摘要:

The research on transmission and filter operations has two purposes. The first purpose is to reduce channel distortion and the second is to locate a source. It uses impulse responses of transmissions between a source and a receiver in a waveguide. A time reversal of the impulse response gives the matched filter for the transmission. The matched filter is an optimum filter for the reduction of transmission distortion. A numerical example demonstrates distortion reduction. Since the impulse response between a source and receiver is a function of waveguide structure, source position, and receiver position, one can use the impulse response to determine source position by passing the received signal through a set of reference or theoretical impulse response functions for trial source positions. The ambiguity of source locations depends on waveguide structure and the complexity of the impulse response. Basically ambiguity decreases as complexity increases. A plane‐layered waveguide requires at least three receivers that are not in a line. The signal processing consists of match filtering each receiver for a trial source location and then cross correlating the trial filter outputs. The pairwise cross correlations have a maximum when the trial location is the same as the source position. The cross correlation at match also gives an estimate of the autocorrelation of the source. The source can radiate impulsive transients or continuous random signals.

ISSN:0001-4966    

DOI:10.1121/1.394834

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The responses of populations of auditory‐nerve fibers to both a 1.0‐kHz tone, and 1.0‐kHz tone in broadband noise, have been measured. Period histograms were generated from fiber spike trains and discrete Fourier transforms (DFTs) with a resolution of 125 Hz were computed from each histogram. Sample mean and sample variance statistics were generated for period histograms of response and for temporal response measures derived from discrete Fourier transforms. It is demonstrated how the statistical properties of auditory‐nerve fiber response determine the strategy for the estimation and discrimination of particular stimulus components. When the tone is presented alone, the entire population of auditory‐nerve fibers provides statistically reliable estimates of the 1.0‐kHz tone. Upon addition of the broadband noise stimulus only those units with characteristic frequencies which are close in frequency to the 1.0‐kHz stimulus provide spectral estimates which have high signal‐to‐noise ratios (mean‐squared‐to‐variance ratios). Estimates of the 1.0‐kHz‐tone stimulus derived from auditory‐nerve fibers with characteristic frequencies which are far from the 1.0‐kHz stimulus are statistically unreliable. Based on the responses of the population of auditory‐nerve fibers, the strategy for estimating the 1.0‐kHz‐tone stimulus is to derive estimates of the 1.0‐kHz stimulus from the subpopulation of neurons with characteristic frequencies close to the 1.0‐kHz stimulus. It is concluded that neurons which are tuned close to 1.0 kHz provide the central nervous system (CNS) with the most salient information about the 1.0‐kHz stimulus in the presence of the broadband background.

ISSN:0001-4966    

DOI:10.1121/1.394835

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The responses of single auditory‐nerve fibers of Mongolian gerbil were studied using tonal stimuli. The peristimulatory adaptation of firing rate in response to tone bursts presented in quiet and during a background stimulus is described quantitatively. The total transient response which can be produced to the onset of a tone burst, whether presented in quiet or as an intensity increment, is limited and appears to demonstrate a form of conservation. Specifically, the total numbers of spikes produced by the rapidly adapting component, and the slower short‐term adaptation component, are proportional at all intensities, and are limited for each fiber. Furthermore, when an incremental stimulus is presented on a background, the total transient response to the background and to the increment is limited and depends upon the final intensity, not the background intensity. When the presumed underlying synaptic drive is derived by removing the effects of refractoriness from the spike train, the same conservation of the transient response components, and proportionality between rapid and short‐term components, are observed.

ISSN:0001-4966    

DOI:10.1121/1.394836

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Seven experiments on the detectability of intensity changes in complex multitonal acoustic spectra are reported. Two general questions organize the experimental efforts. The first question is how the detectability of a change in a flat (equal energy) spectrum depends on the frequency region where a single intensive change is made. The answer is that frequency region plays a relatively minor role. Frequency changes in the midregion of the spectrum are the easiest to hear, but thresholds increase by only about 5 dB over the range from 200 to 5000 Hz. For all frequencies, the psychometric function is of the formd’=k(Δp), wherekis a constant and Δpis the change in pressure. The second question is how can we predict the detectability of complex changes over the entire frequency range from the detectability of change at each separate region. Thresholds for detecting a change from a flat spectrum to a spectrum whose amplitude varies in sinusoidal (‘‘rippled’’) fashion over logarithmic frequency are measured at different frequencies of ripple. The thresholds are found to be independent of ripple frequency and are 7 dB higher than predicted on the basis of an optimum combination rule.

ISSN:0001-4966    

DOI:10.1121/1.394837

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

An auditory enhancement effect occurs when one component of a harmonic series is omitted for a few hundred milliseconds and then reintroduced: The reintroduced harmonic stands out perceptually. Three experiments are reported that studied a version of this effect in which several components of a harmonic series are enhanced to define the formants of a vowel. Using the accuracy of vowel identification to measure the prominence of the formant peaks in the effective auditory representation, forms of the effect were identified that are qualitatively similar to the incremental and decremental responses seen in primary auditory‐nerve fibers. These results are compatible with an origin for the enhancement effect in peripheral auditory adaptation. However, an additional mechanism is required to account for the demonstration [Viemeister and Bacon, J. Acoust. Soc. Am.71, 1502–1507 (1982)] that enhancement can involve a true gain in the frequency region of the reintroduced component. These effects demonstrate one way in which the auditory system may attenuate the prominence of background noises while preserving the ability to represent changes in spectral amplitude produced by newly arriving signals.

ISSN:0001-4966    

DOI:10.1121/1.394838

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Temporal masking curves were obtained from 12 normal‐hearing and 16 hearing‐impaired listeners using 200‐ms, 1000‐Hz pure‐tone maskers and 20‐ms, 1000‐Hz fixed‐level probe tones. For the delay times used here (>40 ms), temporal masking curves obtained from both groups can be well described by an exponential function with a single level‐independent time constant for each listener. Normal‐hearing listeners demonstrated time constants that ranged between 37 and 67 ms, with a mean of 50 ms. Most hearing‐impaired listeners, with significant hearing loss at the probe frequency, demonstrated longer time constants (range 58–114 ms) than those obtained from normal‐hearing listeners. Time constants were found to grow exponentially with hearing loss according to the function τ=52e0.011(HL), when the slope of the growth of masking is unity. The longest individual time constant was larger than normal by a factor of 2.3 for a hearing loss of 52 dB. The steep slopes of the growth of masking functions typically observed at long delay times in hearing‐impaired listeners’ data appear to be a direct result of longer time constants. When iterative fitting procedures included a slope parameter, the slopes of the growth of masking from normal‐hearing listeners varied around unity, while those from hearing‐impaired listeners tended to be less (flatter) than normal. Predictions from the results of these fixed‐probe‐level experiments are consistent with the results of previous fixed‐masker‐level experiments, and they indicate that deficiencies in the ability to detect sequential stimuli should be considerable in hearing‐impaired listeners, partially because of extended time constants, but mostly because forward masking involves a recovery process that depends upon the sensory response evoked by the masking stimulus. Large sensitivity losses reduce the sensory response to high SPL maskers so that the recovery process is slower, much like the recovery process for low‐level stimuli in normal‐hearing listeners.

ISSN:0001-4966    

DOI:10.1121/1.395131

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

An experiment was performed to study the interaction of two narrow‐band noises having correlated temporal envelopes. The detection threshold of a 100‐Hz‐wide noise‐band signal was measured at different center frequencies in the presence of a continuous 100‐Hz‐wide noise band having a center frequency of 1000 Hz. The two noise bands had either correlated or independent temporal envelopes. Measured signal detection thresholds are lower when the two noise bands are independent, but the magnitude of this difference is not a simple function of the frequency separation between the two noise bands.

ISSN:0001-4966    

DOI:10.1121/1.394839

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

This study was designed to investigate the effects of masker level and frequency on binaural detection and interaural time discrimination. Detection and interaural time discrimination of a 700‐Hz sinusoidal signal were measured as a function of the center frequency and level of a narrow‐band masking noise. The masker was a continuous, diotic, 80‐Hz‐wide noise that varied in center frequency from 250 to 1370 Hz. In the detection experiment, the signal was presented either diotically (NoSo) or interaurally phase reversed (NoSπ). In the interaural time discrimination experiment, the signal level needed to discriminate a 30‐μs interaural delay was measured. As would be expected, the presence of the masker has a greater effect on NoSo detection than NoSπ detection, and for masker frequencies at or near the signal frequency. In contrast, interaural time discrimination can be improved by the presence of a low‐level masker. Also, performance improves more rapidly as the signal/masker frequency separation increases for NoSo detection than for interaural time discrimination and NoSπ detection. For all three tasks, significant upward spread of masking occurs only at the highest masker level; at low masker levels, there is a tendency toward downward spread of masking.

ISSN:0001-4966    

DOI:10.1121/1.394840

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The purpose of this study was to determine the feasibility of using the auditory brain stem response (ABR) as a method of measuring the attenuation characteristics of nonlinear hearing protective devices. Sound field ABRs were recorded from seven normal hearing subjects with and without hearing protection. Three hearing protectors (two nonlinear and one linear) were evaluated. Test stimuli, consisting of 4000‐Hz tone pips, were presented in a sound field. Linearity and the amount of attenuation for each hearing protector were derived by comparing the protected and unprotected latency‐intensity functions for wave I of the ABR. Results indicate that the ABR may be used effectively to measure the attenuation characteristics of linear and nonlinear hearing protectors for high‐frequency impulse‐type stimuli.

ISSN:0001-4966    

DOI:10.1121/1.394841

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

When subglottal pressure signals which are recorded during normal speech production are spectrally analyzed, the frequency of the first spectral maximum appears to deviate appreciably from the first resonance frequency which has been reported in the literature and which stems from measurements of the acoustic impedance of the subglottal system. It is postulated that this is caused by the spectrum of the excitation function. This hypothesis is corroborated by a modeling study. Using an extended version of the well‐known two‐mass model of the vocal folds that can account for a glottal leak, it is shown that under realistic physiological assumptions glottal flow waveforms are generated whose spectral properties cause a downward shift of the location of the first spectral maximum in the subglottal pressure signals. The order of magnitude of this effect is investigated for different glottal settings and with a subglottal system that is modeled according to the impedance measurements reported in the literature. The outcomes of this modeling study show that the location of the first spectral maximum of the subglottal pressure may deviate appreciably from the natural frequency of the subglottal system. As a consequence, however, the comfortable assumption that in normal speech the glottal excitation function is constant and zero during the ‘‘closed glottis interval’’ has to be called into question.

ISSN:0001-4966    

DOI:10.1121/1.394842

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP