摘要:

As a study of human sensation, psychoacoustics would seem to mesh well with appealing lecture demonstrations. To be meaningful, the study demands that students experience sounds personally. At the same time, the psychoacoustics literature offers a rich source of sonic effects, paradigms, and illusions. However, there are potential problems. Whereas psychoacoustical experiments normally involve trained subjects listening to headphones in an acoustically ideal environment, lecture demonstrations involve naive subjects listening to a loudspeaker in a room that may be far from ideal. There is always a risk that an important psychoacoustical effect will fail as a demonstration, either because listeners are not prepared to recognize the effect or because of the acoustical properties of the room. For example, rooms effects can seriously compromise demonstrations of the asymmetry of masking; room effects do not compromise critical‐bandwidth measurement by masking. Some demonstrations (pitch shift effects and pitch ambiguity, for example) risk failure because of individual differences. Other demonstrations incorporate sequencing, required to make an effect apparent, which itself introduces unexpected artifacts. These points are discussed with particular reference to the auditory demonstrations on compact disc, now distributed by the Acoustical Society of America. [Work supported by the National Institutes of Health.]

ISSN:0001-4966    

DOI:10.1121/1.2028164

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The following experiments done with very intense sound in an air‐filled, plane‐wave tube are described: (1) progressive distortion of traveling waves of finite amplitude, both tones and noise; (2) saturation, which is the limit set by nonlinear effects on the amplitude (and intensity) of sound that may be transmitted a given distance; (3) interaction of a tone with noise; (4) suppression of sound by sound; and (5) acoustic levitation. Some of the experiments are illustrated by live demonstrations, others by descriptions and reported data. [Work supported by the Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.2028169

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The resonance frequencies of an open pipe are harmonics of the fundamental frequency:fn=nf1. Each of these resonances can be excited by sound pulses occurring at themth submultiple of the resonance frequencyfn/m=n/mf1. These lead to a large number of “privileged frequencies” at which a woodwind reed or the brass player's lips can “lock in” to a wind instrument bore [A. H. Benade,Horns, Strings&Harmony(Doubleday, Garden City, NY, 1960), pp. 166–170]. Resonances and privileged frequencies of a 60‐cm pipe will be demonstrated with simple apparatus.

ISSN:0001-4966    

DOI:10.1121/1.2028173

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This paper introduces a new method for three‐dimensional active sound‐field cancellation. Analytical considerations include the problem of an incident plane wave interacting upon a rigid sphere as the scattering object. An array with elements consisting of a set of rings perpendicular to the sphere's pole axis is arranged on the surface of the sphere. This discussion will present an analytical technique for cancellation of the scattered sound field to arbitrary extent over either the whole space or the partial area of interest, as long as the number of the array elements is sufficient. Further considerations include a fixed and a variable incident plane‐wave direction with respect to the pole axis of the sphere.

ISSN:0001-4966    

DOI:10.1121/1.2028179

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A neural network was used to classify laser welds based upon their acoustical signatures. During laser welding of metal, a plasma (a region of ionized gas) is present above the surface of the material. Characteristics of the process cause this plasma to fluctuate over time, generating an airborne acoustical signal. In this work, the signals from laser welds were detected by a microphone, digitized in16‐stime slices and Fourier transformed. The 2048‐point power spectrum of the transformed signal was input to backpropagation networks of variable size. It was possible to train the backpropagation networks to classify laser welds as full or partial penetration based upon their acoustical signature (in a full penetration weld, the molten zone fully penetrates through the thickness of the metal being welded). Furthermore, it was also found that backpropagation networks with two hidden layers could learn to classify weld signals more efficiently than single hidden layer networks. The ability to classify welds as full or partial penetration will be useful in real‐time process control algorithms to be developed in future work.

ISSN:0001-4966    

DOI:10.1121/1.2028185

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The accuracies of four pitch extraction methods are introduced and compared for high‐precision perturbation measurement. They include combinations of peak‐picking, zero‐crossing, and waveform‐matching strategies. The effects of sampling frequency, signal‐to‐noise ratio, pitch frequency, and signal modulation on the accuracies are explored. It is shown that methods with the waveform‐matching technique give the best results for most cases. For near‐sinusoidal stimuli (e.g., EGG signals), the zero‐crossing technique gives higher accuracy than the peak‐picking technique. At a low signal‐to‐noise ratio, a higher sampling frequency does give better results for the waveform‐matching technique, but the accuracy of the peak‐picking method may reduce as sampling frequency increases. As the signal‐to‐noise ratio increases, the effect of sampling frequency on accuracy diminishes when interpolation is used. A variety of waveforms are currently being tested to check the suitability of these methods for different applications. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2028187

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

It has been noted that there are certain limitations in current methods for quantifying the subjective responses to computer and business equipment noise spectra containing discrete tones. Specifically, these difficulties arise when the noise spectra contain unusual spectral irregularities, such as when two tones occur closely together within a single critical band or when noise spectra include very steeply sloping noise bands. The present authors have recently introduced the concept of prominence ratio as a potentially useful index of subjective responses to computer and business equipment spectra containing pure‐tone components with unusual spectral irregularities. For the present study, 30 subjects were presented with tape‐recorded sounds of laboratory spectra as well as various computer and business equipment spectra containing closely spaced tones centered at unusual spectral irregularities. Subjects rated these sounds for their levels of loudness, tonal prominence, and annoyance. The research data are discussed with special attention to the usefulness of the prominence ratio for describing computer and business equipment spectra containing closely spaced discrete tones and spectral irregularities.

ISSN:0001-4966    

DOI:10.1121/1.2028193

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In October 1989, the authors went to the People's Republic of China (P.R.C.) to advise their National Institute for Occupational Safety and Health in planning the development of hearing conservation programs to protect the hearing of 33 million noise‐exposed Chinese workers. Visits to industries and discussions with scientists within government and universities revealed the challenges they face. The Chinese have emphasized a centralized approach to noise control to reduce both occupational noise exposures and community noise in housing adjacent to factories. They plan to increase the acceptance of hearing protection devices among industrial workers by making available more comfortable and practical devices. The P.R.C. currently has a draft noise standard that is being revised before being made final. Because Chinese scientists and practitioners hope to use the experiences of Western nations to help shape their policies, the questions they ask about progress in hearing conservation bring into focus issues that the U.S.A. should consider in determining future funding priorities. Ways in which individuals and institutions can assist hearing conservation efforts in the P.R.C. will be suggested.

ISSN:0001-4966    

DOI:10.1121/1.2028196

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Linear prediction coding (LPC) parameters are widely used in various speech processing applications for representing the spectral envelope information of speech. For low‐bit‐rate speech coding application, it is important to quantize these parameters accurately using as few bits as possible without sacrificing the speech quality. Though the vector quantizers are more efficient than the scalar quantizers, their use for fine quantization of LPC information (using 24–26 bits/frames) is impeded due to their prohibitively high complexity. In this paper, a split vector quantization approach is used to overcome the complexity problem. Here, the LPC vector is divided into two parts and each part is vector‐quantized separately. The splitting of LPC vector is studied in the following three domains: (1) line spectral‐pair frequency (LSF), (2) arc‐sine reflection coefficient, and (3) log area ratio. Splitting in LSF domain is found to be the best. Using the localized spectral properties of the LSF parameters, a weighted LSF distance measure is proposed. Using this distance measure, it is shown that the split vector quantizer can quantize LPC information in 24 bits/frame with 1‐dB average spectral distortion. In terms of average spectral distortion and number of outliers, its performance is better than the 32 bits/frame scalar quantizer.

ISSN:0001-4966    

DOI:10.1121/1.2028201

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A novel improvisation‐oriented live performance situation is proposed. Its implementation is described, and results from actual performances are presented. This performance context involves a musician performing on an instrument outfitted with sensors which feed a computer system that monitors certain aspects of the instrument's behavior such as its pitch, loudness, and timbre. Another performer interacts with the system to selectively record, transform, and play electroacoustics materials derived from the instrumentalist's performance. This situation might be characterized as one involving an improvising soloist with an accompanist who constructs the accompaniment from phrases attentively trapped from the soloist's ongoing performance. The system requires a running or short‐term memory mechanism with procedures that aid in the parsing of selected phrases, a supple user interface for the accompanist that facilitates the selection and transformation of the musical materials as well as their expressive performance, and a rich set of procedures for producing variations. A number of successively refined implementations of this idea have been made, the most recent of which uses the MAX programming environment developed by Miller Puckette at IRCAM. The system provides for musical intimacy between the performers. It also provides the accompanist with an interesting set of tasks and the soloist with a stimulating accompaniment based on variations of his own materials.

ISSN:0001-4966    

DOI:10.1121/1.2028208

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP