bluuebunny/crossref_metadata_2025 huggingface dataset:
Creaky phonation in Tianjin: Phonetic or phonological?
Authors: Davison Deborah
Published: October 2005

Tianjin Mandarin has four lexical tones: 1, low; 2, high; 3, rising; and 4, falling. Low and rising tones in stressed position sometimes sound creaky, so that these tones differ from the other two in phonation type as well as f0. Acoustic analysis indicates that tone 1 shows occasional use of fry limited to very low f0 values. In contrast, rising tone 3 uses creak systematically, regardless of f0 value. This suggests that for tone 1, the auditory effect is an incidental, phonetic, consequence of low f0, whereas, for tone 3, it is part of the phonological specification of the tone. This claim is tested further by examination of tone 3's positional variants (high, low level, and low rising). If tone 3 is found to be creaky even in its higher pitched variants, then the creak cannot be a phonetic result of low f0. Furthermore, if the creak of only tone 3 is systematic, then a supposed neutralization of tone 1 and 3 before tone 1 is incomplete: the f0 may be neutralized, but the distinction is still carried by the phonation type.
Vowel production in four Swedish glossectomy patients
Authors: Almé Ann-Marie , Engstrand Olle , Öberg Eva
Published: October 2005

This study examines the production of the tense vowels /i e a u/ in four Swedish speakers. Acoustic measurements from spectrograms show that the speakers have smaller vowel spaces postoperatively compared to data obtained preoperatively, with a particularly strong reduction along the F2 dimension. Furthermore, the vowel spaces are more reduced in connected speech than in isolated word forms suggesting that, in connected speech, subjects do not exploit their full potential for articulatory compensation in vowels. Acceptability of glossectomy speech will be discussed. Preliminary observations show very clearly that the extent of glossectomy is reflected in listener judgments of articulatory impairment. [Work supported by The Swedish Cancer Society and The Swedish Council for Planning and Coordination of Research.]
Rediscovering auditory coherence in phonetic patterns
Authors: Gagnon Deborah A. , Sawusch James R.
Published: October 2005

It has been suggested that phonetic percepts are achieved by invoking the use of a specialized speech mode in processing the acoustic signal [A. M. Liberman and I. G. Mattingly, Cognition 21, 1–36 (1985)]. In support of this contention are demonstrations of differences between speech and nonspeech perception of the same set of stimuli. For example, subjects provided with speech labels (/ra/ and /la/) for categorizing a three-formant tone analog continuum that varied in only the F3 transition dimension demonstrated categorical perception, while those subjects provided with nonspeech labels did not [C. T. Best et al., Percept. Psychophys. 45, 237–250 (1989)]. However, an alternative explanation is that the nonspeech group's poor categorization performance may have resulted from a failure to provide adequate training. In the present study, providing more extensive training resulted in steep identification functions for both speech and nonspeech groups. In addition, peaked discrimination functions were found for nonspeech subjects. Indicating that the stimuli were being perceived categorically. The data support a methodological explanation of dissociations in categorization performance between speech and nonspeech instructed groups and suggest that a “speech is special” claim remains tentative. [Work supported by NIDCD Grant DC00219 to SUNY at Buffalo.]
Reaction time and dichotic evidence for central processing of complex auditory signals
Authors: Kat Donna
Published: October 2005

Extensive work has been done to clarify the number of stages and the mechanisms involved in the recognition of speech. This selective adaptation study examines the effect that individual second and third formants have. compared to the combined effect of both formants; the combination is tested both monaurally and dichotically. Experiment 1 compares the added effects of the individual second and third formants to the effect of an adaptor with combined second and third formants. Experiment 2 examines the effect of variations in amplitude of the adapting formants. The third experiment examines dichotic presentation of the second formant in one ear and the third formant in the other versus binaural presentation of the combined second and third formants. Reaction time results and the labeling shifts suggest a post-peripheral and integrative mechanism for complex signal processing. [Work supported by AFOSR.]
Reflection tomography in the presence of wave front distortion
Authors: Smith James F. , Waag Robert C. , Gaumond Charles F.
Published: October 2005

The performance of an imaging algorithm [P. B. Abraham and C. F. Gaumond, “Reflection tomography,” J. Acoust. Soc. Am. 82, 1303–1314 (1987)] that replaces a scattering object by an equivalent source or reflectivity distribution is investigated in the presence of wave front distortion arising from sound-speed variations in the path between the scattering object and the detectors. The wave front distortion is modeled by weighting the expression for the far field pressure, which is the Fourier transform of the effective source distribution, with a phase factor. The phase factor is determined by the travel time change produced by the sound-speed variations. Travel times are computed by ray tracing. Measured scattering from a solid aluminum sphere is employed in a geometry in which the detectors are below the sphere, and span a plane in a half-space out to the reliable acoustic path. The incident wave is assumed to travel in a direction parallel to the surface of the detector plane and the sound-speed variations are assumed to depend only on the distance between the scattering object and the detector plane. Images obtained using the algorithm with and without wave front distortion show the degrading effect of a sound speed that varies with depth.
Extracting nasality from speech signals
Authors: Reetz Henning
Published: October 2005

“Nasality” is commonly defined as resulting from speaking with a more or less lowered velum. Although this phenomenon appears in every language, sometimes as a distinctive feature, and can be perceived clearly, there is no reliable way to automatically extract it from the speech signal. An algorithm is being developed that segments the speech waveform into “nasal” and “non-nasal” parts. The algorithm works without presegmenting and does not need information about whether nasal sounds are present or not. The algorithm searches voiced areas in the speech signal by means of a pitch extraction algorithm. In these areas, a resonance in the range of 200–400 Hz is searched. The frequency of this resonance may vary between speakers, but is assumed to be constant for individual speakers. If this resonance with constant frequency persists for more than 100 ms, the area is labeled nasal. The bandwidth of the low resonance can be used as a rough indicator for the amount of nasality existing in the speech signal.
Shot propagation from the Arctic Basin
Authors: Del Huston R. , Brooke Gary H. , Thorliefson Jon M.
Published: October 2005

Shot experiments provide a means of measuring dispersion and mode excitation. The Arctic Ocean, with its rough ice canopy, variable bottom geoacoustics, and bathymetry, contains many complex acoustic environments with interesting modal propagation characteristics. At three deep-water sites, a series of explosive charges was detonated at three different depths. The signals were recorded with a nine-element vertical array located on the continental shelf. Sonograms were used to determine the dispersive properties and depth-dependent nature of the modes. Dispersive properties observed in the data were formed in the deep-water environment and were only slightly modified by the shallow (500-m) waveguide at the vertical array. The depth dependence of the observed mode shape is computed by mode fitting with theoretical shapes and applying weights to the complex summation of these modes. Shear properties play a dominant role in determining the mode shapes in this shallow-water environment.
Vertical array matched-field/mode processing results from marginal ice zone data
Authors: Smith G. B. , Lawrence Thomas N.
Published: October 2005

Matched-field/mode processing (MFP) has been used to successfully detect and localize submerged acoustic sources in shallow water, arctic waters, and open ocean environments. A very challenging environment for the application of these techniques is the marginal ice zone. The spatial and temporal oceanographic variability of this region makes precise acoustic modeling impossible with the modeling techniques commonly available today. Hence, successful MFP in the marginal ice zone requires the use of robust processing schemes that can perform satisfactorily in an inherently mismatched environment. In this paper, successful MFP results are reported for marginal ice zone data from a vertical, near-surface array deployed as part of the MIZEX-88 experiment. A robust, dimensional reduction processing scheme, the reduced maximum likelihood method [Byrne et al., J. Acoust. Soc. Am. 87, 2493–2502 (1990)] applied to a few of the low-order modes, was used for successful localization of a 190-dB source at a range of 9 km, with some depth error, using measured environmental parameters. The depth error was eliminated by refinements made to the environmental and array element location parameters. [This work is supported by the AEAS program.]
Arctic abyssal T phases: Coupling seismic energy to the ocean sound channel via under-ice scattering
Authors: Keenan Ruth Eta , Merriam Lynn R. L.
Published: October 2005

Earthquakes along the mid-Arctic ridge radiate earthborne compressional and shear waves that couple into the Arctic acoustic channel and propagate as T phases. The T-phase energy is transmitted above the epicenter through the seafloor at near vertical angles. Scattering from the ice surface couples some of this energy into waterborne angles. At 5 Hz, the coupled energy is about 40 dB down from the incident levels and at 15 Hz, it is about 30 dB down. Scattering accounts for the characteristic spectral shape of the abyssal T phase that is more energetic at 15 Hz than 5 Hz. Several T-phase arrivals were recorded on hydrophones during the FRAM II experiment. From the measured acoustic levels, a transmission loss prediction between source and receiver, and the scattering conversion losses, the microearthquake acoustic source level in the water column is estimated to be about 250 dB re: 1 μPa/Hz at 5 Hz and 235 dB re: 1 μPa/Hz at 15 Hz. These levels lead to a crustal attenuation estimate of 0.52 dB/km at 5 Hz that is consistent with FRAM II refraction measurements. [Work supported by ONR.]
Modeling of under-ice reflectivity measurements
Authors: Wolf J. W. , Diachok O. I. , Yang T. C.
Published: October 2005

A technique to model under-ice reflection loss based on new analysis of data from the Fram IV experiment is described. Using Burke-Twersky scattering theory, the under-ice/water boundary is modeled as a set of rigid, elliptical cylinders fixed to a free surface. Ice draft measurements taken during the Fram IV experiment are used to identify individual ice-ridge keels resulting in a keel depth distribution function spatially coincident with the acoustic measurement track. The Burke-Twersky scattering function is weighted against the keel depth distribution providing an effective scattering as a function of frequency. Ice reflectivity as a function of grazing angle is then calculated for a particular frequency, which provides predictions that are in good agreement with those inferred from low-frequency, long-range acoustic field measurements.
The subjective and objective evaluation of three buildings for music
Authors: Cervone Richard P. , Siebein Gary W. , Doddington Harold W. , Schwab Wilhelm , Fausz Jerry L.
Published: October 2005

Subjective responses and physical acoustic measurements were collected in three rooms: University auditorium and the band rehearsal room at the Univ. of Florida, and Naples Philharmonic Hall in Naples, Florida. An evaluation sheet comprised of nine criteria—clarity, intimacy, envelopment, balance, reverberance, loudness, overall impression, background noise, and echoes—was utilized to gather the subjective data. Objective data were collected by recording pistol shots in each of the rooms and calculating the following parameters from the impulse responses: reflectograms, early-to-late and early-to-total temporal energy ratios, center time (TS), early reverberation time (R1), early decay time (EDT), initial time delay gap (ITDG), and bass ratio (BRRT). Significant intercorrelations were identified between several of the subjective criteria evaluated and also between several of the objective parameters measured. Independent subjective qualities significantly correlated with overall acoustic impression, objective measurements, and physical room characteristics, as well.
Musician's preference for concert stage acoustics
Authors: Bruck Daniel C.
Published: October 2005

Musician preference studies frequently employ simulated sound fields and anechoic chambers or sound-attenuated booths for test conditions. The purpose of this research was to examine musician preference for various stage enclosures in an actual concert hall setting while playing standard musical selections in ensemble conditions. Thirty-six musicians performed in string and brass trios in four stage shell configurations and gave preference ratings for the configurations based on “ease of ensemble,” “ability to hear oneself,” and “ability to hear the other players.” The judgments indicate differences in preference between string and brass players for “ease of ensemble,” and a stage preference across all subjects for “ability to hear oneself.” Aspects of musician loudness levels and the relationship between subjective judgments and early-to-late energy ratios will also be reported.
Progress report on a pulse technique for wind instrument bores
Authors: Stanbridge Dale R. , Ayers R. Dean
Published: October 2005

The piezoelectric driver discussed by A. H. Benade and M. I. Ibisi [J. Acoust. Soc. Am. 81, 1152–1167 (1987)] has been employed as a pulse generator by using Wiener filtering to shape the applied voltage [E. A. Robinson, Multichannel Time Series Analysis (Goose Pond, Houston, TX, 1983), 2nd ed.]. Several refinements have been implemented since this technique was first described [Ayers et al., J. Acoust. Soc. Am. Suppl. 1 77, S90 (1985)]. Instrumental improvements include the use of a Spectral Dynamics SD380 spectrum analyzer and a Hewlett-Packard 330SPU work station. Time averaging and further compensation for low-frequency noise now yield cleaner results in both time and frequency domains. Reflection impulse responses and transfer functions are found with a single microphone on a long pipe. Input impedances and their corresponding Green's functions are obtained by comparing a bore's response with that of a uniform pipe on the other side of the driver. [Work supported in part by a CSULB Summer Research Grant and Equipment Grants from Hewlett-Packard.]
Acoustic microsensors and micromotors
Authors: White Richard M.
Published: October 2005

The presentation will focus on four applications of the use of waves in thin membranes: (1) physical sensing of various parameters (e.g., viscosity, differential pressure); (2) nonspecific gravimetric sensing (e.g., liquid density, chemical vapor sensing with polymers, cell, or bacterial cultures); (3) ligand-based gravimetric sensing (e.g., antibody-antigen, DNA binding); and (4) kinetic devices (e.g., moving solids, pumping fluids, and mixing devices).
Acoustic analogs for solving problems in solid-state physics
Authors: Maynard J. D. , McKenna M. J.
Published: October 2005

A basic problem in theoretical solid-state physics is to solve the Schrödinger equation for an electron in the scattering field of some very large number of ions, which is certainly a formidable problem. Fortunately, for a crystal the scattering field is periodic, and one may use Bloch's theorem and obtain a manageable calculation. Unfortunately, real crystals have defects, or one may have an alloy, an amorphous material, or a quasicrystal, for which there is no known “quasi-Bloch theorem;” solving the Schrödinger in these cases is difficult, if not impossible. However, the Schrödinger equation is a wave equation, the same as for sound waves, and it is possible to construct acoustic systems that have scattering fields analogous to those in a solid-state system, and whose governing equations may be mathematically identical to a complicated solid-state model system. For the acoustic system, one may measure eigenvalues and eigenfunctions directly, as well as study inelastic and nonlinear effects. Research has been undertaken for a random field (involving Anderson localization) and for a quasicrystallization system. [Work supported by NSF Grant DMR 9000549 and ONR.]
Vibration signature analysis using artificial neural networks
Authors: Unal Aynur , Wasserman Philip D.
Published: October 2005

Vibration signatures are useful predictors of incipient equipment failures in mechanical systems such as reciprocating engines, generators, and turbines. Properly interpreted, they can prevent expensive and potentially dangerous failures. Also, these signatures can be used to indicate the need for maintenance, allowing scheduled versus costly and inconvenient unscheduled downtime. Analyzing and classifying these signatures has proven difficult. Often, they are the result of multiple inputs from highly complex nonlinear coupled systems. With this kind of data, traditional classification methods often produce inaccurate and misleading results. Attempts have been made to use expert systems to perform the classification. This approach presupposes the availability of an expert with the ability to accurately perform the classification, as well as the willingness to undergo the lengthy process of rule development working with a knowledge engineer. This method has failed in many cases. Often the expert is simply unable to explain how he performs the classification; his actual methods may be largely the result of subjective decisions, not reducible to the precise rules needed for an expert system. Artificial neural networks have proven ideal under such circumstances. Learning by example, they automatically develop arbitrarily complex nonlinear relationships directly from experimental data; hence, there is no need for humans to identify the rules. Given an adequate training set they exhibit generalization, correctly classifying signatures despite noise and the inevitable variations in the system. This paper describes research done on artificial neural network classification of actual vibration signatures from large rotating machines. A group of these signatures and their correct classifications were collected from operating machines. These were then used as a training set for two types of artificial neural network classifiers; the first using backpropagation, the second using a probabilistic neural network. Once trained, both networks were then tested for accuracy on previously unseen signatures. Relative classification accuracy was then determined between the two networks, a conventional Baysian classifier, and a human expert.
Acoustic signaling in teleost fishes: Model systems for vertebrate vocalization
Authors: Bass Andrew
Published: October 2005

Teleost fishes can vocalize by contracting striated muscles attached to the lateral walls of their swimbladder. The rhythmic, oscillatory-like, firing properties of a brain-stem sonic motor circuit determine the fundamental frequency of the acoustic signals. In the midshipman Porichthys notatus only large, nest-building, egg-guarding males generate long duration (up to 1 h) “hums” that attract females to the nests. Females, and smaller, “sneak-spawning” males, do not hum. Behavorial sex differences in sound production are correlated with: (a) the soma-dendritic dimensions and discharge frequency of individual sonic motoneurons and their presynaptic pacemaker neurons, (b) the functional architecture of sonic muscle fibers and myofibrils, and (c) the density of neuromodulator inputs to the sonic motor nucleus. The sonic motor circuit can serve as a “simple” model system for a detailed analysis of the synaptic and electro-responsive properties of single neurons controlling the generation of sex- and species-typical acoustic communication signals. The collaboration of Harriet Baker, Robert Baker, Richard Brantley, and Margaret Marchaterre is acknowledged. [Work supported by NSF, NIH, and Hatch Grants.]
Acoustic communication and hearing in electric fish
Authors: Crawford John D.
Published: October 2005

The African electric fish Pollimyrus isidori (Mormyridae) is distinguished among sound-producing fish by a relatively elaborate repertoire of temporally patterned sounds, produced by males while courting females. Courtship occurs in darkness, and the male's sonic display is evoked by the particular pattern of electrical discharges the female emits. Courtship communication thus involves a bimodal exchange of information mediated by both the auditory and electrosensory systems. Anatomically, these fish exhibit a peripheral specialization for underwater sound-pressure transduction consisting of the attachment of the sacculus to the wall of a small gas-filled bladder within the labyrinth. Single-unit neuro-physiology has been used to examine responses to sounds propagated through water and to examine the representation of temporally patterned sounds in the central nervous system. The Pollimyrus auditory system is quite sensitive to sounds in the frequency range of those used in communication, with some midbrain neurons having thesholds more than 60 dB below the pressure levels recorded close to sound-producing males (thresholds of −30 dB or less, re: 1.0 dyn/cm2). The auditory midbrain shows a number of properties expected of a system involved in processing communication and other low-frequency, temporally patterned sounds. [Work supported by NIH: NRSA DC00020-02 and CDR P50 DC00293-06.]
Applications of higher-order spectra to some acoustics problems
Authors: Mendel Jerry M.
Published: October 2005

During the past few years there has been an increasing interest in applying higher-order spectra (statistics) to a wide range of signal processing and system theory problems. These statistics are very useful in problems where either non-Gaussianity, nonminimum phase, colored noise, or nonlinearities are important and must be accounted for. When signals are random processes, then cumulants are used as the higher-order statistics. When they are nonrandom, then moments are used. New methods have been developed that work either in cumulant or moment domains; in their multidimensional Fourier transform (i.e., “polyspectral”) domains; or, even in inverse logarithmic (e.g., high-order “cepstral”) domains. Applications of higher-order spectra to acoustics problems include transient signal reconstruction based on moving average, autoregressive, or autoregressive moving average models, when measurements are colored and Gaussian; detection of transient signals (in additive colored Gaussian noise); time delay estimation when measurement noises are correlated but Gaussian; and harmonic retrieval.
Systems theory in musical acoustics
Authors: Smith Julius O.
Published: October 2005

Recent digital synthesis techniques for woodwind bores and strings (bowed, plucked, and the like) have been devised using long delay lines and sparsely distributed filter elements to efficiently simulate solutions to the one-dimensional wave equation. In the simplest case, a string or bore can be modeled using a single delay line and a single, low-order digital filter. This presentation describes techniques used to simulate specific physical phenomena in the context of these models. As is well known, in the lossless case, solutions to the 1-D wave equation can be expressed in terms of left-going and right-going traveling waves, and these are efficiently simulated using pure delay lines plus, perhaps, a sign inversion at a termination. Abutting two waveguides of differing characteristic impedance gives rise to a scattering junction at the interface, leading to the ladder and lattice digital filter structures used extensively in the field of signal processing. When there are losses, or when string stiffness is important, there is linear filtering along the waveguide. Because linear, time-invariant filters commute, the distributed losses and dispersion can be lumped at convenient places in the waveguide network without changing an input-output transfer function. Once they are thus consolidated, it is usually possible, especially in audio applications, to find a very accurate approximation using a low-order lumped digital filter in place of the distributed filtering. On top of this physically accurate yet efficient model, it is straightforward to introduce nonlinear extensions such as (1) bow-string slippage due to absolute string displacement, (2) pitch decay due to the gradual decline of the average string tension, (3) wave-front sharpening due to increased speed of sound at higher air pressures, (4) closure forces on double reeds and vocal folds due to the Bernoulli effect, (5) heat conduction losses, and (6) spontaneous generation of turbulence due to high volume velocity through a narrow aperture.
System theory in teaching acoustics
Authors: Cook Bill D. , Finch Robert D.
Published: October 2005

System theory can be used in teaching acoustics to provide insights that students might not otherwise appreciate. In this paper, some instances of the application of linear system theory, involving the Laplace transform technique to some simple problems in acoustics will be provided. The oscillations of a bubble provide an example of instability in a one-degree-of-freedom system. The loudspeaker can be presented as an example of a simple electromagnetic system. Diffraction theory can be explained in terms of linear system filters. Beyond that, how a paradigm such as Rapoport's general system theory can provide a framework for expounding on more complex acoustic systems will be discussed.
Active control of higher-order acoustic modes in duets
Authors: Zander Anthony C. , Hansen Colin H.
Published: October 2005

The examination of the physical mechanisms describing active control of acoustic plane waves propagating in rectangular section ducts [S. D. Snyder and C. H. Hansen, J. Acoust. Soc. Am. 86, 184–194 (1989)] has been extended to encompass the active control of higher-order modes and has led to the development of an analytical model. The model allows calculation of acoustic power flow from both simple and finite size primary and control sources, radiation impedances of all sources with and without control sources operating, and total downstream power flow for a particular source of configuration. Taken into account in the analysis are the following: influence of secondary source location, both within the duct cross section and axially; number of secondary sources; relative source strengths; and relative phase angles between source signals. Results are presented showing the effect of various source arrangements on the optimal attenuation of downstream power flow.
On the validity of the liquid wedge technique for generating Scholte waves
Authors: Chamuel Jacques R.
Published: October 2005

The “liquid wedge technique” is shown to be invalid for the generation of scholte waves at a liquid/solid interface, and a mechanism is described explaining the experimentally observed Scholte waves reported by Luppae and Doucet [Acustica 64, 46–49 (1987); J. Acoust. Soc. Am. 83, 1276–1279 (1988)], and by de Billy and Quentin [J. Acoust. Soc. Am. 88, 535–541 (1990)]. Selection of an incident angle θ such that sin θ = Ca/CSch, where Ca is the compressional wave velocity in the alcohol wedge and CSch is the water/aluminum Scholte wave velocity, does not satisfy the alcohol/aluminum or the water/aluminum interfaces. The role of the subsonic Scholte wave velocity inside the liquid wedge region has to be taken into account. In view of reciprocity, a Scholte wave propagating along a water/aluminum region slows down as it crosses to an alcohol/aluminum region without leaking its energy to the alcohol. Ultrasonic experimental results from an alcohol wedge on ice/water, aluminum/water, and limestone/water are compared. A liquid wedge with a vertical membrane wall was utilized. A point source in the liquid wedge generated leaky Rayleigh waves and no Scholte waves along the water/aluminum interface when the distance between source and interface was greater than 1 wavelength. [Work supported by ONR.]
Selective attention in absolute pitch listeners
Authors: Plamondon Lyne , Hafter Ervin R.
Published: October 2005

The role of attention in detection under conditions of frequency uncertainty has been extensively studied in a masking paradigm using auditory cues to alleviate the uncertainty. Studies of cues requiring higher-order processing, for example, cues related to the signal in a fixed musical relation, show that such cues can be as effective as iconic (same frequency) cues [E. R. Halter and R. S. Schlauch, J. Acoust. Soc. Am. Suppl. 1 86, S112 (1989)]. Reported here is further evidence for higher-order processing in cuing. Subjects with absolute pitch (AP) detected pure tones in noise in conditions with (1) no cues, (2) iconic cues, or (3) visual cues intended to operate through auditory memory. Visual cues consisted of various symbols corresponding to the frequency of the signal presented in musical notation on a display terminal. In all cases, these were better than no cues and in the most effective cases, the visual cues were as effective as the iconic (auditory) cues. These experiments reflect upon the representation of frequency in AP listeners. [Work supported by NINCDS.]
Supercomputer modeling of delphinid sonar beam formation
Authors: Aroyan J. L. , Cranford T. W. , Kent J. , Norris K. S.
Published: October 2005

It has been established that some dolphins possess well-developed acoustic orientation (echolocation) and information gathering abilities, though substantially less is known about the system of sound generation and beam formation. Dolphins use a narrowly focused sound beam that emanates from the forehead and rostrum during echolocation. The primary objectives of this study were to simulate the effects of modeled tissues on beam formation, and to test the viability of various hypothetical sound source locations. 2-D simulations of sound propagation using parasagittal outlines from reconstructions of CT scans through the forehead tissues of two delphinids were conducted. Finite difference wave propagation programs were run on a Cray supercomputer. Preliminary simulations suggest that beam formation results primarily from reflection off of the skull and air sacs. These results do not depend strongly upon the precise values of velocity and density assumed for the bone. Beam angles closely approximate those measured by experimental methods for a source located in a region of the model corresponding to the monkey lip/dorsal bursae complex (MLDB), and not elsewhere. These results suggest that: (1) the skull and air sacs play the central role in beam formation; (2) the geometry of reflective tissue is more important than the exact acoustical properties assumed; and (3) experimentally observed beam patterns are best reproduced in the simulations when the sound source is placed in the region of the dolphin's head known as the MLDB (Cranford, 1988).
Cylinder wall thickness difference discrimination by an echolocating dolphin
Authors: Au Whitlow W. L. , Pawloski Deborah A.
Published: October 2005

The capability of an Atlantic bottlenose dolphin to discriminate wall thickness differences of hollow cylinders by echolocation was studied. A standard cylinder of 0.635-cm wall thickness was compared with cylinders having wall thickness that differed from the standard by ±0.2, ±0.3, ±0.4, and ±0.8 mm. All cylinders had an o.d. of 3.81 cm and a length of 12.7 cm. The dolphin was required to station in a hoop while the standard and comparison targets, separated by an angle of ±11° from a center line, were simultaneously presented at a range of 8 m. The dolphin was required to echolocate and indicate on which side of the center line the standard target was located. Target location on each trial was randomized. The dolphin could discriminate wall thickness differences of −0.23 and +0.27 mm at the 75% correct response threshold. Results of backscatter measurements suggest that if the dolphin used time domain echo cues, it may be able to detect difference in the time between two echo highlights to within approximately ±500 ns. If the dolphin used frequency domain cues, it may be able to detect frequency shifts as small as 3 kHz in broadband echoes having a center frequency of approximately 110 kHz.
Level discrimination of tones as a function of duration for normal and cochlearly impaired listeners
Authors: Florentine Mary , Buus Søren
Published: October 2005

Difference limens for level (ΔL = 20 log[(p = Δp)/p], where p is pressure) were measured as a function of duration in seven normal and six cochlearly impaired ears. Stimuli were tones ranging from 0.25 to 14 kHz and broadband noise. Stimulus durations ranged from 2 ms to 2 s and the stimulus power was held constant. Rise and fall times were 1 ms. The interstimulus interval was 250 ms. Levels ranged from 30 to 90 dB SPL. An adaptive two-alternative force-choice procedure with feedback was used. For both normal and impaired listeners, ΔL's decreased as duration increased up to 1 or 2 s, except for broadband noise and tones at 250 Hz. For the latter stimuli, ΔL stopped decreasing at about 0.5 s. In a double logarithmic plot of ΔL versus duration, the rate of decrease is generally well fitted by a sloping line. The slope is about the same for normal and impaired listeners. For all listeners and conditions, it is considerably shallower than the −0.5 slope predicted for an optimum detector. These results are similar to earlier results for normal listeners [M. Florentine, J. Acoust. Soc. Am. 79, 792–798 (1986)]. The similarity of the effect of duration on ΔL's in normal and impaired listeners contrasts with the abnormal temporal integration functions generally obtained for impaired listeners at absolute threshold. [Work supported by NIDCD.]
On direct method of calculation of degenerate elastodynamic solutions of elastic wave propagation in a thick plate
Authors: Ghorieshi Agha J.
Published: October 2005

The elastostatic eigenvalue equations are commonly obtained by taking the limit of their elastodynamic counterparts as frequency tends to zero. However, this limiting procedure is not convenient. It is cumber-some when applied to the solutions obtained using Stokes' potentials and, in the case of utilizing Lame's potentials, it does not produce static solutions that are a function of position alone. In this paper it is shown that the exact solutions of elastostatic problems can, in general, be obtained in a straightforward manner by the use of harmonic potentials without recourse to any special limiting form of analysis. This method is applied to an infinite, elastic thick plate with traction-free parallel surfaces and the elastostatic eigenvalue equation. It is shown that the problem can be solved exactly in terms of harmonic functions, one of which is a scalar and the other of which is a vector. It is noted that results are in agreement with the published solutions.
Intrinsic velar height in supine vowels
Authors: Whalen D. H.
Published: October 2005

Intrinsic velar height, the tendency of the velum to be higher during high vowels than during low vowels, is assumed to be the result of adjustments for the tongue height and pharyngeal cavity of the vowel. But does gravity's pull on the velum contribute as well? This question was studied with magnetic resonance imaging (MRI), a technique that gives a three-dimensional view of the vocal tract during an extended production of a single sound. Due to the design of the equipment, MRI subjects must lie down, in this case, in the supine position, thus placing the vocal tract at a 90-deg offset from its usual relation to the Earth's gravity. Measurements of the English vowels [i ɪ u ᴜ a] showed differences on the order of 3 mm in velar height between the low vowel and the high vowels in four subjects. There may be a difference between the tense and lax vowels (which could be expected if there is a height difference as well), but it was on the same order as the resolution (about 1 mm) so no firm conclusions could be drawn for the tense/lax feature. The magnitude found here was similar to that found with cineradiography, suggesting a limited role of gravity in the shift of velar height due to vowel articulation. [Work supported by NIH Grant DC-00121.]
Spectral factors in the organization of vowel sequences into words
Authors: Chalikia Magdalene H. , Warren Richard M.
Published: October 2005

Previous research [Warren et al., Percept. Psychophys. 47, 423–432 (1990)] has shown that listeners presented with recylced sequences of steady-state vowels hear illusory syllables and words rather than a succession of vowels. Often the signal is split perceptually into two simultaneous words differing in both timbre and phonemic content. The present study investigated the spectral composition of such dual organizations and found that it is possible to isolate for further study spectral bands corresponding to each word. When one such narrow band is presented to one ear and the broadband vowel sequence to the other, the narrow band word can be extraced from the lateralized broadband spectrum and heard at the medial plane. Under appropriate conditions, a monaural narrow band noise spanning the same frequency range as the narrow band word also can, through contralateral induction, excise the word from the broadband vowel sequence and move it to the medial plane. In contrast, it is not possible to delateralize a spectral segment of a recycled actual word under either of the conditions described above, indicating a weaker spectral cohesion for the broadband vowels. [Work supported by NIH and AFOSR.]
Application of the canonical eigenvalue method to an underwater acoustic double duct, II
Authors: Gordon D. F. , Hosmer F. , Pedersen M. A.
Published: October 2005

This paper converts the canonical results of Part I into physical solutions for a specific sound-speed profile. These physical results are the frequency and the normal-mode phase velocity, group velocity, and eigenfunction normalization all given as functions of frequency. Sample eigenfunctions (standing waves) are presented at critical and other frequencies. These functions all exhibit the special characteristics of propagation in double ducts. At the critical frequencies the phase velocity curves of adjacent modes are pinched together, while the group velocity and normalization curves cross each other. The standing waves display near-equal amplitudes in both ducts at the critical frequencies; whereas at other frequencies the standing waves have high amplitude in one duct and low amplitude in the other duct. For closely coupled modes, the eigenfunction amplitudes are almost identical. Orthogonality is preserved by one of the adjacent mode amplitudes changing sign at a node, whereas the other mode amplitude forms a relative minimum but does not change sign.
Appropriate starting fields for different PE approximations
Authors: Jensen Finn B. , Porter Michael B.
Published: October 2005

The suite of parabolic wave equations available today for solving range-dependent propagation problems in ocean acoustics encompasses forms ranging from the standard narrow-angle PE originally introduced by Tappert to very wide-angle PEs based on Padé series expansions. Each PE form has inherent phase errors that increase with increasing angle away from the main propagation direction (horizontal). These phase errors also affect the angular energy distribution in space so that a given initial field leads to different farfield radiation patterns in different PE's. This is explicitly illustrated by solving the classical Lloyd mirror problem for a point source near the free surface in a homogeneous half-space. The results clearly show the importance of selecting a starting field compatible with the particular PE being solved. Thus it is seen that the use of a wide-angle source with a narrow-angle PE may result in an amplitude over-shoot of 3–4 dB for propagation directions around 30° off the main propagation direction.
An accurate and stable elastic parabolic equation with application to interface wave propagation
Authors: Collins Michael D.
Published: October 2005

The parabolic equation (PE) method has recently been extended to handle sound propagation in an ocean overlying an elastic bottom. Of the two original elastic PE implementations, however, one has stability limitations [Collins, J. Acoust. Soc. Am. 86, 1459–1464 (1989)], and the other has accuracy limitations [Wetton and Brooke, J. Acoust. Soc. Am. 87, 624–632 (1990)]. An elastic PE that is very accurate and completely stable and is based on a new higher-order Padé approximation has been derived by combining and generalizing the original models. Accuracy is achieved by placing several constraints on the derivatives of the Padé series at the point corresponding to the reference wave number. By requiring that the Padé series map part of the lower left quadrant of the complex plane into the upper half of the complex plane, an instability associated with nonpropagating modes can be eliminated. The complex coefficients of the desired Padé series are determined by solving a system of nonlinear equations with Newton's method. The new elastic PE is accurate and efficient for problems involving compressional, shear, and interface waves, very wide propagation angles, and large depth and weak range dependence in the geoacoustic parameters. With this upgrade, the elastic PE is suitable for general use.
Elastic parabolic equations and the fluid/elastic interface
Authors: Knightly G. H. , Li G.-Q. , St. Mary D. F. , Lee D.
Published: October 2005

The fluid/elastic interface boundary is investigated in a weakly range-dependent environment, within the context of elastic parabolic approximating equations, and finite-difference methods. The development provides consistency between the standard parabolic approximation in the fluid medium and an elastic parabolic approximation of the potential equations for the elastic wave equations, and thus allows the use of existing finite-difference marching schemes in the liquid medium. Here, stability of the numerical scheme is discussed, a new implementation of the linear solver is presented, and numerical comparisons are made with a known solution and with a numerical solution obtained for the elastic parabolic equations without the interface treatment. [Work supported in part by ONR.]
Eigenray solutions for cross-shelf propagation
Authors: Smith Donald F. , Ehret Laura L. , Miller James H. , Chiu Ching-Sang , Newhall Arthur E.
Published: October 2005

In order to determine the sections of a water mass being sampled by a tomographic array the eigenrays for the given transmitter and receiver geometries must be found. In deep water experiments, the three-dimensional propagation effects on the eigenrays have been modeled using the assumption that small perturbations of transmitted ray angle lead to small perturbations of ray angles at the receiver. This allows for determination of the eigenrays using linear interpolation. In December 1988, a tomography experiment was held in Monterey Bay in which one source transmitted from deep water near Point Sur, south of the Monterey Canyon to a number of receivers on the shelf, north of the Monterey Canyon. The severe bottom bathymetry precluded the use of the deep-water assumptions previously stated. A three-dimensional ray-tracing model, HARPO, was used to determine the eigenrays and better examine bottom effects by using a densely packed shooting method and modified bottom interaction. [Work supported by the NPS Research Council and the Monterey Bay Aquarium Res. Inst.]
Reflection at a fluid-solid interface and complex rays
Authors: Tindie C. T. , Zhang Z. Y.
Published: October 2005

The underwater sound field due to spherical waves reflected from a solid interface is examined in terms of complex rays. The corresponding contour integral can be evaluated numerically to provide an exact result for comparison with approximations. Saddle point analysis of the integrand leads to the association of saddle points with acoustic rays. Asymptotic evaluation of the integral leads to simple accurate results in terms of complex rays. At short and long ranges, the complex rays are approximately real and correspond to the conventional specular reflection and lateral wave. At intermediate ranges a caustic is formed and conventional ray theory is inadequate. In the vicinity of the caustic, the complex rays are combined using Airy functions. When source or receiver are both within a fraction of a wavelength of the interface the contribution of the Scholte wave pole must be included.
A method for ranking the acoustic disturbance potential of noise sources in the environment of marine mammals
Authors: Malme Charles I.
Published: October 2005

A standardized noise contribution model (SNC) has been developed to provide a means of comparing the contributions from diverse noise sources to facilitate assessment of their potential environmental impact. The output of the SNC model is a logarithmically scaled number proportional to the acoustic energy density produced by a specific type of source operating in a defined reference area. An associated standardized exposure rating model (SER) has been developed to rate the potential response of marine mammals to noise exposure. The SER model is designed to evaluate the degree of potential impact of a specific source on a specific species by producing a log-scaled number proportional to the degree of matching between a noise source output bandwidth and a species hearing sensitivity characteristic. The SNC value for a given source type is used together with information on population density to weight the SER values for specific source and species encounter probabilities. [Work supported by the Minerals Management Service.]
Measurements of the effects of bottom slope on sound propagation in shallow water
Authors: House Ian , Glegg Stewart A. L.
Published: October 2005

Laboratory scale measurements have been made of sound propagation in shallow water over a sloping bottom. The measurements were made in a large test pool in a water layer over a model of the ocean floor that consisted of an epoxy layer on a concrete base. The properties of the model were consistent with those found in typical ocean sediments and substrates. The results presented in this paper will demonstrate downslope- and across-slope propagation for several different bottom angles, and comparisons will be made with measurements in a uniform depth water column over the same bottom. Important differences were found even in the special case of across slope propagation where the water depth was constant with range. Shadow zones and modal absorption will be demonstrated. [Work supported by ONR.]