摘要:

Adding a second channel to a Fourier analyzer greatly increases its capability by allowing investigation of the relationship between two signals which occur simultaneously. A number of important two‐channel frequency functions can be measured, all derived from the cross‐power spectral function. These include frequency response, ordinary coherence, and sound intensity. This presentation reviews the definitions, physical significance, and some practical applications of these data types. Practical considerations for two‐channel measurements with typical dual‐ or multiple‐channel analyzers are discussed.

ISSN:0001-4966    

DOI:10.1121/1.2023794

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The analysis of many actual engineering problems can be greatly enhanced through the application of fast Fourier transform (FFT) signal processing. The purpose of this paper is to demonstrate some typical problem solving approaches and subsequent solutions obtainable through FFT analysis. The problems and solution techniques are chosen to illustrate the use of the various available spectral quantities. The topics discussed include: (1) source identification and preventative maintenance monitoring through comparison of power spectra; (2) the estimation of radiated acoustic intensity using the cross spectrum between two closely spaced microphones; (3) machinery noise source identification via the ordinary coherence function; and (4) the measurement and estimation of dynamic structural characteristics from frequency response functions. Techniques to assess the spectral quality for each application are discussed to ensure that accurate results are obtained. Each topic area is presented in a pragmatic fashion to illustrate the use and interpretation of the spectra required for each application.

ISSN:0001-4966    

DOI:10.1121/1.2023798

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The American National Standard for measuring noise emitted by business equipment, ANSI S12.10‐1985, includes a new procedure for identifying prominent discrete tones. The procedure is based upon comparing the sound pressure level in the tone to the sound pressure level in the Zwicker bandwidth centered around the tone. In general this new procedure is a substantial improvement over the previous procedure described in ANSI S1.29‐1979, and based on Appendix B of ANSI S.13, which uses sound pressure levels outside the Zwicker handwidth to determine the strength of the masking noise. However, after several months of use with a FFT analyzer it is dear that the S12.10 procedure raises questions that should be addressed. This paper presents examples of tones that sound prominent but do not calculate to be prominent by the new procedure, and examples that do not sound prominent but calculate to be prominent. This paper also presents limitations on use of one‐twelfth‐octave‐band filters to make the measurements required by the S12.10 procedure.

ISSN:0001-4966    

DOI:10.1121/1.2023801

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

It has been found that surface acoustic waves (SAW) exhibit a very large interaction with appropriately prepared thin magnetic films through the magnetoelastic effect. For a 600 Å 90Ni 10Fe thin film, the interaction can produce changes in attenuation of 30 dB/cm at 700 MHz by changing from 2 to 12 G a magnetic field applied parallel to the film plane and perpendicular to the SAW. Measurements of the frequency dependence of this large effect yield values for the Gilbert damping constant and the anisotropy field. This interaction has been studied in the series ofxNi (1 −x)Fe alloy films. Forx>80 wt %, the magnetoelastic constant η is negative. It is positive forx<80 wt%. An amorphous film with positive η has also been studied. Some device concepts which make use of this effect will be presented. [Work supported by the National Science Foundation under Grant No. ESC 8519695.]

ISSN:0001-4966    

DOI:10.1121/1.2023807

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The flexural modes of a circular steel disk (diameter ≈25.7 cm, thickness ≈0.061 cm) were excited by an electromagnetic force to large amplitudes of motion, and the nonlinear tuning curves of the (p,q) modes, wherep= nodal diameters andq= nodal circles, were determined. The results disagree with those of S. A. Tobias [Engineering51(11 July 1958) and Proc. Inst. Mech. Eng. London171, 691 (1957)]. It is found that, as the drive level is increased, the peak frequencies of the tuning curves can shift to lower frequencies, such as (0,1), (1,1), (0,2) modes, or higher frequencies, such as (10,0), (3,1), (4,0) modes; the direction of shifting is a property of the particular modes being driven. [Work supported by ONR and DOE.]

ISSN:0001-4966    

DOI:10.1121/1.2023810

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Contralateral masking is often recommended in auditory brainstem response (ABR) testing in order to reduce or eliminate the participation of the nontest ear. The present study evaluates the effects of contralateral sound on the ABR. Vertex‐mastoid recordings were made on a total of 30 young‐adult subjects with normal heating. Stimulus paradigms employed a 4‐kHz probe and a contralateral continuous tone or a contralateral forward masker. Both the continuous‐tone and forward‐masking experiments resulted in statistically significant amplitude changes in the probe‐evoked ABR. Waves III and VI, averaged across experiments, conditions, and subjects, showed a 28.7% increase in amplitude in the presence of a contralateral stimulus. In contrast, the amplitude of wave V, averaged across experiments, conditions, and subjects, was reduced by 11.2%. Latency measures for all waves often showed a slight, but statistically significant, increase. In regard to the enhancement of wave III by contralateral sound, we speculate that the descending auditory system is involved. The amplitude changes obtained for waves III, V, and VI contrast strongly with earlier results on ipsilateral masking.

ISSN:0001-4966    

DOI:10.1121/1.2023816

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The effects of stimulus rate, intensity, and tonal frequency on the auditory middle latency and steady‐state responses (MLR/SSR) were investigated in 29 normal infants (1–36 months) and in eight normal adults. Adultlike MLRs (10/s) were recordable in only 5 infants, 14 demonstrated responses with “immature” morphology, and ten demonstrated no MLR components after Na. Compared to adults, infant SSRs were lower in amplitude and demonstrate different scalp distributions. Unlike the adult data, no consistent amplitude peak was seen across rate, and phase coherence increased up to highest rate tested (59/s). Infants required higher stimulus intensities to produce adultlike SSR phase coherence values: 83% of the recordings to 70‐dB nHL tones presented at 43.4/s showed significant values (p<0.01), decreasing to 35% at 40 dB nHL. These results are very different from those we previously reported for adults [Stapells, Makeig, and Galambos, J. Acoust. Soc. Am. Suppl. 177, S66 (1985)], and suggest that infant MLRs and SSRs undergo complex changes with maturation. [Work supported by DRF and NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2023822

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Otoacoustic emissions, evoked by clicks and brief tone bursts, were measured in normal‐hearing subjects and patients with sensorineural hearing loss. The emissions were recorded using an electret microphone assembly inserted in the meatus. The stimulus was delivered through a transducer attached to a 1.3‐mm plastic tube terminating at approximately 1 cm from the eardrum. Spectral analysis of the click‐emitted emissions showed discontinuities similar to those observed in spontaneous emission recordings. In addition, the comparison of emission and audiometric data in the impaired ears will be reported. [Supported by the Veterans Administration.]

ISSN:0001-4966    

DOI:10.1121/1.2023826

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Previous investigations into creak (vocal fry or pulse phonation) concentrated on two aspects: establishment of the physiological, acoustic, or perceptual nature of creak compared with other phonations; or separation of its characteristics in normal speech from pathological voices. The approach here is entirely different. Taking the phonetic and linguistic incidence of creak in normal speech in two accents of English as a starting point, quantitative description of its occurrence is provided. Data are taken from large numbers of speakers producing meaningful utterances in a recording task unrelated to voice quality. Support is given to the previous (unquantified) notion that creak accompanies utterance‐final low falls and may be a turn‐relinquishing signal. In addition, important cross‐accent and cross‐sex differences in the usage of creak are revealed. The results indicate that future descriptions of male‐female voice quality differences should acknowledge creak as an important sociophonetic marker. Furthermore, phonological accounts of accents should incorporate information about a community voice quality. Last, clinicians will benefit from a quantitative account of creak in “normal voice” and may be led to adjust their parameters of abnormality accordingly.

ISSN:0001-4966    

DOI:10.1121/1.2023837

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Reported here are results from an investigation of the alignment of speech segments with the fundamental frequency (F0) contour at the end of an intonational phrase. Findings suggest that theF0 peak on the main sentence stress (nuclear stress) occurs at some proportion of the length of the vowel, instead of at a fixed distance into the vowel. The vowel may be shortened by a faster speaking rate, an intrinsically shorter vowel, and added post‐nuclear syllables. TheF0 peak delay, however, is shortened by faster speaking rate and intrinsically shorter vowels, but lengthened or unaffected by added syllables. Thus vowel length and post‐nuclear syllables interact to determine the location of theF0 peak.

ISSN:0001-4966    

DOI:10.1121/1.2023842

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP