The goal of this paper is to study and propose a new technique for noise reduction used during the reconstruction of speech signals, particularly for biomedical applications. The proposed method is based on Kalman filtering in the time domain combined with spectral subtraction. Comparison with discrete Kalman filter in the frequency domain shows better performance of the proposed technique. The performance is evaluated by using the segmental signal-to-noise ratio and the Itakura-Saito`s distance. Results have shown that Kalman`s filter in time combined with spectral subtraction is more robust and efficient, improving the Itakura-Saito`s distance by up to four times. (C) 2007 Elsevier Ltd. All rights reserved.

O ruído acústico produzido pelos transformadores elétricos de potência, instalados em áreas urbanas, gera problemas ambientais e desconforto na população vizinha. Neste trabalho propõe-se desenvolver uma metodologia de projeto para reduzir o ruído dos transformadores com o objetivo de atingir níveis de ruído que a legislação ambiental exige. Um transformador elétrico de potência contém um núcleo, no qual encontram-se as bobinas, dentro de um tanque, ao ativar-se o núcleo e a bobina produz ruído e vibração em todos os componentes do transformador. Para diminuir a vibração e o ruído propõe-se o uso de Absorvedores Dinâmicos (AD) fixados nas paredes do tanque, e amortecedores automotivos ligados à base do tanque. Com os amortecedores procura-se atenuar os deslocamentos da base do tanque impostos pelo núcleo. Este procedimento, isoladamente, diminui a vibração da base do tanque e das paredes do tanque. Adicionalmente, utilizando absorvedores dinâmicos de vibração, projetados e alocados de acordo com resultados de simulações numéricas, é possível reduzir a amplitude de vibração das paredes do tanque. A redução de amplitude de vibração das paredes do tanque leva necessariamente a uma redução do ruído acústico...

This papers reviews the main studies on traffic management and analyzes the numeric noise results of several current options. It was found that between speed cushions or humps the noise reduction is about 1 to 2 dB(A) but there is an increase of 2 to 3 dB(A) (depending on vehicle and hump types) and annoyance (harsh deceleration and acceleration) near the humps. Speed reduction induced by diminution of road width can lead to a noise reduction of 1 to 3 dB(A) especially if it is combined with other traffic management measures. Road noise models usually introduce a penalty up to 3 dB(A) near intersections. The introduction of traffic lights coordination or roundabouts can locally reduce the noise from 1 to 2 dB(A) (free flowing according to interrupted traffic). Speed limitation (from 50 to 30 km/h) induces a noise reduction of 2 to 4 dB(A) for passenger cars and 0 to 2 dB(A) for heavy vehicles (and 2 dBA more for the maximum noise level). Other measures investigated are the selective limitation of the traffic and the low noise driving.

The daily closing prices of several stock market indices are examined to analyse whether noise reduction matters in measuring dependencies of the financial series. We consider the effect of noise reduction on the linear and nonlinear measure of dependencies. We also use singular spectrum analysis as a powerful method for filtering financial series. We compare the results with those obtained by ARMA and GARCH models as linear and nonlinear methods for filtering the series. We also examine the findings on an artificial data set namely the Hénon map.

We have previously developed a dual-energy digital mammography (DEDM) technique for calcification imaging under full-field imaging conditions using a commercially available flat-panel based digital mammography system. Although dual-energy (DE) imaging could suppress the obscuration of calcifications by tissue-structure background, it also increases the intrinsic noise in the DE images. Here we report on the effects of three different noise reduction techniques on DE calcification images: a simple smoothing (boxcar) filter applied to the DE image, a median filter applied to the HE image prior to the computation of the DE image and an adaptation of the Kalender’s correlated-noise reduction (KNR) technique for DEDM. We compared the different noise reduction techniques by evaluating their effects on DE calcification images of a 5 cm thick breast-tissue-equivalent slab with continuously varying glandular-tissue ratio superimposed with calcium carbonate crystals of various sizes that simulate calcifications. Evaluations of different noise reducing techniques were performed by comparison of the root-mean-square signal in background regions (no calcifications present) of the DE calcification images and the contrast-to-noise ratios (CNR) of the calcifications in the DE calcification images. Amongst the different noise reduction techniques evaluated in this study...

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.

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.

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.

The development and testing of an aircraft sidewall treatment using a smart foam lining is discussed. Smart foam is an active /passive hybrid noise control approach and consists of a passive acoustic matrix with embedded active elements. In the first phase, laboratory experiments were conducted on a double-wall system to evaluate the acoustic performance of several passive and active configurations of smart foam actuators attached to the base panel. In the second series of tests, active control using smart foam actuators was implemented on a stiffened aircraft sidewall configured with a trim panel. A multi-input multi-output (MIMO) filtered-X feedforward controller with realistic reference sensors (e.g., accelerometers) was used to accomplish active control through the smart foam elements by minimizing the error signal provided by an array of error microphones. The active control through smart foam actuators improved the noise reduction of the sidewall in the low- to mid-frequency range (200-800 Hz).; http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=200111055100MT&recid=A0130870AH&q=&uid=1022577&setcookie=yes

We report the results of meta-analyses on 3 types of free-response study: (a) ganzfeld (a technique that enhances a communication anomaly referred to as "psi"); (b) nonganzfeld noise reduction using alleged psi-enhancing techniques such as dream psi, meditation, relaxation, or hypnosis; and (c) standard free response (nonganzfeld, no noise reduction). For the period 1997-2008, a homogeneous data set of 29 ganzfeld studies yielded a mean effect size of 0.142 (Stouffer Z = 5.48, p = 2.13 x 10(-8)). A homogeneous nonganzfeld noise reduction data set of 16 studies yielded a mean effect size of 0.110 (Stouffer Z = 3.35, p = 2.08 x 10(-4)), and a homogeneous data set of 14 standard free-response studies produced a weak negative mean effect size of -0.029 (Stouffer Z = -2.29, p = .989). The mean effect size value of the ganzfeld database was significantly higher than the mean effect size of the standard free-response database but was not higher than the effect size of the nonganzfeld noise reduction database [corrected].We also found that selected participants (believers in the paranormal, meditators, etc.) had a performance advantage over unselected participants, but only if they were in the ganzfeld condition.; Lance Storm, Patrizio E. Tressoldi and Lorenzo Di Risio

This paper presents an experimental study on the noise reduction potential of sawtooth trailing edge serrations at low-to-moderate Reynolds number (1.6 x 105 < Rec < 4.2 x 105, based on chord). The noise radiated by flat plates with both straight and serrated trailing edges has been measured in an anechoic wind tunnel at the University of Adelaide. The trailing edge serrations were found to reduce narrowband noise levels by up to 13 dB. The straight and serrated trailing edge far-field acoustic spectra are scaled according to existing theory and compared to predictions of trailing edge noise obtained using current semi-empirical methods. In addition, velocity spectra measured in the trailing edge near wake region using hot-wire anemometry are related to the far-field noise measurements to give further insight into the serration noise reduction mechanism.; Danielle J. Moreau, Laura A. Brooks and Con J. Doolan

Tuning cables of various designs are commonly included in automotive power steering systems to reduce the undesirable effects of pressure pulsations generated in the power steering pump. A recent development which has the potential to reduce noise is the plastic tuner (PT). The main benefit of this device when compared with the existing spiral wound steel tuner (SWST) is the vastly reduced cost associated with the methods of manufacturing. Despite the apparent attractiveness of such a device, the PT has not been widely implemented by automotive fluid system suppliers. The main reason is relatively little is known about the performance of these devices and indeed their comparative performance with respect to a SWST. This research seeks to address this issue by developing a better understanding of the PT using experimental and analytical techniques to examine the acoustic noise reduction mechanisms of a variety of PT designs. This thesis examines the relevant literature associated with the subject and covers several noise reduction techniques that can be applied to this research. The literature review section highlights a general gap in the knowledge base, where little specific detail exists that has not been derived experimentally from SWSTs. As such the general aim of this research is to further the knowledge into PTs...

This paper presents the results of an experimental investigation exploring the noise reduction potential of sawtooth trailing edge serrations on a flat plate at low-to-moderate Reynolds number (1:6 × 105 < Rec < 4.2 × 105). Acoustic and aerodynamic measurements have been taken using a flat plate with both sharp and serrated trailing edges in the anechoic wind tunnel at the University of Adelaide. Trailing edge serrations are found to achieve up to 13 dB of attenuation in the narrowband noise levels without modifying the directivity of the radiated noise. The noise reduction achieved with trailing edge serrations is found to be dependent on their geometrical wavelength and Strouhal number, Stδ = fδ=U∞, where f is frequency, δ is boundary layer thickness and U∞ is free-stream velocity. Far-field acoustic data are compared with theoretical noise reduction predictions showing that significant differences exist between measurements and theory. Velocity data measured in the very near trailing edge wake with hot-wire anemometry are related to the far-field noise measurements to give insight into the trailing edge serration noise reduction mechanism. The results suggest that for this particular configuration, the noise reduction capability of trailing edge serrations is related to their influence on the hydrodynamic field at the source location.; Danielle J. Moreau...

Conference Paper; A novel approach for noise reduction is presented. Similar to Donoho, we employ thresholding in some wavelet transform domain but use a nondecimated and consequently redundant wavelet transform instead of the usual orthogonal one. Another difference is the shift invariance as opposed to the traditional orthogonal wavelet transform. We show that this new approach can be interpreted as a repeated application of Donoho's original method. The main feature is, however, a dramatically improved noise reduction compared to Donoho's approach, both in terms of the l₂ error and visually, for a large class of signals. This is shown by theoretical and experimental results, including synthetic aperture radar (SAR) images.

Tech Report; A novel approach for noise reduction is presented. Similar to Donoho, we employ thresholding in some wavelet transform domain but use a nondecimated and consequently redundant wavelet transform instead of the usual orthogonal one. Another difference is the shift invariance as opposed to the traditional orthogonal wavelet transform. We show that this new approach can be interpreted as a repeated application of Donoho's original method. The main feature is, however, a dramatically improved noise reduction compared to Donoho's approach, both in terms of the l₂ error and visually, for a large class of signals. This is shown by theoretical and experimental results, including synthetic aperture radar (SAR) images.

The electroretinogram (ERG) is an essential method for diagnosing and monitoring hereditary eye diseases, because it allows an objective assessment of retinal function. However, high-level intrinsic electrical and physiological noise often interferes with the physiological signals of interest, rendering the results difficult, if not impossible, to evaluate, especially when the retinal function is already impoverished. For several years, nonlinear time series analysis has been applied to developing signal processing methods that rely on transforming a scalar sequence of measurements into a multidimensional vector space, known as "phase space". This transformation, or embedding, allows one to recover implicit information about the system of interest that is not accessible by analysis of the recorded scalar time series alone. Moreover, embeddings form a fundamental starting point for several mathematical-physical noise reduction (NR) algorithms that exploit the signal's nonlinear properties. Therefore, the application of such methods to the analysis of complex systems seems very promising, particularly when nonlinear behaviour is observed, as is the case for the voltage-time series comprising the ERG. Until now, however, the feasibility of applying such methods to the ERG has not been considered. The aims of this thesis were twofold: first...

Noise reduction aims to improve the quality of noisy speech by suppressing the background noise in the signal. However, there is always a tradeoff between noise reduction and signal distortion--more noise reduction is always accompanied by more signal distortion. An evaluation of the intelligibility of speech processed by several noise reduction algorithms in [23] showed that most noise reduction algorithms were not successful in improving the intelligibility of noisy speech. In this thesis, we aim to utilize acoustic-phonetic knowledge to enhance the intelligibility of noise-reduced speech. Acoustic-phonetics studies the characteristics of speech and the acoustic cues that are important for speech intelligibility. We considered the following questions: what is the noise reduction algorithm that we should use, what are the acoustic cues that should be targeted, and how to incorporate this information into the design of the noise reduction system. A Bayesian noise reduction method similar to the one proposed by Ephraim and Malah in [16] is employed. We first evaluate the goodness-of-fit of several parametric PDF models to the empirical speech data. For classified speech, we find that the Rayleigh and Gamma. with a fixed shape parameter of 5...

A noise reduction scheme on digitized mammographic phantom images is presented. This algorithm is based on a direct contrast modification method using an optimal function which is obtained by means of the mean squared error as a criterion. Computer simulated images containing objects similar to those observed in the phantom are built to evaluate the performance of the algorithm. Noise reduction results obtained on both simulated and real phantom images show that the developed method may be considered as a good pre-processing step from the point of view of automating phantom film evaluation by means of image processing.

A method of noise reduction by the successive partial printings of identical negatives was investigated. Image enhancement in terms of granularity reduction and resolution increase was obtained.