摘要:

A method for distinguishing burst onsets of voiceless stop consonants in terms of place of articulation is described. Four speakers produced the voiceless stops in word‐initial position in six vowel contexts. A metric was devised to extract the characteristic burst‐friction components at burst onset. The burst‐friction components, derived from the metric as sensory formants, were then transformed into log frequency ratios and plotted as points in an auditory‐perceptual space (APS). In the APS, each place of articulation was seen to be associated with a distinct region, or target zone. The metric was then applied to a test set of words with voiceless stops preceding ten different vowel contexts as produced by eight new speakers. The present method of analyzing voiceless stops in English enabled us to distinguish place of articulation in these new stimuli with 70% accuracy.

ISSN:0001-4966    

DOI:10.1121/1.1894648

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Native speakers of Japanese learning English generally have difficulty differentiating the phonemes /r/ and /l/, even after years of experience with English. Previous research that attempted to train Japanese listeners to distinguish this contrast using synthetic stimuli reported little success, especially when transfer to natural tokens containing /r/ and /l/ was tested. In the present study, a different training procedure that emphasized variability among stimulus tokens was used. Japanese subjects were trained in a minimal pair identification paradigm using multiple natural exemplars contrasting /r/ and /l/ from a variety of phonetic environments as stimuli. A pretest‐posttest design containing natural tokens was used to assess the effects of training. Results from six subjects showed that the new procedure was more robust than earlier training techniques. Small but reliable differences in performance were obtained between pretest and posttest scores. The results demonstrate the importance of stimulus variability and task‐related factors in training nonnative speakers to perceive novel phonetic contrasts that are not distinctive in their native language.

ISSN:0001-4966    

DOI:10.1121/1.1894649

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Using the approach first pioneered by Raman, the Helmholtz motion of a bowed string is discussed as a special case of “two‐velocity motions,” in which a given point (at which the bow is located) alternates, in the course of a cycle, between two constant velocities. The fact that the bow typically presents a negative resistance to the string during the “slipping” part of the cycle is adduced as a reason for the “duty cycle,” that is, the fraction of the period that corresponds to slipping, to try to become as short as possible. It is shown that, for a string without dissipation or stiffness, this duty cycle can be arbitrarily low for general bow positions; data obtained with the “digital bow” illustrate this behavior. It is shown theoretically, and confirmed with computer simulations, that instabilities arising from the negative slipping resistance cannot be eliminated by assigning a finite positive value to the sticking resistance. The apparent stability of Helmholtz motion observed in real playing situations remains a puzzle.

ISSN:0001-4966    

DOI:10.1121/1.1894650

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A beluga (Delphinapterus leucas) was trained to detect different length cylinders in front of a clutter screen at five separation distances. The clutter screen consisted of 300, 5.1‐cm‐diam cork spheres located behind the targets. The clutter screen was used in two positions: perpendicular to the body axis of the beluga (90° grazing angle) and rotated 22° (68° grazing angle). Five hollow stainless‐steel cylinders (3.2‐cm‐diameter and 0.38‐cm wall thickness) of different lengths (14, 10, 7, 5, and 3 cm) were used as targets. Detection data were collected on the beluga's performance as a function of the separation between targets and the clutter screen. The beluga's performance was above 80% correct detection for the 14‐ and 10‐cm cylinders as the separation distance decreased from 10.1 to 5.1 cm for both grazing angles. For all targets except the 3‐cm cylinder, the beluga's detection was higher at 0‐cm separation than at 2.5‐cm separation. The beluga's detection performance was higher at 68° than at 90° grazing angle. The target strength of the cylinders and the clutter screen was measured in peak‐to‐peak amplitude and the energy of the incident and reflected echoes. For 0‐cm target‐to‐clutter screen separation at 90° grazing angle, the echo‐to‐reverberation ratio at 50% correct detection was − 1.0 dB, based on the peak‐to‐peak measurements, and − 5.1 dB based on the energy measurement. The results of this experiment suggest that a beluga can detect targets in 3.6 to 5.4 dB more reverberation than previously reported for a bottlenose dolphin (Tursiops truncatus).

ISSN:0001-4966    

DOI:10.1121/1.1894651

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Feline isolation calls were analyzed, and a model was developed to relate the acoustical features of these calls to the physical processes used in their production. Fifty isolation calls were recorded from each of five cats for a total sample of 250 vocalizations. By combinations of Fourier transform, autocorrelation, and linear prediction methods, the fundamental frequency (glottal‐pulse period)F0, the energy ofF0, the frequency having maximum energyFmax(not alwaysF0), and the energy at this frequency were computed. MeanF0ranged from 400–600 Hz for individual cats. For some catsF0was consistent within calls, but for other cats sudden shifts inF0occurred within calls. Here,Fmaxwas almost always a harmonic ofF0and generally ranged from 1–2 kHz. For individual cats, the energy ratioE= (energy ofFmax/energy ofF0) varied from 1 to 60 and the grand averageEover the time course of the call varied from about 12 to 38. The mean rms call intensity was an inverted‐U function of time. Measured jaw opening was strongly correlated with acoustical features of call. A Bessel‐horn model with time‐varying flare gave a good account of acoustical parameters such asFmax. The presence of formantlike resonances in cat vocalizations and the important role of jaw movements (vocal gestures) in the production of these calls suggest that cats may provide a useful model for some aspects of human vocal behavior.

ISSN:0001-4966    

DOI:10.1121/1.1894652

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

An experimental system for the measurement of porosity, the volume fraction of air contained in a material, is described. Porosity is important as one of several parameters required by acoustical theory to characterize a porous material. As with the technique described by Beranek [J. Acoust. Soc. Am.13, 248–260 (1942)], the isothermal pressure change in a closed volume containing a sample material is measured for a known change in the volume. The volume of air contained in the sample, and hence the porosity, is inferred from these two quantities. The new system, though, avoids the use of liquids, either directly in the technique or for temperature stabilization. Instead, a piston of accurately known diameter is used to produce the change in volume, and the change in pressure is measured with an electronic pressure transducer. Model calculations and measurements on real materials confirm that porosity can be measured rapidly and conveniently with this apparatus, with an accuracy of better than 1% over a broad range of sample volumes and porosities.

ISSN:0001-4966    

DOI:10.1121/1.1894653

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

For many thickness‐drive transducer applications, it is desirable to have a good estimate of the radiation conductance (or other property based on power output) of the transducer. Generally,however, it is difficult to measure directly transducer power output. It is therefore desirable to have a procedure for estimating radiation conductance from easily measured quantities. Themeasured quantities used in this paper are electrical admittances at the terminals of thetransducer when it is in air, and when in water. The transducer model used to interpret the measured admittance is a lumped‐constant equivalent circuit; it hasbeen refined to represent an electrically excited thickness‐drive transducer over the frequency range 0.5–40 MHz. Two methods are used to estimate radiation conductanceGrad(f), and efficiency. One, the general‐case method, gives values ofGradover a wide range of frequencies, the other gives values ofGradonly for the special case in which the transducer is at a half‐wave resonance. For the general case, a novelprocedure, similar to iterative optimization, is used to estimate parameters for the equivalent circuit. Provision is made for estimating a tuning‐coil resistance that isfrequency dependent. The validity of the two methods is tested by comparing resultantGrad(f) values with those measured by the National Institute of Standards and Technology (formerly National Bureau of Standards). The maximumdiscrepancy at the lowest transducer resonance is approximately 15% for the small number of transducers on which measurements have at present been made. The transducers studiedherein have active elements with characteristic impedance much higher than that of water.Polymer‐film transducers are not considered.

ISSN:0001-4966    

DOI:10.1121/1.1894654

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The radiation characteristics of a magnetohydrodynamic (MHD) acoustic transmitter radiating into a free medium are examined. Two source mechanisms are associated with the transducer: an electromagnetic force associated with the MHD operation, and a density fluctuation associated with heating of the medium by an electrical current. The wave equation is derived and a solution is found for impedance boundary conditions using a Green's function approach. Measurements obtained in a large water tank are shown to compare favorably with the predictions.

ISSN:0001-4966    

DOI:10.1121/1.1894655

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This Letter describes a numerical method for solving Poisson's formula for an impulsive initial condition and uniform pressure throughout a specified region in space. Four examples are presented, three with known analytical solutions and one (a finite cylindrical source) with no known closed‐form solution.

ISSN:0001-4966    

DOI:10.1121/1.1894656

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The effect of the sharpness of a wedge on the diffraction pattern of an acoustic beam incident at 90 deg on a metallic sample immersed in water is studied in this letter.

ISSN:0001-4966    

DOI:10.1121/1.1894657

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP