摘要:

“Wiener's theorem” relating the autocorrelation function to the power spectrum of a time function has been modified and extended to the cases in which measurements are made withrealizablefilters having finite integration times. Similar relationships derived earlier by Fa no are valid only for the case when the power spectrum is measured by means of a bandpass filter with all impulse responsee−αtcosωtor the auto‐correlation function is measured by averaging through a simple R‐C integrator. The generalized relationships derived in this paper are valid for integrators with arbitrary impulse responses. Several different forms of short time representations and their experimental realizations are also discussed. The emphasis in this paper is on physical realizability—not mathematical existence.

ISSN:0001-4966    

DOI:10.1121/1.1909090

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Sound spectrographs typically displayed complex signals, such as speech, on teledeltos (facsimile) paper with frequency and time plotted along the ordinate and abscissa, and shades of gray to indicate the relative intensity of the frequency components. The gray scale is usually limited by the teledeltos paper to a marking range of 12 dB, whereas the signal may have amplitude variations of 40 to 50 db. A voltage quantizer has been designed which will plot equal‐level contours in the frequency/time plane. The equal‐level plateaus were selected at 6‐dB intervals over a 42‐db range. Gray‐scale compression is also obtained as a by‐product of this quantizer to shade each contour level such that a 42‐dB change in signal level causes a 12‐dB change in marking voltage. A discussion of the design and operating principles is given so that one can incorporate the circuit into a spectrograph or modify the circuit for other applications.

ISSN:0001-4966    

DOI:10.1121/1.1909092

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Speech‐intelligibility testing is an expensive and time‐consuming operation that requires laboratory test conditions. In an attempt to short‐cut or make unnecessary this type of testing, a procedure was developed by French and Steinberg [J. Acoust. Soc. Am.19, 90–119 (1949)] for calculating from physical and acoustical measurements made on a communication system a measure that is indicative of the intelligibility scores that would be obtained for that system under actual test conditions. This measure is called the “Articulation Index” (AI). Methods of calculating AI have been improved and elaborated to the point where several methods for its calculation, herein reported, can be proposed for use in the evaluation of most speech communication systems.

ISSN:0001-4966    

DOI:10.1121/1.1909094

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

French and Steinberg proposed the basic concept and method of calculating the Articulation Index (AI) approximately 15 years ago. Although improvements and modifications of AI have been made over the years, it has not been generally accepted, perhaps because of insufficient evidence as to its validity. On the basis of studies reported in the literature and on new studies herein reported, it is shown that AI is a valid predictor of the intelligibility of speech under a wide variety of conditions of noise masking and speech distortion.

ISSN:0001-4966    

DOI:10.1121/1.1909096

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An apparatus to measure the dynamic mechanical behavior of polymeric materials from 4°K to room temperature and at frequencies in the mid‐audio range is described. The specimen is driven in its fundamental longitudinal mode of vibration by a transducer which is coupled to the sample by a glass fiber. The lower end of the sample, which hangs vertically, is coated with a thin layer of iron filings. A small permanent magnet is rigidly supported close to and directly below the lower end of the specimen, and a pickup coil detects the motion of the latter. This apparatus uses either the free decay or bandwidth method of determining the internal frictionQ−1and values as low as 6×10−6have been obtained. Measurements from 8° to 300°K for lead and from 20° to 130°K for polystyrene are reported.

ISSN:0001-4966    

DOI:10.1121/1.1909098

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The propagation of a cylindrical wave in an infinite viscoelastic (standard linear) solid is studied by means of the Laplace transformation. Numerical results are obtained over a time interval encompassing the most significant characteristics of wave propagation, namely, attenuation of the initial peak, formation of the delayed peak, and asymptotic decline to the steady state. It is found that no marked change in the wave shape occurs until the distance from the axis exceeds a certain characteristic length (which is infinite in a perfectly elastic solid) and that the change becomes more marked at greater distances.

ISSN:0001-4966    

DOI:10.1121/1.1909100

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The principal parameters governing the generation of almost pure tones (Aeolian tones) by a roll in a wind have been identified and measured, guided by a theory due to Etkin. In particular, the connection between rms fluctuating lift and the correlation length of the shedding vortices has been recognized, and light has been shed on both by measurements. This has been a group program and has been partially reported elsewhere. Reported herein are the comprehensive measurements of the fluctuating forces on the rod and of the sound field they generate. Sealing or unsealing the ends and the addition of disks at various spacings are found to have major effects. Substitution of the measured parameters in the theoretical equation yields sound pressures in acceptable agreement with experiment. The experiments covered a Reynolds number range of approximately 3000⩽Re⩽100 000.

ISSN:0001-4966    

DOI:10.1121/1.1909102

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The mutual forces between two spheres having their line of centers parallel to the direction of propagation of traveling plane waves may be many times greater than the usual radiation forces of repulsion exerted on a single sphere. Expressions are derived for the forces on each sphere in terms of diverging wavefunctions and coordinate‐transformation functions. Numerical calculations show that the mean force on the sphere nearest the sound source has a value which oscillates with increasing amplitude as the separation between spheres is decreased, reaching a maximum value of repulsion from the source when the spheres are a quarter‐wavelength apart. At smaller separations mutual repulsion between the spheres dominates. For the other sphere, the forces are always of repulsion, but increase in magnitude as the spheres are brought together.

ISSN:0001-4966    

DOI:10.1121/1.1909104

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The return by the deep ocean bottom of the sound produced by an explosive charge consists of a decaying burst representing scattering at successively decreasing grazing angles with the bottom. An analysis of shot records at three deep‐water locations between Cape Hatteras and Bermuda has yielded the backscattering strength of the sea bottom over a range of frequencies and angles between 30° and 90°. In the range 30° to about 65° the bottom appears to behave as a diffuse backscatterer of sound; between 65° and 90° (normal incidence) an increased return may represent reflection from inclined flat facets of the sea bed or from sub‐bottom sediment layers. Analyses in several frequency bands between 0.5 and 8.0 kc indicate no frequency dependence of the scattering strength that could not be due to shock‐wave attenuation effects in the sea. The coefficients agree with those obtained with pulsed sinusoidal sound sources.

ISSN:0001-4966    

DOI:10.1121/1.1909106

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The nontorsional extensional axisymmetric modes and frequencies of elastic prolate spheroidal shells are obtained by a perturbation solution which converges rapidly for small ratios of major to minor axis.

ISSN:0001-4966    

DOI:10.1121/1.1909108

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP