bluuebunny/crossref_metadata_2025 huggingface dataset:
Rate discrimination of high-pass filtered pulse trains
Authors: Long Glenis R. , Cullen John K.
Published: January 2006

Difference limens (DLs) for trains of 30-μs impulses were determined for repetition rates of 50-, 100-, 200-, 400-, and 800 pulses per second under conditions of no filtering and high-pass filtering (115 dB/oct) with corner frequencies of 2.5-, 5.0-, 7.5-, and 10 kHz. Noise, at 15-dB spectrum level, was low passed (115 dB/oct) at the corner frequency of each high-pass filter condition and mixed with the trains of pulses to preclude discrimination on the basis of potential low-frequency signal compounds. Measures were obtained from four trained listeners at a signal level of 30 dB SL relative to individually determined thresholds for each filter condition and repetition rate. A two alternative forced choice adaptive procedure was used. The data support the hypothesis that resolution of pulse-train repetition rate involves both temporal and pitch-based processes; the latter becoming ineffective when frequency resolution of the ear is insufficient to resolve separate harmonics of the signal. [Work supported by NIH.]
Detection of tones in synthetic plosive bursts
Authors: Farrar C. L. , Ito Y. , Zurek P. M. , Durlach N. I. , Reed C. M.
Published: January 2006

The general goal of our research is to understand discrimination between sounds that differ only in spectral shape. The objective of this specific study was to test the notion that the discriminability of two sounds is monotonically related to the difference between their simultaneous masking pattern (or, its corollary, that two sounds that produce equal masking are indiscriminable.) Measurements were made of the thresholds for tones in two masking noises, one with a /p/-shaped spectrum and the other with a /t/-shaped spectrum. Data on discriminating between these two masking noises have been previously obtained. We attempt to relate discrimination and detection results through transformations of “masking difference patterns,” which show the difference, as a function of frequency, between signal thresholds for the two maskers. Further, we will describe our progress in developing a general psychoacoustic model for discriminating between sounds that differ only in their spectral shapes.
Dolphin sound production: Physiologic, diurnal, and behavioral correlations
Authors: Ridgway Sam H.
Published: January 2006

The mechanics of dolphin sound production will be reviewed but many questions remain. For example, do the diagonal membranes function somewhat as vocal cords? Does the nasal plug serve as a primary vibrating source? Do the nasofrontal sacs serve as tuned, or tunable, resonators? Do the nasal sacs serve as acoustic reflectors and help to focus sound? In general, there are three types of sounds produced by T. truncatus and other closely related dolphins—whistles, burst pulse sounds, and click trains. Click trains, generally of high peak frequency, are used by dolphins that are trained to perform echolocation tasks. All three types of sound have also been suggested as having potential value for communication. I have found that: (1) A single dolphin may produce as many as 50 000 separate sonic episodes in a single 24-h day (The average daily sound production is more like a tenth this figure); (2) Peaks in sound production occur in the hour before and during feeding, especially the first feeding of the day, and during the hour after sunset. It appears that dolphins display aggression and agitation by increasing the pulsatile content of sounds and by emphasizing the harmonic structure of whistles. It is possible that echolocation evolved from sounds first used in aggression.
Incidental evidence for echolocation in polar pinnipeds
Authors: Thomas Jeanette A. , Awbrey Frank T. , Fisher Sheldon R.
Published: January 2006

Efforts to experimentally demonstrate echolocation in California sea lions, Zalophus californianus [W. Evans and R. Haugen, Bull. So. Cal. Acad. Sci. 62, 165–175 (1963); R. J. Schusterman, Psych. Rec. 16, 129–136 (1966)] and in grey seals, Halichoerus grypus [B. Scronce and S. Ridgway, in Animal Sonar Systems, pp. 991–993 (1980)] have been unsuccessful. However, similar studies on polar pinnipeds have not been conducted previously. No studies have investigated the potential for ultrasonic vocalizations in pinnipeds. Echolocation in polar pinnipeds has been suggested because of their highly developed vocal abilities and their need to find food and navigate during the dark austral winter [G. Kooyman, Ant. Res. Ser. 11, 227–261 (1968); J. Thomas and V. Kuechle, J. Acoust. Soc. Am. 72, 1730–1738 (1982)]. This presentation will summarize observations and evidence that indicates the presence of echolocation in polar pinnipeds and report the production of ultrasonic vocalizations by a captive leopard seal (Hydrurga leptonyx). Clicks, buzzes, and frequency-modulated chirps were produced with peak frequencies from 4 to 164 kHz, but generally between 50 and 60 kHz. This study demonstrates the importance of investigating ultrasonic vocalizations in all pinnipeds and implies that polar pinnipeds may be the best test group for echolocation.
Seal blindfolded discrimination: Echolocation not proven in Halichoerus grypus
Authors: Scronce B. L. , Ridgway S. H.
Published: January 2006

A four-year-old female gray seal from Iceland was trained to wear an opaque elastic band that blocked vision. Echolocation capability was evaluated in two experiments: (1) The seal was required to retrieve an air-filled plastic ring 20 cm in diameter placed at random in a 5×1 m section of a 10-m redwood tank. (2) The seal was required to detect the flat surface of a 25-cm styrofoam disk as opposed to the edge of the same disk (−30 dB target strength), placed randomly on either side of a divider. Without the blindfold, the seal's ring retrieval rate was 100% with a latency of 3.8 s. In 427 blindfolded trials there were 99% correct responses, but latency increased to 6.5 s. Head scanning movements were observed on about half the blindfolded trials and click trains were recorded on about 10% of the trials observed. In the second experiment, the blindfolded seal approached the divider and made a choice about target location (right or left) at least 1.5 m away. Correct responses in a session never exceeded 65% and averaged 46% on 617 trials. Without the blindfold, the seal's performance was almost 100%. The gray seal makes sound underwater but does not appear to use the clicks for echolocation in any way similar to the demonstrated capabilities of dolphins.
A precision method of determining wide-bandwidth pulse delay in highly dispersive media
Authors: Carleton Herbert R. , Austerlitz Howard
Published: January 2006

The high attenuation of certain classes of materials result in extensive distortion of the transmitted pulse due to dispersion. A system has been developed which enables the measurement of the attenuation and phase of highly absorbtive materials over the frequency range of 0.1 to 20 MHz. Using a high-speed data acquisition system and a dedicated computer, the delay and dispersion component of the FFT transmission spectrum are separately computed by using a series of Hilbert transforms of the spectrum. The minimum delay component is first computed and subtracted from the phase spectrum. The resulting phase data are then used to determine the pure delay component to a high degree of accuracy. Experimental results will be presented on both model systems and on materials with attenuations as high as 100 dB/cm and dispersion as high as 20%.
Bandlimited cross correlation in a multipath environment: Simulation study results
Authors: Herstein Peter D. , Sternberg Helen M. , Cole Bernard F. , Weinberg Henry
Published: January 2006

The technique of intersensor cross correlation of acoustic signals is used to obtain such information as the spatial coherence of the environment or the position parameters of a broadband source. In general, acoustic energy propagates from a source to a sensor along multiple raypaths. However, cross-correlation performance is frequently analyzed in terms of a single wavefront (planar) model. For the planar model, the signal received at each sensor is approximated as the sum of the delayed and attenuated source signal plus uncorrelated Gaussian noise. This enables the use of performance criterion based on receiver signal-to-noise ratios. Extensive analysis of cross-correlation performance under the assumption of the planar model has been reported [G. C. Carter, IEEE Trans. Acoust. Speech Signal Process. ASSP-29(3) (1981)]. In this paper, modeling of the cross correlation between two sensors is extended to analyze the situation of a bandlimited signal propagating in a multipath environment. Using the generic sonar model (H. Weinberg, NUSC TD 5971C), a representative deep ocean configuration was simulated in which the propagation was dominated by four first-order bottom bounce type rays. Results are presented as functions of (a) the range and bearing of the source, and (b) the vertical tilt of the baseline of the sensors. It is shown that multipath effects can profoundly effect the level of the normalized cross-correlation peak. Signal-to-noise ratio at each sensor is found to be an inadequate estimator of correlation performance for this type of multipath environment. [This work was sponsored by the Naval Sea Systems Command, Washington, DC.]
Passive source ranging by using mode filtering and mode phase comparing in waveguide
Authors: Shang E. C. , Clay C. S. , Wang Y. Y.
Published: January 2006

The conventional beamforming technique could not be used for source locating in waveguide owing to the modal interference structure of the field. In this paper a new method of passive source ranging in a layered waveguide has been proposed. The mode-filtering processor was used to process the field data of a vertical array in order to obtain individual modes. The source range information can be extracted by measurement of three individual mode phases. The source range was expressed in terms of the “mode interference distance” as following: r = LijDij + Δrij; Δrij = Dij(δφij/2π), where Lij is a certain integer; δφij is the phase difference of the ith mode and the jth mode; Dij is the “mode interference distance” defined by: Dij = 2π/(ki − kj); ki is the wavenumber of the ith mode given by a numerical mode code. The information of Lij can be estimated by means of comparing the phase of the jth mode with another mode, say mth mode, and then Lij was estimated by solving the following equation: (δφij/2π) = Fractional part {(Dij/ Djm) [Lij + (δφjm/2π)]}.
Dependence of array gain on aperture angle for cylindrical and spherical arrays of directional sensors
Authors: Cox Henry , Steele J. Michael
Published: January 2006

When receiving arrays are placed on air-backed structures in water, the effect of the structure or baffle is to alter the response of the hydrophones from their free field characteristics. The exact response characteristics are complicated and frequency dependent. Typically the response is reduced near grazing incidence. When a beam is formed for maximum response in a selected direction, increasing the aperture to include elements for which the selected beam direction is near grazing is inefficient in increasing array signal gain and may actually lead to a loss in signal-to-noise ratio. The array gain dependence upon aperture angle for cylindrical and spherical arrays is presented for parametric families of effective element directivities. Both uniform and optimum shadings are considered. Results are presented in the form of parametric curves which can be used in system design tradeoffs.
Transient effects in acoustic scattering and radiation problems
Authors: Gaunaurd G. C.
Published: January 2006

We consider examples of acoustic radiation and scattering problems that we have worked out over the years where transient effects are investigated. In chronological order, we first study the sound radiation emitted by (multipole) point sources of various types, undergoing accelerated motions along various rectilinear, circular, or helicoidal paths. Changes in source acceleration results in an emission of a transient burst of radiation, and in a “headlight” effect, that we have quantitatively examined by techniques similar to those developed by J. Schwinger for accelerated electrons. We then analyze the scattering of a sound δ-pulse incident on a rigid sphere. When the transient pulse hits the sphere, it gives it its momentum and makes it undergo an impulsive acceleration in the same direction by radiation pressure. The so-called Kirchhoff solution [G. R. Kirchhoff, Mechanic (Teubner, Leipzig, 1883-one hundred years ago!) 3rd. ed., pp. 316–320] for the radiation field from an impulsively accelerated sphere is shown to exactly coincide with the first-order terms of the complete scattered field expression that we have obtained via the Resonance Scattering Theory (RST). This exhibits very enlightening connections between transient solutions of radiation and scattering problems.
Tow-powered low-frequency sound source
Authors: Schau H. C. , Van Buren A. L. , Radosta F. J.
Published: January 2006

A novel method for production of low-frequency sound from a submerged rigid body with a clamped gas-filled hemispherical membrane is discussed. The device is driven hydrodynamically through the motion of a ship or other towing vehicle. Analytical models are developed for the device which includes both bending and membrane theories for the shell deformations with the inclusion of the pressures from the driving jet and the acoustic radiation. Jet stability of the driving mechanism is discussed relative to the normal mode of vibration of the hemisphere. The hemispherical displacements are presented as a sum of resonant modes and forced modes which are in turn employed in a parametric study of optimizing acoustic output. Results include analysis of resonant vibration modes and prediction of acoustic radiation in both the nearfield and the farfield. Experimental data are compared with the model and future experiments are presented.
Some reflections on room acoustics
Authors: Harris Cyril M.
Published: January 2006

This paper reviews selected aspects of the field of room acoustics, emphasizing the contributions of V. O. Knudsen and his close associates and former students. The work done by the author with Knudsen in establishing so-called “optimum” reverberation time curves for “Acoustical Designing in Architecture” is discussed. Finally, the author describes what he considers the most important unsolved problem in room acoustics and gives suggestions for an approach that may be useful in its solution.
An auditorium design based upon subjectively optimal acoustics for The Washington Center, Olympia, Washington, USA
Authors: Ando Yoichi , Noson Dennis
Published: January 2006

Recently developed acoustical design criteria, derived from an exhaustive program of subjective testing at Kobe University and the University of Göttingen, have been applied to the acoustical design of The Washington Center, a multipurpose performing arts facility in Olympia, Washington, USA. In response to the programmatic emphasis on high-quality acoustics for orchestral music, the architectural configuration progressed from a wide, single-balcony scheme to one that is narrower with two balconies. The acoustical design effort was concentrated on the size and shape of wall reflectors, room asymmetry, and diffusing elements. The first reflection time delay, binaural dissimilarity, and total energy of the sound field were predicted with a computer model of the auditorium. Adjustments were made to the shape, cheeked by computer, and synthesized into the architectural design, arriving at optimum values for selected seat locations.
Determining the necessary number of reflections for an accurate image source simulation of room acoustics
Authors: Zagar Lawrence E. , Thompson James K.
Published: January 2006

Previous attempts at using image source computer models to determine sound pressures in rooms or large enclosures have had mixed results. One evident feature of these studies is that the maximum number of reflections simulated from each room surface is critical. An investigation was conducted using measured data for three rooms and computer simulations to evaluate various means of predicting the necessary number of reflections for accurate modeling. Schemes have been presented in the literature for predicting the necessary number of reflections for specific levels of accuracy. These tests have indicated that such formulas are highly inaccurate. There have also been remainder formulas presented in the literature for correcting computations with a limited number of reflections. The remainder formulas currently available were found to be unable to accurately compensate for model errors in analyzing actual rooms. Where others had indicated a maximum of only three or four reflections need be considered, these investigators found that as many as 40 reflections may sometimes be required. More typically, ten to 20 reflections from each room surface must be modeled for acceptable results. The required number of reflections was found to be a complex function of room size, room proportions, and the distribution and amount of absorption.
New ultrasonic modeling findings on Rayleigh wave propagation and their implications
Authors: Chamuel Jacques R.
Published: January 2006

The presence of unexplained large attenuation of low-frequency components and inverted dispersion of Rayleigh waves crossing the ocean-continent margin, the Tibetan Plateau, and the Iranian Plateau are examples of complex unsolved problems on Rayleigh wave propagation across vertical boundaries. In this paper, new ultrasonic modeling findings on Rayleigh wave propagation across step changes in elevation using two- and three-dimensional models are presented explaining the previously mentioned phenomena. Laboratory seismic ultrasonic modeling results on Tibet are presented matching actual field data. Physical insights into the cause of the inverted dispersion and attenuation are obtained from the reported results. Implications of the new findings indicate the need to reconsider the current ocean-continent margin, the Tibetan Plateau, and the Iranian Plateau crustal structure models. Opposite to the current belief of the presence of a low-velocity high-damping layer (possibly partially molten) near 30 km below the surface of the Tibetan Plateau [P. Bird et al., Nature 266, 162–163 (1977); W. P. Chen et al., J. Geophys. Res. 86, 5937–5962 (1981); K. Y. Chun et al., Bull. Seism. Soc. Am. 67, 735–750 (1977)] the new reported findings support the author's concept of a solid low attenuation solid crustal structure. A brief discussion on liquid/solid interface waves propagation past a step change in elevation will follow the Rayleigh wave results.
On the mechanism of F0 downdrift in Japanese
Authors: Poser William J.
Published: January 2006

In Japanese, as in many other languages, fundamental frequency (F0) tends to fall during the course of an utterance. Previous studies attribute this fall to a single mechanism: accent reduction, downstep, or a declining tonal reference line. Data are presented showing that two mechanisms are involved. First, sentences containing only unaccented words were constructed in such a way as to permit perfect balancing of segmental content. Measurements of both average and peak F0 on the high toned syllables of these words show a small but consistent decrease from left to right. The contour is approximately exponential, with a sharp downturn at the end. Second, the rate of fall is greater in sequences of accented nonsense words than in segmentally identical sequences of unaccented words. Similarly, the F0 peak of a word of either type is lower following an accented word than following an unaccented word, in otherwise matched utterances. It is suggested that these facts are consequences of the simultaneous existence of downstep and declination in Japanese.
Electrical stimulation of the auditory nerve: Membrane models applied to the interpretation of electrophysiological and psychophysical responses
Authors: White M.
Published: January 2006

Electrophysiological and psychophysical measures of threshold as a function of sinusoidal stimulus frequency deviate from those predicted by Hill's excitation model. Several membrane models (e.g., the Frankenhauser-Huxley model and the Hodgkin-Huxley model) suggest possible mechanisms responsible for the deviations. For example, by using a modified Hodgkin-Huxley model more accurate threshold “predictions” were obtained over the 50–500-Hz frequency range. The Hodgkin-Huxley model was modified by increasing the sodium inactivation rate constant, beta-h, by a factor of 4. This modification caused the hyperpolarizing phase of the stimulus to become more effective at increasing the simulated membrane's excitability to the subsequent depolarizing phase, particularly when the hyperpolarizing phase was on the order of 10 ms in duration. Consistent with this model, recordings in the AVCN of eat indicate that a hyperpolarizing electrical stimulus applied to the auditory nerve significantly increases the excitability of the nerve to a depolarizing stimulus that follows. [Work supported by NIH.]
Vowel allophones and the vowel-formant phonetic space
Authors: Keating Patricia , Huffman Marie , Jackson Ellen
Published: January 2006

Through assimilation and other phonetic processes, a language may have more segments on the phonetic surface than in lexical representation. Consider English vowels: nasalized, long, front rounded, and central vowels are all introduced in derivations. Conceivably, then, languages could be much more similar phonetically than phonemically; possibly they could even fill the phonetic space equally. In that case, languages with fewer phonemes would have to show much more phonetic variation per phoneme, compared to languages with many phonemes. The alternative situation would be that languages with fewer phonemes would leave parts of the phonetic space unused. We are testing these possibilities by comparing the F1-F2-F3 space for vowel allophones in different languages. Here we report on two five-vowel languages, Japanese and Russian. Seven speakers of each language read word lists and free text, and vowel formants are compared across conditions and languages. Preliminary results indicate that Japanese, the language expected to show the least variation, has widely separated vowels in word lists, but fills up the phonetic space in prose. [Work supported by USPHS grant NS 18163-02 to Peter Ladefoged.]
Narrow-band random response of a nonlinear oscillator
Authors: Davies Huw G. , Nandlall Dennis
Published: January 2006

The mean-square response of an oscillator with a nonlinear spring to narrow-band random excitation can exhibit multiple values in some frequency ranges. The randomly occurring jumps in level are similar to the jump phenomenon seen in the case of a swept sinusoidal excitation. The mean-square response of a Duffing oscillator is calculated here using equivalent linearization. The excitation is pink noise passed through a first-order resonant filter. Triple values of the response can occur at some frequencies only when the filter bandwidth is narrower than the oscillator bandwidth. The correct sinusoidal excitation limit is obtained as the filter bandwidth is decreased. On the other hand, the mean-square response is wholely single-valued if either the filter or oscillator bandwidths are large. The narrow-band mean-square response can be treated as a spectrum level. Integration of this level over all excitation frequencies shows good agreement with the exact mean-square response to white noise excitation. When multiple values occur the integrations using either the “upper” or “lower” part of the response spectrum bracket the exact value and can hence be used to give a crude estimate of the relative times the response is at the two pseudostable levels. Further work to estimate the expected time spent at each level is in progress. [Work supported by NSERC, Canada.]
Measuring the effectiveness of industrial hearing conservation programs
Authors: Doswell Royster Julia , Royster Larry H.
Published: January 2006

The performance orientation of the hearing conservation amendment underscores the need to standardize methods for evaluating how adequately hearing conservation programs (HCPs) protect employees' hearing. The authors will review HCP evaluation procedures based on analysis of group audiometric data for exposed populations. Techniques include comparisons of mean thresholds for selected worker groups of hearing levels for nonindustrial noise exposed populations matched by race and sex, calculation of rates of change in mean thresholds, and analysis of threshold variability in the database toward better hearing or toward poorer hearing in baseline comparisons and sequential test comparisons. Acceptable ranges for the incidence of defined threshold shifts have been identified. Analysis results for additional industrial databases will be presented, as well as newly developed approaches to data analysis. Applying age corrections to individuals' thresholds before combining records into group data allows assessment of HCPs with fewer employees by pooling race/sex groups together. Year-to-year variability in thresholds for annual audiograms has been correlated with daily temporary threshold shifts for employees wearing different types of hearing protectors.
On normal mode attenuation
Authors: Brooke Gary H.
Published: January 2006

The attenuation of normal modes due to viscous-type absorption losses in a layered bottom is examined. A standard perturbational approach is used to relate the modal attenuation coefficient to the energy stored and the power flow in each mode and to the intrinsic viscous loss in each layer. As such, the method is straightforwardly applied to geoacoustic waveguide configurations involving solid layers. Numerical examples are presented which illustrate the relationship between normal mode attenuation and energy concentration in the various layers.
Shallow-ocean fronts: Effects on array performance and acoustic prediction of properties
Authors: Rousseau T. H. , Jacobson M. J. , Siegmann W. L.
Published: January 2006

A parametric model is introduced which includes the location and orientation of a shallow-water front, as well as jumps in sound speed and current across it. In order to investigate frontal effects on array performance, a cw point source and a horizontal linear array of point receivers is considered. The error in predicted source direction, resulting from a frontally induced displacement in peak array output, is examined. Also, it is shown how the peak level and shape of the main-lobe array output are degraded significantly by the presence of a front as a point source approaches the nearfield. Finally, two sources and two receivers are placed at known locations on either side of the front. It is shown how travel times over direct rays between source-receiver pairs are affected by the various frontal parameters. A corresponding system of equations may be inverted so that travel-time changes can be used to predict estimates for frontal geometry and sound-speed and current discontinuities across a front. [Work supported by ONR.]
Computerized measurement and analysis of sonar transducer equivalent circuit parameters
Authors: Skowronek L. J. , Conte D. V. , Wilson O. B. , Garrett S. L.
Published: January 2006

Measurements of the electrical and mechanical properties of transducers are of importance in both their design and service in their evaluation. Following the formalism of Hunt [Electroacoustics (Acoustical Society of America, New York, 1982)], these properties can be determined by accurate measurements of complex impedance or admittance made throughout the frequency range of interest. Manual collection of the necessary data is tedious and particularly error prone for transducers with sharp resonances. A computer-controlled system, using an H-P 85, will be described which automatically acquires and plots the electrical data and calculates the equivalent electrical circuit parameters, coupling constants, and efficiencies. Sample data will be presented for piezoelectric and magnetostrictive transducers. [Work supported by ONR and the NPS Foundation Research Program.]
Noncontacting, acoustic vibration sensor
Authors: Richarz W. G. , Sullivan P. A. , Ma Tao
Published: January 2006

The measurement of vibration of lightweight structures requires that any loading due to a vibration transducer be eliminated. A noncontacting displacement sensor has been developed to assist in the understanding of the dynamics of lightweight air cushion vehicle skirts. A remote vibration sensor is required to monitor the unsteady motion of these membranelike structures. A low-cost acoustic displacement sensor has been developed. A piezoelectric driver aimed at the vibrating surface; the reflected beam is detected by a microphone. The motion of the reflector introduces a “Doppler shift” which is detected by a lock-in amplifier whose internal electronics transform this information into a signal proportional to displacement. The resolution of the system is governed by the wavelength of the incident beam, high frequencies (f0 < 20 kHz) affording peak to peak values of the order of 10 mm; for larger excursions lower frequencies are used. The system is sensitive to changes in air temperature, the speed of sound figuring in the Doppler factor. In addition the directivity of the transducer plays a role, the resultant amplitude modulated signal affording additional sensitivity. The displacement transducer is readily configured from standard components found in many laboratories and is ideal for the detection of low-frequency displacements (f < 100 Hz). [Work supported by the Natural Science and Engineering Research Council and Transport Canada.]
Finite element method applied to characterization of piezoelectric ceramics
Authors: Tocquet B. , Boucher D. , Decarpigny J. N. , Debus J. C. , Tierce P.
Published: January 2006

Finite element computation of piezoelectric transducers requires the knowledge of elastic, piezoelectric, and dielectric coefficients of ceramics. These constants are generally not available from the manufacturer, and even, variations up to 20% can be expected in the worse cases. The classical experimental method, proposed by Mason, is based on admittance measurements and a complete determination of all the materials properties requires five resonator geometries. An interesting method, based on an adjustment of first modes of ceramic rings with a finite element code, is described. It has three advantages over the Mason method. First, it does not require particular resonator geometries; second, the experimental method is summed up on a simple impedance measurement of the whole ceramics; and third, the adjustment is unaffected by local nonhomogeneity of materials. In this paper, the whole method is developed. Then experimental and numerical results are compared for several ceramics.
Behavioral evidence for central coding of azimuth as a function of stimulus frequency
Authors: Musicant Alan D.
Published: January 2006

In a previous report to the Society [Musicant and Butler, J. Acoust. Soc. Am. Suppl. 1 72, S93 (1982)] we presented data on the orderly progression of perceived azimuth of narrow bands of noise as a function of stimulus frequency. The patterns that resulted have been called Spatial Referent Maps (SRMs). A recent experiment suggests that these SRMs must involve a central mechanism for coding location in the horizontal plane. In this experiment, stimuli consisted of 1-kHz-wide noise bands with center frequency (CF) ranging from 4–14 kHz. There were 13 loudspeakers placed 15° apart at locations from 360° to 180° azimuth. Stimuli were presented from only that loudspeaker located at 270°. Subjects, listening monaurally, responded with the loudspeaker position from which they perceived the sound as originating. SRMs were then constructed. Subjects next performed the same task, but now listened monaurally with the pinna cavity of the open ear filled. The external meatus was open. Azimuthal judgements of stimulus location were collected and compared to the data collected earlier. Correlations between the means of the azimuthal judgements at each frequency for the two conditions ranged from 0.81–0.97 for seven subjects. The high degree of correlation suggests that, at least for narrow bands of noise, a central mechanism must exist that codes azimuthal sound source location as a function of stimulus frequency.
Modulation transfer function using temporal-probe tones
Authors: Ahlstrom Christopher , Humes Larry E.
Published: January 2006

Psychoacoustic MTFs were measured by embedding a probe tone in SAM speech noise. The speech noise was 70 dB SPL overall, and the modulation depth of this noise was 60 dB. The modulation frequencies were: 0, 2.5, 5, 10, 20, and 35 Hz. The duration of each tone pip was 4.7 ms for frequencies 500, 1414, and 4000 Hz. Bandwidths (3 dB) at each of the frequencies were 19, 22, and 18 Hz. Skirt slopes were between 6 and 7 dB/octave. Simple masking nearly predicted changes in these MTFs in noise. A Speech Transmission Index (STI) derived from the MTFs in noise was no better correlated (r = 0.95) with speech recognition scores than was the STI calculated according to H. J. M. Steeneken and T. Houtgast, J. Acoust. Soc. Am. 67, 318–326 (1980). [Work supported by the Veteran's Administration.]
Stepwise coupled mode scattering of ambient noise by a cylindrically symmetric seamount
Authors: Evans Richard B.
Published: January 2006

The question of how underwater ambient noise, at low frequencies, interacts with seamounts is addressed. The vertical directivity of the ambient noise, with and without the seamount interaction, is of particular interest. The problem of ambient noise scattering by seamounts motivates the development of a numerical modeling procedure, based on stepwise coupled modes. The procedure is designed to analyze scattering from a cylindrically symmetric seamount. The stepwise coupled mode procedure is extended to more general boundary conditions and brought up to date in the process. An example, using the geometry of the Dickins seamount, suggests that the seamount removes energy from the steeply traveling ambient noise, for this case. The energy is not converted into angles near the horizontal; the energy is lost through bottom interaction and attenuation.
Discrimination of depth of sinusoidal amplitude modulation with and without roved carrier levels
Authors: Stellmack Mark A. , Viemeister Neal F. , Byrne Andrew J.
Published: January 2006

Thresholds for the discrimination of the depth of sinusoidal amplitude modulation with a broadband noise carrier were measured for three listeners in a two-alternative, forced-choice task for modulation frequencies of 8, 32, and 128Hz. Thresholds were measured with the spectrum level of the carrier fixed at 20dB across all trials and, separately, with the carrier spectrum level roved randomly over a 20-dB range (10–30dB) in each interval. Mean thresholds were equal or slightly lower (but not significantly so) for the fixed conditions relative to the roved conditions, and the differences between thresholds were too small to be explained by assuming that listeners compared instantaneous intensity at corresponding phases of the modulation cycle (for example, in the troughs). Rather, it appears that listeners discriminated modulation depth by extracting an estimate of the modulation depth within each interval that was independent of the overall level. Consequently, models of envelope extraction must include normalization of the envelope fluctuations to the envelope dc.
Influence of primary-level and primary-frequency ratios on human distortion product otoacoustic emissions
Authors: Johnson Tiffany A. , Neely Stephen T. , Garner Cassie A. , Gorga Michael P.
Published: January 2006

The combined influence of primary-level differences (L1-L2) and primary-frequency ratio (f2∕f1) on distortion product otoacoustic emission (DPOAE) level was investigated in 20 normal-hearing subjects. DPOAEs were recorded with continuously varying stimulus levels [Neely et al. J. Acoust. Soc. Am. 117, 1248–1259 (2005)] for the following stimulus conditions: f2=1, 2, 4, and 8kHz and f2∕f1=1.05 to 1.4; various L1-L2, including one individually optimized to produce the largest DPOAE. For broadly spaced primary frequencies at low L2 levels, the largest DPOAEs were recorded when L1 was much higher than L2, with L1 remaining relatively constant as L2 increased. As f2∕f1 decreased, the largest DPOAEs were observed when L1 was closer to L2 and increased as L2 increased. Optimal values for L1-L2 and f2∕f1 were derived from these data. In general, average DPOAE levels for the new L1-L2 and f2∕f1 were equivalent to or larger than those observed for other stimulus combinations, including the L1-L2 described by Kummer et al. [J. Acoust. Soc. Am. 103, 3431–3444 (1998)] and those defined by Neely et al. in which L1-L2 was evaluated, but f2∕f1 was fixed at 1.2.
Scan-based near-field acoustical holography and partial field decomposition in the presence of noise and source level variation
Authors: Lee Moohyung , Bolton J. Stuart
Published: January 2006

Practical holography measurements of composite sources are usually performed using a multireference cross-spectral approach, and the measured sound field must be decomposed into spatially coherent partial fields before holographic projection. The formulations by which the latter approach have been implemented have not taken explicit account of the effect of additive noise on the reference signals and so have strictly been limited to the case in which noise superimposed on the reference signals is negligible. Further, when the sound field is measured by scanning a subarray over a number of patches in sequence, the decomposed partial fields can suffer from corruption in the form of a spatially distributed error resulting from source level variation from scan-to-scan. In the present work, the effects of both noise included in the reference signals, and source level variation during a scan-based measurement, on partial field decomposition are described, and an integrated procedure for simultaneously suppressing the two effects is provided. Also, the relative performance of two partial field decomposition formulations is compared, and a strategy for obtaining the best results is described. The proposed procedure has been verified by using numerical simulations and has been applied to holographic measurements of a subsonic jet.
Hybrid compliance-stiffness matrix method for stable analysis of elastic wave propagation in multilayered anisotropic media
Authors: Tan Eng Leong
Published: January 2006

This paper presents the hybrid compliance-stiffness matrix method for stable analysis of elastic wave propagation in multilayered anisotropic media. The method utilizes the hybrid matrix of each layer in a recursive algorithm to deduce the stack hybrid matrix for a multilayered structure. Like the stiffness matrix method, the hybrid matrix method is able to eliminate the numerical instability of transfer matrix method. By operating with total stresses and displacements, it also preserves the convenience for incorporating imperfect or perfect interfaces. However, unlike the stiffness matrix, the hybrid matrix remains to be well-conditioned and accurate even for zero or small thicknesses. The stability of hybrid matrix method has been demonstrated by the numerical results of reflection and transmission coefficients. These results have been determined efficiently based on the surface hybrid matrix method involving only a subset of hybrid submatrices. In conjunction with the recursive asymptotic method, the hybrid matrix method is self-sufficient without hybrid asymptotic method and may achieve low error level over a wide range of sublayer thickness or the number of recursive operations.
Speech perception from monaural and binaural information
Authors: Culling John F. , Edmonds Barrie A. , Hodder Kathryn I.
Published: January 2006

Two experiments explored the concept of the binaural spectrogram [Culling and Colburn, J. Acoust. Soc. Am. 107, 517–527 (2000)] and its relationship to monaurally derived information. In each experiment, speech was added to noise at an adverse signal-to-noise ratio in the NoSπ binaural configuration. The resulting monaural and binaural cues were analyzed within an array of spectro-temporal bins and then these cues were resynthesized by modulating the intensity and/or interaural correlation of freshly generated noise. Experiment 1 measured the intelligibility of the resynthesized stimuli and compared them with the original NoSo and NoSπ stimuli at a fixed signal-to-noise ratio. While NoSπ stimuli were ≈50% intelligible, each cue in isolation produced similar (very low) intelligibility to the NoSo condition. The resynthesized combination produced ≈25% intelligibility. Modulation of interaural correlation below 1.2kHz and of amplitude above 1.2kHz was not as effective as their combination across all frequencies. Experiment 2 measured three-point psychometric functions in which the signal-to-noise ratio of the original NoSπ stimulus was increased in 3-dB steps from the level used in experiment 1. Modulation of interaural correlation alone proved to have a flat psychometric function. The functions for NoSπ and for combined monaural and binaural cues appeared similar in slope, but shifted horizontally. The results indicate that for sentence materials, neither fluctuations in interaural correlation nor in monaural intensity are sufficient to support speech recognition at signal-to-noise ratios where 50% intelligibility is achieved in the NoSπ configuration; listeners appear to synergistically combine monaural and binaural information in this task, to some extent within the same frequency region.
Pressure-sensitive paint as a distributed optical microphone array
Authors: Gregory James W. , Sullivan John P. , Wanis Sameh S. , Komerath Narayanan M.
Published: January 2006

Pressure-sensitive paint is presented and evaluated in this article as a quantitative technique for measurement of acoustic pressure fluctuations. This work is the culmination of advances in paint technology which enable unsteady measurements of fluctuations over 10kHz at pressure levels as low as 125dB. Pressure-sensitive paint may be thought of as a nano-scale array of optical microphones with a spatial resolution limited primarily by the resolution of the imaging device. Thus, pressure-sensitive paint is a powerful tool for making high-amplitude sound pressure measurements. In this work, the paint was used to record ensemble-averaged, time-resolved, quantitative measurements of two-dimensional mode shapes in an acoustic resonance cavity. A wall-mounted speaker generated nonlinear, standing acoustic waves in a rigid enclosure measuring 216mm wide, 169mm high, and 102mm deep. The paint recorded the acoustic surface pressures of the (1,1,0) mode shape at ∼1.3kHz and a sound pressure level of 145.4dB. Results from the paint are compared with data from a Kulite pressure transducer, and with linear acoustic theory. The paint may be used as a diagnostic technique for ultrasonic tests where high spatial resolution is essential, or in nonlinear acoustic applications such as shock tubes.
Monaural and binaural hearing directivity in the bottlenose dolphin: Evoked-potential study
Authors: Popov Vladimir V. , Supin Alexander Ya. , Klishin Vladimir O. , Bulgakova Tatyana N.
Published: January 2006

Hearing thresholds as a function of sound-source azimuth were measured in bottlenose dolphins using an auditory evoked potential (AEP) technique. AEP recording from a region next to the ear allowed recording monaural responses. Thus, a monaural directivity diagram (a threshold-vs-azimuth function) was obtained. For comparison, binaural AEP components were recorded from the vertex to get standard binaural directivity diagrams. Both monaural and binaural diagrams were obtained at frequencies ranging from 8to128kHz in quarter-octave steps. At all frequencies, the monaural diagram demonstrated asymmetry manifesting itself as: (1) lower thresholds at the ipsilateral azimuth as compared to the symmetrical contralateral azimuth and (2) ipsilateral shift of the lowest-threshold point. The directivity index increased with frequency: at the ipsilateral side it rose from 4.7to17.8dB from 11.2to128kHz, and from 10.5to15.6dB at the contralateral side. The lowest-threshold azimuth shifted from 0° at 90–128kHz to 22.5° at 8–11.2kHz. The frequency-dependent variation of the lowest-threshold azimuth indicates the presence of two sound-receiving apertures at each head side: a high-frequency aperture with the axis directed frontally, and a low-frequency aperture with the axis directed laterally.
Perceptual similarity of regional dialects of American English
Authors: Clopper Cynthia G. , Levi Susannah V. , Pisoni David B.
Published: January 2006

Previous research on the perception of dialect variation has measured the perceptual similarity of talkers based on regional dialect using only indirect methods. In the present study, a paired comparison similarity ratings task was used to obtain direct measures of perceptual similarity. Naive listeners were asked to make explicit judgments about the similarity of a set of talkers based on regional dialect. The talkers represented four regional varieties of American English and both genders. Results revealed an additive effect of gender and dialect on mean similarity ratings and two primary dimensions of perceptual dialect similarity: geography (northern versus southern varieties) and dialect markedness (many versus few characteristic properties). The present findings are consistent with earlier research on the perception of dialect variation, as well as recent speech perception studies which demonstrate the integral role of talker gender in speech perception.
Improved parametrization of Antarctic krill target strength models
Authors: Lawson Gareth L. , Wiebe Peter H. , Ashjian Carin J. , Chu Dezhang , Stanton Timothy K.
Published: January 2006

There are historical discrepancies between empirical observations of Antarctic krill target strength and predictions using theoretical scattering models. These differences are addressed through improved understanding of key model parameters. The scattering process was modeled using the distorted-wave Born approximation, representing the shape of the animal as a bent and tapered cylinder. Recently published length-based regressions were used to constrain the sound speed and density contrasts between the animal and the surrounding seawater, rather than the earlier approach of using single values for all lengths. To constrain the parameter governing the orientation of the animal relative to the incident acoustic wave, direct measurements of the orientation of krill in situ were made with a video plankton recorder. In contrast to previous indirect and aquarium-based observations, krill were observed to orient themselves mostly horizontally. Averaging predicted scattering over the measured distribution of orientations resulted in predictions of target strength consistent with in situ measurements of target strength of large krill (mean length 40–43mm) at four frequencies (43–420kHz), but smaller than expected under the semi-empirical model traditionally used to estimate krill target strength.