摘要:

Three experiments were carried out to investigate the importance of dynamic cues in monaural and binaural detection tasks. All experiments employed a two‐interval forced‐choice procedure, in which the signal, a 500‐Hz tone, 128 msec in duration, was added to the masker prior to gating in one of the two intervals. Both monaural (signal and masker diotic: M0–S0) and binaural (diotic masker, signal phase‐reversed in one ear relative to the other: M0–Sπ) conditions were investigated. The masker (70 dB SPL) was either a tone of 500 Hz (Experiment 1), a 500‐Hz carrier tone modulated by a 50‐Hz tone (Experiment 2), or a 500‐Hz carrier tone modulated by a band‐pass noise centered at 60 Hz (Experiment 3). The angle of addition of the signal to the masker (α) was either 0°, 45°, 90° or 135°. In general, for all values of α, S0 thresholds increased from Experiment 1 to Experiment 3, indicating that monaural signal detection is more difficult in a dynamic than in a static environment. Sπ thresholds did not change significantly from Experiment 1 to Experiment 2, thus giving no support to the notion that detection of regularly varying interaural cues (at a modulation frequency of 50 Hz) is easier than detection of static cues. However, Sπ thresholds in Experiment 3 were slightly higher than in Experiment 2, indicating that detection of randomly fluctuating interaural cues is more difficult than detection of regularly fluctuating cues.

ISSN:0001-4966    

DOI:10.1121/1.381296

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The masking of silent intervals, or gaps, by surrounding noise bursts was investigated. The durations and the spectrum levels of the two noises were varied and the just detectable gap ΔTdetermined. The first experiment demonstrated the conditions in which duration judgments may have provided a cue. The remaining experiments were therefore designed so that this duration cue was not available. The second experiment indicated that changing the second noise duration from 200 to 2 msec did not greatly affect ΔT, suggesting a close relationship between forward masking and gap detection. Finally, Plomp [J. Acoust. Soc. Am. 36, 277–282 (1964)] has argued that a graph of the level of the second noise in decibels as a function of log ΔTtraces the time course of decay of the first noise. If so, the data from the third experiment indicate that this decay rate depends on the spectrum level of the noise but not on its duration.

ISSN:0001-4966    

DOI:10.1121/1.381297

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Trained chinchillas were exposed to 6 h of noise followed by 18 h of quiet for nine days. Thresholds (0.5–8.0 kHz) were measured immediately before and after each day’s exposure. The decay of threshold shift after the ninth day was followed until stable thresholds were again observed. This procedure was repeated for six levels (57–92 dB SPL) of an octave‐band noise centered at 4.0 kHz. The threshold shift measured after 4 min of quiet (TS4) appears to reach an asymptotic level (ATS4) after the first or second exposure. ATS4, measured at frequencies exhibiting greatest shift (5.7 kHz), increases with the level of the noise with the same slope (1.7 dB/dB) for the daily 6‐h exposures as for nearly continuous exposures. ATS4is smaller for 6 h than nearly continuous exposures by about 5 dB and this difference can be explained by an equivalent‐power hypothesis. The decay of threshold shift was nearly complete after 18 h of quiet for the lowest levels of noise, while it was nearly complete only after 3–5 days for the intermediate levels of noise. The decay of threshold shift was never complete and small amounts of permanent threshold shift were observed for the highest levels of noise.

ISSN:0001-4966    

DOI:10.1121/1.381298

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Tones below 500 Hz show masking effects that are different from those of higher‐frequency tones. Where middle‐ and high‐frequency tones have their maximum effect at the masking frequency, and most of the rest of their effect at frequencies higher than themselves, low‐frequency tones are consistently most effective in the 400‐ to 600‐Hz range. Possible explanations are offered.

ISSN:0001-4966    

DOI:10.1121/1.381299

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Intelligibility, redundancy (frequency domain), and phoneme confusions of speech were investigated through narrow‐band filtering. Filtered syllables (CV) and words (CVC) were presented to twelve paid, normally hearing subjects. Stimuli consisted of 17 English consonants paired with three vowels /i, u, a/, and filtered through five conventional one‐third octave bands centered at 0.5, 1, 2, 3.15, and 4 kHz, and one ’’critical’’ band (500 Hz wide) centered at 3.15 kHz. Results revealed (1) no significant differences between syllable and word intelligibility; (2) word or syllable intelligibility was maximum (50%) for the band centered at 2 kHz, and was greater for the bands above 2 kHz compared to those situated below this frequency; (3) speech intelligibility was reduced for the critical band compared to the one‐third octave band centered at 3.15 kHz; (4) about half of the syllables or words were perceived correctly in more than one band reflecting redundant perceptual cues along the frequency domain; and (5) consonantal‐confusion data revealed thatmannerandvoicingfeatures were least affected, and theplacefeature was most affected by filtering.

ISSN:0001-4966    

DOI:10.1121/1.381300

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The acoustic manifestation of nasal murmurs is significantly context dependent. To what extent can the class of nasals be automatically detected without prior detailed knowledge of the segmental context? This contribution reports on the characterization of the spectral change accompanying the transition between vowel and nasal for the purpose of automatic detection of nasal murmurs. The speech is first segmented into syllable‐sized units, the voiced sonorant region within the syllable is delimited, and the points of maximal spectral change on either side of the syllabic peak are hypothesized to be potential nasal transitions. Four simply extractible acoustic parameters, the relative energy change in the frequency bands 0–1, 1–2, and 2–5 kHz, and the frequency centroid of the 0–500‐Hz band at four points in time spaced 12.8 msec apart are used to represent the dynamic transition. Categorization of the transitions using multivariate statistics on some 524 transition segments from data of two speakers resulted in a 91% correct nasal/non‐nasal decision rate.

ISSN:0001-4966    

DOI:10.1121/1.381301

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The action of the guitar has been studied in detail in the vicinity of the Helmholtz air resonance and the first resonance of the top plate. Measurements of the input mechanical admittance, the output sound pressure, and their phases suggest an analogous acoustical circuit for the guitar identical with that used to describe the action of a loudspeaker in a bass‐reflex enclosure. Below the Helmholtz resonance sound radiated from the rose and from the top plate are out of phase. As a result sound radiated from the guitar is not enhanced by the rose. Above this resonance sound output from the rose and top plate are more nearly in phase with a resulting enhancement of radiated sound.

ISSN:0001-4966    

DOI:10.1121/1.381302

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

This article presents a nonconventional way using the ring‐function method for the analysis of the nearfield of a circular piston in an infinite baffle for the case where the velocity distribution across the face of the piston has a parabolic profile.

ISSN:0001-4966    

DOI:10.1121/1.381303

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

In a number of papers, equations have been derived which govern acoustic propagation in the ocean from an initial plane surface. In this paper we present the governing equation in cylindrical coordinates and then give the simplification introduced by cylindrical symmetry. The loss of coherence along a horizontal direction is then treated in three special cases.

ISSN:0001-4966    

DOI:10.1121/1.381304

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The contour integration method is used to compute nearfield axial levels for two exponentially shaded end‐fire arrays of finite cross section: a plane‐collimated cylindrical array and a spherically divergent conical array. The results are of interest in modeling parameteric virtual arrays.

ISSN:0001-4966    

DOI:10.1121/1.381305

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP