized joint entropy between the accelerated image and a reference image. We describe a simple algorithm that can accomplish similar results without a time-consuming search. Significant reductions in g-factor-related noise were achieved using this new algorithm with in vivo acquisitions at 1.5 T with an eight-element array. Copyright © 2011 John Wiley & Sons, Ltd.

  12. Supersonic Transport Noise Reduction Technology Program - Phase 2, Volume 2

    DTIC Science & Technology

    1975-09-01

    10 m •<r V >* tf IO in lO m C^l M M CO n co CO CO co co CO co co CO CO CO H i) u 4*9 Efl 0 0 ■H it >. fa M o « o • O • • • « in • o • O...Airplane Company, July - September 1974. Rakl, R., "Two Causality Correlation Techniques Applied to Jet Noise," Ph.D. Thesis , University of British

  13. Studies of blade-vortex interaction noise reduction by rotor blade modification

    NASA Astrophysics Data System (ADS)

    Brooks, Thomas F.

    Blade-vortex interaction (BVI) noise is one of the most objectionable types of helicopter noise. This impulsive blade-slap noise can be particularly intense during low-speed landing approach and maneuvers. Over the years, a number of flight and model rotor tests have examined blade tip modification and other blade design changes to reduce this noise. Many times these tests have produced conflicting results. In the present paper, a number of these studies are reviewed in light of the current understanding of the BVI noise problem. Results from one study in particular are used to help establish the noise reduction potential and to shed light on the role of blade design. Current blade studies and some new concepts under development are also described.

  14. Comparison of noise reduction of earplugs between fit test and coal mine work and observed variability of real-time noise reduction in coal mine work.

    PubMed

    Wu, Mingyu; Guffey, Steve E; Takacs, Brandon C

    2016-11-22

    The coal mining industry relies heavily on a hearing protector (HP) for noise protection. Researchers suggested that individual HP fit tests be conducted to estimate the noise attenuation. This study examined whether individual fit tests accurately predicted workers' ear plug noise protection while working and whether the real-time noise reduction (NR) remained constant in mining work while an ear plug was worn. A total of 11 subjects from 3 coal mines each was fit tested using the microphone-in-real-ear (MIRE) technique on their E-A-Rtrademark earplugs in a typical mine office. The same fit tested miners each wore the same type of earplugs in his usual manner doing his normal work. The minute-by-minute real-time NRwork values were determined continuously during full shifts of work. Results showed there was a modest prediction relationship (R2 = 0.53) between NRfit and NRwork. NRwork values of each miner's earplug fluctuated over 20 dBA while the earplug was worn. However, each was still able to achieve an average NRwork of more than 10 dBA, indicating the earplug was somewhat effective in reducing noise, if worn. Refitting was an important cause of the low NRwork values. Low-frequency noise sources might be also important causes.

  15. Progress Towards Fuselage Drag Reduction via Active Flow Control: A Combined CFD and Experimental Effort

    NASA Technical Reports Server (NTRS)

    Schaeffler, Norman W.; Allan, Brian G.; Lienard, Caroline; LePape, Arnaud

    2010-01-01

    A combined computational and experimental effort has been undertaken to study fuselage drag reduction on a generic, non-proprietary rotorcraft fuselage by the application of active ow control. Fuselage drag reduction is an area of research interest to both the United States and France and this area is being worked collaboratively as a task under the United States/France Memorandum of Agreement on Helicopter Aeromechanics. In the first half of this task, emphasis is placed on the US generic fuselage, the ROBIN-mod7, with the experimental work being conducted on the US side and complementary US and French CFD analysis of the baseline and controlled cases. Fuselage simulations were made using Reynolds-averaged Navier-Stokes ow solvers and with multiple turbulence models. Comparisons were made to experimental data for numerical simulations of the isolated fuselage and for the fuselage as installed in the tunnel, which includes modeling of the tunnel contraction, walls, and support fairing. The numerical simulations show that comparisons to the experimental data are in good agreement when the tunnel and model support are included. The isolated fuselage simulations compare well to each other, however, there is a positive shift in the centerline pressure when compared to the experiment. The computed flow separation locations on the rear ramp region had only slight differences with and without the tunnel walls and model support. For the simulations, the flow control slots were placed at several locations around the flow separation lines as a series of eight slots that formed a nearly continuous U-shape. Results from the numerical simulations resulted in an estimated 35% fuselage drag reduction from a steady blowing flow control configuration and a 26% drag reduction for unsteady zero-net-mass flow control configuration. Simulations with steady blowing show a delayed flow separation at the rear ramp of the fuselage that increases the surface pressure acting on the ramp

  16. Wavelet-based pavement image compression and noise reduction

    NASA Astrophysics Data System (ADS)

    Zhou, Jian; Huang, Peisen S.; Chiang, Fu-Pen

    2005-08-01

    For any automated distress inspection system, typically a huge number of pavement images are collected. Use of an appropriate image compression algorithm can save disk space, reduce the saving time, increase the inspection distance, and increase the processing speed. In this research, a modified EZW (Embedded Zero-tree Wavelet) coding method, which is an improved version of the widely used EZW coding method, is proposed. This method, unlike the two-pass approach used in the original EZW method, uses only one pass to encode both the coordinates and magnitudes of wavelet coefficients. An adaptive arithmetic encoding method is also implemented to encode four symbols assigned by the modified EZW into binary bits. By applying a thresholding technique to terminate the coding process, the modified EZW coding method can compress the image and reduce noise simultaneously. The new method is much simpler and faster. Experimental results also show that the compression ratio was increased one and one-half times compared to the EZW coding method. The compressed and de-noised data can be used to reconstruct wavelet coefficients for off-line pavement image processing such as distress classification and quantification.

  17. Nature-Inspired Airfoils for Environmental Noise Reduction

    NASA Astrophysics Data System (ADS)

    Han, Suyeong; Kyung, Richard

    2013-11-01

    Recently, study on the insects' flapping flight became one of the challenging research subjects in the field of environmental engineering and aeronautics because of its potential applicability to intelligent micro-robots capable of autonomous flight and the next generation aerial-vehicles. In order to uncover its curious unsteady characteristics, many researchers have conducted experimental and computational studies on the unsteady aerodynamics of insects' flapping flight. In the present work, the unsteady flow physics around insect wings are conducted by utilizing numerical and computational simulation. The e-AIRS [6] (e-Science Aerospace Integrated Research System) gives a balanced service between computational and experimental aerodynamics, along with integrated research process of these two research activities. This paper presents the wing motions and their aerodynamics with a two dimensional approach to reduce environmental noise during the airflight. Also this paper shows an optimal phase angle, where the thrust is maximized at the position of minimized drag, which occurs when noise is minimized. Aside from the two-dimensional approach, stroke angles and phase angles of the airfoils are set as parameters, to determine which motion yields the best aerodynamic characteristics.

  18. Noise reduction of video imagery through simple averaging

    NASA Astrophysics Data System (ADS)

    Vorder Bruegge, Richard W.

    1999-02-01

    Examiners in the Special Photographic Unit of the Federal Bureau of Investigation Laboratory Division conduct examinations of questioned photographic evidence of all types, including surveillance imagery recorded on film and video tape. A primary type of examination includes side-by- side comparisons, in which unknown objects or people depicted in the questioned images are compared with known objects recovered from suspects or with photographs of suspects themselves. Most imagery received in the SPU for such comparisons originate from time-lapse video or film systems. In such circumstances, the delay between sequential images is so great that standard image summing and/or averaging techniques are useless as a means of improving image detail in questioned subjects or objects without also resorting to processing-intensive pattern reconstruction algorithms. Occasionally, however, the receipt of real-time video imagery will include a questioned object at rest. In such cases, it is possible to use relatively simple image averaging techniques as a means of reducing transient noise in the images, without further compromising the already-poor resolution inherent in most video surveillance images. This paper presents an example of one such case in which multiple images were averaged to reduce the transient noise to a sufficient degree to permit the positive identification of a vehicle based upon the presence of scrape marks and dents on the side of the vehicle.

  19. Noise reduction in elastograms using temporal stretching with multicompression averaging.

    PubMed

    Varghese, T; Ophir, J; Céspedes, I

    1996-01-01

    Elastography uses estimates of the time delay (obtained by cross-correlation) to compute strain estimates in tissue due to quasistatic compression. Because the time delay estimates do not generally occur at the sampling intervals, the location of the cross-correlation peak does not give an accurate estimate of the time delay. Sampling errors in the time-delay estimate are reduced using signal interpolation techniques to obtain subsample time-delay estimates. Distortions of the echo signals due to tissue compression introduce correlation artifacts in the elastogram. These artifacts are reduced by a combination of small compressions and temporal stretching of the postcompression signal. Random noise effects in the resulting elastograms are reduced by averaging several elastograms, obtained from successive small compressions (assuming that the errors are uncorrelated). Multicompression averaging with temporal stretching is shown to increase the signal-to-noise ratio in the elastogram by an order of magnitude, without sacrificing sensitivity, resolution or dynamic range. The strain filter concept is extended in this article to theoretically characterize the performance of multicompression averaging with temporal stretching.

  20. Research and constructive solutions on the reduction of slosh noise

    NASA Astrophysics Data System (ADS)

    Manta (Balas, M.; Balas, R.; Doicin, C. V.

    2016-11-01

    The paper presents a product design making of, over a “delicate issue” in automotive industry as slosh noise phenomena. Even though the current market tendency shows great achievements over this occurrence, in this study, the main idea is to design concepts of slosh noise baffles adapted for serial life existing fuel tanks in the automotive industry. Moreover, starting with internal and external research, going further through reversed engineering and applying own baffle technical solutions from conceptual sketches to 3D design, the paper shows the technical solutions identified as an alternative to a new development of fuel tank. Based on personal and academic experience there were identified several problematics and the possible answers based on functional analysis, in order to avoid blocking points. The idea of developing baffles adapted to already existent fuel tanks leaded to equivalent solutions analyzed from functional point of view. Once this stage is finished, a methodology will be used so as to choose the optimum solution so as to get the functional design.

  1. Comparison of speech intelligibility in cockpit noise using SPH-4 flight helmet with and without active noise reduction

    NASA Technical Reports Server (NTRS)

    Chan, Jeffrey W.; Simpson, Carol A.

    1990-01-01

    Active Noise Reduction (ANR) is a new technology which can reduce the level of aircraft cockpit noise that reaches the pilot's ear while simultaneously improving the signal to noise ratio for voice communications and other information bearing sound signals in the cockpit. A miniature, ear-cup mounted ANR system was tested to determine whether speech intelligibility is better for helicopter pilots using ANR compared to a control condition of ANR turned off. Two signal to noise ratios (S/N), representative of actual cockpit conditions, were used for the ratio of the speech to cockpit noise sound pressure levels. Speech intelligibility was significantly better with ANR compared to no ANR for both S/N conditions. Variability of speech intelligibility among pilots was also significantly less with ANR. When the stock helmet was used with ANR turned off, the average PB Word speech intelligibility score was below the Normally Acceptable level. In comparison, it was above that level with ANR on in both S/N levels.

  2. Helicopter Noise Reduction Design Trade-Off Study

    DTIC Science & Technology

    1977-01-01

    Nomte oni Address 10.h Wark Untt No. ( KTRAiS Kaman Aerospace Corporation Bloomfield, Connecticut 06002 trac . . rtM.-b DOT-FAT 6WA-3791 _i_,, _ _ _,i...performed by Karan Aerospace Corporation , Bloomfield, Connecticut, with subcontracting assistance provided by Bolt Beranek and Newman, Inc., Cambridge...Massachusetts. Kaman Aerospace Corporation personnel participating in this effort included Mr. M. A. Bowes, Mr. N. Giansante, Mr. 14. Smyth, Mr. A. Plaks

  3. Noise reduction in muon tomography for detecting high density objects

    NASA Astrophysics Data System (ADS)

    Benettoni, M.; Bettella, G.; Bonomi, G.; Calvagno, G.; Calvini, P.; Checchia, P.; Cortelazzo, G.; Cossutta, L.; Donzella, A.; Furlan, M.; Gonella, F.; Pegoraro, M.; Rigoni Garola, A.; Ronchese, P.; Squarcia, S.; Subieta, M.; Vanini, S.; Viesti, G.; Zanuttigh, P.; Zenoni, A.; Zumerle, G.

    2013-12-01

    The muon tomography technique, based on multiple Coulomb scattering of cosmic ray muons, has been proposed as a tool to detect the presence of high density objects inside closed volumes. In this paper a new and innovative method is presented to handle the density fluctuations (noise) of reconstructed images, a well known problem of this technique. The effectiveness of our method is evaluated using experimental data obtained with a muon tomography prototype located at the Legnaro National Laboratories (LNL) of the Istituto Nazionale di Fisica Nucleare (INFN). The results reported in this paper, obtained with real cosmic ray data, show that with appropriate image filtering and muon momentum classification, the muon tomography technique can detect high density materials, such as lead, albeit surrounded by light or medium density material, in short times. A comparison with algorithms published in literature is also presented.

  4. Noise reduction in selective computational ghost imaging using genetic algorithm

    NASA Astrophysics Data System (ADS)

    Zafari, Mohammad; Ahmadi-Kandjani, Sohrab; Kheradmand, Reza

    2017-03-01

    Recently, we have presented a selective computational ghost imaging (SCGI) method as an advanced technique for enhancing the security level of the encrypted ghost images. In this paper, we propose a modified method to improve the ghost image quality reconstructed by SCGI technique. The method is based on background subtraction using genetic algorithm (GA) which eliminates background noise and gives background-free ghost images. Analyzing the universal image quality index by using experimental data proves the advantage of this modification method. In particular, the calculated value of the image quality index for modified SCGI over 4225 realization shows an 11 times improvement with respect to SCGI technique. This improvement is 20 times in comparison to conventional CGI technique.

  5. Light aircraft sound transmission studies - Noise reduction model

    NASA Technical Reports Server (NTRS)

    Atwal, Mahabir S.; Heitman, Karen E.; Crocker, Malcolm J.

    1987-01-01

    Experimental tests conducted on the fuselage of a single-engine Piper Cherokee light aircraft suggest that the cabin interior noise can be reduced by increasing the transmission loss of the dominant sound transmission paths and/or by increasing the cabin interior sound absorption. The validity of using a simple room equation model to predict the cabin interior sound-pressure level for different fuselage and exterior sound field conditions is also presented. The room equation model is based on the sound power flow balance for the cabin space and utilizes the measured transmitted sound intensity data. The room equation model predictions were considered good enough to be used for preliminary acoustical design studies.

  6. Optimal periodic disturbance reduction for active noise cancelation

    NASA Astrophysics Data System (ADS)

    Kinney, C. E.; de Callafon, R. A.; Dunens, E.; Bargerhuff, R.; Bash, C. E.

    2007-08-01

    The design of an optimal internal model-based (IMB) controller by extending standard discrete time optimal control theory for IMB controllers is described. The optimal observer and state feedback gains of the IMB controller are given via the solution of discrete time algebraic Riccati equations. The design method is applied to an acoustic system that is subjected to disturbances from a server fan. Periodic disturbances from the server fan appear as harmonics of the fundamental frequency of the fan. Parametric models for the plant and non-periodic part of the disturbance are identified from experimental data. An internal model is designed in discrete time and the internal model principle is used to design a feedback controller that rejects periodic disturbances in the acoustic system. The controller is implemented in real-time and successfully attenuates the first four harmonics of the fan noise.

  7. Noise Reduction Techniques and Scaling Effects towards Photon Counting CMOS Image Sensors

    PubMed Central

    Boukhayma, Assim; Peizerat, Arnaud; Enz, Christian

    2016-01-01

    This paper presents an overview of the read noise in CMOS image sensors (CISs) based on four-transistors (4T) pixels, column-level amplification and correlated multiple sampling. Starting from the input-referred noise analytical formula, process level optimizations, device choices and circuit techniques at the pixel and column level of the readout chain are derived and discussed. The noise reduction techniques that can be implemented at the column and pixel level are verified by transient noise simulations, measurement and results from recently-published low noise CIS. We show how recently-reported process refinement, leading to the reduction of the sense node capacitance, can be combined with an optimal in-pixel source follower design to reach a sub-0.3erms- read noise at room temperature. This paper also discusses the impact of technology scaling on the CIS read noise. It shows how designers can take advantage of scaling and how the Metal-Oxide-Semiconductor (MOS) transistor gate leakage tunneling current appears as a challenging limitation. For this purpose, both simulation results of the gate leakage current and 1/f noise data reported from different foundries and technology nodes are used.

  8. Noise reduction by the application of an air-bubble curtain in offshore pile driving

    NASA Astrophysics Data System (ADS)

    Tsouvalas, A.; Metrikine, A. V.

    2016-06-01

    Underwater noise pollution is a by-product of marine industrial operations. In particular, the noise generated when a foundation pile is driven into the soil with an impact hammer is considered to be harmful for the aquatic species. In an attempt to reduce the ecological footprint, several noise mitigation techniques have been investigated. Among the various solutions proposed, the air-bubble curtain is often applied due to its efficacy in noise reduction. In this paper, a model is proposed for the investigation of the sound reduction during marine piling when an air-bubble curtain is placed around the pile. The model consists of the pile, the surrounding water and soil media, and the air-bubble curtain which is positioned at a certain distance from the pile surface. The solution approach is semi-analytical and is based on the dynamic sub-structuring technique and the modal decomposition method. Two main results of the paper can be distinguished. First, a new model is proposed that can be used for predictions of the noise levels in a computationally efficient manner. Second, an analysis is presented of the principal mechanisms that are responsible for the noise reduction due to the application of the air-bubble curtain in marine piling. The understanding of these mechanisms turns to be crucial for the exploitation of the maximum efficiency of the system. It is shown that the principal mechanism of noise reduction depends strongly on the frequency content of the radiated sound and the characteristics of the bubbly medium. For piles of large diameter which radiate most of the acoustic energy at relatively low frequencies, the noise reduction is mainly attributed to the mismatch of the acoustic impedances between the seawater and the bubbly layer. On the contrary, for smaller piles and when the radiated acoustic energy is concentrated at frequencies close to, or higher than, the resonance frequency of the air bubbles, the sound absorption within the bubbly layer

  9. NASA's Space Launch System Advanced Booster Engineering Demonstration and/or Risk Reduction Efforts

    NASA Technical Reports Server (NTRS)

    Crumbly, Christopher M.; Dumbacher, Daniel L.; May, Todd A.

    2012-01-01

    . Demonstrations and/or risk reduction efforts were required to be related to a proposed booster concept directly applicable to fielding an advanced booster. This paper will discuss, for the first time publicly, the contract awards and how NASA intends to use the data from these efforts to prepare for the planned advanced booster DDT&E acquisition as the SLS Program moves forward with competitively procured affordable performance enhancements.

  10. NASA's Space Launch System Advanced Booster Engineering Demonstration and Risk Reduction Efforts

    NASA Technical Reports Server (NTRS)

    Crumbly, Christopher M.; May, Todd; Dumbacher, Daniel

    2012-01-01

    /or risk reduction efforts were required to be related to a proposed booster concept directly applicable to fielding an Advanced Booster. This paper will discuss, for the first time publicly, the contract awards and how NASA intends to use the data from these efforts to prepare for the planned Advanced Booster DDT&E acquisition as the SLS Program moves forward with competitively procured affordable performance enhancements.

  11. Evaluating the Effort Expended to Understand Speech in Noise Using a Dual-Task Paradigm: The Effects of Providing Visual Speech Cues

    ERIC Educational Resources Information Center

    Fraser, Sarah; Gagne, Jean-Pierre; Alepins, Majolaine; Dubois, Pascale

    2010-01-01

    Purpose: Using a dual-task paradigm, 2 experiments (Experiments 1 and 2) were conducted to assess differences in the amount of listening effort expended to understand speech in noise in audiovisual (AV) and audio-only (A-only) modalities. Experiment 1 had equivalent noise levels in both modalities, and Experiment 2 equated speech recognition…

  12. Evaluating the Effort Expended to Understand Speech in Noise Using a Dual-Task Paradigm: The Effects of Providing Visual Speech Cues

    ERIC Educational Resources Information Center

    Fraser, Sarah; Gagne, Jean-Pierre; Alepins, Majolaine; Dubois, Pascale

    2010-01-01

    Purpose: Using a dual-task paradigm, 2 experiments (Experiments 1 and 2) were conducted to assess differences in the amount of listening effort expended to understand speech in noise in audiovisual (AV) and audio-only (A-only) modalities. Experiment 1 had equivalent noise levels in both modalities, and Experiment 2 equated speech recognition…

  13. High Bypass Ratio Jet Noise Reduction and Installation Effects Including Shielding Effectiveness

    NASA Technical Reports Server (NTRS)

    Thomas, Russell H.; Czech, Michael J.; Doty, Michael J.

    2013-01-01

    An experimental investigation was performed to study the propulsion airframe aeroacoustic installation effects of a separate flow jet nozzle with a Hybrid Wing Body aircraft configuration where the engine is installed above the wing. Prior understanding of the jet noise shielding effectiveness was extended to a bypass ratio ten application as a function of nozzle configuration, chevron type, axial spacing, and installation effects from additional airframe components. Chevron types included fan chevrons that are uniform circumferentially around the fan nozzle and T-fan type chevrons that are asymmetrical circumferentially. In isolated testing without a pylon, uniform chevrons compared to T-fan chevrons showed slightly more low frequency reduction offset by more high frequency increase. Phased array localization shows that at this bypass ratio chevrons still move peak jet noise source locations upstream but not to nearly the extent, as a function of frequency, as for lower bypass ratio jets. For baseline nozzles without chevrons, the basic pylon effect has been greatly reduced compared to that seen for lower bypass ratio jets. Compared to Tfan chevrons without a pylon, the combination with a standard pylon results in more high frequency noise increase and an overall higher noise level. Shielded by an airframe surface 2.17 fan diameters from nozzle to airframe trailing edge, the T-fan chevron nozzle can produce reductions in jet noise of as much as 8 dB at high frequencies and upstream angles. Noise reduction from shielding decreases with decreasing frequency and with increasing angle from the jet inlet. Beyond an angle of 130 degrees there is almost no noise reduction from shielding. Increasing chevron immersion more than what is already an aggressive design is not advantageous for noise reduction. The addition of airframe control surfaces, including vertical stabilizers and elevon deflection, showed only a small overall impact. Based on the test results, the best

  14. Assessment of Soft Vane and Metal Foam Engine Noise Reduction Concepts

    NASA Technical Reports Server (NTRS)

    Jones, Michael G.; Parrott, Tony L.; Sutliff, Daniel L.; Hughes, Chris

    2009-01-01

    Two innovative fan-noise reduction concepts developed by NASA are presented - soft vanes and over-the-rotor metal foam liners. Design methodologies are described for each concept. Soft vanes are outlet guide vanes with internal, resonant chambers that communicate with the exterior aeroacoustic environment via a porous surface. They provide acoustic absorption via viscous losses generated by interaction of unsteady flows with the internal solid structure. Over-the-rotor metal foam liners installed at or near the fan rotor axial plane provide rotor noise absorption. Both concepts also provide pressure-release surfaces that potentially inhibit noise generation. Several configurations for both concepts are evaluated with a normal incidence tube, and the results are used to guide designs for implementation in two NASA fan rigs. For soft vanes, approximately 1 to 2 dB of broadband inlet and aft-radiated fan noise reduction is achieved. For over-the-rotor metal foam liners, up to 3 dB of fan noise reduction is measured in the low-speed fan rig, but minimal reduction is measured in the high-speed fan rig. These metal foam liner results are compared with a static engine test, in which inlet sound power level reductions up to 5 dB were measured. Brief plans for further development are also provided.

  15. Cascaded systems analysis of noise reduction algorithms in dual-energy imaging.

    PubMed

    Richard, Samuel; Siewerdsen, Jeffrey H

    2008-02-01

    An important aspect of dual-energy (DE) x-ray image decomposition is the incorporation of noise reduction techniques to mitigate the amplification of quantum noise. This article extends cascaded systems analysis of imaging performance to DE imaging systems incorporating linear noise reduction algorithms. A general analytical formulation of linear DE decomposition is derived, with weighted log subtraction and several previously reported noise reduction algorithms emerging as special cases. The DE image noise-power spectrum (NPS) and modulation transfer function (MTF) demonstrate that noise reduction algorithms impart significant, nontrivial effects on the spatial-frequency-dependent transfer characteristics which do not cancel out of the noise-equivalent quanta (NEQ). Theoretical predictions were validated in comparison to the measured NPS and MTF. The resulting NEQ was integrated with spatial-frequency-dependent task functions to yield the detectability index, d', for evaluation of DE imaging performance using different decomposition algorithms. For a 3 mm lung nodule detection task, the detectability index varied from d' < 1 (i.e., nodule barely visible) in the absence of noise reduction to d' > 2.5 (i.e., nodule clearly visible) for "anti-correlated noise reduction" (ACNR) or "simple-smoothing of the high-energy image" (SSH) algorithms applied to soft-tissue or bone-only decompositions, respectively. Optimal dose allocation (A*, the fraction of total dose delivered in the low-energy projection) was also found to depend on the choice of noise reduction technique. At fixed total dose, multi-function optimization suggested a significant increase in optimal dose allocation from A* = 0.32 for conventional log subtraction to A* = 0.79 for ACNR and SSH in soft-tissue and bone-only decompositions, respectively. Cascaded systems analysis extended to the general formulation of DE image decomposition provided an objective means of investigating DE imaging performance across

  16. An adaptive way for improving noise reduction using local geometric projection

    NASA Astrophysics Data System (ADS)

    Leontitsis, Alexandros; Bountis, Tassos; Pagge, Jenny

    2004-03-01

    We propose an adaptive way to improve noise reduction by local geometric projection. From the neighborhood of each candidate point in phase space, we identify the best subspace that the point will be orthogonally projected to. The signal subspace is formed by the most significant eigendirections of the neighborhood, while the less significant ones define the noise subspace. We provide a simple criterion to separate the most significant eigendirections from the less significant ones. This criterion is based on the maximum logarithmic difference between the neighborhood eigendirection lengths, and the assumption that there is at least one eigendirection that corresponds to the noise subspace. In this way, we take into account the special characteristics of each neighborhood and introduce a more successful noise reduction technique. Results are presented for a chaotic time series of the Hénon map and Ikeda map, as well as on the Nasdaq Composite index.

  17. ERA's Open Rotor Studies Including Shielding for Noise Reduction

    NASA Technical Reports Server (NTRS)

    Van Zante, Dale; Thomas, Russell

    2012-01-01

    The Open Rotor is a modern version of the UnDucted Fan (UDF) that was flight tested in the late 1980's through a partnership between NASA and General Electric (GE). Tests were conducted in the 9' x 15' Low Speed Wind Tunnel and the 8' x 6' Supersonic Wind Tunnel starting in late 2009 and completed in early 2012. Aerodynamic and acoustic data were obtained for takeoff, approach and cruise simulations. GE was the primary partner, but other organizations were involved such as Boeing and Airbus who provided additional hardware for fuselage simulations. This test campaign provided the acoustic and performance characteristics for modern open rotor blades designs." NASA and GE conducted joint systems analysis to evaluate how well new blade designs would perform on a B737 class aircraft, and compared the results to an advanced higher bypass ratio turbofan." Acoustic shielding experiments were performed at NASA GRC and Boeing LSAF facilities to provide data for noise estimates of unconventional aircraft configurations with Open Rotor propulsion systems." The work was sponsored by NASA's aeronautics programs, including the Subsonic Fixed Wing (SFW) and the Environmentally Responsible Aviation (ERA) projects."

  18. Reduction of phase noise in nanowire spin orbit torque oscillators.

    PubMed

    Yang, Liu; Verba, Roman; Tiberkevich, Vasil; Schneider, Tobias; Smith, Andrew; Duan, Zheng; Youngblood, Brian; Lenz, Kilian; Lindner, Jürgen; Slavin, Andrei N; Krivorotov, Ilya N

    2015-11-23

    Spin torque oscillators (STOs) are compact, tunable sources of microwave radiation that serve as a test bed for studies of nonlinear magnetization dynamics at the nanometer length scale. The spin torque in an STO can be created by spin-orbit interaction, but low spectral purity of the microwave signals generated by spin orbit torque oscillators hinders practical applications of these magnetic nanodevices. Here we demonstrate a method for decreasing the phase noise of spin orbit torque oscillators based on Pt/Ni80Fe20 nanowires. We experimentally demonstrate that tapering of the nanowire, which serves as the STO active region, significantly decreases the spectral linewidth of the generated signal. We explain the observed linewidth narrowing in the framework of the Ginzburg-Landau auto-oscillator model. The model reveals that spatial non-uniformity of the spin current density in the tapered nanowire geometry hinders the excitation of higher order spin-wave modes, thus stabilizing the single-mode generation regime. This non-uniformity also generates a restoring force acting on the excited self-oscillatory mode, which reduces thermal fluctuations of the mode spatial position along the wire. Both these effects improve the STO spectral purity.

  19. Reduction of phase noise in nanowire spin orbit torque oscillators

    PubMed Central

    Yang, Liu; Verba, Roman; Tiberkevich, Vasil; Schneider, Tobias; Smith, Andrew; Duan, Zheng; Youngblood, Brian; Lenz, Kilian; Lindner, Jürgen; Slavin, Andrei N.; Krivorotov, Ilya N.

    2015-01-01

    Spin torque oscillators (STOs) are compact, tunable sources of microwave radiation that serve as a test bed for studies of nonlinear magnetization dynamics at the nanometer length scale. The spin torque in an STO can be created by spin-orbit interaction, but low spectral purity of the microwave signals generated by spin orbit torque oscillators hinders practical applications of these magnetic nanodevices. Here we demonstrate a method for decreasing the phase noise of spin orbit torque oscillators based on Pt/Ni80Fe20 nanowires. We experimentally demonstrate that tapering of the nanowire, which serves as the STO active region, significantly decreases the spectral linewidth of the generated signal. We explain the observed linewidth narrowing in the framework of the Ginzburg-Landau auto-oscillator model. The model reveals that spatial non-uniformity of the spin current density in the tapered nanowire geometry hinders the excitation of higher order spin-wave modes, thus stabilizing the single-mode generation regime. This non-uniformity also generates a restoring force acting on the excited self-oscillatory mode, which reduces thermal fluctuations of the mode spatial position along the wire. Both these effects improve the STO spectral purity. PMID:26592432

  20. Imperceptible electrical noise attenuates isometric plantar flexion force fluctuations with correlated reductions in postural sway.

    PubMed

    Magalhães, Fernando Henrique; Kohn, André Fabio

    2012-03-01

    Optimal levels of noise stimulation have been shown to enhance the detection and transmission of neural signals thereby improving the performance of sensory and motor systems. The first series of experiments in the present study aimed to investigate whether subsensory electrical noise stimulation applied over the triceps surae (TS) in seated subjects decreases torque variability during a force-matching task of isometric plantar flexion and whether the same electrical noise stimulation decreases postural sway during quiet stance. Correlation tests were applied to investigate whether the noise-induced postural sway decrease is linearly predicted by the noise-induced torque variability decrease. A second series of experiments was conducted to investigate whether there are differences in torque variability between conditions in which the subsensory electrical noise is applied only to the TS, only to the tibialis anterior (TA) and to both TS and TA, during the force-matching task with seated subjects. Noise stimulation applied over the TS muscles caused a significant reduction in force variability during the maintained isometric force paradigm and also decreased postural oscillations during quiet stance. Moreover, there was a significant correlation between the reduction in force fluctuation and the decrease in postural sway with the electrical noise stimulation. This last result indicates that changes in plantar flexion force variability in response to a given subsensory random stimulation of the TS may provide an estimate of the variations in postural sway caused by the same subsensory stimulation of the TS. We suggest that the decreases in force variability and postural sway found here are due to stochastic resonance that causes an improved transmission of proprioceptive information. In the second series of experiments, the reduction in force variability found when noise was applied to the TA muscle alone did not reach statistical significance, suggesting that TS

  1. Numerical filtering techniques for the reduction of noise in digital telemetry data

    NASA Astrophysics Data System (ADS)

    Helfrich-Stone, Thomas M.

    Telemetry data noise is due to the marginal or complete loss of telemetry carrier signal, leading to errors in the PCM data received. Attention is presently given to several postflight numerical filtering techniques for the reduction and/or removal of noise in digital telemetry data, prior to use in automated computer data analysis. The techniques encompass manual filtering, upper/lower bound filtering, mean-plus/minus standard deviation filtering, rate-of-change filtering, multiple-measurement filtering, and multiple filters.

  2. Effect of Bypass Capacitor in Common-mode Noise Reduction Technique for Automobile PCB

    NASA Astrophysics Data System (ADS)

    Uno, Takanori; Ichikawa, Kouji; Mabuchi, Yuichi; Nakamura, Atushi

    In this letter, we studied the use of common mode noise reduction technique for in-vehicle electronic equipment, each comprising large-scale integrated circuit (LSI), printed circuit board (PCB), wiring harnesses, and ground plane. We have improved the model circuit of the common mode noise that flows to the wire harness to add the effect of by-pass capacitors located near an LSI.

  3. A research program to reduce interior noise in general aviation airplanes. Influence of depressurization and damping material on the noise reduction characteristics of flat and curved stiffened panels

    NASA Technical Reports Server (NTRS)

    Navaneethan, R.; Streeter, B.; Koontz, S.; Roskam, J.

    1981-01-01

    Some 20 x 20 aluminum panels were studied in a frequency range from 20 Hz to 5000 Hz. The noise sources used were a swept sine wave generator and a random noise generator. The effect of noise source was found to be negligible. Increasing the pressure differential across the panel gave better noise reduction below the fundamental resonance frequency due to an increase in stiffness. The largest increase occurred in the first 1 psi pressure differential. The curved, stiffened panel exhibited similar behavior, but with a lower increase of low frequency noise reduction. Depressurization on these panels resulted in decreased noise reduction at higher frequencies. The effect of damping tapes on the overall noise reduction values of the test specimens was small away from the resonance frequency. In the mass-law region, a slight and proportional improvement in noise reduction was observed by adding damping material. Adding sound absorbtion material to a panel with damping material beneficially increased noise reduction at high frequencies.

  4. Noise and speckle reduction in synthetic aperture radar imagery by nonparametric Wiener filtering.

    PubMed

    Caprari, R S; Goh, A S; Moffatt, E K

    2000-12-10

    We present a Wiener filter that is especially suitable for speckle and noise reduction in multilook synthetic aperture radar (SAR) imagery. The proposed filter is nonparametric, not being based on parametrized analytical models of signal statistics. Instead, the Wiener-Hopf equation is expressed entirely in terms of observed signal statistics, with no reference to the possibly unobservable pure signal and noise. This Wiener filter is simple in concept and implementation, exactly minimum mean-square error, and directly applicable to signal-dependent and multiplicative noise. We demonstrate the filtering of a genuine two-look SAR image and show how a nonnegatively constrained version of the filter substantially reduces ringing.

  5. Hybrid feedforward-feedback active noise reduction for hearing protection and communication.

    PubMed

    Ray, Laura R; Solbeck, Jason A; Streeter, Alexander D; Collier, Robert D

    2006-10-01

    A hybrid active noise reduction (ANR) architecture is presented and validated for a circumaural earcup and a communication earplug. The hybrid system combines source-independent feedback ANR with a Lyapunov-tuned leaky LMS filter (LyLMS) improving gain stability margins over feedforward ANR alone. In flat plate testing, the earcup demonstrates an overall C-weighted total noise reduction of 40 dB and 30-32 dB, respectively, for 50-800 Hz sum-of-tones noise and for aircraft or helicopter cockpit noise, improving low frequency (<100 Hz) performance by up to 15 dB over either control component acting individually. For the earplug, a filtered-X implementation of the LyLMS accommodates its nonconstant cancellation path gain. A fast time-domain identification method provides a high-fidelity, computationally efficient, infinite impulse response cancellation path model, which is used for both the filtered-X implementation and communication feedthrough. Insertion loss measurements made with a manikin show overall C-weighted total noise reduction provided by the ANR earplug of 46-48 dB for sum-of-tones 80-2000 Hz and 40-41 dB from 63 to 3000 Hz for UH-60 helicopter noise, with negligible degradation in attenuation during speech communication. For both hearing protectors, a stability metric improves by a factor of 2 to several orders of magnitude through hybrid ANR.

  6. Transient Noise Reduction in Cochlear Implant Users: a Multi-Band Approach

    PubMed Central

    Dyballa, Karl-Heinz; Hehrmann, Phillipp; Hamacher, Volkmar; Lenarz, Thomas; Buechner, Andreas

    2016-01-01

    A previously-tested transient noise reduction (TNR) algorithm for cochlear implant (CI) users was modified to detect and attenuate transients independently across multiple frequency-bands. Since speech and transient noise are often spectrally distinct, we hypothesized that benefits in speech intelligibility can be achieved over the earlier single-band design. Fifteen experienced CI users (49 to 72 years) were tested unilaterally using pre-processed stimuli delivered directly to a speech processor. Speech intelligibility in transient and soft stationary noise, subjective sound quality and the recognition of warning signals was investigated in three processing conditions: no TNR (TNRoff), single-band TNR (TNRsgl) and multi-band TNR (TNRmult). Notably, TNRmult improved speech reception thresholds (SRTs) in cafeteria noise and office noise by up to 3 dB over both TNRoff and TNRsgl, and yielded higher comfort and clarity ratings in cafeteria noise. Our results indicate that multi-band transient noise reduction may be advantageous compared to a single-band approach, and reveal a substantial overall potential for TNR to improve speech perception and listening comfort in CI users. PMID:27942372

  7. SVD-Based Optimal Filtering Technique for Noise Reduction in Hearing Aids Using Two Microphones

    NASA Astrophysics Data System (ADS)

    Maj, Jean-Baptiste; Moonen, Marc; Wouters, Jan

    2002-12-01

    We introduce a new SVD-based (Singular value decomposition) strategy for noise reduction in hearing aids. This technique is evaluated for noise reduction in a behind-the-ear (BTE) hearing aid where two omnidirectional microphones are mounted in an endfire configuration. The behaviour of the SVD-based technique is compared to a two-stage adaptive beamformer for hearing aids developed by Vanden Berghe and Wouters (1998). The evaluation and comparison is done with a performance metric based on the speech intelligibility index (SII). The speech and noise signals are recorded in reverberant conditions with a signal-to-noise ratio of [InlineEquation not available: see fulltext.] and the spectrum of the noise signals is similar to the spectrum of the speech signal. The SVD-based technique works without initialization nor assumptions about a look direction, unlike the two-stage adaptive beamformer. Still, for different noise scenarios, the SVD-based technique performs as well as the two-stage adaptive beamformer, for a similar filter length and adaptation time for the filter coefficients. In a diffuse noise scenario, the SVD-based technique performs better than the two-stage adaptive beamformer and hence provides a more flexible and robust solution under speaker position variations and reverberant conditions.

  8. Mixing noise reduction for rectangular supersonic jets by nozzle shaping and induced screech mixing

    NASA Technical Reports Server (NTRS)

    Rice, Edward J.; Raman, Ganesh

    1993-01-01

    Two methods of mixing noise modification were studied for supersonic jets flowing from rectangular nozzles with an aspect ratio of about five and a small dimension of about 1.4 cm. The first involves nozzle geometry variation using either single (unsymmetrical) or double bevelled (symmetrical) thirty degree cutbacks of the nozzle exit. Both converging (C) and converging-diverging (C-D) versions were tested. The double bevelled C-D nozzle produced a jet mixing noise reduction of about 4 dB compared to a standard rectangular C-D nozzle. In addition all bevelled nozzles produced an upstream shift in peak mixing noise which is conducive to improved attenuation when the nozzle is used in an acoustically treated duct. A large increase in high frequency noise also occurred near the plane of the nozzle exit. Because of near normal incidence, this noise can be easily attenuated with wall treatment. The second approach uses paddles inserted on the edge of the two sides of the jet to induce screech and greatly enhance the jet mixing. Although screech and mixing noise levels are increased, the enhanced mixing moves the source locations upstream and may make an enclosed system more amenable to noise reduction using wall acoustic treatment.

  9. Use of a plane jet for flow-induced noise reduction of tandem rods

    NASA Astrophysics Data System (ADS)

    Kun, Zhao; Xi-xiang, Yang; Patrick, N. Okolo; Wei-hua, Zhang

    2016-06-01

    Unsteady wake from upstream components of landing gear impinging on downstream components could be a strong noise source. The use of a plane jet is proposed to reduce this flow-induced noise. Tandem rods with different gap widths were utilized as the test body. Both acoustic and aerodynamic tests were conducted in order to validate this technique. Acoustic test results proved that overall noise emission from tandem rods could be lowered and tonal noise could be removed with use of the plane jet. However, when the plane jet was turned on, in some frequency range it could be the subsequent main contributor instead of tandem rods to total noise emission whilst in some frequency range rods could still be the main contributor. Moreover, aerodynamic tests fundamentally studied explanations for the noise reduction. Specifically, not only impinging speed to rods but speed and turbulence level to the top edge of the rear rod could be diminished by the upstream plane jet. Consequently, the vortex shedding induced by the rear rod was reduced, which was confirmed by the speed, Reynolds stress as well as the velocity fluctuation spectral measured in its wake. This study confirmed the potential use of a plane jet towards landing gear noise reduction. Project partially supported by the European Union FP7 CleanSky Joint Technology Initiative “ALLEGRA” (Grant No. 308225).

  10. Noise reduction of a tilt-rotor aircraft including effects on weight and performance

    NASA Technical Reports Server (NTRS)

    Gibs, J.; Stepniewski, W. Z.; Spencer, R.; Kohler, G.

    1973-01-01

    Various methods for far-field noise reduction of a tilt-rotor acoustic signature and the performance and weight tradeoffs which result from modification of the noise sources are considered in this report. In order to provide a realistic approach for the investigation, the Boeing tilt-rotor flight research aircraft (Model 222), was selected as the baseline. This aircraft has undergone considerable engineering development. Its rotor has been manufactured and tested in the Ames full-scale wind tunnel. The study reflects the current state-of-the-art of aircraft design for far-field acoustic signature reduction and is not based solely on an engineering feasibility aircraft. This report supplements a previous study investigating reduction of noise signature through the management of the terminal flight trajectory.

  11. Full-Scale Investigation of Several Jet-Engine Noise-Reduction Nozzles

    NASA Technical Reports Server (NTRS)

    Coles, Willard D; Callaghan, Edmund E

    1958-01-01

    A number of noise-suppression nozzles were tested on full-scale engines. In general, these nozzles achieved noise reduction by the mixing interference of adjacent jets, that is, by using multiple-slot-nozzles. Several of the nozzles achieved reductions in sound power of approximately 5 decibels (nearly 70 percent) with small thrust losses (approx. 1 percent). The maximum sound-pressure level was reduced by as much as 18 decibels in particular frequency bands. Some of the nozzles showed considerable spatial asymmetry; that is, the sound field was not rotationally symmetrical. A method of calculating the limiting frequency effected by such nozzles is presented. Furthermore data are shown that appear to indicate that further reductions in sound power will not be easily achieved from nozzles using mixing interference as a means of noise suppression

  12. Evaluation of model-based versus non-parametric monaural noise-reduction approaches for hearing aids.

    PubMed

    Harlander, Niklas; Rosenkranz, Tobias; Hohmann, Volker

    2012-08-01

    Single channel noise reduction has been well investigated and seems to have reached its limits in terms of speech intelligibility improvement, however, the quality of such schemes can still be advanced. This study tests to what extent novel model-based processing schemes might improve performance in particular for non-stationary noise conditions. Two prototype model-based algorithms, a speech-model-based, and a auditory-model-based algorithm were compared to a state-of-the-art non-parametric minimum statistics algorithm. A speech intelligibility test, preference rating, and listening effort scaling were performed. Additionally, three objective quality measures for the signal, background, and overall distortions were applied. For a better comparison of all algorithms, particular attention was given to the usage of the similar Wiener-based gain rule. The perceptual investigation was performed with fourteen hearing-impaired subjects. The results revealed that the non-parametric algorithm and the auditory model-based algorithm did not affect speech intelligibility, whereas the speech-model-based algorithm slightly decreased intelligibility. In terms of subjective quality, both model-based algorithms perform better than the unprocessed condition and the reference in particular for highly non-stationary noise environments. Data support the hypothesis that model-based algorithms are promising for improving performance in non-stationary noise conditions.

  13. RANS Analyses of Turbofan Nozzles with Wedge Deflectors for Noise Reduction

    NASA Technical Reports Server (NTRS)

    DeBonis, James R.

    2008-01-01

    Computational fluid dynamics (CFD) was used to evaluate a promising concept for reducing the noise at take-off of dual-stream, turbofan nozzles. The concept, offset stream technology, reduces the jet noise observed on the ground by diverting (offsetting) the majority of the fan flow below the core flow, thickening this layer between the high velocity core flow and the ground observers. In this study a wedge placed in the internal fan stream is used as the diverter. Wind, a Reynolds Averaged Navier-Stokes (RANS) code, was used to analyze the flowfield of the exhaust plume and to calculate nozzle performance. Results showed that the wedge effectively diverts the fan flow and the turbulent kinetic energy on the observer side of the nozzle is reduced. The reduction in turbulent kinetic energy should correspond to a reduction in noise. The blockage due to the wedge reduces the fan massflow proportional to its blockage and the overall thrust is consequently reduced. The CFD predictions are in very good agreement with experimental data. This noise reduction concept shows promise for reduced jet noise at a small reduction in thrust. It has been demonstrated that RANS CFD can be used to optimize this concept.

  14. Noise reduction in rhythmic and multitrial biosignals with applications to event-related potentials.

    PubMed

    Celka, Patrick; Le, Khoa N; Cutmore, Timothy R H

    2008-07-01

    A new noise reduction algorithm is presented for signals displaying repeated patterns or multiple trials. Each pattern is stored in a matrix, forming a set of events, which is termed multievent signal. Each event is considered as an affine transform of a basic template signal that allows for time scaling and shifting. Wavelet transforms, decimated and undecimated, are applied to each event. Noise reduction on the set of coefficients of the transformed events is applied using either wavelet denoising or principal component analysis (PCA) noise reduction methodologies. The method does not require any manual selection of coefficients. Nonstationary multievent synthetic signals are employed to demonstrate the performance of the method using normalized mean square error against classical wavelet and PCA based algorithms. The new method shows a significant improvement in low SNRs (typically 0 dB). On the experimental side, evoked potentials in a visual oddball paradigm are used. The reduced-noise visual oddball event-related potentials reveal gradual changes in morphology from trial to trial (especially for N1-P2 and N2-P3 waves at Fz), which can be hypothetically linked to attention or decision processes. The new noise reduction method is, thus, shown to be particularly suited for recovering single-event features in nonstationary low SNR multievent contexts.

  15. Optimization of the poro-serrated trailing edges for airfoil broadband noise reduction.

    PubMed

    Chong, Tze Pei; Dubois, Elisa

    2016-08-01

    This paper reports an aeroacoustic investigation of a NACA0012 airfoil with a number of poro-serrated trailing edge devices that contain porous materials of various air flow resistances at the gaps between adjacent members of the serrated-sawtooth trailing edge. The main objective of this work is to determine whether multiple-mechanisms on the broadband noise reduction can co-exist on a poro-serrated trailing edge. When the sawtooth gaps are filled with porous material of low-flow resistivity, the vortex shedding tone at low-frequency could not be completely suppressed at high-velocity, but a reasonably good broadband noise reduction can be achieved at high-frequency. When the sawtooth gaps are filled with porous material of very high-flow resistivity, no vortex shedding tone is present, but the serration effect on the broadband noise reduction becomes less effective. An optimal choice of the flow resistivity for a poro-serrated configuration has been identified, where it can surpass the conventional serrated trailing edge of the same geometry by achieving a further 1.5 dB reduction in the broadband noise while completely suppressing the vortex shedding tone. A weakened turbulent boundary layer noise scattering at the poro-serrated trailing edge is reflected by the lower-turbulence intensity at the near wake centreline across the whole spanwise wavelength of the sawtooth.

  16. Reduction of randomness in seismic noise as a short-term precursor to a volcanic eruption

    PubMed Central

    Glynn, C. C.; Konstantinou, K. I.

    2016-01-01

    Ambient seismic noise is characterized by randomness incurred by the random position and strength of the noise sources as well as the heterogeneous properties of the medium through which it propagates. Here we use ambient noise data recorded prior to the 1996 Gjálp eruption in Iceland in order to show that a reduction of noise randomness can be a clear short-term precursor to volcanic activity. The eruption was preceded on 29 September 1996 by a Mw ~5.6 earthquake that occurred in the caldera rim of the Bárdarbunga volcano. A significant reduction of randomness started occurring 8 days before the earthquake and 10 days before the onset of the eruption. This reduction was observed even at stations more than 100 km away from the eruption site. Randomness increased to its previous levels 160 minutes after the Bárdarbunga earthquake, during which time aftershocks migrated from the Bárdarbunga caldera to a site near the Gjálp eruption fissure. We attribute this precursory reduction of randomness to the lack of higher frequencies (>1 Hz) in the noise wavefield caused by high absorption losses as hot magma ascended in the upper crust. PMID:27883050

  17. Static and wind tunnel model tests for the development of externally blown flap noise reduction techniques

    NASA Technical Reports Server (NTRS)

    Pennock, A. P.; Swift, G.; Marbert, J. A.

    1975-01-01

    Externally blown flap models were tested for noise and performance at one-fifth scale in a static facility and at one-tenth scale in a large acoustically-treated wind tunnel. The static tests covered two flap designs, conical and ejector nozzles, third-flap noise-reduction treatments, internal blowing, and flap/nozzle geometry variations. The wind tunnel variables were triple-slotted or single-slotted flaps, sweep angle, and solid or perforated third flap. The static test program showed the following noise reductions at takeoff: 1.5 PNdB due to treating the third flap; 0.5 PNdB due to blowing from the third flap; 6 PNdB at flyover and 4.5 PNdB in the critical sideline plane (30 deg elevation) due to installation of the ejector nozzle. The wind tunnel program showed a reduction of 2 PNdB in the sideline plane due to a forward speed of 43.8 m/s (85 kn). The best combination of noise reduction concepts reduced the sideline noise of the reference aircraft at constant field length by 4 PNdB.

  18. Reduction of randomness in seismic noise as a short-term precursor to a volcanic eruption

    NASA Astrophysics Data System (ADS)

    Glynn, C. C.; Konstantinou, K. I.

    2016-11-01

    Ambient seismic noise is characterized by randomness incurred by the random position and strength of the noise sources as well as the heterogeneous properties of the medium through which it propagates. Here we use ambient noise data recorded prior to the 1996 Gjálp eruption in Iceland in order to show that a reduction of noise randomness can be a clear short-term precursor to volcanic activity. The eruption was preceded on 29 September 1996 by a Mw ~5.6 earthquake that occurred in the caldera rim of the Bárdarbunga volcano. A significant reduction of randomness started occurring 8 days before the earthquake and 10 days before the onset of the eruption. This reduction was observed even at stations more than 100 km away from the eruption site. Randomness increased to its previous levels 160 minutes after the Bárdarbunga earthquake, during which time aftershocks migrated from the Bárdarbunga caldera to a site near the Gjálp eruption fissure. We attribute this precursory reduction of randomness to the lack of higher frequencies (>1 Hz) in the noise wavefield caused by high absorption losses as hot magma ascended in the upper crust.

  19. Interior Noise Reduction by Adaptive Feedback Vibration Control

    NASA Technical Reports Server (NTRS)

    Lim, Tae W.

    1998-01-01

    The objective of this project is to investigate the possible use of adaptive digital filtering techniques in simultaneous, multiple-mode identification of the modal parameters of a vibrating structure in real-time. It is intended that the results obtained from this project will be used for state estimation needed in adaptive structural acoustics control. The work done in this project is basically an extension of the work on real-time single mode identification, which was performed successfully using a digital signal processor (DSP) at NASA, Langley. Initially, in this investigation the single mode identification work was duplicated on a different processor, namely the Texas Instruments TMS32OC40 DSP. The system identification results for the single mode case were very good. Then an algorithm for simultaneous two mode identification was developed and tested using analytical simulation. When it successfully performed the expected tasks, it was implemented in real-time on the DSP system to identify the first two modes of vibration of a cantilever aluminum beam. The results of the simultaneous two mode case were good but some problems were identified related to frequency warping and spurious mode identification. The frequency warping problem was found to be due to the bilinear transformation used in the algorithm to convert the system transfer function from the continuous-time domain to the discrete-time domain. An alternative approach was developed to rectify the problem. The spurious mode identification problem was found to be associated with high sampling rates. Noise in the signal is suspected to be the cause of this problem but further investigation will be needed to clarify the cause. For simultaneous identification of more than two modes, it was found that theoretically an adaptive digital filter can be designed to identify the required number of modes, but the algebra became very complex which made it impossible to implement in the DSP system used in this study

  20. Noise Reduction with Lobed Mixers: Nozzle-Length and Free-Jet Speed Effects

    NASA Technical Reports Server (NTRS)

    Mengle, Vinod G.; Dalton, William N.; Bridges, James C.; Boyd, Kathy C.

    1997-01-01

    Acoustic test results are presented for 1/4th-scaled nozzles with internal lobed mixers used for reduction of subsonic jet noise of turbofan engines with bypass ratio above 5 and jet speeds up to 830 ft/s. One coaxial and three forced lobe mixers were tested with variations in lobe penetration, cut-outs in lobe-sidewall, lobe number and nozzle-length. Measured exit flow profiles and thrusts are used to assist the inferences from acoustic data. It is observed that lobed mixers reduce the low-frequency noise due to more uniformly mixed exit flow; but they may also increase the high-frequency noise at peak perceived noise (PNL) angle and angles upstream of it due to enhanced mixing inside the nozzle. Cut-outs and low lobe penetration reduce the annoying portion of the spectrum but lead to less uniform exit flow. Due to the dominance of internal duct noise in unscalloped, high-penetration mixers their noise is not reduced as much with increase in free-jet speed as that of coaxial or cut-out lobed mixers. The latter two mixers also show no change in PNL over the wide range of nozzle-lengths tested because most of their noise sources are outside the nozzle; whereas, the former show an increase in noise with decrease in nozzle-length.

  1. Optimum Noise Reduction Methods for the Interior of Vehicles and Aircraft Cabins

    NASA Astrophysics Data System (ADS)

    Tavossi, Ph. D., Hasson M.

    The most effective methods of noise reduction in vehicles and Aircraft cabins are investigated. The first goal is to determine the optimal means of noise mitigation without change in external shape of the vehicle, or aircraft cabin exterior such as jet engine or fuselage design, with no significant added weight. The second goal is to arrive at interior designs that can be retrofitted to the existing interiors, to reduce overall noise level for the passengers. The physical phenomena considered are; relaxation oscillations, forced vibrations with non-linear damping and sub-harmonic resonances. The negative and positive damping coefficients and active noise cancelations methods are discussed. From noise power-spectrum for a prototype experimental setup, the most energetic vibration modes are determined, that require the highest damping. The proposed technique will utilize the arrangement of uniformly distributed open Helmholtz resonators, with sound absorbing surface. They are tuned to the frequencies that correspond to the most energetic noise levels. The resonators dissipate noise energy inside the vehicle, or aircraft cabin, at the peak frequencies of the noise spectrum, determined for different vehicle or aircraft cabin, interior design models.

  2. [Noise-reduction function and its affecting factors of urban plant communities in Shanghai].

    PubMed

    Zhang, Qing-Fei; Zheng, Si-Jun; Xia, Lei; Wu, Hai-Ping; Zhang, Ming-Li; Li, Ming-Sheng

    2007-10-01

    The factor analysis on the relationships between excess noise attenuation (decrement after noise propagating 30 m) and 8 structural characteristics of 19 urban plant communities in Shanghai showed that all the plant communities had notable effects on reducing noise, and the noise attenuation ability of the communities was significantly higher than that of lawn (P < 0.01). The plant communities could be divided into three groups base on their noise attenuation ability, i.e., those of > or = 10 dB(A), 6-10 dB(A), and < or = 6 dB(A). The main factors affecting the noise attenuation ability of the communities were leaf area index, average bifurcate height, average height, coverage, and average canopy diameter, and their correlation coefficients with noise attenuation were 0.343, 0.318, 0.285, 0.226 and 0.193, respectively. These five factors had a cumulative contribution rate of 65.47%, suggesting that they should be considered in stress when designing urban greenbelt for noise reduction.

  3. Reduction of SEM noise and extended application to prediction of CD uniformity and its experimental validation

    NASA Astrophysics Data System (ADS)

    Kim, Hoyeon; Hwang, Chan; Oh, Seok-hwan; Yeo, Jeongho; Kim, Young hee

    2011-03-01

    As the design rule of Integrated Circuits(IC) becomes smaller, the precise measurement of Critical Dimension (CD) of features and minimization of deviation in CD measured becomes a vital issue. In this paper, a simple frequency analysis method to extract the noise from SEM images was used to evaluate the contribution of SEM noise in CD Uniformity. Multiple SEM images of simple Line and Space (L/S) patterns were analyzed and a model of frequency profile (Power Spectrum Density (PSD) model) was made using an offline analyzing tool based on Matlab®. From this profile, white noise and 1/f profile were separated. Noises are eliminated to generate a noise reduced PSD profile to make CD results. The contribution of white noise on CD measurement can be assessed using Line Width Roughness (LWR) measurement. Furthermore, CD uniformity can be also predicted from the model. This prediction is based on an assumption that CD uniformity is equal to LWR if the inspection area is extended to infinity and appropriate sampling method is applied. The results showed that the contribution of white noise on LWR can be up to around 70% (in power) without any noise reduction measures (sum line averaging) after imaging in photo resist image. For experimental validation, CD uniformity is predicted from the model for different measurement conditions and compared with real measurement. For a result, CD uniformity prediction (3sigma) from the model shows within 20% in accuracy with real CD uniformity value measured from the photo resist image.

  4. Local surface plasmon mediated extraordinary optical transmission of multi-spatial-mode quantum noise reduction

    SciTech Connect

    Lawrie, Benjamin J; Evans, Philip G; Pooser, Raphael C

    2013-01-01

    We demonstrate the coherent transduction of quantum noise reduction, or squeezed light, by Ag localized surface plasmons (LSPs). Squeezed light, generated through four-wave-mixing in Rb vapor, is coupled to a Ag nanohole array designed to exhibit LSP mediated extraordinary-optical transmission (EOT) spectrally coincident with the squeezed light source at 795 nm. We demonstrate that quantum noise reduction as a function of transmission is found to match closely with linear attenuation models, thus demonstrating that the photon-LSP-photon transduction process is coherent near the LSP resonance.

  5. Optimization and Modeling of Noise Reduction for Turbulent Jets with Induced Asymmetry

    NASA Astrophysics Data System (ADS)

    Rostamimonjezi, Sara

    This project relates to the development of next-generation high-speed aircraft that are efficient and environmentally compliant. The emphasis of the research is on reducing noise from high-performance engines that will power these aircraft. A strong component of engine noise is jet mixing noise that comes from the turbulent mixing process between the high-speed exhaust flow of the engine and the atmosphere. The fan flow deflection method (FFD) suppresses jet noise by deflecting the fan stream downward, by a few degrees, with respect to the core stream. This reduces the convective Mach number of the primary shear layer and turbulent kinetic energy in the downward direction and therefore reduces the noise emitted towards the ground. The redistribution of the fan stream is achieved with inserting airfoil-shaped vanes inside the fan duct. Aerodynamic optimization of FFD has been done by Dr. Juntao Xiong using a computational fluid dynamics code to maximize reduction of noise perceived by the community while minimizing aerodynamic losses. The optimal vane airfoils are used in a parametric experimental study of 50 4-vane deflector configurations. The vane chord length, angle of attack, and azimuthal location are the parameters studied in acoustic optimization. The best vane configuration yields a reduction in cumulative (downward + sideline) effective perceived noise level (EPNL) of 5.3 dB. The optimization study underscores the sensitivity of FFD to deflector parameters and the need for careful design in the practical implementation of this noise reduction approach. An analytical model based on Reynolds Averaged Navier Stokes (RANS) and acoustic analogy is developed to predict the spectral changes from a known baseline in the direction of peak emission. A generalized form for space-time correlation is introduced that allows shapes beyond the traditional exponential forms. Azimuthal directivity based on the wavepacket model of jet noise is integrated with the acoustic

  6. Statistical CT noise reduction with multiscale decomposition and penalized weighted least squares in the projection domain

    SciTech Connect

    Tang Shaojie; Tang Xiangyang

    2012-09-15

    Purposes: The suppression of noise in x-ray computed tomography (CT) imaging is of clinical relevance for diagnostic image quality and the potential for radiation dose saving. Toward this purpose, statistical noise reduction methods in either the image or projection domain have been proposed, which employ a multiscale decomposition to enhance the performance of noise suppression while maintaining image sharpness. Recognizing the advantages of noise suppression in the projection domain, the authors propose a projection domain multiscale penalized weighted least squares (PWLS) method, in which the angular sampling rate is explicitly taken into consideration to account for the possible variation of interview sampling rate in advanced clinical or preclinical applications. Methods: The projection domain multiscale PWLS method is derived by converting an isotropic diffusion partial differential equation in the image domain into the projection domain, wherein a multiscale decomposition is carried out. With adoption of the Markov random field or soft thresholding objective function, the projection domain multiscale PWLS method deals with noise at each scale. To compensate for the degradation in image sharpness caused by the projection domain multiscale PWLS method, an edge enhancement is carried out following the noise reduction. The performance of the proposed method is experimentally evaluated and verified using the projection data simulated by computer and acquired by a CT scanner. Results: The preliminary results show that the proposed projection domain multiscale PWLS method outperforms the projection domain single-scale PWLS method and the image domain multiscale anisotropic diffusion method in noise reduction. In addition, the proposed method can preserve image sharpness very well while the occurrence of 'salt-and-pepper' noise and mosaic artifacts can be avoided. Conclusions: Since the interview sampling rate is taken into account in the projection domain

  7. Statistical CT noise reduction with multiscale decomposition and penalized weighted least squares in the projection domain.

    PubMed

    Tang, Shaojie; Tang, Xiangyang

    2012-09-01

    The suppression of noise in x-ray computed tomography (CT) imaging is of clinical relevance for diagnostic image quality and the potential for radiation dose saving. Toward this purpose, statistical noise reduction methods in either the image or projection domain have been proposed, which employ a multiscale decomposition to enhance the performance of noise suppression while maintaining image sharpness. Recognizing the advantages of noise suppression in the projection domain, the authors propose a projection domain multiscale penalized weighted least squares (PWLS) method, in which the angular sampling rate is explicitly taken into consideration to account for the possible variation of interview sampling rate in advanced clinical or preclinical applications. The projection domain multiscale PWLS method is derived by converting an isotropic diffusion partial differential equation in the image domain into the projection domain, wherein a multiscale decomposition is carried out. With adoption of the Markov random field or soft thresholding objective function, the projection domain multiscale PWLS method deals with noise at each scale. To compensate for the degradation in image sharpness caused by the projection domain multiscale PWLS method, an edge enhancement is carried out following the noise reduction. The performance of the proposed method is experimentally evaluated and verified using the projection data simulated by computer and acquired by a CT scanner. The preliminary results show that the proposed projection domain multiscale PWLS method outperforms the projection domain single-scale PWLS method and the image domain multiscale anisotropic diffusion method in noise reduction. In addition, the proposed method can preserve image sharpness very well while the occurrence of "salt-and-pepper" noise and mosaic artifacts can be avoided. Since the interview sampling rate is taken into account in the projection domain multiscale decomposition, the proposed method is

  8. Statistical CT noise reduction with multiscale decomposition and penalized weighted least squares in the projection domain

    PubMed Central

    Tang, Shaojie; Tang, Xiangyang

    2012-01-01

    Purposes: The suppression of noise in x-ray computed tomography (CT) imaging is of clinical relevance for diagnostic image quality and the potential for radiation dose saving. Toward this purpose, statistical noise reduction methods in either the image or projection domain have been proposed, which employ a multiscale decomposition to enhance the performance of noise suppression while maintaining image sharpness. Recognizing the advantages of noise suppression in the projection domain, the authors propose a projection domain multiscale penalized weighted least squares (PWLS) method, in which the angular sampling rate is explicitly taken into consideration to account for the possible variation of interview sampling rate in advanced clinical or preclinical applications. Methods: The projection domain multiscale PWLS method is derived by converting an isotropic diffusion partial differential equation in the image domain into the projection domain, wherein a multiscale decomposition is carried out. With adoption of the Markov random field or soft thresholding objective function, the projection domain multiscale PWLS method deals with noise at each scale. To compensate for the degradation in image sharpness caused by the projection domain multiscale PWLS method, an edge enhancement is carried out following the noise reduction. The performance of the proposed method is experimentally evaluated and verified using the projection data simulated by computer and acquired by a CT scanner. Results: The preliminary results show that the proposed projection domain multiscale PWLS method outperforms the projection domain single-scale PWLS method and the image domain multiscale anisotropic diffusion method in noise reduction. In addition, the proposed method can preserve image sharpness very well while the occurrence of “salt-and-pepper” noise and mosaic artifacts can be avoided. Conclusions: Since the interview sampling rate is taken into account in the projection domain

  9. The effect of multimicrophone noise reduction systems on sound source localization by users of binaural hearing aids.

    PubMed

    Van den Bogaert, Tim; Doclo, Simon; Wouters, Jan; Moonen, Marc

    2008-07-01

    This paper evaluates the influence of three multimicrophone noise reduction algorithms on the ability to localize sound sources. Two recently developed noise reduction techniques for binaural hearing aids were evaluated, namely, the binaural multichannel Wiener filter (MWF) and the binaural multichannel Wiener filter with partial noise estimate (MWF-N), together with a dual-monaural adaptive directional microphone (ADM), which is a widely used noise reduction approach in commercial hearing aids. The influence of the different algorithms on perceived sound source localization and their noise reduction performance was evaluated. It is shown that noise reduction algorithms can have a large influence on localization and that (a) the ADM only preserves localization in the forward direction over azimuths where limited or no noise reduction is obtained; (b) the MWF preserves localization of the target speech component but may distort localization of the noise component. The latter is dependent on signal-to-noise ratio and masking effects; (c) the MWF-N enables correct localization of both the speech and the noise components; (d) the statistical Wiener filter approach introduces a better combination of sound source localization and noise reduction performance than the ADM approach.

  10. Experimental and numerical analysis on noise reduction in a multi-blade centrifugal fan

    NASA Astrophysics Data System (ADS)

    Chen, X. J.; Y Cao, T.; Su, J.; Qin, G. L.

    2013-12-01

    In this work, analysis on noise source and reduction in a multi-blade centrifugal fan used for air-conditioners was carried out by experimental and numerical methods. Firstly, an experimental system using microphone mounted on volute surface for measuring surface pressure fluctuations of volute was designed and introduced, then surface pressure fluctuations of the whole volute for a multi-blade centrifugal fan were measured by this system, and the inlet noise for this fan was also obtained. And then, based on the experimental results, the aerodynamic noise source of the studied fan was analysed. The surface pressure fluctuations of the volute showed that there were largest surface pressure fluctuations near the volute tongue, and peaks appeared at the Blade Passing Frequency (BPF). The spectra of fan inlet noise showed that the peaks also appeared at BPF, and noise levels in a wide range of frequency were also larger. Secondly, the internal flow of the fan was simulated by commercial software under the same conditions with the experiment, and then the fluid flow and acoustic power field were obtained and discussed. The contours of acoustic power level showed that the larger noise was generated at the impeller area close to the outlet of scroll and at the volute tongue, which is same as that from experiment. Based on all of the results, we can find that the vortex noise is an important part of fan noise for the studied fan, and the rotation noise also cannot be neglected. Finally, several reduction methods that are thought to be effective based on experimental and numerical results were suggested.

  11. Effects of digital noise reduction on speech perception for children with hearing loss

    PubMed Central

    Stelmachowicz, Patricia; Lewis, Dawna; Hoover, Brenda; Nishi, Kanae; McCreery, Ryan; Woods, William

    2010-01-01

    Objective While numerous studies have investigated the effects of single-microphone digital noise reduction algorithms for adults with hearing loss, similar studies have not been conducted with young hearing-impaired children. The goal of this study was to examine the effects of a commonly-used digital noise reduction scheme (spectral subtraction) in children with mild-moderately severe sensorineural hearing losses. It was hypothesized that the process of spectral subtraction may alter or degrade speech signals in some way. Such degradation may have little influence on the perception of speech by hearing-impaired adults who are likely to use contextual information under such circumstances. For young children who are still developing various language skills, however, signal degradation may have a more detrimental effect on the perception of speech. Design Sixteen children (eight 5–7 year olds and eight 8–10 year olds) with mild-moderately severe hearing loss participated in this study. All participants wore binaural behind-the-ear hearing aids where noise reduction processing was performed independently in 16 bands with center frequencies spaced 500 Hz apart up to 7500 Hz. Test stimuli were nonsense syllables, words, and sentences in a background of noise. For all stimuli, data were obtained with noise reduction on and off. Results In general, performance improved as a function of SNR for all three speech materials. The main effect for stimulus type was significant and post hoc comparisons of stimulus type indicated that speech recognition was higher for sentences than for both nonsense syllables and words, but no significant differences were observed between nonsense syllables and words. The main effect for noise reduction and the two-way interaction between noise reduction and stimulus type were not significant. Significant age group effects were observed, but the two-way interaction between NR and age group was not significant. Conclusions Consistent with

  12. Shock associated noise reduction from inverted-velocity-profile coannular jets

    NASA Technical Reports Server (NTRS)

    Tanna, H. K.; Tam, C. K. W.; Brown, W. H.

    1981-01-01

    Acoustic measurements show that the shock noise from the outer stream is virtually eliminated when the inner stream is operated at a Mach number just above unity, regardless of all the other jet operating conditions. At this optimum condition, the coannular jet provides the maximum noise reduction relative to the equivalent single jet. The shock noise reduction can be achieved at inverted-as well as normal-velocity-profile conditions, provided the coannular jet is operated with the inner stream just slightly supersonic. Analytical models for the shock structure and shock noise are developed indicate that a drastic change in the outer stream shock cell structure occurs when the inner stream increases its velocity from subsonic to supersonic. At this point, the almost periodic shock cell structure of the outer stream nearly completely disappears the noise radiated is minimum. Theoretically derive formulae for the peak frequencies and intensity scaling of shock associated noise are compared with the measured results, and good agreement is found for both subsonic and supersonic inner jet flows.

  13. Reduction of blade-vortex interaction noise using higher harmonic pitch control

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Booth, Earl R., Jr.; Jolly, J. Ralph, Jr.; Yeager, William T., Jr.; Wilbur, Matthew L.

    1989-01-01

    An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in Langley's Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of matched flight conditions, where prescribed (open-loop) higher harmonic pitch was superimposed on the normal (baseline) collective and cyclic trim pitch. For the inflow-microphone noise measurements, advantage was taken of the reverberance in the hard walled tunnel by using a sound power determination approach. Initial findings from on-line data processing for three of the test microphones are reported for a 4/rev (4P) collective pitch control for a range of input amplitudes and phases. By comparing these results to corresponding baseline (no control) conditions, significant noise reductions (4 to 5 dB) were found for low-speed descent conditions, where helicopter BVI noise is most intense. For other rotor flight conditions, the overall noise was found to increase. All cases show increased vibration levels.

  14. Reduction of blade-vortex interaction noise through higher harmonic pitch control

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Booth, Earl R., Jr.; Jolly, J. Ralph, Jr.; Yeager, William T., Jr.; Wilbur, Matthew L.

    1990-01-01

    An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in Langley's Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of matched flight conditions, where prescribed (open-loop) higher harmonic pitch was superimposed on the normal (baseline) collective and cyclic trim pitch. For the inflow-microphone noise measurements, advantage was taken of the reverberance in the hard walled tunnel by using a sound power determination approach. Initial findings from on-line data processing for three of the test microphones are reported for a 4/rev (4P) collective pitch control for a range of input amplitudes and phases. By comparing these results to corresponding baseline (no control) conditions, significant noise reductions (4 to 5 dB) were found for low-speed descent conditions, where helicopter BVI noise is most intense. For other rotor flight conditions, the overall noise was found to increase. All cases show increased vibration levels.

  15. Large Engine Technology (LET) Task XXXVII Low-Bypass Ratio Mixed Turbofan Engine Subsonic Jet Noise Reduction Program Test Report

    NASA Technical Reports Server (NTRS)

    Hauser, Joseph R.; Zysman, Steven H.; Barber, Thomas J.

    2001-01-01

    NASA Glenn Research Center supported a three year effort to develop the technology for reducing jet noise from low-bypass ratio engines. This effort concentrated on both analytical and experimental approaches using various mixer designs. CFD and MGB predictions are compared with LDV and noise data, respectively. While former predictions matched well with data, experiment shows a need for improving the latter predictions. Data also show that mixing noise can be sensitive to engine hardware upstream of the mixing exit plane.

  16. Noise reduction in long‐period seismograms by way of array summing

    USGS Publications Warehouse

    Ringler, Adam; Wilson, David; Storm, Tyler; Marshall, Benjamin T.; Hutt, Charles R.; Holland, Austin

    2016-01-01

    Long‐period (>100  s period) seismic data can often be dominated by instrumental noise as well as local site noise. When multiple collocated sensors are installed at a single site, it is possible to improve the overall station noise levels by applying stacking methods to their traces. We look at the noise reduction in long‐period seismic data by applying the time–frequency phase‐weighted stacking method of Schimmel and Gallart (2007) as well as the phase‐weighted stacking (PWS) method of Schimmel and Paulssen (1997) to four collocated broadband sensors installed in the quiet Albuquerque Seismological Laboratory underground vault. We show that such stacking methods can improve vertical noise levels by as much as 10 dB over the mean background noise levels at 400 s period, suggesting that greater improvements could be achieved with an array involving multiple sensors. We also apply this method to reduce local incoherent noise on horizontal seismic records of the 2 March 2016 Mw 7.8 Sumatra earthquake, where the incoherent noise levels at very long periods are similar in amplitude to the earthquake signal. To maximize the coherency, we apply the PWS method to horizontal data where relative azimuths between collocated sensors are estimated and compared with a simpler linear stack with no azimuthal rotation. Such methods could help reduce noise levels at various seismic stations where multiple high‐quality sensors have been deployed. Such small arrays may also provide a solution to improving long‐period noise levels at Global Seismographic Network stations.

  17. Acoustic noise reduction in T 1- and proton-density-weighted turbo spin-echo imaging.

    PubMed

    Ott, Martin; Blaimer, Martin; Breuer, Felix; Grodzki, David; Heismann, Björn; Jakob, Peter

    2016-02-01

    To reduce acoustic noise levels in T 1-weighted and proton-density-weighted turbo spin-echo (TSE) sequences, which typically reach acoustic noise levels up to 100 dB(A) in clinical practice. Five acoustic noise reduction strategies were combined: (1) gradient ramps and shapes were changed from trapezoidal to triangular, (2) variable-encoding-time imaging was implemented to relax the phase-encoding gradient timing, (3) RF pulses were adapted to avoid the need for reversing the polarity of the slice-rewinding gradient, (4) readout bandwidth was increased to provide more time for gradient activity on other axes, (5) the number of slices per TR was reduced to limit the total gradient activity per unit time. We evaluated the influence of each measure on the acoustic noise level, and conducted in vivo measurements on a healthy volunteer. Sound recordings were taken for comparison. An overall acoustic noise reduction of up to 16.8 dB(A) was obtained by the proposed strategies (1-4) and the acquisition of half the number of slices per TR only. Image quality in terms of SNR and CNR was found to be preserved. The proposed measures in this study allowed a threefold reduction in the acoustic perception of T 1-weighted and proton-density-weighted TSE sequences compared to a standard TSE-acquisition. This could be achieved without visible degradation of image quality, showing the potential to improve patient comfort and scan acceptability.

  18. Local-geometric-projection method for noise reduction in chaotic maps and flows

    NASA Astrophysics Data System (ADS)

    Cawley, Robert; Hsu, Guan-Hsong

    1992-09-01

    We describe a method for noise reduction in chaotic systems that is based on projection of the set of points comprising an embedded noisy orbit in openRd toward a finite patchwork of best-fit local approximations to an m-dimensional surface M'⊂openRd, m<=d. We generate the orbits by the delay coordinate construction of Ruelle and Takens [N. H. Packard et al., Phys. Rev. Lett. 45, 712 (1980); F. Takens, in Dynamical Systems and Turbulence, Warwick, 1980, edited by D. A. Rand and L.-S. Young (Springer, Berlin, 1981)] from time series v(t), which in an experimental situation we would assume to have come, together with additional high-dimensional background noise, from an underlying dynamical system ft: M-->M existing on some low m-dimensional manifold M. The surface M' in openRd is the assumed embedded image of M. We give results of systematic studies of linear (tangent plane) projection schemes. We describe in detail the basic algorithm for implementing these schemes. We apply the algorithm iteratively to known map and flow time series to which white noise has been added. In controlled studies, we measure the signal-to-noise ratio improvements, iterating nM times until a stable maximum δM is achieved. We present extensive results for δM and nM for a wide range of values of embedding trial dimension d, projection dimension k, number of nearest-neighbor points for local approximation ν, embedding delay Δ, sampling interval ΔT, initial noise amplitude scrN, and trajectory length N. We give results for very low and very high noise amplitudes 0%<=scrN<=100%. We develop an empirical method for estimating the initial noise level for a given experimental time series, and for the optimal choice of algorithm parameters to achieve peak reduction. We present interesting results of application of the noise-reduction algorithm to a chaotic time series produced from a periodically driven magnetoelastic ribbon experiment on the control of chaos. Two noteworthy elements of the

  19. Full-scale Investigation of Several Jet-engine Noise-reduction Nozzles

    NASA Technical Reports Server (NTRS)

    Coles, Willard D; Callaghan, Edmund E

    1957-01-01

    A number of nozzles which use the mixing interference of adjacent jets for noise suppression were investigated. Reductions in sound power of nearly 70 percent (5 db) with thrust losses of 1 percent were achieved. A method of calculating the limiting frequency affected by this type of suppression nozzle, that is , multiple-slot nozzles, is presented. Data are shown which indicate that further large reductions in sound power are not likely with mixing-interference nozzles.

  20. Noise reduction in multiple-echo data sets using singular value decomposition.

    PubMed

    Bydder, Mark; Du, Jiang

    2006-09-01

    A method is described for denoising multiple-echo data sets using singular value decomposition (SVD). Images are acquired using a multiple gradient- or spin-echo sequence, and the variation of the signal with echo time (TE) in all pixels is subjected to SVD analysis to determine the components of the signal variation. The least significant components are associated with small singular values and tend to characterize the noise variation. Applying a "minimum variance" filter to the singular values suppresses the noise components in a way that optimally approximates the underlying noise-free images. The result is a reduction in noise in the individual TE images with minimal degradation of the spatial resolution and contrast. Phantom and in vivo results are presented.

  1. Noise reduction and estimation in multiple micro-electro-mechanical inertial systems

    NASA Astrophysics Data System (ADS)

    Waegli, Adrian; Skaloud, Jan; Guerrier, Stéphane; Eulàlia Parés, Maria; Colomina, Ismael

    2010-06-01

    This research studies the reduction and the estimation of the noise level within a redundant configuration of low-cost (MEMS-type) inertial measurement units (IMUs). Firstly, independent observations between units and sensors are assumed and the theoretical decrease in the system noise level is analyzed in an experiment with four MEMS-IMU triads. Then, more complex scenarios are presented in which the noise level can vary in time and for each sensor. A statistical method employed for studying the volatility of financial markets (GARCH) is adapted and tested for the usage with inertial data. This paper demonstrates experimentally and through simulations the benefit of direct noise estimation in redundant IMU setups.

  2. In vivo evaluation of mastication noise reduction for dual channel implantable microphone.

    PubMed

    Woo, SeongTak; Jung, EuiSung; Lim, HyungGyu; Lee, Jang Woo; Seong, Ki Woong; Won, Chul Ho; Kim, Myoung Nam; Cho, Jin Ho; Lee, Jyung Hyun

    2014-01-01

    Input for fully implantable hearing devices (FIHDs) is provided by an implantable microphone under the skin of the temporal bone. However, the implanted microphone can be affected when the FIHDs user chews. In this paper, a dual implantable microphone was designed that can filter out the noise from mastication. For the in vivo experiment, a fabricated microphone was implanted in a rabbit. Pure-tone sounds of 1 kHz through a standard speaker were applied to the rabbit, which was given food simultaneously. To evaluate noise reduction, the measured signals were processed using a MATLAB program based adaptive filter. To verify the proposed method, the correlation coefficients and signal to-noise ratio before and after signal processing were calculated. By comparing the results, signal-to-noise ratio and correlation coefficients are enhanced by 6.07dB and 0.529 respectively.

  3. Noise Reduction Potential of Large, Over-the-Wing Mounted, Advanced Turbofan Engines

    NASA Technical Reports Server (NTRS)

    Berton, Jeffrey J.

    2000-01-01

    As we look to the future, increasingly stringent civilian aviation noise regulations will require the design and manufacture of extremely quiet commercial aircraft. Indeed, the noise goal for NASA's Aeronautics Enterprise calls for technologies that will help to provide a 20 EPNdB reduction relative to today's levels by the year 2022. Further, the large fan diameters of modem, increasingly higher bypass ratio engines pose a significant packaging and aircraft installation challenge. One design approach that addresses both of these challenges is to mount the engines above the wing. In addition to allowing the performance trend towards large, ultra high bypass ratio cycles to continue, this over-the-wing design is believed to offer noise shielding benefits to observers on the ground. This paper describes the analytical certification noise predictions of a notional, long haul, commercial quadjet transport with advanced, high bypass engines mounted above the wing.

  4. Evaluation of a Transient Noise Reduction Algorithm in Cochlear Implant Users

    PubMed Central

    Hehrmann, Phillipp; Hamacher, Volkmar; Nogueira, Waldo; Lenarz, Thomas; Büchner, Andreas

    2015-01-01

    Dealing with environmental noises presents a major issue for cochlear implant (CI) users. Hence, digital noise reduction (DNR) schemes have become important features of CI systems. Many noises like for example clinking glasses or slamming doors, have impulsive onsets and decay quickly. Common DNR algorithms cannot handle this type of noise in an appropriate way. In this study, we investigated the effect of an algorithm specially designed for such noises with 12 CI users (age range: 45 to 75 years). Speech scores in noise and quiet as well as subjective ratings of speech clarity, comfort and overall preference were measured. The main finding was a significant improvement of up to 1.7 dB of the speech reception threshold in noise as well as increased speech clarity. Speech in quiet was not negatively affected by the algorithm. The study revealed that the tested algorithm has the potential to improve CI listening. However, further research is needed regarding the effectiveness and suitability of the algorithm in daily use. PMID:26779325

  5. Comparative performance of an adaptive directional microphone system and a multichannel noise reduction system.

    PubMed

    Yuen, Kevin C P; Kam, Anna C S; Lau, Polly S H

    2006-04-01

    The amplification outcomes of two hearing aid prescriptions, NAL-NL1 and Digital Perception Processing (DPP), of nine moderate to moderately severe hearing-impaired adults were compared in the same digital hearing instrument. NAL-NL1 aims at optimizing speech intelligibility while amplifying the speech signal to a normal overall loudness level (Dillon, 1999). DPP focuses on restoring loudness based on normal and impaired cochlear excitation models (Launer and Moore, 2003). In this comparison, DPP resulted in better sentence recognition performance than the NAL-NL1 algorithm in the signal-front/noise-side condition, and the two prescriptions gave similar performance in the signal-front/noise-front condition. Subjective evaluations by the participants using the Abbreviated Profile for Hearing Aid Benefit and sound quality comparisons did not give conclusive results between the two prescriptions. With each hearing aid prescription, the ability of the hearing aid circuitry to reduce the effects of noise was evaluated by a sentence-in-noise test in three conditions: (1) adaptive directional microphone (DAZ), (2) multichannel noise reduction system (FNC), and (3) a combination of FNC and DAZ (FNC + DAZ). In the signal-front/noise-side condition, DAZ and FNC + DAZ gave better performance than FNC in nearly all participants, whereas in the signal-front and noise-front evaluation, the conditions revealed no significant differences.

  6. Reduction of the recorded speckle noise in holographic 3D printer.

    PubMed

    Utsugi, Takeru; Yamaguchi, Masahiro

    2013-01-14

    A holographic 3D printer produces a high-quality 3D image reproduced by a full-color, full-parallax holographic stereogram with high-density light-ray recording. In order to produce a high-resolution holographic stereogram, we have to solve the problem of speckle noise in this system. For equalizing an intensity distribution inside the elementary hologram, the object beam is modulated by a diffuser. However the diffuser typically generates speckles, which is recorded in the holographic stereogram. It is localized behind the reconstructed image as a granularity noise. First we show the problems of some conventional ways for suppressing the granularity noise using a band-limited diffuser, and then we analyze an approach using a moving diffuser for the reduction of this noise. In the result, it is found that recording with a moving diffuser is effective for reducing the granularity noise at infinity of reconstructed image, although an alternative noise occurs. Moreover we propose a new method introducing multiple exposures to suppress the noise effectively.

  7. Intelligent background noise reduction technology in cable fault locator using the magneto-acoustic synchronous method

    NASA Astrophysics Data System (ADS)

    Mi, JianWei; Huang, JiFa; Fang, XiaoLi; Fan, LiBin

    2017-01-01

    The magneto-acoustic synchronous method has found wide application in accurate positioning of power cable fault due to its advantages of high accuracy and strong ability to reject interference. In the view of principle, the magneto-acoustic synchronous method needs to detect the discharge sound signal and electromagnetic signal emitted from the fault point, but the discharge sound signal is easy to be interfered by the ambient noise around and the magnetic sound synchronization. Therefore, it is challenging to quickly and accurately detect the fault location of cable especially in strong background noise environment. On the other hand, the spectral subtraction is a relatively traditional and effective method in many intelligent background noise reduction technologies, which is characterized by a relatively small computational cost and strong real-time performance. However, its application is limited because the algorithm displays poor performance in low Signal to Noise Ratio (SNR) environment. Aiming at the shortcoming of the spectral subtraction that de-noising effect is weak in low SNR environment, this paper proposes an improved spectral subtraction combining the magnetic sound synchronous principle and analyzing the properties of discharging sound. This method can accurately estimate noise in real time and optimize the performance of the basic spectral subtraction thus solving the problem that the magneto-acoustic synchronous method is unsatisfactory for positioning cable fault in the strong background noise environment.

  8. Cabin noise and weight reduction program for the Gulfstream G200

    NASA Astrophysics Data System (ADS)

    Barton, C. Kearney

    2002-11-01

    This paper describes the approach and logic involved in a cabin noise and weight reduction program for an existing aircraft that was already in service with a pre-existing insulation package. The aircraft, a Gulfstream G200, was formally an IAI Galaxy, and the program was purchased from IAI in 2001. The approach was to investigate every aspect of the aircraft that could be a factor for cabin noise. This included such items as engine mounting and balancing criteria, the hydraulic system, the pressurization and air-conditioning system, the outflow valve, the interior shell and mounting system, antennae and other hull protuberances, as well as the insulation package. Each of these items was evaluated as potential candidates for noise and weight control modifications. Although the program is still ongoing, the results to date include a 175-lb weight savings and a 5-dB reduction in the cabin average Speech Interference Level (SIL).

  9. Gabor-based anisotropic diffusion for speckle noise reduction in medical ultrasonography.

    PubMed

    Zhang, Qi; Han, Hong; Ji, Chunhong; Yu, Jinhua; Wang, Yuanyuan; Wang, Wenping

    2014-06-01

    In ultrasound (US), optical coherence tomography, synthetic aperture radar, and other coherent imaging systems, images are corrupted by multiplicative speckle noise that obscures image interpretation. An anisotropic diffusion (AD) method based on the Gabor transform, named Gabor-based anisotropic diffusion (GAD), is presented to suppress speckle in medical ultrasonography. First, an edge detector using the Gabor transform is proposed to capture directionality of tissue edges and discriminate edges from noise. Then the edge detector is embedded into the partial differential equation of AD to guide the diffusion process and iteratively denoise images. To enhance GAD's adaptability, parameters controlling diffusion are determined from a fully formed speckle region that is automatically detected. We evaluate the GAD on synthetic US images simulated with three models and clinical images acquired in vivo. Compared with seven existing speckle reduction methods, the GAD is superior to other methods in terms of noise reduction and detail preservation.

  10. An experimental study of USB flap noise reduction through mean flow modification. [Upper Surface Blown

    NASA Technical Reports Server (NTRS)

    Joshi, M. C.; Yu, J. C.

    1979-01-01

    The effect of mean flow modification on the noise production of upper surface blown flaps has been studied experimentally. Mean velocity profile at the nozzle exit was modified from the usual 'top-hat' shape to 'Gamma' and 'L'-shaped profiles. The 'L'-modification caused noise reduction around and above the peak frequency of the 'top-hat' spectrum when compared on an equal thrust per exit area basis. Modification to 'Gamma'-shaped profile resulted in a shift of the spectrum to lower frequencies and a lower overall noise reduction. These modifications alter the development of the large scale disturbances in the upper shear layer and trailing edge wake of the wall jet geometry.

  11. Speckle noise reduction in high speed polarization sensitive spectral domain optical coherence tomography

    PubMed Central

    Götzinger, Erich; Pircher, Michael; Baumann, Bernhard; Schmoll, Tilman; Sattmann, Harald; Leitgeb, Rainer A.; Hitzenberger, Christoph K.

    2015-01-01

    We present a high speed polarization sensitive spectral domain optical coherence tomography system based on polarization maintaining fibers and two high speed CMOS line scan cameras capable of retinal imaging with up to 128 k A-lines/s. This high imaging speed strongly reduces motion artifacts and therefore averaging of several B-scans is possible, which strongly reduces speckle noise and improves image quality. We present several methods for averaging retardation and optic axis orientation, the best one providing a 5 fold noise reduction. Furthermore, a novel scheme of calculating images of degree of polarization uniformity is presented. We quantitatively compare the noise reduction depending on the number of averaged frames and discuss the limits of frame numbers that can usefully be averaged. PMID:21934820

  12. Reduction of high-speed impulsive noise by blade planform modification of a model helicopter rotor

    NASA Technical Reports Server (NTRS)

    Conner, D. A.; Hoad, D. R.

    1982-01-01

    The reduction of high speed impulsive noise for the UH-1H helicopter was investigated by using an advanced main rotor system. The advanced rotor system had a tapered blade planform compared with the rectangular planform of the standard rotor system. Models of both the advanced main rotor system and the UH-1H standard main rotor system were tested at 1/4 scale in the 4 by 7 Meter Tunnel. In plane acoustic measurements of the high speed impulsive noise demonstrated that the advanced rotor system on the UH-1H helicopter reduced the high speed impulsive noise by up to 20 dB, with a reduction in overall sound pressure level of up to 5 dB.

  13. Children's Performance in Complex Listening Conditions: Effects of Hearing Loss and Digital Noise Reduction

    ERIC Educational Resources Information Center

    Pittman, Andrea

    2011-01-01

    Purpose: To determine the effect of hearing loss (HL) on children's performance for an auditory task under demanding listening conditions and to determine the effect of digital noise reduction (DNR) on that performance. Method: Fifty children with normal hearing (NH) and 30 children with HL (8-12 years of age) categorized words in the presence of…

  14. Children's Performance in Complex Listening Conditions: Effects of Hearing Loss and Digital Noise Reduction

    ERIC Educational Resources Information Center

    Pittman, Andrea

    2011-01-01

    Purpose: To determine the effect of hearing loss (HL) on children's performance for an auditory task under demanding listening conditions and to determine the effect of digital noise reduction (DNR) on that performance. Method: Fifty children with normal hearing (NH) and 30 children with HL (8-12 years of age) categorized words in the presence of…

  15. TEM Cell Testing of Cable Noise Reduction Techniques from 2 MHz to 200 MHz -- Part 2

    NASA Technical Reports Server (NTRS)

    Bradley, Arthur T.; Evans, William C.; Reed, Joshua L.; Shimp, Samuel K., III; Fitzpatrick, Fred D.

    2008-01-01

    This paper presents empirical results of cable noise reduction techniques as demonstrated in a TEM cell operating with radiated fields from 2 - 200 MHz. It is the second part of a two-paper series. The first paper discussed cable types and shield connections. In this second paper, the effects of load and source resistances and chassis connections are examined. For each topic, well established theories are compared to data from a real-world physical system. Finally, recommendations for minimizing cable susceptibility (and thus cable emissions) are presented. There are numerous papers and textbooks that present theoretical analyses of cable noise reduction techniques. However, empirical data is often targeted to low frequencies (e.g. <50 KHz) or high frequencies (>100 MHz). Additionally, a comprehensive study showing the relative effects of various noise reduction techniques is needed. These include the use of dedicated return wires, twisted wiring, cable shielding, shield connections, changing load or source impedances, and implementing load- or source-to-chassis isolation. We have created an experimental setup that emulates a real-world electrical system, while still allowing us to independently vary a host of parameters. The goal of the experiment was to determine the relative effectiveness of various noise reduction techniques when the cable is in the presence of radiated emissions from 2 MHz to 200 MHz.

  16. TH-A-18C-03: Noise Correlation in CBCT Projection Data and Its Application for Noise Reduction in Low-Dose CBCT

    SciTech Connect

    ZHANG, H; Huang, J; Ma, J; Chen, W; Ouyang, L; Wang, J

    2014-06-15

    Purpose: To study the noise correlation properties of cone-beam CT (CBCT) projection data and to incorporate the noise correlation information to a statistics-based projection restoration algorithm for noise reduction in low-dose CBCT. Methods: In this study, we systematically investigated the noise correlation properties among detector bins of CBCT projection data by analyzing repeated projection measurements. The measurements were performed on a TrueBeam on-board CBCT imaging system with a 4030CB flat panel detector. An anthropomorphic male pelvis phantom was used to acquire 500 repeated projection data at six different dose levels from 0.1 mAs to 1.6 mAs per projection at three fixed angles. To minimize the influence of the lag effect, lag correction was performed on the consecutively acquired projection data. The noise correlation coefficient between detector bin pairs was calculated from the corrected projection data. The noise correlation among CBCT projection data was then incorporated into the covariance matrix of the penalized weighted least-squares (PWLS) criterion for noise reduction of low-dose CBCT. Results: The analyses of the repeated measurements show that noise correlation coefficients are non-zero between the nearest neighboring bins of CBCT projection data. The average noise correlation coefficients for the first- and second- order neighbors are about 0.20 and 0.06, respectively. The noise correlation coefficients are independent of the dose level. Reconstruction of the pelvis phantom shows that the PWLS criterion with consideration of noise correlation (PWLS-Cor) results in a lower noise level as compared to the PWLS criterion without considering the noise correlation (PWLS-Dia) at the matched resolution. Conclusion: Noise is correlated among nearest neighboring detector bins of CBCT projection data. An accurate noise model of CBCT projection data can improve the performance of the statistics-based projection restoration algorithm for low

  17. Reduction of ground noise in the transmitter crowbar instrumentation system by the use of baluns and other noise rejection methods

    NASA Technical Reports Server (NTRS)

    Daeges, J.; Bhanji, A.

    1987-01-01

    Electrical noise interference in the transmitter crowbar monitoring instrumentation system creates false sensing of crowbar faults during a crowbar firing. One predominant source of noise interference is the conduction of currents in the instrumentation cable shields. Since these circulating ground noise currents produce noise that is similar to the crowbar fault sensing signals, such noise interference reduces the ability to determine true crowbar faults.

  18. Direct-to-digital holography reduction of reference hologram noise and fourier space smearing

    DOEpatents

    Voelkl, Edgar

    2006-06-27

    Systems and methods are described for reduction of reference hologram noise and reduction of Fourier space smearing, especially in the context of direct-to-digital holography (off-axis interferometry). A method of reducing reference hologram noise includes: recording a plurality of reference holograms; processing the plurality of reference holograms into a corresponding plurality of reference image waves; and transforming the corresponding plurality of reference image waves into a reduced noise reference image wave. A method of reducing smearing in Fourier space includes: recording a plurality of reference holograms; processing the plurality of reference holograms into a corresponding plurality of reference complex image waves; transforming the corresponding plurality of reference image waves into a reduced noise reference complex image wave; recording a hologram of an object; processing the hologram of the object into an object complex image wave; and dividing the complex image wave of the object by the reduced noise reference complex image wave to obtain a reduced smearing object complex image wave.

  19. A comparative intelligibility study of single-microphone noise reduction algorithms.

    PubMed

    Hu, Yi; Loizou, Philipos C

    2007-09-01

    The evaluation of intelligibility of noise reduction algorithms is reported. IEEE sentences and consonants were corrupted by four types of noise including babble, car, street and train at two signal-to-noise ratio levels (0 and 5 dB), and then processed by eight speech enhancement methods encompassing four classes of algorithms: spectral subtractive, sub-space, statistical model based and Wiener-type algorithms. The enhanced speech was presented to normal-hearing listeners for identification. With the exception of a single noise condition, no algorithm produced significant improvements in speech intelligibility. Information transmission analysis of the consonant confusion matrices indicated that no algorithm improved significantly the place feature score, significantly, which is critically important for speech recognition. The algorithms which were found in previous studies to perform the best in terms of overall quality, were not the same algorithms that performed the best in terms of speech intelligibility. The subspace algorithm, for instance, was previously found to perform the worst in terms of overall quality, but performed well in the present study in terms of preserving speech intelligibility. Overall, the analysis of consonant confusion matrices suggests that in order for noise reduction algorithms to improve speech intelligibility, they need to improve the place and manner feature scores.

  20. Experimental investigation of the noise reduction of supersonic exhaust jets with fluidic inserts

    NASA Astrophysics Data System (ADS)

    Powers, Russell William Walter

    The noise produced by the supersonic, high temperature jets that exhaust from military aircraft is becoming a hazard to naval personnel and a disturbance to communities near military bases. Methods to reduce the noise produced from these jets in a practical full-scale environment are difficult. The development and analysis of distributed nozzle blowing for the reduction of radiated noise from supersonic jets is described. Model scale experiments of jets that simulate the exhaust jets from typical low-bypass ratio military jet aircraft engines during takeoff are performed. Fluidic inserts are created that use distributed blowing in the divergent section of the nozzle to simulate mechanical, hardwall corrugations, while having the advantage of being an active control method. This research focuses on model scale experiments to better understand the fluidic insert noise reduction method. Distributed blowing within the divergent section of the military-style convergent divergent nozzle alters the shock structure of the jet in addition to creating streamwise vorticity for the reduction of mixing noise. Enhancements to the fluidic insert design have been performed along with experiments over a large number of injection parameters and core jet conditions. Primarily military-style round nozzles have been used, with preliminary measurements of hardwall corrugations and fluidic inserts in rectangular nozzle geometries also performed. It has been shown that the noise reduction of the fluidic inserts is most heavily dependent upon the momentum flux ratio between the injector and core jet. Maximum reductions of approximately 5.5 dB OASPL have been observed with practical mass flow rates and injection pressures. The first measurements with fluidic inserts in the presence of a forward flight stream have been performed. Optimal noise reduction occurs at similar injector parameters in the presence of forward flight. Fluidic inserts in the presence of a forward flight stream were

  1. Detection threshold for sound distortion resulting from noise reduction in normal-hearing and hearing-impaired listeners.

    PubMed

    Brons, Inge; Dreschler, Wouter A; Houben, Rolph

    2014-09-01

    Hearing-aid noise reduction should reduce background noise, but not disturb the target speech. This objective is difficult because noise reduction suffers from a trade-off between the amount of noise removed and signal distortion. It is unknown if this important trade-off differs between normal-hearing (NH) and hearing-impaired (HI) listeners. This study separated the negative effect of noise reduction (distortion) from the positive effect (reduction of noise) to allow the measurement of the detection threshold for noise-reduction (NR) distortion. Twelve NH subjects and 12 subjects with mild to moderate sensorineural hearing loss participated in this study. The detection thresholds for distortion were determined using an adaptive procedure with a three-interval, two-alternative forced-choice paradigm. Different levels of distortion were obtained by changing the maximum amount of noise reduction. Participants were also asked to indicate their preferred NR strength. The detection threshold for overall distortion was higher for HI subjects than for NH subjects, suggesting that stronger noise reduction can be applied for HI listeners without affecting the perceived sound quality. However, the preferred NR strength of HI listeners was closer to their individual detection threshold for distortion than in NH listeners. This implies that HI listeners tolerate fewer audible distortions than NH listeners.

  2. Acoustic noise reduction in MRI using Silent Scan: an initial experience.

    PubMed

    Alibek, Sedat; Vogel, Mika; Sun, Wei; Winkler, David; Baker, Christopher A; Burke, Michael; Gloger, Hubertus

    2014-01-01

    Acoustic noise during magnetic resonance imaging (MRI) is the main source for patient discomfort and leads to verbal communication problems, difficulties in sedation, and hearing impairment. Silent Scan technology uses less changes in gradient excitation levels, which is directly related to noise levels. Here, we report our preliminary experience with this technique in neuroimaging with regard to subjective and objective noise levels and image quality. Ten patients underwent routine brain MRI with 3 Tesla MR750w system and 12-channel head coil. T1-weighted gradient echo (BRAVO) and Silenz pulse sequence (TE=0, 3D radial center-out k-space filling and data sampling with relatively small gradient steps) were performed. Patients rated subjective sound impression for both sequences on a 6-point scale. Objective sound level measurements were performed with a dedicated device in gantry at different operation modes. Image quality was subjectively assessed in consensus by two radiologists on a 3-point scale. Readers rated image quality as fully diagnostic in all patients. Measured mean noise was reduced significantly with Silenz sequence (68.8 dB vs. 104.65 dB with BRAVO, P = 0.024) corresponding to 34.3% reduction in sound intensity and 99,97% reduction in sound pressure. No significant difference was observed between Silenz sound levels and ambient sounds (i.e., background noise in the scanner room, 68.8 dB vs. 68.73 dB, P = 0.5). The patients' subjective sound level score was lower for Silenz compared with conventional sequence (1.1 vs. 2.3, P = 0.003). T1-weighted Silent Scan is a promising technique for acoustic noise reduction and improved patient comfort.

  3. Development of a SMA-Based, Slat-Gap Filler for Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Turner, Travis L.; Long, David L.

    2015-01-01

    Noise produced by unsteady flow around aircraft structures, termed airframe noise, is an important source of aircraft noise during the approach and landing phases of flight. Conventional leading-edge-slat devices for high lift on typical transport aircraft are a prominent source of airframe noise. Many concepts for slat noise reduction have been investigated. Slat-cove fillers have emerged as an attractive solution, but they maintain the gap flow, leaving some noise production mechanisms unabated, and thus represent a nonoptimal solution. Drooped-leading-edge (DLE) concepts have been proposed as "optimal" because the gap flow is eliminated. The deployed leading edge device is not distinct and separate from the main wing in DLE concepts and the high-lift performance suffers at high angles of attack (alpha) as a consequence. Elusive high-alpha performance and excessive weight penalty have stymied DLE development. The fact that high-lift performance of DLE systems is only affected at high alpha suggests another concept that simultaneously achieves the high-lift of the baseline airfoil and the noise reduction of DLE concepts. The concept involves utilizing a conventional leading-edge slat device and a deformable structure that is deployed from the leading edge of the main wing and closes the gap between the slat and main wing, termed a slat-gap filler (SGF). The deployable structure consists of a portion of the skin of the main wing and it is driven in conjunction with the slat during deployment and retraction. Benchtop models have been developed to assess the feasibility and to study important parameters. Computational models have assisted in the bench-top model design and provided valuable insight in the parameter space as well as the feasibility.

  4. Evaluation of Airframe Noise Reduction Concepts via Simulations Using a Lattice Boltzmann Approach

    NASA Technical Reports Server (NTRS)

    Fares, Ehab; Casalino, Damiano; Khorrami, Mehdi R.

    2015-01-01

    Unsteady computations are presented for a high-fidelity, 18% scale, semi-span Gulfstream aircraft model in landing configuration, i.e. flap deflected at 39 degree and main landing gear deployed. The simulations employ the lattice Boltzmann solver PowerFLOW® to simultaneously capture the flow physics and acoustics in the near field. Sound propagation to the far field is obtained using a Ffowcs Williams and Hawkings acoustic analogy approach. In addition to the baseline geometry, which was presented previously, various noise reduction concepts for the flap and main landing gear are simulated. In particular, care is taken to fully resolve the complex geometrical details associated with these concepts in order to capture the resulting intricate local flow field thus enabling accurate prediction of their acoustic behavior. To determine aeroacoustic performance, the farfield noise predicted with the concepts applied is compared to high-fidelity simulations of the untreated baseline configurations. To assess the accuracy of the computed results, the aerodynamic and aeroacoustic impact of the noise reduction concepts is evaluated numerically and compared to experimental results for the same model. The trends and effectiveness of the simulated noise reduction concepts compare well with measured values and demonstrate that the computational approach is capable of capturing the primary effects of the acoustic treatment on a full aircraft model.

  5. Measured noise reductions resulting from modified approach procedures for business jet aircraft

    NASA Technical Reports Server (NTRS)

    Burcham, F. W., Jr.; Putnam, T. W.; Lasagna, P. L.; Parish, O. O.

    1975-01-01

    Five business jet airplanes were flown to determine the noise reductions that result from the use of modified approach procedures. The airplanes tested were a Gulfstream 2, JetStar, Hawker Siddeley 125-400, Sabreliner-60 and LearJet-24. Noise measurements were made 3, 5, and 7 nautical miles from the touchdown point. In addition to a standard 3 deg glide slope approach, a 4 deg glide slope approach, a 3 deg glide slope approach in a low-drag configuration, and a two-segment approach were flown. It was found that the 4 deg approach was about 4 EPNdB quieter than the standard 3 deg approach. Noise reductions for the low-drag 3 deg approach varied widely among the airplanes tested, with an average of 8.5 EPNdB on a fleet-weighted basis. The two-segment approach resulted in noise reductions of 7 to 8 EPNdB at 3 and 5 nautical miles from touchdown, but only 3 EPNdB at 7 nautical miles from touchdown when the airplanes were still in level flight prior to glide slope intercept. Pilot ratings showed progressively increasing workload for the 4 deg, low-drag 3 deg, and two-segment approaches.

  6. Method for inserting noise in digital mammography to simulate reduction in radiation dose

    NASA Astrophysics Data System (ADS)

    Borges, Lucas R.; de Oliveira, Helder C. R.; Nunes, Polyana F.; Vieira, Marcelo A. C.

    2015-03-01

    The quality of clinical x-ray images is closely related to the radiation dose used in the imaging study. The general principle for selecting the radiation is ALARA ("as low as reasonably achievable"). The practical optimization, however, remains challenging. It is well known that reducing the radiation dose increases the quantum noise, which could compromise the image quality. In order to conduct studies about dose reduction in mammography, it would be necessary to acquire repeated clinical images, from the same patient, with different dose levels. However, such practice would be unethical due to radiation related risks. One solution is to simulate the effects of dose reduction in clinical images. This work proposes a new method, based on the Anscombe transformation, which simulates dose reduction in digital mammography by inserting quantum noise into clinical mammograms acquired with the standard radiation dose. Thus, it is possible to simulate different levels of radiation doses without exposing the patient to new levels of radiation. Results showed that the achieved quality of simulated images generated with our method is the same as when using other methods found in the literature, with the novelty of using the Anscombe transformation for converting signal-independent Gaussian noise into signal-dependent quantum noise.

  7. Assessing the Role of Effort Reduction in the Reinforcing Efficacy of Timeout from Avoidance

    ERIC Educational Resources Information Center

    Galuska, Chad M.; Mikorski, Jeff; Perone, Michael

    2012-01-01

    Rats responded on concurrent schedules of shock-postponement or deletion (avoidance) and timeout from avoidance. In Experiment 1, 3 rats' responses on one lever postponed shocks for 20 s and responses on a second lever produced a 1-min timeout according to a variable-interval 45-s schedule. Across conditions, a warning signal (white noise) was…

  8. Assessing the Role of Effort Reduction in the Reinforcing Efficacy of Timeout from Avoidance

    ERIC Educational Resources Information Center

    Galuska, Chad M.; Mikorski, Jeff; Perone, Michael

    2012-01-01

    Rats responded on concurrent schedules of shock-postponement or deletion (avoidance) and timeout from avoidance. In Experiment 1, 3 rats' responses on one lever postponed shocks for 20 s and responses on a second lever produced a 1-min timeout according to a variable-interval 45-s schedule. Across conditions, a warning signal (white noise) was…

  9. Clutter noise reduction for phased array imaging using frequency-spatial polarity coherence

    NASA Astrophysics Data System (ADS)

    Gongzhang, Rui; Gachagan, Anthony; Xiao, Bo

    2015-03-01

    A number of materials used in industry exhibit highly-scattering properties which can reduce the performance of conventional ultrasonic NDE approaches. Moving Bandwidth Polarity Thresholding (MBPT) is a robust frequency diversity based algorithm for scatter noise reduction in single A-scan waveforms, using sign coherence across a range of frequency bands to reduce grain noise and improve Signal to Noise Ratio. Importantly, for this approach to be extended to array applications, spatial variation of noise characteristics must also be considered. This paper presents a new spatial-frequency diversity based algorithm for array imaging, extended from MBPT. Each A-scan in the full matrix capture array dataset is partitioned into a serial of overlapped frequency bands and then undergoes polarity thresholding to generate sign-only coefficients indicating possible flaw locations within each selected band. These coefficients are synthesized to form a coefficient matrix using a delay and sum approach in each frequency band. Matrices produced across the frequency bands are then summed to generate a weighting matrix, which can be applied on any conventional image. A 5MHz linear array has been used to acquire data from both austenitic steel and high nickel alloy (HNA) samples to validate the proposed algorithm. Background noise is significantly suppressed for both samples after applying this approach. Importantly, three side drilled holes and the back wall of the HNA sample are clearly enhanced in the processed image, with a mean 133% Contrast to Noise Ratio improvement when compared to a conventional TFM image.

  10. Improvements to local projective noise reduction through higher order and multiscale refinements.

    PubMed

    Moore, Jack Murdoch; Small, Michael; Karrech, Ali

    2015-06-01

    The broad spectrum characteristic of signals from nonlinear systems obstructs noise reduction techniques developed for linear systems. Local projection was developed to reduce noise while preserving nonlinear deterministic structures, and a second order refinement to local projection which was proposed ten years ago does so particularly effectively. It involves adjusting the origin of the projection subspace to better accommodate the geometry of the attractor. This paper describes an analytic motivation for the enhancement from which follows further higher order and multiple scale refinements. However, the established enhancement is frequently as or more effective than the new filters arising from solely geometric considerations. Investigation of the way that measurement errors reinforce or cancel throughout the refined local projection procedure explains the special efficacy of the existing enhancement, and leads to a new second order refinement offering widespread gains. Different local projective filters are found to be best suited to different noise levels. At low noise levels, the optimal order increases as noise increases. At intermediate levels second order tends to be optimal, while at high noise levels prototypical local projection is most effective. The new higher order filters perform better relative to established filters for longer signals or signals corresponding to higher dimensional attractors.

  11. Engine isolation for structural-borne interior noise reduction in a general aviation aircraft

    NASA Technical Reports Server (NTRS)

    Unruh, J. F.; Scheidt, D. C.

    1981-01-01

    Engine vibration isolation for structural-borne interior noise reduction is investigated. A laboratory based test procedure to simulate engine induced structure-borne noise transmission, the testing of a range of candidate isolators for relative performance data, and the development of an analytical model of the transmission phenomena for isolator design evaluation are addressed. The isolator relative performance test data show that the elastomeric isolators do not appear to operate as single degree of freedom systems with respect to noise isolation. Noise isolation beyond 150 Hz levels off and begins to decrease somewhat above 600 Hz. Coupled analytical and empirical models were used to study the structure-borne noise transmission phenomena. Correlation of predicted results with measured data show that (1) the modeling procedures are reasonably accurate for isolator design evaluation, (2) the frequency dependent properties of the isolators must be included in the model if reasonably accurate noise prediction beyond 150 Hz is desired. The experimental and analytical studies were carried out in the frequency range from 10 Hz to 1000 Hz.

  12. Noise-Reduction Benefits Analyzed for Over-the-Wing-Mounted Advanced Turbofan Engines

    NASA Technical Reports Server (NTRS)

    Berton, Jeffrey J.

    2000-01-01

    As we look to the future, increasingly stringent civilian aviation noise regulations will require the design and manufacture of extremely quiet commercial aircraft. Also, the large fan diameters of modern engines with increasingly higher bypass ratios pose significant packaging and aircraft installation challenges. One design approach that addresses both of these challenges is to mount the engines above the wing. In addition to allowing the performance trend towards large diameters and high bypass ratio cycles to continue, this approach allows the wing to shield much of the engine noise from people on the ground. The Propulsion Systems Analysis Office at the NASA Glenn Research Center at Lewis Field conducted independent analytical research to estimate the noise reduction potential of mounting advanced turbofan engines above the wing. Certification noise predictions were made for a notional long-haul commercial quadjet transport. A large quad was chosen because, even under current regulations, such aircraft sometimes experience difficulty in complying with certification noise requirements with a substantial margin. Also, because of its long wing chords, a large airplane would receive the greatest advantage of any noise-shielding benefit.

  13. Anthropogenic noise is associated with reductions in the productivity of breeding Eastern Bluebirds (Sialia sialis).

    PubMed

    Kight, Caitlin R; Saha, Margaret S; Swaddle, John P

    2012-10-01

    Although previous studies have related variations in environmental noise levels with alterations in communication behaviors of birds, little work has investigated the potential long-term implications of living or breeding in noisy habitats. However, noise has the potential to reduce fitness, both directly (because it is a physiological stressor) and indirectly (by masking important vocalizations and/or leading to behavioral changes). Here, we quantified acoustic conditions in active breeding territories of male Eastern Bluebirds (Sialia sialis). Simultaneously, we measured four fitness indicators: cuckoldry rates, brood growth rate and condition, and number of fledglings produced (i.e., productivity). Increases in environmental noise tended to be associated with smaller brood sizes and were more strongly related to reductions in productivity. Although the mechanism responsible for these patterns is not yet clear, the breeding depression experienced by this otherwise disturbance-tolerant species indicates that anthropogenic noise may have damaging effects on individual fitness and, by extraction, the persistence of populations in noisy habitats. We suggest that managers might protect avian residents from potentially harmful noise by keeping acoustically dominant anthropogenic habitat features as far as possible from favored songbird breeding habitats, limiting noisy human activities, and/or altering habitat structure in order to minimize the propagation of noise pollution.

  14. Reduction of Return Current Noise Using Double-Series Resonant Filter

    NASA Astrophysics Data System (ADS)

    Azuma, Satoshi; Itoh, Daisuke; Sugahara, Kengo

    A novel double-series resonant filter is implemented in order to reduce the high-frequency return current noise generated by AC-powered electric cars with AC/DC PWM converters and inverters. The double-series resonant filter is placed between a main transformer and a converter. The resonant filter is tuned so that the noise signal due to the return current is attenuated at the exact noise frequency; for example, the 105-kHz component of an ATS (Automatic Train Stop) signal is attenuated by this filter. The filter has two LCR resonant circuits, one of which is in parallel with a resistance. This filter design helps achieve good attenuation at the noise frequency and helps limit unnecessary amplification at other frequencies. First, a test filter is realized, and the inductance and capacitance of this filter are in good agreement with the corresponding values in the filter design. Then, the filter is included in a full-scale test system with a main transformer and a converter. Then it is confirmed that a 5-dB reduction in the return current noise is achieved by using the proposed filter. Finally, the return current noise in the test system is confirmed to be well below the desired regulation level. This is expected to help realize simple methods for dealing with the effects of impedance at high frequencies in the main transformer.

  15. Improvements to local projective noise reduction through higher order and multiscale refinements

    NASA Astrophysics Data System (ADS)

    Moore, Jack Murdoch; Small, Michael; Karrech, Ali

    2015-06-01

    The broad spectrum characteristic of signals from nonlinear systems obstructs noise reduction techniques developed for linear systems. Local projection was developed to reduce noise while preserving nonlinear deterministic structures, and a second order refinement to local projection which was proposed ten years ago does so particularly effectively. It involves adjusting the origin of the projection subspace to better accommodate the geometry of the attractor. This paper describes an analytic motivation for the enhancement from which follows further higher order and multiple scale refinements. However, the established enhancement is frequently as or more effective than the new filters arising from solely geometric considerations. Investigation of the way that measurement errors reinforce or cancel throughout the refined local projection procedure explains the special efficacy of the existing enhancement, and leads to a new second order refinement offering widespread gains. Different local projective filters are found to be best suited to different noise levels. At low noise levels, the optimal order increases as noise increases. At intermediate levels second order tends to be optimal, while at high noise levels prototypical local projection is most effective. The new higher order filters perform better relative to established filters for longer signals or signals corresponding to higher dimensional attractors.

  16. Bulk Current Injection Testing of Cable Noise Reduction Techniques, 50 kHz to 400 MHz

    NASA Technical Reports Server (NTRS)

    Bradley, Arthur T.; Hare, Richard J.; Singh, Manisha

    2009-01-01

    This paper presents empirical results of cable noise reduction techniques as demonstrated using bulk current injection (BCI) techniques with radiated fields from 50 kHz - 400 MHz. It is a follow up to the two-part paper series presented at the Asia Pacific EMC Conference that focused on TEM cell signal injection. This paper discusses the effects of cable types, shield connections, and chassis connections on cable noise. For each topic, well established theories are compared with data from a real-world physical system.

  17. Phase noise reduction of a semiconductor laser in a composite optical phase-locked loop

    NASA Astrophysics Data System (ADS)

    Satyan, Naresh; Sendowski, Jacob; Vasilyev, Arseny; Rakuljic, George; Yariv, Amnon

    2010-12-01

    The bandwidth and residual phase noise of optical phase-locked loops (OPLLs) using semiconductor lasers are typically constrained by the nonuniform frequency modulation response of the laser, limiting their usefulness in a number of applications. It is shown in this work that additional feedback control using an optical phase modulator improves the coherence between the master and slave lasers in the OPLL by achieving bandwidths determined only by the propagation delay in the loop. A phase noise reduction by more than a factor of two is demonstrated in a proof-of-concept experiment using a commercial distributed feedback semiconductor laser.

  18. Median Filter Noise Reduction of Image and Backpropagation Neural Network Model for Cervical Cancer Classification

    NASA Astrophysics Data System (ADS)

    Wutsqa, D. U.; Marwah, M.

    2017-06-01

    In this paper, we consider spatial operation median filter to reduce the noise in the cervical images yielded by colposcopy tool. The backpropagation neural network (BPNN) model is applied to the colposcopy images to classify cervical cancer. The classification process requires an image extraction by using a gray level co-occurrence matrix (GLCM) method to obtain image features that are used as inputs of BPNN model. The advantage of noise reduction is evaluated by comparing the performances of BPNN models with and without spatial operation median filter. The experimental result shows that the spatial operation median filter can improve the accuracy of the BPNN model for cervical cancer classification.

  19. Acoustic noise reduction. January 1970-November 1988 (Citations from the US Patent data base). Report for January 1970-November 1988

    SciTech Connect

    Not Available

    1988-12-01

    This bibliography contains citations of selected patents concerning methods, devices, and materials for acoustic-noise reduction. Included are noise-reduction techniques for engines, turbines, machinery, motor vehicles, pumps, aircraft cabins, and compressors. (Contains 189 citations fully indexed and including a title list.)

  20. Initial results of a model rotor higher harmonic control (HHC) wind tunnel experiment on BVI impulsive noise reduction

    NASA Astrophysics Data System (ADS)

    Splettstoesser, W. R.; Lehmann, G.; van der Wall, B.

    1989-09-01

    Initial acoustic results are presented from a higher harmonic control (HHC) wind tunnel pilot experiment on helicopter rotor blade-vortex interaction (BVI) impulsive noise reduction, making use of the DFVLR 40-percent-scaled BO-105 research rotor in the DNW 6m by 8m closed test section. Considerable noise reduction (of several decibels) has been measured for particular HHC control settings, however, at the cost of increased vibration levels and vice versa. The apparently adverse results for noise and vibration reduction by HHC are explained. At optimum pitch control settings for BVI noise reduction, rotor simulation results demonstrate that blade loading at the outer tip region is decreased, vortex strength and blade vortex miss-distance are increased, resulting altogether in reduced BVI noise generation. At optimum pitch control settings for vibration reduction adverse effects on blade loading, vortex strength and blade vortex miss-distance are found.