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At least 217 records · Page 12Linked to original sources
PubMed2002

Estimation of noise level and signal to noise ratio of laplacian electrocardiogram during ventricular depolarization and repolarization.

Body surface Laplacian ECG (LECG) has demonstrated its enhanced capability to localize cardiac electrical sources closest to the recording site. The aim of the present study was to evaluate the noise level and signal to noise ratio (SNR) in the LECG as compared to the potential ECG (PECG). Such evaluation is important to determine the applicability of the LECG to localizing and imaging of cardiac electrical activity in an experimental setting. Experimental studies were conducted in six healthy men. A 150-channel PECG was recorded from the anterolateral chest and the LECG was estimated using the finite difference algorithm. The noise level in the PECG and LECG was evaluated using multiple estimation protocols. The signal level during ventricular depolarization and repolarization was also estimated, and the corresponding SNR was calculated. Different filtering techniques were examined to evaluate their effects on the noise level and SNR of the LECG and PECG. The experimental results indicate that with basic signal processing techniques (baseline adjustment, three-point moving average filter, and Wiener spatial filter), the SNR of the LECG is about 30-40% of that of the PECG. Furthermore, the SNR estimated during ventricular depolarization is about three times that obtained during ventricular repolarization for the PECG and LECG. The present study indicates that the LECG derived from the PECG using a local finite difference estimation procedure has satisfactory SNR during the periods of ventricular depolarization and repolarization, and suggests the feasibility of estimating the LECG from the recorded PECG in human subjects in an experimental setting.

Body Surface Potential Mapping↗
PubMed1994

Reduction of brain noise influence in evoked neuromagnetic source localization using noise spatial correlation.

In magnetoencephalographic measurements, magnetic fields caused by spontaneous brain activities not related to the neural activities under study are often referred to as brain noise. This is because the accuracy in neural source localization is considerably degraded by such spontaneous neuromagnetic fields. This paper reports the experimental results of applying the previously proposed noise covariance method to reducing the degradation caused by brain noise and to improving the accuracy in localizing auditory-evoked neural sources. Firstly we present the results of our experiments using measured brain noise and computer-generated signal fields. These results confirm that the covariance method can, in principle, improve the accuracy of evoked neural source localization. Next, the method was applied to source localization for actual neuromagnetic fields evoked by speech sounds. The results obtained strongly suggest that the method is effective in processing actual evoked neuromagnetic data.

Adult↗
PubMed2002

Statistical and heuristic image noise extraction (SHINE): a new method for processing Poisson noise in scintigraphic images.

Poisson noise is one of the factors degrading scintigraphic images, especially at low count level, due to the statistical nature of photon detection. We have developed an original procedure, named statistical and heuristic image noise extraction (SHINE), to reduce the Poisson noise contained in the scintigraphic images, preserving the resolution, the contrast and the texture. The SHINE procedure consists in dividing the image into 4 x 4 blocks and performing a correspondence analysis on these blocks. Each block is then reconstructed using its own significant factors which are selected using an original statistical variance test. The SHINE procedure has been validated using a line numerical phantom and a hot spots and cold spots real phantom. The reference images are the noise-free simulated images for the numerical phantom and an extremely high counts image for the real phantom. The SHINE procedure has then been applied to the Jaszczak phantom and clinical data including planar bone scintigraphy, planar Sestamibi scintigraphy and Tl-201 myocardial SPECT. The SHINE procedure reduces the mean normalized error between the noisy images and the corresponding reference images. This reduction is constant and does not change with the count level. The SNR in a SHINE processed image is close to that of the corresponding raw image with twice the number of counts. The visual results with the Jaszczak phantom SPECT have shown that SHINE preserves the contrast and the resolution of the slices well. Clinical examples have shown no visual difference between the SHINE images and the corresponding raw images obtained with twice the acquisition duration. SHINE is an entirely automatic procedure which enables halving the acquisition time or the injected dose in scintigraphic acquisitions. It can be applied to all scintigraphic images, including PET data, and to all low-count photon images.

Algorithms↗
PubMed2004

Noise suppression and spectral decomposition for state-dependent noise in the presence of a stationary fluctuating input.

It recently has been shown that the observed noise amplitude of an intrinsically noisy system may be reduced by causing the underlying state to fluctuate [Phys. Rev. Lett. 86, 950 (2001)]]. This paper extends the previous theory by considering the full power spectrum of the output signal, interpreting noise reduction in terms of the low-frequency end of the spectrum as well as the integrated spectrum. Our treatment accounts for arbitrarily sized fluctuations and deals with both continuous and discretely sampled observations. We show that noise suppression is possible if and only if the stationary average of the intensity of state-dependent noise decreases. We apply our analysis to an example involving saturable electrical conduction discussed in the original paper by Vilar and Rubí.

Biophysics↗
PubMed2000

Microscopic identification of the origin of generation-recombination noise in hydrogenated amorphous silicon with noise-detected magnetic resonance

Spin-dependent changes in the noise power of undoped amorphous hydrogenated silicon ( a-Si:H) are observed under electron spin resonance conditions. The noise-detected magnetic resonance (NDMR) signal has the g value of holes in the valence band tail of a-Si:H. Both the sign of the NDMR signal and the frequency dependence of its intensity can be quantitatively accounted for by a resonant reduction of the generation-recombination noise time constant tau. This identifies hopping in the valence-band tail as the dominant spin-dependent step governing noise in this material.

Journal Article↗
PubMed2000

Adaptive beamforming at very low frequencies in spatially coherent, cluttered noise environments with low signal-to-noise ratio and finite-averaging times

Realistic simulations with spatially coherent noise have been run in order to compare the performance of adaptive beamforming (ABF), inverse beamforming (IBF), and conventional beamforming (CBF) for the case of finite-averaging times, where the actual spatial coherence of the acoustic field, or covariance matrix, is not known a priori, but must be estimated. These estimation errors cause large errors in the ABF estimate of the directionality of the acoustic field, partly because ABF is a highly nonlinear algorithm. In addition, it is shown that ABF is fundamentally limited in its suppression capability at very low frequency (VLF), based on the sidelobe level of the conventional beampattern in the direction of the noise interferer [G. L. Mohnkern, "Effects of Errors and Limitations on Interference Suppression," NOSC Technical Document 1478, Naval Ocean Systems Center (1989)]. The simulations include a low-level plane wave signal of interest, a stronger noise plane wave interferer, and spatially random background noise. Both IBF and ABF performed significantly better than CBF, and IBF's performance was slightly better than ABF's performance. The performances of IBF and the ABF algorithm, the minimum variance distortionless response (MVDR) [A. H. Nuttall and D. W. Hyde, "Unified Approach to Optimum and Suboptimum Processing for Arrays," USL Report Number 992, Naval Underwater Systems Center, New London, CT (22 April 1969)] were recently compared independently [J. S. D. Solomon, A. J. Knight, and M. V. Greening, "Sonar Array Signal Processing for Sparse Linear Arrays," Defense Science and Technology Organization (DSTO) Technical Report (June 1999)] using measured data, with the result that IBF outperformed MVDR. This result is significant because MVDR requires orders of magnitude more processing power than IBF or CBF.

Journal Article↗
PubMed1980

Noise and noise texture in CT images before and after post-processing.

Two homogeneous water phantoms were recorded under various CT scanner settings, and the reducing effect of various convolution filters on the noise level was evaluated. The change in noise texture introduced by the filtering process was assessed for a limited range of scanner settings by noise analysis of the autocovariance matrix before and after filtering. The results indicate that reduction of noise expressed as RMSD by a factor of about 8 is possible with the filters available in the software package of the Ohio-Nuclear Delta 50 FS tomograph, with some sacrifice in spatial resolution. Results of preliminary experiments with an inhomogeneous phantom are in agreement with this finding and indicate that filtering allows smaller lesions to be detected.

Computers↗
PubMed1983

Effect of tinnitus masker noise on speech discrimination in quiet and two noise backgrounds.

Use of masking devices is achieving recognition as a means of providing tinnitus relief. While palliative results have been described, possible disruptive consequences have not yet received attention. The present study examined the effects of tinnitus masker noise on speech intelligibility. Twenty young normals listened to NU-6 word lists presented in sound field in quiet white noise, and cocktail party noise backgrounds (S/N = O dB) with and without a tinnitus masker. Although there was little impairment while wearing the masker in quiet, substantial discrimination loss was observed in the two noise backgrounds. The potential disruption in communication function while wearing a masking device is discussed.

Adult↗
PubMed1996

Noise Induced Hearing Loss and the Individual Susceptibility to the Noise.

Although there is no specific treatment for modality of occupational noise-induced hearing loss (NIHL), the best way to manage this problem is the prevention. The fundamental prevention of NIHL is to find the persons who are more susceptible to the noise and to avoid work in the noisy environment prior to or during employment. The purpose of this study is to investigate the actual status of NIHL in the industrial complex of Pusan and Kyongnam area in Korea and to evaluate the individual susceptibility to the noise and to set-up the preventive indices of NIHL, using temporary threshold shift (TTS) and its recovery time after noise stimulation.

Journal Article↗
PubMed1986

The interaction of noise and aspirin in the chick basilar papilla. Noise and aspirin toxicity.

The possible synergism between noise and aspirin for causing cochlear damage was examined histologically. Six chicks fed aspirin for five days and five chicks fed a normal diet only were paired and placed in sound chambers. They were exposed to a 1500-Hz tone at 115 dB sound pressure level for eight hours. The mean serum salicylate level just before noise exposure was 24 mg/dL (1.74 mmol/L). Ten days later they were killed, and the temporal bones were processed. Hair cell counts were made at 100-microns intervals throughout the length of the basilar papilla (cochlea). The noise produced a discrete cochlear lesion centered about 30% of the distance from the base to apex. The addition of aspirin did not significantly alter the extent or location of this lesion. One aspirin-fed chick had a unilateral middle ear effusion, and a striking shift in the center of damage toward the apex was noted in this cochlea.

Animals↗
PubMed1992

[Expert assessment of noise-induced hearing loss with special reference to differentiation between noise-induced damage and other degenerative diseases of the ear].

In patients with noise-induced hearing loss (NIHL) who also suffer from other degenerative diseases of the ear, a medicolegal opinion must be based on detailed knowledge of the pathophysiology of Corti's organ and on audiometric findings. Only with this special knowledge is it possible to differentiate accurately between NIHL and other types of hearing loss. At the same time, interactions must be considered between endogenous dysfunctions of the hair cells and their sensitivity to overload by severe noise. On the other hand, the diagnosis of NIHL is not valid when there were uncertainties with respect to the type of hearing dysfunction or the risk of noise at the place of work. These difficulties also apply to the estimation of the individual disability from NIHL when associated with other types of hearing loss.

Audiometry, Pure-Tone↗
PubMed1990

[Hearing, noise and noise-induced trauma].

As a result of preventive auditory measures in the Norwegian Armed Forces conscripts as a group no longer develop noise induced hearing loss during their service. But the incidence of hearing impairments among 18-year-old Norwegian men before entering military service has increased in recent years and indicates that Norway--and other countries?--should issue noise restrictions also for leisure noise.

Adolescent↗
PubMed1994

Impaired word recognition in noise by patients with noise-induced cochlear hearing loss: contribution of temporal resolution defect.

Fifteen patients with mild noise-induced cochlear hearing loss reported a selective difficulty in understanding speech in noisy settings. To examine the hypothesis that a temporal resolution defect was responsible for this difficulty, the patients were tested for their recognition of monosyllabic words presented against continuous and interrupted wide-band noise backgrounds, at each of seven signal-to-noise ratios. Their recognition performance was compared with that of normal listeners studied with the same paradigms. By comparison with the controls, the group with cochlear hearing loss showed a significant recognition impairment only for words presented against the interrupted masker. This finding was in keeping with the existence of a temporal resolution defect in cochlear disease, though it need not indicate a stimulus timing defect at the level of individual cochlear neurons.

Adult↗
PubMed2006

PINCHE's policy recommendations on noise: how to prevent noise from adversely affecting children.

BACKGROUND: Noise can have auditory and non-auditory effects on children. Very few noise episodes affect children's hearing instantaneously; most effects are long-term and cumulative. Describing the risks of noise on children's health and well-being in a life-course perspective can illustrate the prospects of cumulative effects. CONCLUSION: The policy recommendations the Policy Interpretation Network on Children's Health and Environment (PINCHE) prepared for each age group or setting are described here.

Advisory Committees↗
PubMed2005

Aircraft noise annoyance in recreational areas after changes in noise exposure: comments on Krog and Engdahl (2004).

When Gardermoen replaced Fornebu as the main airport for Oslo, aircraft noise levels increased in recreational areas near Gardermoen and decreased in areas near Fornebu. Krog and Engdahl [J. Acoust. Soc. Am. 116, 323-333 (2004)] estimate that recreationists' annoyance from aircraft noise in these areas changed more than would be anticipated from the actual noise changes. However, the sizes of their estimated "situation" effects are not credible. One possible reason for the anomalous results is that standard regression assumptions become violated when motivational factors are inserted into the regression model. Standardized regression coefficients (beta values) should also not be utilized for comparisons across equations.

Aircraft↗
PubMed2006

Noise annoyance and activity disturbance before and after the erection of a roadside noise barrier.

Questionnaire studies were conducted in a residential area before and after the erection of a 2.25 m high noise barrier of conventional type along a heavily traveled road (19,600 vehicles/24 h). The interval between studies was two years. Houses closest to the barrier received a sound-level reduction from -70.0 to 62.5 dB Lden at the most exposed facade. The sound-level reduction decreased with distance to the road, and was negligible for houses at more than 100 m distance. Up to this distance, the noise barrier reduced residents' noise annoyance outdoors and indoors as well as improved speech communication outdoors. Indoors, speech communication and sleep disturbance were slightly but nonsignificantly improved. Predictions of the number of annoyed persons from published exposure-response curves (in Lden) agreed with the percentage of residents being annoyed when indoors, before and after the barrier. Conversely, the percentage of residents being annoyed when outdoors clearly exceeded the predictions. These results suggest that these exposure-response curves may be used in predicting indoor situations, but they should not be applied in situations where outdoor annoyance is at focus.

Architectural Accessibility↗
PubMed1997

Directivity of binaural noise reduction in spatial multiple noise-source arrangements for normal and impaired listeners.

Speech reception thresholds (SRTs) were obtained for different azimuths of up to three interfering sound sources in a simulated ("virtual") spatial arrangement. For the SRT measurements a fast subjective threshold assessment method was used. The reduction in SRT relative to the reference threshold caused by spatial separation of target and interference signal is called the intelligibility level difference (ILD). For normal listeners, the maximum ILD was achieved at 105 degrees or 255 degrees azimuth of a single noise source when the target emanated from the front (0 degree azimuth). The ILD decreased rapidly if the number of interfering signals was increased and if they were located on opposite sides of the head. When using continuous speech as interference, this decrease of ILD was less pronounced. These findings indicate that the binaural system can suppress interference from only one azimuthal region at a time and can utilize temporal pauses in the interference to suppress a second interference from a different direction. For eight sensorineural impaired listeners, the maximum attainable ILD for one interfering noise source was reduced in a way not predictable from the audiogram. The ability to exploit pauses in the signal of an interfering talker was also reduced. Hence, hearing-impaired listeners are handicapped in realistic spatial interference situations both by an increased monaural SRT and a reduced binaural noise reduction ability.

Adult↗
PubMed1999

The normalized interaural correlation: accounting for NoS pi thresholds obtained with Gaussian and "low-noise" masking noise.

Recently, Eddins and Barber [J. Acoust. Soc. Am. 103, 2578-2589 (1998)] and Hall et al. [J. Acoust. Soc. Am. 103, 2573-2577 (1998)] independently reported that greater masking of interaurally phase-reversed (S pi) tones was produced by diotic low-noise noise than by diotic Gaussian noise. Based on quantitative analyses, Eddins and Barber suggested that their results could not be accounted for by assuming that listeners' judgments were based on constant-criterion changes in the normalized interaural correlation produced by adding the S pi signal to the diotic masker. In particular, they showed that a model like the one previously employed by Bernstein and Trahiotis [J. Acoust. Soc. Am. 100, 3774-3784 (1996)] predicted an ordering of thresholds between the conditions of interest that was opposite to that observed. Bernstein and Trahiotis computed the normalized interaural correlation subsequent to half-wave, square-law rectification and low-pass filtering, the parameters of which were chosen to mimic peripheral auditory processing. In this report, it is demonstrated that augmenting the model by adding a physiologically valid stage of "envelope compression" prior to rectification and low-pass filtering provides a remedy. The new model not only accounts for the data obtained by Eddins and Barber (and the similar data obtained by Hall et al.), but also does not diminish the highly successful account of the comprehensive set of data that gave rise to the original form of the model. Therefore, models based on the computation of the normalized interaural correlation appear to remain valid because they can account, both quantitatively and qualitatively, for a wide variety of binaural detection and discrimination data.

Auditory Perception↗