bluuebunny/crossref_metadata_2025 huggingface dataset:
Beam-to-mode conversion of a high-frequency Gaussian P-wave input in an elastic plate embedded in vacuum
Authors: Lu I. T. , Felsen L. B. , Klosner J. M.
Published: October 2005

Gaussian beams, either individually or as synthesizing basis fields, provide useful models for the response due to Gaussian or more generally shaped high-frequency source inputs, respectively. When propagating into a layered environment, an initially well-collimated beam undergoes diffusion after successive reflections, and is converted essentially into the oscillatory pattern of one or more guided modes. The diffusion process is accelerated in the presence of multiwave coupling at interfaces, for example, the P-SV coupling at the free boundary of an elastic solid. This phenomenology is examined here for a two-dimensional P-wave beam input into an elastic plate embedded in vacuum. The beam is modeled via the complex source point method whereby a Gaussian-waisted input is generated from a line forcing function by assigning complex values to the source coordinates. This scheme avoids the need for plane-wave spectral decomposition and synthesis, but the analytic continuation to complex source coordinates of various line force Green's function representations in a layered medium requires precautions, which are discussed. Numerical calculations of P and SV potentials, stresses and motions, performed by beam tracking and mode summation at successive cross sections, reveal the beam-to-mode transition process, and suggest that a hybrid beam-mode algorithm provides the most direct and cogent physical explanation. [Work supported by AFOSR and ONR.]
Measurement of the universal gas constant R using a spherical acoustic resonator
Authors: Moldover M. R. , Trusler J. P. M. , Edwards T. J. , Mehl J. B. , Davis R. S.
Published: October 2005

A spherical acoustic resonator has been used to redetermine the universal gas constant R with an uncertainty of 1.8 ppm (standard deviation). To accomplish this, three subtasks were completed. (1) The volume of a spherical shell was determined by weighing the mercury required to exactly fill it at the temperature of the triple point of water, 273.16 K. (2) With the resonator filled with commercially supplied argon, the resonance frequencies of the radial modes were measured as a function of pressure. Using our theoretical model for the cavity, the frequency measurements were combined with the mean resonator radius determined in subtask (1) to obtain the speed of sound in commercially supplied argon. (3) Finally, the speed of sound in the commerically supplied argon was compared to the speed of sound in a “standard” sample whose chemical and isotopic composition was accurately established.
Eigenmodes of quasicrystals
Authors: Maynard J. D. , He Shanjin
Published: October 2005

Recently, a new state of matter, referred to as quasicrystalline, was discovered. Previously, solids could be classified as crystalline, with periodic lattice spacing, or as glassy, with random site spacing. The new quasicrystal structures appear to have long-range order, showing sharp peaks in the Fourier transform space as in a periodic system, but they also have properties that are impossible for any periodic structure, such as fivefold rotational symmetry. For periodic systems, Bloch's theorem may be used to understand physical properties such as wave transmission, and it is of current interest to learn if any such symmetry theorems apply to quasiperiodic systems. Rigorous theorems for one-dimensional quasiperiodic patterns based on a Fibonacci sequence suggest that such a pattern may be useful in control of vibration transmission in rib-stiffened plates. However, in two and higher dimensions, little is known about the consequences of quasiperiodic structure. Recently, acoustic measurements have been made on a two-dimensional quasiperiodic system and the frequency spectrum, density of states, and eigenmode patterns, showing some features unique to the quasiperiodic pattern, have been determined. [Work supported, in part, by NSF DMR 8701682 and the Office of Naval Research.]
Interaction of a sound beam with a two-fluid interface
Authors: Tjøtta Jacqueline Naze , Sagen Hanne , Tjøtta Sigve
Published: October 2005

The reflection and transmission of a real sound beam at the interface between two homogeneous and dissipative fluid layers are considered. Numerical results are obtained by using a fast Fourier transform algorithm. For the transmitted field, they show that, at a given incident angle, the direction and displacement of the beam depend critically on the absorption coefficient, and on the distance between the source and the interface. Various asymptotic formulas are also presented, which allow for a physical interpretation of the numerical results.
The role of cutoff modes in waveguides with boundary discontinuities
Authors: Sen R. , Thompson Charles
Published: October 2005

When a waveguide with a boundary discontinuity is excited by a low-frequency plane wave, cutoff cross modes are induced by the discontinuity. Although these modes are discernible only in the vicinity of the discontinuity, they act as sources in the incompressible local flow, and thereby affect the mean acoustic pressure. This has a profound effect on the farfield reflection and transmission coefficients R and T, and, consequently, on the junction impedance Z. The method of matched asymptotic expansions shall be used and it will be shown that, by properly accounting for the cross modes, the frequency range of validity of asymptotic estimates of R, T, and Z can be greatly extended. The possibility of improving these estimates by the use of Padé fractions will also be discussed. Finally, the formal difficulties of incorporating cutoff modes into the acoustic field description are discussed, and an extension of the method of matched asymptotic expansions to circumvent them is presented.
Hot-film anemometer response to hydroacoustic particle motion under imposed bias flow
Authors: Dubbelday Pieter S.
Published: October 2005

The response of a hot-film anemometer to vertical hydroacoustic particle motion is influenced by free convection, which acts as a bias flow. The output was shown to be proportional to particle displacement for a wide range of parameters [P.S. Dubbelday, J. Acoust. Soc. Am. 79, 2060-2066 (1986)]. It was expected that an imposed bias flow would increase the output and remove the dependence on the direction of gravity. Therefore, a hot-film sensor (diameter d) was subjected to an underwater jet from a nozzle. The ratio of the voltage outputs, due to a hydrostatic field, with and without this dc flow, was measured as a function of frequency for various flow speeds. The output showed a transition from being proportional to particle speed, to being proportional to particle displacement, depending on the angular frequency ω and imposed flow speed v. The transition takes place when a dimensionless number Ω, defined as Ω = ωd/v, is of order 1. This phenomenon has consequences for the interpretation of the measurement of turbulence, where it is customary to use the dc velocity calibration without reference to frequency dependence. [Work supported by the ONR.]
On the extension of the acoustic variational principle, from media at rest to potential mean flows
Authors: Campos L. M. B. C.
Published: October 2005

The well-known acoustic variational principle for sound in a medium at rest [e.g., Morse and Ingard, Theoretical Acoustics (McGraw-Hill, New York, 1968), p. 248], is generalized to the acoustics of a potential mean flow, and is used to derive: (i) the energy equation for sound in free and ducted flows; (ii) the wave equation in an inhomogeneous fluid at rest, in low Mach number and in high-speed convection. (iii) the Websters' horn wave equations and wave equations for low Mach number and high-speed nozzles. Case (iii) above applies to quasi-one-dimensional sound propagation in nonuniform ducts, and generalizes the variational principle of Weibel [J. Acoust. SOc. Am. 75, 105-106 (1955)] to include the effects of potential mean flow. The linear acoustic wave equations derived from the variational principle are checked by comparison with exact nonlinear equations obtained by a distinct method.
Photoacoustic effect from fine particles: Grain size and frequency dependence of the acoustic yield
Authors: Pelzl J. , Netzelmann U. , Schmalbein D.
Published: October 2005

The audioacoustic response of air in contact with fine copper-sulfate particles that are heated periodically by resonant microwave absorption has been investigated as a function of the modulation frequency (10 Hz to 5 kHz) of the microwave power for different particle sizes (10μ to 1 mm). Absolute values of the photoacoustic (PA) yield are obtained by normalization with the simultaneously detected conventional EPR signal. The PA-signal generation efficiency has been found to increase strongly with decreasing particle size with the maximum value occurring at a distinct size-dependent frequency. The size and frequency behaviors of the amplitude and phase shift of the PA-signal are analyzed theoretically on the basis of a model that considers a single isolated particle.
Recent advances in Arctic high-frequency acoustics
Authors: François R. E.
Published: October 2005

In the past few years, research in Arctic high-frequency acoustics (f > 5 kHz) has brought about a much better understanding of the effect of environmental factors on acoustics. Our knowledge of the effect of water properties continues to increase as well-known phenomena are routinely treated in greater detail. Ice properties, on the other hand, and the effect of these properties on acoustics, require new ideas and diligent research. For example, and perhaps of foremost importance, consider reflections from sea ice. Studies of the reflecting properties of the lower surface of sea ice, with its dendritic layer, show that at low frequencies the reflection coefficient at normal incidence depends only on the bulk properties of the medium. At higher frequencies (up to 200 kHz) Gaussian distributions for reflection coefficients are observed, with standard deviations that increase with frequency and averages that decrease with frequency, as much as 28 dB below that predicted by bulk properties alone. Studies of the target strength characteristics of ice block shapes have shown that rigid body theory for simple shapes, while good for hard ice surfaces, only crudely predicts actual response for freezing surfaces. As for in situ ice keels, the variation in return with frequency shows that reflections are often the coherent sum of several reflectors near the same range and close enough in azimuth that such returns appear to be pointlike. [Work is supported by Office of Naval Technology.]
A review of applied Arctic acoustic models
Authors: Cavanagh R. C. , Davis J. A. , Hanna J. S.
Published: October 2005

Basic acoustic model development related to the Arctic environment has been carried out by various researchers over the past 25 years. This work is being incorporated into applied models for propagation and noise that attempt to provide useful predictive capability given suitable environmental data bases. A review is presented of the candidate theories and some history of their development. In particular, ice scattering theories are described that show promise of utility and their incorporation into the several standard propagation models is discussed. Some comparisons of these models with data are presented and the outstanding issues related to model development and the adequacy of existing data are presented. Although the development of a corresponding ambient noise model is a much less mature activity, current attempts at such development are reviewed. [Work supported by the ASW Environmental Acoustic Support Program.]
High-frequency acoustic backscatter from the Arctic ice canopy: Theory and experiment
Authors: McDaniel Suzanne T.
Published: October 2005

