摘要:

By automatically reassembling periodic samples of recorded speech, Fairbanks and associates have shown that comprehension is good for: (1) connected speech compressed 50% (0.5) in time, and (2) a single well‐learned PB list compressed up to 0.15. In 1919–1925 Fletcher and associates, using turntable speedup with its attendant frequency distortion, found that the intelligibility of syllables began to drop rapidly at speedups corresponding to time reductions of 0.8 (down about 25% at 0.7). In one case a complex technique using simple language showed only slight losses in comprehension for large time compressions. In the other case, a simple technique using difficult speech material showed marked deterioration. In our work on message (simple language) storage schemes, the desirability of obtaining time compressed speech with simple modifications of existing equipment has become evident. By merely speeding up the playback of a tape recorder, we have found that numbers and simple phrases can tolerate a time compression of 0.67 without serious losses in intelligibility, and PB words lose only 10%, in intelligibility with a time compression of 0.75.

ISSN:0001-4966    

DOI:10.1121/1.1908636

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The study deals with the formant movements associated with transitions, glides, and diphthongs in spoken American English. The transitional characteristics associated with all initial and final consonant phonemes were studied in a large sample of utterances. The rate of change of the transition from a consonant hub to the steady state vowel formant position and conversely was investigated for vowels which are commonly considered monophthongs. It is assumed that such changes are cues for the perception of the consonants rather than linguistically significant components of the vocalic nucleus. The rate of change associated with syllable nuclei commonly perceived as diphthongs, [ɑɪ], [ɔɪ], [ɑᴜ] was investigated and compared with the changes due to consonant transitions in monophthongs. Criteria are suggested by which the formant movements due to transitions may be distinguished from movements that have linguistic signalling value within the syllable nucleus.

ISSN:0001-4966    

DOI:10.1121/1.1908638

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The velocity of propagation and the absorption of longitudinal waves has been measured in a hydrocarbon oil for which the shear modulus together with the spectrum of shear relaxation times has been determined previously. A volume viscosity is found which is approximately equal to the shear viscosity and the results are surprisingly similar to those found by Litovitz and his co‐workers for associated liquids. Structural relaxation appears to play an equally important part in determining the second viscosity of the hydrocarbon oil as it does in associated liquids. The effects of association are found to give slightly higher values for the limiting moduli at high frequencies (the instantaneous moduli) and are also responsible for the marked temperature dependence of these moduli. In the present case the relaxing partK2of the modulus of compression and the limiting value of the shear modulus are each sensibly independent of temperature. It also appears that for the liquids studied so farK2≅43⋅G∞. The spectrum of compressional relaxation times is determined and good agreement is found between the measured values of the components of the complex compression modulus and the curves recalculated from the spectrum. The absorption at frequencies above the main part of the dispersion region is governed not by an hysteresis type of loss, as found in associated liquids, but by a residual high‐frequency contribution to (α/f2) due to the (unrelaxed) contribution of the vibrational specific heat relaxation.

ISSN:0001-4966    

DOI:10.1121/1.1908640

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Expressions for the power radiated by either a dipole or a quadrupole reflected in an infinite rigid plane are presented. These expressions are perfectly general in that they admit any orientation of the multipole and any kind of a quadrupole. The results include the special cases considered previously by U. Ingard and G. L. Lamb, Jr. [J. Acoust. Soc. Am.29, 743 (1957)]. The large variations in radiated power observed for a single multipole tend to diminish when averages over a distribution of such multipoles are considered.

ISSN:0001-4966    

DOI:10.1121/1.1908642

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Procedures are described whereby acoustical systems supporting one‐dimensional harmonic waves may be synthesized for a prescribed frequency dependence of the input reflection coefficient. An important design latitude is gained by allowing the nominal characteristic impedance of the structure to vary in a stepwise manner with the independent space variable. An initial simplified model is presented which assumes only propagating plane waves and neglects multiple reflections between discontinuities. These results are corrected to include the effects of multiple reflections by techniques from signal flow graph theory. Effects of local higher‐order modes existing at the discontinuities are represented as lumped shunt susceptive elements. Data obtained from measurements on an acoustic matching section design operating between a 5.76:1 impedance mismatch over a 50% bandwidth centered about 1333 cps confirm the theoretical predictions. Further data, obtained from standing‐wave measurements at the input to coupled resonator sections, indicate the importance of higher‐order nonpropagating modes when the discontinuities are large. It is found that effects of these modes upon the input reflection coefficient are readily obtained from Smith chart calculations.The synthesis procedures constitute a simple, rapid means for initial design of a stepped structure to yield a prescribed frequency dependence of input reflection coefficient by essentially graphical techniques. The most important unsolved problems are the direct inclusion of multiple reflections and susceptive discontinuity effects in the synthesis procedure and the establishment of general physical realization criteria. Finally, it remains to relate the response of stepped systems to a more general smoothly varying system.

ISSN:0001-4966    

DOI:10.1121/1.1908644

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The method of separation of both the dependent and independent variables of the vector wave equation of elasticity has heretofore been applied almost exclusively to problems of wave propagation in homogeneous media. In this paper, a generalization of this method that extends its applicability to several types of inhomogeneous media is developed. The mechanical properties of the media considered here depend on one Cartesian coordinate, and Poisson's ratio is taken to be constant. Formulations are given for axially symmetric waves in three dimensions and for waves in two dimensions. Three linearly independent vector solutions of the wave equation are expressed in terms of three scalar potential functions. One of these functions represents generalizedSHwaves and satisfies an independent second‐order wave equation in all the problems considered here. Certain functional forms for the mechanical properties are found for which the remaining two potential functions also satisfy independent second‐order wave equations; these potentials may be identified with generalizedPandSVwaves, respectively. TheSHwaves are solenoidal, but in general thePandSVwaves are not purely irrotational and solenoidal, respectively, for the problems treated.

ISSN:0001-4966    

DOI:10.1121/1.1908646

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The speed of sound has been measured in heavy water,D2O, by a pulse technique. An equation is presented to express the results of these measurements in analytic form and is used to compute tables of sound speed inD2O. A comparison of the sound speeds inD2Oat atmospheric pressure obtained by an optical method, an interferometer method, and the present pulse method is made. The results from the pulse method and the optical method agree within the experimental error; however, the interferometer method gave higher sound speeds than the other two.

ISSN:0001-4966    

DOI:10.1121/1.1908648

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A model for acoustic scattering of an arbitrary pressure wave is developed from the fundamental wave equation. A statistical distribution of scatterers in the medium is assumed and is described by a spatial correlation function. It is shown that the predominant features of volume reverberation can be derived from the model. Furthermore, under certain simplifying conditions, it is shown that the reverberation signal can be represented as a random noise passed through a narrow band filter whose properties are determined by the mode of transmission. The determination of the dependence of reverberation level on operating frequency, and the possibility of optimizing an acoustic system by the choice of transmission is suggested.

ISSN:0001-4966    

DOI:10.1121/1.1908650

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A method is developed for the numerical evaluation of the integral solution to the wave equation for a point source in shallow water overlying a “hard” liquid type bottom; i.e.,c2>c1. This method is especially useful for intermediate horizontal ranges where satisfactory approximations to the sound field have not been found. In general the integral cannot be evaluated directly because there are singularities in the integrand. Instead it has been transformed into the complex plane in such a way that the resulting integrals and residues can be evaluated on a high speed digital computer. A limited number of calculations were made to illustrate the use of the numerical method.

ISSN:0001-4966    

DOI:10.1121/1.1908652

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The problem which Lord Rayleigh considered (reflection from a corrugated surface) and which several have treated approximately in recent years, is developed in a general form. An exact solution is obtained by extensive use of Wiener's generalized harmonic analysis. This solution is readily extended to include electromagnetic waves, general elastic waves, and nonplanar, nonharmonic sources. Numerical evaluation of the formulas is considered by means of an operational representation, from which various types of successive approximations can be constructed. Applications can be of special interest in scatter communications and in underwater sound transmission and reverberation. Experimental evidence from the latter area indicates that a rather detailed theory is necessary for an adequate account of the situation.

ISSN:0001-4966    

DOI:10.1121/1.1908654

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP