摘要:

Thresholds for temporal gaps within periodic and jittered pulse patterns were determined. Gap thresholds within periodic pulse trains are in close agreement with those obtained in a previous study. Extremely fine temporal gap detection (10–20 μsec) is achieved for high‐frequency pulse trains consisting of many intervals. Reduction in the number of intervals, or introduction of jitter to the pulse train, sharply increases temporal‐gap thresholds for high‐frequency pulse trains. By contrast, temporal‐gap sensitivity for low‐frequency pulse trains is relatively independent of the number of intervals or of the amount of jitter. Acute temporal‐gap sensitivity is apparently achieved at high pulse frequencies by a spectral analysis of the temporal information, rather than by a direct temporal analysis.

ISSN:0001-4966    

DOI:10.1121/1.1910766

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

An aural difference tone attributed to nonlinearity of the ear was produced by the use of four pairs of pure tones, 750 and 1000, 1750 and 2000, 3750 and 4000, and 7750 and 8000 Hz. A binaural loudness balance, which demonstrated the difference tone produced by 750 and 1000 Hz at 100 dB, had a frequency equal to the numerical difference between the paired tones, and had an intensity of approximately 90 dB. Instrumentation difference tones were maintained at a level of at least 70 dB below that of the primary tones. The aural difference tone used as a monaural masking stimulus for a pure tone of 250 Hz produced more threshold shift when the pairs of tones were presented simultaneously than when each of the tones was presented individually. The masking effect of the aural difference tone is a function of the frequency and intensity of the primary tones. The spread of masking over a 2‐oct range, 125–500 Hz, using 750 and 1000 Hz simultaneously as the masking stimulus, was similar to that of a 250‐Hz pure‐tone masking stimulus.

ISSN:0001-4966    

DOI:10.1121/1.1910767

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A common speech‐communications problem is to maximize speech intelligibility over a noisy channel when the transmitter is peak‐power limited. An optimum linear solution is analytically derived, and consists of a speech‐processing filter in the transmitter. The degree of improvement due to use of the filter is derived for a number of bandwidths and signal‐to‐noise ratios. The filter was experimentally verified by articulation tests as the optimum linear configuration, and was significantly more intelligible than other filters that bounded it. Although the optimum filter depends on the noise spectrum, there is no significant difference between it and a noise‐invariant filter for white or speech‐shaped noise. The use of the filter is equivalent to raising the transmitter power between 1 and 10 dB, depending on the speech bandwidth and the signal‐to‐noise ratio.

ISSN:0001-4966    

DOI:10.1121/1.1910768

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Observers gave magnitude estimations of the difference in sound quality between the members of pairs of vowellike synthesized sounds. The observers in one set of experiments were asked to judge differences in vowel quality; those in an analogous set of experiments, differences in musical timbre. The first sound in each pair—the standard—was an imitation of one of six English vowels. The second sound in each pair—the test sound—was derived from the first by modifications of the fundamental frequency, the formant frequencies, or certain combinations of both. When the fundamental of the second sound was raised an octave above the frequency of the first, the estimates of difference—both in vowel quality and in musical timbre—could be reduced to a minimum, if the frequencies of the two lower formants of the sound with the higher fundamental were multiplied by a factor of 1.10. The judgments both of vowel quality and of musical timbre indicated that small changes in the frequencies of the two lower formants made large differences in quality, that small differences in quality could be attributed simply to changes in the fundamental frequency, and that still smaller quality differences could be attributed to changes in the frequencies of the higher formants alone. Shifts in the spectrum envelopes of sounds corresponding to thecompactvowels resulted in greater apparent differences in both vowel quality and musical timbre than comparable shifts in the spectrum envelopes of thenoncompactsounds. The results suggest that vowel quality and musical timbre are similar functions of their common acoustic correlates, that perceived invariances in the quality of sound cannot be attributed to learning, and they support a modified “fixed pitch” or formant theory of quality.

ISSN:0001-4966    

DOI:10.1121/1.1910769

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Measurements of the velocity of ultrasonic pulses in water are presented for pressures up to about 10 000 kg/cm2and for temperatures up to 80°C. Coefficients obtained from least‐squares polynomial fittings of the data are also given, together with an analysis of the reliability and reproducibility of the experimental results.

ISSN:0001-4966    

DOI:10.1121/1.1910739

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A computer‐aided procedure has been developed for obtaining specific volumes from measured ultrasonic velocities in any nondispersive medium. Newly measured velocities up to 80°C and 10 000 kg/cm2have yielded values of specific volumes and a number of thermodynamic coefficients for water over this same range. P. W. Bridgman's measurements of specific volumes in the high‐pressure range showed systematic differences of a few tenths of a percent; the present calculations yield values believed to be good to 0.05% or better for most of the range.

ISSN:0001-4966    

DOI:10.1121/1.1910740

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The spectrum of light inelastically scattered from density fluctuations is considered both for nonrelaxing and relaxing fluids. When the thermal conductivity of the liquid is small, the functions describing these spectra take on particularly simple forms. In addition to the unshifted Rayleigh line, caused by scattering from isobaric density fluctuations, the spectrum for a nonrelaxing liquid is just the response of a resonant system driven by thermal energy. For a relaxing liquid, the spectral distribution function has a somewhat more complicated form, but its interpretation is still quite straightforward. The use of electric circuit equivalents illustrates the principal features of the response spectrum. These results are formal ones, but while they are useful in understanding the scattering process, they are not particularly suited for the analysis of experimental results. For this purpose, approximations are developed that enable one to relate the out‐standing characteristics of the spectrum (for example, the positions and half‐widths of shifted lines) to fundamental relaxation parameters, such as the longitudinal storage and loss moduli.

ISSN:0001-4966    

DOI:10.1121/1.1910741

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The theory of Rayleigh scattering from density fluctuations is applied to data taken in glycerol andn‐butanol over wide temperature ranges. It is shown that Brillouin scattering is useful in evaluating the viscoelastic parameters of a liquid when all corrections are properly applied. The position, half‐width, and intensity of the Brillouin lines as well as the total intensity are the main features of the spectrum used. The definition of the Landau‐Placzek ratio was generalized to be applicable to relaxing liquids and glasses and its behavior was studied over a 200°C temperature range in glycerol. The hypersonic data indicate that at high temperatures (∼70°C) in glycerol the distribution of relaxation times is narrower than that ultrasonically found at lower temperatures (∼−10°C). This result is in agreement with the concept that the origin of the distribution is related to cooperative behavior which is less pronounced at higher temperatures.

ISSN:0001-4966    

DOI:10.1121/1.1910742

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Instrumental distortions of the Brillouin light spectrum induce systematic errors into the observed sound velocity and sound absorption. A model is given by which certain distortions may be reduced. The model involves Voigt functions, which are a generalization of Gaussian and Lorentzian functions. It is shown that corrections in general involve both an instrumental linewidth and a parameter which measures the line shape of the instrumental spectrum.

ISSN:0001-4966    

DOI:10.1121/1.1910743

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A one‐dimensional approximate theory is derived that accounts for the first eight modes of propagation of extensional waves in uniform, isotropic, linear elastic bars of rectangular cross section. The theory provides an optimal quadratic approximation to the lateral spatial dependence of the three‐dimensional bar response. Applicable to motions in bars of arbitrary rectangular section, it is possible to predict bar responses that are neither plane stress nor plane strain, but are transitional between the two. The relation of bar to plate theory is established, and an identification of bar and plate modes is proposed. Discussion of dispersion of harmonic waves is limited to bars of square section. Typical spectra are given, and their variation with Poisson's ratio is established.

ISSN:0001-4966    

DOI:10.1121/1.1910744

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP