bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity of the deconvolution of ocean transients to environmental mismatch.
Authors: Broadhead Michael K. , Field Robert L. , Leclere James H.
Published: October 2005

The single-channel deconvolution of acoustic transients for source classification purposes can be sensitive to small errors in the computed ocean Green’s functions. These errors arise due to incomplete environmental and source location information. The sensitivity was studied by perturbing the Green’s functions in such a way as to produce improved source estimates from field measurements. A systematic technique to do this was developed using a weighted, linear optimization approach. It was discovered that small changes in the computed Green’s functions could improve the source estimate significantly. It was also determined that the match between the simulations and the measured data is closely connected to the match between the source estimates and the measured source waveform, hence the sensitivity is not just due to deconvolution. This relationship was quantified by using the correlation coefficient. This study is part of an effort to determine the applicability of deterministic deconvolution to the problem of transient classification. [Work supported by ONR under NRL program management.]
The learning capabilities of an artificial neural network for classifying acoustic signatures.
Authors: DeMetz Fred C.
Published: October 2005

The ability of an artificial neural network to learn to identify acoustic sources from a digital series of their spectral or temporal features has been studied experimentally. The learning system was comprised of a feedforward network employing a backward propagating delta rule for error correction. A three-layered network configuration of 30 input units, 15 hidden units, and 1 output unit was utilized. The network was first trained with patterns of 30 line spectra, some containing source lines and some containing noise only. Then the ability of the trained network to correctly identify new patterns of the source and noise data was tested. The results indicated several interesting characteristics relating to the utility of neural networks in the classification of acoustic waveforms. The network achieved classification accuracies exceeding 95%, with low false alarm rates, for frequency stable, high signal-to-noise spectra. For low signal-to-noise spectra, with fluctuations on both the frequency and amplitude of the source lines, the network tended to perform poorly.
Acoustic pulse spreading and distortion due to frequency-dependent attenuation in water at high frequencies.
Authors: Cole J. B.
Published: October 2005

For high-resolution imaging sonar, short high-frequency pulses are needed to reconstruct surface features. For example, 1-cm range resolution or better requires pulse durations of 12 μs or less at frequencies of 1 MHz or greater. Because large bandwidths are required to synthesize the pulses, the signals spread in the time domain and distort as they propagate through the water due to frequency-dependent attenuation that rises as the square of frequency. These effects were studied for various combinations of signal parameters, and the results are related to signal design considerations for high-resolution sonar ranging and imaging.
Nonorthogonal signal decomposition.
Authors: Yen Nai-chyuan
Published: October 2005

To gain physical interpretations and insights from observed phenomena, it is often desirable to decompose a given function, i.e., the observed signal, into a set of nonorthogonal functions. This paper describes a signal processing algorithm based on the minimization of the mean-square error formulation of the decomposition analysis. The computation scheme is derived from a recursive gradient descent method to approach the correct answer for a set of over-determined simultaneous equations. The traditional matrix inversion technique is usually not workable for numerical operation because the matrices are often ill-conditioned. This suggested approach not only alleviates the computation problem, but also can more easily be implemented in a parallel architecture computer or a neural-like network. The signal received from a synthetic circular array [N. Yen, IEEE/JOE, Jan. 1992, pp. 40–47] is used, as a practical example, to illustrate that a composite signal can be reduced to a combination of the corresponding signals from various directions. Comparison of the results obtained by this algorithm with the traditional beamforming method supports the use of this new signal processing technique.
Evaluation high-resolution frequency estimators for the determination of the eigenvalues of modes in a shallow water waveguide.
Authors: Rajan Subramaniam D. , Bhatta Saurav
Published: October 2005

In shallow water, the acoustic field due to a point source can be modeled as a sum of contributions from trapped modes propagating in the waveguide. The performances of two high-resolution methods (MUSIC and ESPRIT) in estimating the eigenvalues of the modes and in resolving closely spaced modes are studied using noisy synthetic data and field measurements. Simulation performed to investigate the effect of modeling errors indicate, that for a weakly range-dependent medium the performance of the algorithms is not adversely affected. However, errors in ranging and presence of colored noise in data have considerable impact on the performance of these algorithms. [Work supported by ONR.]
Extracting ocean sound-speed information from acoustic ambient noise measurements using vertical hydrophone arrays in shallow water.
Authors: Berman David H. , Wolf Stephen N.
Published: October 2005

The ocean sound-speed profile near a vertical hydrophone array in shallow water may be determined from measurements of the acoustic field due to distant noise sources. Sound speeds are obtained from second spatial derivatives of the noise covariance matrix. The distance to, and the bandwidth of, the noise generator and the geometric dispersion of the duct must yield a covariance matrix that is an incoherent sum of the acoustic modal components. The array need not span the water column; however, sound speeds are determined only at hydrophone locations. This technique may be useful for monitoring sound-speed changes in situations in which it would not be feasible to deploy or monitor independent sound-speed sensors near the acoustic array. Computer simulations show that sound-speed estimates are insensitive to noise that is uncorrelated between hydrophones. [Work supported by the Office of Naval Technology, Code 234.]
A research program on the ‘‘tenora,’’ a Catalan folk woodwind.
Authors: Barjau Ana
Published: October 2005

The ‘‘tenora’’ is a Catalan folk woodwind with a conical bore and a double reed. The modern ‘‘tenora’’ evolved from the medieval tenor shawm to fit the needs of more demanding composers and players. This evolution has been mainly artisanal, and as a consequence there is not a standardized design for the instrument. Although much better than old shawms, all tenoras show a non-negligible degree of imperfection in the tuning, stability, and spontaneity of many notes. In order to improve this instrument without impairing its identity, a small group in the Department of Mechanical Engineering of Barcelona started a research program that includes three main parts: experimental measurements (acoustical impedance, impulse response, starting transients, and tuning) to characterize its acoustical identity, theoretical model of the instrument (bore model and reed model) and simulation of it, and redesign algorithm to improve the existing instrument. This research program and its latest results will be presented in this paper. The attention is focused on the last two points, whose development has led to interesting theoretical work applicable to other instruments.
Acoustics of handbells.
Authors: Rossing Thomas D. , Sathoff H. John , Hansen Uwe J.
Published: October 2005

Although handbells date back at least several centuries B.C., tuned handbells of the type played today were developed in England in the 18th century. One early use of handbells was to provide tower bellringers with a convenient means to practice change ringing. In more recent years, handbell choirs have become popular in schools and churches−some 2000 choirs are reported in the USA alone. In the so-called English tuning of handbells, followed by most handbell makers in England and the United States, the (3,0) mode is tuned to three times the frequency of the (2,0) mode. The fundamental (2,0) mode radiates a rather strong second harmonic partial, however, so that the sound spectrum has prominent partials at the first three harmonics. Modes of vibration of handbells have been studied by means of holographic interferometry, scanning the near-field sound with a microphone, and by modal analysis with impact excitation. Handbells are usually scaled so that the diameter is inversely proportional to the square root of frequency, except in the smallest bells in which it varies inversely with the cube root of frequency. The thickness h is then adjusted so that h/d2 is nearly proportional to the frequency.
Phase-matching filter techniques for low signal-to-noise data.
Authors: Orris G. J. , McDonald B. E. , Kuperman W. A.
Published: October 2005

A digital filter is being developed for use in low signal-to-noise situations where the shape of the noise spectrum is known apriori. Candidate noise signals are generated and subtracted from ‘‘observed’’ (real or idealized) pressure-time series by minimizing total power in the output with respect to the phases of the noise components. The minimization process results in matching the phase of each candidate noise component to that of the input signal at the same frequency. When the noise spectrum is sufficiently smooth and distinct in shape from that of the signal, good results have been obtained for idealized cases involving signal-to-noise ratios of −80 to −100 dB. At these levels there are no identifiable peaks in the power spectrum to indicate even the existence of a signal. With no apriori knowledge of the phase of either the signal or noise, an almost undistorted signal can be recovered. In more realistic cases involving recorded noise, however, filter performance is degraded. Methods to improve filter performance in nonidealized cases are under investigation.
Uncoupling supersonic Lamb waves on plates and shells from the surrounding fluid: Approximate condition on the phase velocity.
Authors: Marston Philip L.
Published: October 2005

Lamb waves propagating with a phase velocity cl along a fluid-loaded plate or shell generally leak or radiate wavefronts at an angle determined by the trace velocity matching condition when cl exceeds the velocity of sound in the surrounding fluid. Ray representations of the backscattering by spherical and cylindrical shells show the leaky wave contributions are proportional to the radiation damping βl of the wave [S. G. Kargl and P. L. Marston, J. Acoust. Soc. Am. 89, 2545–2558 (1991); N. H. Sun and P. L. Marston, J. Acoust. Soc. Am. (accepted for publication)]. A curious numerical result is that for certain leaky rays, the function βl(ka) can exhibit a minimum where βl can be as small as 10−4 Np/rad and the associated resonances are very narrow. An approximate condition for such minima is evident by considering the particle displacement at the surface of a flat plate in a vacuum. It has been shown [D. C. Worlton, J. Appl. Phys. 32, 962–971 (1961)] that there is no normal displacement of the plate’s surface when the phase velocity of a Lamb wave equals the longitudinal wave speed cL of the material. In the present work it is shown that the radiation damping exactly vanishes at this condition for a flat plate with an unbounded fluid on one or both sides. Normal displacements are essential for radiation by curved shells so that βl should be minimized for cl≊cL. This condition was numerically verified. The phenomenon allows for the supersonic transport of mechanical energy with negligible sound production. [Work supported by ONR.]
Generalized Lamb waves near mode thresholds of spherical shells.
Authors: Hughes D. H. , Marston P. L.
Published: October 2005

Pole trajectories as a function of frequency in the complex angular momentum plane for backscattering from empty spherical shells with and without significant fluid loading are presented. These are correlated with Lamb wave threshold features (that depend on Poisson’s ratio) found on a flat plate in vacuum. [R. D. Mindlin, ‘‘Waves and Vibrations in Isotopic, Elastic Plates,’’ in StructuralMechanics (Pergamon, New York, 1960); A. H. Meitzler, J. Acoust. Soc. Am. 38, 835–842 (1965).] The trajectories for the fluid-loaded case are relevant to the high-frequency enhancements and longitudinal (or thickness) resonance of recent investigations [see, e.g., S. G. Kargl and P. L. Marston, J. Acoust. Soc. Am. 89, 2545–2558 (1991)]. The usual poles lie in the first quadrant of the upper half-plane. Near the longitudinal resonance condition a pole associated with a symmetric wave is present in the second and fourth quadrants and is associated with the high-frequency enhancement. Its pole trajectory indicates that the phase and group velocity are oppositely directed over a small range of ka where the enhancement occurs. [Work supported by ONR.]
A method for simultaneously determining structural response and bistatic target strength of immersed structures.
Authors: Clark Joseph A. , Sartori Michael A.
Published: October 2005

Structural response measurements can reveal the physical mechanisms that control scattering of acoustic waves by an immersed structure. Bistatic target strength measurements provide a means for fully evaluating effects of the physical mechanisms on far-field scattering. Phase-coherent, simultaneous measurements of both quantities would permit structural acoustics investigators to relate in detail scattering mechanisms with corresponding far-field scattering effects. The simultaneous measurement method to be described in this talk utilizes pressure measurements made with a two-layer conformal array to determine pressure and pressure gradient distributions on a measurement surface that is located in the evanescent near field of the immersed structure and conforms to its shape. The acoustic field is back-projected to the structure surface with a near-field-holography algorithm to determine structural response and is forward-propagated to the acoustic far field with an algorithm based on the exterior Helmholtz integral to determine bistatic target strength. The method is illustrated with a simulated study of scattering from an idealized cylinder. [Work supported by ONT.]
Asymptotically correct shell theories with fluid loading for the thin spherical shell.
Authors: Dean Cleon E. , Werby Michael F.
Published: October 2005

So-called 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 can 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. The results derived from these theories are compared with the exact results 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. [Work supported by ONR/NRL and by ONT Postdoctoral Fellowship Program.]
The acoustic radiation efficiency of metal and composite panels.
Authors: Szwerc Richard P. , Weyer Richard M.
Published: October 2005

The acoustic radiation efficiency of solid metal and composite panels submerged in water has been analytically and experimentally determined. The experimental results validate the theoretical expressions of Blake [W. K. Blake, MechanicsofFlow-InducedSoundandVibration, Vol. I, 331–333 (1986)]. The dependence of the radiation efficiency upon the wave speed of the panels when excited by a point force has been observed, thus emphasizing the independence of the radiation efficiency and the structural damping of the panels.
Acoustic scattering from a fluid-loaded thin plate/shell with a reinforcing rib.
Authors: Lu I-Tai , Bertoni Henry L. , Yao Yuqi
Published: October 2005

Acoustic waves incident from water are partially reflected at the outer shell of a submerged vessel. In addition, they excite elastic vibrations of the internal structure of the vessel, which in turn re-radiate into the water. Thus, predicting the scattered acoustic field requires the ability to model and account for the internal structures. This discussion considers methods for computing scattering from a flat plate or a cylindrical shell with a reinforced rib. Full elastic properties of the rib are taken into consideration. The leaky modes excited by incident waves are coupled to other modes in the fluid-loaded plate/shell as well as in the rib. The mode coupling coefficients at the rib are highly dispersive because waves reverberate between its free edge and the junction where the rib is joined to the plate/shell element. These plate/shell waves induced by the rib can re-radiate to the water through two mechanisms: leakage and diffraction (see the preceding companion paper). The effects of the rib on the scattered field will be examined in detail. [Work supported by ONR.]
Low-frequency pressure wave propagation in liquid-filled, flexible tubes.
Authors: Bjelland Cato , Bjo/rno/ Leif
Published: October 2005

A model has been developed for propagation of low-frequency pressure waves in viscoelastic tubes with distensibility of greater importance than compressibility of the liquid. The dispersion and attenuation are shown to be strongly dependent on the viscoelastic properties of the tube wall. The complex, frequency-dependent moduli of relevant tube materials have been measured in a series of experiments using three different experimental procedures, and the data obtained are compared. The three procedures were: (1) ultrasonic wave propagation, (2) transversal resonance in bar samples, and (3) moduli determined by stress wave transfer function measurements in simple extension experiments. The moduli are used in the model to produce realistic dispersion relations and frequency dependent attenuation. Signal transfer functions between positions in the liquid-filled tube can be synthesized from the model and are compared with results of experimental pressure wave propagation in the liquid-filled, flexible tube. A good agreement between experimental data and theoretical predictions is found.
Improved vowel recognition using the discrete cosine transform.
Authors: Burr D. J.
Published: October 2005

