摘要:

A procedure is described for determining the absolute sound pressure at the inner end of the ear canal when a sound source is coupled to the ear, for frequencies in the range 8–20 kHz. The transducer that generates the sound is coupled to the ear canal through a lossy tube, yielding a source impedance that is approximately matched to the characteristic impedance of the ear canal. A small microphone is located in the coupling tube close to the entrance to the ear canal. Calibration is carried out by measuring the response at this microphone when an impulse is applied at the transducer. To estimate the sound pressure at the medial end of the ear canal, the Fourier transform of this impulse reponse is corrected by an all‐pole function in which the poles are estimated from the minima in this Fourier transform. Data on individual ear canals are presented in terms of gain functions relating the sound pressure at the medial end of the ear canal to the sound pressure when the coupling tube is blocked. The average gain function for a group of adult ears increases from 2 to 12 dB over the frequency range 8–20 kHz, in rough agreement with data from ear‐canal models. Possible sources of error in the calibration procedure are discussed.

ISSN:0001-4966    

DOI:10.1121/1.394913

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The hearing thresholds of 37 young adults (18–26 years) were measured at 13 frequencies (8, 9,10,...,20 kHz) using a newly developed high‐frequency audiometer. All subjects were screened at 15 dB HL at the low audiometric frequencies, had tympanometry within normal limits, and had no history of significant hearing problems. The audiometer delivers sound from a driver unit to the ear canal through a lossy tube and earpiece providing a source impedance essentially equal to the characteristic impedance of the tube. A small microphone located within the earpiece is used to measure the response of the ear canal when an impulse is applied at the driver unit. From this response, a gain function is calculated relating the equivalent sound‐pressure level of the source to the SPL at the medial end of the ear canal. For the subjects tested, this gain function showed a gradual increase from 2 to 12 dB over the frequency range. The standard deviation of the gain function was about 2.5 dB across subjects in the lower frequency region (8–14 kHz) and about 4 dB at the higher frequencies. Cross modes and poor fit of the earpiece to the ear canal prevented accurate calibration for some subjects at the highest frequencies. The average SPL at threshold was 23 dB at 8 kHz, 30 dB at 12 kHz, and 87 dB at 18 kHz. Despite the homogeneous nature of the sample, the younger subjects in the sample had reliably better thresholds than the older subjects. Repeated measurements of threshold over an interval as long as 1 month showed a standard deviation of 2.5 dB at the lower frequencies (8–14 kHz) and 4.5 dB at the higher frequencies.

ISSN:0001-4966    

DOI:10.1121/1.394914

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

This study examines measures of glottal flow for vowels of Hmong, a Southeast Asian language which uses breathy and normal phonation contrastively. A software inverse filter was used to recover glottal airflow from oral airflow recordings. Properties of glottal flow measured in the time domain were glottal pulse symmetry and relative closed‐phase duration. In the frequency domain, measures of spectral tilt and the amplitude difference betweenF0 andH2 were applied to discrete Fourier transforms (DFTs) of the glottal flow waveforms. Spectral tilt could not be reliably measured for many tokens. For the other measures, values were available for all tokens and were compared across phonation types. Flow pulse symmetry is not significantly different for breathy and normal‐voice vowels. On the other hand, prominence of the fundamental relative to the second harmonic is a very significant correlate of the breathy/normal distinction, as is the relative closed‐phase duration. These results are considered in light of an existing model of the voice source.

ISSN:0001-4966    

DOI:10.1121/1.394915

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Closants, or consonantlike sounds in infant vocalizations, were described acoustically using 16‐kHz spectrograms and LPC or FFT analyses based on waveforms sampled at 20 or 40 kHz. The two major closant types studied were fricatives and trills. Compared to similar fricative sounds in adult speech, the fricative sounds of the 3‐, 6‐, 9‐, and 12‐month‐old infants had primary spectral components at higher frequencies, i.e., to and above 14 kHz. Trill rate varied from 16–180 Hz with a mean of about 100, approximately four times the mean trill rate reported for adult talkers. Acoustic features are described for various places of articulation for fricatives and trills. The discussion of the data emphasizes (1) dimensions of acoustic contrast that appear in infant vocalizations during the first year of life, and (2) implications of the spectral data for auditory and motor self‐stimulation by normal‐hearing and hearing‐impaired infants.

ISSN:0001-4966    

DOI:10.1121/1.394916

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The present study investigated anticipatory labial coarticulation in the speech of adults and children. CV syllables, composed of [s], [t], and [d] before [i]and [u], were produced by four adult speakers and eight child speakers aged 3–7 years. Each stimulus was computer edited to include only the aperiodic portion of fricative‐vowel and stop‐vowel syllables. LPC spectra were then computed for each excised segment. Analyses of the effect of the following vowel on the spectral peak associated with the second formant frequency and on the characteristic spectral prominence for each consonant were performed. Perceptual data were obtained by presenting the aperiodic consonantal segments to subjects who were instructed to identify the following vowel as [i]or [u]. Both the acoustic and the perceptual data show strong coarticulatory effects for the adults and comparable, although less consistent, coarticulation in the speech stimuli of the children. The results are discussed in terms of the articulatory and perceptual aspects of coarticulation in language learning.

ISSN:0001-4966    

DOI:10.1121/1.394917

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Vowel matching and identification experiments were carried out to investigate the perceptual contribution of harmonics in the first formant region of synthetic front vowels. In the first experiment, listeners selected the best phonetic match from anF1 continuum, for reference stimuli in which a band of two to five adjacent harmonics of equal intensity replaced theF1 peak;F1 values of best matches were near the frequency of the highest frequency harmonic in the band. Attenuation of the highest harmonic in the band resulted in lowerF1 matches. Attenuation of the lowest harmonic had no significant effects, except in the case of a 2‐harmonic band, where higherF1 matches were selected. A second experiment investigated the shifts in matchedF1 resulting from an intensity increment to either one of a pair of harmonics in theF1 region. These shifts were relatively invariant over different harmonic frequencies and proportional to the fundamental frequency. A third experiment used a vowel identification task to determine phoneme boundaries on anF1 continuum. These boundaries were not substantially altered when the stimuli comprised only the two most prominent harmonics in theF1 region, or these plus either the higher or lower frequency subset of the remainingF1 harmonics. The results are consistent with an estimation procedure for theF1 peak which assigns greatest weight to the two most prominent harmonics in the first formant region.

ISSN:0001-4966    

DOI:10.1121/1.394918

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

As an important preliminary exercise for understanding excitation of real piano strings, the general solution for a point mass hammer hitting a perfectly flexible string is developed. The extensive literature on this problem is critically reviewed, and the previously known analytic theory presented in such a way as to emphasize its physical meaning. Use of a microcomputer to overcome the difficulties of multiple contacts between string and hammer is described, and representative results obtained by this method are presented. While this approach constitutes a general solution of the problem in principle, it is most practical for moderate values of the ratio of hammer mass to string mass. For extremely heavy hammers, it is argued that there is no good way to predict any details of the string energy spectrum without allowing for additional physical processes such as damping.

ISSN:0001-4966    

DOI:10.1121/1.394919

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

As an important preliminary exercise for understanding excitation of real piano strings, the general solution for a point hammer of massmhitting a perfectly flexible string of linear density μ is developed further by allowing for hammer compliance. Previous work on this problem is critically reviewed, and the existing analytic theory is summarized. The role of the critical complianceC0=m/16μTis discussed, and inclusion of a resistive force is also considered briefly. In close parallel with our earlier general solution for a hard hammer, the analytic solutions are implemented with a microcomputer to overcome the difficulties of multiple contacts between string and hammer, and representative results obtained by this method are presented. While this approach constitutes a general solution of the problem in principle, it is most practical for moderate values of the ratio of hammer mass to string mass and forCnot too close toC0.

ISSN:0001-4966    

DOI:10.1121/1.394920

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

It is a well‐known fact that fish can determine the direction of an underwater sound source. For bony fish without Weberian ossicles the mechanism proposed here is the analysis of the elliptical movement of the otolith macula relative to the otolith in case a pure tone is emitted. This movement results from the superposition of the direct displacement wave and the displacement wave scattered by the swimbladder acting as a damped harmonic oscillator. A derivation of a closed analytical expression of the scattered wave is given for a prolate spheroidal air bubble (representing the swimbladder) in water. The elliptical displacement orbits of the surrounding medium were calculated. A general numerical approach is given for irregular gas bodies.

ISSN:0001-4966    

DOI:10.1121/1.394921

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The authors propose an alternative approach which is quite simple and convenient when determining the fundamental frequency of transverse vibration of sandwich plates if the mapping function which transforms a unit circle onto the given, complicated domain is known in advance.

ISSN:0001-4966    

DOI:10.1121/1.394922

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP