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PubMed2002

Noise, anti-noise and fluid flow control.

This paper celebrates Thomas Young's discovery that wave interference was responsible for much that is known about light and colour. A substantial programme of work has been aimed at controlling the noise of aerodynamic flows. Much of that field can be explained in terms of interference and it is argued in this paper that the theoretical techniques for analysing noise can also be seen to rest on interference effects. Interference can change the character of wave fields to produce, out of well-ordered fields, wave systems quite different from the interfering wave elements. Lighthill's acoustic analogy is described as an example of this effect, an example in which the exact model of turbulence-generated noise is seen to consist of elementary interfering sound waves; waves that are sometimes heard in advance of their sources. The paper goes on to describe an emerging field of technology where sound is suppressed by superimposing on it a destructively interfering secondary sound; one designed and manufactured specifically for interference. That sound is known as anti-sound, or anti-noise when the sound is chaotic enough. Examples are then referred to where the noisy effect to be controlled is actually a disturbance of a linearly unstable system; a disturbance that is destroyed by destructive interference with a deliberately constructed antidote. The practical benefits of this kind of instability control are much greater and can even change the whole character of flows. It is argued that completely unnatural unstable conditions can be held with active controllers generating destructively interfering elements. Examples are given in which gravitational instability of stratified fluids can be prevented. The Kelvin-Helmholtz instability of shear flows can also be avoided by simple controls. Those are speculative examples of what might be possible in future developments of an interference effect, which has made anti-noise a useful technology.

Acoustics↗
PubMed1980

Potentiation of noise-induced audiogenic seizure risk by salicylate in mice as a function of salicylate-noise exposure interval.

Audiogenic seizure risk can be induced in genetically seizure-resistant BALB/c mice by exposure to an intense noise. Results of this experiment showed that combined exposure to noise and sodium salicylate could produce a greater priming effect than exposure to the noise alone, and the greatest potentiation effect was obtained when animals were exposed to the noise 6 hr after the intake of salicylate. The findings were taken as indirect evidence suggesting that the ototoxic action of sodium salicylate could potentiate vulnerability of the mouse cochlea to noise damage.

Acoustic Stimulation↗
PubMed2001

Increased catecholamine levels in urine in subjects exposed to road traffic noise: the role of stress hormones in noise research.

The nocturnal excretion of catecholamines in urine was studied in 30-45-year-old women whose bedroom and/or living room were facing streets of varying traffic volume. The traffic volume of the streets was used as an indicator of noise exposure; adrenaline and noradrenaline concentrations were assessed as indicators of the outcome of the physiological stress. Significant associations between traffic volume and noradrenaline concentrations in urine were found with regard to the exposure of the bedroom (not the living room), indicating a higher chronic physiological arousal in noise-exposed subjects as compared to less exposed. Subjective measures of disturbance due to traffic noise were positively correlated with the noradrenaline level. However, this was only found in subjects where closing the window could not reduce the perceived disturbance, which points to the effectiveness of individual coping mechanisms. Stress hormones are useful indicators to study associations, mechanisms, and interactions between noise, health outcomes, and effect modifiers in epidemiological noise research.

Adaptation, Psychological↗
PubMed1998

Perceptual learning reflects external noise filtering and internal noise reduction through channel reweighting.

To investigate the nature of plasticity in the adult visual system, perceptual learning was measured in a peripheral orientation discrimination task with systematically varying amounts of external (environmental) noise. The signal contrasts required to achieve threshold were reduced by a factor or two or more after training at all levels of external noise. The strong quantitative regularities revealed by this novel paradigm ruled out changes in multiplicative internal noise, changes in transducer nonlinearites, and simple attentional tradeoffs. Instead, the regularities specify the mechanisms of perceptual learning at the behavioral level as a combination of external noise exclusion and stimulus enhancement via additive internal noise reduction. The findings also constrain the neural architecture of perceptual learning. Plasticity in the weights between basic visual channels and decision is sufficient to account for perceptual learning without requiring the retuning of visual mechanisms.

Adult↗
PubMed2002

Influences of current mood and noise sensitivity on judgments of noise annoyance.

Noise annoyance is one of the most studied reactions to auditory events. Previous research has demonstrated that annoyance reactions may be mediated by individual characteristics such as personality, attitudes, and noise sensitivity (traits). Transient temporary states such as an individual's current mood have been studied to a lesser extent. The author studied annoyance reactions to an everyday noise in participants who either were slightly annoyed or in a neutral affective state. The results showed that current mood had an overall effect on judgments of annoyance and on a participant's preference for sound. In addition, a participant's current mood interacted with noise sensitivity. These results indicate that both individual noise sensitivity (traits) and transient moods (states) are important for human auditory perception and evaluation.

Adult↗
PubMed1982

Comparison of hearing loss in the first year of employment in workers assigned to noise-hazard and non-noise-hazard areas at the state prison industries.

Experience in hearing loss at Utah State Prison in noise-hazard and non-noise-hazard areas suggested a matched-pair study of these two groups. The study of noise induced hearing loss and its relation to age has become more and more of scientific and economic interest in the past few years. Since the creation of OSHA and the enforcement of its standards, great strides have been undertaken at USP to protect the worker in noise areas, with both noise abatement and hearing protection. The need became apparent for a measurement of this progress and a comparison on hearing loss between the two worker groups. A retrospective chart study was designed utilizing one hundred pairs of workers matched for age, sex and initial hearing loss. The results suggest no significant difference between the two groups during one year of exposure.

Adult↗
PubMed1996

Comparison of daily noise exposures in one workplace based on noise criteria recommended by ACGIH and OSHA.

The objective of this study was to determine the impact of the new American Conference of Governmental Industrial Hygienists (ACGIHnew) noise criteria, as compared to the current U.S. Occupational Safety and Health Administration (OSHA) hearing conservation criteria, on the number of employees to be included in the hearing conservation program at one industrial facility. This study also compares the combined effects of a 3-dB versus a 5-dB exchange rate and an 80-dBA versus a 90-dBA measurement threshold on daily noise doses and equivalent 8-hr time-weighted averages (TWAs). Employee noise exposures were measured using paired Ametek MK-3 noise dosimeters, one dosimeter set to the ACGIHnew noise criteria and one to the present OSHA hearing conservation criteria. Samples were collected over 4-hr periods (half-shifts) for 50 employees in 7 job categories. Results indicate that the majority of the employees' exposures fell below an 8-hr TWAOSHA of 85 dBA. The differences between the predicted TWAACGIHnew and the TWAOSHA ranged between 0.2 and 12.6 dB for paired samples, with an average difference of 4.6 dB. Overall, these differences in employee 8-hr TWAs would project a 36% increase in the percent of the population enrolled in the hearing conservation program and a 50% increase in the percent of the population required to wear hearing protection.

Environmental Monitoring↗
PubMed2001

Isolating the auditory system from acoustic noise during functional magnetic resonance imaging: examination of noise conduction through the ear canal, head, and body.

Approaches were examined for reducing acoustic noise levels heard by subjects during functional magnetic resonance imaging (fMRI), a technique for localizing brain activation in humans. Specifically, it was examined whether a device for isolating the head and ear canal from sound (a "helmet") could add to the isolation provided by conventional hearing protection devices (i.e., earmuffs and earplugs). Both subjective attenuation (the difference in hearing threshold with versus without isolation devices in place) and objective attenuation (difference in ear-canal sound pressure) were measured. In the frequency range of the most intense fMRI noise (1-1.4 kHz), a helmet, earmuffs, and earplugs used together attenuated perceived sound by 55-63 dB, whereas the attenuation provided by the conventional devices alone was substantially less: 30-37 dB for earmuffs, 25-28 dB for earplugs, and 39-41 dB for earmuffs and earplugs used together. The data enabled the clarification of the relative importance of ear canal, head, and body conduction routes to the cochlea under different conditions: At low frequencies (< or =500 Hz), the ear canal was the dominant route of sound conduction to the cochlea for all of the device combinations considered. At higher frequencies (>500 Hz), the ear canal was the dominant route when either earmuffs or earplugs were worn. However, the dominant route of sound conduction was through the head when both earmuffs and earplugs were worn, through both ear canal and body when a helmet and earmuffs were worn, and through the body when a helmet, earmuffs, and earplugs were worn. It is estimated that a helmet, earmuffs, and earplugs together will reduce the most intense fMRI noise levels experienced by a subject to 60-65 dB SPL. Even greater reductions in noise should be achievable by isolating the body from the surrounding noise field.

Adult↗
PubMed2001

Performance of an adaptive beamforming noise reduction scheme for hearing aid applications. I. Prediction of the signal-to-noise-ratio improvement.

Adaptive beamformers have been proposed as noise reduction schemes for conventional hearing aids and cochlear implants. A method to predict the amount of noise reduction that can be achieved by a two-microphone adaptive beamformer is presented. The prediction is based on a model of the acoustic environment in which the presence of one acoustic target-signal source and one acoustic noise source in a reverberant enclosure is assumed. The acoustic field is sampled using two omnidirectional microphones mounted close to the ears of a user. The model takes eleven different parameters into account, including reverberation time and size of the room, directionality of the acoustic sources, and design parameters of the beamformer itself, including length of the adaptive filter and delay in the target signal path. An approximation to predict the achievable signal-to-noise improvement based on the model is presented. Potential applications as well as limitations of the proposed prediction method are discussed and a FORTRAN subroutine to predict the achievable signal-to-noise improvement is provided. Experimental verification of the predictions is provided in a companion paper [J. Acoust. Soc. Am. 109, 1134 (2001)].

Acoustics↗
PubMed2006

The effects of digital noise reduction on the acceptance of background noise.

Modern hearing aids commonly employ digital noise reduction (DNR) algorithms. The potential benefit of these algorithms is to provide improved speech understanding in noise or, at the least, to provide relaxed listening or increased ease of listening. In this study, 22 adults were fitted with 16-channel wide-dynamic-range compression hearing aids containing DNR processing. The DNR includes both modulation-based and Wiener-filter-type algorithms working simultaneously. Both speech intelligibility and acceptable noise level (ANL) were assessed using the Hearing in Noise Test (HINT) with DNR on and DNR off. The ANL was also assessed without hearing aids. The results showed a significant mean improvement for the ANL (4.2 dB) for the DNR-on condition when compared to DNR-off condition. Moreover, there was a significant correlation between the magnitude of ANL improvement (relative to DNR on) and the DNR-off ANL. There was no significant mean improvement for the HINT for the DNR on condition, and on an individual basis, the HINT score did not significantly correlate with either aided ANL (DNR on or DNR off). These findings suggest that at least within the constraints of the DNR algorithms and test conditions employed in this study, DNR can significantly improve the clinically measured ANL, which may result in improved ease of listening for speech-in-noise situations.

Adult↗
PubMed1993

Hemodynamic effects of short-term noise exposure--comparison of steady state and intermittent noise at several sound pressure levels.

The purpose of the present study was to investigate the extent of blood pressure elevation during noise exposure, to elucidate the underlying hemodynamic mechanisms and to assess baroreceptor cardiac reflex sensitivity in connection with blood pressure elevation. Twenty-two young normotensive males participated in the experiment and underwent six noise exposure conditions of 20 min each: steady state and intermittent pink noises of 80 dB (sound pressure level (SPL)), 90 dB (SPL) and 100 dB (SPL). The results indicate that elevations in mean arterial pressure, as well as diastolic and systolic blood pressure, were significant or almost significant in the intermittent 100 dB (SPL) and 90 dB (SPL) conditions. Habituation occurred particularly with the steady state noises. In at least the intermittent 100 dB (SPL) condition, an increase in peripheral vascular resistance was the underlying hemodynamic mechanism of blood pressure elevation. Decreases in cardiac output and stroke volume were also associated with the peripheral vasoconstriction. Baroreceptor reflex sensitivity was maintained near the baseline level for all of the noise exposure conditions. Therefore, reflex sensitivity may not have been suppressed even in the intermittent 100 dB (SPL) condition during which blood pressure elevations occurred.

Adult↗
PubMed1982

Hearing defects of noise trauma type with lack of noise exposure.

Screening audiometry in children not infrequently reveals a 4 kHz dip. Evidence for noise trauma as the etiological background of this 4 kHz dip have been presented in the literature. Thirty children with hearing defects of this characteristic type and no history of noise exposure were studied. Their mean age was 14 years and the average observation time 4.2 years. Slight progression of hearing impairment (greater than 15 dB at two frequencies) was noted in 3 children (10%). A history of hearing defects in the family was found in 76%, as against 17% in a control group. Abnormal elevation of stapedius reflex thresholds was observed in 83% of the material. It is concluded that in children with a 4 kHz dip and no history of significant exposure to noise, genetic disposition is the predominant etiological element underlying the hearing defect. There was no indication of increased sensitivity to general noise exposure, but as always in sensorineural high frequency hearing loss avoidance of significant exposure to noise is to be recommended.

Adolescent↗
PubMed2005

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

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.

Adult↗
PubMed1976

[Effect of noise on the physiological functions in fowl. 2. Adaptation to noise of white leghorns and broilers].

Two experimental groups and series were compared (leghorns and broilers as well as two age groups of broilers) for their adaptive responses to repeated noise application. The noise was 100 dB and applied daily 30 minutes. The reference for comparison was the plasma-11-hydroxycorticosteroid concentration (11-OHKS). The results differed somewhat from those obtained earlier from one first short-time noise application, in that the rise in plasma glucocorticosteroid concentrations dropped from 431 to 210 per cent of the initial values in adult leghorns exposed to repeated noise stress over seven days. Adult broilers, however, did not exhibit any difference in the magnitude of rise of 11-OHKS concentrations by comparison between first and seven days of repeated stress. The initial values, however, were reached earlier by repeated noise application.

11-Hydroxycorticosteroids↗
PubMedDate not supplied

Low frequency noise and stress: bronchitis and cortisol in children exposed chronically to traffic noise and exhaust fumes.

A correlation of respiratory diseases to traffic related air pollution and noise was observed in an interview study. Since in that study the exposure was subjectively assessed, in the present field study nitrogen dioxide as indicator for vehicle exhausts and the mean night-time noise level were measured outside the children's windows in representative locations. Based on these measurements each child was placed in one of the following categories: low, medium or high traffic immission (ambient emissions). The physician contacts due to bronchitis of 68 children were assessed retrospectively from the files of the participating paediatricians. Saliva samples were collected from all children and the cortisol concentration was estimated. Children under high noise exposure (L(night, 8h) = 54-70dB(A)) had in comparison to all other children significantly increased morning saliva cortisol concentrations, indicating an activation of the hypothalamus-pituitary-adrenal (HPA) axis. Analysing a subgroup of children without high noise exposure showed, that children with frequent physician contacts due to bronchitis did not have increased morning saliva cortisol. However, multiple regression analysis with stepwise exclusion of variables showed that bronchitis was correlated more closely to morning salvia cortisol than to traffic immissions. On the other hand, the rate of physician contacts due to bronchitis increased in a dose dependent manner and significantly with increasing traffic immissions. From these results it can be concluded that high exposure to traffic noise, especially at nighttime, activates the HPA axis and this leads in the long term to an aggravation of bronchitis in children. This seems to be more important than the effect of exhaust fumes on bronchitis symptoms. The results of the present study should be subjected to further investigation using specially designed studies.

Bronchitis↗
PubMed1979

[Behaviour of the fast brain stem response P6 under noise influence, an "objective noise audiometry" (author's transl)].

The fast brain stem response can be recorded even at the threshold; it informs on hearing in the high frequency range of greater than or equal to 2000 cps. Especially in those frequencies often the differentiation between sensorial and neural hearing impairment is of interest--f. e. controlling the pure tone threshold in noise: at sensorial hearing loss tones remain heard within noise of equal loudness unaltered, at neural hearing loss the tone vanishes in noise, e. g. the tone-intensity must be increased to make the tone arise again. This phenomenon known from subjective audiometry mentally can be transferred to the recording of acoustic evoked potentials and can be proved by the behaviour of latency of P6: at sensorial hearing loss the latency is prolonged (corresponding to minus 20 dB) but the response furthermore is recorded in the noise as well as at the click masked threshold; at neural hearing loss, however, the response can be recorded again with a click-intensity, which exceeds that of the noise clearly.

Audiometry↗
PubMed1994

[Dependence of noise-induced individual and group reactions on stimulus variables and moderators in the reference laboratory for community noise production of former East Germany].

The Reference Laboratory for Local Noise Protection in the former German Democratic Republic selected a random sample of 1000 citizens in the City of Erfurt, who were written to and personally interviewed, also having their exposure to noise emissions measured. This enabled a quantitative estimate to be made of the level of noise pollution to which the population was subjected, while simultaneously contributing towards determining an annovance threshold and demonstrating the important role played by subject-specific factors in any one person's perception of the annoyance caused by noise. However, it proved impossible to develop any universal, objective procedure which at the same time would be practicable and would correctly assess all types of noise in terms of the effects they generate.

Adaptation, Psychological↗
PubMed1993

Effects of noise and noise reduction processing on the operation of the Nucleus-22 cochlear implant processor.

Cochlear implants, like other types of auditory sensory aids, become increasingly ineffective with increasing ambient noise levels. One method of signal processing to reduce additive random wideband noise, the INTEL method, has been used to good effect as an input preprocessor for the Nucleus-22 cochlear implant. The implant's own signal processor estimates and encodes pitch frequency and the frequencies of Formants 1 and 2. The study reported here shows that additive noise results in substantial deviations in formant frequency estimates from those that would be observed in the absence of noise. When noisy speech is preprocessed by the INTEL method to reduce noise intensity, the deviations in the frequency estimates for Formant 2 are substantially reduced.

Acoustic Stimulation↗