The method of physical optics is applied to treat the backscatter of high-frequency acoustic signals from the Arctic ice canopy. Theoretical results are obtained for both the mean backscattering strength and the spatial coherence of the scattered field. The mean backscattering strength is found to be dependent on the fractional surface area covered by underwater ice ridges. Using measured ice distributions, the variability in mean scattering strength is predicted to vary by at most ± 2.5 dB from its average value for a wide variety of ice conditions. The theory is then applied to treat the spatial coherence of backscatter. The coherence is found to depend on the ice draft distribution and ensonified surface area. The results of experiments to measure the vertical spatial coherence of bistatic backscatter are presented. These results not only confirm the theoretically predicted dependences on measurement geometry but also support predictions of the relative importance of ice roughness versus ensonification. [Research supported by ONT with technical management by NORDA.]
Individual differences in the perception of cues for initial stop place and voicing contrasts
Authors: Hazan Valerie
Published: October 2005

Fifteen normal-hearing adults were tested on their ability to identify synthesized stimuli from three initial stop contrasts. Two place contrasts, BAIT-DATE and DATE-GATE, were presented in three conditions. In the “full-cue” condition, the place contrast was signaled by changes in burst frequency and F2/F3 transition. In the two “reduced-cue” conditions, the contrasts were signaled by only one of these two cues. A voicing contrast, GATE-KATE, was presented in two conditions: a “full-cue” condition, in which the contrast was marked by changes in VOT and F1 onset; and a “VOT cue” condition in which the F1 onset was flat. Group results show significant variance across conditions, both in terms of the phoneme boundaries and identification function gradients obtained. In addition, individual differences were found in the labeling of reduced-cue conditions. Some subjects showed little difference between the labeling of the full-cue and the reduced-cue conditions of the BAIT-DATE and GATE-KATE contrasts, while others were totally unable to establish a contrast for some conditions.
Perception of S-to-unvoiced-stop transitions in natural and synthetic speech
Authors: van Santen Jan P. H. , Glasgow Beverly M.
Published: October 2005

The perceptual role of the preclosure portion of S-K, S-T, and S-K transitions was investigated. Mahalanobis distances between reflection coefficient vectors (derived from linear predictive coding analysis) showed that differences between the stops are as large before the closure as during the release. In a paired-comparison experiment using natural speech, listeners preferred consistent words (e.g., S-T followed by TOUT) over inconsistent words (e.g., S-K followed by TOUT). However, perceptual differences were subtle, and the stop identity was never in question. In a subjective quality rating experiment using synthetic speech, there were no differences between consistent words and stop-neutral words (S-silence followed by, e.g., TOUT), but inconsistent words were given lower ratings. It is concluded that the perceptual role of the preclosure portion of S-to-unvoiced stop transitions is small, and can be ignored in current speech synthesizers. This apparent conflict between the experimental results and the Mahalanobis distance analysis may involve the perceptual saliency of the dimensions along which vectors differ and the effects of amplitude. Finally, the results demonstrate the sensitivity of subjective quality ratings.
Recognition of consonant clusters
Authors: Yuchtman Moshe , Stemberger Joseph , Martin Christopher
Published: October 2005

Perceptual processing of speech has been frequently studied using analyses of consonant recognition errors. Typically, nonsense CV or VC syllables are used as stimulus materials. Nonsense consonant clusters constitute a class of sounds that are largely devoid of semantic context, yet they represent a higher level of phonological organization. Consequently, the recognition of these sounds may reflect processing levels that are not involved in the perception of simpler stimuli. In the present study, consonant clusters (CCV or CCCV in /a/ vowel context), as well as their singletone members, were presented to listeners against a background noise at 10, 5, and 0 dB S/N. The results show systematic trends in terms of the frequency and the patterns of recognition errors. In general, the proportion of substitutions, additions, and deletions resemble the pattern of errors observed in production errors of consonant clusters. These and further results will be presented and discussed at the meeting.
The role of rate of transition in place perception
Authors: Zakia Renee A. E. , Kingston John
Published: October 2005

Kewley-Port, Pisoni, and Studdert-Kennedy [“Perception of static and dynamic acoustic cues to place of articulation in initial stop consonants,” J. Acoust. Soc. Am. 73, 1779–1793 (1983)] showed that initial bilabial and alveolar stops can be reliably identified from information in the first 20 ms of the syllable, including the burst and the beginning of the transition. Identification of stops as velars required a longer stimulus, indicating that a slow change in formant frequencies is characteristic of this place of articulation. If rate of change of formant frequencies is a positive cue to the identification of velar stops, it would be predicted that varying rate of change would affect their identification. To test this prediction, synthetic stop-vowel stimuli, derived from natural tokens, consisting of all combinations of [b,d,g] and the vowels [i,a], were edited to produce stimuli with four rates of formant transition: 100, 75, 50, and 25 ms. Listeners in this experiment identified place of articulation consistently regardless of rate of transition; specifically, there was no significant interaction between place and rate of transition. This would indicate that a slow formant transition is not necessary if a stop is to be identified as a velar. There was, however, a significant interaction between vowel and place of articulation, which implies that the magnitude, if not the rate, of the transition is a significant cue to place.
Central and peripheral representation of whispered and voiced speech
Authors: Samuel Arthur G.
Published: October 2005

