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Journal of the Acoustical Society of America

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Aug 1976

Volume 60, Issue 2, pp. 305-516

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Spatial coherence in multipath or multimodal channels

P. W. Smith, Jr.

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 305-310 (1976); (6 pages) | Cited 1 time

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An integral expression for the spatial coherence function of pure‐tone sound fields is formulated under hypotheses that the component fields of individual paths or modes are locally plane waves and mutually incoherent in the average. The total field is not assumed to be a Gaussian random variable. The resulting coherence is quasi or locally homogeneous, varying slowly with average position as the strength of the component fields change. Statistical estimates for the contributions of these components are taken from existing literature on average transmission loss. The expression for coherence has an explicit dependence on the environmental parameters, the range, and the depths of source and receivers. Numerical results and approximate expressions are developed for channels characteristic of shallow and deep water.
Subject Classification: [43]20.15; [43]60.20.
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43.20.+g General linear acoustics
43.60.+d Acoustic signal processing

Analysis of diffraction in acoustic nonlinear parametric convolvers

James M. White

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 311-314 (1976); (4 pages)

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Acoustic parametric convolvers operate by spatially integrating a term produced by the nonlinear interaction of two propagating strain waves. The integrand will have an additional spatially dependent weighting factor and inaccuracies in the convolution output will result if the product term is not uniformly produced and summed. Under appropriate assumptions, the expansion of the acoustic field into an angular spectrum of plane waves is used to show that no erroneous weighting is introduced by diffraction, although diffraction does contribute a uniform loss to the convolver output. Under additional assumptions, the diffraction loss for the convolved output is shown to equal that which occurs in transmitting from one transducer to the other.
Subject Classification: [43]25.30, [43]25.35; [43]35.54; [43]60.30.
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43.25.-x Nonlinear acoustics
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
43.60.+d Acoustic signal processing

Spatial correlation of wind‐generated noise at very low frequencies

James H. Wilson

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 315-319 (1976); (5 pages)

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Analysis of the ambient‐noise horizontal directionality data from a recent environmental acoustic exercise indicates that wind‐generated noise at 10 Hz is spatially correlated over large apertures. The noise levels measured by a large aperture, linear towed array were highest near broadside during high‐wind conditions. Spatially correlated wind‐generated noise arriving from the sea surface directly above the array is offered as a possible explanation and is consistent with results of previous wind‐noise experiments. In the limiting case of very high wind speeds (?35 knots), the array response measured for this nearfield effect closely approximated the farfield broadside beam pattern at 10 Hz. At lower wind speed, the array response was wider near broadside. This implies that the spatial correlation of wind‐generated noise at 10 Hz becomes greater as the wind speed increases.
Subject Classification: [43]28.20, [43]28.65; [43]50.80.
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43.28.+h Aeroacoustics and atmospheric sound
43.50.+y Noise: its effects and control

Ambient sea noise in waters near Australia

D. H. Cato

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 320-328 (1976); (9 pages) | Cited 5 times

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Ambient sea noise has been measured at 40 positions in mainly tropical waters near Australia: in the Indian Ocean; the Arafura and Timor Seas; and in the Coral and Tasman Seas (Pacific Ocean). Wind‐speed dependence was observed at all frequencies of measurement from 22 to 5000 Hz. At hydrophones suspended at depths between 8 and 25 m, the wind‐ dependent noise appeared to be independent of bottom depth which varied from 26 to 6700 m. The rate at which wind‐dependent noise increased with increasing wind speed was found to be significantly less than has been observed in the North Atlantic Ocean. Non‐wind‐dependent noise, observed at frequencies below 250 Hz, varied by about 10 dB within a particular sea and by up to 20 dB between seas, and could be broadly related to the relative shipping densities and propagation conditions in the individual seas. In the shallow Arafura and Timor Seas north of Australia, there is evidence that noise of distant shipping is not a significant component of the ambient noise. A model of traffic noise in the Tasman Sea predicts levels in agreement with observed noise levels.
Subject Classification: [43]30.70.
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92.10.Vz Underwater sound

Use of phase measurements for arrival‐time extraction of overlapping sinusoidal signals in shallow water

Per O. Fjell

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 329-333 (1976); (5 pages)

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The use of phase measurement for sinusoidal signal arrival‐time extraction of overlapping signals subjected to multipath conditions in shallow water is considered. The phase‐measurement method is applied to signal data from a research cruise. The method does not give convincing results. For distances greater than 10 000 m the results are negative. The results obtained are strongly dependent on the sound velocity profile. The signal pulse length was a very important parameter in the results. The optimal pulse length was shown to be greater than 10 msec and less than 100 msec regardless of the hydrophone depth for the two depths investigated.
Subject Classification: [43]30.20; [43]60.30.
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92.10.Vz Underwater sound
43.60.+d Acoustic signal processing

Attenuation of shear waves in marine sediments

Edwin L. Hamilton

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 334-338 (1976); (5 pages) | Cited 4 times

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The objectives of this report are to review selected published measurements of the attenuation, or energy damping, of low‐strain shear waves in surficial water‐saturated sands and silt clays (mud) which might occur as marine sediments. In various computations, a linear viscoelastic model is favored in which velocity dispersion is negligible, the linear attenuation is proportional to the first power of frequency, and the specific dissipation function, 1/Q, and the logarithmic decrement are independent of frequency. The logarithmic decrement is favored as a measure of energy damping because of research in soil mechanics. The very sparse data indicate that in water‐saturated sands and silt clays, the logarithmic decrements are mostly between 0.1 and 0.6. If approximate values of shear wave energy losses are required for generalized computations, it is suggested that a value for the logarithmic decrement of 0.30±0.15 be assumed for sands, and 0.2±0.1 for silt clays. Measured logarithmic decrements of compressional waves in sands average about 0.10±0.03; in silt clays about 0.02±0.01. The average values of the ratio of compressional‐to‐shear‐wave logarithmic decrements, using the above average values, would be 0.3 for sands and 0.1 for silt clays.
Subject Classification: [43]30.20; [43]40.50, [43]30.30.
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92.10.Vz Underwater sound
43.40.+s Structural acoustics and vibration

High‐frequency model for sound transmission from an airborne source into the ocean

William C. Meecham

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 339-342 (1976); (4 pages) | Cited 1 time

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The problem of the transmission of sound from an airborne source into the ocean, through the rough ocean surface, is considered. A high‐frequency approximation is adopted, requiring for its validity that the sound wavelength in air be (much) less than typical radii of curvature and than typical displacements of the ocean surface. This condition is approximately met in many applications. Attention is focused on observation directions with small grazing angles. The result is approximately unaffected by surface roughness when the grazing angle is greater than the rms surface slope, and approaches a limit (proportional to the variance of the surface slope) when the grazing angle is less than the slope. The result is independent of the source height, under the stated approximations, as is also the case for the transmission through a plane surface. The enhancement due to surface roughness, even at moderate wind speed, ranges up to 10 dB.
Subject Classification: [43]30.25.
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92.10.Vz Underwater sound

Eikonal approximation and the parabolic equation

D. R. Palmer

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 343-354 (1976); (12 pages) | Cited 2 times

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We discuss two aspects of the general problem of sound propagation in an ocean characterized by a range‐dependent profile. We first consider a normal‐mode formalism for describing a situation in which the eikonal approximation can be applied in the horizontal plane. The difficulty with this approach is shown to be an ordering in the geometric optics path‐length parameter due to mode coupling. By example we indicate how this difficulty can be overcome. We then use the formalism to discuss the approximations which make up the parabolic equation method. The parabolic equation is derived by assuming the eikonal approximation in the horizontal plane and a degenerate spectrum approximation. The degeneracy approximation is reflected in a stationary phase approximation to an integral representation for the pressure field. We then derive improved equations by relaxing these assumptions. We relax the degeneracy assumption by considering an improved stationary‐phase approximation and we relax the eikonal assumption by considering the ’’supereikonal’’ approximation.
Subject Classification: [43]30.20, [43]30.25, [43]30.50.
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92.10.Vz Underwater sound

Deep‐ocean dynamics for environmental acoustics models

J. G. Watson, W. L. Siegmann, and M. J. Jacobson

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 355-364 (1976); (10 pages)

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A hydrodynamic model for flows in the deep ocean is developed in order to determine the velocity field and sound‐speed distribution for use in acoustic transmission problems. A scaling of the governing equations is constructed that explicitly includes sound speed. A subsequent perturbation expansion yields a set of approximate equations for motions nearly in geostrophic and hydrostatic balance, such as large‐scale, quasisteady currents and Rossby waves. The quasigeostrophic potential vorticity equation or a simpler limiting case of this equation arises from the perturbation scheme to govern higher‐order dynamics of the stream function for these flows. The results of the analysis are used to obtain a significant simplification of the ray equations of geometrical acoustics for moving media. For the particular class of flows considered here, the model equations are applicable if the ocean depth is about 1 km or greater and if the spatial and temporal scales of variation of the motions are of the order of 100 km and 10 days, respectively. A solution for a flow such as the Antilles current is derived. Isospeed curves for this solution are shown in a plane perpendicular to the current, and specific features of the curves are discussed and interpreted.
Subject Classification: [43]30.25, [43]30.20; [43]28.60.
Show PACS
92.10.Vz Underwater sound
43.28.+h Aeroacoustics and atmospheric sound

Experiments with two types of electromagnetic ultrasonic transducers

Katsuhiro Kawashima

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 365-373 (1976); (9 pages) | Cited 2 times

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Two types of electromagnetic ultrasonic transducers were made and tested on mild steel, stainless steel, and aluminum. One of the transducers generates and detects a relatively large amount of longitudinal wave and simultaneously a small amount of radially polarized transverse wave in nonmagnetic metal. The other is for a large amount of radially polarized transverse wave and a small amount of longitudinal wave, also in nonmagnetic metal. Both transducers showed different characteristics for ferromagnetic metal, giving greater efficiency to the radially polarized transverse wave. It was also shown experimentally with an electromagnetic transducer that the mode conversion between longitudinal waves and radially polarized transverse waves occurs fairly efficiently at a vertical reflection.
Subject Classification: [43]35.60, [43]35.80; [43]85.40, [43]85.48.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
43.58.+z Acoustical measurements and instrumentation

Theoretical similarities of Rayleigh and Lamb modes of vibration

Leslie E. Pitts, Thomas J. Plona, and Walter G. Mayer

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 374-377 (1976); (4 pages) | Cited 6 times

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Poles of the infinite plane‐wave reflection coefficient are used to show a correspondence between Rayleigh and Lamb modes of vibration. It is demonstrated that a Rayleigh vibrational mode is a special type of Lamb mode of vibration. Further, it is shown that it should be expected that one vibrational mode for a thick plate should be similar to the theoretically predicted vibrational mode of an infinite half space, a Rayleigh mode. Thus, it is consistent to use a thick plate as an approximation to an infinite half space and expect results predicted by Rayleigh‐wave analysis.
Subject Classification: [43]35.54; [43]40.24.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
43.40.+s Structural acoustics and vibration

Experiments involving sonification of liquid helium at 4.2 K in the cathode–anode interspace of a photodiode tube

C. W. Smith, G. F. Burke, and J. A. Rooney

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 378-383 (1976); (6 pages)

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An experimental study of the photo‐injection of electrons into liquid helium at 4.2 K during sonification shows a dramatic increase in the observed photocurrent. The increase in photocurrent results from a sonically induced increase of the electron bubble mobility and a reduction in mean thermalization time due to an increase in local density fluctuations in the vicinity of the photocathode. The increase in mobility of the electron bubbles in the sound field has the same functional dependence as static pressurization, suggesting an effective rectification mechanism. Studies in which the sound field is abruptly turned off show that the half‐life of potential cavitation nuclei within the microbubble field is 7.6 sec. These sonically induced changes in the electron microbubble photocurrent provide a unique method for the study of the formation and population dynamics of cavitation nuclei.
Subject Classification: [43]35.47, [43]35.32.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
67.25.dg Transport, hydrodynamics, and superflow

Acoustical effects in panel response to supersonic turbulence

Larry D. Pope

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 384-394 (1976); (11 pages)

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Acoustical coupling of a turbulence‐excited panel and a supersonically moving fluid is investigated. Response of a panel with a single rib discontinuity is considered. Radiation from the panel into the fluid induced by a uniform line force is investigated and the line admittance of the panel in the presence of supersonic flow is obtained. Numerical results are presented for the line admittance and for the ribbed and unribbed infinite panel response. A relation is given which upon integration will yield the radiation damping of a finite panel (radiation into the supersonic flow).
Subject Classification: [43]40.35; [43]28.65; [43]20.60.
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43.40.+s Structural acoustics and vibration
43.28.+h Aeroacoustics and atmospheric sound
43.20.+g General linear acoustics

Gap detection: Two‐channel detection of the missing event

J. D. Gilliom and W. M. Mills

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 395-404 (1976); (10 pages)

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The ability to detect gaps in continuous sinusoids was studied in both single‐ and two‐channel tasks. From single‐channel tasks, psychometric functions were obtained. Pulse and gap functions were found to be essentially parallel, with gap detection being 3–4 dB poorer than pulse detection. In two‐channel tasks, two‐channel detection of gap signal events produced a lower level of performance than two‐channel detection of pulse signal events. However, in an unusual condition where a gap stimulus produced what sounded like a pulse to the observer, performance in two‐channel gap detection and two‐channel pulse detection was quite similar. This latter result suggests (1) gap stimuli enter the system as efficiently as pulse stimuli, and (2) it is the system’s inferior ability to process perceptual gaps which leads to the lower performance normally observed in two‐channel gap detection. In a fourth two‐channel task which required the observer to detect gap stimuli in one channel and pulse stimuli in the other, no detrimental effect on performance could be detected—a result illustrating the flexibility of the two‐channel processing mechanism. Implications of the results for the INR model of two‐channel processing are discussed.
Subject Classification: [43]65.75, [43]65.58, [43]65.68.
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42.66.-p Physiological optics

Subharmonic pitches of a pure tone at low S/N ratio

T. Houtgast

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 405-409 (1976); (5 pages) | Cited 6 times

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2AFC scores were obtained on 50 untrained subjects who had to respond to a 3% increment or decrement of the fundamental frequency of two successive signals. The first signal in each trial was a reference, containing six harmonics of 200 Hz. Main variables were the number of harmonics of the second signal in a trial (either 3, 2, or 1) and the presence or absence of continuous background noise. Low scores were observed in the absence of the noise (typically 65% for the 3‐ and 2‐component signals, and virtually 50% for the 1‐component signals), whereas in the presence of the noise much higher scores were observed (typically 90% and 80%, respectively). The results indicate that background noise has great impact on the perceptibility of a ’’low pitch’’ related to the fundamental frequency, even more so than the number of components presented (within the range of three, two, or one components): at a low S/N ratio, even a single harmonic may give rise to the perception of a subharmonic low pitch. Subsequent experiments with three trained subjects indicated that this potential of a single pure tone to evoke a subharmonic pitch deteriorates for harmonic numbers of about n=7 to 11. The theoretical implications of these subharmonic pitches of a pure tone to pitch perception in general are discussed.
Subject Classification: [43]65.54, [43]65.75, [43]65.35.
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42.66.-p Physiological optics

Discrimination and labeling of noise–buzz sequences with varying noise‐lead times: An example of categorical perception

James D. Miller, Craig C. Wier, Richard E. Pastore, William J. Kelly, and Robert J. Dooling

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 410-417 (1976); (8 pages) | Cited 2 times

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The onset of a noise [0.9–2.1 kHz, 55 dB SPL (A weighted)] preceded that of a buzz [100 Hz, 0.5–3.0 kHz, 70 db SPL (A weighted), 500 msec] by −10 to +80 msec and both terminated simultaneously. Eight adults discriminated among noise‐lead times in an oddity task. In separate sessions, they labeled singly presented stimuli with either of the two responses: ’’no noise’’ or ’’noise.’’ The results are highly similar to those reported for the categorical perception of synthetic plosive consonants differing in voice‐onset time. On the average, discrimination was best across a noise‐lead‐time boundary of about 16 msec, where labeling also shifted abruptly. These results and those of categorical perception, generally, are interpreted in terms of Weber’s law as applied to a single component within a stimulus complex. It is concluded that categorical perception of sounds is not unique to speech and suggested that it may be a general property of sensory behavior.
Subject Classification: [43]65.75; [43]70.30.
Show PACS
42.66.-p Physiological optics
43.70.-h Speech production

Susceptibility to auditory fatigue: Comparison of changes in cochlear nerve potentials in the guinea pig and chinchilla

Curt Mitchell

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 418-422 (1976); (5 pages)

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The susceptibilities of the guinea pig and chinchilla to acoustic fatigue are compared. For this comparison they were exposed to a 6‐kHz tone. The exposures were within the range of 60–110 dB SPL. The N1 potential of the cochlear nerve and the cochlear potential were recorded before and after exposure. Both species suffered greatest N1 changes a 1/2 octave above the exposure tone. No appreciable changes in cochlear potential were observed. In agreement with previous studies for equal SPL’s, the chinchilla was found to be more susceptible to fatigue than the guinea pig. However, when the exposures are based on maximum cochlear‐potential output, these animals suffer similar losses in N1. This suggests that impedance differences in their ears accounts for the susceptibility difference. Nerve fatigue is described and found related to hair cell distortion.
Subject Classification: [43]65.66, [43]65.40, [43]65.42.
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42.66.-p Physiological optics

Gap detection with three auditory events—a single‐channel process

Kendrick N. Williams and Lloyd F. Elfner

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 423-428 (1976); (6 pages) | Cited 2 times

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Temporal resolution of a silent interval (gap) imbedded in a three‐tonal‐pulse train was investigated. Two frequencies were alternated in a three‐event array where the gap could appear between the first and second or second and third auditory event. Frequency and gap position effects were systematically explored using a temporal two‐interval forced‐choice paradigm and a modified tracking procedure. Gap detection was found to vary as a function of antecedent event duration and signal‐comparison stimulus similarity. Indications of a filter process similar in bandwidth to the empirical critical band was found in fully correlated signal‐comparison stimulus conditions. Obtained results are consistent with fixed‐filter signal‐envelope detection models found in the simultaneous and forward‐masking literature.
Subject Classification: [43]65.75, [43]65.68.
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42.66.-p Physiological optics

Masking period patterns of harmonic complex tones

E. Zwicker

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 429-439 (1976); (11 pages) | Cited 1 time

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Masking period patterns, i.e., the SPL of just audible triggered sequences of short high‐frequency test tone bursts as a function of their temporal spacing throughout the period of a masker, were measured using the following maskers: low‐frequency two‐tone and three‐tone complexes, Gaussian‐shaped impluses and differentiated Gaussian impulses with both condensation and rarefaction peaks. The similarity between masking period patterns and neurophysiologically measured period histograms was confirmed with respect to the temporal structure. However, distinct differences appear in the amplitude structure of both patterns, indicating a strong nonlinearity involved in the transformation of the masker’s time function into the masking period pattern. Starting a few decibels above threshold in quiet, the peaks of the patterns are elevated by 10 dB for each 5‐dB increment of masker level. This fact points towards a square law for high‐frequency test signals and low‐frequency maskers. The steepness of slope of the masking period pattern seems to reach a maximal value of 10 dB/msec. Relations between neurophysiological period histograms and corresponding masking period patterns as well as differences between the patterns produced by condensation and rarefaction peak maskers, respectively, are discussed.
Subject Classification: [43]65.58, [43]65.35, [43]65.68.
Show PACS
42.66.-p Physiological optics

Inter‐ and intraspeaker variability in fundamental voice frequency

James E. Atkinson

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 440-445 (1976); (6 pages) | Cited 1 time

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A measure was obtained of the amounts of variability in fundamental voice frequency F0 in simple sentences produced by several adult male speakers. A comparison was made of intra‐ and interspeaker variability, and a detailed analysis was performed to determine the nature of this variability. Great variability was found between speakers, but more important was the finding that the intraspeaker variability was essentially as great as the interspeaker. This indicates that even for a single speaker’s utterances, considerable ’’noise’’ is present which can obscure the prosodic ’’signals.’’ The F0 variability involves seemingly random interleavings that affect the relative F0 values within an utterance, as well as, simple shifts in average F0 that affect the absolute F0 of the contour as a whole.
Subject Classification: [43]70.40, [43]70.70.
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43.70.-h Speech production

Digital analysis of laryngeal control in speech production

J. L. Flanagan, L. R. Rabiner, D. Christopher, D. E. Bock, and T. Shipp

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 446-455 (1976); (10 pages)

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Physiological measurements are made directly on human talkers to determine several dynamic laryngeal functions. The functions are control variables in a speech synthesizer which utilizes acoustic models of the vocal cords and vocal tract. The functions are measured simultaneously and recorded on multichannel FM tape. They are the time variation of vocal‐cord (glottal) opening (Ag); the electromyographic (EMG) potentials of three laryngeal muscles−−posterior crico‐arytenoid (PCA), interarytenoid (IA), and crico‐thyroid (CT); the subglottal air pressure (Ps); the speech output sound pressure waveform (P); and timing pulses from a digital clock. Preliminary data for ten utterances by a man are digitized by a multiplexed A/D converter on a DDP−516 computer, and the results are stored in disk file for analysis. Bandwidth of the multitrack FM playback is 2800 Hz. Each function is sampled at 6250 sec−1 and quantized to 16 bits. Digital filtering is applied to remove dc offsets and enhance information features. The acoustic functions (Ag, Ps, and P) are submitted to programmed pitch analysis. The results show how voice periodicity can be manifested differently at the glottal and sound‐output levels. A typical instance is vocal‐cord vibration throughout the occluded phase of a voiced stop consonant. The EMG functions are analyzed by computing short‐time energy. The results are correlated with voicing onset/offset and with voice pitch. PCA energy is shown to be correlated with voicing offset, and anticipatory to it by about 20–30 msec. IA energy is shown to be correlated with voicing onset, and anticipatory to it by about 40–50 msec. CT energy is found to be nearly directly correlated with the frequency contour for voice pitch. Direct utilization of these physiological parameters for speech synthesis is suggested.
Subject Classification: [43]70.20, [43]70.60.
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43.70.-h Speech production

Identification of dichotic fusions

Bruno H. Repp

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 456-469 (1976); (14 pages)

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Seven synthetic syllables from a ’’place continuum’’ (/bae/–/dae/–gae/) were presented in all dichotic combinations for identification. These syllables fused completely, so that dichotic pairs were perceived as single stimuli. The response pattern could not easily be explained by an ’’auditory averaging’’ hypothesis. Rather, stimuli that were good instances of a category seemed to ’’dominate’’ stimuli that were closer to a category boundary. To account for this finding, a three‐stage pattern recognition (’’prototype’’) model is proposed, according to which the information from the two ears is linearly combined after ’’multicategorical’’ processing, which follows auditory processing and precedes the final phonetic decision. Electronically mixed stimuli led to a response pattern that was similar to that for dichotic syllables (apart from some systematic deviations ascribed to peripheral masking), so that the same processes of central interaction seem to be involved. Average dichotic right‐ear advantages of small magnitude were obtained for the dichotic fusions. They could not be reliably discriminated from binaural stimuli, and selective attention to one ear had little effect. With respect to the measurement of dichotic ear asymmetries, dichotic fusions offer certain methodological advantages over other dichotic stimuli. The problem of determining the ’’true’’ ear advantage is discussed.
Subject Classification: [43]70.30; [43]65.75.
Show PACS
43.70.-h Speech production
42.66.-p Physiological optics

Input impedance curves for the brass instruments

John Backus

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 470-480 (1976); (11 pages) | Cited 6 times

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Apparatus previously described [J. Acoust. Soc. Am. 56, 1266–1279 (1974)] to obtain input impedance curves for the woodwind instruments has been applied to the brass instruments. These curves show, for example, the importance of the bell and the mouthpiece in putting the resonance frequencies in their musically necessary places. The mouthpiece also has the important effect of increasing the input impedance presented to the player. The trumpet has input impedances at the various resonance frequencies ranging up to 1000 cgs acoustic ohms; trombones and French horns have about one‐third as much. Trumpet mutes were investigated and found to behave as bandpass or high‐pass filters which change the instrument’s radiated tone quality. The long‐argued question about hand‐stopping of horns was investigated; it was concluded that the effect of hand stopping is to lower the frequencies of all the modes.
Subject Classification: [43]75.40.
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43.75.+a Music and musical instruments

Jet‐drive mechanism in organ pipes

N. H. Fletcher

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 481-483 (1976); (3 pages) | Cited 4 times

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The analysis given by Elder [J. Acoust. Soc. Am. 54, 1554 (1973)] of the mechanism of interaction between a time‐varying air jet flow velocity and a resonant organ pipe is extended to deal with the case in which a jet of fixed flow velocity is deflected to cut a sharp pipe lip. Similar terms arise in the analysis but the nonlinearities are less important than in Elder’s case. The generation of higher transverse pipe modes by the jet asymmetry is considered and it is concluded that such modes may play a significant part in coupling ordinary pipe modes to pipe‐wall vibrations.
Subject Classification: [43]75.60.
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43.75.+a Music and musical instruments
47.27.wg Turbulent jets

Energy spectrum analysis: A model of echolocation processing

Richard A. Johnson and Edward L. Titlebaum

J. Acoust. Soc. Am. Volume 60, Issue 2, pp. 484-491 (1976); (8 pages)

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Previous analyses of echolocation have suggested that correlation‐equivalent processing might be used in certain cases. A frequency domain approach based on energy spectrum analysis of the signal and its echoes combined is proposed as the processing mechanism for echolocation. It is a generalized wide‐band mechanism and can account for the large diversity of wide‐band signals known to be used for orientation. Neurobiological investigations neither confirm nor deny any specific kind of correlation equivalent processing, but this proposal offers the first frequency domain correlation‐equivalent possibility. A review of time separation pitch reveals that an identical analysis has been used to explain that phenomenon. Extensions of the model can explain many of the phenomena observed in echoloction.
Subject Classification: [43]80.50, [43]80.60; [43]60.40; [43]65.62, [43]65.68.
Show PACS
43.80.-n Bioacoustics
43.60.+d Acoustic signal processing
42.66.-p Physiological optics
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