Some experiments are described that use a discrete cosine transform (DCT) to represent vowel spectra for classification by a neural network. The recognition accuracy of a neural network trained by back propagation was compared to that of a simple Gaussian classifier. Twelve English vowel categories from the TIMIT database were used {aa, ae, ah, ao, ax, eh, er, ih, ix, iy, uh, uw}. Training was done in a speaker-dependent manner using 152 male speakers from all geographic regions. Eight 16-ms DFT spectra were computed at 8-ms intervals about the center of each vowel. Sixteen DCT coefficients were derived from the 250- to 4250-Hz interval in each 8-kHz spectrum. Average DCT and delta DCT vectors over the eight frames were used as input features. Additional features included the first six peak frequencies of the DCT spectrum and two pitch parameters from the DCT coefficients. Best performance was obtained by the neural network with all 40 input features, resulting in 58.2% recognition accuracy. This compares favorably to a cochleagram representation using the same vowel classes [Muthusamy etal., ICASSP-90]. The DCT also appears to require fewer coefficients than an equivalent cepstrum-based vowel classifier [Burr, ICASSP-92].
Acoustical profile of trained low male classical singing voices ranked as to perceptions of relative ‘‘beauty.’’
Authors: Robison Clayne W. , Bounous Barry , Bailey Ross
Published: October 2005

Based upon a uniform 20-s musical excerpt, a score of classically trained lower male singers will be ranked as to vocal ‘‘beauty’’ by a series of ‘‘expert’’ witness groups: (1) a panel of nationally published classical voice instructors, (2) a panel of classical voice instructor colleagues from a single unified voice faculty (with this group complete anonymity could not be preserved), and (3) a panel of knowledgeable, but amateur opera listeners. Correlation studies will be done among the witnesses in each ‘‘expert’’ group and between groups. From those correlations acoustical spectrum comparisons will be made among the ranked singers to determine which acoustical parameters seem most consistently present in those singers ranked as most ‘‘beautiful.’’ From a simultaneous video-taping of the sung excerpts, hypotheses concerning the physiological (postural) and aerodynamic events which led to those acoustical parameters will be spun out. This lecture will report the results of this study and discuss the related hypotheses.
Advanced methods for voice analysis.
Authors: Qi Yingyong
Published: October 2005

The harmonics-to-noise ratio (HNR) has been widely accepted as a measure for quantifying the irregular or noise component of voice. The use of the HNR assumes that: (1) the noise or irregularity in voice is a stationary process, and (2) errors introduced by the cycle-to-cycle pitch period variations are trivial. When either of these assumptions is violated, the HNR is inappropriate for estimating irregularities in the shape of acoustic wavelets. Methods for eliminating these assumptions (or limitations) of the original HNR have been developed based on advanced techniques of signal processing. In these methods, nonstationary irregularities in voice are identified using an adaptive Wiener filter. The effects of pitch period perturbations on the measurement of wavelet irregularities are minimized by optimal time normalization of wavelet assemble using procedures of dynamic time warping. These methods have been evaluated using natural and synthetic voices and results have indicated that they significantly increase the accuracy and reliability of voice analysis.
‘‘Within’’ and ‘‘between’’ sound comparisons.
Authors: Pollack Irwin
Published: October 2005

An isolated sound can be judged to be of ‘‘high pitch or low pitch’’ without direct explicit comparison with another sound. However, the comparative judgment of ‘‘higher than or lower than’’ implies a comparison between two sounds, although the two sounds need not be physically presented together, as in a one-interval test. On the other hand, the judgment of whether an isolated sound is harmonically ‘‘pure or impure’’ can be based upon the information within an isolated sound, and, in theory at least, does not imply a comparison between sounds. The discrimination of frequency differences within the mixture of two complex periodic signals (repeated random waveforms) was examined in a one-interval test. When the fundamental frequencies of the components within the mixture have a small-numbered ratio, the harmonic ‘‘purity’’ of the mixture could be judged. Judgments of harmonic purity were substantially more accurate than judgments of equivalent frequency differences, presumably in terms of pitch.
Observation of a medication-induced change in pitch perception.
Authors: Chaloupka Vladimir , Muirhead Richard , Mitchell Stephen
Published: October 2005

This paper reports on a study of an absolute pitch possessor who, upon administration of the psychoactive drug Tegretol (carbamazepine), experienced a significant change in her pitch perception. The subject’s performance both in producing as well as in identifying random tones was measured, covering the period of administration of the drug, as well as control periods before and after. The main effect was a downward shift of the pitch perceived when a synthesized tone was heard, as compared to the perception during the two control periods. The magnitude of the shift was observed to increase with increasing frequency of the stimulus; the average shift was about one semitone. Detailed results on the frequency dependence and time dependence of the pitch shifts are presented. An upward pitch shift of comparable magnitude was observed when the subject was requested to produce a musical note identified by its name. To our knowledge, this is the first documented report of a significant, reversible change of pitch perception caused by a medication. [Work partially supported by the University of Washington Graduate School Research Fund.]
Duration discrimination of affricate silent intervals: Performance in fixed- and roving-standard tasks.
Authors: Boyle Timothy A. , Espinoza-Varas Blas
Published: October 2005

Duration discrimination for the silence preceding the frication noise in the word /watsh/ was measured. The utterance was produced by a female talker and digitized at 20 kHz. The 200-ms affricate silence was edited to obtain: (a) seven tokens with silence ranging from 15–45 ms in steps of 5 ms (‘‘short’’ range); and (b) seven tokens with silence ranging from 100–200 ms in steps of about 17 ms (‘‘long’’ range). The ‘‘short’’ and ‘‘long’’ range were perceived as /wash/ and /watsh/, respectively. With each range, discrimination was measured in both fixed-standard and roving-standard 2IFC tasks, using a constant-stimuli method. Listeners discriminated 5%–60% decrements in the duration of the silence. Thresholds were interpolated at the 75%-correct level from probits fitted to five-point psychometric functions. For the ‘‘long’’ silence tokens, thresholds (expressed as Weber fractions) ranged from 0.08–0.18 and 0.07–0.13 for roving- and fixed-standard tasks, respectively. For ‘‘short’’ silence tokens, the corresponding Weber fractions ranged from 0.09–0.82 and 0.08–0.73. [Work supported by OCAST Grant No. HSO-005 and Presbyterian Health Foundation.]
Cavitation bioeffects: Spin-offs from lithotripsy.
Authors: Carstensen Edwin L.
Published: October 2005

Lithotripter fields can produce cavitation in the organs of the body at pressure amplitudes significantly lower than those required to fragment stones. Because of limits on the expansion of the gaseous nuclei imposed by the surrounding tissue structures, cavitation in tissue is qualitatively different from that described by classical cavitation theory for a spherical bubble in an infinite fluid. Thresholds for structural and functional changes in kidney, liver, lung, heart, and blood, developmental effects in the embryo/fetus, and killing of Drosophilia larvae have been determined. Studies of the biological effects of shock waves generated by lithotripters have guided us in the search for effects of diagnostically relevant pulsed ultrasound. In particular, lung hemorrhage occurs with pulsed ultrasound at acoustic pressures of the order of 1 MPa and effects on the dynamic behavior of heart tissue have been seen with single 1–10 ms pulses at pressure amplitudes of the order of 10 MPa. The effects in lung occur at temporal average intensities orders of magnitude lower than previously associated with biological effects in mammals.
Generation of cavitation by extracorporeal shock waves in vivo.
Authors: Delius M. , Gambihler S.
Published: October 2005

Extracorporeal shock waves are used in medicine to destruct kidney and gallstones. As a side effect, they can cause hemorrhage in tissues. During shock wave application, a transiently increased tissue echogenicity is observed by diagnostic ultrasound suggesting temporary generation of gas. When shock waves were applied to piglet livers, gas bubbles persisted for several hundred milliseconds in liver vessels. Three different findings suggest that the interaction between gas bubbles and shock waves is involved in the generation of tissue damage: First, the extent of renal hemorrhages depended on the rate of shock wave administration. Damage was most severe when the identical number of shocks was administered at a rate at which gas bubbles had not been flushed out of the high pressure field by the blood flow. Second, Prat etal. have demonstrated that injection of air microbubbles into the hepatic artery of rabbits greatly enhanced tissue damage. Third, tissue damage occurred in canine livers at the same sites as focal and transient accumulations of gas bubbles.
Very low-frequency seismo-acoustic noise below the seafloor.
Authors: Bradley C. R. , Stephen R. A.
Published: October 2005

The low-frequency acoustic seismic experiment (LFASE), conducted in the Blake Bahama Basin in August and September of 1989, was the first experiment to measure VLF ambient ocean noise on a seismic array within a DSDP borehole. Four three-component geophones were clamped to the borehole wall at 10, 40, 70, and 100 m below the seafloor. The frequency response of the acquisition system was flat from 4.5 to 40 Hz but meaningful ambient noise measurements were acquired down to 0.3 Hz. Both discrete sources (interpreted as local microearthquakes) and a continuous distributed source (identified as a mid-Atlantic storm) were observed. The earthquakes are characterized as sudden arrivals of high-amplitude (at least 10 dB above background), high-frequency (above 20 Hz) signals with a coda decaying to background levels within 30 s. Within the upper 10 m of the seafloor these events have dominantly horizontal motion. Vertical motion becomes dominant at 70 m and by 100 m the events are indistinguishable from background noise. These amplitude effects with depth in the array suggest that these are Stoneley waves trapped near the seafloor. Noise levels associated with the continuous source (storm) also decay significantly below the sediment/water interface. The noise levels associated with the storm appeared below 2 Hz. Between 0.3 and 1.0 Hz there is a strong directionally coherent signal. Analysis of particle motions indicates that the source is in the direction of Hurricane Erin, which was located off the West African and European coast. Below 1.0 Hz the particle motion of the storm-related energy is clearly retrograde elliptical at the seafloor indicating Stoneley wave modes. [Work supported by ONR.]
Space-time characteristics of broadband seismic noise: Results of the onshore component of SAMSON.
Authors: Nábĕlek John , Lin Guibiao , Tréhu Anne
Published: October 2005

In Oct. and Nov., 1990, data from an array of 37 three-component seismometers (16 broadband, 6 5 s, 15 1 s) deployed on the coastal plain of northeastern North Carolina and southeastern Virginia were collected as a part of the multidisciplinary SAMSON (Sources of Ambient MicroSeismic Oceanic Noise) experiment. The array extended from a few hundred meters to 170 km from the coastline. Large variations in the broadband noise level are observed as a function of time with the power during the noisiest time periods being more than 100 times higher than during the quiet times. Many of these noise variations are directly related to regional environmental changes (e.g., hurricane Lily and a ‘‘nor-easter’’) and changes in ocean wave heights observed near Duck, NC); however, some seismic noise variation is uncorrelated with local environmental variables, indicating much more distant sources. The correlation with the ocean wave heights is better at higher frequencies (0.2–0.4 Hz) than at lower. Looking more closely, the ‘‘double-frequency’’ (0.15–1 Hz) and ‘‘single frequency’’ (0.05–0.15 Hz) microseisms show interesting patterns. At certain times, the variations of the power in the two spectral bands are independent of each other, but at other times the power increases occur across the entire 0.05–1 Hz frequency band. When broadband increases in the noise power are observed, the higher frequency noise increase always precedes the lower frequency noise increase, and the noise peak in 0.09–0.2 Hz band typically lags the peak in the 0.4–1.0 Hz band by about 7 h.

In several instances, ocean wave heights display similar reddening of the spectra with time, indicating an offshore origin for the low-frequency microseismic noise and reflecting the longer time required by the regional offshore storm systems to generate low-frequency waves. The high-frequency (0.2–1 Hz) band is dominated by a number of peaks lasting about 12 h, primarily during daylight hours, and is also correlated with the local sea state. The character of these peaks indicates a regional offshore source in response to increases in wind-speed during daylight hours. Preliminary frequency–wave-number analysis indicates clear directionality for noise associated with the noise peaks that are not correlated with the local sea state. This indicates a dominant source at a large distance from which seismic waves travel essentially as plane waves across the array. The seismic noise field, however, becomes highly heterogeneous when the noise increase is correlated with the local sea state and is presumably of regional origin. In that case, the energy arrives from many azimuths along the coast line.
Enhancement of hydrodynamic flow noise radiation by the regulation of air bubbles in a turbulent water jet.
Authors: Korman Murray S. , Roy Ronald A. , Crum Lawrence A.
Published: October 2005

Experimental results show that the near-field hydrodynamic radiated flow noise (generated by a turbulent submerged circular water jet) is enhanced when the turbulent flow is modified to become a two-phase flow containing air bubbles. Acoustic intensity spectra, in the frequency band between 20 and 7000 Hz, are measured using a digital spectrum analyzer from signals generated by a hydrophone placed at the position of Z=4d and R=4d. Here, Z and R are the axial and radial positions from the nozzle exit, respectively. The water velocity is 12 m/s at the nozzle exit (of diameter d=0.635 cm). An amplification factor defined by the ratio of intensities Itwo-phase flow/Ifluid flow is measured as a function of the void fraction β of the air bubbles in an effort to verify the theoretical amplification predictions made by Crighton and Ffowcs-Williams [J. Fluid Mech. 36, 585–603 (1969)] and more recently by Prosperetti [J. Acoust. Soc. Am. 84, 1042–1054 (1988)]. A short video-tape of the experiment will be shown. [Work supported by the National Center for Physical Acoustics, ONR, and the Naval Academy Research Council.]
Resonant vibrations of fluid-loaded plates. Axisymmetric case.
Authors: Kauffmann Christiaan
Published: October 2005

Vibrational properties of hull plates of ships are considerably modified by the presence of water. A simple model problem is presented, consisting of a thin, transversely vibrating plate with a compressible fluid at one side and clamped along a circular contour. The forced vibrations are studied by means of a Green integral representation along with a set of coupled boundary integral equations. The kernel of the integral representation is found by using the Fourier–Hankel integral transform technique and by evaluating numerically the inverse transform in the complex wave-number plane. For the axisymmetric case the boundary integral equations collapse down into a system of algebraic equations, thus yielding an exact representation for the solution. The integration along the circular contour is performed analytically by employing addition theorems for cylinder functions. The Green kernels thus obtained correspond to the response of an infinite plate subject to fluid-loading and ring-driven by constant forces and moments. Numerical results are presented that show the fluid-loading effect on the resonant frequencies of the plate, which are shifted downwards relative to the in-vacuo natural frequencies, while acoustic radiation contributes to the damping of the plate’s resonant modes. [Work supported by the TNO Institute of Applied Physics, Delft, The Netherlands.]
Using beam elements to model the vocal fold length in breathy voicing.
Authors: Johnson Mark A.
Published: October 2005

During breathy voicing, the vocal folds close in a zipperlike fashion from front to back, rather than closing all at once as they do during modal voicing [D. H. Klatt and L. C. Klatt, J. Acoust. Soc. Am. 87, 820–857 (1990)]. The two-mass model of fold vibration can only simulate this nonuniform closure if it is modified to allow nonuniform displacement along the length of the folds. A simple model is obtained if the rigid masses of the two-mass model are replaced by three-node Mindlin beam elements, with the anterior and posterior ends of each beam pinned. During modal voicing, the two-beam model is almost identical to the two-mass model. With the arytenoids separated for breathy voicing, the two-beam model behaves like the two-mass model, until the folds start to close. As the beam elements close from front to back, the shear stiffness of the open part increases relative to its mass, so that the back part never quite closes. The combination of gradual closure and posterior ducting gives the spectral tilt characteristic of breathy voicing. Waveforms and spectra from preliminary simulation will be presented. [Research supported in part by an NIH grant.]
Patterns of correlation of tongue movement and electromyographic signal in vowel production.
Authors: Harris Katherine S. , Bateson Eric , Alfonso Peter
Published: October 2005

X-ray microbeam data from pellets on the jaw, tongue, and lips were compared with EMG signals from eight muscles for production of multiple tokens of 11 vowels in /schwapVp/ context, for an American English speaker. Pellet data were obtained from the Tokyo x-ray microbeam while electromyographic data were obtained at Haskins Laboratories. Acoustic recordings and a comparison of orbicularis oris electromyographic records with lip pellet movement data were used to link the two data sets, so that an estimate of muscle contraction time could be made and appropriate correlations of time functions across the sets generated. Tongue pellet data were adjusted to compensate for the effects of jaw position. Relations between EMG and movement signals for the point vowels /i/, /open aye/, and /u/ were as expected, in that movements up and front were accompanied by large signals from anterior and posterior genioglossus, movements up and back were accompanied by large signals from styloglossus, while tongue lowering movements were accompanied by substantial hyoglossus signals. However, relations among muscle signals were unique to each vowel. [Work supported by NIDCD grants to Haskins Laboratories.]
Forward-reverse evaluations of American English monophthongs.
Authors: Miller James D. , Meyer D. J. , Gottfried Michael
Published: October 2005

Members of a corpus of 2304 vowels [Fourakis, J. Acoust. Soc. Am. 90, 1816–1827 (1991)] were assessed for steady-state and dynamic spectral bases for their perceptual identities. Each putative steady-state segment as well as the entire vocalic nucleus was studied. Four listeners participated in a series of perceptual experiments. All sounds were identified as one of nine monophthongs. Only correctly identified tokens were studied in a ‘‘forward-reverse rating task’’ and a ‘‘forward-reverse identification task.’’ In the rating task, the listeners judged the phonetic similarity of forward and backward playings of each token. In the identification task they identified forward and backward playings as one of 16 monophthongs and diphthongs. Stimuli reliably and correctly identified whether played forward or backward are treated as ‘‘steady state.’’ Stimuli reliably and correctly identified when played forward, but not so identified when played backward, are treated as ‘‘asymmetrical spectral glides’’ or, similarly, as exhibiting ‘‘vowel inherent spectral change’’ [Nearey and Assmann, J. Acoust. Soc. Am. 80, 1297–1308 (1986)]. Classification schemes are discussed. [Work supported by NIDCD.]
Acoustic correlates of American English diphthongs.
Authors: Gottfried Michael , Miller James D. , Meyer D. J.
Published: October 2005

Various studies on diphthongs suggest that they can be effectively classified in terms of either (1) the pattern of the fundamental frequency and formants at the onset and offset of the production, (2) the onset pattern and the F2 rate of transition, or (3) the onset pattern and the direction of formant movement in an acoustic space [Nearey and Assmann, J. Acoust. Soc. Am. 80, 1297–1308 (1986)]. Extending earlier reports [Gottfried, J. Acoust. Soc. Am. 89, 1997 (1991)] these three hypotheses were assessed in (a) a log F1×log F2 space and (b) an auditory-perceptual space. Values for the relevant parameters were obtained for a corpus of 768 productions of American English diphthongs (6 diphthongs ×4 speakers ×2 tempos ×2 stress conditions ×2 consonantal contexts). The hypotheses were then evaluated in terms of classification performance using a statistical pattern recognition procedure. Results indicate that the acoustic parameters specified in each hypothesis were effective in obtaining correct classification of diphthongs. [Work was supported by NIDCD.]
A cross-language study of vowel production and perception: A pilot study.
Authors: Bradlow Ann R.
Published: October 2005

This paper presents the results of a pilot experiment for a larger study of the effect of inventory size and structure on vowel production and perception. This study will use acoustic and perceptual data from languages which vary in the size and structure of their vowel inventories to address questions regarding the connection between vowel production and perception, and regarding the universality of language specificity of vowel space categorizations. The data for this pilot study are from four speakers of each of two languages (English and Spanish), which differ in the size of their vowel inventories: English has 11 distinct vowel qualities whereas Spanish has 5. For the production study, recordings of words which illustrate the vowel contrasts were digitized and the formant frequencies of the target vowel steady states were measured from LPC spectra. The resultant vowel charts were plotted using various scales (koenig, mel, bark, log frequency), which were then compared in terms of their efficiency in representing the distinct acoustic categories. A perceptual experiment is planned in which listeners will be asked to categorize synthetic stimuli which will be constructed on the basis of the acoustic parameters measured in the production study.
The phonemic transformation effect: Intersubject agreement on verbal forms.
Authors: Chalikia Magdalene H. , Warren Richard M. , Bashford James A.
Published: October 2005

Earlier studies found that repeated sequences of brief steady-state vowels are heard as verbal forms consisting of syllables occurring in English. The present investigation employed six different arrangements of four 60-ms vowels. Unlike earlier studies, a 300-ms silent gap separated two of the items, so that verbal organization of different subjects started at the same stimulus position. Individual listeners reported their verbal organizations corresponding to each arrangement. Then, listeners were assigned to a partner, and each member of the pair attempted to match the verbal organization reported by the other to the appropriate sequence. Most listeners achieved a perfect correspondence of verbal forms with sequences for each of the six stimuli. The procedure was repeated substituting whispered for voiced vowels, and similar results were obtained. It appears that verbal organization of vowel sequences is not completely idiosyncratic, but is based upon objective acoustic characteristics resembling specific English syllables. [Work supported by NIH Grant. No. DC00208.]
Estimation of the acoustical transfer function from vowel confusions.
Authors: Wesselkamp Matthias , Kollmeier Birger
Published: October 2005

An attempt is made to estimate a spectral alteration in the acoustical transfer function (including the transmission characteristic of the peripheral auditory system) from vowel confusions. To study the relation between a predetermined spectral alteration and the resulting vowel confusions in a closed nonsense-syllable test, different conditions of filtered speech stimuli were employed with and without interfering speech-spectrum-shaped noise. The number of available perceptional cues and the variability of the material was restricted by synthesizing speech with a LAR vocoder. The vowel confusions between 14 syllables were analyzed with the transinformation analysis for the different filtered conditions. For this purpose, a set of 15 acoustical features was constructed. Each feature represents the average log power within one out of 15 auditory critical bands. Using these features, the ‘‘transinformation spectrum’’ is computed, i.e., the transmitted speech information as a function of frequency.This quantity might be used to predict the acoustical transfer function. Based on the empirical results, the correspondence between alterations in the acoustical transfer function and changes in the transinformation spectrum will be discussed.
On the effects of structural joints on sound scattering.
Authors: Guo Yue-Ping
Published: October 2005

By examining scattering from a joint connecting two perpendicularly attached plates, this paper addresses the acoustic effects of different structural joints, ranging from clamped connection, which transmits both forces (normal and tangential) and bending moment, to various pinned connections that allow free motions in one or two dimensions at the attachment point. It is shown that the normal force and the bending moment dominate the scattering process, respectively, in the low- and high-frequency domains. For low frequencies well below the plate coincidence frequency, the scattered field is dominantly given by the contribution from the normal force so that joints which support normal forces of equal value, but are otherwise different, lead to identical scattered fields. In the high-frequency region well above the coincidence frequency, the bending moment yields the dominant contribution.

Thus, joints such as rotation-free hinges scatter much less sound at high frequencies than those that transmit bending moment. It is shown that the amplitude ratio of the bending moment contribution to that due to the normal force closely follows a power law of frequency (normalized by the coincidence frequency) with the power index being 1.25, which results both from the respective dipole and quadrupole characteristics of the equivalent acoustic sources due to the force and the bending moment, and from the frequency-dependent strengths of these sources that are determined by the dynamic balance of the overall coupled problem. The predominance of the normal force and the bending moment in different frequency domains is shown to also govern the energy flow into the structure. At low frequencies, this energy is in the form of longitudinal motions associated with the normal force, while at high frequencies, transverse vibrations in the structure are most energetic because most of the energy is then transmitted to the structure through the bending moment. [Work supported by ONR.]