bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoacoustic generation of narrow-band signals with high repetition rate pulsed lasers
Authors: Berthelot Yves H.
Published: October 2005

The generation of sound by absorption of laser light in water is analyzed for the case of lasers pulsating at high repetition rates. It is shown that pulsating the laser at any arbitrary repetition rate is, in general, not a very effective way to produce a narrow-band signal. In order to produce a signal with a narrow frequency band, one should instead pulsate the laser at an optimum repetition rate that is determined by the optical frequency of the laser and, to a lesser extent, by the laser beam diameter. Expressions for the optimum repetition rate are derived from both a frequency domain analysis and a time domain analysis. It is found that, with the present laser technology, significant gain in signal-to-noise ratio can be achieved by pulsating the laser at its optimum repetition rate, as compared with the more conventional methods for generation of narrow-band signals, such as the method of laser intensity modulation. As a result, it now seems possible to generate continuous thermoacoustic highly collimated sound beams with high repetition pulsed lasers in such a way that these signals are easily detectable several kilometers away from the source. Spatially periodic laser deposition configurations on the water surface are also discussed, and it is shown that further improvement in signal-to-noise ratio is achievable, in principle, for a spatial periodicity tuned to the optimum temporal periodicity of the repetition rate of the pulsed laser.
An acoustic head simulator for hearing protector evaluation. II: Measurements in steady-state and impulse noise environments
Authors: Giguère Christian , Kunov Hans
Published: October 2005

The attenuation characteristics of hearing protection devices (HPDs) were measured using a modular acoustic head simulator. The effect in changes in the head configuration was assessed in a steady-state diffuse sound field. The use of artificial circumaural skin had a relatively small influence on the insertion loss of earmuffs (max. 6–7 dB at low frequencies). This contrasts to the very large effects found for the artificial intraaural skin on the insertion loss of earplugs (in excess of 40 dB at low frequencies for some devices). Results were also compared with real-ear attenuation at threshold (REAT) data (ANSI S3.19-1974). In general, there is good agreement between the two methods, especially for earmuffs. Design improvements are proposed for earplugs. The result of an exploratory study aimed at measuring the complex (amplitude and phase) insertion loss of HPDs using an impulse noise source are also reported.
Early lateral reflections in some modern concert halls
Authors: Cremer Lothar
Published: October 2005

This article describes some of the means by which early lateral reflections (ELR) of sound have been provided in recent concert halls in which the author has been involved as acoustical consultant. Special problems are encountered nowadays. In earlier times, the disposition of audience seating in acoustical design was only a question of access: aisles, staircases, etc. Now, special account of the seating arrangement must be taken in order to provide suitable lateral sound reflections; and, particularly in large halls, this requires some departure from traditional seating plans.
Noise susceptibility and immunity of phase locking in amphibian auditory-nerve fibers
Authors: Narins Peter M. , Wagner Ingeborg
Published: October 2005

Recordings from auditory-nerve fibers in the anesthetized frog revealed that addition of broadband noise results in a reduction in the ability of a fiber to phase lock to a continuous pure tone. In particular, our results suggest that: (i) there is a threshold below which masking noise has little or no effect on vector strength (VS); then with increasing masking noise level, VS appears to decrease monotonically for all test frequencies (TFs); (ii) there exist subpopulations of auditory-nerve fibers in the frog for which the deterioration of phase locking to tones in wideband noise depends critically on the relationship of the TF to the fiber’s CF. Specifically, in one subpopulation (43% of the fibers studied), the rate of VS decrease with increasing levels of masking noise is greater for CF tones than it is for TFs>CF. The net result is a ‘‘crossing’’ of the VS versus masking noise functions (e.g., Fig. 6); (iii) there exists a small subpopulation of amphibian papillar (a.p.) fibers for which the rate of VS decrease with increasing levels of masking noise is less for TFsCF, whereas, for stimulus tones at or below CF, the preferred firing phase is nearly noise-level independent; (v) the remainder of the sample consists of fibers in which the VS-falloff rates appear to be test-frequency independent; (vi) addition of wideband masking noise to a CF tone, and increasing the CF-tone level in the absence of noise, produced (qualitatively) similar effects on the preferred firing phase of auditory-nerve fibers (e.g., Figs. 1 and 7). Thus amphibian auditory-nerve fibers appear to be energy detectors, i.e., exhibit phase shifts corresponding to the total energy within the filter passband defined by the frequency-threshold curve.
Detection of temporal gaps in sinusoids by normally hearing and hearing-impaired subjects
Authors: Moore Brian C. J. , Glasberg Brian R. , Donaldson Emma , McPherson Tracy , Plack Christopher J.
Published: October 2005

A two-alternative forced-choice task was used to measure psychometric functions for the detection of temporal gaps in a 1-kHz, 400-ms sinusoidal signal. The signal always started and finished at a positive-going zero crossing, and the gap duration was varied from 0.5 to 6.0 ms in 0.5-ms steps. The signal level was 80 dB SPL, and a spectrally shaped noise was used to mask splatter associated with the abrupt onset and offset of the signal. Two subjects with normal hearing, two subjects with unilateral cochlear hearing loss, and two subjects with bilateral cochlear hearing loss were tested. The impaired ears had confirmed reductions in frequency selectivity at 1 kHz. For the normal ears, the psychometric functions were nonmonotonic, showing minima for gap durations corresponding to integer multiples of the signal period (n ms, where n is a positive integer) and maxima for durations corresponding to (n−0.5) ms. For the impaired ears, the psychometric functions showed only small (nonsignificant) nonmonotonicities. Performance overall was slightly worse for the impaired than for the normal ears. The main features of the results could be accounted for using a model consisting of a bandpass filter (the auditory filter), a square-law device, and a sliding temporal integrator. Consistent with the data, the model demonstrates that, although a broader auditory filter has a faster transient response, this does not necessarily lead to improved performance in a gap detection task. The model also indicates that gap thresholds do not provide a direct measure of temporal resolution, since they depend at least partly on intensity resolution.
Comodulation masking release using SAM tonal complex maskers: Effects of modulation depth and signal position
Authors: Grose John H. , Hall Joseph W.
Published: October 2005

The purpose of this investigation was to examine two stimulus parameters that were reasoned to be of importance to comodulation masking release (CMR). The first was the degree of fluctuation, or depth of modulation, in the masker bands, and the second was the temporal position of the signal with respect to the modulations of the masker. The investigation began by demonstrating the efficacy of sinusoidally amplitude-modulated (SAM) tonal complex maskers in eliciting CMR. ‘‘Nine-band’’ maskers, 650 ms in duration, were constructed by adding together nine SAM tones spaced at 100-Hz intervals from 300 to 1100 Hz. The rate of modulation for each SAM tone was 10 Hz, and the depth of modulation was 100%. Using such maskers, it was shown that when the on-frequency SAM tone had a modulation depth of 100%, the threshold for a 250-ms, 700-Hz tone improved monotonically as the modulation depths of the flanking SAM tones increased from 0% to 100%. When the on-frequency SAM tone had a modulation depth of 63%, some listeners perfomed optimally when the flanking SAM tones also exhibited a modulation depth of 63%, whereas others performed best when the flankers had modulation depths of 100%. With regard to signal position, a typical CMR effect was observed when the signal, consisting of a train of three 50-ms, 700-Hz tone bursts, was placed in the dips of the on-frequency masker. However, when the signal was placed at the peaks of the envelope, an increase in masking was observed for a comodulated masker. The results were considered in terms of proposed mechanisms underlying CMR, and it was concluded that the evidence did not clearly support a single CMR mechanism.
The sound emission pattern of the echolocating bat, E
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Authors: Hartley David J. , Suthers Roderick A.
Published: October 2005

The emission pattern of Eptesicus fuscus was found to be consistent with those of the other frequency-modulating (FM) bats studied in similar detail in that there is a mainlobe aimed forward of the animal together with a prominent −6-dB ventral lobe. This ventral lobe cannot be explained as the first sidelobe of a piston source mounted in an infinite baffle and must be formed by some other acoustic means. Nevertheless, a piston source with a radius comparable to that of the open mouth can nicely explain the changes in the width of the mainlobe with frequency, so that the open mouth alone can explain the observed directionality. At wavelengths greater than the mouth dimensions, however, some additional sound ‘‘focusing’’ may occur, presumably due to diffraction by the head.
Comments on ‘‘Speech understanding and aging’’ [J. Acoust. Soc. Am. 8
3, 859–895 (1988)]
Authors: Jerger James , Stach Brad , Pruitt Jeanine , Harper Robert , Kirby Henry
Published: October 2005

The hypothesis advanced by the CHABA Working Group on Speech Understanding and Aging [J. Acoust. Soc. Am. 83, 859–895 (1986)] that the systematic decline in speech understanding with age might be explained by concommitant decline in extra-auditory cognitive factors was tested by examining speech audiometric findings in patients with dementia. The fact that performance was consistent with normal central auditory function in 12 of 23 such patients, in spite of deficits in immediate memory for spoken material, tolerance of distraction, mental tracking and sequencing, cognitive flexibility, and set shifting argues against the hypothesis that speech understanding deficits in the elderly can be explained as the simple consequence of cognitive decline.
An approximation for the on-axis field of an elliptical piston transducer
Authors: Newberry Byron P. , Rose James H.
Published: October 2005

An approximate analytic formula is given for the on-axis pressure of a baffled, elliptically shaped piston transducer. This approximate formula results from truncating an exact series expansion for the integral that determines the on-axis pressure. The reported formula is considerably more accurate than the previous expression. The accuracy and range of validity of the new result are determined by comparison with a numerical evaluation of the relevant integral.
Observations and modeling of the backscattering of short tone bursts from a spherical shell: Lamb wave echoes, glory, and axial reverberations
Authors: Kargl Steven G. , Marston Philip L.
Published: October 2005

Tone bursts having durations of 3 or 4 cycles were incident on an air-filled stainless steel shell in water. The resulting sequence of echoes included a specular reflection and echoes radiated by Lamb waves on the shell. Echo structure was studied for ka of 24 to 75, where a denotes the outer radius; b/a=0.838, where b denotes the inner radius. The amplitudes of Lamb wave echoes were modeled using an elastic generalization of the geometrical theory of diffraction (GTD) [P. L. Marston, J. Acoust. Soc. Am. 83, 25–37 (1988)]. The required Lamb wave parameters (the phase velocity cl and damping βl ) were found by the Sommerfeld–Watson method; an efficient numerical method for the computation of the required complex root νl is described. The echoes were identified by comparing arrival times with predictions; bursts reflected from a solid tungsten carbide sphere were used for a reference amplitude. Measurements with ka=24 of the largest Lamb wave echo (which was due to a flexural wave) were made at various backscattering angles γ. The echo was largest for small γ in agreement with predictions. This is a manifestation of the glory pertinent to other bistatic measurements. The ringing of longitudinal wave reverberations (which could be seen following the specular reflection) may be useful for determining the thickness of a shell.
The ONION method: A reflection coefficient measurement technique for thick underwater acoustic panels
Authors: Piquette Jean C.
Published: October 2005

An earlier report [J. C. Piquette, ‘‘An extrapolation procedure for transient reflection measurements made on thick acoustical panels composed of lossy, dispersive materials,’’ J. Acoust. Soc. Am. 81, 1246–1258 (1987)] described a new technique for evaluating underwater panel measurements. The method is based on least-squares fitting to a multiple-layer model. The present article describes further research on the technique, including a description of a successful application to measurements made under nonatmospheric hydrostatic pressure. Also described are enhancements that increase the speed of the algorithm as implemented on a digital computer, and that render the technique practical for use in reducing the massive amounts of data that can be obtained in panel calibration measurements. The method is currently being transitioned to an on-line panel-measurement capability in the Anechoic Tank Facility (ATF) of the Underwater Sound Reference Detachment of the Naval Research Laboratory (NRL-USRD), located in Orlando, Florida.
On the topology of the complex wave spectrum in a fluid-coupled elastic layer
Authors: Rokhlin S. I. , Chimenti D. E. , Nayfeh A. H.
Published: October 2005

The behavior of the complex leaky Lamb wave (LLW) spectrum of a plate immersed in a fluid has been studied as a function of the ratio of fluid-to-solid densities. It has been shown that widely accepted assumptions concerning the similarities between the classical Lamb wave spectrum and the LLW spectrum are not valid as the fluid density approaches that of the solid. Recent experimental and theoretical results demonstrate that there is a strong anomaly in the reflectance of composite plates in water. This anomaly is related to the details of the complex LLW spectrum. The spectrum is composed of both the familiar propagating Lamb wave branches and the mostly imaginary, nonpropagating branches. From the character of the complex spectrum, it is demonstrated that topological changes in the fundamental symmetric mode are related to its nearness to the first complex branch of the spectrum. Increasing the fluid–solid density ratio leads to interaction between these modes and to mutual interchange between portions of their branches. As the density ratio increases from zero to infinity, the complex spectrum is gradually transformed from a classical Lamb wave spectrum to one appropriate for a plate with zero normal surface displacements.
Atmospheric acoustic noise as a function of altitude
Authors: Griffy T. A. , Hixson E. L.
Published: October 2005

Previous measurements of ambient acoustic noise in the atmosphere have been limited to a few meters from the ground. Here, a hot-air balloon was used as a platform to measure noise as a function of altitude up to 3400 m with ‘‘A’’ and ‘‘flat’’ weighting. The frequency spectrum was also measured at 3400 m. Measurements were made in the early morning over a rural area. The spectrum level was greatest at low frequency and decreased with frequency. Levels decreased with height due to absorption and a limited acoustical horizon caused by refraction.
Saddle point analysis of the reflected acoustic field
Authors: Plumpton N. G. , Tindle C. T.
Published: October 2005

The field due to reflection of spherical sound waves at the plane interface between two homogeneous fluids is examined in terms of saddle points of an integrand. The resulting new expression for the field is valid at all ranges including the vicinity of the critical ray and the caustic due to beam displacement. A simple interpretation of the field in terms of wave fronts and eigenrays, which is valid at all ranges, is obtained. At some ranges, the wavenumber for eigenrays is complex. The new result provides an alternative to the usual specular ray and lateral wave interpretation.
Interaural cross-correlation coefficients in stereo-reproduced sound fields
Authors: Tohyama Mikio , Suzuki Akira
Published: October 2005

I_nteraural c_ross-c_orrelation c_oefficients (ICCCs) were measured in stereo-reproduced fields where a KEMAR (K_nowles e_lectric m_anikin for a_coustic r_esearch) was located. These ICCCs were then compared with those in an ideal, diffuse sound field. The ICCCs in a reverberant field are not reproduced accurately using a conventional two-channel stereo-reproduction technique. In four-channel stereo reproduction, however, the ICCCs can, for the most part, be reproduced accurately as in an ideal, diffuse sound field. Some experimental results are also shown for binaural discrimination of the ICCCs.
Long-term memory for unfamiliar voices
Authors: Papcun George , Kreiman Jody , Davis Anthony
Published: October 2005

From a sample of young male Californians, ten speakers were selected whose voices were approximately normally distributed with respect to the ‘‘easy-to-remember’’ versus ‘‘hard-to-remember’’ judgments of a group of raters. A separate group of listeners each heard one of the voices, and, after delays of 1, 2, or 4 weeks, tried to identify the voice they had heard, using an open-set, independent-judgment task. Distributions of the results did not differ from the distributions expected under the hypothesis of independent judgments. For both ‘‘heard previously’’ and ‘‘not heard previously’’ responses, there was a trend toward increasing accuracy as a function of increasing listener certainty. Overall, heard previously responses were less accurate than not heard previously responses. For heard previously responses, there was a trend toward decreasing accuracy as a function of delay between hearing a voice and trying to identify it. Information-theoretic analysis showed loss of information as a function of delay and provided means to quantify the effects of patterns of voice confusability. Signal-detection analysis revealed the similarity of results from diverse experimental paradigms. A ‘‘prototype’’ model is advanced to explain the fact that certain voices are preferentially selected as having been heard previously. The model also unites several previously unconnected findings in the literature on voice recognition and makes testable predictions.
Ultrasonic propagation in suspensions—A comparison of a multiple scattering and an effective medium approach
Authors: Anson L. W. , Chivers R. C.
Published: October 2005

The methods of an effective medium and of multiple scattering for determining the velocity and attenuation of suspensions of spherical particles have been compared in order to identify the source of unphysical results obtained using the former. With a suspension of elastic spheres (polystyrene) in an inviscid fluid (water), the cause of the discrepancy was found to be the approximations used in calculating the scattering coefficients An. When full expressions for the An are used, the results obtained by the two methods agree both for elastic spheres in a fluid and for elastic spheres (glass) in an elastic matrix (epoxy). The computational simplicity of the effective medium method compared to the multiple scattering method is significantly reduced if the approximations cannot be made.
Basic equations for shocks in nonlinear electroelastic materials
Authors: Ani Wafa , Maugin Gérard A.
Published: October 2005

The complete set of balance equations and jump relations useful in the study of the propagation of strong discontinuities of the shock-wave type is deduced both in its Eulerian form and material form (the latter being the most useful one) for nonlinear anisotropic electroelastic materials such as piezoelectric ceramics. In particular, the relevant form of the so-called Hugoniot equation is obtained, and all expressions are given a useful form in terms of the displacement gradient and the material electric field (or the gradient of electric potential in the quasielectrostatic approximation). The equations obtained are based on a strict use of nonlinear continuum mechanics and the electrodynamics of continua with electromechanical interactions.
The effective depth of a Pekeris ocean waveguide, including shear wave effects
Authors: Chapman David M. F. , Ward Peter D. , Ellis Dale D.
Published: October 2005

Weston’s [J. Acoust. Soc. Am. 32, 647–654 (1960)] concept of the effective depth of a Pekeris-type shallow water waveguide has been extended to admit seabeds that support shear waves. The amended effective depth formula leads to estimates of normal mode phase speeds that are surprisingly accurate, without numerical iteration. Results for six hypothetical, though realistic, bottom types are compared with an ‘‘exact’’ normal mode model that includes shear wave effects and another normal mode model that does not.
Amplitude and phase fluctuations of Arctic cw signals
Authors: Giellis George R.
Published: October 2005

Low-frequency Arctic continuous wave (cw) signals recorded during the FRAM IV experiment were analyzed for purposes of measuring amplitude and phase fluctuations over time periods of about 1-h duration. The fluctuations were measured in a statistical sense by fitting probability density functions to histograms generated by the amplitude and phase time series data. The measurements were made at signal frequencies of 20, 35.5, 47, 55, and 97 Hz. The 20- and 35.5-Hz data can be fitted by either the Rician or the partially saturated density function [P. N. Mikhalevsky, J. Acoust. Soc. Am. 72, 151–158 (1982)]. However, the 47-, 55- and 97-Hz data can only be fitted by the partially saturated density function. This suggests that multipath fluctuations are non-negligible at frequencies above a certain level for shallow sources (less than 150 m). Below this frequency, the signal is dominated by the lowest-order modes; above this frequency, higher-order modes are non-negligible, resulting in a partially saturated distribution.
Acoustic emission from the Arctic ice sheet
Authors: Langley A. J.
Published: October 2005

A theoretical analysis of the sound field in the Arctic Ocean due to a crack occurring in the ice sheet is given. Particular attention is paid to the contribution of that field to Arctic Ocean ambient noise. The crack is modeled by an approximate ‘‘equivalent source,’’ and the example chosen represents a small failure of the ice sheet under tension. It is shown that if the ice sheet were completely continuous, only a very small fraction of the energy released by the crack could be trapped as sound in the surface half-channel of the ocean, where it would contribute to the ambient noise. This suggests that scattering of energetic elastic waves in the ice by natural inhomogeneities may be an important additional mechanism by which acoustic energy can leak into the surface channel. The analysis is relevant to acoustic emission from any unbounded, elastic plate in contact with two, possibly different, fluid half-spaces.
Stress-induced anisotropy in sediment acoustics
Authors: Stoll R. D.
Published: October 2005

A model to describe seismic wave propagation in both dry and water-saturated, particulate materials is derived on the basis of the response of a regular array of like elastic spheres. The theories of Hertz and Mindlin are used to model the normal and tangential compliances at the intergranular contacts and the overall response of the array is found to be governed by a set of nonlinear equations that depend on the quasistatic loading history. These equations are integrated over a particular stress history that simulates the normal buildup and relief of geostatic stress (overburden pressure) in nature. Wave velocities are evaluated at various stages during this stress history and the response is found to be anisotropic with respect to both p- and s-wave velocities. In order to simulate the response of marine sediments, the effects of water saturation are investigated by using the compliances calculated for the dry skeletal frame in conjunction with the Biot theory. Predictions of the model were compared with laboratory experiments and all the general trends in response were found to agree.
Stop-consonant recognition for normal-hearing listeners and listeners with high-frequency hearing loss. II: Articulation index predictions
Authors: Dubno Judy R. , Dirks Donald D. , Schaefer Amy B.
Published: October 2005

Articulation index (AI) theory was used to evaluate stop-consonant recognition of normal-hearing listeners and listeners with high-frequency hearing loss. From results reported in a companion article [Dubno et al., J. Acoust. Soc. Am. 85, 347–354 (1989)], a transfer function relating the AI to stop-consonant recognition was established, and a frequency importance function was determined for the nine stop-consonant–vowel syllables used as test stimuli. The calculations included the rms and peak levels of the speech that had been measured in 1/3 octave bands; the internal noise was estimated from the thresholds for each subject. The AI model was then used to predict performance for the hearing-impaired listeners. A majority of the AI predictions for the hearing-impaired subjects fell within ±2 standard deviations of the normal-hearing listeners’ results. However, as observed in previous data, the AI tended to overestimate performance of the hearing-impaired listeners. The accuracy of the predictions decreased with the magnitude of high-frequency hearing loss. Thus, with the exception of performance for listeners with severe high-frequency hearing loss, the results suggest that poorer speech recognition among hearing-impaired listeners results from reduced audibility within critical spectral regions of the speech stimuli.
Single-channel vibrotactile supplements to visual perception of intonation and stress
Authors: Bernstein Lynne E. , Eberhardt Silvio P. , Demorest Marilyn E.
Published: October 2005

Two experiments were conducted to explore the effectiveness of a single vibrotactile stimulator to convey intonation (question versus statement) and contrastive stress (on one of the first three words of four 4- or 5-word sentences). In experiment I, artificially deafened normal-hearing subjects judged stress and intonation in counterbalanced visual-alone and visual–tactile conditions. Six voice fundamental frequency-to-tactile transformations were tested. Two sentence types were voiced throughout, and two contained unvoiced consonants. Benefits to speechreading were significant, but small. No differences among transformations were observed. In experiment II, only the tactile stimuli were presented. Significant differences emerged among the transformations, with larger differences for intonation than for stress judgments. Surprisingly, tactile-alone intonation identification was more accurate than visual–tactile for several transformations.
A boundary element method for acoustic radiation valid for all wavenumbers
Authors: Cunefare Kenneth A. , Koopmann Gary , Brod Klaus
Published: October 2005

A boundary element method for solving the exterior acoustic radiation problem that is valid for all wavenumbers has been developed. The new formulation derives from the earlier work of Burton and Miller [Proc. R. Soc. London Ser. A 323, 201–210 (1971)], which uses a linear combination of the Helmholtz integral equation and its gradient to overcome the uniqueness problem. A main feature of this formulation is the absence of integral singularities. By restricting the field points of the kernels of the integrals to interior regions well away from radiating boundaries, the usual complication of dealing with singular kernels is circumvented. The new formulation has been named CHI, for coupled Helmholtz integrals. A corresponding computer program, CHI 4.35, can be used to compute the surface acoustic pressure on an arbitrary body for a given specified surface normal velocity. Results generated with CHI 4.35 are presented for the spherical monopole and dipole, along with results for parametric studies on the accuracy of the results. A useful feature of this work is that the computations have been implemented on a personal computer that presents the results in a graphical format.
The elastic microstructure of various tissues
Authors: Daft C. M. W. , Briggs G. A. D.
Published: October 2005

Previous work has indicated that a modified Quate-Lemons scanning acoustic microscope (SAM) is capable of measuring the acoustic propagation properties of sections of biological tissue. The lens is excited by an impulse, rather than a tone burst, and the undemodulated returning signal from the tissue is recorded. The variations in received signal with time are used to deduce the sound speed, attenuation, impedance, and section thickness. In this article, the technique is applied to various types of tissue, and the variations in acoustic propagation properties are computed. Conventional tone burst SAM images at 425 MHz are compared with the time resolved data in order to elucidate the contrast mechanisms. The effects of varying the frequency and position of the focal plane on the tone burst images are interpreted in the light of the broadband results.
Digital interpolation beamforming using recursive filters
Authors: Çetin A. Enis , Ansari Rashid
Published: October 2005

The problem of steering delay quantization in beamforming can be circumvented by using digital interpolation and digital interpolation can be implemented using recursive filters. The recursive interpolation scheme offers considerable computational savings over conventional finite impulse response (FIR) digital interpolation methods.
The use of optical fibers to enhance the laser generation of ultrasonic waves
Authors: Jarzynski Jacek , Berthelot Yves H.
Published: October 2005

It is shown that optical fibers offer a convenient way to control, both spatially and temporally, the laser light used to generate ultrasound in a solid. Proper phasing between the acoustic signals received at the transducer can enhance the ultrasonic signal in a particular direction. The principle is validated experimentally, with two optical fibers guiding the light emitted by a cw argon-ion laser.
Postbeamformer interference canceler with improved performance
Authors: Godara Lal C.
Published: October 2005

A postbeamformer interference canceler (PIC) processes the signals derived from an antenna array by forming two beams using fixed beamforming weights. The weighted output of one beam, referred to as the interference beam, is subtracted from the other beam, referred to as the target beam. In a conventional beamforming method, both beams are formed using equal weighting on each element. For this case the PIC processor suppresses a substantial amount of the signal; its output contains a large amount of residual interference when the weight of the interference channel is adjusted to minimize the mean output power of the PIC. This article presents and analyzes two methods to reduce the signal suppression by the PIC. The analysis shows that in one case the signal suppression has been completely eliminated, while in the second case the output of the PIC does not contain any residual interference. The examples presented show that the output signal to noise ratio (SNR) of the PIC using these beamforming methods is larger than the output SNR of the PIC using conventional beamforming methods.
Acoustic distortion products in humans: Systematic changes in amplitude as a function of f2/f1 ratio
Authors: Harris F. P. , Lonsbury-Martin B. L. , Stagner B. B. , Coats A. C. , Martin G. K.
Published: October 2005

The effects of primary-tone separation on the amplitude of distortion-product emissions (DPEs) at the 2f1−f2 frequency were systematically examined in ten ears of five subjects. All individuals had normal hearing and middle-ear function based upon standard clinical measures. Acoustic-distortion products were elicited at 1, 2.5, and 4 kHz by equilevel primaries at 65, 75, and 85 dB SPL, while f2/f1 ratios were varied in 0.02 increments from 1.01–1.41 (4 kHz), 1.01–1.59 (2.5 kHz), or 1.01–1.79 (1 kHz). A principal outcome reflected in the detailed structure of both average and individual ratio functions was a nonmonotonic change in DPE amplitude as the ratio of f2/f1 increased. Despite the presence of amplitude nonmonotonicities, there was clearly a region of f1 and f2 separation that generated a maximum DPE. The effects of primary-tone separation on DPE amplitudes were systematically related to DPE frequency and primary-tone level. For all three levels of stimulation, the f2/f1 ratio was inversely related to DPE frequency. Thus larger ratios reflecting a greater separation of f1 and f2 were more effective in generating DPEs at 1 kHz rather than at 4 kHz. The optimal ratio for 2.5 kHz fell at an intermediate value. Conversely, acoustic distortion-product amplitude as a function of primary-tone level was directly related to the frequency separation of the primary tones. Regardless of the frequency region of the primary tones, smaller f2/f1 ratios were superior in generating DPEs in response to 65-dB stimuli, whereas larger ratios elicited bigger DPEs with primaries at 75 and 85 dB SPL. Within any specific stimulus–parameter combination, individual variability in DPE amplitude was noted. When all stimulus conditions describing the variations in frequency and level were considered, an f2/f1 ratio of 1.22 was most effective in maximizing DPE amplitude.
Comodulation masking release for various monaural and binaural combinations of the signal, on-frequency, and flanking bands
Authors: Schooneveldt Gregory P. , Moore Brian C. J.
Published: October 2005

The threshold for a signal masked by a narrow band of noise centered at the signal frequency (the on-frequency band) may be reduced by adding to the masker a second band of noise (the flanking band) whose envelope is correlated with that of the first band. This effect is called comodulation masking release (CMR). These experiments examine two questions. (1) How does the CMR vary with the number and ear of presentation of the flanking band(s)? (2) Is it possible to obtain a CMR when a binaural masking level difference (BMLD) is already present, and vice versa? Thresholds were measured for a 400-ms signal in a continuous 25-Hz-wide noise centered at signal frequencies (fs) of 250, 1000, and 4000 Hz. This masker was presented either alone or with one or more continuous flanking bands whose envelopes were either correlated or uncorrelated with that of the on-frequency band; their frequencies ranged from 0.5fs to 1.5 fs. CMRs were measured for six conditions in which the signal, the on-frequency band, and the flanking band(s) were presented in various monaural and binaural combinations. When a single flanking band was used, the CMR was typically around 2–3 dB. The CMR increased to 5–6 dB if an additional flanking band was added. The effect of the additional band was similar whether it was in the same ear as the original band or in the opposite ear. At the lowest signal frequency, a large CMR was observed in addition to a BMLD and vice versa. At the highest signal frequency, the extra release from masking was small. The results are interpreted in terms of the cues producing the CMR and the BMLD.
Minimum audible angle thresholds obtained under conditions in which the precedence effect is assumed to operate
Authors: Perrott David R. , Marlborough Kent , Merrill Paul , Strybel Thomas Z.
Published: October 2005

Two experiments were conducted to examine the ability of human listeners to localize the ‘‘lag’’ or ‘‘echo’’ source in a precedence effect paradigm. A 5-ms noise burst was presented from a source located between 554–279 cm from the subject. This ‘‘lead’’ source was always located at 0° azimuth. At the same time, one of two sources located at a distance of 610 cm from the subject was also activated with the same 5-ms noise burst. The subject’s task was to identify which lag source had been active. Across sessions, the angular distance between the lag sources was varied, so as to allow a determination of the minimum audible angle (MAA) that could be resolved. Tests were run in a room designed to minimize reflections and in a hallway that was acoustically quite complex. No systematic differences in MAA thresholds were observed as a function of the environment employed. MAA thresholds obtained without the signal from the lead speaker were less than 1° for four of the five subjects tested. The precedence effect, as measured by the change in the MAA threshold, appears to have only a modest influence on localization performance. Under conditions in which the lead source was concurrently active, the thresholds were generally elevated by only 2°–4°. A reduction of this magnitude in the ability to resolve the position of the lag source does not seem to be sufficient, in itself, to account for the excellent localization performance frequently observed in reflective environments.
Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). II: Effects of broadband noise level and high-pass masker cutoff frequency across click polarity
Authors: Burkard Robert , Voigt Herbert F.
Published: October 2005

Two experiments concerning the effects of masking noise on the gerbil brain-stem auditory-evoked response (BAER) are reported. Experiment 1 evaluated the effects of broadband masking noise on the BAER obtained to condensation and rarefaction clicks. With increasing noise level, there was an increase in BAER peak latencies, an increase in the i–v interval, and a decrease in peak amplitudes. Experiment 2 evaluated the effects of high-pass masking noise on the BAER obtained to condensation and rarefaction clicks. Both high-pass responses and derived-band responses were evaluated. For high-pass responses, with decreasing masker cutoff frequency, there was an increase in BAER peak latencies, a decrease in the i–v interval, and a decrease in peak amplitudes. For derived-band responses, with decreasing derived-band frequency, there was an increase in peak latencies and a decrease in the i–v interval. A comparison of wave i and wave v amplitudes across derived-band frequency demonstrates a greater contribution of high-frequency cochlear regions to wave i than wave v. Small, insignificant, effects of click polarity on BAER peak amplitudes were observed. These trends were in the direction seen in a companion paper [R. Burkard and H. F. Voigt, J. Acoust. Soc. Am. 85, xxx–xxxx (1989)] and were, in general, reduced by the presence of broadband or high-pass maskers.
Modulation masking: Effects of modulation frequency, depth, and phase
Authors: Bacon Sid P. , Grantham D. Wesley
Published: October 2005

Modulation thresholds were measured for a sinusoidally amplitude-modulated (SAM) broadband noise in the presence of a SAM broadband background noise with a modulation depth (mm) of 0.00, 0.25, or 0.50, where the condition mm=0.00 corresponds to standard (unmasked) modulation detection. The modulation frequency of the masker was 4, 16, or 64 Hz; the modulation frequency of the signal ranged from 2–512 Hz. The greatest amount of modulation masking (masked threshold minus unmasked threshold) typically occurred when the signal frequency was near the masker frequency. The modulation masking patterns (amount of modulation masking versus signal frequency) for the 4-Hz masker were low pass, whereas the patterns for the 16- and 64-Hz maskers were somewhat bandpass (although not strictly so). In general, the greater the modulation depth of the masker, the greater the amount of modulation masking (although this trend was reversed for the 4-Hz masker at high signal frequencies). These modulation-masking data suggest that there are channels in the auditory system which are tuned for the detection of modulation frequency, much like there are channels (critical bands or auditory filters) tuned for the detection of spectral frequency.
Application of an auditory model to speech recognition
Authors: Cohen Jordan R.
Published: October 2005

Some aspects of auditory processing are incorporated in a front end for the IBM speech-recognition system [F. Jelinek, ‘‘Continuous speech recognition by statistical methods,’’ Proc. IEEE 64 (4), 532–556 (1976)]. This new process includes adaptation, loudness scaling, and mel warping. Tests show that the design is an improvement over previous algorithms.
Tuning of bells by a linear programming method
Authors: Mills R. G. J.
Published: October 2005

A carillon bell is tuned by the removal of metal from the inner surface of the bell. Van Heuven [Acoustical Measurements on Church-Bells and Carillons (De Gebroeders van Cleef, ’s-Gravenhage, The Netherlands, 1949), Chap. IV] determined a set of tuning curves and derived a set of equations that relate the amount of metal removed to the relative alterations in the partial frequencies. This paper uses these equations as constraints in the formulation of the tuning problem as a linear program. An example illustrates the procedure.
A class of density profiles for constructing analytical solutions to a variable-density parabolic equation
Authors: Robertson J. S.
Published: October 2005

A class of depth-dependent density profiles is described that permits the construction of analytical solutions to a variable-density parabolic equation (VDPE). These solutions can serve as accuracy benchmarks for numerical algorithms that solve VDPEs.
Off-resonance contributions to acoustical bubble spectra
Authors: Commander Kerry , Moritz Elan
Published: October 2005

Comparisons of experimental optical and acoustical bubble size spectra disagree in size distribution at the low end of the spectrum. Previous methods of obtaining acoustic bubble size information relied strictly on resonant acoustical scattering and absorption theory. For some plausible distributions, these traditional methods greatly overpredict the number of bubbles present in a volume of fluid for bubble radii of 50 μ or less. Two cases are investigated that show the magnitude of departure from a priori bubble size distributions and are used to benchmark traditional acoustical scattering and absorption-based methods for obtaining spectra. A third possible bubble distribution is presented that is consistent with resonant approximation theory; however, the acoustic properties of this distribution are inconsistent with measurements from naturally occurring bubble populations. It is argued that off-resonance contributions to acoustical bubble spectra determinations need to be included.
Transient ultrasonic waves in a viscoelastic plate: Applications to materials characterization
Authors: Weaver Richard L. , Sachse Wolfgang , Niu Lin
Published: October 2005

The ray arrival behavior of an ultrasonic signal propagated through a thick viscoelastic plate is analyzed to determine the material dispersion and attenuation. Signal processing algorithms are developed and demonstrated with synthetic and real signals obtained in elastic and viscoelastic materials. Recovery of material properties is found to proceed reliably except for the case of attenuation recovery from real signals, where there were difficulties related to the use of a finite aperture receiver.
On the existence of the Rayleigh wave dipole resonance
Authors: Hackman Roger H. , Sammelmann Gary S.
Published: October 2005

The acoustic scattering resonances of a solid elastic sphere are thoroughly analyzed in the low-ka frequency region. No evidence is found to support the existence of the recently reported (1,1) Rayleigh wave dipole resonance.
Intermodulation and generation of elastic and piezoelectric waves in anisotropic solids
Authors: Daher Naoum , Maugin Gérard A.
Published: October 2005

A study of nonlinear waves of small amplitude is presented in elastic and electroelastic media through an asymptotic iterative procedure known as ‘‘Poincaré’s expansion.’’ The controversy surrounding the nonlinear elastic solution derived by use of different approaches is resolved and the resulting expressions are compared to recent experimental verifications. After the reconciliation of the various theoretical and experimental results, the new version of Poincaré’s method is extended to electroelastic anisotropic solids. Analytical, as well as numerical, evaluations concerning the relative velocity change due to electroelastic nonlinearities are presented.
The generation of sound by the convection of inhomogeneities through space-varying flows, by analogy with the scattering of acoustic and evanescent waves
Authors: Powell Alan
Published: October 2005

It is pointed out that the scattering theory of Rayleigh for sound waves interacting with inhomogeneities of a stationary medium can also be applied to evanescent waves. By considering the fluid to be moving and the wave system stationary and caused by a fixed wavy wall, the problem of the sound generated by inhomogeneities of a fluid carried through a supersonic or subsonic space-varying flow field past the wall can then be addressed. As in that scattering theory, the inhomogeneities must be small in extent compared to the scale of the pressure gradient of the basic flow and also of the resultant sound: This is the low-frequency approximation (which excludes application of the theory to shockwaves). It is found that inhomogeneities in density and compressibility of the gas (i.e., of the gas constant) both result in sound power that varies as the sixth power of the speed in all the cases of supersonic and subsonic flow, and when the interaction takes place far from, or close to, the wall or body, except that, at supersonic speed, interactions close to the body result in the sound power due to density fluctuations varying with only the fourth power of the Mach number and that due to the gas constant (compressibility) at subsonic speeds varying as the eighth power. In all cases, the sound power depends acutely on the shortness of the length characterizing the pressure gradients in the flow; specifically, it varies inversely as the sixth power of the characteristic length. It is pointed out that, in most engineering applications, the effects of density inhomogeneities are likely to overwhelm those due to variations in the compressibility of the gas, and interactions in the subsonic case must be close to the body to be significant, due to the very rapid decay of the pressure field away from the body.