摘要:

Small differences in quality may affect the ease with which various speech samples can be understood even though they are all highly intelligible according to articulation tests. Such quality differences were reliably discriminated by a speech‐interference test which determined how easily the speech samples could be heard against a background of interfering speech. The communication quality of a degraded speech sample was measured by the difference,A = T − T0, whereTandT0were the interference thresholds for the degraded and reference speech, respectively. An interference threshold was defined as the value of the signal‐to‐interference intensity ratio where the signal speech was 50% intelligible in the presence of interfering speech.Qmeasures and subjective quality ratings were obtained for speech degraded by low‐ and high‐pass filtering, additive noise, and transmission over a telephone line. TheQmeasures successfully discriminated differences in speech quality, and were monotonically related to the ratings, thereby validating the speech interference test for speech‐quality evaluation.

ISSN:0001-4966    

DOI:10.1121/1.1913428

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The frequencies and levels of the first three formants of 12 Dutch vowels were measured. The vowels were spoken by 50 male speakers in an h (vowel) t context. Statistical analysis of these formant variables confirmed thatF1andF2are the most appropriate two distinctive parameters for describing the spectral differences among the vowel sounds. Maximum likelihood regions were computed and used to classify the vowels, and a score of 71.3% correct classification in the logF1‐logF2plane was obtained (87.3% if three related pairs are grouped together). These scores rose to 78.3% and 95.2%, respectively, when a simple speaker‐dependent correction was applied. The scores are comparable with those obtained in an earlier study in which a principal‐components analysis was applied to the 1/3‐oct filter levels of the same vowel sounds [Klein, Plomp, and Pols, J. Acoust. Soc. Amer.48, 999–1009 (1970)]. From the latter data a two‐dimensional representation (“optimal plane”) equivalent to the logF1‐logF2plane could be derived. The relative merits of the two approaches are discussed. For automatic speech recognition in particular, the dimensional analysis is much more attractive than the formant analysis because it is much simpler and can be carried out in real time.

ISSN:0001-4966    

DOI:10.1121/1.1913429

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

In the simple pulse‐echo technique succesive multiply reflected pulses, received by the quartz transducer, are amplified by a wide‐band amplifier, detected, and finally displayed on the screen of a cathode ray oscilloscope. The observed pulse heights are compared for determination of ultrasonic absorption in the medium. In the present development, the received pulses after amplification, detection, and sufficient reamplification, are connected to a T‐adapter. From one of the outputs of this adapter the pulse pattern is observed on one of the beams of a double‐beam oscilloscope, while the second output is connected to the input of a single‐channel analyzer. Using the analyzer in this way, the pulse heights can be determined directly in volts and then their decibel level can be read on a calibration curve to determine the ultrasonic absorption coefficient in medium. The same has been demonstrated in this paper. Some results of measurements on a few steels, using this technique, have also been reported.

ISSN:0001-4966    

DOI:10.1121/1.1913430

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The diffraction of a Bleustein‐Gulyaev surface wave by a semi‐infinite conductive surface layer is investigated. It is assumed that the direction of propagation is normal to the edge of the semi‐infinite conductive layer. It appears that, if the dielectric constant ε1of the piezoelectric material is large compared with the dielectric constant ε0of the adjacent half‐space, the relative power flow associated with the reflected surface wave is of the order (ε0/ε1)2. The relative power flow of the transmitted surface wave is of the order ε0/ε1. Hence, if ε0/ε1≪ 1, the largest part of the incident power is converted into a bulk wave. The angular power distribution of the diffracted bulk waves appear to be very asymmetric and concentrated preponderantly in a direction making an angle κ2/(1 + ε1/ε0) with the incident wave, κ being the piezoelectric coupling coefficient.

ISSN:0001-4966    

DOI:10.1121/1.1913431

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A method of computing the eigenmodes of acoustic waveguides of arbitrary cross section is described. It is a finite‐element technique, based on a variational formulation of the guided‐wave problem. The accuracy of the method is assessed by comparing numerical and experimental results for a few specific structures. In particular we describe an acoustic surface ridge waveguide with low dispersion over a broad band.

ISSN:0001-4966    

DOI:10.1121/1.1913432

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Anisotropic beamsteering and diffraction enhancement‐retardation effects are analyzed. An anisotropic scaling theorem and an analytic, anisotropic lens maker's equation are deduced. Experimental results, illustrating near‐ and farfield diffraction pattern scaling, and contrasting aberration‐corrected and cylindrical surface wave lenses are presented.

ISSN:0001-4966    

DOI:10.1121/1.1913433

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Making use of newly derived equations for dc‐ac coupled elastic motion, the effect of a static axial stress and strain upon the velocity of the lowest‐order flexural mode in solid circular cylinders has been demonstrated. It is rigorously shown that the “transverse” wave in a stretch string configuration is the general form of which the lowest‐order Pochammer mode is the special case, i.e., for zero static stress. Applications of the results to stringed instruments, high‐speed turbines, and deep‐sea vehicles are briefly discussed.

ISSN:0001-4966    

DOI:10.1121/1.1913434

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A design and calibration data are presented for velocity hydrophones which operate vertically or horizontally. The simplicity of construction, broad frequency range, and relatively high sensitivity of these units make them particularly practical for use in bioacoustic research.

ISSN:0001-4966    

DOI:10.1121/1.1913435

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

This paper presents a theoretical study of sound propagation in an ocean‐surface duct. It deals with several aspects of the theory from a point of view which has not heretofore been taken in the analyses of this problem. The model used to describe a duct assumes the ocean surface to be smooth and the square of the refractive index to be bilinear. Alternative representations of the sound field excited by a point source are derived, the two playing the most significant role in this paper being the residue series and the normal‐mode representation. It is shown that the depth functions of the residue series do not form a complete set, as those of a normal‐mode representation must, and that the normal‐mode spectrum is continuous, rather than discrete. The completeness properties of the normal‐mode functions are then utilized in a study of the energy‐trapping capabilities of the duct. In this connection, virtual modes are introduced and shown to lead naturally to the derivation of a leakage coefficient characteristic of the exponential leakage of energy out of the duct with increasing range. In addition, a cutoff‐frequency criterion, useful in determining when a surface duct can trap energy, is derived.

ISSN:0001-4966    

DOI:10.1121/1.1913436

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

An experimental and theoretical investigation is presented of farfield distortion of a finite‐amplitude wave generated by a circular‐piston source. Nearfield distortion is neglected. Thus the boundary condition is that the acoustic signal at the beginning of the farfield is a pure sine wave of amplitude proportional to the small‐signal directivity factor for the piston. The method of applying weak‐shock theory to obtain directivity patterns and propagation curves is outlined. A criterion for the maximum range at which weak‐shock theory is valid is derived for each harmonic. Anad hocmethod of matching at this range the small‐signal solution, with absorption included, to the weak‐shock solution is proposed. Data obtained for a fundamental frequency of 450 kHz and source levels of 109 and 127 dB (re1 μbar at 1 yd) are presented. Theoretical and experimental beam patterns are in good agreement. Propagation data presented for the 127‐dB source level are in poor agreement with the predictions of unmodified weak‐shock theory but in good agreement with the matched solution. In general, the experimental data support the hypothesis that harmonic generation in waves from directive sources may be described by specifying a boundary condition for each direction and then assuming that the distortion developing in that direction is not affected by distortion along any other direction.

ISSN:0001-4966    

DOI:10.1121/1.1913437

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP