bluuebunny/crossref_metadata_2025 huggingface dataset:
Attenuation characteristics of audiometric earphones fitted on children
Authors: Wright Diana C. , Bigger Mark E. , Frank Tom
Published: October 2005

The attenuation provided by TDH-49 earphones and ER-3A insert earphones was determined for 20 children (5–14 years old) using one-third octave bands of noise in a diffuse sound field (re: ANSI S12.6-1984). The TDH-49 earphones in P/N 51 cushions were fitted on each subject as normally done for audiometry. For the ER-3A, an appropriate size (small or normal) modified foam earplug was inserted into each subject's ear canal so that the outer edge was flush with the floor of the concha. The attenuation provided by the ER-3A was considerably greater than the TDH-49 at each frequency regardless of earplug size. Further, the attenuation provided by the ER-3A using the small (N = 10) or normal (N = 10) size modified foam earplug was similar. Comparisons with the attenuation provided by the TDH-49 and ER-3A using adult subjects and clinical implications relative to permissible ambient noise levels for audiometry will be discussed.
Bone conduction clicks and related observations
Authors: Durrant John D. , Hyre Rick , Piroth Walter W.
Published: October 2005

The frequency responses of bone vibrators, as measured on the artificial mastoid, and earphones, as measured on a 6-cc coupler, predict substantial differences in bone (BC) and air conduction (AC) clicks, which are evident perceptually. Since clicks continue to be used widely in clinical evaluations of brain-stem auditory evoked potentials (BAEPs), it seemed worthwhile to assess the effective frequency response of standard BC versus AC transducers. Steady-state stimuli were first used in a modified version of the SAL test. Although BC and AC differences were evident, they were not as great as suggested by coupler and artificial-mastoid measurements. In the same subjects, skull vibration was examined in response to BC clicks, using a miniature accelerometer. The results demonstrate propagationlike delays in BC stimuli applied and monitored at different points on the skull. Implications for BAEP measurement, utilizing BC click stimulation, are presented (supplemented by samples of recordings) and suggest greater similarities than differences in BC versus AC clicks. [Work supported by Ben Franklin Partnership, Commonwealth of Pennsylvania and Radioear Corporation.]
Influence of contralateral noise stimulation on wave I of the ABR, elicited with condensation and rarefaction clicks in humans
Authors: Rawool Vishakha W. , Heinz John M. , Pillion Joseph P.
Published: October 2005

Sound-evoked efferent effects can be examined by comparing the response amplitudes of the auditory nerve with and without contralateral stimulation. It has been suggested that the efferent system modifies the mechanical characteristics of the cochlear partition by varying outer hair cell tonus and regulating the mean position of the basilar membrane [E. L. LePage, Hear. Res. 38, 177–198 (1989)]. If this is the case, the effect of contralateral stimulation may be different for responses elicited with clicks of opposite polarity (condensation versus rarefaction), as such stimuli cause initial movement of the basilar membrane either toward scala tympani or scala vestibuli. Furthermore, such stimuli are known to elicit dissimilar ABR waveforms [V. Rawool and S. Zerlin, Stand. Audiol. 17 (1988)]. Results of the surface recorded wave of the ABR obtained from human subjects, with and without contralateral noise, for rarefaction and condensation clicks as well as the possible underlying mechanisms will be presented.
Repeated-measures auditory brain-stem responses (ABRs): Comparisons of stability profiles based on different time schedules
Authors: Lauter Judith L. , Lord-Maes Jan
Published: October 2005

Demonstrations of dramatically increased information from ABRs based on variability analysis [J. L. Lauter and R. L. Loomis, Scand. Audiol. 15, 167–172 (1986); 17, 87–92 (1988); J. L. Lauter and R. G. Karzon, Scand. Audiol. (in press)] have to date all been based on within-subject series of weekly test sessions. Toward making repeated-measures EPs more feasible as a research and clinical tool, the current experiment compares ABR stability profiles based on different test schedules: four waveforms per ear of presentation collected from each subject with (1) minimal separation between ear sets (i.e., four right-ear, left-ear, and binaural waveforms, all collected within the same 1-h session), (2) 1-h separation between ear sets, and (3) 1-week separation between ear sets. Results to date indicate (1) very good matches between stability profiles based on same-session versus weekly collections, validating an earlier claim that these profiles reflect real individual characteristics; and (2) distinctions between profiles from these two schedules versus the hourly collections, possibly reflecting the influence of diurnal variations in ABRs reported by earlier research [Kerkhof et al., Neurosci. Lett. 16, 11–15 (1980)]. [Work supported by AFOSR.]
Nondestructive evaluation of ceramic preforms
Authors: Goodlin Drew L. , Conway J. C. , Pangborn R. N. , Tittmann B. , Green D. J.
Published: October 2005

In order to identify and eliminate flawed ceramic preforms prior to metal infiltration, several approaches for nondestructive evaluation were studied. The techniques chosen include immersion ultrasonics, scanning acoustic microscopy (SAM), and radiography. Undesirable irregularities in the preforms include cracks, voids, density gradients, and shot. The latter represents spherically shaped particles of alumina, with diameters that may exceed ten times that of the fibers, and that are incorporated into the porous fiber preform. It is generally thought that shot with sizes greater than 100 μm affects the mechanical properties of the resulting metal matrix composite. With the aid of SAM and scanning electron microscopy (SEM), shot in near-surface areas could be evaluated. Cracks and voids could also be located using SAM and SEM. On a larger scale, the ultrasonic immersion equipment was capable of detecting and quantifying density gradients, which were verified using radiographic techniques. Examples will be given to illustrate the sensitivity and resolution of the various techniques with regard to examination of the flawed preforms. [Work supported by Center for Advanced Materials, Pennsylvania State University.]
Elastic wave scattering from debonded fibers in composite materials
Authors: Kim Yong Woo , Varadan Vasundara V. , Lakhtakia Akhlesh
Published: October 2005

A modified null-field approach has been applied to study the elastic wave scattering response of an inclusion with an interface crack; e.g., a rotationally debonded fiber in a fiber-reinforced composite. A fictitious mathematical surface to include the debonded region is introduced. Appropriate field expansions are introduced in all regions of interest, and used in integral representations. After using the orthogonality properties of the expansion functions, a T matrix is obtained to relate the scattered field to the incident field. The range of validity is checked for computational purposes. Scattering cross sections of infinitely long debonded fibers are computed as functions of frequency and the extent of debonding for P-, SV-, and SH-plane wave incidence conditions.
Acoustic emission testing of fiber composite materials
Authors: Dent Alan M. , Bakis Charles E.
Published: October 2005

Acoustic emissions (AE) can be used to nonintrusively monitor and, in some instances, characterize the progression of damage in composite materials during deformations. In the present investigation, AE from graphite epoxy tape laminates and acrylonitrile butadiene styrene (ABS) specimens with and without short glass fibers were monitored and analyzed during cyclic loadings and monotonic proof tests. Usual AE parameters such as hits, counts, and amplitude were correlated with spectral analyses of acoustic emissions recorded during various portions of the loading waveform. Due to bandpass limitations of the acoustic emissions device, few correlations of the spectral content of the acoustic emissions could be made with the loadings or mechanisms of damage. However, some useful information for users of the AE technique was obtained from a wideband spectral analysis measurement made with the acousto-ultrasonic (AU) technique. With the simulated acoustic emission events generated with the AU technique, it was shown that physical parameters such as transducer resonance, source-to-receiver distance, specimen geometry, and material properties such as fiber orientation and composition have distinct and reproducible effects on the measured spectral response.
New panel measurement methodologies relevant to damping material characterization
Authors: Piquette Jean C.
Published: October 2005

New techniques for evaluating measurements acquired in panel calibration tests are described. A summary of the ONION panel-measurement method is provided. This method is based on least-squares fitting of panel calibration data to a multiple-layer panel model. The technique produces not only the reflection and transmission coefficients for the sample panel, but also sound speeds and losses for each individual panel layer as a function of test temperature, test pressure, and test frequency. Applications of the technique to data acquired using a normal-incidence interrogating wave, as well as to data acquired using an offnormal incidence interrogating wave, are discussed.
Active underwater acoustic damping coating
Authors: Varadan Vijay K. , Howarth Thomas R. , Bao Xiaoqi , Varadan Vasundara V.
Published: October 2005

An active control coating for the absorption of normally reflected acoustic pressure waves is presented. This polymer matrix coating encapsulates large area polyvinylidene fluoride (PVDF) plates for characterization of the impressed acoustic field and a piezocomposite actuator for the absorption of the reflected acoustic pressure. The sensing and actuating devices are connected via an external electronic network. Background analysis will describe the adopted system and component methodologies. Experimental data of the individual components and the complete system, as measured in a underwater acoustic pulse tube, will be presented.
Comparison of dielectric and Young's modulus in four types of elastomers
Authors: Burns J. , Capps R. N. , Dubbelday P. S.
Published: October 2005

Underwater Sound Reference Detachment, Naval Res. Lab., P.O. Box, 568337, Orlando, FL 32856-8337. The complex Young's modulus is compared with the complex dielectric modulus in four different types of elastomer in the rubbery regime above the glass transition temperature. The elastomers measured included 5109G unfilled neoprene, PR1526 polyurethane, 334-270 natural rubber, and B252 butyl rubber. Results of the comparison support the view that there is a correspondence between the two effects as predicted from thermodynamic considerations. Possible models for the coupling are discussed.
Shear and pressure wave transmission into and through elastomeric layers on infinite plates
Authors: Alberghini John C. , Burroughs Courtney B.
Published: October 2005

An analytic model for the transmission of shear and pressure waves into and through an elastomeric layer on an elastic infinite plate is developed. The effects of fluid viscosity on the transmission of incident pressure waves into and through the layers are assessed. The dependencies of the transmission of pressure waves through the layer into the transverse vibration response of the plate on wavenumber and frequency, and coating and plate geometric and physical properties are explored by example.
The wavenumber-frequency filtering characteristics of compliant layers
Authors: Phillips James E. , Burroughs Courtney B. , Hughes W. Jack
Published: October 2005

Techniques for the measurements of the wavenumber-frequency filtering characteristics of compliant layers mounted on an elastic structure and subject to unsteady pressures were developed. In order to measure the performance of the layer at arbitrary wavenumbers and frequencies, an array of shakers was fabricated and used to generate a standing wave pattern of the input forces where the maximum spectrum levels of the input forces could be concentrated at selected wavenumbers independent of the selected frequency. The wavenumber-frequency admittances of a coated and uncoated beam were measured and used to determine the effectiveness of compliant layers in reducing the vibration response of the beam as a function of wavenumber and frequency. Arrays of thin-film transducers were designed, fabricated, and used to measure the wavenumber-frequency pressure spectra above and below compliant layers. The measured wavenumber-frequency pressure spectra were then used to determine the wavenumber-frequency transmission loss of compliant layers as a function of wavenumber and frequency.
Reduction of plate vibrations by fluid-layer attenuators
Authors: Önsay Taner , Akay Adnan
Published: October 2005

Experimental results on the attenuation of bending vibrations of a plate by a thin layer of fluid applied at different locations of the plate surface are presented. Small stiff blocks were positioned parallel to a thin plate where a layer of air is squeezed by the transverse vibrations of the plate. Effects of layer thickness and the location of the blocks on the attenuation of plate vibrations are discussed. For fluid gaps of the order of the viscous boundary layer thickness, up to 37-dB reduction of modal amplitudes were obtained. Highest attenuations were achieved by positioning the blocks near the antinodes of the free-plate modes. It is shown that selective modal attenuation can be obtained by adjusting the location of the attenuators. [Work supported by NSF.]
Effects of large-scale wind-driven turbulence on sound propagation
Authors: Noble John M. , Bass Henry E. , Raspet Richard
Published: October 2005

A large-scale wind-driven turbulence model is put forth to account for long-term (1–5 min) phase variations observed in outdoor sound propagation experiments. The long-term variations experimentally observed cannot be explained with small-scale turbulence models. Fourier analysis of phase variations show outer scales of 200 m and greater, which corresponds to turbulence in the energy-containing subrange. Turbulence in this region corresponds to turbule sizes as large as the planetary boundary layer. The large-scale turbulence in the boundary layer is assumed to be elongated longitudinal vortex pairs roughly aligned with the mean wind. Large-scale turbulence is a range-dependent problem that is best handled by the parabolic equation. The parabolic equation is a solution to the one-way wave equation that is applicable to sound propagation where back-scattered energy is negligible. The algorithm computes the pressure and phase at a receiver as the vortex pair traverses the propagation path with the mean wind speed. The model provides good results with the same trends and variations in the magnitudes of the phase observed experimentally.
Turbulent scattering in an upward-refracting atmosphere
Authors: Gilbert Kenneth E. , Di Xiao , Wang Lintao , Raspet Richard
Published: October 2005

Weiner and Keast observed that in an upward-refracting atmosphere the relative sound pressure level versus range follows a characteristic “step” function that depends strongly on the sound-speed gradient but weakly on frequency [J. Acoust. Soc. Am. 31, 724–733 (1959)]. The observed step function has recently been predicted qualitatively and quantitatively by including the effects of small-scale turbulence in a parabolic equation (PE) calculation [Gilbert, Raspet, and Di, J. Acoust. Soc. Am. Suppl. 1 80, S209 (1988); J. Acoust. Soc. Am. (to be published)]. The present paper presents results from a simpler calculation based on a single scattering approximation. The purpose of the calculation is to obtain a better understanding of the physical mechanisms that produce the step function. As an initial test, an analytic single scattering calculation is compared to the PE calculation for a nonrefracting atmosphere. For upward-refracting atmospheres, the unscattered upward-refracted field is numerically integrated in a distorted-wave single scattering calculation. The results are compared to the PE calculation and to the data of Weiner and Keast. [Work supported by ONR.]
Uniform formulation of the problem of distortion of sonic booms or bangs by atmospheric turbulence
Authors: Pierce Allan D.
Published: October 2005

A now-classic paper relating to wave propagation through turbulence is S. C. Crow's “Distortion of sonic bangs by atmospheric turbulence” [J. Fluid Mech. 37, 529–563 (1969)]. Crow treats the linear acoustics problem of an (initially) step discontinuity in pressure (weak shock} propagating through a nominally uniform atmosphere with weak turbulence superimposed, uses a first-order perturbation theory to determine the turbulence-induced corrections to the waveform, and obtains some simple predictions concerning the variance at times somewhat later than shock onset, which have subsequently been well confirmed by field data. The singular nature of Crow's solution near the nominal time of shock onset, however, has always been somewhat disquieting to the present author, so a formulation is here given that avoids this singularity using a version of the method of strained coordinates. The recently derived approximate wave equation [Pierce, J. Acoust. Soc. Am. (in press)] for wave propagation through a fluid with inhomogeneous unsteady flow is used as a starting point. The solution for the acoustic pressure is taken in the form of a rippled wavefront (Δp)(1 + ψ)H(1 − c−1x + φ), where φ is a function of position, while ψ is a function of position and time. Here, H(t) is the Heaviside unit step function and Δp is the nominal pressure jump at the start of the boom. Linear perturbation equations governing the functions φ and ψ are developed and solved by approximate methods. [Work supported by NASA Langley Research Center and by the William E. Leonhard endowment to Pennsylvania State University.]
System attractor dynamics for a low-frequency acoustical signal propagated in the atmosphere
Authors: Henderson Harry W. , Wilson D. Keith , Thomson Dennis W.
Published: October 2005

An experimental study of low-frequency propagation over flat terrain has been previously reported [J. Acoust. Soc. Am. Suppl. 1 86, S120 (1989)]. The sound pressure level of a 27.7-Hz acoustical source was monitored at a distance of 770 m, the level being recorded at 1-min intervals over a 5-day period in March 1989. Additional micrometeorological measurements of the turbulent momentum, heat, and moisture fluxes were made adjacent to the path, and a Doppler sodar was used to monitor the boundary layer wind profile. We have now analyzed the signal for the system attractor size, and found it to possess an unexpectedly small dimension of about 2.3. A low-order reconstruction of the dynamical phase space revealed that most of the measurements fell within a small portion of that space, but spurious noise on the microphone showed large excursions. Implications for signal smoothing, interpolation, or rejection that are based on reconstructed system dynamics are discussed and illustrated.
Models of speech production for speech analysis and synthesis
Authors: Sondhi M. M.
Published: October 2005

Coding (i.e., analysis and resynthesis) of speech signals on the basis of physiological models of speech production mechanisms has received considerable attention during the past several years. One of the reasons for this renewed interest is that the known coding algorithms give unacceptably poor quality of speech at low bit rates (e.g., at 2400 bits/s). A coding scheme that mimics human speech production may have advantages at such low bit rates. Basically, three aspects of speech production need to be modeled. First, the geometry of the vocal and nasal tracts needs to be parametrized. Second, a model must be selected to describe wave propagation in the tract. Finally, the sound sources (vocal cords and turbulent airflow) and their interactions with the tract must be modeled. In this talk the current models being used for each of these categories will be briefly described, and the way in which these models are employed for coding will also be described. Also, the use of such models for text-to-speech synthesis will be mentioned. Finally, some examples of speech produced by such models, both from text as well as by analysis and resynthesis of a given speech utterance will be played.
Simulations of the second-order nonlinear effects near hard and porous ground surfaces due to small explosion waves
Authors: Sparrow Victor W. , Raspet Richard
Published: October 2005

Over the last several years a 2-D finite difference acoustic propagation program for finite amplitude interactions has been developed at the University of Illinois and USA-CERL. In this presentation the addition of the numerical coupling of the air to the hard surface and porous media models of the ground will be described. The porous model used was the time-dependent form of the phenomenological model presented by Morse and Ingard as interpreted by Attenborough for low frequencies [K. Attenborough, J. Acoust. Soc. Am. 73, 785–799 (1983)]. Simulation results will be presented for the nonlinear pressure variations evident due to the cumulative interactions along the air-ground interface for small explosions, when the ground was either hard or porous. [Computations performed at the National Center for Supercomputing Applications, Champaign, IL.]
Sound radiation from a vibrating body in relative motion with its surrounding medium
Authors: Wu Xiao-Feng , Akay Adnan
Published: October 2005

As an extension of the authors' previous work [J. Acoust. Soc. Am. Suppl. 1 83, S77 (1988)], this paper considers sound radiation from a vibrating body in relative motion with its surrounding medium, namely, either a vibrating body radiating sound into a homogeneous inviscid fluid in uniform motion or a moving vibrating body radiating sound into a stationary inviscid fluid. The resulting sound fields in both cases can be expressed in terms of volume integrals and surface integrals based on the exact theory of Lighthill's acoustic analogy and generalized function theory. However, quantities involved in the volume integrals are not known a priori. Determination of these quantities is equivalent to solving an inhomogeneous wave equation governing the entire flow field, which is virtually impossible for most problems of interest. This paper shows that for a vibrating body in constant and rectilinear relative motion with its surrounding medium, the volume integrals can be transformed into surface integrals. Consequently, the acoustic field can be completely determined given the boundary conditions on the vibrating surface. The total radiated power is calculated and shown to be greatly enhanced by the Mach number. [Work supported in part by ONR, NSF, and Institute for Manufacturing Research at Wayne State University.]
Control of sound-induced boundary layer transition over a flat plate
Authors: Maestrello L. , Grosveld F. W.
Published: October 2005

Delay of boundary layer transition induced by upstream sound on a flat plate with a leading edge is demonstrated experimentally at low speed using localized surface heating. The experiment deals with the receptivity of the laminar boundary layer to an upstream acoustic disturbance incident at the leading edge. This disturbance is a source of transition in many wind tunnels. The laminar boundary layer at the leading edge reacts to very small external unsteady disturbances due to a stream wise gradient in pressure. The experiment demonstrates that a nominal sound pressure level incident at the leading edge can effectively trigger early transition. By activating a localized heat source at the leading edge transition can be delayed.
Optical holographic characterization of a radio ear bone vibrator
Authors: Hayek Emil R. , Pechersky Martin J. , Stuart Alan D.
Published: October 2005

Bone vibrators are driven by an electrodynamic transducer that is suspended from the upper portion of the vibrator's case; while the lower portion of the case is mounted on the area above the subject's mastoid. As a result, the structural response of the vibrator's case plays an important role in the overall transfer function from the electrical input to the mastoid input. Holographic investigations of the case mode shapes at resonances up to 5 kHz were performed to supply data for input into a semiempirical model of the bone vibrator. Optical holography was chosen since the small size and mass of this transducer precluded any type of measurement that involved contact. Measurements were performed for both hard mounting of the bone vibrator and with the bone vibrator mounted on a Beltone model MB5 artificial mastoid. Time-averaged holograms of the case resonances were recorded on a thermoplastic holographic plate and transformed into digital images in a microcomputer-based image processing system. They were then analyzed to determine the details of the vibrations.
Nearfield acoustic holography in cylindrical spaces
Authors: Konzelman Charles J. , Burroughs Courtney B.
Published: October 2005

Nearfield acoustic holography is used to reconstruct the velocity distribution of an acoustic source located in a cylindrical space. Two reconstruction algorithms have been developed, both of which account for the boundary effects of the cylindrical walls. The first algorithm models the space as an infinite duct, while the second models the space as a finite duct. A known source velocity distribution is used to simulate a pressure field in the space. Pressures on the holography surface are processed by the holography algorithms to reconstruct the source velocity distribution. The results of the algorithms are compared, with particular attention to the sensitivity of reconstructions to the location, number, and spacing of sensors, aperture lengths, and measurement noise.
Application of laser holographic interferometry to vibration response of highly damped structures
Authors: Xu Zhaoshun , Önsay Taner , Akay Adnan
Published: October 2005

Application of laser holographic interferometry to the measurement and analysis of the response of highly damped structures is shown. Time-averaged holograms were made for the lower modes of a thin steel plate whose damping was adjusted by an air layer attenuator. Damping of the plate was varied from very light to overdamped by adjusting the air layer thickness of the attenuator. Vibration response amplitudes were recovered from the holographic fringe patterns. As expected, for low damping, the results correspond to free vibration mode shapes. As damping was increased to overdamped conditions, the zero-order holographic fringe, corresponding to the nodal line, was replaced by higher-order fringes. A series of holograms are presented which shows the degeneration of the undamped mode shapes. [Work supported by NSF.]
Comparison of nearfield and farfield structural intensity by scanning laser vibrometry
Authors: Suen Benjamin C. , Hayek Sabih I. , Pechersky Martin J. , Stuart Alan D.
Published: October 2005

A new measurement technique is being developed to measure true nearfield and farfield structural intensity by remote sensing and noncontacting instrumentation. A system composed of a scanning laser vibrometer with computer-controlled optical scanner allows for noncontacting measurement of the amplitude and phase of the vibration velocity of a structural member. The laser vibrometer has a dynamic range of 160 dB and broadband frequency response of up to 25 kHz. The vibrometer is held steady on a seismically isolated optical table and a mirror is positioned accurately by a computer-controlled stepper motor. The measurement of nearfield or farfield structural intensity at a point requires the measurement of the structural velocity at a minimum of four points for a beam and eight points for a plate about that point. Thus the amplitude and phase of the velocity field on the surface of a structure is measured at a fine mesh of discrete number of points. Error analysis is performed to assess the theoretical error introduced by the mesh size, number of points used for evaluating the structural intensity, random phase and amplitude errors, and errors introduced by nonsimultaneous measurements.
Improving performance for matched-field processing
Authors: Ozard John M. , Dean Charlene L.
Published: October 2005

Minimum energy beamforming (MEB) is frequently employed in matched-field processing (MFP) because it is optimal for the noise field prevailing at the time of measurement. However, when signal phase errors or mismatch are present, MEB is no longer optimal for signal detection. Under such conditions various methods such as reduced minimum energy beamforming (RMEB), modal beamforming, and dimension reduction have been employed. For vertical arrays, these methods have been shown to be virtually identical and to improve performance dramatically over that obtained with MEB. In this paper RMEB is extended to arbitrary array configurations and the normalizations of the ambiguity surface for various noise fields are investigated. The generalized form of RMEB is shown to produce significantly improved performance for both vertical and horizontal arrays and thus demonstrates the benefits of modal style beamforming for horizontal arrays. The improved performance was obtained for both modal and isotropic noise fields. An eigenvector decomposition of RMEB shows that the underlying cause for improved performance for both horizontal and vertical arrays is similar.
Matched-field processing of 200-Hz cw data
Authors: Tran Jean-Marie , Hodgkiss W. S.
Published: October 2005

The 200-Hz cw data were collected in the NE Pacific with the Marine Physical Laboratory's acoustic vertical line array (a 900-m aperture with 120 sensors) and processed with matched-field processing (MFP) techniques. The environmental information collected during the experiment was used with a normal mode model assuming a range-independent medium to generate full wave field replica vectors for various array tilt angles. The MFP ambiguity surfaces were calculated using the Bartlett and minimum variance processors for two input signal-to-noise ratios (− 9.2 and 11.8 dB) and were characterized by localization and processing gain performance indices. The acoustic modeling leads to the detection and localization of the source near its expected location (20-m depth and 165-km range). While the minimum variance processor lacks robustness, the MFP Bartlett processor produces more processing gain than the conventional FFT beamformer and, for a 0.4° array tilt angle, has an estimated array gain only a few dB below its theoretical value of 21 dB. [Work supported by ONR.]
Source localization of an acoustic target by artificial neural networks
Authors: Chin Steven H. , Howard, Jr. James H.
Published: October 2005

The problem of source localization of an acoustic target is studied in the context of neural networks. A performance evaluation is given for different source/array configurations. The means by which a neural network, employing backpropagation, can generalize this problem for accurate source localization is discussed based on experimental results. The application of these findings to practical situations is examined.
Time-domain Doppler expression: Implications for three-dimensional acoustic scattering
Authors: Brill Michael H.
Published: October 2005

The Doppler effect is equivalent to warping of the transmit time of a signal as registered by a receiver. This warping occurs when source, reflectors, and/or receiver move relative to the transmitting medium. It can be shown that the relative Doppler shift of a cw signal is Q = (f − f0)/f0 = 1/(dT/dt + 1) − 1, where f0 and f are the transmitted and received frequencies, T is the propagation delay from source to receiver, and t is the transmit time. In one dimension [S. Braun, J. Acoust. Soc. Am. 59, 1495–1497 (1976)], constant source and receiver velocities cause this time-domain formulation to replicate the textbook expression for Q (in a homogeneous medium with sound speed c). In two or three dimensions, a single source and receiver give an expression that differs from the textbook expression at second order in quantities v/c. Finally (and startlingly), a reflecting path causes Q to depend on the distance from source to reflector (R 1) relative to that from reflector to receiver (R 2). When R 1 ≫ R 2, the exact expression for Q can differ from the textbook expression at first order in v/c. Implications of these results are noted for underwater frequency shifts and spreads.
Performance bounds for the overlap-correlator synthetic aperture technique
Authors: Edelson Geoffrey S. , Sullivan Edmund J.
Published: October 2005

The performance bounds on a new high-performance method for passive acoustic synthetic aperture array processing are computed. The overlap-correlator synthetic aperture technique [S. Stergiopoulos and E. J. Sullivan, J. Acoust. Soc. Am. 86, 158–171 (1989)] is a method whereby the effective aperture of a towed array in the passive mode can be successfully extended. This is achieved by using the existing aperture of the physical array to estimate the phase correction factor for the successive measurement, thus eliminating the need for accurate knowledge of the source frequency when computing the phase correction factor. The performance bounds on the bearing error variance are given as a function of signal-to-noise ratio, the number of elements in the physical array, and the size and number of the overlaps. These bounds are then compared to the corresponding Cramer-Rao bounds for static line arrays and towed synthetic aperture line arrays. Results using both simulated and real data will be presented.
Detection of across-frequency differences in F0
Authors: Carlyon Robert P.
Published: October 2005

Listeners were required to discriminate between pairs of complex sounds. The standards consisted of two groups of harmonics, 1 to 5 and M to N, of a common fundamental. The signals differed from the signals in that either the F0 of harmonics 1 to 5 was decreased and that of harmonics M to N increased (“stretched condition”), or vice versa (“compressed condition”). To prevent listeners from basing discrimination on the F0 of a single group of components, the overall F0 was varied by randomizing the playback rate from presentation to presentation. Psychometric functions revealed that performance was better for M = 9, N = 19 than for M = 11, N = 21, and was better in the compressed than in the stretched condition. Thresholds were measured as a function of N − M using an adaptive procedure, with M always equal to 11. They agreed with those predicted from the psychometric functions when N − M = 11, and increased as N − M dropped below 5. However, the size of the increase varied markedly across listeners and conditions, probably due to the existence of weak timbre cues. The effects of limiting timbre cues will be described, and the implications of the results for the perceptual separation of concurrent sounds discussed.
Pattern recognition memory spans: Effects of frequency, intensity, and duration
Authors: McFarland Dennis J. , Cacace Anthony T.
Published: October 2005

A three-interval, three-alternative forced choice adaptive psychophysical procedure was used to examine the effects of stimulus frequency, intensity, and duration on pattern recognition memory. Stimuli were digitally synthesized and controlled by a computer system that interleaved test series between left and right ears. Just-noticeable differences (jnd's) in isolation were first determined for frequency (Hz), intensity (dB), and duration (ms), using 70-dB SPL, 200-ms, 1000-Hz pure tones in four well-practiced subjects. Next, subjects were presented randomly generated binary patterns differing along one of the stimulus dimensions at 4, 8, or 12 jnd's. In each run, two of the patterns were the same and one was different. The subjects' task was to select the odd pattern. The system adapted on the length of the pattern. ANOVA on span length indicated that the effects of stimulus dimension (p < 0.001) and jnd magnitude (p < 0.001) were significant. Post hoc analyses indicated that span length was significantly longer for frequency as compared to intensity and duration patterns. Thus frequency information is of particular importance to the encoding of stimuli in acoustic short-term memory.
Within- and cross-channel mechanisms in the detection of frequency modulation coherence and incoherence
Authors: McAdams Stephen , Marin Cécile M. H.
Published: October 2005

Mechanisms involved in the detection of frequency modulation coherence and incoherence in harmonic sounds were studied. In a 14-component harmonic series, subsets of one or more components were modulated coherently among themselves, but independently of the rest. The locus of target harmonics in the series was varied, as was their disposition: adjacent or interleaved with the background. Subjects were presented a test tone containing a target subset and a comparison tone with no target. The modulation coherence of the comparison was the same as that of the test tone background. The task was to detect which of two 500-ms intervals contained the target tone. Threshold was measured as function of frequency modulation width. For coherent backgrounds, thresholds generally decreased as a function of the relative proximity of target and background components. However, results from stimuli with incoherent backgrounds indicate that detection thresholds were closely related to the distribution of regions of relative coherence and incoherence across auditory channels, implying a mechanism of cross-channel comparison.
Detection of unexpected signals: Effect of shifts in response criteria
Authors: Small Arnold M. , Parker Barbara J.
Published: October 2005

The percentage of trials in which listeners were able to detect (in a single-interval, forced-choice task) a faint expected signal compared to an unexpected signal was determined when the signal was a click presented in a noise background. The signal was positioned 0.5 s from the beginning of a 1.5-s observation interval in 80% of the signal trials and elsewhere in the interval in the remainder. Detection of the unexpected signal was best when it occurred close to the expected temporal position. An analysis of the false alarms following each type of trial—expected signal, unexpected signal, and noise only—showed no differences. It is argued that differences would have been anticipated if degradation of performance for remotely positioned, unexpected signals had been a result of changes in the listener's response criterion. Alternatively, these findings are interpreted to indicate that performance was related to attentional factors that influenced detection directly, perhaps through a temporal window analogous to a critical band in the frequency domain.
Comodulation masking release (CMR) using speech stimuli
Authors: Grose J. H. , Hall J. W.
Published: October 2005

Most investigations of CMR have examined the threshold detection of a tonal signal. However, the ecological significance of CMR would be bolstered if it could be shown that CMR contributes to the discrimination of suprathreshold signals, in particular speech. As a first step toward examining this possibility, six monosyllabic words, differing only in their vowels, were used as stimuli. These were filtered into three narrow passbands, each 40 Hz wide, centered on 445, 890, and 1780 Hz, and then equated for overall rms pressure. The threshold discrimination of this (much-degraded) speech was measured under three masking conditions. The first consisted of three narrow bands of comodulating noise, each 40 Hz wide, centered on 445, 890, and 1780 Hz. The second consisted of these same three bands but with an additional 12 bands now mixed with them, and all 15 bands coherently modulating. The center frequencies of the additional 12 bands were 245, 345, 545, 645, 765, 1015, 1140, 1265, 1380, 1580, 1980, and 2180 Hz. In the third condition, the additional 12 bands were presented only to the contralateral ear. Discrimination thresholds were generally lower in the 15-band monaural masker than in the 3-band masker; the presence of a dichotic effect was less marked. An appreciable overall learning effect was observed. [Research supported by NIDCD.]
Effect of attentional demands and auditory memory degradation on vowel discrimination
Authors: Fox Robert Allen
Published: October 2005

This study explores the effects of attentional demands in a vowel discrimination test when auditory memory has been degraded by irrelevant intervening nonspeech stimuli. The experiment utilized a same—different (AX) discrimination task with both within- and between-category pairs from an [i-I-ɛ] continuum. The interstimulus interval was 2000 ms in duration and was filled either with silence or 1, 2, or 3 short noise bursts. Listeners were required to make pairwise discriminations under two different attend conditions: (1) They either ignored any possible noise burst in the ISI and made only same/different judgments or (2) they made the same/different judgments and then indicated how many noise bursts occurred. Neither the noise condition nor the attend condition produced significant difference on the within-category discriminations. Increasing the number of noise bursts affected the listeners' ability to make between-category discriminations but there were no significant attend condition effects. Possible differences between younger and older adults will be addressed in terms of short-memory availability and/or attentional effects in speech discrimination. [Supported by Grant 1 R01 AG08353-01 from the National Institute on Aging.]
Psychoacoustic evidence for a contextual effect model
Authors: Akagi Masato
Published: October 2005

In previous work toward speech recognition [M. Akagi, J. Acoust. Soc. Am. Suppl. 1 85, S86 (1989)], a model was developed that predicted target formants in reduced vowels based on the interaction between spectral peak pairs. To substantiate this model, two psychoacoustic experiments were carried out that measured the amount of phoneme boundary shift with (1) a single-formant stimulus as a preceding anchor and (2) a vowel as a preceding anchor. The results of the first experiment were compared with the spectral peak interaction obtained from real speech data using the model. This comparison showed that the perceptual boundary shift with a single-formant anchor is similar to the spectral peak interaction analyzed by the model. Thus the neutralization recovery model is formulated as the sum of the contextual effects resulting from interaction between spectral peaks. Additionally, the comparison of these results with those of the second experiment showed that the phoneme boundary shift with a vowel anchor can be postulated as the sum of the shift with the single-formant anchor and a feedback factor from the perceived preceding anchor.
The role of the critical band in learning vowel categorizations
Authors: Weitzman Raymond S.
Published: October 2005

The role of the critical band in learning to categorize steady-state, synthesized vowels was examined in a series of concept formation experiments. Five groups of subjects were given the task of learning to assign sets of vowels, whose only difference was in the frequency of F2, to one of two possible categories, and were then tested to see how well they learned them. The sets of vowels in each experiment differed from each other on average by 0.4, 0.6, 0.8, 1.0, or 1.2 Bark. In the learning phase of the experiment, it was found that the error rate in categorizing vowels that differed by 1.0 and 1.2 Bark was significantly lower than the error rate in categorizing vowels that differed by 0.4, 0.6, and 0.8 Bark. Furthermore, the test phase of the experiment showed that over 60% of the subjects learned the two categories when they differed by 1.0 and 1.2 Bark, while less than 23% learned the two categories when they differed by 0.4, 0.6, and 0.8 Bark. The implications of these findings will be discussed.
Thresholds for formant-frequency discrimination in isolated vowels
Authors: Kewley-Port Diane
Published: October 2005

The threshold of discrimination (or DL) of a shift in formant frequency is thought to be in the range of 3%-6%, based on the oft-replicated results of Flanagan [J. Acoust. Soc. Am. 27, 613-617 (1955)]. This range may not, however, represent the limits of resolution in the auditory system because, for most experiments, subjects were not trained and several pairs of stimuli were presented within trial blocks. In present experiments, thresholds were obtained from well-trained subjects listening to vowels under minimal stimulus uncertainty using an adaptive-tracking paradigm. Thresholds were determined for increments and decrements in F 1 and F 2 for ten synthetic, steady-state vowels modeling a female talker. Results indicated that the DL for both increments and decrements in frequency of the formants increased linearly as a function of frequency, with the exception of 50% higher thresholds where a harmonic fell exactly on the formant frequency. About 80% of the ΔF/F ratios were below 0.02 for formant frequencies greater than 600 Hz. Thus the DL for formant-frequency discrimination appears to be in the range of 1%-2%, or a factor of 3 lower than previous estimates. [Research supported by NIH and AFOSR.]
Vowel perception: Spectral shape versus formants
Authors: Jagharghi Amir J. , Zahorian Stephen A.
Published: October 2005

Traditional theories of vowel perception favor formants over global spectral shape as the primary perceptual cues to vowel identity. In previous ASA meetings, results of speaker-independent automatic recognition experiments for vowels were reported that contrasted global spectral shape versus formants [A. J. Jagharghi and S. A. Zahorian, J. Acoust. Soc. Am. Suppl. 1 81, S18 (1987); S. A. Zahorian and A. J. Jagharghi, J. Acoust. Soc. Am. Suppl. 1 82, S37 (1987)]. These results indicate that automatic recognition rates based on global spectral shape are generally slightly superior to recognition rates based on formants. In the present study, the perception of vowels is investigated for vowels synthesized such that the synthesized tokens contain conflicting cues to vowel identity based on overall spectral shape versus formants. Two distinct but close vowels are selected. The spectral shape of the first vowel is modified to match, to the extent possible, the spectral shape of the second vowel without any change in the formant frequencies for F1, F2, and F3. Thus the modified vowel has the same formants as the first vowel, but its spectral shape matches that of the second vowel. Listening experiments indicate that, for most conditions, the modified vowel segments are perceived according to spectral shape cues rather than formant cues. The details of the experimental procedures and the results of the listening experiments will be presented at the meeting. [Work supported by NSF.]
The role of peak amplitude in vowel recognition
Authors: Garrison-Shaffer L. , Dutton D. L. , Sawusch J. R.
Published: October 2005

Many theories of speech perception rely on the loci of spectral peaks as at least one factor upon which pattern recognition is based. However, when a peak is lower in amplitude than its neighbors, it may not be used in phonetic recognition. In the first experiment, a [u]-[i] series was constructed by manipulating the amplitude of a spectral peak (851 Hz). Subjects readily identified an item from the series with a low-amplitude, 851-Hz spectral peak as an [i]. It would appear that this peak, at a low amplitude, is not used at a phonetic level of processing. Further experiments test the perceptual locus of the use (or nonuse) of this low-amplitude peak information. Selective adaptation experiments were run in which the adaptors, including the [i] from the first experiment, varied in spectral overlap with a [u]-[u] test series in order to determine the degree to which the low-amplitude, 851-Hz peak is utilized in processing. The results will be discussed in terms of how peaks are analyzed at different levels of processing and how this relates to various theories of speech perception. [Work supported by NIDCD DC00219.]