摘要:

A matched filter operates on a signal to yield an output that is the autocorrelation of the input signal. To study the use of matched filters with an additive array, we did the following experiments: A loudspeaker was driven with an impulse, and the sound observed with an array of microphones. The electrical outputs of the microphones were added without time delays to yield a single channel of information. The matched filter‐shift register delay line was adjusted to match the signal from the array when the array was in the end‐fire direction. The array‐matched filter combination had a correlation maximum for the direction in which the array output and filter were matched and the maximum decreased as the array was turned away from this direction. A single receiver near several reflectors also yields several arrivals on a single channel of information. The balance of the experiment was similar to the array‐matched filter experiment. [Columbia University, Hudson Laboratories Informal Documentation No. 15. This work was supported by the Office of Naval Research under Contract Nonr‐266(84).]

ISSN:0001-4966    

DOI:10.1121/1.1937102

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

In a system for which we have complete control of both the outgoing signal and the spacing of elements in a receiving array, proper choices of the signal and the array spacing allow us to treat the array as a 2‐terminal device, summing all elements outputs together with no time delays, without losing the ability to make directional discriminations. After summing, the output of the array is passed through a delay‐line filter designed for the input signal, array spacing, and direction of interest. The output of the filter is a correlation function peaked for the proper signal arriving in the correct direction. In general, the side‐lobe structure and signal‐to‐noise performance will be poor, but special choices of signal and spacing exist for which both characteristics are acceptable. [Columbia University, Hudson Laboratories Informal Documentation No. 14. This work was supported by the Office of Naval Research under Contract Nonr‐266(84).]

ISSN:0001-4966    

DOI:10.1121/1.1937103

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Short‐duration samples of white noise were transmitted through 3 voice‐communication systems and reduced to visual spectrum displays (sonagraph sections). Likewise, samples of residual noise were taken from each system during no‐signal intervals and similarly displayed. By means of a transparent frequency‐amplitude overlay scale, S+N/N ratios were determined at the midfrequencies of the octaves between 150 and 4800 cps. These ratios were used as the basis for calculating an articulation index (AI) for each system, after the octave‐band method of Kryter. PB‐word‐articulation scores corresponding to the calculated AI's were taken from published curves; these scores compared favorably with scores obtained from tests made by transmitting PB wordlists through the three systems. Suggestions are made for refining and simplifying the octave noise‐band technique.

ISSN:0001-4966    

DOI:10.1121/1.1937114

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An optimum condition for increasing the comprehension of a meaning‐dynamic system (E. Colton, “On the Contribution of Synchronization Patterns to Semantic Meaning,” to be published in the proceedings of the Fourth International Congress on Acoustics) is approached by providing suitable aural and visual communication isolation for the creative‐source aggregates, while their coordinating links should be placed in the opposite conditions and agminated. The concept of noise addiction is introduced. It is concluded that (a) excessive “well‐adjusted togetherness” in any quasi‐permanent group, e.g., in the home or the work area, restrains creativity; and (b) many repetitions of long exposures to noise (even of low intensity) are very likely to reduce the comprehension of a meaning‐dynamic system.

ISSN:0001-4966    

DOI:10.1121/1.1937116

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An approximation is obtained for the power spectral density of the response of a hard‐spring resonator to a class of random inputs by 2 methods of equivalent linearization. Comparison of the theoretical spectral densities is made with those obtained experimentally from an analog computer with white‐noise excitation.

ISSN:0001-4966    

DOI:10.1121/1.1937122

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

To determine the absorption in a reverberation chamber for PWL measurements. the reverberation‐time method (using the Sabine formula) is preferable to the calibrated‐source method. This preferred method, which is independent of the source or measuring‐equipment calibrations, involves a device attached to a graphic level recorder to indicate the reverberation time on an electronic counter. The 10 logafactors for three reverberation chambers determined with this device are compared to determinations which were obtained with: (1) a graphic level recorder and (2) a calibrated source.

ISSN:0001-4966    

DOI:10.1121/1.1937125

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The synthesis of speech by joining together segments derived from natural speech has not proven to be satisfactory with segments smaller than words, especially because of discontinuities in pitch and formant frequencies at the junctions. It appears that segmentation of the control signals for an analog synthesizer may avoid these difficulties. This paper describes an experimental system to investigate this method. A library of synthesizer control signals corresponding to subword segments of speech is now being developed. The equipment used to generate the library of control signals, as well as that used to synthesize connected speech from the library, is described. The synthesizer is a transistorized terminal analog of the cascade type. The synthesizer control signals are originally derived from functions drawn on a transparent plastic belt by opaque tape and scanned by a CRT and photomultiplier. The control‐signal functions are varied until the speech segment being studied is satisfactory. The resulting control signals corresponding to the speech segment are then automatically digitized and recorded on punched cards for addition to the library. Connected speech may be generated by computer assembly of the synthesizer control signals corresponding to a sequence of speech segments. In the assembly of connected speech from the library segments, pitch and timing may be specified independently of the sequence of segments if desired.

ISSN:0001-4966    

DOI:10.1121/1.1937131

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

We consider the response spectrum of a dynamical system described byLr(t)+εN[r,ṙ,r̈⋯]=f(t), for whichLis a linear differential operator in time,Nis a nonlinear analytic function of the responser(t) and its derivatives, andf(t) is a Gaussian random process with a given power spectrum. A perturbation technique is applied, which yields the spectral density of the response in a series in powers of the coupling constant ε. The methods is, therefore, applicable only if the system remains stable in the range of ε. Some general properties of the expansion are presented, and a sample calculation of a perturbed spectrum is outlined. The method is applicable to such problems as Brownian motion with nonlinear viscous forces and the coupling of energy from a nonlinear mode into other modes in a complex structure.

ISSN:0001-4966    

DOI:10.1121/1.1937138

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Conventionally, the study of sound radiation from vibrating boundaries refers to impervious boundaries. By allowing the surface to be pervious, we introduce into the problem an additional parameter that can be varied independently. Using the conventional radiation characteristics for piston sources as reference, we show by special examples that reductions, as well as gains in radiated power, can be obtained by such surface treatment. Therefore, this kind of “radiation control” might be of practical interest both in noise‐control and communication applications. [This work was supported in part by the U. S. Army Signal Corps, the U. S. Air Force Office of Scientific Research, and the Office of Naval Research under Contract No. Nonr‐1841(42).]

ISSN:0001-4966    

DOI:10.1121/1.1937144

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP