摘要:

The VobancVOiceBANdCompressor) is a speech band‐width reduction system which provides a reduction of two in transmission channel band width, without a comparable loss in articulation. A description is given of an experimental system and results obtained with it are described.

ISSN:0001-4966    

DOI:10.1121/1.1908340

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

This study concerns the intelligibility of speech under various periodic switching operations. In diphasic speech the signal is separated into successive segments which are reversed in phase. The intelligibility of this speech was found to be high for switching frequencies below about 100 cps; in the intermediate audio‐frequency region the intelligibility fails to very low values. Throughout this intermediate frequency region, the intelligibility of diphasic speech is markedly less than that of interrupted speech. Some explanation for this difference is found in the Fourier expansion for the two cases. In interrupted speech the original spectrum is retained, but in diphasic speech terms for the spectrum in its normal form do not appear. It was experimentally observed that throughout the intermediate frequency region binaural diphasic speech, in which the signal is switched alternately from one ear to the other, is more intelligible than monaural diphasic speech or interrupted speech.

ISSN:0001-4966    

DOI:10.1121/1.1908342

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The “identification” and “discrimination” of components of elementary auditory displays are here differentiated in terms of the relative contiguity between the unknown signal and the set of possible signals that may be chosen. Listeners attempted to match arbitrary designations to sound levels of a tone under three conditions of relative contiguity between the unknown sound level and the set of possible sound levels. Significant improvements in matching are associated with increasing contiguity, especially under finely subdivided conditions encompassing a wide range of sound levels.

ISSN:0001-4966    

DOI:10.1121/1.1908344

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Many of the phenomena of masking can be explained on the basis of two models, one for monaural listening, and the other for binaural. The monaural model is the familiar narrow band‐pass filter followed by a detector responsive to changes in output level. The binaural model is a series of coincidence detectors associated with a delay‐network capable of matching delay in the stimulus with a delay in the neural path.The two models have proved helpful in understanding the phenomena of tonal masking, and have led to a number of predictions which have been subsequently verified by experiments reported here. Some of the new findings are related to monaural masking and some to binaural. Among the latter are the fact that masking‐level differences can be observed in the masking of one pure tone by another when a short signal is employed, and that a binaural signal can be heard in the presence of uncorrelated noise at the two ears better than a monaural signal can be heard against noise presented monaurally, again provided that a short signal is employed.Many studies of the masking of tones have appeared during the past few years. They have been characterized by close agreement in results wherever they have had common conditions, and they provide a large body of dependable quantitative information. With this body of fact there also grew, at least in the minds of present writers, a considerable state of bewilderment. Many of the facts appeared to contradict inferences drawn from others. The present paper discusses a number of these facts and attempts to encompass them under a few explanatory principles.

ISSN:0001-4966    

DOI:10.1121/1.1908346

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Noise during jet aircraft launching operations seriously interferes with communications in important island spaces aboard aircraft carriers. Measurements of sound pressure levels made in these spaces during normal jet operations at sea are reported. It was found that these levels could be estimated from a knowledge of jet engine operating conditions [A. C. Pietrasanta, J. Acoust. Soc. Am.28, 434 (1956)] and the physical properties of the structures involved. The problem of the selection of criteria for speech communication is discussed. Noise reduction requirements for island spaces, based on estimated noise levels of present and future jet aircraft, are presented.

ISSN:0001-4966    

DOI:10.1121/1.1908348

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The noise fields around several jet aircraft have been measured for various engine operating conditions. Directivity patterns as a function of octave bands of frequency are presented. Acoustic power levels have been computed and found to agree with a previously published correlation of power level with engine operating conditions [O. K. Mawardi and I. Dyer, J. Acoust. Soc. Am.25, 389 (1953)]. Analysis of these data has led to the development of a procedure for estimating the characteristics of the noise fields around non‐afterburner jet aircraft operating at military power.

ISSN:0001-4966    

DOI:10.1121/1.1908350

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A hydrophone monitoring a constant level sound source in the open ocean records a sound whose intensity fluctuates over short periods of time. Previously it has been demonstrated that much of this fluctuation can be accounted for by the temperature microstructure. It has been suggested that another cause of the observed fluctuation could be inhomogeneities the velocity field (turbulence). This paper is an attempt to estimate the magnitude of turbulence in the ocean. The conclusion is reached that turbulence contributes very little to the fluctuation observed in the intensity of underwater sound signals.

ISSN:0001-4966    

DOI:10.1121/1.1908352

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The pressure wave produced by the collapse of an electrically generated spherical cavity (∼1 cm in radius) in water was measured by means of a small electroacoustic hydrophone (116 in.in diameter) at a distance of 50 cm. The pressure was found to increase as the bubble collapsed according to thet−4/5(time) law in the interval corresponding to subsonic flow. The pressure then suddenly jumped to a higher value and rapidly decayed to zero. This rapid increase in pressure is assumed to be a shock wave. Using Gilmore's theory for the collapse of the cavity and finite amplitude‐wave theory for the pressure wave, we find that the value of the pressure‐amplitude characteristic at the shock front corresponds to a cavity‐wall velocity approximately equal to the velocity of sound. Since the shock wave has been attenuated, the peak wall velocity must be greater than this value.

ISSN:0001-4966    

DOI:10.1121/1.1908354

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The effect on the vibrational and rotational relaxation time of de‐excitation by photon emission in four gases possessing a permanent electric dipole moment is investigated. Such radiative energy losses are independent of pressure, and may be expected to control the relaxation process at low pressure when collisions become relatively infrequent. Calculations are shown forN2O, OCS, andSO2. Estimates of the efficiency of collisions to deactivate a vibrational level in HCl, indicate that the radiation effect on the vibrational relaxation time of this gas should be the easiest to measure; at a pressure of 10−2–10−3atmos, de‐excitation by radiation should be as important as collisional de‐excitation. Radiative de‐excitation will become increasingly important at low temperatures because of the consequent increase of the collisional relaxation time.

ISSN:0001-4966    

DOI:10.1121/1.1908356

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Ultrasonic absorption measurements were made to compare the relative effectiveness ofH2OandD2Omolecules in influencing thermal vibrational relaxation inN2Omolecules. The displacement rates of the absorption per wavelength maxima induced byH2OandD2Owere compared inN2O ‐ H2OandN2O ‐ D2Omixtures. Experimental apparatus was constructed for these measurements which utilized the “direct” absorption technique in conjunction with pulsed sound waves, having a frequency of approximately 113 kc. The parameter of frequency/pressure was varied by changing the gas pressure.The data were taken at a temperature of 21°C in the frequency/pressure range of 100–700 kc/atmos. The maximum amplitude of the molecular absorption coefficient per wavelength in dryN2Owas 0.153 and this occurred at 210 kc/atmos. Measurements were taken inN2O ‐ H2OandN2O ‐ D2Omixtures atH2O‐vapor andD2O‐vapor concentrations of 0.39%, 0.77%, and 1.14%.The usual single relaxation time theoretical absorption curve could be fitted to the data for driedN2O. However, in the mixtures there was some evidence of two separate relaxation times, one possibly associated withN2O ‐ N2Ocollisions and the other withN2O ‐ H2OorN2O ‐ D2Ocollisions. The maximum absorption coefficient in the mixtures was somewhat less than that observed in the driedN2O. TheH2Omolecules were 1.72 times more effective than theD2Omolecules in shifting the frequency associated with the absorption maximum.

ISSN:0001-4966    

DOI:10.1121/1.1908358

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP