bluuebunny/crossref_metadata_2025 huggingface dataset:
Seafloor mapping and 3-D visualization: An integration of technologies providing new insights into seafloor processes
Authors: Mayer Larry A. , de Moustier Christian
Published: July 2002

The past few years have seen rapid advancements in sonar development, in vessel orientation and positioning technology, and in our ability to manage and visualize the massive amounts of data that modern seafloor sonars are capable of collecting. The confluence of these technologies has resulted in revolutionary changes in our ability to map and visualize the seafloor. Until recently, maps of the seafloor were based on the interpolation (typically through the construction of contours) of sparsely spaced discrete soundings or lines of soundings. With the advent of multibeam or swath-sonar technology, we can now produce near-100% coverage of large areas of the seafloor with high resolution (both vertical and horizontal) in a timely and cost-effective manner. More recently multibeam sonars have also begun to collect coregistered acoustic backscatter information (and inteferometric sidescan sonars have begun to collect coincident bathymetric information), potentially providing information on the composition (texture or material type) as well as the morphology of the seafloor. When combined with modern interactive 3-D visualization tools, these new data sets result in a radically different representation of the seafloor than that provided by traditional echo sounders that can lead to unprecedented levels of understanding of seafloor processes.
Mode analyses in a fluid-filled borehole surrounded by a concentrically layered formation
Authors: Wang Xiuming , Dodds Kevin
Published: July 2002

Acoustic wave modes including normal modes and leaky modes in a fluid-filled borehole surrounded by a concentrically layered medium are analyzed. Dispersions and excitation spectra of various modes related to monopole, dipole, including hexapole, octepole, and decapole sources, are calculated for typical well logging environments. The numerical results demonstrate that the cutoff frequencies of nonsymmetrical modes vary greatly with the orders. A Stoneley mode has no cutoff frequency in a fast formation, while at a very slow formation, it possesses a cutoff frequency. Multiple pseudo-Rayleigh modes, flexural modes, and the other higher modes have their correspondent cutoff frequencies. As frequency decreases from the cutoff frequencies, these modes correspond to the complex pole on the other Riemann sheets and become leaky modes. Also, followed by our previous work (Wang et al., 1994, 1995), it is shown that head compressional and shear arrivals cannot be totally described by contributions of vertical branch cuts in a wave field representation when the Poisson’s ratio is larger than 0.36 for dipole and quadrupole sources. The numerical results also show that the radial penetration of the normal modes is very shallow. The Stoneley modes are limited to 10 cm for a typical logging environment for a lower frequency than 3 kHz.
New geometric sound absorbers
Authors: Warnaka Glenn E.
Published: July 2002

In a previous paper of the same name, two new geometric sound absorbers were discussed. The geometric absorbers use closely coupled quarter-wave resonators to absorb sound. Because the structures absorb sound by their configuration, they do not require the use of conventional porous or fibrous sound-absorbing materials and can be made of nearly any substance such as plastic, wood, metal, etc. The absorbers can be made very rugged and long-lasting for industrial, military, and outdoor use. The previous paper discussed two basic sound absorbers, configuration delta and flat absorber, but the paper concentrated on the former sound-absorber configuration. This paper will review configuration delta but will concentrate on describing the structure and performance of the flat absorber. This absorber can be made in a thin treament, less than 25 mm thick, that provides high acoustic absorption. A number of different designs will be shown, and the results of standing wave tube and reverberation room tests will be given. Combining the two treatments described in this paper provides a broad frequency range absorber that is both compact and rugged. Helmholtz resonators can also be used with the flat absorber concept, and this is discussed.
Noise attenuation using a parabolic muffler.
Authors: Zalben Jonathan
Published: July 2002

This project is a patent-pending muffler design with paraboloid baffle chambers to reduce noise pollution from internal combustion engines (especially those of lawn mowers and leaf blowers). After theorizing the most reasonable design, experiments were conducted on wood and steel (18 gauge) models. The experiments show that for a wood model, white noise produced by a radio is reduced from 80 to 64 dB (97.5% intensity reduction). The wood model amplifies sound for pure frequencies around 1000 Hz and attenuates at higher frequencies. The steel model attenuates engine noise by 75% with varying rates of attenuation for pure frequencies. [Work supported by Residents for a More Beautiful Port Washington, the Nassau–Suffolk Landscapers Association, and Port Washington School System.]
A malleable audio representation for data compression
Authors: Levine Scott N.
Published: July 2002

The boundaries between audio data compression and audio synthesis/modifications are blurring as research in both fields progresses. New results using a sines + transients + noise parametric representation allows for coding gains as efficient as the most recent nonparametric transform coding schemes. Because the audio input is decomposed into separate sinusoidal, transient, and noiselike signals, aggressive quantization can be performed independently on each signal in a perceptually meaningful manner. While the sines + transients + noise representation allows for good compression rates, it also allows for high-quality time-scale modification in the compressed domain. The multiresolution sinusoidal modeling and the Bark-band noise modeling utilized in this representation have been used in both the music synthesis and audio/speech coding arenas. The transient modeling in this representation uses similar algorithms to those used in transform coding systems.
New approaches to sound compression that use algorithmic synthesis
Authors: Scheirer Eric D.
Published: July 2002

Research into the use of perceptual models to compress sounds has achieved fruitful success in recent years. However, quantized filterbanks and linear-predictive coding are not the only techniques that can be used for audio compression. Recent research has tightened the connection between sound processing normally conceived as ‘‘compression’’ and that normally conceived as ‘‘synthesis.’’ By making this connection explicit, it becomes possible to apply methods taken from the broad literature on the synthesis of sound signals to applications in sound compression [B. L. Vercoe et al., Proc. IEEE 85, 622–640 (1998)]. New techniques that use audio synthesis to enable compression have recently emerged. One of these is termed algorithmic structured audio, and builds on research into software synthesis and sound-description languages. A particular implementation of this method forms the new MPEG-4 Structured Audio standard, in which the software-synthesis language SAOL is used to represent sound algorithmically. Recent research also suggests that the development of so-called generalized audio coding techniques, in which algorithmic-structured-audio formats carry customized perceptual decoders, might increase the overall efficiency of the marketplace of coding by allowing a more flexible approach to the selection of coding models.
Encoding considerations for MP3 and MPEG-2/MPEG-4 advanced audio coding
Authors: Brandenburg Karlheinz
Published: July 2002

Perceptual coding of high-quality audio has found widespread applications for broadcasting, internet delivery of music and storage of music as used in portable music players. The success of formats like MPEG-1 Layer-3 (AKA MP3) can be attributed to the standardization philosophy of MPEG: A universal format is specified and available for licensing for everybody. This leaves the encoder up to technical improvements. The presentation will (i) introduce the basics of high-quality audio coding, (ii) give an overview on MP3 and MPEG-2/4 AAC, (iii) explain encoding strategies, and (iv) give special consideration to parameters affecting coding quality.
Attenuating stress waves during the fracture of a brittle carbon foam using ferrofluid damping
Authors: Krysac L. C.
Published: July 2002

Brittle fracture is a complex problem where details of defects and disorder on the microscopic scale affect the macroscopic strength of a material. We have found that during the fracture of disordered brittle carbon foam samples, stress waves produced by the breaking of individual struts may initiate avalanches of further strut-breaking events. If conditions are right for a macroscopic, sample-sized avalanche to be produced in this manner, the sample ruptures. If the stress waves are damped, by acoustic damping techniques, it may be possible to delay the onset of fracture in this material. The effect of damping the stress waves using viscous and magnetic ferrofluids on the measured fracture strength will be discussed.
A measure of the dynamic tortuosity in stratified fibrous porous materials
Authors: Solana Quiros Pedro E. , Picard Lopez Miguel A. , Arizo Serrulla Juan V.
Published: July 2002

Fibrous porous materials are an important element for noise control. The dynamic tortuosity is a magnitude that contains phenomenological and physical information of these materials and represents a tool of great usefulness for acoustical models and studies of fluid mechanics within them. From a phenomenological approach, this dynamic parameter includes the density of the fluid in the pores and the dynamic flow resistance and, from a microscopic point of view, contains information of the structure shape and the dynamic structure factor. It can be obtained theoretically through microscopic approximations, but it can also be calculated through acoustic procedures. From a phenomenological approximation in this work, an acoustic method of calculation is proposed to obtain it based on the measurement of the complex flow impedance of the thin samples. This will be more accurate when the sample is more rigid. Finally, the experimental procedure by a two-microphone method and the existence of relationships to microscopic parameters can facilitate the studies of acous-tic behavior and optimization of these materials for the manufacturer as well as for the technician that employs them in projects of noise control.
The use of compressional and shear wave velocities to measure the shear strength of soil
Authors: Shields F. Douglas , Sabatier Jim
Published: July 2002

Compressional and shear wave velocities have been measured in soil contained in a rigid-walled cylinder in both the axial and radial direction. This oedometer cell was fitted with a piston so that the soil could be axially compressed. The velocities and axial strain in the soil were measured as the axial stress was increased from zero to 35 lbs./sq. in. Measurements were made on both dry and wet soil. The axial and radial velocities were used to determine the radial stress. The ratio of the radial to axial stress gave the coefficient of earth pressure at rest and the angle of shearing resistance. For both the wet and dry soil, this angle was approximately 33 degrees. The velocities in wet and dry soils had approximately the same dependence upon axial stress, but the wet soil was much more compressible than the dry soil. Both wet and dry compressed soils maintained their strain and strained velocities upon decompression. However, when water was introduced into the decompressed soil, it expanded significantly and the velocities dropped to their precompression values. [Work supported by the USDA.]
An effect of auditory-filter envelope modulation variability on masking
Authors: Treurniet William
Published: July 2002

In an earlier report [W. C. Treurniet and D. R. Boucher, J. Acoust. Soc. Am. 106, 2146 (1999)], the threshold for a noise probe masked by a complex masker was shown to be lower when the masker partials were harmonically related than when the frequencies of the partials were perturbed by small amounts. The results suggest that the improved detection may arise from differences in the pattern of modulations across auditory-filter outputs in response to harmonic and inharmonic maskers. That is, envelope modulations are identical across filters for a harmonic masker, but the modulations vary for an inharmonic masker or a noise probe. The variable modulation rates across filters due to the noise probe are easier to detect against the invariant background rates generated by the harmonic masker than against the variable background rates resulting from the inharmonic masker. In support of this hypothesis, the difference in masked threshold was strongly related to the variance of the dominant period of envelope modulations measured across auditory-filter outputs. Further, the masking level differences were minimal when the average variance of modulation amplitude was small, as in the case of a single partial per auditory filter.
Masking period patterns in listeners with cochlear hearing loss
Authors: Wojtczak Magdalena , Schroder Anna C. , Nelson David A.
Published: July 2002

Masking period patterns (MPPs) were measured in listeners with hearing loss of cochlear origin, using a short 6-kHz probe presented at different times within the envelope of a 100% sinusoidally amplitude-modulated (AM) masker (4-Hz modulation rate). The carrier frequency of the AM masker was 3 kHz (off-frequency masking) or 6 kHz (on-frequency masking). MPPs obtained from hearing-impaired listeners were compared to those obtained from normal-hearing listeners using the same stimuli. A model used previously to simulate MPPs from normal-hearing listeners [Wojtczak et al., J. Acoust. Soc. Am. 106, 2147 (1999)] was used to predict data from the hearing-impaired listeners. In contrast to MPPs from normal-hearing ears, MPPs from ears with moderate to profound hearing loss did not exhibit large differences in MPP shapes for on- and off-frequency maskers, i.e., they did not exhibit longer MPP valleys for the off-frequency masking situation. Results of the modeling suggest that the similar shapes for on- and off-frequency MPPs reflect a lack of compression (or reduced compression) in the hearing-impaired listeners. The implications of this effect for speech understanding in the presence of competing talkers will be discussed. [Work suported by NIH NIDCD DC00149 and the Lions 5M Hearing Foundation.]
The influence of noise, harmonic structure, and temperament on tonal consonance judgments
Authors: Kondash James , Hallgren Rodney
Published: July 2002

Although a large body of research exists on tonal consonance in which dyadic musical intervals have been systematically rank ordered via psychophysical experiments and models, none of these studies has addressed how tonal consonance judgments may change in the presence of a masking stimulus. Presenting musical intervals and maskers simultaneously could reduce elements potentially contributing to dissonance, such as beats between upper partials or distortion products. This study investigated consonance ratings of musical dyads as influenced by (1) the level of broadband and band-limited noise, (2) the number and level of upper partials in the tones, and (3) the use of equal or just intonation. In a randomized factorial experiment, participants rated musical dyads in the various conditions on a consonance/pleasantness scale. Preliminary results for equal-tempered dyads presented in the quiet show good agreement with consonance ratings reported in similar studies [e.g., Kameoka and Kuriyagawa, J. Acoust. Soc. Am. 45, 1460–1469 (1969)]. The presence of noise decreased consonance ratings across most intervals. [Work supported by a NASA fellowship.]
A hybrid finite-element formulation for midfrequency analysis of systems with excitation applied on short members
Authors: Zhao Xi , Vlahopoulos Nickolas
Published: July 2002

The hybrid finite-element analysis combines conventional finite-element analysis with energy finite-element analysis for midfrequency computations. A hybrid FEA fomulation has been published for systems with excitation applied on long members. [N. Vlahopoulos and X. Zhao, ‘‘A Basic Development of a Hybrid Finite Element Method for Mid-Frequency Computations of Structural Vibrations,’’ AIAA J. 37(11), 1495–1505 (1999).] In this presentation, theoretical developments associated with applying the excitation on short members will be discussed. Validation cases will be presented for several systems by comparing analytical solutions to hybrid FEA results. It will be demonstrated that the resonant behavior of the short members and the interaction between long and short members are captured correctly by the hybrid FEA. [Work supported by the Automotive Research Center established at the University of Michigan by the US Army Tank Automotive Command.]
The effects of audiovisual speech on sentential phoneme detection
Authors: Cox Ethan A.
Published: July 2002

Many previous studies in audiovisual speech perception concentrate on situations where auditory information is degraded, or stimuli with conflicting auditory and visual information. However, relatively little work has addressed the issue of how the availability of visual information contributes to postphonetic levels of processing. Presented here are results from a series of studies targeting audiovisual processing in lexical and sentential structures. Subjects in a phoneme-monitoring task for target words in sentences showed significantly faster RTs for audiovisual conditions as compared to auditory-only conditions. Additionally, a lexical frequency effect was observed in the auditory-only, but not the audiovisual condition. These initial findings focused on the bilabial viseme group and were compatible with an interpretation based on the earlier temporal availability of the visual information as compared to the auditory. Subsequent experimentation with the same general procedures incorporated catch trials with nontarget bilabials, and indicates a more complex account. Comparison of the original findings with other viseme groups also supports the view that the availability of visual information contributes more than a simple temporally earlier trigger for target identification. Monitoring performance cannot be well accounted for by treating the auditory and visual information as separate channels for controlling the response.
Inference of source–receiver motion from phase measurements in the Modal Mapping Experiment
Authors: Frisk George V.
Published: July 2002

In March 1997, the Modal Mapping Experiment (MOMAX) was conducted aboard the R/V Endeavor in about 70 m of water off the New Jersey coast. Three drifting MOMAX buoys, each containing a hydrophone, GPS navigation, and radio telemetry received signals up to ranges of 10 km from a NUWC J15-3 source suspended from the moving ship and transmitting pure tones at 50, 75, 125, and 175 Hz. A striking feature of the data is the remarkable stability and regularity of the phase, even though the magnitude displays a complex multimodal interference pattern. This phase behavior occurs even at the higher frequencies and higher source/receiver speeds (up to 3 kts) measured in the experiment. A phase model is developed which indicates that the leading-order behavior of the time rate-of-change of the phase is simply equal to the product of a typical wave number in the water column and the source-receiver speed. This model accurately predicts the source-receiver speed from the phase measurements obtained in MOMAX. The implications of this model for other scenarios, such as long-range, deep-water situations are also discussed. [Work supported by ONR.]
An echoic room model for acoustic simulations by non-reflection boundaries using the Bergeron method
Authors: Shimoda Hidemaro
Published: July 2002

An analytical model of anechoic rooms by distributed equivalent circuits is constructed in the computer using the Bergeron method [Shimoda et al., ‘‘Analysis of sound fields in rooms using Bergeron’s method,’’ Trans. I.E.C.E. Japan, 72 A, 1, 1–11 (1989); English transl., 1989 Electronics and Communications in Japan, Part 3, Vol. 72(12), Scripta Technica, Inc. (Wiley, New York, 1990)]. In this analytical method, the nonreflection boundaries are modeled by gradually increasing sound transmission losses in specific regions near boundaries just like a sand beach exposing sea waves. Also, the sound transmission characteristics or the sound pressure distributions in the room are investigated. The model can be applied to the sound scattering analysis by an arbitrary object.
Analysis of spatial acoustic qualities from listening in rooms
Authors: Gold Martin A.
Published: July 2002

Statistical analysis was conducted on data from in-room listening studies to evaluate the effects of spatial impression and auditory source width as independent variables with regard to overall acoustic impression. The listening studies were conducted with groups of listeners (30+) in the rooms under evaluation. Subjects in each circumstance were asked to evaluate the acoustic environment using a bi-polar semantic rating scale for the acoustical qualities of overall impression, loudness, clarity, reverberance, treble response, bass response, spatial impression, auditory source width, echoes, and background noise. Ratings were taken in a variety of listening environments ranging from outdoors to a 2000-seat auditorium to elicit a range of qualitative assessments. Both live music and recorded music and speech sources were evaluated in the study. The study also includes a comparison of in-room ratings. Results indicate that, in most cases, it is difficult to statistically isolate independent spatial variables with regard to overall room ratings in complex environments. In specific room locations, these variables appear to be statistically independent.
A maximum likelihood estimation algorithm for tracking two multipaths
Authors: Barton Alan , Di Iorio Daniela
Published: July 2002

A high-frequency (67 kHz) acoustical scintillation experiment was carried out in the northern entrance to Hood Canal, Puget Sound, WA. This experiment made use of a 4-transmitter and 4-receiver array configured as a T-shape. The two-dimensional feature of this array was designed to measure both along-channel small-scale properties as a result of advection and vertical properties as a result of refraction from temperature/salinity stratification. Sampling was carried out at 5 Hz for all transmitters so as to understand the turbulent effects of the medium on acoustic scattering. This experiment tested if acoustical scintillation techniques can be extended to long distances (2380 m) and in deep (100 m) coastal channels having strong tidal currents and temperature/salinity stratification. With the longer path lengths and stable stratification, acoustic propagation resulted in multipath arrivals which were separable for most of the measurement period. In order to study the oceanographic effects on the direct path signal at 20-m depth and the upward refracted signal into the surface mixed layer, a maximum likelihood estimation algorithm is developed that tracks the two paths and calculates amplitude, phase, and travel time for each. [Experiment was carried out by SAIC of Bellevue, WA, and student support was from the University of Georgia.]
A three-dimensional model for elastic waves in the ground
Authors: Schroeder Christoph T. , Kim Kangwook , Scott Waymond R.
Published: July 2002

A three-dimensional finite-difference time-domain model for elastic waves in the ground has been developed and implemented on a massively parallel computer. The model is based on the three-dimensional equation of motion and the stress–strain relation, from which a first-order stress-velocity formulation is obtained. The boundary between the soil and the air is modeled as a free surface. A perfectly matched layer is implemented at the remaining grid edges to absorb the outward traveling waves. The numerical model has been developed as part of a project in which elastic and electromagnetic waves are used synergistically to detect buried landmines. The numerical model is being used to study the interaction of the elastic waves with the buried mines. To verify that the model accurately predicts the mine–wave interaction, the eigenfrequencies of various solid bars and plates are determined numerically and compared to analytical solutions. Currently, the model is being refined to incorporate loss within the bulk medium. Results will be shown for various landmines buried in both loss-free and lossy ground. [Work supported by ARO and ONR.]
Sound propagation through thermal turbulence near a convex surface
Authors: Blanc-Benon Ph. , Wasier J. , Juvé D.
Published: July 2002

Making use of an acoustic analogy, we study the sound propagation above a convex surface, to simulate the propagation of sound in an upward-refracting medium and to investigate the scattering of sound by turbulence into an acoustic shadow zone. An experimental study was achieved under well-controlled laboratory conditions. A heated grid is placed horizontally in a large anechoic room and the mixing of the free convection plumes above the grid generates a homogeneous isotropic random thermal field. The convex surface is simulated by a vertical cylinder. Experimental data are obtained by varying both the frequency of the acoustic source and the distance of propagation. Measurements will be presented for a rigid convex surface. In this paper, we concentrate on the mean sound-pressure levels and the intensity fluctuations. Experimental values will be compared with results of numerical simulations based on a wide-angle parabolic code.
Directional microphone theory
Authors: Fournier Patrick C.
Published: July 2002

An alternate to the cochlear amplifier and resonant tectorial membrane models, this theory models the cochlea as a type of directional microphone. The main source of cochlear nonlinearity is a mechanical canceling of more intense signals from the interaction of the cochlea’s various diaphragms. These interactions allow both the inner and outer hair cells to focus a wide range of environmental amplitude into the relatively invariant encoded signal that is sent to the auditory brain. This cancellation of intense signals allows concurrent weak signals in the environment to be perceptively enhanced as compared to the more intense concurrent signals. This model explains Yates dual-wave mode in the cochlea, how and why the outer hair cells are stimulated at low intensities, and how the cochlea performs a fast Fourier transform. Loudness growth charts recalculated in pascals clearly show the enhanced perception of soft signals in comparison to intense ones. Detection of pure-tone signals delivered in a sound field of narrow-band white noise showed equivalent intensity differences for both impaired and nonimpaired ears for perceived loudness levels when calculated in pascals. Expected focus or enhancement of normal soft to intense sound perception was recreated artificially for the impaired ears.
The phases of auditory-nerve fiber responses to tones: Dependence on stimulus frequency and intensity
Authors: Temchin Andrei N. , Ruggero Mario A.
Published: July 2002

As stimulus intensity increases, the phases of responses to tones of squirrel monkey auditory-nerve fibers [ANFs; Anderson et al., J. Acoust. Soc. Am. 49, 1131–1139 (1971)] and guinea pig inner hair cells [IHCs; Dallos, Hearing Res. 22, 185–198 (1986)] undergo lags and leads, respectively, at frequencies lower and higher than the characteristic frequency (CF) and remain relatively constant at frequencies near CF. A similar pattern holds for basal sites of the basilar membrane (BM) in several species. In contrast, tectorial-membrane (TM) vibrations at apical sites of the chinchilla cochlea exhibit phase shifts of opposite polarity [Rhode and Cooper, Aud. Neurosci. 3, 101–121 (1996)]. To explore this inconsistency between neural and mechanical behavior at apical cochlear regions, we investigated the phases of responses to tones of ANFs recorded in deeply anesthetized chinchillas. For stimulus intensities lower than 70 dB SPL, responses of most ANFs (regardless of CF) exhibited phase shifts similar to those observed in squirrel monkey ANFs, guinea pig IHCs, and basal BM sites in several species. Thus, the inconsistency between neural and TM mechanical data cannot be ascribed to species differences or a dependence of phase behavior on CF. [Work supported by NIH Grant DC-00419.]
Articulatory kinematic and formant frequency changes across vocalic nuclei: Some preliminary analyses
Authors: Weismer Gary , Jeng Jing-Yi
Published: July 2002

There are few data relating changes in articulatory position to changes in vocalic formant frequencies. This kind of information is useful for speech-production theory in general and specifically in understanding the relationship in neurogenic speech disorders between movement effects and resulting speech-intelligibility deficits. The purpose of this study was therefore to assemble a fairly large kinematic/acoustic database on normal speakers, for a few words that have proven useful in our studies of the intelligibility deficit in dysarthria. Data were part of the x-ray microbeam database, and for the present study included the words ‘‘hail,’’ ‘‘shoot,’’ and ‘‘coat.’’ The position histories of four tongue pellets and two lip pellets as well as the time histories of the first and second formant frequencies were studied for 45 young adult speakers. The F2 transition extent (change in F2 across a defined time interval) was significantly correlated with some combination of the pellet time histories for each word, and the magnitude of the correlation showed clear gender effects. Results will be discussed in terms of the linkage between planar kinematic data and acoustic data in predicting speech-intelligibility deficits. [Work supported by NIH DC03723 and DC000820.]
A quasi-one-dimensional model for speech production
Authors: Zhao Wei , Zhang Zhaoyan , Frankel Steven H. , Mongeau Luc
Published: July 2002

A quasi-one-dimensional model for speech production was developed. The unsteady quasi-one-dimensional Euler equations with temporal and spatial area variation were solved using a fourth-order accurate Runge–Kutta scheme for time integration and a sixth-order compact finite-difference scheme for spatial discretization. A model for wall friction was used, and a model for the pressure loss associated with flow separation at the glottis was derived. The code was validated by calculations of steady isentropic flow through a nozzle and an acoustic standing wave in a tube with uniform cross-sectional area. A simple geometry was then used to simulate the acoustic wave generated in the vocal tract. The results are in qualitative agreement with data from experiments obtained using a dynamic model of the larynx. [Work supported by NIH DCO 3577-02, RO1 grant from NICDC.]
Comparing single- and two-channel telephone speech enhancement for elderly hearing-impaired listeners
Authors: Sheffield Amy E. , Krishnamurthy Ashok , Davidson Stephanie , Feth Lawrence L.
Published: July 2002

Elderly listeners with sensorineural hearing loss have difficulty understanding speech over the telephone. Hearing aids and telephone amplifiers help, but many elderly individuals do not have the access to these devices. One possible solution to the problem is to ‘‘preprocess’’ the speech at the talker before transmitting it to the hearing-impaired listener. The purpose of this research is to compare processing techniques applied at the talker end that can significantly improve the speech understanding of these persons. Intelligibility enhancement of single- and two-channel amplitude compression schemes are compared by objective and subjective means. The articulation index (AI) and the diagnostic rhyme test (DRT) are used as the objective and subjective measures, respectively. In a preliminary study, we used normal listeners with speech that is passed through Moore’s [(1999)] hearing loss model. The hearing loss model simulates the effects of loudness recruitment and reduced frequency selectivity as well as elevated thresholds of hearing. In addition, elderly hearing-impaired subjects were tested for a subset of the processing schemes. We present results comparing relative intelligibility of the various processing schemes. [Work supported by a grant from the Ohio State University College of Social and Behavioral Sciences.]
Spatial modulation using vertical arrays in an underwater acoustic telemetry channel
Authors: Kilfoyle Daniel , Preisig James , Baggeroer Arthur
Published: July 2002

Multiple propagation paths between sound sources and receivers in an underwater acoustic channel are a common component of underwater acoustic telemetry. The temporal reverberation that results may adversely affect performance measures such as bit error rate and output signal-to-noise (SNR) ratio. With the use of transducer and hydrophone arrays, however, resolvable paths may also be exploited as additional bandwidth in a manner completely analogous to frequency bandwidth using a parallel channel model. In this discussion, we describe an experiment conducted in Buzzards Bay, MA, that utilized moving, vertical arrays to spatially modulate and demodulate two acoustic communication signals that fully occupied identical time-frequency spaces. Decomposition of the composite shallow water channel into two, parallel communication channels was accomplished solely with spatial degrees of freedom. Performance is compared with a conventional, single signal transmission. In addition, in situ channel impulse response measurements are analyzed to explain the success of the spatial modulation experiment. Performance improvements comparable to those yielded by a 3–6-dB SNR increase are achieved without using additional signal power. We will conclude with a brief discussion regarding the challenges as well as potential applications of the spatial modulation technique.
Plate equations and equivalent circuit for micromachined piezoelectrically actuated flextensional transducers
Authors: Percin Gokhan , Khuri-Yakub Butrus T.
Published: July 2002

In the absence of analytical expressions for the equivalent circuit parameters it is difficult to calculate the optimal design parameters and dimensions and to chose suitable materials. The influence of coupling between flexural and extensional deformation and coupling between structure and acoustic volume on the dynamic response of piezoelectrically actuated flextensional transducer is analyzed using three analytical methods: classical plate theory, Mindlin plate theory, and simple variational procedure. The transducer design is based on a flextensional transducer that excites the axisymmetric resonant modes of a clamped circular plate. It is constructed by depositing a thin piezoelectric annular plate onto a thin, edge clamped, circular plate. An ac voltage is applied accross the piezoelectric material to set the compound membrane into flexural vibration. The devices have a range of operating resonance frequencies starting from 450 kHz up to 4.5 MHz. The device is manufactured by silicon surface micromachining and implemented in the form of two-dimensional arrays. Individual elements are made of thin silicon nitride membranes covered by a coating of piezoelectric zinc oxide. Classical thin plate theory, Mindlin plate theory, and variational methods are applied to derive two-dimensional plate equations for the transducer, and to calculate the coupled electromechanical field variables such as mechanical displacement. These methods use classical kinematic relations for a plate and a variational equation for the coupled electromechanical field to reduce three-dimensional field equations to two-dimensional plate equations. As a result, three different exact solutions to corresponding systems are obtained. An equivalent circuit of the transducer is also obtained from these solutions.
Characterization of single-crystal silicon paddle oscillators: Dynamic behavior and loss mechanisms
Authors: Morse Scot F. , Houston Brian H. , Photiadis Douglas M. , Vignola Joseph F. , Liu Xiao
Published: July 2002

Micro-scale mechanical devices continue to be of interest in a broad range of sensor and device applications. Many fundamental issues pertaining to the operation and performance of these devices remain to be thoroughly investigated. This is especially true in the recently developed field of nanoelectromechanical systems (NEMS). Resonant devices are now being produced in single-crystal silicon with released features as small as 30 nm. Besides novel device applications these structures may be used to explore fundamental properties and mechanisms that include internal friction as a function of scale. Measurements and analysis are reported here that, for the first time, characterize the detailed vibratory response of micro-scale oscillators (∼100 μm). The devices are placed in a vacuum chamber, excited inertially, and measured optically with a laser Doppler vibrometer (LDV) instrument. Single-point swept frequency measurements are used to investigate the vibrational spectrum of the oscillators and determine the Q. Spatial scans allow for mode identification and help to identify energy loss mechanisms into the supporting structure. In addition to observing the fundamental torsional and translational modes, we also observe numerous flexural modes of the devices. Both linear and nonlinear behavior are observed. [Work supported by ONR.]
A simple method for comparing waveform distortion of nonlinear surface waves in different cubic crystals
Authors: Kumon R. E. , Hamilton M. F.
Published: July 2002

Simulations of monofrequency, nonlinear surface acoustic waves propagating in cubic crystals were performed using the theory of Hamilton, Il’inskii, and Zabolotskaya [J. Acoust. Soc. Am. 105, 639–651 (1999)]. Nonlinearity matrix elements, which describe the coupling strength of harmonic interactions, provide a useful tool for characterizing the nature of the waveform distortion and can be computed without integrating large systems of equations. In cases where the surface is a plane of mirror symmetry, the nonlinearity matrix elements are real valued, and the longitudinal components of the waveforms typically form either compression or rarefaction shocks. However, in cases where the surface has lower symmetry, the nonlinearity matrix elements are complex valued, and the resulting waveform distortion is typically asymmetric, sometimes with low-frequency oscillations forming near peaks and shocks. A simple transformation based on the phase of the dominant nonlinearity matrix element was shown to provide a reasonable approximation of the asymmetric distortion in many cases. Comparisons will be presented between approximate and exact solutions in the (111) plane for several real crystals. These results are consistent with measured surface wave pulses reported previously [R. E. Kumon et al., J. Acoust. Soc. Am. 103, 2926(A) (1998)]. [Work supported by ONR.]
Filter shapes for long-duration signals and for short-duration signals as a function of signal delay from masker onset
Authors: Strickland Elizabeth A.
Published: July 2002

Filter shapes were measured as a function of level for long-duration (350-ms) signals, and for short-duration (10-ms) signals delayed from masker onset by 2 or 202 ms. Masker duration was 400 ms for the long-duration and long-delay signals, and 200 ms for the short-delay signal. Signal frequencies were 1 and 4 kHz. The level of a notched-noise masker was varied to find threshold. This study extends previous studies by fixing the signal level rather than the masker level, and by measuring filter shapes for several signal levels. Filter widths for the long-duration signal and the long-delay signal could be fit for the multiple levels, keeping efficiency constant. Filter widths were similar for these two conditions. This agrees with previous results measured with the masker level fixed [B. A. Wright and H. Dai, J. Acoust. Soc. Am. 95, 931–938 (1994)]. Filter widths for the short-delay signal were broader, and efficiency varied with level. The broader filter at a short delay as compared to a long delay is also consistent with results measured with masker level fixed [B. A. Wright, J. Acoust. Soc. Am. Suppl. 1 86, S1, S121]. Results will be discussed in terms of overshoot. [Work supported by NIH (NIDCD).]
Acoustic effects of middle-ear cavities in the cat family
Authors: Huang Gregory T. , Peake William T. , Taberner Annette M. , Rosowski John J. , Atencio Craig A.
Published: July 2002

The acoustic effect of the middle-ear air-filled space is to add an impedance in series with that of the tympanic membrane and ossicular chain. In the cat family, a bony septum divides the space into two volumes, coupled through a small opening (foramen); this configuration is well modeled as a lumped circuit of two parallel compliances (the cavities) coupled by an acoustic mass and resistance (the foramen). The model impedance magnitude has a minimum and a maximum, whose frequencies are predictable from structure. A narrow-band notch in hearing sensitivity near 2–4 kHz is caused by the pole. Measurements of cavity impedance in four felid species are consistent with this structure-based model. Acoustic measurements in ears of three species with the septum removed show that the minimum and maximum in impedance magnitude are eliminated, as predicted by the lumped model. However, new impedance maxima appear at 8–12 kHz; these maxima are assumed to result from distributed resonances in the enlarged cavity. Thus the inferred effect of the septum on hearing is to introduce a notch in the midfrequencies, while avoiding such notches at higher frequencies where they could interfere with sound-source localization. [Work supported by NIH and NSF.]
Amplitude-modulation detection in two patients with left- or right-hemisphere damage
Authors: Lorenzi Christian , Wable Jocelyne , Moroni Christine , Belin Catherine , Frachet Bruno
Published: July 2002

The modulation depth required for the detection of sinusoidal amplitude-modulation applied to a white noise carrier was measured as a function of modulation frequency, giving temporal modulation transfer functions (TMTFs). The modulation frequency was 4, 16, 64, 256, or 1024 Hz. Measurements of intensity discrimination thresholds for white noise were performed as a control task. In both tasks, white noise stimuli had a 2-s duration and were presented monaurally at 75 dB SPL. Two adult listeners with left- or right-hemisphere damage and three normal-control adult listeners were tested in each ear. Lesions encompassed the primary auditory cortex in the two patients. All listeners had normal audiometric thresholds. The modulation detection data showed no sign of ear asymmetry. For all listeners, the TMTFs displayed a typical low-pass characteristic. Modulation detection was 10–14 dB poorer-than-normal at modulation frequencies between 4 and 256 Hz in the patient with left-hemisphere damage. In contrast, modulation detection was normal in the patient with right-hemisphere damage. Intensity discrimination was within the normal range (0.5–1 dB) for both patients. These results support the hypothesis that cortical structures within the left hemisphere play a crucial role in temporal envelope processing. [Work supported by the Fondation de l’Avenir and the Cognitique Program.]
On the perception of voicing for plosives in noise
Authors: Chen Marcia , Alwan Abeer
Published: July 2002

Previous research has shown that the VOT and first formant transition are primary perceptual cues for the voicing distinction for syllable-initial plosives (SIP) in quiet environments. This study seeks to determine which cues are important for the perception of voicing for SIP in the presence of noise. Stimuli for the perceptual experiments consisted of naturally spoken CV syllables (six plosives in three vowel contexts) in varying levels of additive white Gaussian noise. In each experiment, plosives which share the same place of articulation (e.g., /p, b/) were presented to subjects in identification tasks. For each voiced/voiceless pair, a threshold SNR value was calculated. It was found that the perception of voicing has a strong dependence on vowel context with /Ca/ syllables being significantly better discriminated than /Ci/ and /Cu/ syllables. In addition, labials consistently had a higher threshold SNR (or more easily confusable) than alveolars and velars. Threshold SNR values were then correlated with measurements of several acoustic parameters of the speech tokens. It was found that VOT did not appear to influence the perception of voicing in noise as much as the first formant transition. [Work supported in part by NIH and an NSF Fellowship.]
Effects of talker voice on lexical neighborhood and speech perception
Authors: Zimack Liza K. , Sawusch James R.
Published: July 2002

Previous research has shown that the number of words that a syllable is similar to (lexical neighborhood) influences the perception of the syllable and its phonemes. For example, in ‘‘bowth’’ ‘‘powth’’ and ‘‘bows’’ ‘‘pows’’ series, ‘‘bowth’’ is similar to more words than ‘‘powth,’’ while ‘‘pows’’ is similar to more words than ‘‘bows.’’ Listeners report more syllables beginning with /b/ in ‘‘bowth’’ ‘‘powth’’ and more that begin with /p/ in ‘‘bows’’ ‘‘pows.’’ However, with one particular talker, no effects of lexical neighborhood were found. This research focused on two explanations for the lack of neighborhood effects for this talker. One possibility is that the previous method of determining lexical neighborhood is inaccurate for this talker. Alternatively, the time course for phonetic and lexical information processing may be different for this talker. In this research, listeners identified the final consonant in two nonword CVC series: ‘‘faesh’’ ‘‘faech’’ and ‘‘taesh’’ ‘‘taech.’’ With a syllable final target phoneme, lexical neighborhood influences should build up prior to the processing of the target phoneme. Implications of the data for models of word recognition and perception with different talkers will be discussed. [Work supported by NIDCD Grant No. R01DC00219 to SUNY at Buffalo.]
Perceptual assessment of intoxication level
Authors: Hollien Harry , Hill Rebecca , Martin Camilo A.
Published: July 2002

Data are reviewed and summarized from ten perceptual experiments wherein groups of listeners assessed the levels of intoxication for various types of talkers speaking at specific windows of sobriety and inebriation. The speakers included both sexes. Subjects were selected on the basis of a number of rigorous criteria; they produced several classes of speech when sober and at three highly controlled levels of intoxication. Listener groups included prescreened university students and professionals trained in appropriate areas. The task was to judge intoxication level from speech samples. It was found that speakers were judged as drunker than they actually were at mild levels of intoxication but that auditors sharply underestimated their involvement for severe intoxication. Data from three subprocedures led to the identification of a number of trends. However, no significant differences were found when the judgments by men and women were contrasted, nor were they significant between professionals and lay auditors or between the classes of speech produced. [Research supported by NIAAA.]