摘要:

When two synthetic vowels are presented concurrently and monaurally, listeners identify the members of the pair more accurately if they differ in fundamental frequency (F0), or if one of them is preceded or followed by formant transitions that specify a glide or liquid consonant. However, formant transitions do not help listeners identify the vowel to which they are linked; instead, they make thecompetingvowel easier to identify. One explanation is that the formant transition region provides a brief time interval during which the competing vowel is perceptually more prominent. This interpretation is supported by the predictions of two computational models of the identification of concurrent vowels that (i) perform a frequency analysis using a bank of bandpass filters, (ii) analyze the waveform in each channel using a brief, sliding temporal window, and (iii) determine which region of the signal provides the strongest evidence of each vowel. Model A [Culling and Darwin, J. Acoust. Soc. Am.95, 1559–1569 (1994)] computes the rms energy in each channel at successive time intervals to generaterunningexcitationpatternsthat serve as input to a vowel classifier, implemented as a linear associative neural network. Model B uses a temporal analysis in each channel to generaterunningautocorrelationfunctions, and it includes a further stage of source segregation [Meddis and Hewitt, J. Acoust. Soc. Am.91, 233–245 (1992)] to partition the channels into two groups, one group containing evidence of the periodicity of the vowel with the dominantF0, the other group providing evidence of the competing vowel. Both models predicted effects ofF0and formant transitions on identification, but model B provided more accurate predictions of the pattern of listeners’ identification responses. Taken together, the empirical and modeling results support the idea that the identification of concurrent vowels involves an analysis of the composite waveform using a sliding temporal window, combined with a form ofF0‐guided source segregation.

ISSN:0001-4966    

DOI:10.1121/1.416299

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Two experiments were run to determine whether individual differences in auditory speech‐recognition abilities are significantly correlated with those for speech reading (lipreading), employing a total sample of 90 normal‐hearing college students. Tests included single words and sentences, recorded on a videodisc by a male speaker [Bernstein and Eberhardt, Johns Hopkins Lipreading Corpus, The Johns Hopkins University, Baltimore, MD, 1986]. The auditory speech was presented with a white noise masker, at −7 dB Sp/N. The correlations between overall auditory and visual performance were 0.52 and 0.43 in the two experiments, consistent with the existence of a modality‐independent ability to perceive linguistic ‘‘wholes’’ on the basis of linguistic fragments. Subjects in the second experiment also identified printed sentences, with 40%–60% portions of the printed characters deleted. Performance on this graphical ‘‘fragmented‐sentences test’’ also correlated significantly with auditory speech recognition, providing a possible clue to the cognitive basis for the look‐versus‐listen correlation. The existence of a modality‐independent source of variance in speech‐recognition abilities may be a partial explanation of the difficulty in demonstrating strong associations between psychoacoustic measures of spectral or temporal acuity, and speech discrimination or identification. Female subjects in both experiments were significantly better lipreaders than their male counterparts.

ISSN:0001-4966    

DOI:10.1121/1.416300

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

This paper describes a new algorithm that composes blues melodies to fit a given chord sequence. It comprises an analysis stage followed by a synthesis stage. The analysis stage produces a Markov model composed of zero, first‐, and second‐order transition tables covering both pitches and rhythms. In order to capture the relationship between harmony and melody, a set of transition tables is produced for each chord in the analyzed songs. The synthesis stage uses the output tables from analysis to generate new melodies; second‐order tables are used as much as possible, with fall back procedures to lower‐order tables. Some constraints are encoded in the form of rules to control the placement of rhythmic patterns within measures, pitch values for long duration notes and pitch values for the start of new phrases. The model was evaluated by a listening experiment; results showed that listeners were unable to reliably distinguish human from computer composed melodies.

ISSN:0001-4966    

DOI:10.1121/1.416220

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The action of the soundpost in a violin is not well understood and fundamental knowledge is needed. Therefore low‐frequency forced modes, operating deflection shapes, 250–600 Hz of a violin were investigated. Harmonic, sine wave, excitation was applied via the bridge (resembling playing) or via the sound from a loudspeaker. The latter excitation gives a reciprocal measure of radiativity. The modes were investigated with TV‐holography and electro‐acoustical admittance measurements. A carefully selected violin was investigated without soundpost, with soundpost, and with the soundpost position shifted toward the centerline. Answers were sought to three questions: Which are the violin modes forced via the bridge? To what extent do they radiate sound? What is the action of the soundpost? The observed modes were mostly not pure normal modes but mode combinations. Generally there is a nodal line close to the soundpost position of the plates. Schelleng has hypothesized that the main action of the soundpost is to make the violin nonsymmetric. The first top plate mode with soundpost can be looked upon as a combination of the first symmetric top plate mode and the first asymmetric mode without soundpost. The first mode is an efficient radiator and the second mode transfers the string vibrations via the bridge to the top plate efficiently. The asymmetric first mode with the soundpost is thus both excited and radiates sound. Our experimental results make the hypothesis plausible, but show that body (global) modes play an important role too. In the range 500 to 600 Hz, a body mode,C3, constitutes a major part. TheC3 mode has a nodal line close to the normal soundpost position and is especially interesting as it seems to form a quality mark of a good violin.

ISSN:0001-4966    

DOI:10.1121/1.416301

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The dynamics of a saxophone reed has been analyzed by means of the simplest model—one pure spring—acceptable for frequencies below the resonance frequency of the reed. As proposed in the context of bowed string dynamics [J. Acoust. Soc. Am.90, 754–763 (1991)], a reactive power is defined for the air‐column of a saxophone and its reed. When the instrument sustains a harmonic tone, a balance between those two reactive powers can be established, as a generalization onto a multimodal system of the usual condition sin(φ)=0 that a simple oscillator fulfills when it vibrates at its resonance frequency. The stiffness of the reed can be derived from that condition. Experiments were carried out on a saxophone played by a professional musician. The reed stiffness under playing conditions is determined after separate measurements of the input impedance (TMTC method) and of the internal pressure spectrum. Results are comparable with compliance values measured on isolated reeds by other authors.

ISSN:0001-4966    

DOI:10.1121/1.416302

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

This paper generalizes the linear part of Robert T. Schumacher’s approach for modeling wind instruments [R. T. Schumacher, Acustica48, 71–85 (1981)]. A reinterpretation of that work shows that the general problem is one of deconvolving an infinite series of multiple reflections, rather than attempting to define an anechoic termination for the input end. In order for the deconvolution to yield the desired results, the reflection impulse response from which the series is generated must not include long‐period multiple reflections itself. That condition is satisfied automatically in an air column that begins with a cylindrical segment of appreciable length. For air columns that are tapered or more complicated at their input ends, the impulse responses needed are already available from previous work [R. D. Ayers, J. Acoust. Soc. Am.98, 81–87 (1995)]. Calculated impulse responses for a primitive trumpet are presented and discussed.

ISSN:0001-4966    

DOI:10.1121/1.416303

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The purpose of this work is to provide measurements in well‐characterized media in order to better understand inertial (transient) cavitation phenomena. Focused transducers with megahertz center frequencies (2.5 MHz, 4.3 MHz) and a clinical diagnostic ultrasound system (4.0 MHz) were used to generate pulsed ultrasound to induce cavitation. An improved active cavitation detector which utilizes a highly focused transducer with much higher center frequency (30 MHz) was used to measure the threshold of inertial cavitation. In order to study the effect of the concentration of nucleation agents on cavitation thresholds, experiments were conducted in distilled water seeded with polystyrene particles. Inertial cavitation thresholds were measured for various concentrations of polystyrene particles. It was observed that the threshold decreased from 2.5 MPa at concentration of about 106particles/ml to 1.6 MPa at a concentration of about 109particles/ml. The effect of the concentration is not significant for smaller changes of the concentration. Measurements of the cavitation thresholds were then made in specially developed phantom materials to study the effect of viscosity on the cavitation threshold when surface tension and other mechanical properties of the materials are kept relatively constant. Experimental results show that the threshold increases with increasing viscosity, consistent with theoretical predictions. Cavitation was also detected in water seeded with polystyrene particles using a clinical ultrasound system at an acoustic pressure of 3.84 MPa. Results are comparable with those obtained in the laboratory using a 4.3‐MHz focused transducer.

ISSN:0001-4966    

DOI:10.1121/1.416304

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The application of dynamic time warping (DTW) to the automated analysis of continuous recordings of animal vocalizations is evaluated. The DTW algorithm compares an input signal with a set of predefined templates representative of categories chosen by the investigator. It directly compares signal spectrograms, and identifies constituents and constituent boundaries, thus permitting the identification of a broad range of signals and signal components. When applied to vocalizations of an indigo bunting (Passerinacyanea) and a zebra finch (Taeniopygiaguttata) collected from a low‐clutter, low‐noise environment, the recognizer identifies syllables in stereotyped songs and calls with greater than 97% accuracy. Syllables of the more variable and lower amplitude indigo bunting plastic song are identified with approximately 84% accuracy. Under restricted recording conditions, this technique apparently has general applicability to analysis of a variety of animal vocalizations and can dramatically decrease the amount of time spent on manual identification of vocalizations.

ISSN:0001-4966    

DOI:10.1121/1.415968

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Noninvasive surgery using high‐powered, focused ultrasound transducers in conjunction with magnetic resonance imaging has been shown to be feasible in previous studies. For clinical treatments, the geometry of standard MRI equipment limits the space available for ultrasound surgical equipment. This space requirement can be reduced in one dimension by using phased arrays to control the focal depth, thus eliminating the space required for the motion of a fixed focus transducer. Because of its symmetry, an annular array is ideal for changing the focal depth. Previous works have simulated, built, and characterized various concentric‐ring transducers; however, no study has thoroughly examined the potential and limitations of the concentric‐ring design for MRI guided ultrasound surgery. The present work is a systematic examination of the capabilities of the concentric‐ring array, using numerical simulations to predict the power field, temperature distribution, and accumulated thermal dose. The results presented here illustrate the effects of ring size, center‐to‐center spacing configurations, number of rings, and radius of curvature on transducer performance. A 10‐cm radius of curvature transducer with 14 evenly spaced rings has been built and characterized in order to verify the accuracy of the numerical simulations. The pressure‐squared fields produced by this transducer are in excellent agreement with the simulated fields.

ISSN:0001-4966    

DOI:10.1121/1.416217

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

It is shown that theoretically, in most cases of interest, the acoustic radiation pressure exerted by plane traveling waves on small rigid and liquid spheres is determined by viscous and heat effects whereas the classical King [Proc. R. Soc. London, Ser. A147, 212–240 (1934)] and Yosioka and Kawasima [Acustica5, 167–173 (1955)] results are only negligible corrections.

ISSN:0001-4966    

DOI:10.1121/1.415969

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP