摘要:

Presented here is the echosonde (acoustic echosounding) synthesis based on a more rigorous analytical tool than hitherto available. The basic problem addressed in this paper is that of specifying a pattern and solving for the source distribution capable of reproducing the pattern specified. We focus attention on the determination of suitable practical source fields that can provide acceptable pattern approximations to certain prescribed echosonde beams. Numerical and analytical examples discussed, describe patterns synthesizing into physically realizable source fields confined within finite antenna‐aperture regions. Also, other analytical results provided, reveal very clearly that the pattern synthesis problem is not unique. In order to highlight the importance of the present echosonde contribution to the general problem of circular synthesis, we present a brief survey of the synthesis works to date where certain technical problems which still remain unresolved are pointed out. A substantial set of new results for circular echosonde synthesis which has received little attention in the literature, is presented in comprehensive tables for ease of reference. The paper also finally examines an error analysis of certain aspects of the results obtained.

ISSN:0001-4966    

DOI:10.1121/1.391137

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A new model for piezoelectric ultrasonic transducers is proposed. Using a systems engineering approach, the concept of feedback is used to explain secondary piezoelectric effects and to clearly describe electromechanical interaction. The model is derived from the fundamental piezoelectric equations and it embraces the relevant practical situations where the transducer is subject to arbitrary electrical and mechanical loading. Block diagram representations of the piezoelectric transducer acting as a generator and receiver of ultrasound are developed. The physical significance of each element in the block diagrams are explained to provide a clear and distinct relationship between electrical and mechanical quantities. This permits the factors which control secondary piezoelectric action to be readily defined, along with the importance of this effect on the overall transfer function. It is considered that no other transducer model illustrates these concepts with the same degree of clarity and the technique offers significant advantages over existing transducer analogies. A number of computer simulations and experimental water tank measurements of acoustic wave profiles are presented. Close substantiation of the theoretical analysis is shown.

ISSN:0001-4966    

DOI:10.1121/1.391138

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

This study reassessed the role of the nasal murmur and formant transitions as perceptual cues for place of articulation in nasal consonants across a number of vowel environments. Five types of computer‐edited stimuli were generated from natural utterances consisting of [m n] followed by [i e a o u]: (1) full murmurs; (2) transitions plus vowel segments; (3) the last six pulses of the murmur; (4) the six pulses starting from the beginning of the formant transitions; and (5) the six pulses surrounding the nasal release (three pulses before and three pulses after). Results showed that the murmur provided as much information for the perception of place of articulation as did the transitions. Moreover, the highest performance scores for place of articulation were obtained in the six‐pulse condition containing both murmur and transition information. The data support the view that it is the combination of nasal murmur plus formant transitions which forms an integrated property for the perception of place of articulation.

ISSN:0001-4966    

DOI:10.1121/1.391139

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

This study explored the claim that invariant acoustic properties corresponding to phonetic features generalize across languages. Experiment I examined whether the same invariant properties can characterize diffuse stop consonants in Malayalam, French, and English. Results showed that, contrary to theoretical predictions, we could not distinguish labials from dentals, nor could we classify dentals and alveolars together in terms of the same invariant properties. We developed an alternative metric based on the change in the distribution of spectral energy from the burst onset to the onset of voicing. This metric classified over 91% of the stops in Malayalam, French, and English. In experiment II, we investigated whether the invariant properties defined by the metric are used by English‐speaking listeners in making phonetic decisions for place of articulation. Prototype CV syllables—[b d] in the context of [i e a o u]—were synthesized. The gross shape of the spectrum was manipulated first at the burst onset, then at the onset of voicing, such that the stimulus configuration had the spectral properties prescribed by our metric for labial and dental consonants, while the formant frequencies and transitions were appropriate to the contrasting place of articulation. Results of identification tests showed that listeners were able to perceive place of articulation as a function of the relative distribution of spectral energy specified by the metric.

ISSN:0001-4966    

DOI:10.1121/1.391580

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Many older people have greater difficulty processing speech at suprathreshold levels than can be explained by standard audiometric configurations. Some of the difficulty may involve the processing of temporal information. Temporal information can signal linguistic distinctions. The voicing distinction, for example, that separates pairs of words such as ‘‘rapid’’ and ‘‘rabid’’ can be signaled by temporal information: longer first vowel and shorter closure characterize ‘‘rabid’’; shorter vowel and longer closure characterize ‘‘rapid.’’ In this study, naturally produced tokens of ‘‘rabid’’ were low‐pass filtered at 3500 Hz and edited to create vowel and (silent) closure duration continua. Pure‐tone audiograms and speech recognition scores were used to select the ten best‐hearing subjects among 50 volunteers over age 55. Randomizations of the stimuli were presented for labeling at intensity levels of 60 and 80 dB HL to this group and to ten normal‐hearing volunteers under age 25. Results showed highly significant interactions of age with the temporal factors and with intensity: the older subjects required longer silence durations before reporting ‘‘rapid,’’ especially for the shorter vowel durations and for the higher intensity level. These data suggest that age may affect the relative salience of different acoustic cues in speech perception, and that age‐related hearing loss may involve deficits in the processing of temporal information, deficits that are not measured by standard audiometry.

ISSN:0001-4966    

DOI:10.1121/1.391581

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Can a shift in interaural phase between a subthreshold signal and an audible contralateral probe tone affect perception of the probe? To obtain an answer, an 800‐Hz tone was presented to both ears. The tone was presented continuously to one ear (−25 to + 10 dB SL) and in a sequence of four bursts per trial to the other ear (+10 dB SL). Interaural phase was reversed for either the second or the fourth burst in a 2 AFC task. Interaural phase‐shift detection threshold (65% correct) varied with the intensity of the continuous signal; across subjects, this threshold varied from −21 to +1 dB SL. When a 300‐or 500‐Hz masking tone was added to the ear with the continuous signal, phase‐shift detection accuracy depended primarily upon the sensation level of the signal rather than its sound pressure level. These findings demonstrate temporal encoding at signal levels well below hearing threshold.

ISSN:0001-4966    

DOI:10.1121/1.391582

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A continuous 400‐Hz tone (60–75 dB SPL) and 250‐msec bursts of an 800‐Hz tone (10 dB SL) were delivered dichotically. Four out of nine listeners were able to detect a 180° interaural phase shift. When a subaudible continuous 800‐Hz tone was added to the ear with the 400‐Hz tone, interaural phase‐shift detection depended on the phase relation of the added tone to the 400‐Hz tone. These results are shown to be consistent with the hypothesis of aural harmonic distortion.

ISSN:0001-4966    

DOI:10.1121/1.391583

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

This experiment was designed to measure the shape and asymmetry of the auditory filter over a wider dynamic range than has been measured previously. Thresholds were measured for 2‐kHz sinusoidal signals in the presence of two 800‐Hz‐wide noise bands, one above and one below the signal frequency. The spectrum level of the noise was 45 dB (re: 20 μPa), and the noise bands were placed both symmetrically and asymmetrically about the signal frequency. The deviation of the signal frequency from the nearer edge of each noise band varied from 0 to 0.8 times the signal frequency. Each ear of six subjects was tested, and the subjects’ ages ranged from 22 to 74 years. The auditory filters derived from the data were somewhat asymmetric, with steeper slopes on the high‐frequency side; the degree of asymmetry varied across subjects. The asymmetry could be characterized as a uniform stretching of the (linear) frequency scale on one side of the filter. The dynamic range of the auditory filter exceeded 60 dB in the younger listeners, but the dynamic range and sharpness of the filter tended to decrease with increasing age.

ISSN:0001-4966    

DOI:10.1121/1.391584

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

An experiment was carried out, investigating the relationship between the just noticeable difference of fundamental frequency (jndf0) of three stationary synthesized vowel sounds in noise and the signal‐to‐noise ratio. To this end the S/N ratios were measured at which listeners could just discriminate a series of changes in  f0in the range from 10% to 0.5%. Similar measurements were obtained for pulse trains and for pure tones as a reference for the results. A measure of S/N ratio based on an approximation of the critical bandwidth appeared to provide a fairly good predictor of the masked threshold of each signal, measured in a second experiment. Using this measure, it was found that a given change in the fundamental of a pulse train could be discriminated at a lower S/N ratio than in a pure tone with a frequency equal to that fundamental. The results for the vowel sounds were found to be in between those for a low‐frequency pure tone and those for a pulse train. Owing to the signal‐generation method (viz., changing  f0by changing the sampling frequency), three cues could in principle be used to discriminate a change in the fundamental of a vowel: A change in the residue pitch, a change in the pitch of a single prominent harmonic, or a change in the spectral envelope of the signal. It can be inferred from the results that the subjects used that particular cue which yielded best performance. Which cue was optimal depended not only on the vowel but also on  f0and on the presented change in  f0. It seems, however, that the pitch of a single harmonic was the cue most often used. Another interesting result is that changes in  f0greater than about 5%, could for each signal be discriminated when the signal was just above masked threshold.

ISSN:0001-4966    

DOI:10.1121/1.391134

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The relation between the monaural critical band and binaural analysis was examined using an NoSm MLD paradigm, in order to resolve ambiguities about the width of the masking spectrum important for binaural detection. A 500‐Hz pure‐tone signal was presented with a 600‐Hz‐wide band of masking noise to the signal ear. Bands of noise ranging in width from 25 to 600 Hz, or noise notches (imposed on a 600‐Hz‐wide band centered on the signal frequency) ranging in width from 0 to 600 Hz were presented to the nonsignal ear. All noise bands and notches were centered on 500 Hz, the frequency of the signal. The effects of varying bandwidth were radically different from those of varying notchwidth: the MLD changed from zero to approximately 8 dB over a bandwidth range of 400 Hz; for notchwidths, however, the MLD changed 8 dB over a range of only 50 Hz. The results support an interpretation that the fine frequency selectivity of monaural analysis is preserved in peripheral binaural interaction, but that a relatively wide frequency range of critical bands is scanned at a later stage of binaural processing. It was suggested that the wide spectral range of binaural analysis may provide a background against which binaural differences due to the signal are detected.

ISSN:0001-4966    

DOI:10.1121/1.391135

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP