摘要:

Two methods for determination of the acoustic nonlinearity parameterB/Ain biological media are presented. One is the finite amplitude insert‐substitution method (FAIS), considering the influence of both the sound attenuation of samples and the diffraction of the transducer on the experimental measurement. The other is the improved thermodynamic method (ITD), based on the measurement of phase shifts in the acoustic wave due to the change of ambient pressure. The nonlinearity parameterB/Ahas been measured for various biological solutions and soft tissues using these two methods. Some results of dependence ofB/Avalues on the concentration and temperature are also presented here.

ISSN:0001-4966    

DOI:10.1121/1.398326

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Suspended cells of a human lymphoblastic cell line were exposed to pulsed ultrasound of 775 kHz. The pulse lengths were varied between 16 and 1000 μs. The mark/space ratio was always kept at 1:1. Two ultrasound intensity levels were used: 3.6 and 6.4 W/cm2spatial peak and temporal peak. After an exposure time of 5 min, cell membrane damage was measured cytometrically by a dye exclusion test. No membrane damage was observable at 16 μs, whereas, at pulse lengths of 1000 μs, about one‐third of the cells were damaged.

ISSN:0001-4966    

DOI:10.1121/1.398222

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Many bats change the acoustic parameters of their echolocation calls in a deliberate manner during prey capture. Attempts to quantify these changes have been either of limited scope or subject to potentially severe errors due to an inadequate consideration of the directionality of both the bat and the recording microphone. Therefore, the echolocation pulses emitted by twoN.leporinushave been recorded as they approached and captured stationary prey, with the microphone positioned in such a way that the structure of the pulses incident upon the target could be determined. The results of this study show that: (1) during the last 1.5 m of the approach,N.leporinusreduces the intensity of emitted pulses by 6 dB per halving of distance, so that the intensity incident upon the target is constant; (2) at a point in the pulse train that corresponds to the position of the hypothesized tracking phase of echolocation,N.leporinusselectively reduces the intensity of the frequency‐modulated (FM) fundamental so that the FM pulse component is predominantly second harmonic; and (3) a high degree of temporal overlap occurs between the FM component of emitted pulse and echo whenN.leporinusis within 0.4 m of its prey.

ISSN:0001-4966    

DOI:10.1121/1.398225

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The nonlinear acoustic interaction between a reflected single‐frequency sinusoid and a broadband pump waveform propagating in the opposite direction produces phase changes in the probe proportional to the nonlinear parameterB/Ain the spatial region of interaction. The instantaneous phase change along the received probe can be expressed as the convolution of the pump waveform with the spatial distribution ofB/Aalong the propagation path over which the pump and reflected probe interact. In theory, the phase modulated sinusoidal probe can be processed (phase detection and deconvolution) to produce an ‘‘A‐mode’’ representation ofB/A. If the pump is an intense unipolar impulse and the probe a swept‐frequency sinusoid, then the pump interacts with the probe at each point along the propagation path at a unique frequency. Thus the phase modulation that carries information about the spatial distribution ofB/Acan be extracted from the phase spectrum by a simple Fourier transformation analogous to the space to frequency mapping so basic to magnetic resonance imaging. If the impulsive pump is replaced by another swept‐frequency sinusoid, then the phase change in the probe due toB/Aat a particular point along the propagation path will be spread out for the duration of the pump along the probe. Passage of the received signal through an appropriate matched filter restores spatial coherence to the phase information in the probe so that it can be processed as if the pump were a broadbanded impulse. This approach suggests a means of approaching the design of effective pump waveforms that can resolve a wide range of spatial frequencies in (B/A)(x).

ISSN:0001-4966    

DOI:10.1121/1.398344

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The harmonic balance technique is known as a time‐frequency simulation technique used for the study of large signal regimes of microwave circuits driven in forced oscillation. The technique can be adapted to self‐sustained oscillations, especially for wind musical instruments such as clarinets. The resonator (i.e., the instrument body) is the linear part, treated in the frequency domain, while the driving system (the reed) is the nonlinear part, treated in the time domain. The harmonic balance method is shown to connect the results of two known methods, so‐called weakly nonlinear (in frequency domain) and strongly nonlinear (in time domain). The advantages and disadvantages of the method are discussed.

ISSN:0001-4966    

DOI:10.1121/1.398352

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

This paper provides an analysis of the effect of quantization and measurement errors on two algorithms for measuring short‐time perturbation about a slowly varying or periodically varying mean. While these algorithms can be applied in a variety of applications, they will be discussed in the context of their use in quantification of vowel perturbations associated with hoarseness. The algorithms are referred to as the relative average perturbation and the directional perturbation quotient in speech analysis literature. The analyses indicate that significant errors are present in published studies. Sampling conditions and analysis techniques to minimize these errors are described.

ISSN:0001-4966    

DOI:10.1121/1.398309

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Acoustic analysis of the vocalic portion of consonant–vowel–consonant (CVC) syllables (where V is one of the five vowels [I,q,1,a,v] of American English) spoken by three speakers (two males and one female) in the sentence frame ‘‘The — again’’ is presented. Results of acoustic measurements show that ambiguities between vowels, for each speaker, occur if the vowels are represented by the values ofF1 andF2 sampled at the time whereF1 reaches its maximum. These ambiguities occur primarily in theF1 dimension. Examination of theF1 trajectories of the vowels for which confusion occurs shows variations in the wayF1 reaches its maximum among different vowels. In particular, if two different vowels such as [I] and [q]have the same maximumF1, thenF1 for the lower vowel reaches its maximum value earlier. In addition, results show that theF1 onset frequency also might be important in determining vowel height. The implication is that the spectral characteristics at a particular ‘‘target,’’ represented by the time at whichF1 reaches its maximum, are not invariant attributes of the vowel. The results support a hypothesis that time and/or frequency variations of the first formant must be taken into account if an invariant property is to be associated with a vowel.

ISSN:0001-4966    

DOI:10.1121/1.398220

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Perceptual experiments using consonant–vowel–consonant (CVC) syllables were carried out to examine the perceptual relevance of the first formant frequency (F1) trajectory in the perception of high vowels versus nonhigh vowels. Results show that stimuli characterized by a higher onset frequency andF1 maximum at the beginning of the vocalic portion are perceived as lower vowels than stimuli with a lowerF1 onset frequency andF1 maximum toward the end of the vocalic portion. These findings are in agreement with the hypothesis, based on the acoustic analyses of Di Benedetto (1989), that stimuli with higherF1 onset frequencies andF1 maximum at the beginning of the vocalic portion characterize lower vowels. Results are similar for native speakers of different languages, leading to a suggestion that this phenomenon may have either an articulatory or an auditory basis. Possible interpretations based on an overshoot hypothesis or a formant time average theory were investigated through an additional perceptual experiment. Results of this last experiment agree with a weighted average time formant theory.

ISSN:0001-4966    

DOI:10.1121/1.398221

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The task‐dependent organization of sensorimotor mechanisms during the production of speech was investigated using a perturbation paradigm. Six subjects received unanticipated jaw perturbations before and during tongue elevation for [1d1], in which the lips do not participate, and bilabial closure for [1b1], in which the tongue does not participate. A strain gauge system was used to monitor inferior–superior displacements of the upper lip, lower lip, and jaw, while hooked‐wire electrodes monitored muscle activity in various muscles of the lips, jaw, and tongue. Results indicated significant compensatory kinematic adjustments to jaw perturbations in the lips and/or jaw during [1b1], but no labial compensations during [1d1](with the exception of one subject). EMG responses were inconsistent and not necessarily indicative of the kinematic findings. Individual subjects responded to perturbations reliably but differently, using different combinations of involved articulators to achieve bilabial closure and lingua–alveolar contact. The current study supports earlier research which suggests that the components of the motor system are flexibly assembled, based on the requirements of the specific task. That is, compensatory responses to sensory information occur only when such responses are functionally necessary.

ISSN:0001-4966    

DOI:10.1121/1.398223

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Changes in sound pressures measured in the ear canal are reported for broadband sound sources positioned at various locations about the subject. These location‐dependent pressures are one source of acoustical cues for sound localization by human listeners. Sound source locations were tested with horizontal and vertical resolution of 10°. Sound levels were measured with miniature microphones placed inside the two ear canals. Although the measured amplitude spectra varied with the position of the microphone in the ear canal, it is shown that the directional sensitivity at any particular frequency of the broadband stimulus is independent of microphone position anywhere within the ear canal. At any given frequency, the distribution of sound pressures as a function of sound source location formed a characteristic spatial pattern comprising one or two discrete areas from which sound sources produced maximum levels in the ear canal. The locations of these discrete areas varied in horizontal and vertical location according to sound frequency. For example, around 8 kHz, two areas of maximum sensitivity typically were found that were located laterally and were separated from each other vertically, whereas, around 12 kHz, two such areas were found located on the horizontal plane and separated horizontally. The spatial patterns of sound levels were remarkably similar among different subjects, although some frequency scaling was required to accommodate for differences in the subjects’ physical sizes. Interaural differences in sound‐pressure level (ILDs) at frequencies below about 8 kHz tended to increase monotonically with increasing distance of the sound source from the frontal midline and tended to be relatively constant as a function of vertical source location. At higher frequencies, however, ILDs varied both with the horizontal and with the vertical location of the sound source. At some frequencies, asymmetries between the left and right ears in a given subject resulted in substantial ILDs even for midline sound sources. These results indicate the types of horizontal and vertical spatial information that are available from sound level cues over various ranges of frequency and, within a small subject population, indicate the nature of intersubject variability.

ISSN:0001-4966    

DOI:10.1121/1.398224

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP