摘要:

Thresholds for the detection of increments and decrements in level of 70 dB SPL sinusoidal signals were measured as a function signal duration (10, 20, or 200 ms), pedestal duration before the signal (10 ms, 200 ms, or pedestal on continuously) and frequency (250, 1000, or 4000 Hz). The sinusoids were presented in a low-pass filtered background noise with an overall level of 68–69 dB SPL which had two purposes: (1) to mask spectral splatter; (2) to induce an adaptation effect, which caused the continuous 4000-Hz pedestal (but not the other two pedestals) to decay to inaudibility (adaptation). We were particularly interested in determining whether the difference in noise-induced adaptation across frequency would influence the pattern of results. Seven normal-hearing subjects were used. Thresholds improved with increasing frequency and with increasing duration for both increments and decrements. However, the effect of increment/decrement duration decreased with increasing frequency; at 4000 Hz thresholds were almost the same for increment durations of 10 and 20 ms. The energy of the increments at threshold increased markedly with increasing increment duration (especially from 20 to 200 ms), suggesting a dominant role for the onsets of the increments as opposed to ongoing differences in level. Increasing the pedestal duration before the increment from 10 to 200 ms slightly improved thresholds for increment and decrement durations of 10 and 20 ms. Increment thresholds were similar for the gated and continuous pedestals at all frequencies, even though the 4000-Hz continuous pedestal decayed to inaudibility. However, thresholds for 200-ms increments were somewhat lower for continuous than for gated pedestals, and supplementary experiments found a larger gated-continuous difference for pedestals presented in quiet. Making the pedestal continuous adversely affected performance for the 10- and 20-ms decrements, but not for the 200-ms decrement. We suggest that the results for decrement detection may be affected by neural long-term adaptation, although they are not clearly related to loudness adaptation.

ISSN:0001-4966    

DOI:10.1121/1.420350

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Thresholds were measured for diotic tonal signals in the presence of interaurally delayed bands of Gaussian noise. When the signal frequency was 525 Hz, the spectrum of the noise was either below (highest frequency, 450 Hz) or above (lowest frequency, 600 Hz) the frequency of the signal. When the signal frequency was 450 Hz, the spectrum of the noise was always above the signal frequency (lowest frequency, 600 Hz). Signals had a 250-ms duration and were temporally centered within the 300-ms long bursts of noise. The spectrum level of the noise was 60 dB. Thresholds obtained in all three conditions varied essentially sinusoidally with the interaural delay of the noise. For signals below the spectrum of the noise, the periodicities within the data were close to, but not identical with, the periodicities of thesignals. This outcome is discussed in terms of masking produced by aural distortion products stemming from interactions within the bands of noise [cf. van der Heijden and Kohlrausch, J. Acoust. Soc. Am.98, 3125–3134 (1995)]. For signals above the spectrum of the noise, the periodicities in the data suggested that masking was produced by components within the band of noise. Patterns within the data are also discussed in terms of limitations concerning the magnitude of external delays that can be matched by internal delays that are incorporated in modern models of binaural processing.

ISSN:0001-4966    

DOI:10.1121/1.420351

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

In an anechoic chamber, subjects were required to discriminate a 20° azimuthal change in a lag sound’s position in the presence of a lead sound coming from a different direction. Delay between lead and lag sounds was adaptively varied in several conditions to track discrimination suppression thresholds. In experiment 1, lead and lag stimuli were 5-ms, 1-octave, A-weighted noise bursts (65 dB), with lead and lag parametrically set to center frequencies of 0.5, 2.0, or 3.0 kHz. Discrimination suppression thresholds were higher when lead and lag center frequencies coincided (mean: 11.3 ms) than when they did not coincide (mean: 2.9 ms). These results support the “spectral overlap hypothesis” of Blauert and Divenyi [Acustica66, 267–274 (1988)], but not the “localization strength hypothesis” later proposed by Divenyi [J. Acoust. Soc. Am.91, 1078–1084 (1992)]. Spectral overlap and localization strength appear to be two relatively independent factors governing discrimination suppression. It is proposed here that localization strength is weighted more when stimuli are presented via headphones and the only cue to lateral position is the interaural temporal difference, while spectral overlap is weighted more for free-field presented stimuli. In experiment 2, lead and lag stimuli were 8-ms, 1.5-kHz A-weighted tone bursts (65 dB), with lead and lag rise times parametrically set to 0, 2, or 4 ms. In this case the amount of discrimination suppression increased as lead rise time became more abrupt or as lag rise time became more gradual. These results support the localization strength hypothesis: The greater the localization strength of the lead stimulus (independently assessed by measuring its minimum audible angle in isolation), the greater suppression it exerted on discriminability of the lag sound’s position. It appears that for stimuli presented in the free-field, spectral overlap is the primary factor affecting discrimination suppression, but when overlap is held constant, abruptness of stimulus onsets governs the amount of suppression.

ISSN:0001-4966    

DOI:10.1121/1.420352

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Speaking fundamental frequency levels and usage (SFF,F0) are of interest to many investigators who study human speech and voice. Substantial research in the area has been carried out; common foci include SFF as related to infant cry, age, gender, adolescent voice change, language, race, voice pathology, and so on. Yet there still are a number of relationships which are not well understood and three of them will be addressed in this project. They involve the long-held notions that (1) a secular trend exists with SFF being lowered over time, (2) the use of university students in research of this type will create bias because they are physically different from average individuals, and (3) SFF can vary systematically for different types of speech (especially for oral reading and extemporaneous speaking). Experiments assessing these questions were carried out, but only certain of the postulates were supported. That is, while some evidence of a secular trend was found, it appeared inconsequential during the past quarter of this century; second, although university students were found to be slightly larger than a cohort approaching the average population, only minor vocal differences were found. Finally, it was observed that, in general, oral reading resulted in higher mean SFF’s than those for spontaneous speech. However, this difference was not robust and, due to reversals, the resulting metric did not appear to be of good predictive value for individual speakers.

ISSN:0001-4966    

DOI:10.1121/1.420353

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Normally hearing listeners were presented with vowels, consonants, and sentences for identification through an acoustic simulation of a five-channel cochlear implant with electrodes separated by 4 mm (as in the Ineraid implant). The aim of the experiment was to simulate the effect of depth of electrode insertion on identification accuracy. Insertion depth was simulated by outputing sine waves from each channel of the processor at a frequency determined by the cochlear place of electrodes inserted 22–25 mm into the cochlea. The results indicate that simulated insertion depth had a significant effect on performance. Performance at 22- and 23-mm simulated insertion depths was always poorer than normal, and performance at 25-mm simulated insertion depth was, most generally, the same as normal. It is inferred from these results that, if insertion depth could be unconfounded from other coexisting factors in implant patients, then insertion depth would be found to affect speech identification performance significantly.

ISSN:0001-4966    

DOI:10.1121/1.420354

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Identification curves were estimated for the English consonants /b,d,g/ using five-formant CV synthetic stimuli comprehensively sampling theF2onset–F2vowel acoustic space in the vicinity of /b,d,g/ locus equations [H. Sussman et al., J. Acoust. Soc. Am.90, 1309–1325 (1991)]. The stimuli included 10 English monophthongal vowel contexts, 11 levels ofF2onset per vowel, and 3 levels ofF3onset orthogonally varied with theF2variables (10 vowels×11F2onsets×3F3onsets=330 stimuli). After brief training, each of six subjects, three male and three female, was presented eight trials of each of the stimuli, one or two trials per day over a period of several days. Systems of identification curves were visualized as identification surfaces situated in locus equation acoustic space and were overlaid with acoustic data from five male speakers in order to judge the degree of correspondence between perception and acoustic data. A chi square analysis was also performed in order to quantify the correspondence between the observed perception data and expected frequencies derived from the acoustic data. The results, when interpreted in terms of a dominance hierarchy hypothesis, strongly indicateF2onset andF2vowel, in combination, serve as important cues for stop consonant place of articulation.

ISSN:0001-4966    

DOI:10.1121/1.421012

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Five perception experiments were conducted that investigated how the perceived prominence ofF0maxima in accented syllables in Dutch is affected by the variation ofF0minima that is supposed to relate to variation in global pitch range. The purpose of the first two experiments was to test the predictions of a model in which the reference line is directly given by an interpolation between observableF0minima. The results showed that the model was inadequate, and confirmed earlier research suggesting that the reference line is calculated in a less direct way. The next three experiments investigated the role of theF0of the unaccented portions of speech at the beginning (“onset”) and at the end (“offset”) of the contour, and show that only the (low) onset is used to calibrate the reference line. The results also suggest that longer onsets affect the abstract reference more than do shorter onsets.

ISSN:0001-4966    

DOI:10.1121/1.420355

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Idealized woodwind models assume a well-localized nonlinearity coupled to a linear bore whose mathematical description is usually expressed through a convolution product. For the case of the simplest bore geometries, cylindrical and conical, the convolution can be transformed into a delayed differential equation. When including in it the nonlinearity, the usual concepts of nonlinear dynamical systems allow a better understanding of the system’s evolution. In this paper they are applied to the cylindrical and conical geometries and some characteristics of their behaviors are analyzed at the threshold of oscillation through an analytical study. It is shown that their dynamics cannot be reduced to a finite number of degrees of freedom (effective dynamics). Finally numerical simulations reveal peculiar characteristics of the direct and inverse bifurcations involved in such simple systems for quadratic and cubic nonlinearities respectively.

ISSN:0001-4966    

DOI:10.1121/1.420357

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

In a previous paper [Barjau et al., J. Acoust. Soc. Am.102, 3023–3031 (1997)], a differential formulation has been used to study the stability and bifurcations in geometrically simple woodwindlike systems. For general bore geometries, such differential formulation can be obtained by representing the system through a lumped equivalent mechanical model whose parameters are extracted from a real impedance curve on which a modal analysis has been performed. The present procedure is then applied to a particular case and several time-domain simulations are carried out in order to both assess the validity of the systematically developed procedure and explore the possible system behaviors far from the threshold of oscillation.

ISSN:0001-4966    

DOI:10.1121/1.420358

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Nonlinear wave propagation in a system consisting of a liquid specimen held between twoSiO2buffer rods is studied as a new method of determining the acoustic nonlinearity parameter of liquids at very high frequencies. Since the sign of the nonlinearity parameter ofSiO2is opposite that for liquids, the system can be viewed as a transmission line containing regions of both positive and negative nonlinearity. The nonlinear characterization curve is employed in which the second harmonic component output of the receiving transducer is plotted as a function of propagation distance in liquids between the twoSiO2buffer rods. The nonlinearity parameter is determined by measuring the dip position at which the transducer output becomes zero in the curve. Measurements are reported for water and aqueous solutions of dextrose and dextran in the fundamental frequency range 100–200 MHz.

ISSN:0001-4966    

DOI:10.1121/1.420359

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP