bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of probabilistic phonotactics on the recognition of words in continuous speech
Authors: Gaygen Daniel E. , Luce Paul A.
Published: July 2002

No invariant or highly probable cue to the borders of words exists in continuous speech. Thus recognizing individual words in speech is not a trivial task. The current study investigates the role of probabilistic phonotactics as a possible source of word border information. Specifically, the trough hypothesis is tested. According to the trough hypothesis, biphones spanning the borders of words should provide cues to those borders if the intraword co-occurrence probability of the biphones is near zero. Lexical decision and word spotting experiments provide evidence for the trough hypothesis only for the beginnings of words. [This research was supported (in part) by research Grant No. 1 R01 DC 0265801-A1 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.]
The emergence of word representation independent of context
Authors: DePaolis Rory , Vihman Marilyn , Morey Debbie
Published: July 2002

Eleven-month-old French-learning infants prefer to listen to familiar over unfamiliar words (presented auditorily and independent of context), suggesting that there is a stable (although not necessarily complete) internal representation of word forms by this age [P. A. Halle and B. de Boysson-Bardies, IBAD 17, 463–481 (1994)]. The current study explored word representation by infants learning British English. Infants at 9 and 11 months of age were tested using the headturn preference paradigm as modified by Halle and Boysson-Bardies. Phonetically and phonotactically similar lists of familiar and unfamiliar disyllabic words and phrases were developed and matched for F0, amplitude and duration. The lists contained iambic and trochaic patterns in proportions typical for English. While initial results (based on looking times) suggest that the 11-month-old British infants, like the French, preferred the familiar over the unfamiliar list, 9-month-old infants showed no significant preference for either list. The individual infant results suggest that stable representation of word forms begins to emerge at 11 months, mirroring other cognitive advances at this time (e.g., object permanence, problem solving, language specific phonetic attunement). [Work supported by the ESRC.]
Effects of mismatches in talker and emotion on speech perception
Authors: Mullennix John W. , Mateljan Kelly , Payne Danielle
Published: July 2002

The effects of within-trial mismatches of talker voice and emotional tone of speech on speech perception were examined. Pairs of speech stimuli that matched/mismatched in talker voice and emotional tone of speech were presented to listeners via an AX discrimination paradigm. Results indicated that mismatches in both talker voice and emotional tone produce perceptual interference. However, the interference produced by emotional tone variability was greater under single-talker conditions. The results are discussed within a hierarchical scheme of allocating processing resources to various attributes of the speech signal.
Spectral contrast in perception of VCV syllables
Authors: Holt Lori L. , Lotto Andrew J. , Kluender Keith R.
Published: July 2002

The ability of listeners to recover speech information, despite dramatic articulatory and acoustic assimilation between phonetic units, is central to understanding perception of fluent speech. The present studies investigate the effect of preceding acoustic stimuli on identification of a series of synthetic CVs varying acoustically in F2 onset frequency and perceptually from /ba–da/. Results reveal that naturally produced /i/ and /u/ modulate identification responses to the CV series independent of speaker, suggesting that the effect of preceding V on CV identification is not critically dependent on precise matching of articulatory characteristics between V and CV. Moreover, nonspeech FM glides modeling F2 transitions of natural Vs shift CV identification in a similar manner, suggesting that quite general auditory mechanisms may contribute to observed shifts in CV identification. Further experiments reveal the effect of preceding V maintains for dichotic presentation and persists, but lessens, with intersyllabic silent intervals increasing to 200 ms. All results can be recast as cases of spectral contrast whereby spectral characteristics of preceding sound modulate perception of CV. These data suggest general auditory processes may play a substantive role in perceptual accommodation of coarticulated speech and provide clues to the nature of the putative auditory mechanisms. [Work suported by NSF.]
Acoustic and EM waves for speech processing
Authors: Holzrichter John F. , Burnett Greg C. , Gable Todd A. , Lawrence Ng C.
Published: July 2002

The use of low power EM sensors [Holzrichter, Burnett, Ng, and Lea, J. Acoust. Soc. Am. 103, 62 (1998)] enable the determination of several articulator boundary motions, simultaneously—e.g., glottis, jaw, tongue, palate, lips, etc.—leading to new speech processing algorithms. By comparing EM sensor methods of pitch detection to established cepstral and autocorrelation techniques, a tenfold increase in pitch accuracy, a 100-fold reduction in processing time, and robust performance in the presence of high background acoustic noise are obtained. Investigations of the details of the EM sensor signal from the human glottal region indicate that it can be used to provide information on the instant excitation function of voiced speech. Using the ARMA approach, the excitation information is removed from the acoustic signal, yielding well-defined transfer functions, formant locations, and pitch normalized data. In addition, using the glottal timing information, pitch synchronous processing has been employed using ARMA, LPC, Cepstral, and other approximation techniques. The excitation function and the corresponding filter coefficients for each speech unit (e.g., the a’s and b’s from the ARMA approximation) enable one to reconstruct good quality personalized speech, without the need for residual information.
Time-frequency coding of the line spectrum frequencies
Authors: Petrinovic Davor
Published: July 2002

Line spectrum frequencies (LSF) are one of the most popular representations of the short-time spectrum envelope in speech coding applications. LSF of adjacent speech frames are usually highly correlated, so the bit-rate for spectral envelope coding can be reduced by interframe coding. Several coding methods, such as switched-adaptive interframe vector prediction, vector predictive quantization, segment quantization, and matrix quantization exploit the interframe redundancy. A new method of low bit-rate interframe LSF coding based on the discrete wavelet transform is proposed in this paper. Prior to coding, each of the line spectrum frequencies is transformed to wavelet domain by treating it as a time-varying waveform. By choosing the appropriate mother-wavelet, the higher level approximation coefficient of the wavelet decomposition (residual signal) comprises most of the LSF waveform energy. Since these coefficients, which carry most of the LSF information, are time decimated by a factor of 2 to power of decomposition level, significant bit reduction in coding can be obtained. Several wavelets were investigated, identifying the one with the best energy concentration. Spectral distortion caused by neglecting all of the detail coefficients was also calculated as a function of wavelet type and decomposition level.
On the use of acoustic contrast to distinguish between agglomerates of finely dispersed polymeric particles
Authors: Gupta Sanjay , Feke Donald L.
Published: July 2002

This paper demonstrates how differences in the morphology of agglomerates of fine particles can be detected based on the response of the agglomerates to a low-intensity resonant acoustic field. The technique is based upon observing whether the agglomerates are collected in nodal or antinodal positions when suspended in different fluids spanning an appropriate range of acoustic properties. Experiments performed with agglomerates of acrylonitrile–butadiene–styrene copolymeric particles suspended in 2-propanol–water mixtures illustrate the technique.
Dilatation of S waves in smoothly inhomogeneous isotropic elastic media
Authors: Kiselev Aleksei P. , Rogoff Zigmund M.
Published: July 2002

The propagation of high-frequency linear waves in a smoothly inhomogeneous isotropic elastic medium is considered. The dilatation of the S wave is found via employment of both the zeroth- and first-order terms of the elastic field by a ray analysis. It is observed that the dilatation is necessarily dependent upon the inhomogeneity of the medium, vanishing in the instance the medium is taken homogeneous.
Theory of acoustic radiation near a hyperbolic ridge
Authors: Berger Thomas K.
Published: July 2002

A solution to the acoustic field due to a harmonic point source near a hyperbolic ridge with perfectly reflecting boundaries in an isovelocity ocean is derived and developed. An exact expression for the field is given as a modal sum of integrals. The integrals are in terms of eigenfunctions of the reduced wave equation in the three-dimensional elliptical coordinate system. The eigenfunctions are approximated away from the low-frequency limit by standard WKB techniques. The resulting integrals are estimated by first and second order stationary phase asymptotics, which are matched in the vicinity of the caustics, yielding a complete representation of the field. The field is given in terms of standard elliptic functions for which fast numerical routines are available. The solution includes the locations of the caustics and shadow zones, as well as predicting a complicated intramodal interference pattern resulting from the intersection of up to three rays in a given mode. The explicit representation of these features arising from horizontal refraction makes this theoretical model useful as a new fully three-dimensional benchmark solution.
Subjective evaluations of professional microphones
Authors: Cross Lowell
Published: July 2002

Attempts to evaluate microphone performance by listening to individual models via a reproduction chain often reveal subtle, and not-so-subtle, ‘‘sonic signatures’’ which in turn reveal preferences and dislikes among trained listeners. However, there are many factors contributing to the process of evaluation, even if only one microphone type, and only one listener, are involved: (i) monaural versus stereophonic versus ambisonic reproduction; (ii) headphone versus loudspeaker auditioning (again, mono or stereo?); (iii) choice of music, if indeed listening is limited to music; (iv) ‘‘direct feed’’ versus analog versus digital reproduction; (v) personal and environmental factors; (vi) the enhancing or detrimental aspects of microphone ‘‘coloration.’’ The foregoing partial list has prompted this listener to treat AB and ABX comparisons of microphones, by individuals or groups, with a cetain level of suspicion—in spite of many tests he has conducted involving others. Therefore this presentation will indeed offer subjective views: those of one person with a 35-year history of recording and listening, and with an even longer history of formulating a personal musical taste.
Measurement of modal spectrum of linear internal waves in shallow water and comparison with the Garrett–Munk model
Authors: Yoo Kwang , Yang T. C.
Published: July 2002

The properties of linear internal waves are well studied in deep ocean and are surprisingly well modeled by the Garrett–Munk model. The properties of linear internal waves in shallow water are not well studied. Experimental measurements may be hindered by the contributions of nonlinear internal waves, the complications caused by range-dependent coastal oceanography, and possible interactions with the bottom boundary layers. There is no reason to expect the Garrett–Munk model to work in shallow water, as some of the assumptions made in the model may be violated. In this paper, the modal spectrum (the modal amplitudes) of the linear internal waves are deduced from approximately 2 h of CTD data collected during the SWARM 95 experiment during a period when nonlinear internal waves are absent or negligible. The method of empirical orthogonal decomposition is applied to the covariance matrix of the sound speed variations assuming that the internal waves modes are uncorrelated. One finds that the eigenvectors of this matrix agree well with the theoretical eigenfunctions of the first five modes of the internal waves. The mode amplitudes are deduced from the eigenvalues and compared with the Garrett–Munk model. The measured mode amplitudes agree with the measurements using a different method which projects the sound speed variations onto the theoretically calculated mode depth functions. [This work is supported by the Office of Naval Research.]
Effects of shock-excited harmonic modes on bubble levitation, stability, and SL
Authors: Rueggeberg Matthias , Holzfuss Joachim , Holt R. Glynn
Published: July 2002

Several experimental groups have commented on a sudden change in position of a levitated bubble very near the threshold for light emission at driving acoustic pressures near 1 atm. Often this leads to an uncontrollable nearly periodic wandering instability of the bubble in the acoustic field. Other groups have observed high-frequency discrete components in the received signal from internally mounted pressure hydrophones, and resonator-wall-mounted piezo-transducers and strain gauges. In order to investigate this effect, a broadband hydrophone was monitored in the water during single bubble levitation at near-SL pressures. Using a signal analyzer, it was ascertained that higher harmonic modes (up to 32 times the fundamental) of the acoustic resonator are excited by the bubble. When there is no bubble levitated, the temporal acoustic field is practically linear. The effects on bubble levitation and bubble dynamics of these shock-excited modes are discussed, and it is shown that many instances of bubble levitation instability can be explained by this effect. How to avoid this behavior in position-sensitive experiments is also discussed. [Work supported by DFG and NASA.]
Gas bubble formation in an oscillatory flow
Authors: Og̃uz H.
Published: July 2002

Production of bubbles from an underwater orifice is a common process that is often difficult to control. A possible solution is to impose a flow around an underwater orifice so that the size of the detached bubbles can be regulated. A simple way of accomplishing this task is to place a coaxial needle in a short tube. At constant water flow rate, a precise control of the bubble size can be achieved regardless of the orientation of the tube with respect to gravity. Since this arrangement may not be practical in some applications, an oscillatory flow in which the net water flux is zero is a better alternative. A series of experiments in which the flow is actuated by a rubber membrane driven by a solenoid show that it is possible to phase lock the bubble formation frequency to the forcing frequency under certain conditions. In the inflow phase of the oscillation, the growing bubble that is attached to the needle tip assumes an oblate shape. As a result, when the flow is reversed, the added mass force pushes the bubble away from the needle in a very efficient manner. Axisymmetric boundary integral simulations have been carried out to simulate this process. A very good agreement is found between experiment and the simulations. [Work supported by NASA.]
The action of Bjerknes forces on vapor bubbles
Authors: Harik V. , Hao Y. , Prosperetti A.
Published: July 2002

A considerable fraction of the heat transfer enhancement due to boiling can be ascribed to the buoyant removal of vapor bubbles from the heated surface. Such a mechanism is absent in microgravity where, indeed, transition to film boiling is found to occur at lower heat fluxes than at normal gravity. This problem motivates the present investigation in which the use of acoustic pressure radiation (or Bjerknes) forces for bubble removal is investigated. The paper describes numerical results for the large-amplitude oscillations of a vapor bubble in a liquid accounting for phase change and heat transport both inside and outside the bubble. On the basis of these results, the primary Bjerknes force on the bubble is calculated as a function of the bubble position in the sound field. The secondary Bjerknes force due to a second bubble (simulating a solid wall by the method of images) is also calculated and conditions under which the primary force can overcome the secondary one and dislodge the bubble from the heated surface are determined. [Work supported by NASA.]
Heat transfer measurements on a single stack plate
Authors: Wetzel Martin , Herman Cila
Published: July 2002

Heat transfer in oscillatory flow with zero mean velocity is different when compared to steady-state flow situations. This is one reason that currently no systematic design methodologies for heat exchangers in such flows exist. For example, instead of the expected heat transfer from a single heated stack plate [Wetzel et al., J. Acoust. Soc. Am. 100 (1996)] to the working fluid, the temperature fields visualized with holographic interferometry indicate that heat is transferred from the working fluid into the stack plate at the edge of the plate. To investigate this behavior the local heat fluxes at the edge of the stack plate were measured. These heat fluxes indicate the expected behavior for a low drive ratio. However, as the drive ratio increases, the resulting heat flux vector at the edge of the plate changes its direction and points into the plate, thus confirming the observations made when analyzing the temperature fields. Through an energy balance the magnitudes of the heat fluxes caused by the thermoacoustic effect were determined. The measured data are in good agreement with numerical and analytical predictions. [Work supported by the Office of Naval Research.]
Mode-locking of acoustic resonators and its application to vibration cancellation in acoustic heat engines
Authors: Spoor Philip S. , Swift Gregory W.
Published: July 2002

The problem of two self-maintained acoustic resonators that can ‘‘mode-lock’’ by means of a mutual coupling will be considered; in particular, the effects of varying coupler parameters (such as the diameter of a coupling duct) on the relative phase and amplitude of the oscillations in the two resonators will be explored. Experimental data, numerical simulations, and analytical predictions will be compared. The results will be used to help design a scheme for canceling structural vibrations in a thermoacoustic engine, by rigidly attatching two such engines together and selecting the appropriate coupler, such that the engines are forced to oscillate in antiphase. The interplay between acoustic coupling and ‘‘mass coupling’’ (coupling through the rigid structure) will also be discussed. [Work supported by the Office of Fossil Energy in the US DOE.]
Loudness perception with headphones versus loudspeakers
Authors: Schiffel Jana , Mo/ller Henrik
Published: July 2002

This study examines whether human loudness perception is influenced by the type of sound source, or determined exclusively by the sound pressure received at the eardrum. The literature contains conflicting views on this issue, particularly for the case of listening to earphones compared to, for example, listening to loudspeakers. To begin with, the paper summarizes the controversial results of earlier experiments. Ambiguities and loose ends worth investigating are pointed out; crucial aspects of experimental design are considered, e.g., the test sound material, various ways of binaural versus monaural presentation, and the psychometric method. Following this, new experiments are proposed. They comprise: (1) subjective equal-loudness comparisons (2-AFC) between various types of headphones and loudspeakers at different locations, and (2) probe-microphone measurements of the corresponding sound pressures in the listener’s ear canals. Finally, first results are presented. As a practical application, consequences to techniques of headphone calibration are discussed.
Individual differences and instrumental variation in audiological research
Authors: Bilger Robert C. , Meyer Ted A.
Published: July 2002

Tests used in speech audiometry have traditionally been standardized on young adults with normal hearing. In such cases, the range of test scores has been extended by presenting the materials at different intensity levels or signal-to-noise ratios (S/N). These strategies are essentially attempts to model hearing loss in terms of instrumental changes to a speech test. In the standardization of the Speech Perception In Noise (SPIN) test, we obtained the necessary wide range of test scores by testing a large number of listeners with sensorineural hearing loss. When the variability among SPIN test scores was the result of individual differences, the results were quite different from those in experiments using instrumental differences to extend the range of scores obtained from listeners with normal hearing. The ‘‘simulation of hearing loss’’ fails because instrumental manipulation of signal level or S/N changes the nature of the test not the hearing of the listeners under test. Only when the range in performance is the result of wide individual differences in hearing for speech presented under standard conditions can one evaluate a speech test. Without individual differences, there is no reliability. Predictions of performance derived from experiments driven by instrumental variability have little clinical value. [Work supported by NIH.]
Perception of stops in naturally produced V[l/r][b/d/g]V tokens: a reassessment of acoustic cues to place of articulation
Authors: Denton Jeannette M. , Hirata Yukari , Lowenstein Joanna H. , Perez Candace V. , Landahl Karen L.
Published: July 2002

This perceptual experiment reassesses a traditional assumption that the F3 transition is the primary cue for distinguishing [da] from [ga], evidence of which comes from perceptual experiments using synthetic continua [Mann, Percept. Psychophys. 5, 407–412 (1980); Fowler et al., ibid. 48, 559–570 (1990); Liberman, Speech (1996)]. Stimuli were tokens of /alba/, /alda/, /alga/, /arba/, /arda/, /arga/ produced three times by four speakers at three rates (fast, normal, slow), analyzed acoustically by Dainora et al. [J. Acoust. Soc. Am. 100, 2601 (1996)] and Hemphill et al. [CLS 33, 333–346 (1997)]. Subjects identified tokens in their original carrier sentences using a forced choice paradigm. Stimuli were blocked by speaker and rate; three repetitions of each were randomized within blocks. In five of the 216 tokens, for one or more subjects, the percept of the stop did not match the speaker’s intent. Analysis of these tokens showed a mismatch between formant transitions and burst spectra: formant transitions were characteristic of the stop intended by the speaker, while the burst spectra corresponded to the actual percept. These results suggest that when the burst spectra and formant transitions are in conflict, some listeners use the burst as primary for identifying place of articulation.
Burst spectra of word-medial voiced stops: systematicity and variation across speakers and rates
Authors: Wysocki Tamra M. , Soglasnova Svetlana , Hemphill Rachel M. , Gruber M. Catherine , Billings Sabrina J. , Landahl Karen L.
Published: July 2002

This study extends the investigation of word-medial stop consonants by Hemphill et al. [CLS 33(2), 333–346 (1997)]. They found that burst spectra for /d/ and /g/ for one speaker at one rate show invariant properties. In continuation of this work, linear predictive coding and spectrogram analyses were performed on stops, including /b/, in /alba/, /alda/, /alga/, /arba/, /arda/, and /arga/ spoken in a carrier sentence by two male and two female speakers of Midwestern American English across slow, normal, and fast rates. Schematic application of the criteria established by Blumstein and Stevens [J. Acoust. Soc. Am. 66, 1001–1017 (1979)] revealed characteristic spectral features for the burst of /g/ across all speakers and rates: a compact peak in midfrequency range. Spectra of the /b/ tokens displayed considerable variation, although they were generally characterizable as diffuse-falling or flat. The /d/ tokens displayed even greater variation and failed to show diffuse-rising or any distinctive spectral shape. These findings suggest that while the burst is a relatively more stable correlate for /g/ and /b/, the perception of /d/ may be more dependent upon other cues distributed in the acoustic signal.
Perception of vowel stimuli synthesized with different fundamental frequencies
Authors: Fourakis Marios , Preisel Constance , Hawks John W.
Published: July 2002

This research examined the perception of 465 vowel stimuli synthesized with both a typically male and a female fundamental frequency (F0) by persons with normal hearing, testing the hypothesis that when people listen to male and female speakers they employ different criteria for each speaker in order to decide which vowel the speaker has produced. The subjects, five male and five female native speakers of Midwestern American English, listened to the 465 vowel tokens synthesized with both F0’s. They were asked to decide, for each token, if it was one of eleven possible vowels as in the words: heed, hid, hayed, head, had, hod, hawed, hoed, hood, who’d, hud, or if not, to respond NONE. Next, the token was played again and the subjects indicated their certainty on a scale of 5 (very certain) to 1 (very uncertain). The responses were used to create perceptual maps in which each synthesized point is represented by the vowel code assigned to it by the majority of the subjects. The resulting maps indicate that male and female listeners did not differ in their assignment of vowel categories as a function of F0. There were no differences due to the gender of the listener.
The temporal extent of spectral properties on [voice] judgments
Authors: Molis Michelle R. , Diehl Randy L.
Published: July 2002

Previous results [M. R. Molis and R. L. Diehl, J. Acoust. Soc. Am. 99, 2591(A) (1996)] indicated that, in some instances, changes in spectral properties which extend over the entire length of a consonant–vowel syllable have no effect on the location of stop-consonant [voice] boundaries. Large manipulations in the relative amplitude of the first formant (F1) and the overall spectral tilt produced no changes in subjects’ labeling of velar stops. However, in recent experiments, similar spectral manipulations confined to the initial 50 ms following the onset of voicing energy did produce significant shifts in [voice] boundaries. Under these conditions, both increased relative F1 amplitude and increased spectral tilt resulted in an increase in [-voice] responses. Once again, these results are incompatible with the predictions of the ‘‘low-frequency hypothesis’’ [J. Kingston and R. L. Diehl, Lang. 70, 419–454 (1994)]. [Work supported by NIDCD.]
Acoustic-perceptual correlates of sentence prominence in Italian questions and statements
Authors: D’Imperio Mariapaola
Published: July 2002

Recent research on the acoustic correlates of perceived accentual prominence in speech has generally focused on fundamental frequency (F0), while few studies have attempted to shed light on how other parameters, such as duration and intensity, might interact with F0. A previous study on Italian suggests that duration has a major role in signaling lexical stress placement in isolated words [Bertinetto (1980)]. The present work reports on results of an experiment using synthetic speech to test which aspects of the signal, among F0, duration, and intensity, are more influential in the extraction of prominence structure at the sentence level and if there are differences between questions and statements. To this scope, a series of LPC-resynthesized stimuli were hybridized following a technique first developed by Nakatani and Aston (1978) and later adopted in Beckman (1986) and Hirschberg and Ward (1993) for English. Specifically, two-word sentences with varying modality (question or statement) and accent structure were manipulated in order to shift the location of perceived prominence from that of nonhybrid stimuli. The stimuli were presented to 21 speakers of the Neapolitan variety of Italian. The results suggest a greater role of duration within question stimuli than within statements.
Backscattering enhancements for ‘‘plastic’’ scatterers in water and silt: Novel mechanisms and ray models for solids and shells
Authors: Marston Philip L. , Hefner Brian T. , Blonigen Florian J.
Published: July 2002

Some ‘‘plastic’’ polymer solids have sufficiently low intrinsic dissipation that they can be approximated as purely elastic for the purpose of understanding the main features of their response to sonar. Unlike metallic objects, the typical plastic object has shear and Rayleigh phase velocities that are less than the speed of sound in water or in silt. In addition, the density contrast with the surroundings is less than for metallic objects. These changes cause major differences in the physical mechanisms for producing backscattering enhancements. For example, partial-wave-series predictions for backscattering by some solid plastic spheres show an enhancement in the ka=2–10 region due to tunneling coupling to Rayleigh wave resonances. We have modeled this enhancement with ray theory. For plastic shells, since the high-frequency symmetric (or s0) Lamb wave becomes subsonic, there is predicted to be a coincidence enhancement for the s0 wave. The backscattering by tilted finite-circular plastic solid cylinders [F. J. Blonigen and P. L. Marston, J. Acoust. Soc. Am. 102, 3088 (1997)] was observed to be enhanced due to the merging of rainbow caustics in the meridional plane. [Work supported by the Office of Naval Research.]
Analysis and comparison of recent resonance scattering formulations by M. S. Choi et al. with earlier, traditional RST works
Authors: Gaunaurd G. C.
Published: July 2002

Some comparisons are studied between several recent (1997 and 1998) formulations of acoustic resonance scattering, by M. S. Choi et al. and other earlier, traditional ones. In the practical cases here analyzed, the recent formulations are: (a) more complicated; (b) of purely formal character; (c) make use of information not known or available a priori; (d) eventually reduce to the traditional ones; and (e) seem to offer little new practical advantages. Finally, none of these formulations has been used for target identification purposes, which is the essential underlying reason for these investigations.
Mode scintillation and surface/submerged discrimination in SwellEx-96
Authors: Premus Vincent E.
Published: July 2002

It has been proposed that the short time-scale scintillation of normal mode amplitudes may be an effective discriminant for passive surface/submerged acoustic source classification in a shallow waveguide [V. Premus, J. Acoust. Soc. Am. (submitted)]. The approach is based on a two part hypothesis which states: (1) platform motion in the vertical due to surface or internal wave action induces observable temporal fluctuations in normal mode amplitudes, and (2) the probability densities of mode amplitude scintillation for surface and submerged sources are well separated under modest depth fluctuation conditions. In this work, results from the application of the mode scintillation classifier to narrow-band vertical array data collected during SwellEx-96 Event S5 are reviewed. Classifier output in the form of a thresholded mode scintillation interest image provides empirical evidence to support the classification hypothesis for the lowest order resolvable modes. Limitations imposed by the non-fully spanning nature of the vertical aperture will be discussed. [Work sponsored in part by SPAWAR, under Air Force Contract No. F19628-95-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the U.S. Air Force.]
Reverberation limitations in the active detection and localization of objects submerged in shallow water
Authors: Makris Nicholas C. , Lai Yi-San , Ratilal Purnima
Published: July 2002

A common problem in the active detection and localization of an object submerged in shallow water arises when acoustic returns from the object become indistinguishable from seafloor returns. Given a horizontal receiving array, the intensity of match-filtered and beamformed echo-returns can be plotted as a function of range and azimuth. Difficulties in detecting the presence of a submerged object in such an image arise in two ways. The first is unique to range and azimuth dependent waveguides. Even if the object produces the dominant return in its range-azimuth resolution cell and stands above background reverberation in adjacent cells, it may be camouflaged by prominent returns from neighboring cells that clutter the image. The second occurs when seafloor reverberation from the resolution cell of the object is so intense that the object’s presence is not statistically significant in that cell. The extent to which seafloor reverberation limits the detection and localization of submerged objects in these ways is quantitatively investigated. A model for full-field scattering from a submerged object is combined with a model for reverberation in a shallow-water waveguide. These are used to simulate range-azimuth images of the acoustic returns received by a bistatic system in a range-dependent waveguide.
Mode coupling produced by a cylindrical structure in a shallow water environment
Authors: Sarkissian Angie
Published: July 2002

A structure placed in a shallow water environment between a source and a receiver produces mode coupling with strength that depends on various parameters: the depth of the structure, its orientation, the sound speed profile at the location of the structure, the frequency as well as the mode number of the incident field. The mode coupling produced by a cylindrical shell with hemispherical end-caps is examined by varying the parameters. [Work supported by ONR.]
Ping-to-ping variations in the underwater environment and synthetic aperture sonar performance
Authors: Ruppel Timothy H.
Published: July 2002

In synthetic aperture sonar (SAS), a target is rapidly and repeatedly pinged from a moving acoustic array platform, with the resulting received data combined to achieve a high-resolution acoustic image. SAS technology has demonstrated some real promise in the field of mine hunting, and may have other applications as well. However, if the underwater environment changes between pings, then the individual receiving elements will have random phase errors and the SAS image may be substantially degraded. This paper will quantify the performance losses with simple simulations for a range of frequencies and environmental variabilities, concentrating on those which are consistent with experimental observation for the real ocean. The effect of motion compensation on these errors will also be discussed. [This work was funded by the Office of Naval Research.]
Stochastic dynamical modeling of marine mammal vocalization waveforms
Authors: Hayward Thomas J.
Published: July 2002

Stochastic models have been developed for approximating acoustic waveforms of marine animal sounds. The models provide a general method for replicating the time-frequency features and variations of vocalization waveforms based on limited databases of recorded samples. For each sample waveform, a linear-system model is constructed, and the system parameters are determined so that the impulse response of the system optimally fits the sampled waveform. Then, the statistical variability of the system parameters within the ensemble of recorded samples is characterized, and procedures for generating new waveforms based on those statistical distributions are defined. The linear-system models generate waveforms that are similar to the recorded samples and interpolate among the feature variations of those samples. In addition, the models suggest possible physical mechanisms of sound generation by marine animals. The approach is then extended to provide for representation and simulation of extended time series consisting of patterned repetitions of marine animal sounds, e.g., click bursts and codas of dolphins and whales. Applications to modeling of underwater noise generated by marine animals are presented. [Work supported by the Office of Naval Research.]
Large-scale modeling of ultrasound transducer pulses in lossy, nonlinear tissue
Authors: Wojcik Greg , Mould John , Carcione Laura , Fornberg Bengt , Waag Robert , Ayter Sevig
Published: July 2002

Broadband finite-element modeling codes have proven effective in the hands of medical ultrasound transducer designers. Similar modeling advantages have not yet been realized by image processing engineers concerned with aberrating media. Their principal difficulty is the much larger physical scale of bioacoustic models for imaging, e.g., a 20-cm round trip at 5 MHz is 600 wavelengths. Conventional (low order) finite-element/finite-difference wave solvers are inadequate at this scale because of cumulative numerical errors and computer limits. The solution is more accurate algorithms, based on spectral methods or high-order finite differences, in conjunction with parallel processing. The modeling problem is described, starting from a detailed transducer section, coupled to the heterogeneous abdominal wall and deeper tissue, to the scattering object(s) and back. Computed examples illustrate fundamental modeling and phenomenological issues. Solving the bioacoustic equations in the time domain is essential, and comprehensive models include both frequency-dependent absorption and second-order nonlinearity (B/A parameter). Algorithmic issues involve balanced, high-order space and time differential operators, treatment of discontinuities, radiation boundary conditions, and parallelization. The key is maintaining consistent, high-order accuracy throughout the analysis. An overall capability is demonstrated. [Work supported by DARPA, ONR, NSF, and NIH.]
Active control of mechanical impedance for characterizing actuator performance
Authors: Bras Jean-Marc F. , Johnson Marty E. , Fuller Chris R.
Published: July 2002

The performance of an actuator is often difficult to predict under realistic loads and it is therefore important to characterize actuators using a more sophisticated range of tests than the standard blocked force and free displacement tests. This presentation describes the development of a test apparatus used to conduct such a range of tests. It principally focuses on a method of altering the mechanical impedance seen by the test actuator to be characterized, using an active control system with a control actuator. The mechanical impedance in the test rig can be varied over a range of mechanical conditions experienced in real applications. The test actuator and the control actuator are placed in series and clamped in a rigid structure that has high impedance. The force output (F) and the velocity output (V) of the test actuator can be monitored using a force gauge and an accelerometer. While driving the test actuator with a test signal, an adaptive controller, using the filtered-X LMS algorithm, drives the control actuator such that the measured impedance (Z=F/V) matches the desired load impedance. By including a second control actuator, impedance on both sides of the test actuator can be varied simultaneously. [Work supported by MSI/DARPA.]
An active-passive distributed absorber for vibration and sound radiation control
Authors: Cambou Pierre E. , Fuller Chris R.
Published: July 2002

A new device has been developed to reduce structural vibrations and their associated radiated sound. The work is a contribution to the research of efficient and low cost devices that implement simultaneously the advantages of active and passive noise control techniques. A theoretical model was developed to investigate the potential of a new ‘‘active-passive distributed vibration absorber.’’ From this knowledge, prototypes have been designed and their potential experimentally investigated. The device subsequently developed can be described as a skin that can be mechanically and electrically tuned to reduce unwanted vibration and/or sound in a distributed manner. Preliminary results show that the new distributed treatment out-performs state-of-the-art point active-passive absorbers. The compact design and its efficiency make it suitable for many applications especially in the transportation industry. [Work supported by the ONR.]
Active control of transmission of turbulent boundary layer noise using smart foam elements
Authors: Griffin Jason R. , Johnson Marty E. , Fuller Chris R.
Published: July 2002

Results concerning the active control of transmission of turbulent boundary layer noise using smart foam elements will be presented. Smart foam consists of a cylindrical shaped PVDF film embedded within partially reticulated polyurethane acoustic foam. A smart foam element is an active–passive control device utilizing the passive absorption characteristics of the foam (effective at high frequencies) and the electrically driven PVDF film as the active element (effective at lower frequencies). This lightweight, compact arrangement lends itself well to the control of aircraft cabin noise resulting from an exterior turbulent boundary layer. Six smart foam elements (each 2 in. thick×4 in.×5 in.) are used to control the sound transmission through a 0.05 in. thick×10 in.×20 in. aluminum plate mounted in a wind tunnel. The sound transmission is monitored by measuring the pressure inside an externally mounted anechoic box that encloses the plate. Various control strategies are tested and results compared.
A feedback approach to adapting solid state tuned vibration absorbers for control of sound radiation and structural vibration
Authors: Wright R. I. , Charette F. , Johnson M. , Fuller C. R.
Published: July 2002

To further explore the complementary nature of active–passive systems, a multi-channel feedback approach to adapting tuned vibration absorbers (ATVAs) has been developed. The vibration absorbers consist of lumped mass-spring systems whose resonance behavior can be varied electronically through a feedback loop. The feedback controller consists of a two coefficient FIR filter, implemented on a DSP, where the input is the acceleration of the ATVA mass and the output is a force acting in parallel with the stiffness of the absorber. By separating the feedback signal into the principle real and imaginary components, the effective natural frequency and damping of the ATVA can be altered independently. This approach gives control of the resonance frequency while also allowing simultaneous removal of damping from the ATVA, thus increasing effectiveness. A multiple-channel genetic algorithm is used to adapt the resonant characteristics of each absorber (i.e., detune them) to minimize the structural sound radiated to the far field. Theoretical development of the local feedback tuning laws as well as the global strategy for minimizing the radiated sound will be addressed. Experimental results comparing the globally detuned configuration versus all ATVAs tuned to resonate at the disturbance frequency will be presented for a simply supported plate. By utilizing the passive advantages of this compact system, very good attenuation of structural born sound is seen while requiring only a fraction of the power of a fully active system.
Phonological disorders and spatio-temporal precision of stop consonant gestures
Authors: Edwards Jan , Fourakis Marios , Beckman Mary , Welby Pauline , Xu Ying
Published: July 2002

In previous work, we have explored methods for assessing the production of the velar-alveolar contrast in word-initial stops [Edwards et al., JSHR (in press)]. We found that children with phonological disorders had steeper second formant slopes than their age peers for lingual consonant–vowel transitions, suggesting more ballistic movement patterns for the children with phonological disorders. They also appeared to be initiating the vocalic movement later in the consonant–vowel sequence. Both patterns could contribute to the appearance of less precise spatial targets for lingual closures. These patterns suggested that at least part of the knowledge deficit that constitutes ‘‘phonological disorder’’ is a poor cognitive representation of the motor control structures necessary for producing lingual gestures and coordinating these gestures with each other. In this paper, we continue to examine spatiotemporal precision of stop consonant gestures in preschool children with phonological disorders, age peers, and adults. We have measured both F2 and F3 as well as point velocity over time. Preliminary analyses suggest that the less precise articulations of children with phonological disorders will be observed in measures such as higher and more variably timed F2 peak velocities. [Work supported by NIDCD Grant No. DC02932.]
The effect of perceptual training on the identification of a non-native phoneme contrast and its relationship to the MMN auditory evoked potential
Authors: Stack Janet W. , Dalebout Susan D.
Published: July 2002

The mismatch negativity (MMN) auditory evoked potential reflects the detection of minimal stimulus differences at a pre-attentive level. It has been reported that the MMN reflects acoustic, rather than phonetic processing of speech stimuli. The purpose of the present study was to examine the effects of perceptual training on (1) the behavioral ability of native speakers of American English to label a pair of Hindi stop consonants, and (2) the presence or absence of the MMN. Hindi voiceless unaspirated stop consonants contrasted by dental and retroflexplace of articulation ([t̪ versus [Ṡ]) were used. Prior to training, the MMN was present in 4 of 12 listeners and labeling ability was poor. Ten perceptual training sessions resulted in significant improvement in labeling ability. There was some generalization to a different voicing contrast (voiced unaspirated Hindi stop consonants [d̪] versus [ḍ]). There was also a significant increase in the number of listeners demonstrating an MMN in response to both contrasts after training. The group of listeners who had MMN responses after training also had significantly higher change scores from pre-test to post-test on the behavioral task. These results suggest that the MMN may have utility as an objective indicator of learning.
Voice F0 responds to auditory feedback pitch shifts during both steady and dynamic vocal behaviors
Authors: Burnett Theresa , Larson Charles
Published: July 2002

When trying to hold steady voice fundamental frequency (F0), subjects vocally oppose experimentally introduced small upward or downward shifts in auditory feedback pitch. These voice F0 responses have a latency of 100–150 ms, and occur despite efforts by subjects to ignore the feedback pitch shifts. The consistent and involuntary nature of these responses provides evidence of closed-loop fine control of voice F0. Studies of oculomotor and limb movement systems have revealed different control strategies for static versus dynamic behaviors. It is not clear whether the fine control voice F0 likewise differs. For this reason, a study was undertaken to determine if the voice F0 response to pitch-shifted auditory feedback was affected by task dynamics. Specifically, a comparison was made between responses to pitch shifts introduced during voice F0 hold and ramp tasks. Results indicate a similar role of the voice F0 response across both vocal behaviors, namely, to facilitate production of an intended target, be it static or dynamic.