摘要:

Array processing based on a linear assumption implies degradations in the source bearing estimation when the array is not linear, which is the usual case in real‐world problems. Assuming only that the array is planar (but not necessarily quasilinear), we describe a method to include in an adaptive way information about the sensor locations into the array processing, in order to take into account its geometrical shape. This information can be the relative positions of the sensors given by a mechanical device included in the array. The relative sensor positions can also be estimated using a source with a known bearing, a cooperative target for example. Simulation results in a real underwater noise sample show that these two cases lead to important improvement with respect to the classical array processing, based on a linear assumption, provided that the signal‐to‐noise ratio of the known source is high enough (around 10 dB in our example).

ISSN:0001-4966    

DOI:10.1121/1.394748

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The Wigner distribution function, originally introduced in quantum mechanics, is shown to have a similar formulation as the Fourier transform of the time‐dependent correlation function for a time‐varying signal. Review of its mathematical properties indicates that such an expression is suitable for representing the signal simultaneously in the time and frequency domains. Furthermore, reformating the Wigner distribution function with a certain window function leads to a proof that this modified version, the pseudo‐Wigner distribution function, always has a positive value and hence can be interpreted as a proper description of the dynamics for the signal’s power density spectrum change with time. The implementation of the Wigner distribution function for digital processing can be carried out simply by adapting the fast Fourier transform algorithm. Examples of its application to several types of acoustic signals are used to illustrate their dynamic features jointly in time and frequency representation.

ISSN:0001-4966    

DOI:10.1121/1.395128

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

This article presents frequency responses calculated using a three‐dimensional finite‐element model of the cat eardrum that includes damping. The damping is represented by both mass‐proportional and stiffness‐proportional terms. With light damping, the frequency responses of points on the eardrum away from the manubrium display numerous narrow minima and maxima, the frequencies and amplitudes of which are different for different positions on the eardrum. The frequency response on the manubrium is smoother than that on the eardrum away from the manubrium. Increasing the degree of damping smooths the frequency responses both on the manubrium and on the eardrum away from the manubrium. The overall displacement magnitudes are not significantly reduced even when the damping is heavy enough to smooth out all but the largest variations. Experimentally observed frequency responses of the cat eardrum are presented for comparison with the model results.

ISSN:0001-4966    

DOI:10.1121/1.394749

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Tone‐burst‐evoked otoacoustic emissions were measured as a function of tone‐burst sound pressure level and frequency in normally hearing ears. Although the spectral and temporal properties varied across individual ears, there was a close correspondence between stimulus and response spectra. Both the spectral and latency characteristics of tone‐burst‐evoked emissions are consistent with the hypothesis that they are generated at sites along the cochlear partition corresponding to their frequency.

ISSN:0001-4966    

DOI:10.1121/1.394750

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Recent experiments have shown that frequency selectivity measured in tone‐on‐tone simultaneous masking improves with increasing delay of a brief signal relative to the onset of a longer duration gated masker. To determine whether a similar improvement occurs for a notched‐noise masker, threshold was measured for a 20‐ms signal presented at the beginning, the temporal center, or the end of the 400‐ms masker (simultaneous masking), or immediately following the masker (forward masking). The notch width was varied systematically and the notch was placed both symmetrically and asymmetrically about the 1‐kHz signal frequency. Growth‐of‐masking functions were determined for each temporal condition, for a noise masker without a spectral notch. These functions were used to express the thresholds from the notched‐noise experiment in terms of the level of a flat‐spectrum noise which would produce the same threshold. In simultaneous masking the auditory filter shapes derived from the transformed data did not change significantly with signal delay, suggesting that the selectivity of the auditory filter does not develop over time. In forward masking the auditory filter shapes were sharper than those for simultaneous masking, particularly on the high‐frequency side, which was attributed to suppression.

ISSN:0001-4966    

DOI:10.1121/1.394751

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Growth‐of‐masking functions were obtained from 19 normal and 5 hearing‐impaired listeners using a simultaneous‐masking paradigm. When masker and probe frequency are identical, the slope of masking approximates 1.0 for both normal‐hearing and impaired listeners. For masker frequencies less than or greater than probe frequency, the slopes for impaired listeners are shallower than those of normals. These findings are consistent with previously reported physiological data (single‐fiber rate versus level and AP masking functions) for animals with induced cochlear lesions. Results are discussed in terms of a potential masking technique to estimate the growth of response in normal and impaired ears.

ISSN:0001-4966    

DOI:10.1121/1.394752

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Detection of a change in spectral shape, or profile analysis, appears to be mediated by comparisons across widely separated frequency ‘‘channels’’ rather than by local comparisons among adjacent frequency regions [e.g., Greenetal., J. Acoust. Soc. Am.73, 639–643 (1983)]. Two experiments were conducted in order to determine the ‘‘resolution bandwidth’’ of these channels. The first involved detection of an increment to a single component of a multicomponent background as a function of the number of components in the background. Performance improved as the number of components was increased from 3 to 21. Further increases yieldedpoorerperformance and the estimate of the ‘‘resolution bandwidth’’ from these data suggests that this poorer performance was due simply to masking. The second experiment involved discrimination of a multicomponent complex having a flat amplitude spectrum from one having a sinusoidally ‘‘rippled’’ amplitude spectrum. The latter experiment yielded somewhat larger estimates of the ‘‘resolution bandwidth’’ than did the former. Finally, profile analysis was investigated under a dichotic condition that precluded peripheral masking of the signal. Our results, like those of Green and Kidd [J. Acoust Soc. Am.73, 1260–1265 (1983)], suggest that, although spectral analysis can be achieved using information across ears, performance is inferior to that obtained with diotic stimuli.

ISSN:0001-4966    

DOI:10.1121/1.394753

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The spectral properties of a complex stimulus (rippled noise) were varied over time, and listeners were asked to discriminate between this stimulus and a flat‐spectrum, stationary noise. The spacing between the spectral peaks of rippled noise was changed sinusoidally as a function of time, or the location of the spectral peaks of rippled noise was moved up and down the spectrum as a sinusoidal function of time. In most conditions, listeners were able to make the discriminations up to rates of temporal modulation of 5–10 cycles per second. Beyond 5–10 cps the rippled noise with the temporally varying peaks was indiscriminable from a flat (nonrippled) noise. The results suggest that for temporal changes in the spectral peaks of rippled noise, listeners cannot monitor the output of a single (or small number of) auditory channel(s) (critical bands), or that the mechanism used to extract the perceptual information from these stimuli is slow. Temporal variations in the spectral properties of rippled noise may relate to temporal changes in the repetition pitch of complex sounds, the temporal properties of the coloration added to sound in a reverberant environment, and the nature of spectral peak changes such as those that occur in speech‐formant transitions. The results are relevant to the general issue of the auditory system’s ability to extract information from a complex spectral profile.

ISSN:0001-4966    

DOI:10.1121/1.394754

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

A tactile stimulator array constructed from 88 piezoelectric ceramic plates is described. The array can produce sinusoidal traveling waves with arbitrary temporal frequency, spatial wavelength, and amplitude. Detection thresholds were measured for five temporal frequencies (1, 4, 16, 64, and 256 Hz) and five spatial wavelengths (1.81, 3.62, 7.23, 14.5, and ∞ mm), and were plotted as a three‐dimensional, spatiotemporal threshold surface. Detection thresholds were also measured using a conventional vibrator and a large circular contactor simulating the infinite wavelength stimulus produced by the array. The results describe the spatial and temporal frequency sensitivity of the P and NP I cutaneous receptor populations.

ISSN:0001-4966    

DOI:10.1121/1.394755

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The goal of this study was to determine whether acoustic properties could be derived for English labial and alveolar nasal consonants that remain stable across vowel contexts, speakers, and syllable positions. In experiment I, critical band analyses were conducted of five tokens each of [m] and [n]followed by the vowels [i e a o u] spoken by three speakers. Comparison of the nature of the changes in the spectral patterns from the murmur to the release showed that, for labials, there was a greater change in energy in the region of Bark 5–7 relative to that of Bark 11–14, whereas, for alveolars, there was a greater change in energy from the murmur to the release in the region of Bark 11–14 relative to that of Bark 5–7. Quantitative analyses of each token indicated that over 89% of the utterances could be appropriately classified for place of articulation by comparing the proportion of energy change in these spectral regions. In experiment II, the spectral patterns of labial and alveolar nasals produced in the context of [s]+nasal ([m n])+vowel ([i e a o u]) by two speakers were explored. The same analysis procedures were used as in experiment I. Eighty‐four percent of the utterances were appropriately classified, although labial consonants were less consistently classified than in experiment I. The properties associated with nasal place of articulation found in this study are discussed in relation to those associated with place of articulation in stop consonants and are considered from the viewpoint of a more general theory of acoustic invariance.

ISSN:0001-4966    

DOI:10.1121/1.394756

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP