bluuebunny/crossref_metadata_2025 huggingface dataset:
Connection between various small-waveheight solutions of the problem of scattering from the ocean surface
Authors: Labianca F. M. , Harper E. Y.
Published: October 2005

Careful developments of a number of approximate solutions of the problem of point source acoustic scattering from the ocean surface are presented. The regime of interest is the small-waveheight regime, where the rms waveheight of the ocean surface is small compared to the acoustic wavelength and the correlation length of the ocean surface. The approximate solutions fall into two categories: those derived by utilizing the Kirchhoff approximation and those based on a small-waveheight perturbation expansion. It is shown that within the small-waveheight regime the small-perturbation solution is superior to any solution based on the Kirchhoff approximation, the former being uniformly valid in the ratio of acoustic wavelength to surface-wave wavelength. In that portion of the small-waveheight regime where the ratio of acoustic wavelength to surface-wave wavelength is small, all approximate solutions are shown to be in agreement. Pitfalls which can and have occurred in the misapplication of the Kirchhoff approximation are pointed out.
Behavioral system and apparatus for tone-detection and choice reaction times in the cat
Authors: Orr John L. , Moody David B. , Stebbins William C.
Published: October 2005

An efficacious operant-conditioning procedure for psychophysical experiments with cats is described. The system features (a) restraint of the cat and the use of the liquid reinforcement delivery cup to control orientation with respect to the stimuli, (b) a minimum of apparatus between the cat and a free-field sound source, (c) two response pedals so that separate ’’Yes’’ and ’’No’’ responses are defined, (d) a discrete trial procedure with reaction time (RT) defined as the time from the onset of a trial until the occurrence of a response, and (e) an effective liquid reinforcer and simple delivery system. Operation of the system was demonstrated with the method of constant stimuli. Detectability was directly related, and median RT for correct ’’Yes’’ responses inversely related, to tone sound pressure.
Hydromagnetism induced by submerged acoustic sources: Sonomagnetic pseudoradiation
Authors: Bird J. F.
Published: October 2005

A hydromagnetic field induced by the interaction between acoustic motions and an ambient magnetic field in an electrically conducting medium propagates with the sound radiation, and is transmitted into adjacent sound-free regions. This sonomagnetic pseudoradiation is analyzed for an arbitrary acoustic source submerged in a semi-infinite conducting medium in the presence of a constant applied magnetic field such that the Alfvén speed is much less than the sound speed. We begin by formulating the sonomagnetic field equations, from which we derive a formal solution for unbounded media and earlier source-free results. Then the solution for monopole, dipole, or more general acoustic sources is developed in terms of Sommerfeld-like integrals. Explicit reduction of the solution integrals is illustrated by presenting approximations for both nearfield and farfield sonomagnetism external to the medium in the case of ambient magnetic field normal to the semispace surface. The farfield exhibits sonomagnetic pseudowaves radiated to considerable distances by high-power, low-frequency acoustic sources. Relevance of the calculation to the ocean environment or laboratory conditions is briefly discussed.
On scattering of elastic surface waves by edges of thin surface layers at oblique incidence
Authors: Rulf Benjamin
Published: October 2005

Scattering of a straight-crest surface wave which propagates at an oblique angle towards the edge of a thin surface layer on an elastic half-space is considered. It is demonstrated that the range of incidence (0?ϑi<π/2) is divided into four subranges by three ’’critical angles’’ (ϑ1=arcsinKd/KR, ϑ2=arcsin KS/KR, and ϑ3=arcsin KT/KR). The character of the scattered field changes across these angles. The law of refraction and phenomenon of total reflection for elastic surface waves are derived.
Visualization of ultrasonic waves in air
Authors: Bucaro J. A. , Dardy H. D.
Published: October 2005

It is not generally recognized that airborne ultrasonic waves can be visualized by means of schlieren. We show that waves in the upper kilohertz region generated by an electrostatic transducer can be visualized with a diffraction-limited optical system.
Description of the measurement of an individual’s continuous sound exposure during a 31-day period
Authors: Johnson Daniel L. , Farina Edward R.
Published: October 2005

A dosimeter based on the equal energy rule with range from 55 to 110 dB was used to monitor continuously the nise exposure of one subject. The subject, who is the second author of this report, works in a relatively quiet laboratory area. The daily A-weighted average sound level was measured for each 24-h period [Leq(24)] beginning at approximately 8:00 a.m. During the day the noise exposure associated with specific activities was noted. The 31-day average sound level was 76 dB while the daily Leq(24) values varied from a low of 59 dB to a high of 83 dB. The type of activity that contributed most of the subject’s total sound dose was night-time parties at private homes or nightclubs. Five such parties accounted for 42% of his total sound dose. One exposure at an automobile hobby shop and three outings at a bowling alley contibuted another 27% to the total sound dose. If these outside recreational activities had been avoided, the 31-day average sound level would have been reduced to 71 dB. The problems involved in monitoring a 24-h noise exposure as well as future plans for more elaborate studies are discussed.
Numerical investigation of an acoustic slow waveguide
Authors: King Benson Jay
Published: October 2005

The effect of a cylinder of material whose sound speed is less than that of water on the radiation beam pattern of an omnidirectional sound source is investigated. Specifically a point source is placed near one end of the cylinder. The cylinder serves as an acoustic waveguide and enhances the radiation from the source in the direction of the waveguide. The waveguide is mathematically modeled by use of the surface Helmholtz integral equation together with the requirement of continuity of acoustic pressure and normal velocity on the surface common to the waveguide and surrounding water as reported by P. H. Rogers and . J. Trott [J. Acoust. Soc. Am. 56, 1111–1117 (1974)]. The integral equations are solved numerically. Calculated farfield patterns and directivity gains for waveguides of various length-to-diameter ratios are presented. Directivity gains greater than 14 dB together with farfield patterns having side lobes more than 10 dB down are predicted over fairly broad bandwidths for several waveguides. Experimental results were obtained and are in good agreement with the numerical results.
Piecewise–planar representation of vowel formant frequencies
Authors: Broad David J. , Wakita Hisashi
Published: October 2005

The first three formant frequencies for 778 steady-state tokens of 30 nonretroflex vowel types uttered by a female speaker are found to lie close to a piecewise–planar surface (expressed numerically as 0.634F1+0.603F2−0.485F3−366=0, for F2≳0.027F1+1692 and 0.686F1−0.528F2−0.501F3+1569=0, otherwise). The rms distance of the vowels from this surface is only 86 Hz. The intersection between the two planes is a line of nearly constant F2, corresponding closely to the F2 of a uniform vocal tract of the same length as our speaker’s. The piecewise–planar representation also suggests a way to test the hypotheses of uniform and nonuniform formant-frequency scaling between speakers.
Radial spatial coherence of sound from a distant source near the ocean surface
Authors: Smith P. W. , Stern Raya
Published: October 2005

A prior general analysis for spatial coherence in a multipath channel is applied to a case typical of the deep ocean, with the source close to the surface and the receiver near the channel axis. The radial horizontal coherence interval (at the 1/e level of squared magnitude of normalized complex coherence) is found to be 22λ/Hkm, where λ is the wavelength and Hkm is the excess depth of the channel in km. The magnitude of coherence is approximately a Gaussian function of separation. Analytical considerations indicate that this result is a good approximation for a broad class of problems where (1) the profile has a single minimum with a well-developed SOFAR duct and with depth excess, (2) the source is near the surface, and (3) the receiver is well into the duct. Then λ and H are the only important parameters.
Low-frequency sound absorption in the ocean
Authors: Schulkin M. , Marsh H. W.
Published: October 2005

Recent work on low-frequency sound absorption in the ocean and laboratory has been examined with regard to temperature dependence, pH dependence, boron concentration, and pressure effects in an effort to arrive at a practical expression consistent with existing knowledge for use in sonar prediction and design applications. It is found that, over the range of pH observed in the ocean, the maximum absorption per wavelength depends exponentially on the pH at the sound-channel axis depth. The relaxation-frequency dependence on temperature is examined in terms of the temperature dependence of seawater viscosity and the activation energy of the relaxation process. The relaxation-frequency dependence on the square root of the salinity is consistent with available data and theory.
Quantitative schlieren visualization of unipolar acoustic transients
Authors: Bucaro J. A. , Flax L. , Carome E. F.
Published: October 2005

Image intensity distributions have been calculated for the schlieren observation of Gaussian, unipolar acoustic pulses. The optical intensity distributions in both the Fourier transform plane (stop plane) and the image plane are discussed. Experimental observations are presented for Gaussian-like pressure transients generated by narrow voltage pulse excitation of thick piezoelectric plates. These observations are compared to the results of the calculations. It is suggested that this technique is ideally suited for the determination of transducer transfer functions.
Acoustics of finite beams
Authors: Gaunaurd G. C. , Überall H.
Published: October 2005

We derive the expression for the most general possible finite acoustic beam, i.e., for a beam finite in two dimensions, which emerges from an arbitrarily shaped collimating aperture at an arbitrary angle and with an arbitrary amplitude profile. We investigate the spreading of such a beam for two amplitude profiles; a Gaussian profile and a flat-topped square profile. In both cases the spreading is determined as a function of the ratios between the collimating aperture sizes (σ or Ro) and three parameters; wavelength, axial distance from the aperture plane, and radial distance from the beam axis. The general applications of this analysis are numerous, particularly when one considers that almost all physically realizable acoustic sources project finite sound beams as opposed to waves of infinite extent. As a specific application of this general theory, we evaluate the scattering of a finite beam from a rigid sphere in an exact fashion for the two amplitude profiles of the finite beam mentioned above, and we finally compare plots for the bistatic cross sections to the results obtained in previous work of ours using the approximate Kirchhoff method.
Locally optimum detection of discrete-time stochastic signals in non-Gaussian noise
Authors: Poor H. V. , Thomas J. B.
Published: October 2005

Two basic models are considered for the problem of detecting small, zero-mean stochastic signals in non-Gaussian noise processes. Appying the theory of local tests, a general detector structure is derived for each of these models. A third (suboptimal) scheme based on null-zone detection is also proposed and a technique for optimizing its parameters is discussed. Using the criterion of asymptotic relative efficiency, the performance of these three detectors and of a power detector are compared under each of the proposed models.
Response to Professor Morris Halle’s review of D
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n, by Sadanand Singh (University Park Press, Baltimore, 1976) [J. Acoust. Soc. Am. 62, 801–802 (1977)]
Authors: Singh Sadanand
Published: October 2005

The author comments on Morris Halle’s review of his book, stressing points of disagreement.
Angle estimation and binaural processing in animal echolocation
Authors: Altes Richard A.
Published: October 2005

Physical structures separate the ears of many mammals, and the ears themselves have complex transfer functions that depend upon the direction of a sound source. Neither of these observations is usually incorporated into standard array analysis. The conventional array problem generally assumes that individual elements are omnidirectional, and there are no physical structures between elements to provide partial isolation. This investigation of binaural angle estimation specifically incorporates the effects of partial isolation and directivity patterns that vary with angle and frequency. Cramér–Rao bounds for the variance of maximum likelihood angle estimates are derived. These bounds, along with a generalized ambiguity function, are used to evaluate the significance of isolation between the ears, angle-dependent magnitude, and phase variations in the spatial transfer functions of the ears, the use of wide-band and narrow-band signals in animal echolocation, symmetry of aural directivity patterns, the transmitted beam patterns that are employed by certain bats, and the angle-dependent signal variations that have been observed in cetacean echolocation. Only two broadband hydrophones are sufficient for accurate, unambiguous azimuth measurement if the width of the signal autocorrelation function is small relative to the distance between hydrophones. The analysis indicates that many past measurements of transmitted beam patterns and aural transfer functions in animals are incomplete, since they do not consider direction-dependent phase variations. It may also be necessary to reinterpret the meaning of time difference and pressure difference cues for localization. These insights can be used not only for better correlation of behavioral and physiological measurements, but also for better design of man-made systems for communication, radar, sonar, and ultrasonic medical diagnosis.
The Fourier–Mellin transform and mammalian hearing
Authors: Altes Richard A.
Published: October 2005

A combined Fourier–Mellin transform yields a representation of a signal that is independent of delay and scale change. Such a representation should be useful for speech analysis, where delay and scale differences degrade the performance of correlation operations or other similarity measures. At least two different versions of a combined Fourier–Mellin transform can be implemented. The simplest version (the ‖F‖2−‖M‖2 transform) completely eliminates spectral phase information, while a slightly more complicated version (the ?−? transform) preserves some phase information. Both versions can be synthesized with a Fourier transform and an exponential-sampling algorithm. Exponential sampling produces a frequency scale distortion that is similar to the effect of the cochlea. The ‖F‖2−‖M‖2 transform can also be implemented with a bank of proportional bandwidth filters. If the relative phase between spectral components is preserved, then a Fourier–Mellin transformer can perform compression of linear-period modulated signals. Such signals are used for echolocation by bats and cetaceans. The same approach that gives scale and delay invariance can be used to obtain other transform conbinations that provide insensitivity to a variety of distortions. The combined transforms can also be used for analyzing these distortions.
Lateralization by frequency for repeating sequences of dichotic 400- and 800-Hz tones
Authors: Deutsch Diana
Published: October 2005

Subjects made lateralization judgments involving dichotic sequences of 250-ms tones, which alternated in frequency between 400 and 800 Hz, such that when one ear received 400 Hz the other ear received 800 Hz, and vice versa. With sequences consisting of 20 dichotic tone pairs there was a strong tendency to lateralize each fused tonal percept toward the ear receiving the 800-Hz signal. In certain subjects the effect also occurred even when the 800-Hz tone was substantially lower in amplitude than the 400-Hz tone, and when it was clearly lesser in loudness. However, with sequences consisting of only two dichotic tone pairs, this lateralization-by-frequency effect was substantially weaker.
Decoupling of auditory pitch and stimulus frequency: The Shepard demonstration revisited
Authors: Pollack Irwin
Published: October 2005

With ten successive octave tones, Shepard demonstrated that upward shifts in frequency might be heard as downward shifts in pitch. This decoupling of auditory pitch and frequency has important consequences for any representational theory of pitch. Experiments are reported that attempt to identify the crucial features of Shepard’s demonstration.
Correlation analysis of the physiological factors controlling fundamental voice frequency
Authors: Atkinson James E.
Published: October 2005

A technique has been developed to obtain a quantitative measure of correlation between electromyographic (EMG) activity of various laryngeal muscles, subglottal air pressure, and the fundamental frequency of vibration of the vocal folds (Fo). Data were collected and analyzed on one subject, a native speaker of American English. The results show that an analysis of this type can provide a useful measure of correlation between the physiological and acoustical events in speech and, furthermore, can yield detailed insights into the organization and nature of the speech production process. In particular, based on these results, a model is suggested of Fo control involving laryngeal state functions that seems to agree with present knowledge of laryngeal control and experimental evidence.
Comment on S. Singh’s rejoinder to the review of his D
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n [J. Acoust. Soc. Am. 62, 276–277 (1978)]
Authors: Halle Morris
Published: October 2005

The author comments on Sadanand Singh’s rejionder to the author’s review of Singh’s book.
High-resolution cross-sensor beamforming for a uniform line array
Authors: Bucker Homer P.
Published: October 2005

The methods of high-resolution spectral analysis can be used for high-resolution cross-sensor beamforming for a uniform line array. In this paper two high-resolution techniques (maximum entropy and discrete decomposition) are applied to the cross-sensor field. Sample calculations illustrate the effectiveness of these methods in the case of a realistic multiwave acoustic field plus narrowband Gaussian noise.
Radiated power and radiation loading of cylindrical surfaces with nonuniform velocity distributions
Authors: Stepanishen Peter R.
Published: October 2005

A general approach is presented to evaluate the radiation loading and radiated power from a nonuniform harmonically vibrating surface on an infinite cylinder. The approach utilizes a combined Green’s function and Fourier integral technique to develop integral expressions for the generalized radiation impedance and power radiated from the surface. The general expressions are shown to reduce to previously developed expressions for several problems of interest, i.e., a uniformly vibrating band on a cylinder, a vibrating piston on a cylinder, and various circumferentially varying velocity distributions on a cylinder with no axial variation. Simplified integral expressions are then presented for a particular velocity distribution of interest. Although the integrals can be evaluated asymptotically, in general the integrals must be numerically integrated. Extensive numerical results are presented and discussed in order to illustrate the characteristics of the radiation loading and radiated power.
Statistics of normal mode amplitudes in a random ocean. I. Theory
Authors: Dozier L. B. , Tappert F. D.
Published: October 2005

A statistical theory of acoustic propagation in a model random ocean, valid in the limit of low acoustic frequency, is presented. A random internal-wave model gives sound-speed fluctuations δc (r,z,t) about a deterministic profile ? (z). Using normal modes of ? (z) as a basis, the theory gives quantitative estimates of statistical moments of the mode amplitudes ψn(r,t), which are randomly coupled via δc. Invoking a quasistatic approximation, the theory treats time as a parameter. From any initial (r=0) distribution of modal powers ‖ψn‖2, the evolution of their averages to an equilibrium is predicted by ’’coupled power’’ equations. The theory makes similar predictions for average fluctuations of the modal powers about their means. In the equilibrium limit, the theory gives the full probability distribution of the ψn.
Shear-wave measurements in laboratory sediments
Authors: Shirley Donald J. , Hampton Loyd D.
Published: October 2005

As part of a program to measure in situ acoustic parameters of sediments, transducers capable of measuring shear-wave speed and attenuation in laboratory sediments have been designed and fabricated. Transducers consisting of an array of ceramic benders have been found to be the most useful in measuring shear-wave parameters of high-porosity laboratory sediments. Measurements of shear-wave speed and attenuation in kaolinite clay sediments have been made using the ceramic bender transducers. These clays exhibit calculated shear moduli as low as 1.7×105 dyn/cm2 with shear-wave speeds from 2 to 40 m/s and attenuations from less than 100 dB/m to more than 500 dB/m.
Studies of acoustical parameters in open-plan offices
Authors: Warnock A. C. C.
Published: October 2005

The major acoustical elements of open-plan offices—windows, walls, ceilings, and partial-height screens—have been studied in laboratory simulations of open-office acoustical problems. The basic test environment is an anechoic room with a carpet-covered plywood floor over which the test elements are deployed. Measurements of attenuation provided by various configurations were made in one-third-octave bands and the data processed to permit study of seven single-figure ratings for attenuation between work stations (the ’’interzone attenuation’’). Of the ratings tested the A-weighted level and the Noise Isolation Class correlated best with Articulation Index, which is taken as the ’’true’’ measure of performance. For testing ceiling systems it is confirmed that the commonly used test arrangement is insensitive to significant changes in the ceiling system. A simple modification of the procedure is proposed.
Asymptotic theory of ducted propagation
Authors: Choudhary S. , Felsen L. B.
Published: October 2005

A new high-frequency asymptotic theory of propagation in ducts with continuously varying refractive index is presented. The theory is based on local wave fields with complex phase and constitutes a special application of the evanescent wave tracking theory developed by the authors. It is shown, for analytic profiles and for refractive indexes that vary only transversely to the duct direction, how the coefficients in the asymptotic expansion are evaluated explicitly. When the method is applied to parabolic and hyperbolic secant profiles for which exact solutions of the wave equation are available, the asymptotic expansions so generated agree term by term with the asymptotically expanded exact results. The method is then applied to a class of polynomial profiles for which exact results in terms of known functions are not available.
Reflection of elastic waves by a cylindrical cavity in an absorptive medium
Authors: Flax Lawrence , Neubauer Werner G.
Published: October 2005

The analytical formulation for the total scattering cross section of a cylindrical cavity in an elastic medium is given for the case of inclusion of compressional and shear wave attenuations. Examples are computed of relatively small attenuations exemplified by the material polymethacrylate and relatively large attenuations exemplified by polyethylene. The inclusion of wave attenuations known to exist in these materials cause the scattering cross section to diminish significantly for wave-number cylindrical-cavity-radius product up to 10.
A note on single- and double-correct responses in the dichotic two-response paradigm
Authors: Repp Bruno H.
Published: October 2005

A simple random-guessing model of the dichotic two-response paradigm is used to predict the proportions of single- and double-correct responses at different performance levels. Comparisons with real data show that the proportions of double-correct responses are generally overpredicted. By introducing an additional free parameter to account for nonindependence of channels (ears), the model is made to fit closer to empirical data, but the value of the parameter is not the same for different sets of data. This may be due to differences in stimulus characteristics between experiments. While the model is oversimplified in many ways, it nevertheless provides a rudimentary formal framework for the interpretation of dichotic data, particularly with regard to changes in the proportions of single- and double-correct responses with performance level.
Discrimination by young infants of voiced stop consonants with and without release bursts
Authors: Williams Lee , Bush Marcia
Published: October 2005

Infant discrimination of synthetic voiced stop consonants, contrasting in place of articulation, was investigated using the high-amplitude sucking paradigm. Discrimination of [dα]−[gα] contrasts, with and without release bursts, was compared. The results provide some evidence that the presence of a burst facilitates place discrimination by infants, perhaps by enchancing integrated spectral properties characteristic of the individual stop consonants.
Two-tone suppression in auditory nerve of the cat: Rate-intensity and temporal analyses
Authors: Javel Eric , Geisler C. Daniel , Ravindran A.
Published: October 2005

Responses to two-tone stimuli were recorded from auditory-nerve fibers in anesthetized cats. One tone, the suppressor, was set at a frequency above characteristic frequency and was fixed in intensity. A second tone was set at an excitatory frequency and was varied in intensity. The suppressor tone, when set at a sufficient level, always reduced the response to the excitatory tone by an amount equivalent to a fixed number of decibels, regardless of the excitatory tone’s intensity. Estimates of suppression magnitude were derived from shifts in rate-intensity function obtained when the suppressor tone was present relative to the functions obtained for the excitatory tone alone. When suppressor-tone intensity was increased, suppression magnitude likewise increased. When the two tones were increasingly separated in frequency, either by varying the excitor or by varying the suppressor, suppression magnitude decreased monotonically. Suppression behaved in the same manner regardless of whether the suppressor tone was excitatory or nonexcitatory. When frequency separation was small enough and when both tones were above the neuron’s characteristic frequency, responses synchronized to low-order combination tones could be elicited. These responses usually possessed different rate-intensity characteristics and resulted in estimates of suppression magnitude which were spuriously low. When frequency separation is normalized with regard to position of traveling wave maxima within the cochlear duct, the magnitude of two-tone suppression for a given suppressor-tone intensity is seen to be frequency independent.
Dependence of loudness growth on skirts of excitation patterns
Authors: Hellman Rhona P.
Published: October 2005

Over a range of 50 dB, the loudness of a 100-Hz tone was measured in the presence of a broadband noise with a low-frequency cutoff at 200 Hz. The noise was varied in intensity along with the tone so that the signal-to-noise ratio remained constant at either 0 or −10 dB. Listeners judged the loudness of the tone by loudness matching, magnitude estimation, and magnitude production. The noise markedly decreased the tone’s rate of loudness growth but not the range over which loudness grows. The overall decrease in steepness of the 100-Hz loudness function was greater than that previously reported at higher frequencies. It is hypothesized that the decrease was greater because the spread of excitation at 100 Hz was more effectively contained than at higher frequencies. Support for this hypothesis is given by measures of intensity discrimination at 100 Hz.
Periodicity measures for repeated random auditory patterns
Authors: Pollack Irwin
Published: October 2005

Random auditory patterns were repliated according to defined rules, converted toauditory pulse trains, and presented to listeners. Three ined: the threshold fraction of repeated elements necessary for a fixed level of discrimination from a nonrepeated pattern; the accuracy of periodicity matching; and periodicity magnitude ratings. A short-term periodicity analysis over successive replications appears to be more representative of the behavioral measures than a long-term periodicity analysis. Of the signal measures of periodicity examined, the maximum autocorrelation, irrespective of delay, most closely reflects behavioral measures of periodicity strength.
Psychoacoustical aspects of synthesized vertical locale cues
Authors: Watkins Anthony J.
Published: October 2005

A new method of studying vertical localization is described whereby the high-frequency response of the external ear is synthesized by a computer program incorporating two variable latency delay and add processes. The resulting sounds were evaluated by presentation to subjects via headphones which bypass the external ear. Vertical movement of the sound source was perceived when the latency of one echo was changed dynamically between 100 and 300 μs and this effect required the presence of high-frequency signal components (above around 4 kHz). In further experiments, the variation of perceived elevation with echo delay was measured, and it is shown that the vertical locale of the apparent source is a monotonic function of echo latency in the 160–260 μs region. It is proposed that locale is decoded by a form of spectral pattern recognition, whereby the locale of the source is represented as a peak on an autocorrelation function. The time-axis values (between 160 and 260 μs) corresponding to these peaks are considered to correspond to vertical locale for elevations between, roughly, 60° above horizontal and 40° below.
Pitch and pitch discrimination of broadband signals with rippled power spectra
Authors: Yost William A. , Hill Richard , Perez-Falcon Tony
Published: October 2005

A random-interval pulse train or wide-band noise when delayed (τ) and added back to itself (cos+) produces a stimulus with a cosinusoidally varying (or rippled) power spectrum. The spacing between the peaks in the spectrum is equal to the reciprocal of the delay (1/τ). If the stimulus is delayed and added back at 180° phase reversal (cos−), then a cosinusoidally varying power spectrum is generated whose spectral peaks are separated by 1/τ, but whose peaks are displaced by 1/2τ relative to the power spectrum of the cos+ stimulus generated with the same delay, τ. These stimuli yield a pitch, such that the pitch of the cos+ stimulus is equal to approximately 1/τ and the pitches of the cos− stimuli are equal to approximately 0.9/τ and 1.1/τ. These pitch matching results were studied using a variety of matching stimuli and conditions. Following the identification of the pitches, a method of limits and a same–different procedure were used to study the pitch discriminability of both the cos+ and cos− stimuli. Delays (τ) ranging from 1 to 10 ms were studied covering a pitch range of 90–1100 Hz. The pitch discriminations associated with the cos+ and cos− stimuli were essentially the same for both the random-interval pulse train and the wide-band stimuli. These pitch-discrimination results are compared to those associated with a periodic pulse train. The research is also discussed in terms of discriminations of delayed sounds in reverberant environments. These results are consistent with assumptions concerning the autocorrelation of the rippled stimuli within the dominant frequency region for pitch perception.
Vowel duration measurement: A reliability study
Authors: Allen George D.
Published: October 2005

In recent studies involving the correlation of speech segment durations, the measurement error in locating segment boundaries has usually been ignored or assumed to be constant and small. Since the relative magnitude of the error in locating such a boundary may vary greatly depending upon its phonetic context and the procedures employed, thereby affecting the derived intersegment covariances profoundly, an experiment was designed to estimate these errors directly. Several tokens of four sentences containing syllables differing in the quality, length, degree of stress, and consonantal context of their nuclear vowels were copied onto two-track tapes and sent to several professional phoneticians with instructions to measure the durations of the indicated vowels, on first one track and then, at least two weeks later, the other. The resulting measurement errors varied systematically in several ways: (1) long, stressed vowels had greater errors than short, unstressed ones; (2) initial voiced stops (/b/) were easiest to segment and approximants (/w/) hardest, with voiceless stops (/k/) and fricatives (/f/) intermediate; (3) great differences among phoneticians did not appear to depend in any obvious way upon the instrumentation used. The minimum standard deviation for measurements of vowel duration by the most accurate phoneticians ranged from about 2 to 5 ms; 95% confidence intervals for carefully measured vowel durations may therefore be expected to range from about 10 to 25 ms, depending upon the consonantal context of the vowel. Because of this range of intrinsic measurability of vowel durations, and therefore presumably other phonetic segments as well, the results of studies using covariance statistics of segment durations should be interpreted cautiously.
A method for training and evaluating the reception of ongoing speech
Authors: De Filippo Carol Lee , Scott Brian L.
Published: October 2005

The ’’tracking procedure’’ is a method to train and evaluate the reception of ongoing speech. A talker and a receiver engage in a dialogue for a designated period of time in which the receiver reports his perception of successive segments of read text and is corrected by the talker until the text is repeated verbatim. Performance is measured in number of words of text repeated correctly per unit of time. The procedure is illustrated by its application to a project for training and evaluating use of a vibrotactile–electrotactile aid to lipreading. Differences between experimental conditions are described over time in terms of absolute words per minute, percent increment of aided over unaided words-per-minute scores, and percent of normal listening rate. Data from identification tests with syllables, words, and sentences are also presented. Tracking is suggested as an additional procedure for communication training in aural rehabilitation or classroom settings and for evaluation of other communication systems.
Similarity solution of wave propagation in nonhomogeneous elastic rods
Authors: Singh M. C. , Brar G. S.
Published: October 2005

Similarity solutions are determined for nonhomogeneous elastic semi-infinite thin rods subjected to suddenly initiated and uniformly sustained stress at the origin. The system of governing nonhomogeneous partial differential equations along with its initial and boundary conditions is transformed to an ordinary differential equation and the corresponding auxiliary conditions by means of the similarity transformations. The representation so obtained is integrated. From the general solution of the problem, two special cases, one for the homogeneous rod and the other for the nonhomogeneous rod, are solved in closed form. The difference of behavior in two cases is graphically discussed.
Ultrasonic transducer power output by modulated radiation pressure
Authors: Greenspan M. , Breckenridge F. R. , Tschiegg C. E.
Published: October 2005

We have set up and are using an apparatus for the measurement of total sound power output of a piezoelectric transducer radiating into water. This apparatus combines the better features of previously used methods which depend on radiation pressure. The input is modulated at a low frequency and the output power is intercepted by a target which experiences a force at the modulation frequency. The target is mounted on the armature of an electromagnetic receiver provided with an independent coil through which a current at the modulation frequency is adjusted in amplitude and phase, either manually or automatically by feedback, to arrest the motion of the armature. When the armature is stationary the force depends only on the current, and the apparatus can be calibrated using direct current and dead weights. It is thus absolute. In practice, the carrier frequency is swept over any part of the range 0.1–15 MHz while a recording of power output versus frequency is made. The results of comparisons made with those of other mehtods are encouraging. Examples of curves from normal and defective transducers are shown.
Perception of speech sounds with alternate formants presented to opposite ears
Authors: Ainsworth W. A.
Published: October 2005

The perception of speech syllables with alternate formants presented to opposite ears has been investigated. Using synthesized speech and normal-hearing subjects, it was found that this mode of presentation reduced the recognition scores with stop consonants by about 6%, semivowels by about 4%, and fricatives by about 5%, compared with binaural presentation. Vowel recognition, on the other hand, was not significantly reduced.
Range effect in the perception of voicing
Authors: Brady Susan A. , Darwin C. J.
Published: October 2005

The location of the voicing boundary in the perception of initial stop consonants is shown to vary according to the range of voice-onset times used in a block of trials and according to the order in which blocks covering different ranges are presented. Although these range effects introduce methodological complications into the interpretation of adaptation experiments, they appear to be qualitatively different from adaptation effects and, it is suggested, may provide a metric for assessing the auditory tolerance of phonological categories.
Computer model to characterize the air volume displaced by the vibrating vocal cords
Authors: Flanagan J. L. , Ishizaka K.
Published: October 2005

We use a vocal-cord/vocal-tract model devised earlier to study acoustic effects of the air volume displaced by the vibrating vocal cords. We consider both lateral and longitudinal motion of the cords. We make computer simulations to ?? establish quantitatively the contribution of the displacement current to the total glottal volume velocity (and hence to the total sound excitation for voiced sounds). The displacement current from both lateral and longitudinal motion is found to be second-order by comparison to the total glottal flow. The displacement contribution can, however, be identified in the time waveforms and spectra of the glottal and mouth volume velocities. We use the computer formulation to synthesize speech sounds with and without the displacement current. Auditory observations and spectral calculations on the synthetic output show the displacement current to be discriminable only in close differential comparisons.
Guitar as a reflex enclosure
Authors: Caldersmith Graham
Published: October 2005

The reflex enclosure problem is expressed in terms of Newtonian equations of motion for the moving parts of the enclosure, viz., the driven plate and air piston, and the equations solved. The ’’air’’ and ’’plate’’ resonances of the guitar constitute a resonance doublet, the separation of whose two frequencies is made markedly greater than that between the Helmholtz and simple plate resonances as a result of coupling of the air piston with the under side of the plate via sound pressure in the enclosed air. The effect of overlap between the external nearfield of the vent and that of the driving plate is to reduce separation of resonance frequencies. Experimental measurements of internal sound pressure versus frequency for a ’’simplified guitar’’ and for an actual guitar are compared with theory for different degrees of overlap. In one guitar it was found that the difference between doublet frequencies is about twice that between unperturbed Helmholtz and plate resonances and that the effect of overlap is important.
A numerical method for calculating the nearfield of a parametric acoustic source
Authors: Mellen Robert H. , Moffett Mark B.
Published: October 2005

The nearfield of the difference-frequency sound generated by a spherically spreading dual-frequency primary wave can be represented by a triple integral of an oscillating integrand. The computation is facilitated by a transformation that results in rapid convergence. Finite-amplitude taper is incorporated into the method, but the effect of source aperture is not accounted for.
Auditory duration discrimination in the parakeet (M
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Authors: Dooling Robert J. , Haskell Royal J.
Published: October 2005

Two parakeets were trained by a method of avoidance conditioning to respond to duration differences in successively occurring tone bursts. Difference limens for duration were obtained at six durations (20–160 ms) of a 2.86-kHz tone presented at a sensation level of 60 dB. Calculations of the Weber fractions at each duration showed threshold values which compare favorably to similar measures for man ranging between 0.10 and 0.20.
An improved shear wave transducer
Authors: Shirley Donald J.
Published: October 2005

A new type of shear wave transducer has been developed at Applied Research Laboratories, The University of Texas at Austin (ARL:UT), as part of a program to measure the acoustic parameters of marine sediments. The transducers consist of a ceramic bender element which can be immersed in the medium and has favorable characteristics for the study of the acoustic parameters of unconsolidated sediments.
Calculation of mode conversion rates
Authors: McDaniel Suzanne T.
Published: October 2005

The rate at which energy is exchanged between acoustic normal modes due to scattering from ocean bottom roughness is calculated using measured correlation functions of ocean bottom slopes. Estimates of the resulting attenuation of the coherent component of the first normal mode are obtained and are compared to scattering losses predicted using the Kirchhoff approximation.
Sound propagation through an East Australian Current eddy
Authors: Nysen Paul A. , Scully-Power Paul , Browning David G.
Published: October 2005

Sound transmission through an East Australian Current summer eddy was measured for the frequencies 25 Hz–2 kHz. Such eddies are typified by a central subsurface warm core which caused an elongation of the convergence zone range by 8 km. This isothermal and isohaline core results in the eddy having a double-duct structure: a shallow surface duct and a deeper, thicker, and much lower sound-speed eddy duct. This eddy duct behaved as a classical leaky acoustic waveguide with an optimum transmission frequency of 100 Hz. Strong acoustic coupling was observed from the surface duct to the eddy duct. This coupling was independent of range but dependent on frequency, being weakest around 300 Hz. At lower frequencies, coupling progressively increased due to diffraction, and at higher frequencies it also increased due to scattering. The overall effect, however, of both coupling and leakage was that the highest levels of coupled energy received within the eddy duct were at 100 Hz.
The contribution of ultrasonic measurements to the study of liquid crystals. I. Nematics
Authors: Natale G. G.
Published: October 2005

The investigation of ultrasonic propagation properties in liquid crystals in recent years has provided a considerable contribution to the study of these systems. In this paper most ultrasonic measurements performed to date on nematic liquid crystals are examined and presented in a systematic way, in order to provide a compact and coherent view of the current experimental situation in this field. The review of the available experimental data and their comparison with the predictions of various theories point out areas which necessitate further investigation by ultrasonic experiments.
Test of the Born and Rytov approximations using the Epstein problem
Authors: Hadden W. James , Mintzer David
Published: October 2005

The Born and Rytov approximations for solutions of the Helmholtz equation are compared with the exact solutions of three one-dimensional problems which involve continuously varying indices of refraction (based on Epstein’s model). Limiting values of the spatial parameters which characterize the index of refraction functions are used as the bases for detailed comparisons of expressions for the complex wave field and for its amplitude and phase. The results of these comparisons reaffirm earlier findings that the two approximation methods are equivalent vis-a-vis the perturbation strength parameter of the index of refraction functions. It is shown that in one extreme of the spatial parameter in one of the problems, there is an advantageous range-dependence in the Rytov method. The conceptual extension of the results of this comparison to three-dimensional problems is discussed.
Comparison of reverberation measurements using Schroeder’s impulse method and decay-curve averaging method
Authors: Chu W. T.
Published: October 2005

Utilizing a digital acquisition system and minicomputer, two promising techniques for accurate determination of reverberation times have been studied in detail from the viewpoint of standard reverberation room tests. The first is Schroeder’s ’’integrated impulse method,’’ and special attention was given to the question of repeatability and the influence of signal-to-noise ratio on the successful application of the method. The second technique involves taking an ensemble average of a large number of logarithmic decay curves. It was found that, even for nonuniform decays, the average decay curves obtained by the second method compared well with those determined by the Integrated Impulse Method.
Beamforming a towed line array of unknown shape
Authors: Bucker Homer P.
Published: October 2005

Beamforming a curved towed array of known shape is easily done by matching the received signals to the calculated signals for an incident plane wave. If the array shape is unknown, the beam pattern can be calculated for the array moving along an assumed space–time curve. The sharpness of the beam pattern is defined as the sum of the squares of the beam outputs in different look directions. Next the space–time curve is changed by an iteration procedure until the sharpness is maximum. Sample calculations for simulated and actual data show that this method generates an improved beam pattern and, in the simulated data case, a good estimate of the true array space–time curve.