Whispered speech is very different acoustically from normally voiced speech yet listeners have little trouble perceiving whispered speech. Two selective adaptation experiments explored the basis for the common perception of whispered and voiced speech, using two /ba/-/wa/ continua (one voiced, one whispered). The first experiment used the endpoints of each series as adaptors, and several nonspeech adaptors as well. Speech adaptors produced reliable labeling shifts of syllables matching in periodicity (i.e., whispered-whispered or voiced-voiced); somewhat smaller effects were found with mismatched periodicity. A periodic nonspeech tone with short rise time produced adaptation effects like those for /ha/. These shifts occurred for whispered test syllables as well as voiced, indicating a common abstract level of representation for voiced and whispered stimuli. Experiment 2 replicated and extended experiment 1, using same-ear and cross-ear adaptation conditions. There was perfect cross-ear transfer of the nonspeech adaptation effect, again implicating an abstract level of representation. The results support the existence of two levels of processing for complex acoustic signals. The commonality of whispered and voiced speech arises at the second, abstract level. Both this level, and the earlier, more directly acoustic level, are susceptible to adaptation effects. [Work supported by AFOSR.]
Modeling the perception of vowel-like formant peaks
Authors: Javkin Hector , Hanson Brian , Neyrinck Paul , Wakita Hisashi
Published: October 2005

An improved model of the relationship of harmonic structure to vowel perception is proposed and evaluated. Javkin, Hermansky, and Wakita [11th International Congress of Phonetic Sciences, Tallinn, Estonia, USSR (1987)] compared listeners' responses to one-formant stimuli with the computed weighted average of the two most prominent harmonics [the most important frequency, or MIF of Carlson, Font, and Ganstrom, Auditory, Analysis and Perception of Speech (Academic, London, 1975)] applied with different scaling factors. With this measure, a relatively expanded scale such as magnitude comes closest to perceptual test results. To improve on the characteristics of MIF, a critical band analysis was adopted and Chistovich and Chernova [Speech Common. 5, 3–16 (1986)] were followed in applying a center of gravity formant estimation (CG). Because CG is highly dependent on the integration interval, an iterative process was used, with each iteration choosing the frequency limits for the next analysis until convergence. Initial results suggest that, while CG is less affected by amplitude expansions than MIF, the magnitude space most closely approximates listeners' responses for the one-formant stimuli. Evaluations of the method with multiformant stimuli are also presented.
Identification of “hybrid” vowels in sentence context
Authors: Jenkins James J. , Strange Winifred
Published: October 2005

It has been demonstrated that listeners can identify the intended vowel in a CVC syllable even when the vowel nucleus has been attenuated to silence, leaving only onglides and offglides (silent center syllables). Verbrugge and Rakerd [Lang. Speech 29, 39–57 (1986)] constructed “hybrid” silent center syllables by cross splicing onglides and offglides of citation-form CVC syllables spoken by a male and a female talker such that formant trajectories were discontinuous. Identification of the intended vowel in hybrid syllables was no less accurate than vowel identification of the single-talker silent center syllables. The present study replicates this research with syllables spoken in a carrier sentence, “I say the word /dVd/ some more,” using ten American-English vowels. Hybrid silent center syllables were prepared by crossing the stimulus sentences so that the sentence started with one talker and switched to the other after the silent portion of the test syllable. Silent center stimuli were prepared for each talker separately as controls. Vowel identification was as accurate in the hybrid condition as in the control conditions suggesting that dynamic syllable structure provides talker-independent information about the articulatory/acoustic event. [Research supported by NINCDS.]
Classification of vowel productions by means of perceptual target zones: A response to Ladefoged and Studdert-Kennedy
Authors: Miller James D.
Published: October 2005

In discussion of my paper [Miller, J. Acoust. Soc. Am. Suppl. 81, S16 (1987)] at the 113th Meeting, Dr. Ladefoged and Dr. Studdert-Kennedy requested specific numbers regarding percent correct classifications of vowel productions achievable through use of the auditory-perceptual theory and its perceptual target zones (PTZs). At the time of the 113th Meeting, the estimated shapes and locations of the PTZs were very preliminary and represented only a second iteration (I2). The percents correct for the I2 zones were moderate (50%–95%). Based on reconsideration of older data and on numerous new measurements made in our laboratory, a new set of PTZs is being developed for the vowels. These represent the third iteration or I3 zones. The I3 zones will be presented and percentages of correct classifications for several data sets will be reported. Issues involved in developing decisive tests of the perceptual target zones will be discussed. [Supported by NINCDS and AFOSR.]
Auditory-perceptual approach to the stop consonants
Authors: Miller James D. , Jongman Allard
Published: October 2005

Using natural tokens and the synthetic stimuli of Abramson and Lisker [6th Internat. Congr. Phonet. (1970)], the auditory-perceptual theory shall be applied to syllable-initial stop consonants. The burst-friction components of each token are analyzed for the locations of their second and third sensory formants, BF2 and BF3. These are located in the auditory-perceptual space (APS) by the formulas: x = log(BF3/BF2) and y = log(BF2/SR), where SR is the sensory reference. The glottal-source components are then analyzed for their sensory formants: SF1, SF2, and SF3. These are then located in APS by equations: x = log(SF3/SF2), z = log(SF1/SR), and z = log(SF2/SF1). In this way, a sensory path comprised of burst-friction points and glottal-source points is generated. Next, a sensory-perceptual transformation is applied to generate a unitary perceptual path. Since the sensory-perceptual transformation is reactive, the perceptual path overshoots the burst-friction onset of the token and enters a physically unrealizable octant of APS, wherein the perceptual target zones for the stops are located. Distinct target zones are estimated for the stops [p,t,k,d,b,g], for h-like aspiration, and for voice bars. [Supported by AFOSR and NINCDS.]
Locations of the burst onsets of stops in the auditory-perceptual space
Authors: Jongman Allard
Published: October 2005

Preliminary LPC analyses of the voiceless stop consonants [p,t,k] in the context of the vowels [i,ɪ,ε,a,ᴜ,u] produced in real CVC words by one male and one female speaker suggest a method for locating formants in burst-friction spectra. Specifically, a 24-ms Hamming window was centered over the onset of the burst. First, the spectral peak with maximum amplitude below 6 kHz was located. Then, moving from left to right, the center frequencies of the first two peaks within 10 dB of the maximum were picked as the burst-friction components BF2 and BF3. Furthermore, in those cases where BF2 had been picked and BF3 was separated from BF2 by 2500 Hz or more, the frequency value for BF2 was also used for BF3. These burst-friction prominences were then converted into coordinates of the auditory-perceptual space: x = log(BF3/BF2) and z = log(BF2/SR), where SR is the sensory reference. This method of analysis enabled us to distinguish the stops, in terms of place of articulation, with good accuracy. [Work supported by AFOSR.]
Signal detection analyses of speaker identification accuracy
Authors: Papcun George , Kreiman Jody , Davis Anthony
Published: October 2005

The accuracy of speaker identification can be measured under various experimental paradigms including: (a) multiple-choice, closed-set experiments, in which listeners choose one speaker from among a lineup of n speakers [as in F. McGehee, “The reliability of the identification of the human voice,” J. Gen. Psychol. 17, 249–271 (1937)]; (b) multiple-choice, open-set experiments, in which listeners choose one speaker from among a lineup of n speakers, but can also refuse to choose any of the speakers [as in C. P. Thompson, “Voice identification: Speaker identifiability and a correction of the record regarding sex effects,” Human Learn. 4, 19–27 (1985)]; and (c) independent-judgment, open-set experiments, in which subjects are to make each choice independently of others [as in G. Papcun, J. Kreiman, and A. Davis, “Memory for unfamiliar voices at delays of one, two and four weeks,” submitted for publication]. In this paper, it was demonstrated that signal detection analysis, with certain extensions, makes it possible to compare results across these diverse experimental paradigms, and to see the essential identity of apparently disparate results. A computer program is provided to treat case (b).
Long-term changes in voice characteristics: Implications for speaker identity verification (SIV)
Authors: Feustel Timothy C. , Velius George A.
Published: October 2005

In a typical speaker identity verification (SIV) scenario, a talker first asserts an identity claim via some means other than speech. A reference sample of the claimed individual's speech is then loaded into a pattern matcher and compared against a new sample of the same word or phrase solicited on-line. Based on the similarity of the two utterances, and a predetermined criterion, a decision is made as to the veracity of the claimed identity. One difficult problem for SIV applications is that the spectral characteristics of a speaker's voice change over time in ways that are poorly understood. Utterances were collected from three speakers at regular intervals over a period of 23 weeks, and were analyzed first with respect to the magnitude of spectral dissimilarity over varying time intervals, and, second, with respect to the effect of these differences on error rates for an SIV decision task. The data show an increase in mean utterance dissimilarity of about 8% over a period of 2 weeks, followed by a much more gradual increase over 6 months. While the absolute change in mean dissimilarity was small, it resulted in a doubling of the error rate for the SIV decision task from about 5% to 10%.
A model for the transduction stage of auditory speech processing
Authors: Seneff Stephanie
Published: October 2005

A new model for the transduction stage of auditory processing is proposed. The model is applied independently to each of 40 critical band filter outputs, spanning the frequency range from 100–6400 Hz. The model consists of four components in cascade: an instantaneous nonlinear half-wave rectifier, a short-term adaptation component, a low-pass filter, and, finally, a rapid adaptation component. Model outputs were compared with available auditory data in a number of different dimensions as follows: (1) onset response to tone bursts, (2) forward masking effects, (3) steady-state behavior for vowel-like stimuli, (4) incremental response characteristics, and (5) synchrony loss at high frequencies. Two distinct spectral representations are computed from the model outputs: an amplitude spectrum corresponding to mean-rate response and a synchrony spectrum which makes use of temporal information to enhance spectral peaks. The model is currently being incorporated into a speaker-independent continuous speech recognition system under development. [Work supported by DARPA under Contract N00039-85-C-0254, monitored through Naval Electronics Systems Command.]
Perceptual and acoustic effects of nonlinear signal processing
Authors: Yuchtman Moshe , Jenison Rick , Lasky Robert
Published: October 2005

A common strategy for accommodating reduced dynamic range in the hearing impaired is the use of amplitude compression. In order to address the resulting elevation of the noise floor, an expansion region may be introduced. This study examines the perceptual and acoustic consequences of such nonlinear signal processing of CV and VC monosyllables. Transmitted information for a system of distinctive features as a function of the degree of nonlinearity, S/N ratio, and speaker was evaluated using the SINFA procedure. Acoustic analyses of processed syllables were carried out in an attempt to define articulation index measures that account for the perceptual data.
Longitudinal changes in syllable discrimination among normal and handicapped school children
Authors: Elliott Lois L. , Hammer Michael A.
Published: October 2005

Cross-sectional age-related differences in discrimination of voice onset time (VOT) [L. L. Elliott, J. Acoust. Soc. Am. 80, 1250–1255 (1986)] and the place-of-articulation (POA) feature [L. L. Elliott et al., J. Acoust. Soc. Am. 70, 669–677 (1981)] when just-noticeable differences among five-formant synthesized CV syllables are measured using adaptive test procedures were previously described. Results are reported here for children tested longitudinally for 3 consecutive years. Discrimination of temporal information (VOT) showed larger changes over time than discrimination of frequency-based information (POA). Also, larger performance differences occurred between normally progressing children and those with learning disabilities for VOT than for POA. Children with learning disabilities generally exhibited poorer auditory discrimination than normals; however, they demonstrated as much longitudinal change in performances as did the normally progressing children (i.e., there were no significant interactions between year of test and normal versus handicapped status). [Supported, in part, by NINCDS and NIH.]
Statistical representation of word-initial obstruents: Further data
Authors: Forrest Karen , Weismer Gary , Milenkovic Paul
Published: October 2005

At the 113th Meeting of the Acoustical Society, a procedure was presented for the classification of word-initial obstruents. The procedure involved calculating FFTs at 10-ms intervals from the onset of the obstruent through the third cycle of the following vowel. These FFTs were treated as random probability distributions from which the first four moments (mean, variance, skewness, and kurtosis) were computed; computations were also made on Bark transformed FFTs. Moments calculated over the first 40 ms of voiceless stops discriminated place of articulation with 97% accuracy. Voiceless sibilants were categorized with about 98% accuracy when the Bark transformed moments from the first 20 ms of the fricatives were used. The speech sample used in the previous study only allowed comparison of obstruents across two vowel contexts. In this report, results of the moments analysis of a speech sample are presented in which all voiced and voiceless stops, as well as voiceless sibilants, are paired with six vowels, /i,a,u,æ,ʌ,e/. The efficacy of the moments in discriminating obstruents in this broader context will be discussed. [Work supported by NIH award NS13274.]
Use of multiple speech dimensions in concept formation by Japanese quail
Authors: Kluender Keith R. , Diehl Randy L.
Published: October 2005

Japanese quail (Coturnix coturnix) have learned to form a category for syllable-initial [d], and can discriminate [d] syllables from those beginning with [b] or [g] across vowel contexts [Kluender et al., Science (1987)]. Acoustic analysis of the categorized syllables revealed no single feature that could have supported generalization, suggesting that the quail used some combination of stimulus properties to categorize syllables. Current experiments investigate two ways such a category could be formed. First, initial consonant information may be evaluated conditional upon the vowel that follows. Whether quail can learn to categorize syllables in which, for example, positive exemplars are CVs with either a voiced stop and a front vowel, or a voiceless stop and a back vowel is being tested. A second possibility is that phonetic categories are examples of polymorphous concepts, with no single necessary or sufficient condition for class membership. Two birds have learned a concept in which three stimulus dimensions of syllables are needed to make a category assignment. The best subject has learned a concept that requires her to discriminate: (1) voiced versus voiceless syllable-initial stops, (2) front versus back vowels, and (3) sex of the talker. Responses to novel stimuli reveal a category structure remarkably similar to that hypothesized for humans. The fact that quail can learn a concept in which multiple cues are clearly required suggests that general mechanisms of audition and perceptual learning are sufficient for acquisition of speech categories. [Work supported by NICHD.]
Qualitative separateness in children's speech
Authors: Nittrouer Susan , Whalen D. H.
Published: October 2005

Acoustic analyses of fricative-vowel (FV) syllables spoken by adults and young children (ages 3 to 7 years) have demonstrated several differences. In children's speech: (1) the gross spectra of /∫/ and /s/ segments were more similar than those of adults; (2) fricative F2 frequencies varied more as a function of vowel context; and (3) the relative F2 amplitude was greater. These acoustic differences between children's and adults' speech provided an opportunity to test two competing hypotheses of perceptual segmentation. According to one, listeners divide the signal into temporally discrete, context-sensitive allophones that can be used to make inferences about later-arriving segments. The second hypothesis suggests that listeners can separate simultaneously arriving acoustic information into successive phonetic units. In the present set of experiments, brief portions of fricative noise extracted from FV syllables spoken by adults and children to normal adult listeners were presented. Results showed that listeners were less accurate in fricative identification for child speakers, but more accurate in identifying the vowel context from which the fricative noise came. Thus the greater coproduction found in children's speech was more easily recovered by listeners, even though the most prominent phone was more poorly perceived. This finding was taken as support for the second hypothesis. [Work supported by NIH Grants NS-07237 and HD-01994 to Haskins Laboratories.]
Effects of speaker gender on speech recognition by hearing impaired listeners
Authors: Stieren Angelika , Strange Winifred
Published: October 2005

Audiologists and clients often claim that female speech is less intelligible than male speech for subjects with bilateral high-frequency sensorineural hearing losses. To examine the extent to which source characteristics (voice pitch) and gender-related resonance characteristics contribute to these speech recognition difficulties, two men and two women each produced three sublists of the modified rhyme test (MRT). Within gender groups, one speaker had a relatively low voice pitch, one a high pitch, such that the high-pitched male voice was approximately the same as the low-pitched female voice. Stimuli were presented to listeners at 30 dB SL in quiet, in speech noise (S/N = + 12 dB), and in speech babble (S/N = + 12 dB). Overall results showed significant differences in identification of consonants across speakers. However, contrary to expectations, performance was worst for the male with the low voice pitch, intermediate for the two female speakers, and best for the high-pitched male. There appeared to be gender-related differences in the type of consonant errors.
Are female voices more intelligible than male voices?
Authors: Beinum Florien J. Koopmans-van , Tielen Mirjam T. J.
Published: October 2005

Studies on the intelligibility of female compared to male voices, and studies on the relation between acoustic parameters (such as F0) and speech understanding are rather scarce and indirect. However, particularly in information-providing services, female voices are frequently used, whereas, in speech-technology applications, they are often excluded, probably due to inadequate methods for analyzing female voices. In order to study the relative intelligibility of male and female voices, ten male and ten female speakers were asked to read three phonotactically balanced lists of 50 CVC combinations. Special care was taken with respect to speech level, signal-to-noise ratio, and presentation method using: equivalent peak level, babble noise, and a variation of the Nakatani and Dukes method. For a small number of trained listeners, the intelligibility threshold per speaker is established, providing 20 measuring points per listener. Furthermore, word and phoneme intelligibility per speaker are measured with phonetically balanced sentences and words, at a fixed S/N ratio.
Viscoelasticity of polymers—Consideration of predictive methods for wide frequency response
Authors: Wetton Raymond E.
Published: October 2005

The nature of viscoelasticity in high polymers is discussed in molecular terms. The factors affecting damping and dynamic modulus are outlined. Many commercial polymers are multiphase and the width and magnitude of molecular relaxation are shown to be related to the compatibility of the components. Master curves showing viscoelastic response over a wide range of frequency can be generated using semiempirical procedures of time-temperature shifting of data. The Williams, Landel, and Ferry (WLF) relation, in particular, is discussed for multi- and single-component polymers. In general, predictions of dynamic response via extrapolation over one or two decades in frequency can be made with reasonable confidence, if enough detailed care is taken. The use of dielectric loss peak loci at high frequencies is proposed to aid these predictions.
The temperature dependence of viscoelastic responses above Tg
Authors: Landel Robert F.
Published: October 2005

The origins of the WLF equation will be reviewed, along with the role of the temperature dependence of responses in trying to ascertain relaxation mechanisms. Some pitfalls, misuses, and misunderstandings will be described, together with similar comments on so-called Tg's. The general applicability and utility of the temperature scaling of the time domain will be illustrated with examples from damping, rupture behavior, friction, and crack propagation.
Techniques for noise and signature reduction applications
Authors: Townend D. J.
Published: October 2005

In recent years, DMA test systems have become commercially available. Prior to this, workers in this field developed equipment to meet their own specific needs. Current commercial equipment is aimed at the thermal analysis market and is seen as complimentary to established techniques, such as DSC and TMA. Great emphasis is placed on temperature control, but, in general, less attention is paid to frequency range and mechanical design. Upper frequency limits are usually around 100 Hz. While low frequencies are ideal for the study of molecular relaxation processes and for routine material characterization, they have little immediate application in the field of noise and signature reduction. Recent work at ARE has resulted in the development of computerized WLF technique; this method is based on a reference frequency as well as a reference temperature. In general (though not essential), the reference point selected is the temperature of peak tan at a frequency of 1 Hz. Where multiplexed frequency data are available, it is a simple matter to verify that an unknown material will fit the standard equation by comparing measured shifts in peak tan with computed values based on the standard constants. Signature reduction applications require systems that, in some cases, work at frequencies up to 1 MHz. Computerized predictions based on WLF data, shifted from low-frequency measured data, show very good agreement with high-frequency measured acoustic data, but it would be reassuring to be able to measure dynamic mechanical properties at kilohertz frequencies. Recent improvements to an inertial mass, air-bearing supported system, developed at ARE some 10 years ago, have resulted in a system capable of yielding complex shear modulus data at frequencies up to 10 kHz.
Characterization of anisotropic elastic wave behavior in media with parallel fractures and aligned cracks
Authors: Schoenberg Michael
Published: October 2005

Large parallel fractures or aligned microcracks, whether fluid filled, empty, or debris filled, cause specific types of material compliance increases, which are manifest in the anisotropic behavior of elastic waves in such media. The anisotropy attributable to the fracture system may be triclinic (the most general) with six independent compliances, monoclinic with four, orthorhombic with three, or transversely isotropic (rotationally symmetric fractures) with two. The fracture system may be embedded in an anisotropic elastic background with no restrictions on the type of anisotropy. To compute the long wavelength-equivalent moduli of the fractured medium requires, at most, the inversion of two 3 × 3 matrices. Dilute systems of flat aligned microcracks, assumed on average rotationally symmetric, in an isotropic background yield an equivalent medium of the same form as that of the isotropic medium with large transversely isotropic fractures; i.e., there are two additional parameters due to the presence of the microcracks that play roles in the stress-strain relations of the equivalent medium identical to those played by the parameters due to the presence of large fractures. Thus knowledge of the total of four parameters describing the restricted transverse isotropy of such a fractured medium tells nothing of the size or concentration of the aligned fractures, but does contain information as to the overall excess compliance due to the fractures or cracks and their orientation.
Borehole modes in a fluid-saturated permeable medium: Numerical and experimental results
Authors: Liu Hsui-lin , Winkler Kenneth W.
Published: October 2005

Stoneley waves propagating in boreholes in permeable materials provide a unique opportunity to study the boundary conditions at a fluid/permeable-solid interface. First, a review of the theory and present frequency domain solutions for Stoneley wave velocity and attenuation is presented. Formation premeability is shown to decrease the Stoneley wave velocity and increase the attenuation compared to the nonpermeable case. This effect is most pronounced at low frequencies. Then the theory is applied to finite size cylinders, such as might occur in laboratory experiments. In this case, two classes of extensional modes, besides the Stoneley mode, are found. One class is the fast wave mode, which is analogous to the ordinary extensional mode. The other class is the slow wave mode, so-called because the zeros are located along the Biot slow wave branch cut. For a highly permeable medium, the slow wave modes can obscure the identification of the Stoneley mode. Also presented is the experimental confirmation of the numerical predictions for Stoneley wave propagation. Compared to conventional ultrasonic techniques, the new Stoneley wave technique allows the performance measurements in a broad frequency band above and below the critical frequency of Biot theory. One application of the results is estimating rock permeability using the borehole Stoneley mode in petroleum prospecting.
Coupling of sound with surface waves on fluid-loaded elastic objects described by a generalization of GTD
Authors: Marston Philip L.
Published: October 2005

The geometrical theory of diffraction (GTD) was recently extended to describe surface elastic wave (SEW) contributions of scattering from fluid-loaded spheres and cylinders at high frequencies [P. L. Marston, J. Acoust. Soc. Am. Suppl. 1 81, S14 (1987)]. The coupling ocean SEW with the acoustic field was described by a complex coefficient G. That analysis gave simple physical approximations: |G|≈8πβc/cSW for spheres and |G|≈ 8πβ/(πka)1/2 for cylinders; these were confirmed with other numerical results. The SEW angular attenuation coefficient (due to radiation damping) and phase velocity are β and cSW, while c denotes the sound speed in the fluid, k = ω/c, and a is the object's radius. The present work extends the original analysis of backscattered sound to cases where the SEW only partially circumnavigates the object. If a plane sound wave of amplitude pi excites an SEW on a cylinder, the sound amplitude radiated by the SEW after traveling an arc length L is p≈pi(α/2r)1/2 × |G/2|exp(− βL/a). The observer is a distance r from a virtual source (in the cylinder), from which the radiated rays appear to diverge. A simple approximation of β shows that β∝ the ratio of fluid to solid densities. The ratio of the |G| for spheres and cylinders is confirmed by geometrical considerations. [Work supported by ONR.]
A Gaussian beam representation of wave fields at a liquid-solid interface
Authors: Wen J. J. , Breazeale M. A.
Published: October 2005

A new method of analysis is described to represent the resultant field when a wave beam is subjected to any physical process (e.g., propagation, focusing, reflection, diffraction, etc.). Instead of expressing the field solution as a continuous distribution of plane waves through spatial Fourier analysis, a set of Gaussian beams is employed as the basic unit. The Gaussian beam representation is introduced to replace the traditional planewave representation so that the solution is an analytical one rather than a symbolic integral. This replacement is made possible by a computer optimization routine that overcomes problems introduced by use of nonorthogonal functions, and enables the expression of the field solution in a simple closed analytical form—the sum of Gaussian functions. The technique is applied to the description of the reflected field of a bounded beam incident at the Rayleigh angle with very satisfactory results. [Research sponsored by the Science Alliance, a State of Tennessee Center of Excellence.]