bluuebunny/crossref_metadata_2025 huggingface dataset:
Using TSC to analyze speech sounds
Authors: Vaidya P. G. , Shipley Kenton , Winkle Casey
Published: October 2005

TSC (trans spectral coherence), is a technique that has been shown recently to be effective in analyzing signals that have been generated through nonlinear mechanisms. It deals with the analysis of the components of a spectrum for coherence and transphase. A set of vowels generated by different speakers were analyzed using this technique. Using a model for speech production, an estimate of the glottal waveform and its characteristics was made. A discussion of the implications of this approach to the problem of speaker identification is included.
Spectral envelope features for vowel classification in clean and noisy speech
Authors: Nossair Zaki B. , Zhang Zhong-Jian , Zahorian Stephen A.
Published: October 2005

In previous synthesis experiments with multi-tone vowels it was found that vowel perception is more closely correlated with acoustic cues derived from the envelope of the magnitude spectrum than with cues derived from the overall magnitude spectrum [Zahorian etal., J. Acoust. Soc. Am. 93, 2298–2299 (1993)]. In the present study automatic vowel classification experiments were used to compare spectral magnitude features versus spectral envelope features. The features computed were cepstral coefficients, similar to those typically used in automatic speech recognition, versus cepstral coefficients computed from the envelope spectrum. The two feature sets were compared for four conditions: a single frame of clean speech, a single frame of noisy speech with varying signal-to-noise ratios, multi-frames of clean speech, and multi-frames of noisy speech. For clean speech conditions, the automatic classification results were nearly identical for the two feature sets. However, for both of the noisy speech conditions, the spectral envelope features resulted in a small but consistent improvement in vowel classification relative to results obtained with spectral magnitude features. These results corroborate that, for noise-free conditions, the normal cepstral coefficients indirectly encode the envelope spectrum. However, a more direct envelope representation is preferred to improve noise immunity.
Initial investigation in using an energy operator for pitch estimation
Authors: Whitman Robert K. , Etter Delores M.
Published: October 2005

Numerous techniques have been developed to estimate the pitch periods in speech signals. The determination of the pitch period is an important aspect in speech analysis. The estimation of the pitch is essential in systems for pitch synchronous analysis, speech analysis/synthesis, and in speech coding. Pitch extraction algorithms use a variety of methods in both the time and frequency domains to estimate the pitch periods. In this paper, an investigation is made into the use of an energy operator developed by Teager, to estimate the pitch period of the speech data. The Teager energy operator estimates the energy required to produce an acoustic signal. Since speech signals are the result of acoustic interactions, it is appropriate to make this investigation using the energy operator.
Speech analysis based on a model of articulatory behavior
Authors: Randolph Mark A.
Published: October 2005

A major problem in articulatory-based speech recognition is the need for the recognizer to transform an input sequence of acoustic observations into a set of parameters describing the behavior of the articulatory system during utterance production. This acoustic-to-articulatory transformation is nonunique. In addition, an economical computational framework is needed to describe and recognize patterns of articulatory behavior obtained from acoustic analysis. In this paper, a speech analysis system based on a generative model of articulatory behavior is presented. Articulatory codebooks represent the acoustic-to-articulatory relation. During speech analysis ambiguity is effectively resolved with the aid of a finite-state grammar of articulatory behavior. The grammar, in the form of a finite-state acceptor, is used to constrain codebook search. This analysis procedure is part of a word recognition system, the finite-state grammar of articulatory behavior can be derived automatically from an analysis of phonetic text as part of the process of building a recognition lexicon. This derivation procedure, as well as the speech analysis technique, is illustrated.
Demodulation of AM–FM resonances in speech using energy separation
Authors: Maragos Petros , Quatieri Thomas F. , Kaiser James F. , Potamianos Alexandros
Published: October 2005

Motivated by theoretical and experimental evidences [e.g., in H. Teager and S. Teager, Proc. NATOASI: SpeechProductionandSpeechModeling, Bonas, France (1989)] that various nonlinear phenomena during speech production cause modulations of the airflow, AM–FM models for speech resonances and a novel efficient algorithm to estimate their parameters were proposed in [P. Maragos, J. Kaiser, and T. Quatieri, IEEE Trans. Signal Process. 41, 3024–3051 (1993)]. The algorithm uses the differential operation Ψ(x)=(ẋ)2−xẍ to detect modulations in speech signals by tracking the physical energy implicit in the particular ‘‘source’’ producing the observed acoustic resonance signal and by separating this energy into its time-varying amplitude and frequency components. In this paper experimental results are reported on using refinements of this energy separation algorithm to measure modulations in speech resonances. These results indicate that voiced speech signals, bandpass filtered around speech formants, contain significant amplitude and frequency modulations within a pitch period. These modulation features seem promising for applications to speech coding, synthesis, and recognition. Further, applying the algorithm on synthetic speech produced by conventional linear synthesizers did not yield the modulations patterns found in real speech. [P. Maragos is supported by the National Science Foundation. T. F. Quatieri is supported by the Department of the Air Force.]
Why speech coding isn’t dead
Authors: Cox Richard V.
Published: October 2005

The costs of communications bandwidth and data storage declined dramatically during the past decade while their available capacities increased equally dramatically. Both trends will continue into the future. In spite of this, the decade saw a proliferation of speech coding applications and new standards. Why isn’t speech coding dead? The answer has several parts. First, digital electronic technology has finally made speech coders easy and cost effective to implement. Second, customer demand for communications any place any time relies on speech coding. In the future, one can expect more, not less, demand for speech coders used in new products and services. Third, speech coding technology improved to the point where good tradeoffs could be made among speech coder attributes, such as quality, complexity, bit rate, and delay. New products and services were acceptable to consumers on the basis of both performance and cost. However, current speech coders can still use improvement in all of their attributes. This talk reviews current application areas and focuses on areas for potential improvements to current speech coders. New applications areas and meeting their challenges will continue to make speech coding a lively research topic and a commercially valuable technology for the future.
Perceptual coding of height-quality audio signals
Authors: Brandenburg Karlheinz
Published: October 2005

Perceptual coders promise to deliver true transparent coding. The listener should not be able to hear any difference between original and reconstructed signal. The main elements of perceptual coders are (1) a filterbank to map the time domain input signal to a time- frequency domain representation, (i.e., the masked threshold) and (2) the quantization and coding step that should include proper noise shaping according to the psychoacoustic model. An overview of current and future audio coding systems is given. The completion of ISO/IEC 11172-3 (the MPEG-1 audio coding standard) marks the end of the work on the first generation of audio coding systems. While audio coding is on the way to widespread application, topics for the new coding systems include joint stereo coding of two or more channels, different analysis-by-synthesis systems, and improved psychoacoustic models.
Speech coding based on a sinusoidal speech model
Authors: McAulay R. J. , Quatieri T. F.
Published: October 2005

It has been shown that speech of high quality can be synthesized using a sinusoidal model when the amplitudes, frequencies, and phases are derived from a high-resolution analysis of the short-time Fourier transform (STFT). It has also been shown that if the measured sine-wave frequencies are replaced by a harmonic set of frequencies in which the fundamental frequency is chosen to make the harmonic model a ‘‘best fit’’ to the measured sine-wave data, then synthetic speech of high quality can also be obtained provided the amplitudes and phases are obtained by sampling the STFT at the harmonic frequencies. A model has also been developed for the sine-wave phases that has a linear component corresponding to the onset time of the glottal pulse, a minimum phase component due to the dispersive characteristics of the vocal tract, and a random component that represents the degree to which the speech segment was unvoiced. While conventional methods are used for coding the pitch and voicing, the sine-waves amplitudes are coded using high-order allpole models. Scalar quantization of the line spectral frequencies offers good performance at rates from 4800–8000 bps, while a multiband vector quantizer results in performance that is quite good at 2400 bps.
Element localization for bottomed arrays without transponders
Authors: Shockley R. C. , Rice J. A. , Hursky P.
Published: October 2005

Beamforming for an array typically requires array-element localization (AEL) to within one-tenth of a wavelength. Often it is impractical to install dedicated, large-bandwidth AEL transponders with an array. This paper presents an approach to AEL for fixed, bottom-mounted arrays without transponders. High-SNR signals from multiple near-field imploding lightbulbs and interpolated correlations allow a statistical reduction in the inherent uncertainty in arrival-time measurements imposed by the bandwidth of the sensors. The method is illustrated with an application to the SWSS (shallow-water sensor string) array offshore of San Diego, at depths from 180 to 200 m.
Design and development of a low-frequency torsional shear wave transducer for ocean sediment applications
Authors: Walden Alan K. , Howarth Thomas R. , Tims James A.
Published: October 2005

A new low-frequency torsional shear wave transducer for ocean sediment applications has been developed. The transducer design includes a combination of a lightweight radiating structure and piezoelectric material. The ‘‘spool-shaped’’ structure is composed of solid lexan machined in the form of a cylinder centered between two radiating disks. The piezoelectric material, in the form of ceramic ring segments, is electrically configured for the ‘‘1–5’’ drive mode and rigidly attached circumferentially along each end of the cylinder. Operation of the transducer as a shear wave transmitter is based on a high torque being applied to the structure by the electromechanical action of the electrically driven piezoelectric ceramics. As the ceramics are excited, a resulting torque is coupled through the structure’s disks and radiated into the surrounding medium. The transducer structure is designed to exhibit a torsional resonance at 2 kHz. Based on the reciprocal nature of the piezoelectric ceramic, the transducer can also be employed as a shear wave receiver. Experimental results demonstrate that the transducer is an effective means of transmitting and receiving low-frequency shear waves in sediment. Good control over the acoustic waveform is obtained. Performance is investigated as a function of transmitter–receiver distance.
Diagnosis and repair of research vessel sonar problems
Authors: Greeley David S. , Birmann Michael R. , Kern Fred R.
Published: October 2005

The Research Vessel/Icebreaker (RVIB) Nathaniel B. Palmer, especially designed and built for Antarctic research and being operated by the National Science Foundation under long-term charter, experienced poor underway performance with most of the installed scientific sonar systems. These sonar problems were diagnosed and remedies designed in May 1993. The approaches used to identify the problems (inadequate sonar windows, bubble sweepdown underway, excessive machinery noise) and the solutions developed to rectify these problems will be presented. Modifications to the Palmer were made in August 1993, and the results of the modifications on sonar performance will be discussed. [Work supported by Antarctic Support Associates/NSF.]
Marginal oscillators: High sensitivity, simple detectors of Q changes
Authors: Conradi Mark S.
Published: October 2005

A marginal oscillator is an amplifier with a resonator (electrical, mechanical, or acoustical) incorporated into the positive feedback loop. When the loop gain barely exceeds one (barely oscillating), the oscillation level is extremely sensitive to small changes in the resonator Q. Compared to traditional bridges with frequency locking, marginal oscillators are simple and inexpensive. Being regenerative, they yield useful signal levels with remarkably few stages of gain. The operating frequency automatically follows the resonator frequency. Marginal oscillators have been used to detect magnetic resonance absorption in LC resonators and to detect small impurity particles in a blood-filled ultrasonic resonator. Applications in measurement science will be discussed.
Thermoacoustic enhancement and control of the quality factor in a resonant photoacoustic cell for measurement of light absorption by aerosols and gases
Authors: Arnott W. Patrick , Moosmüller Hans , Purcell Rick , Lightfoot Jay , Raspet Richard , Bass Henry E.
Published: October 2005

When gases or aerosols absorb energy from a modulated laser beam, surrounding air is heated, producing a time varying acoustic pressure that can be measured to quantify the absorption coefficient. Pressure is detected with a microphone in a resonator with resonant frequency that matches the laser beam modulation frequency. Induced pressure is proportional to laser irradiance, to absorption coefficient of aerosol and/or absorbing gas species, and to resonator quality factor, Q . Thermoacoustics is the interaction of heat and sound in resonators containing thin plates separated by a distance proportional to the thermal penetration depth of the gas. Q can be controlled by placing a temperature gradient along the plates in the same direction as acoustical particle velocity. This talk is on a technique for measuring light absorption by gases and aerosols that incorporates both the photoacoustics and thermoacoustics. Thermoacoustics is used to raise resonator Q for increasing the detection sensitivity of the photoacoustic spectrometer, for allowing windowless operation, and for potentially stabilizing resonator Q with respect to environmental parameter changes. Cell design was explored using a numerical model based on recently developed radial wave thermoacoustic theory. [EPA, ONR sponsorship.]
The cellular basis of cochlear inhibition
Authors: Fuchs Paul A.
Published: October 2005

Efferent neurons of the superior olivary complex synapse with auditory hair cells of vertebrates, in particular on outer hair cells (OHCs) of the mammalian cochlea. Efferent activity reduces the sensitivity and frequency selectivity of cochlear afferent fibers, presumably by inhibition of the OHCs. This inhibition is thought to be produced by the release of acetylcholine (ACh) from the efferent neurons. Electrical recordings from hair cells in various vertebrate species have shown that efferent activity, or exogeneously applied ACh, hyperpolarizes the cell by increasing the potassium conductance of the basolateral membrane. This potassium conductance is calcium dependent and so appears to be secondary to an initial effect of ACh to increase the cytoplasmic calcium activity. The increase in calcium-dependent potassium conductance moves the membrane potential toward the potassium equilibrium potential, near −80 mV. That hyperpolarization, in combination with the shunting effect of the underlying conductance increase, will minimize sound-evoked depolarization. OHCs are thought to enhance cochlear vibration by a voltage-dependent mobility elicited by depolarization. The effect of efferent inhibition may be to prevent the participation of OHCs as cellular amplifiers of the traveling wave, and thereby reduce cochlear sensitivity.
Acoustic monitoring of environmental pollution
Authors: Orr Marshall H.
Published: October 2005

High-frequency acoustic backscattering systems have been used to detect, track, and estimate dispersion coefficients for particles formed or released during ocean dumping of industrial wastes. The results of work performed in the late 70’s will be reviewed to illustrate: the effects of environmental variability on vertical dispersion of released particles; the types of vertical mixing processes that have been observed in the presence of strong season thermoclines (large gradients in the isopycnals); the breakdown of those thermoclines during periods of high wind stress; and the difficulties that can be encountered during attempts to navigate ships and perform acoustically guided chemical water sampling in the presence of strong ocean currents and vertical shear. Calibration of acoustic systems and estimates of system sensitivity to particles of known size distribution and concentration will be discussed.
Current monitoring for environmental pollution studies by acoustic Doppler current profiling
Authors: Williams Robert G.
Published: October 2005

NOAA’s National Ocean Service (NOS) has been measuring and predicting coastal currents for over 100 years. In earlier times, measurements were made with current poles, or propeller-type current meters. In the late 1980’s, acoustic Doppler current profilers (ADCPs) were widely adopted. In Tampa Bay, 10 ADCPs (RD Instruments) were deployed in bottom-mounted platforms; a towed ADCP provided spatial contours of current speed. A real-time system provided 6-min averages of current to mariners and environmental managers. This system, still in place, provides vital information for tracking land cleanup of pollutant spills. Recently, an ADCP was added to a conventional current meter array deployed by NOAA/AOML at a wastewater outfall off Miami, Florida. The ADCP measurements compared well with earlier observations and facilitated assessing the effects of mooring motion and bio-fouling. Analysis of ADCP profile data revealed a near-linear velocity gradient from surface to bottom, enabling interpolation of velocity profiles from earlier measurements. ADCP backscatter intensity provided a rough estimate of suspended material. Future applications include mapping the three-dimensional circulation around point sources of pollution. Such maps provide environmental managers with data for effective effluent disposal management at minimum cost.
Acoustical discrimination of estuarine turbidity structure
Authors: Bokuniewicz Henry , Wilson Robert , Chant Robert
Published: October 2005

The distribution of suspended sediment in estuaries is often concentrated in turbidity maxima which, because of the association of many contaminants with fine-grained sediment particles, can be important in determining the overall water quality. Acoustic investigations of the turbidity in the Hudson River estuary were done with a 200-kHz transducer and a 600-kHz broadband acoustic Doppler current profiler. (Water temperature and salinity were also measured and samples of suspended sediment were collected.) High turbidity here was found to be associated with tidally modulated and geomorphically controlled salinity intrusions. A salinity front is arrested at the bottom by the ebbing tide. As the tide turns, the front migrates upestuary producing an intense, local turbidity maximum. The re-establishment of a front in the original position on the next ebb can leave high turbidity pockets stranded upestuary. This is a novel mechanism for the generation of estuarine turbidity maxima but probably not unique to the Hudson River estuary; it may prove to be of widespread importance. [Work supported by the Hudson River Foundation, New York, NY.]
Coastal sediment transport monitoring using high-frequency acoustics in the 1990–91 STRESS II experiment
Authors: Lynch James , Irish James , Newhall Arthur
Published: October 2005

The bottom sediments of many coastal areas are contaminated by a truly awesome witches brew of ingredients (PCB’s, heavy metals, radioactive wastes, to name a few). The eventual fate of these contaminants is intimately tied in with the processes of coastal sediment transport. In recent years, acoustical remote sensing has become a powerful tool in measuring the process involved in coastal and deep sea sediment transport. In this talk, acoustical measurements made as part of a major experiment to understand the processes governing transport on the continental shelves, the ‘‘Sediment Transport on Shelves and Slopes’’ (STRESS) experiments will be discussed. Of particular interest here are the acoustical images of the near-bottom boundary layer, and their implications for sediment transport modeling. [Work supported by ONR.]
Remote acoustic sensing of manganese nodules on the ocean bottom
Authors: Bunchuk A. V. , Ivakin A. N.
Published: October 2005

Experimental and theoretical investigations of acoustic properties of the deep-sea bottom covered with manganese nodules have been conducted. The objectives were (1) to study remote acoustic detection and outlining nodule deposits and (2) to investigate remote acoustic monitoring and estimation of the nodules abundance, mean size, and other parameters. Field experiments were conducted in four regions of the Pacific and Indian Oceans at the frequency range of 2–20 kHz. The field experiments have shown that availability of manganese nodules is displayed by an increase of both the sound reflectivity and scattering strength and by the appearance of their unusual, comparing nodules-free bottom, frequency-angular dependences. A theoretical model of sound scattering and reflection by a set of nodules laid on the bottom has been developed [A. V. Bunchuk and A. N. Ivakin, Sov. Phys. Acoust. 35(1), 5–11 (1989)] in which the explicit form of connection between characteristics of bottom reradiated acoustic signal and nodules parameters have been established. As a result, explanation became possible for all the obtained experimental data. The spatial distribution of amplitudes of signals reflected and scattered from the bottom can be mapped. Finally, real-time algorithms for the inverse problem solution were developed and their validity for adequacy was checked.
Acoustic scattering from rigid shells of revolution using the generalized internal source density and SVD method
Authors: Stepanishen P. R.
Published: October 2005

Acoustic harmonic nonaxisymmetric scattering from rigid shells of revolution is addressed using the generalized internal source density and SVD method. The development of the generalized ISD/SVD method, which entails the use of various internal multipole source distributions along the axis of the shell, will be presented. The approach is based on first expanding the incident pressure and associated velocity field into circumferential harmonics about the axis of the shell. Integral equations of the first kind are developed for the unknown source distributions. A least-mean-squared error formulation of the solution naturally leads to using the SVD method to determine the source distributions. The blocked surface pressure for each circumferential harmonic is then readily evaluated by simple quadrature methods and the associated far-field scattered pressures are shown to be simply related to the Fourier transforms of the source distributions. Numerical results for some selected problems are presented and some limitations of the method as a function of azimuthal wave number and shape of the shells are noted. These limitations are discussed and are readily interpreted in light of the above-noted Fourier transform relationship.
Modeling of echoes from extended targets in shallow water
Authors: Baus T. , Chang W. , Deavenport R.
Published: October 2005

Echoes are generated, and compared, for extended targets in a shallow water environment using the total target–medium broadband frequency response function and the frequency representation of the transmitted signal. The two-way medium response is calculated using the generic sonar model (GSM) environmental model. The target frequency response is found using a model of distributed targets and elastic spheres. The combination of the target and medium frequency responses gives the full frequency response, or form function, for the target–medium system. The product of the total form function with the frequency spectrum of the incident signal is computed and an inverse FFT is performed to predict the received signal, or echo, from the object. [This work was sponsored by the Office of Naval Research—Technology Directorate.]
Merging of launching or detachment points of weakly damped leaky waves on S-shaped surfaces and complex launching or detachment points
Authors: Marston Philip L.
Published: October 2005

In previous work, Fermat’s principle and properties of leaky waves on flat surfaces were combined to obtain a high-frequency approximation to scattering by cylinders of slowly varying curvature [P. L. Marston, J. Acoust. Soc. Am. 94, 1861 (A) (1993)]. The usual assumption was made that only the first derivative of optical-path length (with respect to path variation) vanishes. The present work considers situations where the second (or higher) derivatives vanish at launching or detachment points. The simplest example is for coupling to (or detachment from) a tilted S-shaped surface. Such surfaces may have pairs of launching or detachment points; the pairs can merge at an appropriate surface tilt that results in a k1/6 amplitude enhancement coefficient. The launching or detachment factor becomes proportional to an Airy function of complex argument and launching or detachment in a shadow region of the Airy factor is described approximately by a complex ray. Higher-order launching or detachment points may also result from a sufficiently rapid dependence of the leaky-wave phase velocity on position. [Work supported by ONR.]
Enhancement of the total scattering cross section near the coincidence frequency of thin shells
Authors: Marston Philip L.
Published: October 2005

The total scattering cross section σ is affected by the elastic response of a target and is related to the forward scattering amplitude by the optical theorem. Computations based on the exact partial-wave series for scattering of plane waves by circular-cylindrical and spherical thin shells reveal an enhancement followed by broad oscillations as ka is increased through the coincidence region. This extends previous work on thick shells [S. G. Kargl and P. L. Marston, J. Acoust. Soc. Am. 88, 1103 (1990)]. A ray model shows that the coincidence region enhancement for thin shells is associated with both the subsonic (a0−) wave and the supersonic (a0) Lamb wave, unlike the corresponding backscattering enhancement that primarily results from the contributions of the subsonic wave [P. L. Marston and N. H. Sun, J. Acoust. Soc. Am. 92, 3315 (1992)]. The phase evolution of the coupling coefficient for the subsonic wave limits the associated contribution to σ for increasing ka. When σ is normalized by the area of the scatterer’s profile, the elastic contribution for spheres is approximately twice that of cylinders in the coincidence region. [Work supported by ONR and by the ARL:UT IR&D Program.]
Group delay in resonant scattering
Authors: He Hua , Lyon Richard H.
Published: October 2005

For a slightly damped structural system with low modal overlap, roughly half the zeros of the transfer function (TF) remain on the pole line and the group delay of the TF is π/2 times the structural modal density. But in the sound scattering case, the zeros are translated and rotated randomly and far fewer zeros will remain on the pole line. It is then reasonable to conjecture that the phase of resonance scattering function (RSF) be determined by the number of poles alone and thus the group delay of RSF is roughly a factor of 2 times that of the TF. To verify this conjecture, an in-air plate scattering experiment was carried out and the results show the factor of 1.67. Furthermore, the zero density distribution patterns versus modal overlap for both TF and RSF were obtained through numerical simulation of a 20-DOF system. The simulation shows that in the smaller modal overlap case, the RSF group delay is nearly twice that of TF. When modal overlap increases, however, this factor decreases and approaches 1. Physically this means in a high modal overlap system, like room acoustics, the group delay of RSF approaches the energy decay rate.
Edge effects in finite gratings of cylindrical scatterers
Authors: Denison Douglas R. , Scharstein Robert W.
Published: October 2005

Edge effects in finite arrays are studied via the analysis and interpretation of one canonical geometry—a linear grating of thin circular cylinders. The partial field scattered by each element in a finite array is decomposed into three components: (1) the contribution of the infinite or periodic array, (2) a component due to the presence of the left edge of the array, and (3) a component due to the right edge of the array. The scattered field due to either array edge is derived from a separate analysis of the appropriate semi-infinite array and is interpreted in terms of a decaying wave that is launched from the array end. This solution to the well-posed boundary value problem is numerically verified via boundary condition satisfaction, where the accuracy of the edge-wave decomposition persists for all tested values of element spacing and plane wave incidence angles. [Work supported by NSF.]
Transmission of energy across a discontinuity by fluid-loading
Authors: Photiadis Douglas
Published: October 2005

The presence of a heavy adjoining fluid is known to play an important role in transporting surface vibrational energy across discontinuities in a thin elastic structure. These effects are particularly important if the discontinuities in the elastic properties of the structure are large and would hence tend to reflect a significant amount of vibration. The main results that have been previously obtained refer to the reflection of a normally incident flexural wave from a line discontinuity: The dependence on the incident angle of the flexural wave relative to the line discontinuity has been only briefly considered. Some simple models to examine this phenomena, fluid-loaded infinite membranes and plates with line discontinuities, have been investigated. It has been found that short-circuiting effects due to the fluid become much weaker as the angle of incidence increases. These results and their phenomenological implications will be discussed.
Diffraction of short wavelengths by a circular elastic plate in a contrasting baffle
Authors: Wickham Gerry R.
Published: October 2005

The scattering of sound of wavelength 2π/k by a circular elastic plate of radius a in an infinite planar contrasting baffle is exactly formulated in terms of a singular integral equation of the second kind using a novel extension of the Wiener–Hopf technique. The exact solution of this equation is easily derived analytically as a rigorous convergent expansion that is also asymptotic in the limit ka→∞. Thus it is possible to derive explicit asymptotic formulas for the scattered field in terms of the factorization of the standard Wiener–Hopf kernel corresponding to the canonical diffraction problem for two adjoining semi-infinite compliant surfaces. The special cases of an elastic plate in a rigid baffle and a rigid plate in an elastic baffle are considered in detail. It turns out that the asymptotic forms for the diffracted far fields may be simplified dramatically using a factorization procedure devised by the author and Andrew Norris and that these results are uniform in the fluid loading parameter.
Reduction of backscattering from cylindrical shells by damping treatment
Authors: Guo Yueping
Published: October 2005

For oblique incidence within about 30° off normal incidence, backscattering from cylindrical shells is known to be dominated by reradiation from shear and/or compressional waves in the shell. Thus backscattering can be reduced by dissipating these shell-borne waves through damping treatment to the shell. This paper discusses some possible forms of damping. Three examples are given, namely, a three-layered shell with a homogeneous viscoelastic core, a three-layered shell with a fiber-reinforced viscoelastic layer, and a shell with cavities filled with highly dissipative viscous fluid. It is shown that these kinds of damping treatment reduce the phase speeds of the radiating waves, as well as increase the effective loss of the composite shell, which lead to significant reduction in the backscattered field. [Work supported by ONR.]
Vibration containment by structural joints
Authors: Guo Yueping
Published: October 2005

In controlling vibrations in elastic structures such as trusses, damping treatment is sometimes applied only in parts of the overall structure. In this case, it is important to confine vibrations to such parts to maximize dissipation. This paper demonstrates that this vibration confinement can be achieved by suitable design of structural joints that connect members of the overall structure. For example, joints with flexibility in rotation and with finite mass and eccentricity can practically reflect all bending waves incident upon the joints within a wide frequency domain. [Work supported by ONR.]
Asymptotically correct shell theories with fluid loading for the thin spherical shell: New results
Authors: Dean Cleon E. , Werby Michael F.
Published: October 2005

In a previous paper [C. E. Dean and M. F. Werby, J. Acoust. Soc. Am. 91, 2440 (A) (1992)] further results in the derivation of a so-called ‘‘shell theory’’ incorporating proper high ka asymptotic behavior for the Lamb flexural and extensional modes for a thin spherical shell were given. Shell theories give reasonably good results for the motion of a bounded elastic shell by positing that various parts of the shell move together in some reasonable manner. They also give physical insight into the motions of the shell while using less computational time and resources than exact elastodynamic calculations. The use of various assumptions about the motions and fluid loading of the thin spherical shell gives rise to several shell theories. New results from the derivation of an asymptotically correct shell theory with fluid loading for the thin spherical shell are compared with the exact results from modal analysis with particular emphasis on the large size parameter (large ka) limit for the flexural and extensional Lamb modes. Limitations of each of the methods are then outlined as well as those of shell methods in general. [Initial work in this area supported by ONR/NRL and by ONT Postdoctoral Fellowship Program.]
Studies of laser-generated ultrasound using a micromachined silicon electrostatic transducer in air
Authors: Wright William M. D. , Schindel David W. , Hutchins David A.
Published: October 2005

An air-coupled micromachined silicon electrostatic transducer has been used to detect ultrasound generated by a pulsed laser in metals and polymers. Bulk longitudinal and shear wave modes have been observed, as have Rayleigh waves in thick samples and Lamb waves in thinner plates. The results are in good agreement with surface displacement waveforms obtained using a contact capacitance device as a reference. The result is a flexible noncontact ultrasonic system with potential uses in materials characterization.
Ear-canal standing waves and high-frequency sound calibration using otoacoustic emission probes
Authors: Siegel J. H.
Published: October 2005

Low-noise microphones designed to measure otoacoustic emissions from the human ear canal typically sample the sound field in the canal some 15–20 mm away from the eardrum. The input sound levels to the middle ear are usually defined as the sound-pressure level ‘‘at the eardrum.’’ However, the well-known phenomenon of standing waves produces a spatially nonuniform pressure for frequencies above 2–3 kHz. This phenomenon is demonstrated using physical simulation with a commonly used emission probe and the interpretation of the results are confirmed by simple acoustical theory. In addition, it is shown large (±20 dB) errors in the estimated eardrum sound pressure result from varying the position of the sound source in the canal. Theory, physical simulations and measurements in human ear canals are used to characterize the errors using various calibration procedures commonly employed in otoacoustic emission studies. It is predicted that the reliability of measurements of high-frequency stimulated otoacoustic emissions will be improved if the stimulus sound-pressure levels were measured near the eardrum.
The critical modulation frequency and its relationship to auditory filtering at low frequencies
Authors: Sek Aleksander , Moore Brian C. J.
Published: October 2005

If the thresholds for detecting sinusoidal amplitude or frequency modulation of a sinusoidal carrier with frequency fc are expressed in terms of the respective modulation indices, m and β, the ratio β/m decreases as the modulation frequency increases, and approaches an asymptotic value of unity. The modulation frequency at which the ratio first becomes unity is called the critical modulation frequency (CMF). It has been suggested that the CMF is reached when the spectral sidebands in the stimulus first become detectable and that the CMF corresponds to half the value of the critical bandwidth (CB) at fc. In this paper it is demonstrated that the CMF is confounded as a measure of frequency selectivity at low frequencies, since, for modulation frequencies around the CMF, the sideband that is most detectable changes with fc. For values of fc above 250 Hz, the lower sideband is most detectable. For values of fc below 200 Hz, the upper sideband is most detectable. These findings can account for the fact that the CMF flattens off at low carrier frequencies, reaching an asymptotic value of about 40 Hz, whereas the auditory filter bandwidth continues to decrease down to very low center frequencies.
Pitch perception for different modes of stimulation using the Cochlear multiple-electrode prosthesis
Authors: Busby P. A. , Whitford L. A. , Blamey P. J. , Richardson L. M. , Clark G. M.
Published: October 2005

Numerical estimations of pitch were obtained from nine postlinguistically deafened adults using the 22-electrode cochlear implant manufactured by Cochlear Pty. Limited. A series of electrodes on the array were stimulated using three modes of stimulation: Bipolar (BP), common ground (CG), and monopolar (MONO). In BP stimulation, an electric current was passed between two electrodes separated by one electrode for eight patients and two electrodes for one patient. In CG stimulation, a single electrode was activated and the other electrodes on the array were connected together to serve as the return path for the current. In MONO stimulation, an electric current was passed between a single electrode and the most basal electrode on the array. Pitch estimations were generally consistent with the tonotopic organization of the cochlea. There was a marked reversal in pitch for electrodes in the middle of the array using CG stimulation for three patients. A reduced range of pitch using MONO stimulation was recorded for patients where the most basal electrode was internal to the cochlea. There were also individual differences in pitch estimations between the three modes of stimulation for most patients. The current levels required to elicit threshold (T) and comfortable listening (C) levels were, in general, higher for BP stimulation than for CG stimulation and were lowest for MONO stimulation. For CG stimulation, there was a tendency for T and C levels to be higher for electrodes in the middle of the array than at the basal or apical ends. For MONO stimulation, T and C levels uniformly increased in an apical to basal direction for the majority of patients. There was no consistent pattern in T and C levels for BP stimulation. The size of the range of usable hearing using CG stimulation tended to be similar to that using BP stimulation and was usually higher than that using MONO stimulation.
Cues for perception of the diphthong /ɑi/ in either noise or reverberation. Part I. Duration of the transition
Authors: Nábělek Anna K. , Czyzewski Zbigniew , Crowley Hilary
Published: October 2005

Location of boundaries (the 50% response point) and slopes of identification functions were determined for synthesized /ɑi/ vowel continua. Within each continuum, the stimuli contained a steady-state segment followed by a transition in which the frequencies of formants changed in time. Here, F1 changed in a downward direction and F2 changed in an upward direction. Total duration of each stimulus was 200 ms. The duration of the transition was increased in steps from 0 to 140 ms. Two patterns of formant transition were used: (1) formants changing in the direction of, but not reaching, target frequencies (except in the end-point stimulus), and (2) formants reaching F1 and F2 targets. The data were collected with ten normal-hearing and ten hearing-impaired subjects. The boundaries and slopes were determined for four listening conditions: quiet, noise, short reverberation (0.8 s), and long reverberation (1.1 s). The location of boundaries depended upon: (1) pattern of formant transitions, (2) listening condition, and (3) status of subjects’ hearing. Generally, longer transitions were needed for formants changing in the direction of, but not reaching, target frequencies, than for those reaching F1 and F2 targets. The required transition durations were similar in quiet and noise, but were longer in reverberation. The hearing-impaired subjects generally required longer transitions to reach the boundaries than normal-hearing subjects. The slopes of the identification functions were shallower in either noise or reverberation than in quiet and were shallower for hearing-impaired than for normal-hearing subjects. In reverberation, the slopes for formants reaching targets were shallower than the slopes for stimuli with formants changing in the direction of target frequencies. The relationships between these findings and identification errors for naturally produced tokens of the diphthong /ɑi/ are discussed.
The influence of sentential speaking rate on the internal structure of phonetic categories
Authors: Wayland Sarah C. , Miller Joanne L. , Volaitis Lydia E.
Published: October 2005

In the experiments reported in this paper we compared the effects of syllable-level and sentence-level speaking rate on phonetic perception. In an earlier set of experiments, we found that syllable-level rate influences the internal perceptual structure of phonetic categories [Miller and Volaitis, Percept. Psychophys. 46, 505–512 (1989); Volaitis and Miller, J. Acoust. Soc. Am. 92, 723–735 (1992)]. Specifically, a change in target-syllable rate altered the location of the stimuli judged to be the best category exemplars, as well as the width of this best-exemplar range. In the present investigation, it was asked whether sentence-level rate has the same influence. It was found that slowing sentence rate shifted the location of the best-exemplar range, but did not alter its width. These findings are discussed in terms of timing mechanisms that may operate during speech perception.
Neural processing of musical timbre by musicians, nonmusicians, and musicians possessing absolute pitch
Authors: Crummer Garry C. , Walton Joseph P. , Wayman John W. , Hantz Edwin C. , Frisina Robert D.
Published: October 2005

Cognitive event-related potentials (ERPs) were measured during a timbre discrimination task from three subject groups varying in musical experience. The P3 component of the ERP was recorded from musicians with absolute pitch, musicians without absolute pitch, and nonmusicians during a task comprising timbres of varying difficulty. The three-timbre series, all of which consisted of the same pitch, were (1) string instruments in the same family (cello and viola), (2) flutes made of different materials (silver and wood), and (3) instruments of slightly different size (B-flat versus F tubas). The amplitude and latency of the P3 component varied systematically as a function of musical experience and type of timbre discrimination. The difficult timbre task resulted in mean P3 amplitudes which were larger for musicians relative to nonmusicians, however P3 amplitudes were similar for the two additional timbre series. The mean P3 latencies for musicians were shorter when compared to nonmusicians across all three series. In comparison, the AP subjects displayed the shortest mean P3 latencies, but had smaller P3 amplitudes relative to both musicians and nonmusicians. The implications of these findings suggest that perceptual tasks involving one of the fundamental building blocks of music, namely timbre, does elicit differential brain activity from memory or information processing systems from subjects with varying degrees of musical training.
Acoustic information available to bats using frequency- modulated sounds for the perception of insect prey
Authors: Moss Cynthia F. , Zagaeski Mark
Published: October 2005

Through the present study, the acoustic information available to an echolocating bat that uses brief frequency-modulated (FM) sonar sounds for the pursuit and capture of insect prey has been characterized. Computer-generated sonar pulses were broadcast at tethered insects, and the returning echoes were recorded on analog tape at high speed for off-line analyses. Echoes from stationary and fluttering insects were displayed using time waveform, spectrogram, power spectrum, and cross-correlation representations. The results show echo signatures for the different insect species studied, which change with the angle of incident sound. Sequences of echoes from fluttering insects show irregular changes in sound amplitude and time-frequency structure, reflecting a random temporal relation between the changing wing position and the arrival of incident sound. A set of recordings that controlled the temporal relation between incident sound and insect wing position suggests that information about the spatial profile of a flying insect could be enhanced if the bat were to produce a sequence of sounds that synchronized briefly with the moving target’s wing-beat cycle. From this study, it has been proposed that the FM bat receives stroboscopic-like glimpses of fluttering prey whose spatial representation depends on the operation of the bat’s sonar receiver.