bluuebunny/crossref_metadata_2025 huggingface dataset:
An Equivalence between Magnitude Estimation and Absolute Identification for Sound Intensity
Authors: Braida L. D.
Published: September 2005

Recent work suggests that errors in absolute identification and dispersions of magnitude estimates in ratio scaling arise from common limitations. It is proposed that if the same set of stimuli is used in both types of experiments, it should be possible to use the dispersion of the magnitude estimates to specify the confusion matrix in absolute identification (up to transformations related to response bias). Moreover, the specification should depend only on the ordinal properties of the estimates. This paper describes a series of experiments designed to explore the conjectured equivalence. The experiments use tone-pulse stimuli that are identical except for intensity. The responses are processed using a Thurstonian response model. The results tend to confirm the conjectured equivalence. [Work supported principally by a grant from the National Institutes of Health and in part by the Joint Services Electronics Program.]
Mobile Psychoacoustics Laboratory
Authors: Harris Martin S. , Smith Paul F.
Published: September 2005

A mobile laboratory that provides an adequate environment for a variety of psychoacoustic measurements has been constructed. The mobile unit will be used for psychoacoustic and bioacoustic field studies. The laboratory houses a 10-man audiometric booth. In addition to space within the booth, there are in excess of 120 ft2 of floor space available for installation of equipment. Most clinical or experimental audiometric and otological procedures and group audiometric tests can be administered within the laboratory. Cables may be run to apparatus set up away from the trailer permitting detailed environmental noise analyses, acquisition of bioacoustic data, conducting underwater hearing and communications experiments, etc. Details of construction and acoustical performance will be given.
Intelligibility of Time and Bandwidth-Compressed Vowels
Authors: Daniloff R. , Shriner T. A. , Zemlin W. R.
Published: September 2005

An investigation was made of possible differences in male and female speaker vowel intelligibility under various conditions of time compression (TC) and bandwidth compression (BWC), with and without time restoration. The female's vowels are generally more intelligible than the male's for all distortion conditions. The advantage is largest for BWC as was previously reported, and somewhat less for TC. For a given percentage of distortion (30%–80%), BWC degrades vowel intelligibility more severely than TC. Restoring time to normal for BWC produced by slow playing does not enhance intelligibility and may degrade it. Vowel confusions for TC are related to duration—that is, vowels are increasingly often confused with those of shorter duration as the % TC increases. Errors for BWC conditions are closely related to misperceptions of vowel formant two and to a lesser degree, vowel formant one. Vowel-confusion patterns for male and female are much alike for all conditions of distortion, indicating minimal male-female differences in effects produced by these distortions.
Comparison of Preference Scales
Authors: Pachl Walter P. , Rothauser Ernst H. , Urbanek Günther F.
Published: September 2005

For many practical applications, the well-established parameter preference may be said to describe speech quality sufficiently. For the evaluation of preference, several relative and absolute-measurement methods have been proposed that are different—not only with regard to the test procedure but also with regard to the presentation of the test results. Given a particular practical problem it is difficult to select one of these utilitarian methods, because all methods have some advantages and their comparison is difficult. The present paper proposes a unified preference rating scale similar to the one described by Munson and Karlin in 1962. It can be shown that by projection of the individual rating scales onto the preference unit scale, a meaningful comparison of the different measurement results become possible. Based on this unidimensional rating scale, the performance of the different methods is discussed, especially with regard to preference discriminability within a set of continuously degradable speech signals.
Speech Intelligibility in a Stationary Multipath Channel
Authors: Sachs Murray B. , Sergeant Russell L. , Russotti Joseph S.
Published: September 2005

The intelligibility of speech transmitted through an acoustic channel such as the ocean is limited by multipath “time smearing.” The purpose of this study has been to obtain a quantitative measure of the effects of such time smearing on speech intelligibility. A linear, time-invariant channel was used as a model of the ocean. The impulse response of this channel was a sample of band-limited Gaussian noise. Using fast Fourier transform techniques, words of the modified rhyme test were convolved with (“smeared by”) this channel impulse response. The intelligibility of these “smeared” words was measured as a function of the impulse response duration T. Intelligibility was found to decrease monotonically as a function of T over the range T = 0 to T = 150 msec. Increasing T beyond 150 msec caused little change in intelligibility. With rhyme-test words used in a 6AFC test, average scores of 75%–80% were obtained for T between 150 and 665 msec.
Studies in Word Recognition by Computer
Authors: Bobrow Daniel G. , Klatt Dennis H.
Published: September 2005

A program has been written to learn to recognize a limited vocabulary of words. Functions of the raw spectral data are transformed into sequences of states (features) in order to normalize for word-onset time, speaking rate, and speaking rhythm. State transition thresholds are normalized for speaking level. A hysteresis region is employed about each threshold to reduce the sensitivity of the system to noise. A feature sequence need not be consistently correct because the recognition algorithm makes very efficient use of redundancy to identify the most probable word. The linguistic significance of the binary features incorporated in the algorithm will be discussed. Features related to tense-lax, sibilant, fricative, continuant, several place-of-articulation features, and a stress feature are included. Recognition scores approach 97% correct after three rounds of training on a 54-word vocabulary. [Work supported by the National Aeronautics and Space Administration.]
Ultrasonic Attenuation in Thin Specimens Driven through Buffer Rods
Authors: Papadakis Emmanuel P.
Published: September 2005

A method is presented for measuring ultrasonic attenuation in thin solid specimens. The sample is bonded to one end of a buffer rod, and a transducer is bonded to the other end. All three elements must have plane parallel faces. The system is excited by an rf burst shorter than the round-trip travel time of the elastic wave in the buffer but longer than three times the round-trip travel time in the specimen. The specimen and its interface with the buffer act as a multiple-path elastic wave interferometer. The envelope of the returning echo in the buffer rod shows a stepwise amplitude modulation, one step per round trip in the specimen. The amplitudes of the first three steps are measured at rf frequencies at which the phase delay in the specimen is an integer multiple of π From the amplitudes, the attenuation in the specimen and the reflection coefficient at the buffer-specimen interface are computed. Measurements can be made over a broad frequency band with a single transducer, so the frequency dependence of the attenuation can be determined. The method has been applied to specimens of ferroelectric ceramic and rolled sheet metal samples of a two-phase alloy. The results are presented and interpreted.
Method for Measuring Ultrasonic Attenuation in the Presence of Noise
Authors: McSkimin H. J.
Published: September 2005

In making measurements of attenuation by the ultrasonic pulse-echo method, the amplitudes of the various echoes must be determined. Since the pulse sequence is repeated periodically, correlation techniques can be used—and have been used—to reduce the effect of noise. In the present method, a gated carrier technique allows direct heterodyning of a selected rf echo to produce a video signal with a beat frequency of a few Hz. This signal is sampled at the repetition rate and then filtered to remove high-frequency components, including much of the noise. With an over-all circuit time constant of approximately 0.2 sec, an improvement of signal-to-noise ratio of 30 dB can be obtained. Because the output signal is low-frequency ac, bothersome “zero-base” drift can be eliminated. Furthermore, the detection system is quite sensitive for weak signals, and is linear. Readout can be made on standard recorders. Although the results described were obtained at 40 MHz, extension to higher frequencies is feasible.
Measurement of Small Changes in the Velocity of Ultrasonic Waves in Solids Using an Improved ldquo;Sing-Around” System
Authors: Brammer A. J.
Published: September 2005

Interest in the anharmonic properties of solids has resulted in the development of instruments capable of resolving extremely small changes in the velocity of ultrasonic waves (∼1 part in 107). A “sing-around” system, initially designed for use in studies of the third-order elastic constants of solids, has been developed from the system described by Forgacs [IRE Trans. on Instr. 9, 359 (1960)]. The new apparatus appears to overcome the main limitation of the Forgacs system (viz., its sensitivity to the amplitude of the acoustic signal) by using a zero crossing discriminator to convert the acoustic signal, which consists of a series of echoes, into a number of constant amplitude pulses. The instrument has been used to examine stress-induced velocity changes in some 3–5 semiconductors, especially indium antimonide, and there is some evidence of curvature in the functional relation between transit time and stress at low stress levels.
Measurement of the Velocity of Sound in Water by Optical Methods
Authors: Crandall A. J. , Cook B. D. , Hiedemann E. A.
Published: September 2005

Upon passing through a sound beam, a collimated light beam becomes modulated in phase. The resulting interference produces an amplitude modulation of light that may be detected by a photomultiplier. This amplitude modulation has a spatial periodicity very nearly equal to the wavelength of the sound. The sound velocity may be determined by measuring a translation of the transducer and number of wavelengths indicated by the photomultiplier output. The nature of the systematic error produced by the free-field diffraction is a quasiperiodic function of the distance from the transducer; being able to account for this error permits accurate optical determinations to be extended to frequencies below 1 MHz. [This work was supported by the Office of Naval Research and the National Science Foundation.]
Effect of Rise Time on Amplitude DL
Authors: Dixon James D. , Saslow Michael G.
Published: September 2005

The literature on rise time vs amplitude DL suggested need for an experiment in which the only stimulus parameter varied was rise time and in which the subjects could be expected to be performing as well as possible. The 20-dB SL stimulus was a sine wave of 1000 or 4000 Hz. Its amplitude could be increased stepwise by calibrated small amounts, with exponential rise times of 10, 25, and 50 msec from a positive-going zero crossing. A 2I temporal FC staircase, with feedback, was used. In three subjects, at both frequencies, median DL's were quite small: 0.25, 0.4, and 0.5 dB, at rise times of 10, 25, and 50 msec. Similarity of results at both frequencies agrees with evidence that at those frequencies, signal duration required for transition from click pitch to tone pitch is constant. This consistency may derive from a low-pass property of the auditory system. [This research was supported in part by the Veterans Administration Hospital, Seattle, and the University of Washington, Psychophysics Research Program, Seattle.]
Perception of Intensity Relations
Authors: Durlach N. I. , Braida L. D.
Published: September 2005

Results describing perceived relations among stimuli differing only in intensity are available in studies of scaling, absolute identification, discrimination, and detection. Little is known, however, about how the various results are related. Research is now being conducted to develop a unified theory that will provide insight into these relations. This theory consists of two parts: a response model and an internal-noise model. The response model, derived from Thurstone, is similar to that used in detection theory, and factors the response data into estimates of sensitivity and bias. The internal-noise model includes limitations imposed by imperfect memory, and relates the sensitivity to the stimulus sequence. Associated experiments are being conducted on magnitude estimation, category scaling, aboslute identification, discrimination, and detection, as well as short-term memory. This paper presents an overview of this research. [Work supported principally by a grant from the National Institutes of Health and in part by the Joint Services Electronics Program.]
Stimulus Recognition Model
Authors: Nakatani Lloyd H.
Published: September 2005

A mathematical model for stimulus recognition has been developed that incorporates two processes, and has been applied to the recognition of words in noise. The activation process uses the stimulus information to restrict the possible alternatives to a subset of the total stimulus set. This process employs concepts analogous to signal detection theory but generalized to handle recognition. The decision process assumes that a stimulus is selected from the subset with some biased sampling probability, and that the name of the selected stimulus is then emitted as the recognition response. This process assumes that Luce's choice axiom applies to the sampling probabilities. The model is capable of factoring a confusion matrix into two matrices of sensitivity and bias parameters corresponding to the two processes. Tests with word-recognition data suggest that the model offers a reasonable explanation for the improvement in recognition performance with reduction in stimulus set size and with increase in stimulus probability. The latter is closely related to the word-frequency effect. [Research supported in part by U. S. Public Health Service Grant. The author is a U. S. PHS Predoctoral Fellow.]
Short-Term Memory in Intensity Discrimination
Authors: Berliner J. E. , Durlach N. I.
Published: September 2005

Although imperfect short-term memory is an important limitation on psychoacoustic performance, it has received little attention for nonverbal auditory stimuli. We have studied this limitation in terms of two types of models: rehearsal models, which assume that the subject attempts to maintain the image of the sound itself; and verbal context-coding models, which assume that the subject remembers an imprecise verbal representation of the relation of the sound to the context of sounds in the experiment. Research has been conducted using a 2I, 2AFC, roving-standard, intensity-discrimination paradigm with pulsed-tone stimuli. Performance has been studied as a function of the interstimulus interval, the presence or absence of interpolated stimuli, and the presence or absence of interpolated decision tasks. This paper presents an outline of the models and an interpretation of the data in terms of these models. [Work supported principally by a grant from the National Institutes of Health and in part by the Joint Services Electronics Program.]
Upward Spread of Masking in Normal and Sensorineural Subjects
Authors: Pickett J. M. , Martin Ellen S.
Published: September 2005

In recent years, hearing aids and auditory-training units have been introduced that attempt to present speech information in the low frequencies. The present study is an initial step in the investigation of upward-spread-of-masking effects on discrimination in the middle and high frequencies. The purpose was to study the effect of a low-frequency masker on the threshold of hearing at higher frequencies. The masker was a 250-Hz low-pass noise presented at over-all levels of 77, 97, or 107 dB SPL. Pure-tone thresholds were obtained at 200, 300, 500, 1000, and 2000 Hz. Normal-hearing subjects and 27 subjects with sensorineural losses were tested. Results: Sensorineural subjects, as a group, do not demonstrate a “typical” pattern of masking. Within groups of subjects having similar losses, marked differences in upward spread of masking are found: Some subjects show less-than-normal masking; others, the same as normal. Subjects with moderately severe losses show higher masked thresholds than do subjects with mild losses and subjects with normal hearing. Subjects with severe sensorineural losses show only slight upward spread of masking.
Vowel Classification using a Dispersion-Analysis Method
Authors: Li K. P. , House A. S. , Hughes G. W.
Published: September 2005

The classification of vocalic data by automatic means is under study. The techniques of dispersion analysis are used to determine the set of principal components from data and then to investigate the distribution of spectral data on the principal components. The results given by the analysis are given linguistic interpretations, and a simple method is proposed to construct a decision-tree structure for classifying vowel spectra. The sequence of decisions is described and the results are compared linguistic descriptions involving Jakobsonian distinctive features. The spectral data under study are the rectified outputs of 35 bandpass filters covering the range 250 Hz to 10 kHz, and sampled 60 times/sec. The speech samples were all contributed by one talker. Approximately 1500 time samples were selected from the quasistationary portions of 10 common vowels of American English; each vowel occurred in 23 different utterances, and the phonetic context differed in each utterance. [This work was supported in part by the Air Force Cambridge Research Laboratories under contract.]
Pitch Determination by Measurement of Harmonics
Authors: Miller Ralph L.
Published: September 2005

An experimental pitch-detection system is described based on harmonic measurement. Early work demonstrated that if a particular harmonic could be separated and identified, an accurate measurement of the fundamental was possible. A recent proposal by Schroeder [J. Acoust. Soc. Am. 43, 375–377 (1968)] based on “period-histogram” measurements, gives a relatively simple means of determining the harmonic relation between speech components as separated by narrow-band filters. A period translator converts the essentially sinusoidal wave from each filter to a pulsed wave train of related period but with controllable phase. The pulses are weighted and summed together at a common point with an initial zero phase relation determined by a sampling pulse. A measure of the position of the first major maximum of the combined waves gives the value of the fundamental period. Experimental results indicate that accurate pitch measurement is possible with a limited number of channels even if the fundamental component of speech is missing. Amplitude-weighting information from the narrow-band filters can also be used as spectrum information in a channel-type vocoder thus reducing the total amount of equipment required.
Digital Speech Compression in Time Domain
Authors: Reddy D. R.
Published: September 2005

High-quality compressed speech is of interest for voice response from computers and for some speech-transmission applications. This paper describes some digital techniques for reducing the computer-storage requirement (or the bandwidth of a transmission system) to 10 000 to 20 000 bits/sec (bps). By approximating the speech wave by a piecewise linear wave and just keeping the endpoint information one can reduce the storage required to about 20 000 to 25 000 bps. By using Huffman coding based on the statistical distributions of endpoint information one can reduce the storage required by about 30%. By replacing each quasiperiodic part of the speech wave by a single pitch period and a repeat factor, one can further reduce the storage required by another 20%. This paper describes the details of an experimental system developed using a PDP-6 computer for linearizing the wave, for generating and decoding Huffman codes, and for picking a pitch period of a voiced portion of a sound. This system permits evaluation of various parameters that not only preserve the intelligibility of speech but also speaker identity and naturalness.
Study of 150-kHz Finite Amplitude Plane Waves Reflected from a Pressure-Release Surface
Authors: Browning David G. , Mellen Robert H.
Published: September 2005

Time domain measurements of the pressure waveform are made for an initially sinusoidal plane wave as it becomes progressively distorted, is reflected from a pressure-release surface, and returns along the original path. As expected, the 180° phase shift upon reflection reverses the sense of the finite amplitude distortion; however, the asymmetry of the incident wave does not allow the reflected wave to return to a perfect sinusiodal form.
Propagation of 150-kHz Finite Amplitude Plane Waves in a 0.1M MgSO4 Solution
Authors: Mellen Robert H. , Browning David G.
Published: September 2005

Time domain measurements o[ the pressure waveform are made for an initially sinusoidal plane wave as it propagates through a 0.1M MgSO4 solution. The effect of velocity dispersion due to the relaxation at 180 kHz for MgSO4 appears to be negligible. The Fourier harmonic content of the waveforms is analyzed over a range of 1–8 m. The results show that plane-wave theory predicts approximately the rate of harmonic growth; however, it appears that more accurate results could be obtained by considering the actual field of the transducer. Both low- and high-power (1 bar) cases are considered.
Ray Path in Exponential Plus Random Ocean with Two-Dimensional Mass Velocity
Authors: Hayre H. S.
Published: September 2005

Many experimental studies have demonstrated that the ray path in the ocean is appreciably influenced by one-dimensional mass motion of the water, as well as any random variations of the speed of sound with depth; but a survey of the literature shows no theoretical study of the same. It is this aspect of the subject matter that is covered in this paper. The ocean is assumed to be made of two layers, each with exponential speed of sound and mass velocity variation with depth. The top layer is, furthermore, assumed to have mass velocity along the ocean surface in addition to the velocity decaying along the depth. This characterizes a typical situation at the mouth of a river, and the mass velocity near the ocean bottom represents the usual ocean current. Both a theoretical as well as a numerical solution is attempted to show the significance of each variation by comparing the results with standard exponential and motionless ocean. [This research was supported by The Office of Naval Research—Acoustics Program.]
Effects of Interference on Bottom-Bounce Propagation of Low-Frequency Sound in Deep Water
Authors: Thorleifson J. , Jordan R.
Published: September 2005

A model of surface-to-surface bottom-bounce propagation is described as a summation of plane waves at the receiving hydrophone. The model shows that variations in propagation loss with range consist of long period variations produced by the dipole effect at the source and at the receiver, and faster variations resulting from the interference of two or more bottom bounce arrivals. Theoretical variations derived from the model are compared with the results of propagation experiments for the range interval 0–80 kyd carried out in deep water using hydrophones at depths of 80 and 400 ft and a 230-Hz CW projector as a sound source. The model parameters were based on the significant propagation paths determined by measurements made with explosive charges during the same experiment. The experimental results agreed in general with those derived from the model but also displayed a random component, the magnitude of which varied with the trial site.
Viscoelastic Properties of a Water-Saturated Artificial Sediment
Authors: Hutchins J. R. , Wilson O. B.
Published: September 2005

The complex shear modulus of a kaolin-water mixture has been measured by observing the reaction on a torsional elastic wave propagating in a metal rod when the rod is immersed in the sediment. A preliminary result for the shear modulus at a frequency of 38 kHz for a sample having a porosity of 75% is (4+j1.1)×104 N/m2. This is typical for a bubble-free sample at 25°C which, although undisturbed for a number of days, is still very soft and has qualitative mechanical properties similar to those of unconsolidated shallow-water sediments. Additional experiments and studies are in progress. [Supported in part by the Naval Air and the Naval Ships Systems Commands.]
Directional Microphones with Toroidal Characteristics
Authors: Sessler G. M. , West J. E.
Published: September 2005

Microphones with toroidal directional characteristics, based on solid-dielectric and air-gap condenser transducers, have been designed and studied. Measurements have been taken in the frequency range 0.3–3 kHz. These microphones have minimum sensitivity in the direction of the rotational axis of the toroid and maximum sensitivity in the plane perpendicular to that axis. In this plane, the response is uniform within ±1 dB. In a plane through the rotational axis, the sensitivity is found to obey a cosine-squared law with maximum attenuation of 15 dB. The equalized frequency response of these microphones is constant within ±3 dB in the range under consideration and corresponds to approximately −75 dB V/μbar. Microphones with toroidal directional characteristics may find use in conference telephony and similar applications where pickup in one plane is desired.
Inertial, Tissue-Contacting Underwater Communication Headset
Authors: Sebesta G. J. , Mellen A. J. , Carlisle R. W.
Published: September 2005

The headset utilizes two transducers, a subminiature, variable-reluctance inertial microphone in a vibration-absorbent mounting and a variable-reluctance bone-conduction receiver of conventional size. A multipurpose head strap is arranged to mount the microphone either on top of the head or at the rear; the receiver is generally worn over one ear. An amplifier with self-contained battery is controlled by AGC for the microphone circuit and by a manual volume control, which sets the level at which both the remote station and the speaker's own voice are heard. The frequency range is confined to 300–4000 Hz and thus rejects noises generated by the air hoses and the like. A cable is spun out from a reel and may be disconnected at any time. The device is capable of deep immersion.
Roughness Criteria and the Relationships between Surface Roughness and Flow Noise
Authors: Franz G. J.
Published: September 2005

Roughness criteria are usually given for the surfaces of structures to prevent premature structural failure, added drag, and added flow noise. Structural roughness criteria usually deal only with long-wavelength roughness, or waviness, which is specified in terms of clearance under a batten of a particular length. Drag-roughness criteria usually deal only with the short-wavelength roughness as measured by a profilometer. Flow-noise roughness criteria, however, must include both the long- and short-wavelength components of the roughness and, in the case of water, separate criteria are needed for boundary-layer turbulence and cavitation-induced noise. A more unified description of roughness and roughness criteria is given in terms of its wavelength spectrum. Hydraulically smooth surfaces are believed to have no roughness related component of drag or turbulence induced flow noise. In water, the surface is considered to be hydraulically smooth if the roughness height in inches is less than about 0.01 divided by the free-stream velocity in knots. The expected increase in turbulence induced flow noise in water as a function of roughness and flow speed are then determined from available data on local skin friction.
Acoustic Modes and the Thermal Scattering of Light
Authors: Hanes G. R. , Piercy J. E.
Published: September 2005

The properties of standing-wave solutions to the Navier-Stokes equations are investigated. A simple application of the fluctuation-dissipation theorem to these solutions yields spectra of the fluctuations of the fluid variables, and hence also of the light scattered by them. A standing wave in a fluid is a dynamical system with two normal modes. The normal coordinates in general do not coincide with any of the usual fluid variables. The statistically independent fluctuation along each normal coordinate provides a correlated contribution to the fluctuation of each fluid variable. This result is at variance with the assumption of independent density and temperature fluctuations upon which most previous theories of light scattering are based; a revised version of the classical Einstein-Smoluchowski formula follows from the above argument. A weakness in previous theories is the failure to appreciate that the thermal relaxation occurs at low frequencies in a standing-wave system.
Linear Wave Propagation in Nonhomogeneous Elastic Media
Authors: Reddy Damoder P.
Published: September 2005

Longitudinal wave propagation in a nonhomogeneous semi-infinite elastic rod is considered. The nonhomogeneity may be due to the axial variation of Young's modulus or of density or of both. An arbitrary time-dependent stress is applied at the end, x = 0, of the rod. The normal stress as a function of position and time is obtained using the theory of the propagating surfaces of discontinuity by expanding the stress as a Taylor series about the time of arrival of the wavefront. The coefficients of the Taylor expansion are obtained as solutions of linear ordinary differential equations with variable coefficients. For the case where the Young's modulus E(x) varies as (1+ax)n, it is shown that the stress at the wavefront varies as (1+ax)n/2, where a and n are constants. For n = 2 and 4, the Laplace-transform technique is used to obtain closed-form solutions, which are shown to agree with the analytical solutions obtained by the method presented herein.
Critical Angles Associated with the Reflection-Refraction Problem at an Interface
Authors: McNiven Hugh D. , Mengi Yalcin
Published: September 2005

Goodier and Bishop established that there is a “critical” incident angle that a train of Sv waves makes with the traction-free surface of an elastic half-space and that as the incident angle passes through this critical value, the reflected P wave passes through grazing incidence and emerges as a Rayleigh-type wave. In this paper, we study the fate of a train of Sv waves on striking the plane interface between two elastic materials. We find that there are five critical angles associated with such a wave and the emerging wave, which passes through grazing incidence corresponding to each angle, is transformed into a Rayleigh-type wave. The wave is like a Rayleigh wave in that the magnitude of motions accompanying it decay exponentially away from the interface, particle motions have an elliptical orbit, and the wave travels with a constant phase velocity. The wave is unlike a Rayleigh wave in that its velocity is not the velocity of Rayleigh waves. Indeed, it depends on the incident angle. The method, which we use to establish the nature of the waves that emerge, seems to us to be as important as the results. The method is based on the notion of slowness surfaces developed by J. L. Synge using the solution of the field equations of elasticity. The graphical method itself is the result of a systematic exploitation of an idea introduced by M. J. P. Musgrave. [Work sponsored by the National Science Foundation.]
Rayleigh-Wave Dispersion in Layered Media
Authors: Lawrie W. E.
Published: September 2005

A theortical analysis has been carried out to determine the Rayleigh-wave velocity in an elastic material in which the surface region consists of several layers, each parallel to the plane surface. This model simulates a machined workpiece in which residual stresses, varying rapidly with depth, exist. Elastic properties of each layer in the model represent a corresponding stratum in the stressed material. A computer program has been developed to compute the Rayleigh-wave velocity over a range of frequencies for models with various numbers of layers representing a variety of stress profiles. The Rayleigh-wave velocity was found to be dependent upon a weighted average of the stress in a layer of approximately one wavelength thickness. For example, in a model consisting of two layers overlying an infinite half-space, each 0.0076 cm thick and stressed to 50 and 25 ksi, respectively, the Rayleigh-wave velocity asymptotically approaches 2.9915 (105) cm/sec at low frequencies and is 2.9859 (105) cm/sec at frequencies above 45 MHz. When the stress in the 25-ksi layer is changed from tensile to compressive, a significant change occurs in the velocity dispersion curve between 5 and 40 MHz. The numerical results obtained with the layered models have been used to develop an approximate method to predict Rayleigh-wave velocity. The analysis has been used to optimize the ultrasonic parameters involved in determining residual stress. [Partially supported by Air Force Materials Laboratory, U. S. Air Force.]
Thickness-Twist Vibrations in Contoured AT-Cut Quartz Plates
Authors: Pearman George Timothy
Published: September 2005

An investigation of the thickness-twist vibrations in beveled, rectangular, AT-cut quartz plates is discussed. Calculations similar to those of Mindlin and of Forray and Bleustein show that beveling a flat rectangular quartz plate raises the resonant frequencies slightly and has a pronounced effect on the predicted vibrational mode shapes. The plates described have nonuniform thicknesses along the Z′ axis, and deviations of the twist vibrational amplitudes from sinusoidal behavior along the Z′ axis are found. This ability to change the mode shapes by beveling lends itself to suppression of unwanted modes through proper choice of bevel parameters (length-to-thickness ratio and length of flat portion to total length ratio). A simple method of estimating the best bevel parameters is given, and typical results are shown. Plates were prepared with different bevel parameters, and resonant frequencies were found to agree well with the calculations. X-ray topographs of the vibrational modes were made to ensure that the strong resonances observed were the twist modes, and good agreement between the calculated mode shapes and those determined experimentally were found.
Perception of Distinctive Features Using Two Modes of Inquiry
Authors: Brokaw Sonia Phipps
Published: September 2005

The experimenter recorded 23 consonants in conjunction with three vowels in random sequences. The recorded speech materials were processed through three conditions of signal-to-noise ratios; no experimental noise, + 3 dB S/N ratio, and 0 dB S/N ratio. Twenty-five native American students with normal hearing responded to the recorded stimuli in two modes of responses; the consonants were stimuli and the consonants were the response choices, and the stimuli were the same and subjects' responses were indications of their use of place of articulation or voicing as a cue to identification of a consonant. In the third experiment plosiveness, fricativeness, etc., were used as additional response choices as applicable. The results indicated that (1) voiceless consonants were more affected than voiced in the presence of noise; (2) for voiceless consonants, place was a more preserved category than for voiced consonants; (3) the analysis of the second and third modes of responding showed nasality and place the most preserved features. Significant correlation was found between the different modes of response regarding the relative importance of features.
Some Relations between Perception of Short Silent Intervals and the Production of Speech
Authors: Mahaffey Robert B. , McDill Jim D.
Published: September 2005

A group of “normal-hearing” adults listened to a series of 255 randomized samples of tones that were interrupted by silent intervals, which varied in duration from 5 to 80 msec. Three frequencies were employed: 150, 500, and 3000 Hz at 75 dB SL, using a normative reference intensity. The subjects responded by indicating whether or not the silent intervals were distinguishable. The duration of the shortest interval that could be distinguished was assumed to be a measure of auditory integration time. Two temporal measures were also derived from samples of the subjects' speech; these were average phonation time and average pause time. Correlational analyses of these data showed significant relationships between (1) average pause time and the shortest silent interval perceptible in the 500-Hz tone, and (2) average phonation time and the shortest silent interval perceptible in the 3000-Hz tone. These data, in view of previous data, suggest a relevance to the cybernetic control of speech production.
Perceptual Search for Frequency-Spectral Boundary
Authors: Singh Sadanand , Tishman Abraham
Published: September 2005

The problem in phoneme perception is to discover what acoustic parameters of speech stimuli and what portions of a given parameter are used as perceptual cues. A phoneme and phoneme class can be located on a two- or multidimensional space. In this experiment, phoneme boundaries were located on the frequency-spectral plane of the voiceless fricatives of English. Five 20-yr-old native English speakers, whose audiograms were normal, listened to each of six syllables in approximately 700 predetermined bands of frequencies ranging from 37.5 to 9600 Hz. The subject herself controlled the bandpass-filter knobs (60 dB/oct rolloff), varying the properties of stimuli to which she was listening. This method, suggested by Chistovich, is quite useful when it is necessary to present to subjects large set of stimuli. Also, the responses of different subjects may conveniently be maintained “because the position of the boundary may be different.” In the results for each stimulus consonant, the frequency-spectral location of voiceless plosives and fricatives were shown as determined by the auditory responses. There were some overlaps between their boundaries and the boundaries of different subjects.
Development of Acoustic Features of Phonemes
Authors: Eguchi S. , Hirsh I. J.
Published: September 2005

Recordings were made of several sentences of children ranging in age from 3 to 13, and also by adults. Each subject spoke the test sentences on five different occasions. First and second formant frequencies for each of six vowels were determined from hand-drawn spectrum envelopes on sections made during steady-state portions of the vowels in the test sentences. Accuracy or reliability of pronunciation was measured by calculation of the standard deviation among the five repetitions for such formant frequencies. Results show a gradual decrease in such variability for all vowels from age 3 to an asymptotic value where the variability reaches the same magnitude as for adults. Measures of variability of certain temporal features show a similar decrease but one that reaches its minimum value at an earlier age. Implications for a motor theory of speech perception at different ages will be discussed. [This research was supported in full by a U. S. Public Health Service, Department of Health, Education, and Welfare research grant from the National Institute of Neurological Diseases and Blindness.]
Identification of “Break” between Vocal Registers
Authors: McGlone Robert E. , Brown W. S.
Published: September 2005

The location of the “break” between vocal registers was determined by two methods. First, subjects identified the shift from one register to another while phonating and, second, judges identified where they heard the shift. Nine females and 10 males, with no formal vocal training, phonated up and down the musical scale in semitone steps matching their phonation with tones from an audio-oscillator. They notified the investigator when they “broke” into a different register. This procedure was repeated six times alternating between ascending and descending the scale. Recordings of these phonations were made and from these, a set of tapes was prepared for presentation to judges. The female and male phonations were presented, respectively, to 29 listeners who indicated between which two semitones the break occurred. When the judges' identifications were compared to those given by the subjects, a correspondence of within one semitone was found for males. Greater variation, however, was found for females. These results suggest that the identification of register “breaks” by listeners is less valid for female speakers than for males.
Development of a Synthetic Sentence-Identification Task in Spanish
Authors: Benitez Luis , Speaks Charles
Published: September 2005

The use of a closed-message set of synthetic or artificial sentences has been explored in studies on speech intelligibility in English for the past 4 yr. Each alternative sentence was constructed as an approximation to a real sentence by selecting each successive word on the basis of the conditional probabilities of word sequences. This method for generating test materials can, in theory, be generalized to any language that is characterized by rules of syntax. This paper describes the development and evaluation of synthetic sentence message sets in the Spanish language. Performance-intensity functions in quiet and in the presence of a competing speech message will be described and compared with similar data for English sentences. The advantages of the synthetic sentences for assessing speech-discrimination scores for hearing-impaired Spanish-speaking listeners will be described.
Masking Noise and Jitter-Detection Thresholds
Authors: Pollack Irwin
Published: September 2005

Is the detection of temporal irregularity, or auditory jitter, dependent upon the availability of specific spectral frequency regions? An attempt was made to answer this question by obtaining jitter-detection thresholds in the presence of band-limited noise. Maximum effect is obtained by masking noise at intermediate spectral frequencies, in the region of 1 kHz, for a wide range of auditory pulse frequencies. This frequency region was also implicated by Rosenberg in the discrimination of the pitch of jittered pulse trains. What is this result trying to tell us?
Time-Intensity Trading Relations as a Function of Signal Frequency
Authors: Watson Charles S. , Gengel Roy W.
Published: September 2005

Levels of monaural signals at behavioral threshold were determined by a psychophysical method of adjustment for seven highly trained listeners. Thresholds were studied as a function of signal frequency (octave steps) from 125 to 8 kHz, and of duration, from 16 to 1024 msec. Measurements were made in the presence of a contralateral broad-band masking noise with a spectrum level of 30 dB SPL. The time constant τ was estimated by means of Plomp and Bouman's Hypothesis III [J. Acoust. Soc. Amer. 31, 749–758 (1959)]. Average values of τ, from at least 12 replications of each measurement, are found to range systematically from those considered “normal” (125–175 msec) by some earlier investigators, at low frequencies, 125–500 Hz, to much lower values (30–70 msec) at the higher frequencies. Preliminary comparisons between values of τ for normal listeners and for listeners with sensory-neural loss show this interaction between frequency and the time constant to be similar for both populations. The data are also compared to the results of a control procedure which employed a two-alternative forced-choice method. [Work supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Ocean Surface Bias on Doppler System Output
Authors: Hayre H. S. , Avgeris T. G.
Published: September 2005

Usually, the Doppler output of a sonar system is assumed to be monochromatic. The random variation of ocean surface and bottom significantly alter this assumed monochromatic nature of the Doppler signal into a frequeucy band-limited output. The surface heights are assumed to be normally distributed; the facet approach is used to show their effect on the Doppler term. For instance, a transmitted signal: et(t) = sin ωct becomes: ẽr(t) = Ã sin(ωcf+φ̃d+φ̃a). The random amplitude modulation Ã and its associated phase-angle modulation φ̃a have been previously shown to be strictly surface-caused effects, whereas φ̃d is the surface-caused randomly varying Doppler term, if one takes out the transmitter beam-modulalation effects. The long time averages of Ã and φ̃d have been shown to be statistically independent, Rayleigh and uniformly distributed, respectively. Beating of the received signal ẽr(t) with the local oscillator producing the carrier frequency ωc and passing it through the low-pass filter to get rid of 2ωc term results in ēr′ = Ã sin(φd+φa). Under quite general conditions, the probability density function of ẽr′ was shown to be Gaussian. This result was then verified from experimental data obtained by an underwater Doppler system as well as by its laboratory ultrasonic simulation at the University of Houston in a 20-ft-, 25-ft-deep water tank. Results of the experimental data analysis seem to support the theoretical results discussed earlier. [Work sponsored by the Office of Naval Research (Acoustics Branch).]
Range Focusing in a Deep-Ocean Sound Channel with Parabolic Profile
Authors: Überall H. , Nicholas N. C.
Published: September 2005

We show using the case of the parabolic velocity profile c02/c2=1−α2z2 for an underwater acoustic duct, that the normal mode series of the problem contains a coherent part which dominates, and explicitly exhibits the phenomenon of range focusing, at a range of R=2π/α and its multiples. Owing to the symmetry of the profile, additional focal points are given by R/2 and its odd multiples, situated as far below the channel axis as the source is above, while the even-multiple focal points lie at the height of the source. The coherent part of the series is given in analytic form and is shown to approximate a delta function in the depth variable at the focusing ranges.
Effect of Rain on Underwater Noise Level
Authors: Bom Nicolaas
Published: September 2005

The underwater noise due to precipitation has been measured in a small, shallow lake. The local wind speed, rain rate, atmospheric pressure, and noise level were recorded. It was found that the noise due to wind and the contribution from bottom boundary reflections over the period during which the data were recorded had a negligible effect. The data in the interval 300–9600 Hz have been analyzed in octave bands, and an estimate of the average noise level versus rain rate has been obtained. In comparison with the laboratory work done by Franz [J. Acoust. Soc. Amer. 31, 1080 (1959)] on splashes as a source of sound, our results show significantly higher noise levels and a difference in the shape of the noise-level-versus-frequency curve. However, the average rate of change in noise level with change in rain rate is of the same order of magnitude.