摘要:

A method is devised for evaluating and comparing the performance of receivers used in an active sonar application. The basis of comparison is the level of background noise that will just bring the maximum signal excess, after system adjustment, to zero, given a propagation loss. The better system is the one that can withstand the higher level of background noise before the maximum signal excess goes to zero. This method is applied to the polarity‐coincidence correlator and, for comparison, aural detection. It is found that the polarity‐coincidence correlator compares favorably with aural detection.

ISSN:0001-4966    

DOI:10.1121/1.1910404

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Frequency‐discrimination performance is measured as a function of the ratio of signal energy to noise‐power density (ε‐η0) for several values of frequency separation at 250, 1000, and 4000 cps. Discrimination performance at all frequencies and all frequency separations increases with increasing ε‐η0until ε‐η0reaches 40 dB. No further increase in performance was apparent with a further increase of 40 dB in ε‐η0.

ISSN:0001-4966    

DOI:10.1121/1.1910405

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The basis for detection in those interaural conditions that lead to a masking‐level difference (MLD) is presumed to be quite different from that in the non‐MLD conditions. This experiment examined the effect upon detectability when listeners were uncertain whether an MLD or a non‐MLD condition was to be presented. Detectability was measured at two values of signal energy for each of two interaural conditions, N0‐S0 and Nπ‐S0. The “YES‐NO” psychophysical method was used. On some blocks of trials, the blocks with “no uncertainty,” only one interaural condition was presented. On other blocks of trials, the blocks “with uncertainty,” N0‐S0 signals were mixed with equally detectable Nπ‐S0 signals. The listeners were informed which type of block was to be presented. There was essentially no difference between the data obtained with uncertainty and those obtained with no uncertainty. A supplementary experiment showed that on the blocks with uncertainty the listeners were quite poor at identifying the type of noise presented on a trial.

ISSN:0001-4966    

DOI:10.1121/1.1910406

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

An adaptive procedure for rapid and efficient psychophysical testing is described. PEST (Parameter Estimation by Sequential Testing) was designed with maximally efficient trial‐by‐trial sequential decisions at each stimulus level, in a sequence which tends to converge on a selected target level. An appendix introduces an approach to measuring test efficiency as applied to psychophysical testing problems.

ISSN:0001-4966    

DOI:10.1121/1.1910407

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Monarual bone‐conduction thresholds in the quiet were obtained for 10 normally hearing young adults at both forehead and mastoid positions with two hearing‐aid‐type vibrators of different manufacture. Physical calibration data for the vibrators were obtained by other laboratories with two different Beltone artificial mastoids. Bone‐conduction force thresholds (in root‐mean‐square dynes) are reported, along with identification of sources of variability.

ISSN:0001-4966    

DOI:10.1121/1.1910408

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

A technique is presented for the analysis of musical instrument tones. The end result is a mathematical representation for the tone being investigated. Since no assumptions are made about the frequencies of the partial tones, inharmonic frequencies can be detected and accounted for in the representation. An analog‐digital converter was used to present the signals to theILLIACII digital computer for analysis. Five tones were analyzed, resynthesized, and subjected to listening tests. The trumpet tone was characterized by a frequency change which, if omitted during synthesis, made the tone sound mechanical. The saxophone tone had a short‐duration, inharmonic component which gave it the “bite” characteristic of a jazz tone. The other tones analyzed were produced by a violin, bassoon, and clarinet; and each, when resynthesized, still retained the tonal quality of the original; as examples, the wind tones sounded breathy and the violin sounded bowed. It was thus concluded that this analysis technique can be successfully applied to analyzing tones of the classes of instruments represented by these five tones.

ISSN:0001-4966    

DOI:10.1121/1.1910409

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Physically realizable distributions of pressure and normal velocity over a vibrating surface submerged in an unbounded acoustic medium can not be independently prescribed, but must satisfy someacoustic relationship. The surface pressure and normal velocity can be obtained by solving an acoustic relationship simultaneously with anequilibrium relationshipexpressing dynamic equilibrium of the structure whose surface is vibrating. The present method uses as the acoustic relationship a regular integral equation derived from the classical Helmholtz integral. A numerical technique successful in solving the integral equation and economical of computational effort is described. It represents the solution functions in terms of their values at a set of mesh points but employs another, much larger, set of points for evaluating the integrals. The pressure at any field point is obtained by numerical quadrature in the Helmholtz integral of the calculated surface pressure and normal velocity. Results are presented of calculations for a spheroid and for finite capped cylinders, all with prescribed axisymmetric velocity distributions. The surface pressures calculated for the spheroid agree closely with an exact solution, while those for the cylinders are consistent with understood acoustical phenomena. The far‐field directivities for the cylinders agree reasonably with an independent approximate solution.

ISSN:0001-4966    

DOI:10.1121/1.1910410

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The reflection and transmission of sound waves by a moving fluid layer are investigated theoretically and the reflection and transmission coefficients are determined. Numerical computations for the reflection and transmission coefficients as a function of the velocity of the moving medium are also carried out. It is found that the reflection and transmission coefficients are quite sensitive to the variation of the angle of incidence even if the layer is moving slowly. This fact suggests the possiblity of obtaining the speed of the moving fluid layer by measuring the reflection or transmission coefficient as a function of the angle of incidence.

ISSN:0001-4966    

DOI:10.1121/1.1910411

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The response of a linear system to nonstationary Gaussian shot noise is examined from a more general point of view. The system parameters, including those of a filter, are considered to be of such a general nature that the matrix associated with the rate of the first‐order transition moment in the corresponding Fokker‐Planck equation may have multiple eigenvalues. The more general approach taken here yields a result that may be reduced to the existing one for systems with simple eigenvalues only. An example is given at the end to illustrate the application of the general expressions for the mathematical expectation and the covariance function of the response.

ISSN:0001-4966    

DOI:10.1121/1.1910412

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Some response statistics of a linear oscillator under impulsive‐noise forcing are examined from analytical as well as empirical viewpoints. Specifically, calculation of the first‐order probability density and the crest (level crossing) statistics of the response of a narrow‐band single‐degree‐of‐freedom system under Poisson noise loading are considered. The inability to obtain numerical results from the Gram—Charlier (Type A) series is noted, despite the discovery of a convenient recursion relation between the moments and the semi‐invariants of a random process. Under the simultaneous assumptions of a low impulse rate and high systemQ, analytic expressions for the response first‐order probability density and the response crest statistics are established that are in good agreement with experiment. Finally, a quantitative measure of the degree of deviation of the system random response from a Gaussian process is presented and discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910413

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP