摘要:

Current understanding of the relation between monaural estimates of the critical bandwidth for masking and those obtained in binaural listening situations is poor. The present study was designed to improve this situation by obtaining estimates of critical bandwidth when the signal and masker were presented: (1) monaurally (NmSm), (2) binaurally with both signal and masker in phase at the ears (NoSo), (3) binaurally with masker in phase and signals 180° out of phase (NoSπ). Threshold estimates were obtained in a two‐interval forced‐choice paradigm as a function of masker bandwidth for signal frequencies of 500 and 2000 Hz for the three conditions mentioned above. Maskers were computer‐synthesized and had essentially infinite rejection slopes. For all conditions, as masker bandwidth was narrowed from wide band, threshold remained relatively constant until some critical bandwidth was reached. Further reductions in bandwidth were followed by progressive lowering of threshold, presumably due to removal of masker energy in the critical band. For both signal frequencies, the derived critical bandwidth estimates for the NmSm and NoSo conditions were similar and were smaller than the critical bandwidth estimates obtained in the NoSπ condition.

ISSN:0001-4966    

DOI:10.1121/1.383528

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Human observers detected sinusoidal and pulse‐train signals in noise derived from two computer‐synthesized sources and from a Gaussian noise source. The synthesized noise stimuli were generated from sequences of pulses whose amplitudes were drawn from two divergent types of probability distributions: a centrally peaked distribution and a bimodal distribution. No differences in the detectability of signals in these noise stimuli were evident at pulse rates of 1000, 2000, 4000, or 10 000 Hz. Subjects could not discriminate between the two types of computer‐generated maskers at any pulse rate. The data support a spectrum‐analyzer model of detection in which multiband filtering of the input smooths the masker energy in each spectral region to approximate the Gaussian case.

ISSN:0001-4966    

DOI:10.1121/1.383529

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The results of two complementary detection tasks using digitally synthesized noise are reported. In one experiment the bandwidth of the synthetic noise was varied to reveal the region most effective in masking a 1‐kHz signal. The bandwidth of the internal filter (’’critical band’’) so measured was about 80 Hz. In another experiment, a wideband noise was used as the masker for a synthetic signal whose bandwidth was varied to determine the maximum effective width of the internal filter. Although some earlier experiments suggest maximum effective widths as small as 180–200 Hz (around 1 kHz), the data reported here indicate the range of spectral integraton extends from the critical band to a maximum width that may exceed 3 kHz. In addition, the good agreement between the two experiments suggests a new method for estimating critical bandwidths based on the determination of two thresholds: that of a tonal signal in a wideband masker and that of a supracritical‐width noise signal in a wider‐bandwidth masker.

ISSN:0001-4966    

DOI:10.1121/1.383530

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The detectability of amplitude modulation in the absence of spectral cues provides a quantitative description of temporal resolution for steady‐state signals with relatively small amplitude changes. Modulation thresholds for sinusoidally amplitude‐modulated wideband noise were measured as a function of modulation frequency. The resulting ’’Temporal Modulation Transfer Function’’ (TMTF) shows a lowpass characteristic for modulation frequencies below about 800 Hz. The lowpass characteristic is extended up to approximately 2 kHz when the increment in average power produced by modulation is eliminated. The important parametric effects are summarized as follows: (1) TMTFs are independent of overall level, except at very low intensities; (2) the time constant indicated by the TMTF decreases as the center frequency of the band‐limited, modulated noise is increased; (3) modulation thresholds generally decrease with increasing duration of modulation, particularly at low modulation frequencies; (4) when the carrier is gated for the duration of modulation, the TMTF shows a highpass segment at low modulation frequencies. Although the TMTFs are not directly consistent with the attenuation characteristic of a simple lowpass filter, a model which incorporates such a filter, with a time constant of 2.5 ms, describes the entire TMTF and also describes the modulation functions obtained with square‐wave and pulse modulation. The wide bandwidth of initial filtering indicated by the model raises the important question of the role of peripheral filtering in determining the detectability of high‐frequency modulation.

ISSN:0001-4966    

DOI:10.1121/1.383531

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

This paper is concerned with the representation of the spectra of synthesized steady‐state vowels in thetemporalaspects of the discharges of auditory‐nerve fibers. The results are based on a study of the responses of large numbers of single auditory‐nerve fibers in anesthetized cats. By presenting the same set of stimuli to all the fibers encountered in each cat, we can directly estimate the population response to those stimuli. Period histograms of the responses of each unit to the vowels were constructed. The temporal response of a fiber to each harmonic component of the stimulus is taken to be the amplitude of the corresponding component in the Fourier transform of the unit’s period histogram. At low sound levels, the temporal response to each stimulus component is maximal among units with CFs near the frequency of the component (i.e., near its place). Responses to formant components are larger than responses to other stimulus components. As sound level is increased, the responses to the formants, particularly the first formant, increase near their places and spread to adjacent regions, particularly toward higher CFs. Responses to nonformant components, except for harmonics and intermodulation products of the formants (2F1,2F2,F1+F2, etc.), are suppressed; at the highest sound levels used (approximately 80 dB SPL), temporal responses occur almost exclusively at the first two or three formants and their harmonics and intermodulation products. We describe a simple calculation which combines rate, place, and temporal information to provide a good representation of the vowels’ spectra, including a clear indication of at least the first two formant frequencies. This representation is stable with changes in sound level at least up to 80 dB SPL; its stability is in sharp contrast to the behavior of the representation of the vowels’ spectra in terms of discharge rate which degenerates at stimulus levels within the conversational range.

ISSN:0001-4966    

DOI:10.1121/1.383532

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Optimum beamforming of a line array of either two‐or three‐element closely spaced hydrophone clusters is considered. The objective is the cancellation of convective noise due to the excitation by the turbulent boundary layer. Expressions for array gain using both uniform and optimum cluster‐element weighting are obtained. Suboptimum realizations of the optimum cluster‐element combining schemes are proposed that suggest simplified hardware implementations.

ISSN:0001-4966    

DOI:10.1121/1.383533

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

If the acoustic signal radiated by a moving source is observed at two or more locations, the received signals exhibit differential Doppler shifts which provide information about source motion. This paper calculates minimum mean‐square errors for the estimates of differential Doppler shifts, which can be obtained in a given observation interval. Both Gaussian and sinusoidal signals are considered. The noise is assumed to be Gaussian and independent from sensor to sensor. Dependence of the estimation errors on observation time, signal‐to‐noise ratio, and size of the receiving array are studied. The estimation of differential Dopplers is found to be uncoupled from the estimation of differential delays and from the estimation of signal parameters, such as center frequency and bandwidth. A comparison is made between two possible procedures of differential Doppler estimation: coherent processing of the signals received at two sensors and subtraction of separate frequency estimates obtained at each sensor. The two are equivalent for sinusoidal signals, but for largeTWGaussian signals the coherent procedure yields substantially smaller errors.

ISSN:0001-4966    

DOI:10.1121/1.383534

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

When a plane acoustic wave impinges on a cylindrical array, the leading edge insonifies the first few elements of the array. As the wave front continues past the leading edge of the cylinder, more and more elements are insonified until all elements in the array are insonified. The time between the first and last element to be insonified is called array ’’fill time.’’ For a cylindrical array with a phase‐shift beamformer, in which the insonifying pulse length is long compared to the fill time, the resultant beam pattern is essentially the same as a cylindrical array with a delay line beamformer and is approximately the same as a planar array of similar aperture size. Up to this time there has been no detailed description of how the beam pattern is affected when the pulse length and the fill time are approximately the same. This article reports a thorough analysis of array fill time of a cylindrical array; a phase‐shift beamformer is compared to a delay line beamformer. The conclusion from this study is that fill time has little effect on the array beam pattern as long as the fill time is no greater than the pulse length.

ISSN:0001-4966    

DOI:10.1121/1.383535

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The relationship between the predicted detectability and judged annoyance of 24 low‐level sounds heard in three noise backgrounds was investigated by an adaptive paired comparison procedure under free‐field listening cojditions. The predicted detectability of the set of sounds acco nted for almost 90= per−cent)= of the variance in judgments of anjoyance made in the most commonplace (falling spectru ) background noise environment. Conventional methods of predicting annoyance did not yield significantly higher correlations than a detectability‐based method in two other unusually shaped background noise environments.

ISSN:0001-4966    

DOI:10.1121/1.383536

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A behavioral preference procedure, the ’’acoustic menu,’’ was used to assess human aversion to the sounds from two samples of transmission line audible noise and from samples of other environmental noises. The audible (corona) noise produced by extra‐high voltage (EHV), overhead transmission lines was tape‐recorded during moist weather. Reproduced samples of corona noise, other common environmental noises, and artificial reference stimuli were compared in two experiments. The two corona noise samples were found to be equally preferred to: (1) a 1000 Hz octave band of noise about 11 dB SPL higher than the corona noises and (2) a collection of other environmental noises about 8 dB SPL higher than the corona noises. The corona noise samples were more aversive than the ambient sounds (including rainfall) occurring near rural transmission lines and were roughly equivalent in aversiveness to the noise from a room air conditioner (indoor recording). Knowledge of the source of the corona noise (from photographs and a brief description) did not affect its aversiveness. Of the simple frequency‐weighting scales, theA‐weighted sound level reduced the difference between the two corona noise samples and the set of other environmental sounds from about 8 dB SPL to about 3 dB. TheD‐weighted sound level further reduced this discrepancy to about 2 dB. These results were obtained with only two samples of corona noise; other samples may give different results.

ISSN:0001-4966    

DOI:10.1121/1.383537

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP