摘要:

Amplitude shading techniques are used in arrays to achieve reduced sidelobe levels with reasonably small major lobe width. Most papers on shading consider arrays without restriction of amplitude and location of the shading function to discrete choices. For some arrays such as resonant sonar arrays, it is desirable to achieve the amplitude shading by series‐parallel combinations of discrete elements of the array. Such an arrangement forces a relationship between the width and amplitude of discrete zones. This problem is illustrated in the design of a linear array of 24 elements for which the sidelobe level must be less than −20 dB. One discrete shading configuration had −21.9 dB sidelobe level. The best choice of series‐parallel combinations achieved a narrower beamwidth and a −25.7 dB sidelobe level. [Work supported by Naval Sea Systems Command.]

ISSN:0001-4966    

DOI:10.1121/1.2017193

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A Canada wide survey of the diagnostic, therapeutic, and surgical applications of ultrasound in medicine was conducted in the Fall of 1977. A total of 4154 questionnaires were sent to 1341 hospitals, 1887 chiropractors, 300 physiotherapists, and 726 sports medicine clinics. 62% of the questionnaires were returned, 40% of these completed. The comprehensive questionnaire provides information on the type of equipment used, the operator qualifications, the patient exposure, the number of patients treated, and adverse effects. Statistics of the results of the survey will be presented. The survey is believed to be the most detailed study undertaken to date of the use of ultrasound in medicine, and the results will be of interest to all ultrasound regulatory bodies and physicians working in the field.

ISSN:0001-4966    

DOI:10.1121/1.2017238

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Fresh mammalian tendon threads (diameter ≃110 μm) were examined using the scanning laser acoustic microscope (Sonomicroscope 100R, Sonoscan, Inc., Bensonville, IL) at 100 MHz to make quantitative ultrasonic velocity and impedance measurements. Tendon is high in collagen (about 30% wet weight, 50%–90% dry weight), a structural protein which is believed to be important in the ultrasonic visualization of tissues. Ultrasonic velocity measurements are made by measuring a shift in the phase front of the sound as it propagates through the tissue as compared with the surrounding medium. Ultrasonic impedance measurements are made by comparing the acoustic contrast of the specimen with respect to that of the surrounding medium. The use of different media provides the opportunity to match velocity and impedance of the medium with that of the collagen threads thus yielding quantitative values of these ultrasonic characterization parameters. The use of different media also allows examination of the possibility that the medium itself is affecting the collagen thread. Two reference media at various concentrations were used, viz., aqueous solutions of sodium chloride or glycerine. Initial results using the different media indicate that the velocity of tendon is similar to that of pure glycerine (velocity ≃ 1926 m/s). This is almost 30% greater than the ultrasonic velocity of soft tissues. An impedance match has not been obtained using the reference media of the present study. This result suggests that the collagen thread may not be homogeneous with respect to its ultrasonic properties. This result when considered with the high velocity of the tendon, indicate that there is a marked difference in the ultrasonic characteristics of this tissue and other biological tissue. [This work was supported in part by grants from NIH and a Biomedical Research grant from University of Illinois, Urbana‐Champaign.]

ISSN:0001-4966    

DOI:10.1121/1.2017289

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In order to shed light on a specific theory of peripheral auditory representation (drawn from work by Zwicker and recently formalized by Schroeder, Atal, and Hall) we have used data on how listeners match two‐formant vowels to four‐formant stimuli. We report on two experiments designed to test the hypothesis that such listeners determined their favoredF2′ according to a distance measure (adapted from Plomp) formulated in terms of such auditory representations. This theory models the auditory transformation of the acoustic signal as a conversion of the power spectrum into a sones/Bark representation by computing critical‐band densities and applying a (basilar membrane‐like) frequency smearing function. The computed pseudoauditory vowel distance measure was found to correlate very highly with the listeners judgments of vowel‐quality distance obtained from the two experiments described, which involved the comparison of numerous vowel pairs from reportedF2′ data. The results suggest that a model of peripheral auditory representation is available which would be useful as a building block in any theory of speech perception.

ISSN:0001-4966    

DOI:10.1121/1.2017345

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The objective of the preliminary research to be described is to quantify the psychophysical similarity of vowel‐like stimuli that differ in certain spectral and waveform characteristics. To that end, the vowel /æ/has been synthesized by adding together sinusoidal harmonics of the appropriate frequencies, amplitudes, and phases. Changes to these parameters and to fundamental frequency are made on a period‐by‐period basis. The resulting synthetic waveform is essentially indistinguishable from that produced by a conventional cascade formant synthesizer, but the present synthesis technique permits the experimenter to manipulate certain spectral and temporal details more easily. A set of 65 different vowels acoustically similar to /æ/have been synthesized by manipulating formant frequencies, formant bandwidths, spectral tilt, phase relations among harmonics, and filtering passband/stopband. Subjects are asked to estimate the psychophysical distance between each stimulus and a reference vowel in a 380‐trial randomized test. Results will be discussed in terms of various theories of vowel perception. [Research supported in part by an NIH grant.]

ISSN:0001-4966    

DOI:10.1121/1.2017398

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Previous research has shown that the closure duration cue for a medial voicing distinction, as in the contrastrabidversusrapid, is perceived in relation to the tempo of a carrier sentence: at faster rates of speech, the voicing boundary moves toward a shorter closure duration [R. Port, J. Acoust. Soc. Am.59, S41–S42 (A) (1976)]. In this experiment, we asked whether the voicing judgment is influenced by the overall rate of the sentence, which depends both on the articulation rate (the rate at which the speech itself is produced) and pause time, or whether it is influenced primarily by only one of those variables. By independently manipulating articulation rate and pause time, we found that articulation rate is a significantly better predictor of voicing judgments than either overall rate or pause time. Furthermore, when we asked subjects to provide subjective estimates of the rate of our experimental sentences, we found that those judgements were also based almost entirely on articulation rate. These results suggest first, that the interpretation of the closure duration cue is influenced by the articulation rate of the sentence, with pause time having little effect and, second, that listeners use the same rate information, namely, articulation rate, both when estimating the rate of the sentence, per se, and when adjusting for rate in processing the closure duration cue. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2017449

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Voice‐onset time is a relevant cue to the voice‐voiceless distinction in synthetic initial stop consonant perception. Studies with infants, adults, and animals have all shown the importance of the relative onset times between components of speech signals. Such unanimity could indicate the operation of a basic perceptual mechanism as suggested by Pisoni [J. Acoust. Soc. Am.61, 1352–1361 (1977)]. He used “speech‐like” stimuli consisting of paired tone (500:1500 Hz) differing in onset times, and found that some listeners produce ABX discriminations with peaks in the vicinity of ±20 ms lead‐lag intervals. The purpose of this study is exploration of other frequency:intensity combinations, e.g., the second and third harmonics of 250, 500, and 1000 Hz varied over the 50‐to‐90 dB SPL range. The results are discussed with respect to masking, and the discriminability of differences in temporal order of high‐frequency versus lower‐frequency components.

ISSN:0001-4966    

DOI:10.1121/1.2017507

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Tympanometry was used to follow the maturation of middle‐ear function in neonatal chicks from hatching to 10 days of age. The methods have been described elsewhere [Relkin and Saunders. J. Acoust. Soc. Am.63, Suppl. 1, S42 (1978)]. Subjects in each of five age groups were anesthetized, mounted in a head holder, and the tympanic ring was surgically exposed. A small hole was made in the contralateral tympanic membrane in order to equalize middle‐ear pressure to ambient pressure through the interaural pathways. A tympanometer probe was sealed directly over the tympanic membrane using a short piece of metal tubing to couple the probe to the tympanic ring. The magnitude of the volume velocity required to reach a criterion value of sound pressure was measured at frequencies between 0.4 and 1.8 kHz. Acoustic admittance at the tympanic membrane was calculated from the volume velocities measured when the tympanic membrane was stressed with a pressure of +200 mm H20 and when it was at ambient pressure. In all groups a monotonic increase in admittance magnitude was noted with increasing frequency. Phase, for low frequencies, was about 90° and decreased toward zero as the test frequency increased. There was relatively little change in admittance magnitude over the range of ages tested. These data further reflect the high degree of auditory development in the newly hatched chick.

ISSN:0001-4966    

DOI:10.1121/1.2017552

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Cochlear microphonic 1.0 μV thresholds and phase were measured in pigeons exposed to free‐field sound stimulation of varying horizontal azimuths. The pigeons were anesthetized and mounted on a rotating platform at a distance of one meter from a loudspeaker. The relative azimuth of the speaker to the binaural axis of the pigeon could be controlled remotely. The amplitude and phase responses of the CM to tone sources of varying direction were determined. One ear canal was then filled with plasticine and the measures were repeated. Comparison of the control and ear blocked measures showed differences in angular sensitivity of the CM which were related to sound conduction through the interaural pathway. The effects of interaural sound conduction on the azimuthal sensitivity of the CM were small but in the proper direction to increase the amplitude difference between the two ears. These results suggest that the combination of interaural sound conduction and the diffraction of sound about the head enable the pigeon to localize sounds in their best frequency range. [Work supported in part by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2016933

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A qualitative model based upon the relative contributions of the inner and outer hair cells is proposed as a parsimonious basis for acoustic reflex behavior in response to tonal and broad‐band activators in normal and impaired ears. It calls upon the localized, divergent innervation of the inner hair cells (IHCs); and the convergent; specially distributed innervation of the outer hair cells (OHCs), which have lower thresholds but are more susceptible to damage than the IHCs. The OHCs are viewed as the basis for the lower reflex threshold, bandwidth effect, and the curvilinear portion of the reflex growth function for broad‐band activators in normals. The elevated reflex threshold, and the absence of both the bandwidth effect and the curvilinear portion of the growth function for broad band activators in impaired ears is attributed to the absence/damage of OHCs. The total reflex thresholds in normals and in mildly impaired ears, as well as the linear growth functions for tones and the linear portion of the broad‐band growth function, is attributed to the IHCs. The displacement (in terms of activator SPL) of the linear portion of the broad‐band growth function in impaired ears reflects the absent curvilinear portion due to OHC damage. The tonal reflex threshold is elevated, so that the growth function is displaced, due to damage of the IHCs in moderate to severe hearing losses. The slope of the growth function is unchanged, however, since energy is integrated (due to the recruitment of additional IHCs as the excitation pattern widens). [Supported by Veterans Administration.]

ISSN:0001-4966    

DOI:10.1121/1.2016991

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP