摘要:

From the measurement of the acoustic pressure on a cylindrical, two‐dimensional contour located close to the surface of an underwater, vibrating cylinder, the complete three‐dimensional sound field can be reproduced (reconstructed) with the aid of a computer. This reconstruction technique, called GENAH (generalized nearfield acoustical holography), is unlike conventional holography because it provides a super resolution image of the sound‐pressure field from the surface of the cylinder to the farfield. At the same time, GENAH reconstructs, from this two‐dimensional measurement, the vector velocity and the vector intensity fields (energy flow) in the nearfield of the source, and identifies modes of surface vibration of the cylinder. Experimental results are provided and the accuracy of GENAH is demonstrated by comparison with the two‐hydrophone technique.

ISSN:0001-4966    

DOI:10.1121/1.394904

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Recent experimental observations of otoacoustic emissions suggest the existence of spontaneous emitters of sound on the basilar membrane. These tend to send off waves not only in the normal direction of propagation. It is therefore significant to study the environmental conditions such an emitter finds inside the cochlea. The impedance relations seen by these emitters are described by the Riccati equation for an inhomogeneous transmission line. The results reported in this paper differ considerably for forward and backward excitation. This reflects the quite different behavior of the cochlea pertaining to waves traveling forward and backward. Because of reflections, backward waves cannot be treated with the Liouville–Green approximation.

ISSN:0001-4966    

DOI:10.1121/1.394905

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Decrement in ABR wave V amplitude was measured in the presence of simultaneous tonal maskers. Probe stimuli were 1.0, 4.0, and 8.0‐kHz third‐octave‐filtered clicks. Adults and 3‐month‐old infants served as subjects. The resultant amplitude‐decrement functions for each tonal masker were fit with regression lines. The sound pressure level (SPL) required to reduce wave V to 50% of the unmasked probe amplitude was plotted for each masker to develop tuning curves. The tuning curves were quantified by calculations of tip‐to‐tail difference,Q10, and SPL at maximum masker frequency (MMF). Tuning curves for adult and infant subjects were similar for the 1.0‐kHz probe. For the high‐frequency probes (4.0 and 8.0 kHz), smaller tip‐to‐tail differences and lowerQ10 values were observed for the infant subjects. Ranges of MMF level were similar across adult and infant subjects. For the 8.0‐kHz probe, tuning curves from infant subjects consistently showed maximum masker frequencies which were lower than the probe.

ISSN:0001-4966    

DOI:10.1121/1.394906

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Thresholds for 10‐ms sinusoids simultaneously masked by bursts of bandpass noise centered on the signal frequency were measured for a wide range of signal frequencies and noise levels. Thresholds were defined as the signal power relative to the masker power at the output of an auditory filter centered on the signal frequency. It was found that the presentation of a continuous random noise, with a spectral notch centered on the signal frequency, produced a reduction in signal thresholds of up to 11 dB. A notched noise spectrum level of 0–5 dB above that of the masker proved most effective in producing a masking release, as measured by a reduction in masked threshold. A release from masking of up to 7 dB could be obtained with a continuous bandpass noise. The most effective spectrum level of this noise was 5 dB below that of the masker. The effect of the continuous notched noise was to reduce signal‐to‐masker ratios at threshold to about 0 dB, regardless of the threshold in the absence of continuous noise. Thus the greatest release from masking occurred when ‘‘unreleased’’ thresholds were highest. The release from masking is almost complete within 320 ms of notched noise onset, and persists for about 160 ms after notched noise offset, regardless of notched noise level. The phenomenon is similar in many ways to the ‘‘overshoot’’ effect reported by Zwicker [J. Acoust. Soc. Am.37, 653–663 (1965)]. It is argued that both effects can be largely attributed to peripheral short‐term adaptation, a mechanism which is also believed to be involved in forward masking.

ISSN:0001-4966    

DOI:10.1121/1.395117

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Twenty‐eight audiometrically normal adult listeners were given a variety of auditory tests, ranging from quiet and masked thresholds through the discrimination of simple and moderately complex temporal patterns. Test–retest reliability was good. Individual differences persisted on a variety of psychoacoustic tasks following a period of training using adaptive threshold‐tracking methods, and with trial‐by‐trial feedback. Large individual differences in performance on temporal‐sequence‐discrimination tasks suggest that this form of temporal processing may be of clinical significance. In addition, high correlations were obtained within given classes of tests (as, between all tests of frequency discrimination) and between certain classes of tests (as, between tests of frequency discrimination and those of sequence discrimination). Patterns of individual differences were found which support the conclusion that individual differences in auditory performance are, in part, a function of patterns of independent abilities.

ISSN:0001-4966    

DOI:10.1121/1.394907

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Envelope‐induced pitch shifts were measured for exponentially decaying complex tones consisting of two sinusoidal components with frequencies  f 1=n f 0+50 Hz and  f 2=(n+1) f 0+50 Hz, wherenequals 3, 4, or 5 and exponential decay rates were 0, 0.5, 1, and 2 dB/ms. Four subjects adjusted a sinusoidal comparison tone to match the virtual pitch of the (missing) fundamental and the pitches of the lower and upper partials  f 1and  f 2. Pitch shifts for  f 1are generally less, and pitch shifts for  f 2always greater, than envelope‐induced shifts observed in isolated sinusoidal tones of comparable frequency and envelope decay rate. Pitch‐shift functions for virtual pitch are similar in magnitude and shape to average pitch‐shift functions of the partials, which supports the idea that virtual pitch depends on spectral pitch.

ISSN:0001-4966    

DOI:10.1121/1.394908

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The present study compared the abilities of normal and hearing‐impaired subjects to discriminate differences in the spectral shapes of speechlike sounds. The minimum detectable change in amplitude of a second‐formant spectral peak was determined for steady‐state stimuli across a range of presentation levels. In many cases, the hearing‐impaired subjects required larger spectral peaks than did the normal‐hearing subjects. The performance of all subjects showed a dependence upon presentation level. For some hearing‐impaired subjects, high presentation levels resulted in discrimination values similar to that of normal‐hearing subjects, while for other hearing‐loss subjects, increases in presentation level did not yield normal values, even when the second‐formant spectral region was presented at levels above the subject’s sensitivity thresholds. These results demonstrate that under certain conditions, some sensorineural hearing‐impaired subjects require more prominent spectral peaks in certain speech sounds than normal subjects for equivalent performance. For the group of subjects who did not achieve normal discrimination results at any presentation level, application of high‐frequency amplification to the stimuli was successful in returning those subjects’ performance to within normal values.

ISSN:0001-4966    

DOI:10.1121/1.394909

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

A series of experiments was performed to study the ability of the ear to code the temporal envelope of a waveform as demonstrated by comodulation masking release (CMR). The stimulus for all experiments was composed of a tone‐burst signal, a 100‐Hz‐wide masker band centered at the signal frequency, and a second 100‐Hz‐wide noise band of variable frequency, the cue band. The cue band had a temporal envelope which was either correlated with or independent of that of the masker. The signal was a 100‐Hz tone burst for most experiments. For the monotic stimulus, the correlated cue band results in lowered signal detection thresholds over a range extending from around 2/3 oct below the signal frequency to 1/3 oct above that frequency. When measured dichotically, with the signal and masker band in one ear and the cue band in the opposite ear, that effective range is expanded but the detection threshold shifts are a bit smaller. The greatest CMR is observed when the stimulus is presented diotically. With regard to effects of level and frequency, our data show CMR increasing with increasing stimulus level for a cue band lower in frequency than the signal, but show little effect of level for a cue band higher in frequency. Similarly, CMR increases with increasing stimulus frequency when the cue band is lower in frequency, but shows little effect of frequency for a cue band higher in frequency.

ISSN:0001-4966    

DOI:10.1121/1.394910

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Thresholds for the detection of 500‐ms tones in noise at either 0.25 or 4 kHz and either interaurally in‐phase (NoSo) or out‐of‐phase (NoSπ) were measured as a function of the bandwidth of a diotic masking noise (with total noise power held constant). NoSo thresholds followed the classic trend indicative of an effective critical band in noise masking. NoSπ thresholds also indicated critical‐band filtering, but with a wider effective critical bandwidth. At subcritical masker bandwidths, for both 0.25 and 4 kHz, NoSπ thresholds increased with an increase in noise bandwidth, despite the fact that total noise power was constant. This latter finding is attributed to binaural insensitivity to rapid fluctuations in the interaural cues that subserve detection in the NoSπ condition. These results suggest a new interpretation for the small difference between NoSo and NoSπ thresholds measured with high‐frequency tones in a broadband noise masker. This interpretation is based partly on the inability to utilize rapidly varying interaural cues, partly on out‐of‐band interference effects, and partly on loss of information related to stimulus fine structure.

ISSN:0001-4966    

DOI:10.1121/1.394911

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Within the framework of a study on the merits of a frequency‐dependent automatic gain control in hearing aids, the effect of varying the slope of the amplitude‐frequency response on the speech‐reception threshold (SRT) for sentences in noise was studied for normal‐hearing listeners. Speech and noise were both subjected to the same amplitude‐frequency response. In the first experiment, the effect of a constant slope was investigated (20 listeners). Over a range of about −7 to +10 dB/oct, the SRT in noise remained constant. In the second experiment, a single change in the slope of the amplitude‐frequency response was introduced halfway through the sentence. The effect of varying the transition time over a range down to 0.125 s appeared to be very small. In the third experiment, the slope varied continuously with range and variation frequency (0.25–2 Hz) as the parameters. The masked SRT increased gradually with variation frequency. The results indicate that the masked SRT for sentences is remarkably resistant to dynamic variations in the slope of the amplitude‐frequency response.

ISSN:0001-4966    

DOI:10.1121/1.394912

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP