摘要:

An extension of the normal mode dispersion equation is developed that applies to a variable velocity water layer lying over an absorbing bottom. The effect of bottom absorption on the shape of group‐velocity‐vs‐frequency curves (mode curves) is examined for a special case, showing that there will be no frequency of minimum group velocity (Airy frequency) if the bottom absorption is sufficiently large. A high‐frequency cutoff of the mode curves is predicted as the normal consequence of a velocity structure in the water layer. Calculated mode curves are shown to be in good agreement with experimental curves obtained in a shallow‐water area of the Bering Sea.

ISSN:0001-4966    

DOI:10.1121/1.1918942

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

This paper presents a statistical model of reverberation noise based on the principal assumption that the distribution of the scatterers in the medium is a Poisson process. With approximations, the model is consistent with the known laws of reverberation and permits a study of spectral properties.

ISSN:0001-4966    

DOI:10.1121/1.1918943

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Diffraction constants for a sphere, a long cylinder, a ring, and a piston at the end of a long tube are derived and presented in a form useful in designing acoustic transducers.

ISSN:0001-4966    

DOI:10.1121/1.1918944

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Experiments are reported on the effect ofd‐amphetamine, sleep loss, and continuous intense crossear stimulation on the subjective judgment of octaves of high frequencies. Crossear stimulation produced significant decrements in the subjective octaves of 2000‐, 4000‐, and 8000‐cps tones. The administration ofd‐amphetamine previous to crossear stimulation prevented decrements in the subjective octaves of 2000‐ and 4000‐cps tones. A significant depression of the decrement for the octave of an 8000‐cps tone was noted. Sleep deprivation also produced significant decrements in the pitch of the high frequencies studied.d‐amphetamine produced almost complete recovery of the decrement produced by sleep loss within one‐half hour of administration. Continued crossear stimulation,d‐amphetamine, and the combination of the two, failed to produce significant changes in loudness of the high‐frequency tones used. It can be assumed that all octave determinations were made at equal‐loudness levels, and that the shifts in octave judgments cannot be explained by pitch change with loudness. A theoretical model for pitch discrimination, located in the central nervous system, is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1918945

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The rate of decay of auditory sensation was investigated by measuring the minimum silent interval that must be introduced between two noise pulses to be perceived. The value of this critical time Λtwas determined for different intensity levels of both the first and the second pulse. It is shown that in this case the sensation level of the second pulse may be considered as a very good approximation of the level of auditory sensation after Λt, due to the first pulse. From the experiments, we may conclude (1) expressed in dB as a function of logt, the decay of sensation is represented by a straight line; (2) independent of the sensation level of the stimulating sound, the hearing threshold is reached at the same time of about 200–300 msec. These results are compared with other experiments and the differences are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1918946

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

In one portion of a fixed‐interval‐observation experiment, observers indicated their certainty that a 500‐cps signal had been presented in a thermal‐noise background by positioning a slider after each interval. In a second portion of this experiment, the observers responded by making binary decisions. Slider positions were treated as typical confidence ratings; the conditional probability of a given rating or of one indicating greater confidence, given signal plus noise, was plotted against the probability of these ratings, given noise alone. Functions produced in this manner, for a rating scale divided into thirty‐six positions, were fit closely by the receiver‐operating characteristics (ROC's) of the theory of signal detectability. A psychophysical model using two straight‐line segments did not provide a good approximation to these data. Values ofd′ were generally lower for the rating procedure than for the binary‐decision procedure. The use of a large number of rating categories did not result in large increases information transmitted by the observers, but it did provide the desired fine resolution of the ROC's.

ISSN:0001-4966    

DOI:10.1121/1.1918947

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Subjective noise ratings by executive office personnel, reported at the time that the NC curves were introduced [L. L. Beranek, J. Acoust. Soc. Am.28, 833–852 (1956)], have been correlated with various physical measures derived from the 17 noise spectra originally published. The rank‐order correlation coefficients (in parentheses) for the respective physical measures are: A‐sound level (0.96), B‐sound level (0.96), NC level (0.95), NCA level (0.95), N level per ISO proposal (0.96), speech‐interference level (0.86), speech‐interference level based on the three octave‐band levels from 300 to 2400 cps (0.91), calculated loudness level (0.96), perceived‐noise level (0.96), 40‐noy‐weighted sound level (0.95). With only one exception each, loudness level and perceived‐noise level for the 17 airbase office noises are 13±1 dB greater than the A‐sound level. Some type noise spectra of various shapes are provided, along with an auxiliary table, to facilitate estimation of the several physical measures simply by curve‐matching. Since subjective ratings of office noise appear to be correlated with the A‐sound level as well or better than with other commonly known noise ratings, and since the A‐sound level can be measured readily with widely available meters, it is recommended as a replacement for the NC level in single‐number specifications for office noise.

ISSN:0001-4966    

DOI:10.1121/1.1918948

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

A spectrum analyzer based on a definition of short‐time power spectra has been designed and simulated on a digital computer. The analyzer is primarily intended for use in speech analysis. It has been designed to operate in real time, and to produce high‐resolution spectra without utilizing either heterodyning methods or bandpass filter banks. The logarithm of each consecutive amplitude spectrum thus obtained can be used as the input to a second similar spectrum analyzer. The output of this analyzer is then the “cepstrum” or power spectrum of the logarithm spectrum. The cepstrum of a speech signal has a peak corresponding to the fundamental period for voiced speech but no peak for unvoiced speech. Thus, a cepstrum analyzer can function both as a pitch and as a voiced‐unvoiced detector. Cepstral pitch detection has the important advantages that it is insensitive to phase distortion, and is also resistant to additive noise and amplitude distortion of the speech signal. The method does not require the presence of the fundamental frequency in the speech signal, and will give several separate cepstral peaks if several different pitch periods are present. Cepstral techniques appear to be even more reliable and efficient than visual methods for pitch detection. The short‐time spectrum and cepstrum analyzers described in this paper were simulated by a sampled‐data system on an IBM‐7090 digital computer. The simulation was programmed with the assistance of a special block‐diagram compiler.

ISSN:0001-4966    

DOI:10.1121/1.1918949

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

An analysis‐by‐synthesis procedure for the automatic reduction of vowel spectra is described. The scheme is realized as a program for a general‐purpose digital computer. The output of the program specifies time samples of vocalic utterances in terms of parameters that characterize the transfer function of the vocal tract. The performance is described and evaluated in terms of deviations of formant‐frequency values and magnitudes of error scores; manually derived data provided by a related scheme are used as criteria for comparison.

ISSN:0001-4966    

DOI:10.1121/1.1918950

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The algebraic expressions given by earlier workers are used to compute the properties of longitudinally resonant cones. From the results, it is suggested that conical vibrators, driven by “stepped” amplitude transformers, would make useful resonators for fairly large amplitude. The ease, compared with vibrators having curved tapers, with which such a combination can be made outweighs its disadvantages when a fairly small number (greater than 1) of identical amplitude transformers is required.

ISSN:0001-4966    

DOI:10.1121/1.1918952

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP