bluuebunny/crossref_metadata_2025 huggingface dataset:
Slow dynamics and the Larsen effect at millisecond time scales
Authors: Weaver Richard , Lobkis Oleg
Published: September 2008

At sufficient gain, an ultrasonic feedback circuit rings with a ‘‘Larsen’’ tone that depends on the nonlinear electronics, and also on the acoustic properties of the solid body to which it is attached. Because the spectrum of this tone is extraordinarily narrow and stable, it may be measured with high precision. With a goal of using this to monitor small rapid changes in materials, here the stability of the signal to perturbations is quantified, and the results applied in the monitoring of the evolution of the effective modulus of mesoscopically elastic bodies (cements and stones) after brief transient loads. In accord with other studies, it is found that the modulus drops after the load, but then recovers in a characteristic manner, like log(t). The present technique, using as it does frequencies of order MHz and loads with durations of order 10 μs, extends these studies of slow dynamics to early times. It is found that log(t) behavior can be sustained over the full range investigated, from a couple of μs to hundreds of seconds. [Work supported by NSF CMS 05-28096.]
Elastic constant measurements in heterogeneous systems: Thin films on a substrate
Authors: Gladden Joseph
Published: September 2008

Resonant ultrasound spectroscopy (RUS) has shown itself to be an efficient and accurate method for determining the full elastic tensor of a single crystal sample. Elastic constants are a measure of the curvature of the interatomic potentials, and are thus sensitive to a variety of phase transitions in materials. In this talk, an extension of RUS will be presented that allows for the determination of the elastic constants of a crystalline thin film deposited on a substrate with thicknesses on the order of 100 nm or greater. Both experimental and numerical analysis issues for thin film measurements will be addressed. Some ‘‘proof of principle’’ results will be presented as well as experimental data showing magnetic phase transitions in colossal magnetoresistance films between 200 nm and 400 nm thick. Thin film RUS should prove to be a useful tool in the effort to better understand phase transitions in reduced dimensionality and effects of lattice mismatch between substrate and film.
Making resonant ultrasound spectroscopy measurements from milliKelvin temperatures to well above room temperature
Authors: Betts J. B. , Migliori A. , Stroe I.
Published: September 2008

Measuring elastic moduli using resonant ultrasound spectroscopy (RUS) can be very challenging at the best of times. When the measurement environment needs to be controlled from milliKelvin to many hundreds of Kelvin, this challenge becomes extremely acute. We will present methods and results from such experiments showing that with care, elastic moduli can be very accurately determined over these extreme temperature ranges. [Work supported by the National Nuclear Security Administration, U.S. Dept. of Energy, State of Florida, and the National Science Foundation.]
Common acoustic properties of solid aggregate at micro- and nano-scales
Authors: Tavossi Hasson M.
Published: September 2008

Acoustic properties of solid aggregate, when measured at macroscopic scale, have been found experimentally to have remarkable similarities with the same wave properties observed at the atomic and nano-scales. It can be shown that the elastic moduli and other wave properties such as, wave tunneling, attenuation, cutoff-frequency, and dispersion, depend on the same structural factors at macro- and nano-scales. The model constructed for the acoustic properties of solid aggregate, expressed in terms of wave-number (ka), can be applicable in the wide range of frequencies and length scales. The findings on acoustic properties of solid aggregate at macroscopic scale could lead to a better understanding of the wave properties of solids at nanoscales. These readily analyzable models for acoustic properties at macroscopic scales are convenient tools for verification of theoretical models for acoustic behavior of complex solids at atomic level. Experimental data and numerical results are compared, showing acoustic wave responses of the solid aggregate for a wide range of frequencies, from audible to ultrasound. The relevance of these results to nano systems will be discussed to show that parallel acoustic properties can exist in the range of characteristic lengths from macro- to nano-scales.
Simulating thermoacoustics in random stack materials
Authors: Jensen Carl
Published: September 2008

A lattice Boltzmann based computational fluid solver is being developed to investigate the thermoacoustic properties of stack materials with irregular pore geometries. The goal of the investigation is to perform a direct simulation of the time-varying thermohydrodynamic flow within a porous material and determine the material’s thermoacoustic properties from its base characteristics. Accurately simulating a porous material’s pore scale flow requires methods for handling the irregular boundary conditions presented by the material and the use of high performance computing to handle the large number of elements required to represent the material’s bulk behavior. Progress in both of these areas will be presented as results in applying the use of commodity graphics programming units for high performance computing and a local grid refinement scheme for increased resolution at the wall boundaries. [Work supported by U.S. Army Space & Missile Defense Command.]
Effect of neck geometry on aeroacoustic excitation of a Helmholtz resonator
Authors: Lanier Stephanie , Slaton William
Published: September 2008

The aeroacoustic response of a Helmholtz resonator, when attached to a wind tunnel via junctions with different neck geometries, has been examined. The wind tunnel consists of a 2-inch ID glass tube with variable mean flow at atmospheric pressure connected to a cross-junction with two coaxial 5-liter Helmholtz resonators. During the experiment, the acoustic pressure and corresponding frequency is measured in one of the Helmholtz resonators at different wind tunnel flow velocities. By knowing these quantities, the acoustic velocity of the air at the neck of the resonator can be determined. The ratio of the acoustic velocity to the flow velocity as a function of the Strouhal number can be studied for differing neck geometries. Helmholtz resonator neck geometries studied include 90-deg bends and straight sections in various combinations. [This work was supported by the Arkansas Space Grant Consortium and the University of Central Arkansas University Research Council.]
An analytical model for the design of optimized heat exchangers for thermoacoustic systems
Authors: Berson Arganthaël , Blanc-Benon Philippe , Gusev Vitalyi
Published: September 2008

A 1-D nonlinear model for the heat transport from the edge of a thermoacoustic stack to a heat exchanger is developed. This model is an extension of the previous study by [Gusev et al., J. of Sound and Vibration 235, (2000)] to the case of a finite dimension heat exchanger with a temperature difference between the stack and the heat exchanger plates. The model is based on a relaxation-time approximation for transverse heat transfer that allows for the calculation of the heat flux through an adiabatic gap, separating the stack and the heat exchangers. It shows the generation of temperature harmonics close to the edge of the plates that leads to nonlinear heat transport through the gap. The heat flux extracted by the hot side heat exchanger is calculated, taking into account viscous dissipation along the plates and reverse heat conduction toward the stack. An optimal set of geometrical and relaxation parameters for the heat exchanger is obtained. Results are compared with experimental measurements of temperature fluctuations behind the stack plates, and with the results of numerical simulations from the literature. [This work is supported by ANR (project MicroThermoAc NT05142101).]
Vowel space parameters
Authors: Whalen D. H.
Published: September 2008

Vowels are universal in human languages and have long been categorized in feature systems. However, the feature systems are based on introspection and include a notion of ‘‘height’’ or ‘‘closeness,’’ that is not anatomically straightforward. From x-ray and other imaging data, the important aspects seem to be palatal, velar, and pharyngeal closures, with secondary effects of lip rounding. Describing vowels in terms of location of constriction makes some assimilation patterns more direct, as with palatal vowels (e.g., /i/) conditioning palatal fricatives. Vowels can also be described as intrinsically slower than consonants, which allows for a more straightforward description of their timing relationships, and a possible explanation for the crosslinguistic preference for CV syllables. The use of fricatives for syllabic nuclei is common in languages and derives easily from a narrowing of the constriction to the point at which frication is generated. More and less vowel-like patterns in consonants have also been noted, such as in coarticulation of laterals and rhotics. Gesture-based systems have difficulty describing some phonological patterns (e.g., vowel lowering). The status of schwa, which seems to lack a constriction, is unclear. With two competing systems having different advantages, work directly comparing the approaches is needed within speech science.
Vowels and speech intelligibility
Authors: Kewley-Port Diane
Published: September 2008

Recent research on the contribution of vowel versus consonant segments to sentence intelligibility has demonstrated a 2:1 advantage for vowels in a noise replacement paradigm [Kewley-Port et al., J. Acoust. Soc. Am. (in press)]. The vowel advantage is sustained when boundaries are slightly modified in sentences, but different results have been reported for isolated words. Our follow up research with typical elderly hearing-impaired listeners has demonstrated that the vowel segmental information is especially important in sentence intelligibility, even though it is commonly believed that consonants are more important than vowels for speech recognition. Additional research in our lab has examined the relation between listeners’ ability to discriminate acoustic detail in vowel formants at a more peripheral level of the auditory system, and to identify vowel categories at more cognitive/linguistic levels. Three populations of listeners have participated in these experiments: Normal-hearing Americans, hearing-impaired Americans, and normal-hearing second language learners of English. Moderate correlations between formant discrimination and vowel categorization were observed for all three groups. Implications of our results will be discussed in terms of theories of speech perception and of second language speech learning. [Work supported by NIH.]
Speech intelligibility and the vowel space: Normal speech
Authors: Neel Amy T.
Published: September 2008

Vowel formant frequency values and related vowel space measures have been widely used in the study of speech intelligibility for normal and disordered talkers. The strength of vowel space measures in predicting speech intelligibility for normal talkers, however, is relatively low: [Bradlow et al. (1996)] found that vowel space dispersion predicted 19% of variance in sentence intelligibility, and [Hazan and Markham (2004)] found that the F2 difference between /i/ and /u/ predicted 16% of variance in word intelligibility scores. Using data from the 45 men and 48 women speakers in the Hillenbrand et al. (1995) database, acoustic characteristics of ten vowels were used to predict identification accuracy. Multiple regressions revealed that global measures (mean f0, F1 and F2, duration, and amount of formant movement) and fine-grained measures (vowel space area, mean distance among vowels, ranges for f0, F1, and F2, duration ratio between long and short vowels, and dynamic ratio between dynamic and static vowels) accounted for less than one-quarter of the variance in identification scores across talkers. Focusing on confusions among spectrally similar vowels may provide better information on intelligibility differences among normal talkers. Goodness ratings may provide a wider range of scores for statistical analysis than identification accuracy.
How did a stimulus order in AX discrimination training influence improvement in the ability to perceive an American English /l-r/ and /gl-gr/ among Japanese listeners?
Authors: Tsushima Teruaki
Published: September 2008

Previous research has shown that discriminability of /l-r/ in AX discrimination may be significantly lower when /l/ is presented as the first stimulus than otherwise, among Japanese listeners under certain experimental conditions. The present study examined whether the stimulus order in AX discrimination training had significant effects on improvements of the ability to discriminate and identify English /l-r/ and /gl-gr/. One group of Japanese listeners (N=12) received twelve sessions of AX training in which stimuli (i.e., lexical items) were presented in the order of /l/ to /r/ (e.g., glock-rockh), while the stimulus order was reversed (e.g., grock-lockh) in the other (N=12). A comparison of pre-test and post-test results found the former group showed a significant improvement of the ability to discriminate /l-r/ (p=0.037), to identify /l/ in /l-r/ (p=0.023), and a significantly better-defined category boundary of synthetic /la-ra/ stimuli than the other group in the post-test (p=0.05), while none of the improvements were significant in the other group. The results indicated, unlike what was predicted from the previous findings, the ability to perceive /l-r/ may be better improved when /l/ was presented first than otherwise during AX training. The results will be discussed in terms of models of L2 speech learning.
Effectiveness of a robust computer assisted pronunciation training tool
Authors: Cho Kwansun , Harris John G. , Wayland Ratree
Published: September 2008

A reliable ASR-based pronunciation training tool named STAR (self-training accent reduction) is implemented for native speakers of Korean learning American English. STAR is designed to focus on the most frequent phonemic errors made by Korean adult learners and to provide instantaneous feedback. In order to investigate the effectiveness of STAR, ten Korean participants are recruited for this pilot study. The study consists of three phases: Pre-test, training, and post-test. During the pre-test, the participants read a pre-designed word list containing accent sensitive phonemes into a microphone and participate in one session of training using the STAR system. The participants return for two more sessions of training on the following day. The post-test is administered on the third day, after one additional training session. During the post-test, the participants read the same wordlist as the one administered during the pre-test, and an additional wordlist that they were not trained on. Two trained phoneticians listen and transcribe all recordings to examine whether the participants’ productions are more accurate after the STAR training. The results indicate that most of the participants who practice pronunciation with STAR show improvement in their pronunciation.
The adaptability of laboratory phonemic perception training protocols to common second language instruction situations
Authors: Sawallis Thomas R. , Townley Michael W.
Published: September 2008

For the past two decades, second language pedagogy has de-emphasized phoneme-level pronunciation training. During the same period, laboratory experiments have demonstrated a variety of benefits from training non-natives in the perception of difficult target language contrasts. Experiments have shown that learners’ perceptual performance improves (Jamieson & Morosan, 1986; Flege, 1989 & 1995), that the improvements generalize to new talkers and words (Lively, Logan, & Pisoni, 1993), that perceptual training triggers production improvements (i.e., without specific pronunciation training, Bradlow et al., 1997), and that both perceptual improvements (Flege, 1995; Lively et al., 1994) and production improvements (Bradlow et al., 1999) continue over several months. Protocols for these training experiments are generally intensive, and may include sessions of 40 min, three sessions per day, or sessions for 15 consecutive business days. Such onerous protocols are acceptable for basic research with compensated subjects. They are unacceptable for normal L2 instruction, with paying learners and with limited time for pronunciation training. The present study analyzes the training protocols from selected research articles, and documents the types and amounts of training. It then suggests acceptable alternative regimens for achieving comparable training in typical learning situations, including 16-week college semesters and shorter language institute terms.
The categorical nature of tones and consonants: Evidence from second language perception and production
Authors: Hao Yen-Chen , de Jong Kenneth
Published: September 2008

Tones are commonly considered to be psychologically equivalent to phonetic segments like consonants and vowels [Ladd, Intonational Phonology (1996)]. However, comparing two current studies reveals intrinsic differences between tones and consonants. One study examines ten American learners acquiring Chinese tones. The other examines 40 Korean learners acquiring English obstruents. Both studies include three tasks: Identification—subjects identified the tones or consonants of L2 nonsense words. This task requires auditory perception and associating the sound with a linguistic category. Mimicry—subjects listened and repeated the stimuli. This task requires perception and production. Reading—subjects read a list of nonsense words. This task requires associating linguistic labels with speech production. These two studies yield different patterns. For tones, accuracy rates for Mimicry are the highest, suggesting learners have more problems with linguistic association, the component shared by Identification and Reading. For consonants, accuracy rates for Mimicry are the lowest, signifying difficulty with perception and production, but not with linguistic association. Taken together, these findings suggest a pervasive difference in categorical nature of tones and consonants. These results also highlight the necessity of multiple tasks in assessing how linguistic contrasts function in a phonetic system. [Work supported by the NSF.]
Perceptual learning about word boundaries with familiar and unfamiliar voices and accents
Authors: Smith Rachel
Published: September 2008

An experiment investigated perception of speaker-specific variation in phonetic detail around word boundaries. Two male speakers of standard Southern British English (SSBE) read 24 phonemically-identical sentence pairs that differed in the location of a word boundary, e.g., So he diced them versus So he’d iced them. In pre- and post-tests, 80 SSBE subjects heard the sentences in cafeteria noise (SNR 2 dB) and typed the words they heard. Between these tests, subjects received 40 minutes’ training: They heard different tokens of the same sentences without noise in a disambiguating context, and answered questions about their meaning. A counterbalanced between-groups design manipulated the voices heard in tests (speaker 1 or 2; always the same in pre- and post-test) and in training (Same as in tests, or Different). Training with the Same voice caused significantly more improvement in identification of words and syllable constituents at word boundaries than training with a Different voice. Preliminary data from 13 subjects with a different accent (Glaswegian Scottish) indicate, in contrast, more improvement after training with a Different voice. Apparently, when an accent is familiar, perceptual learning about word boundaries is voice-specific; when the accent is unfamiliar, learning generalizes to other speakers of the accent.
The role of prosodic boundaries in comprehension of Korean pseudo-cleft sentences
Authors: Jeong Jaehoon
Published: September 2008

A large prosodic boundary triggers, in general, a high attachment of an ambiguously attached phrase (e.g., Susie learned that Bill called // on Monday). The informative boundary hypothesis (IBH), however, claims that such an effect of a local prosodic boundary is neutralized by the presence of another boundary (e.g., Susie learned // that Bill called // on Monday). According to the IBH, it is not the absolute size of the later boundary (here, pre-PP boundary) but its size relative to any earlier boundary before a constituent containing only the lower attachment site. Since the IBH implies nothing about the interpretation of an ambiguous phrase whose attachment sites appear later, the current study, as an extension of the IBH, investigates whether the effectiveness of a prosodic boundary can be determined by its size relative to a relevant subsequent boundary. The results showed that the interpretation of the sentence-initial subject NP was affected by the absolute size of the post-NP boundary, but the later boundary type had nothing to do with the interpretation. This provides further evidence that prosodic information is processed in an incremental fashion (left-to-right) and perceivers tend to impose prosodic structures as fast as possible.
Intraglottal pressures in a static physical model of the uniform glottis: Entrance loss coefficients and viscous effects
Authors: Fulcher Lewis , Scherer Ronald
Published: September 2008

Pressure distributions for the uniform glottis were taken with a static physical model (M5) for the diameters d=0.005, 0.0075, 0.01, 0.02, 0.04, 0.08, 0.16, and 0.32 cm for a number of transglottal pressures of interest for phonation. At each pressure and diameter, entrance loss and exit coefficients are calculated. The pressure dependence and the diameter dependence of these coefficients are catalogued and compared with some standard values from the earlier literature. The accuracy with which tabulations of these coefficients reproduce the M5 pressure distributions is examined. To an excellent approximation, the intraglottal pressures at smaller diameters decrease linearly with the axial distance, and remnants of this behavior are seen at d=0.08 cm and 0.16 cm. It is shown that the intraglottal pressure gradients are linear functions of the glottal flow rates. Thus, dividing the pressure gradients by the flow rates allows one to isolate the geometric dependence of viscous effects. It is shown that an inverse five-halves power law for the diameter dependence of the viscous glottal resistance is a better approximation than the inverse cube law proposed by van den Berg, Zantema, and Doornenbal. [Work supported by NIH R01DC03577.]
Response bias, type and token frequency, and prosodic context in segment identification
Authors: Silbert Noah , de Jong Kenneth
Published: September 2008

Frequency effects are well documented in a variety of linguistic domains. However, the relationship between response bias and frequency in segment identification has received little attention. We hypothesize that listeners are biased toward higher frequency segments. In order to evaluate this hypothesis, maximum likelihood response bias parameters from the similarity choice model (Shepard, 1957; Luce, 1963) were obtained for a number of previously published segment identification data sets and rank-order correlated with a number of type and token frequency measures calculated from the Hoosier Mental Lexicon. Results indicate that bias tends to correlate more highly with type than with token frequency. Furthermore, in native and non-native individual listener data [Cutler et al. (2004)], correlations are slightly higher between bias and prosodically conditioned frequency than between bias and position-independent frequency, and correlations between bias and coda frequency are large and positive, whereas bias is not correlated with onset frequency. In addition, coda and position-independent measures of (type) frequency correlate more highly with one another than either do with onset measures. Accuracy variation and range of frequency distributions do not account for these effects. No other explanations for the observed prosodic differences are apparent. [Work supported by the NSF.]
An exemplar-based approach to automatically detect burst in word-initial voiceless stops in spontaneous speech
Authors: Yao Yao
Published: September 2008

This paper discusses a methodological question: How to automatically extract phonetically important but untranscribed information (such as VOT and closure duration) from a large spontaneous speech corpus? In this study, we made use of the exemplar-based similarity scores, first developed in Johnson 2006, to find the point of burst in voiceless stops in the Buckeye speech corpus. A similarity score is in essence a measure of how similar one piece of acoustic information is to another on the spectrogram. When used together with phonal spectral templates of the speaker, it can be used to measure how similar a piece of acoustic data is to, say, the typical [aa], or the typical [f] of the same speaker. We find that a two-dimensional score vector ( score plus  score) is already adequate to recognize burst in stops and the pattern is robust enough across a wide range of context in uncontrolled spontaneous speech. It works confidently on average around 90% of the time; the mean error is estimated to be around 3–5 ms (the optimal error in theory is 2.5 ms due to the 5 ms step size in similarity scores). Its robustness, accuracy, and efficiency is examined in detail in the paper.
Listener sensitivity to spectral slope attributes
Authors: Kreiman Jody , Gerratt Bruce R.
Published: September 2008

Researchers have long known that the shape of the vocal source spectrum is an important determinant of vocal quality, but details regarding the perceptual importance of individual spectral features remain unclear. This study provides preliminary evidence about the perceptual importance of four acoustic source features: H1-H2 and the spectral slopes from 1.52 kHz, from 24 kHz, and above 4 kHz. Vowel stimuli were synthesized by varying each spectral parameter in steps. Because the perceptual salience of source parameters depends on F0 and on the inharmonic source spectrum, different series were created for a male and a female speaker, and for a source with little versus a large amount of inharmonic energy. Listeners heard all possible pairs of voices within each series and were asked whether stimuli were the same or different. We hypothesize 1) that listeners sensitivity to H1-H2 will greatly exceed their sensitivity to other parameters; and 2) that listeners sensitivity to H1-H2 and the slope of the spectrum from 1.52 kHz will be independent of noise, but that sensitivity to changes in the spectral shape above 2 kHz will depend on the presence of noise excitation in the voice.
Broadband, coherent inter-array processing of horizontal arrays
Authors: Debever Claire , Kuperman W. A.
Published: September 2008

We study source localization in a shallow water environment using broadband data recorded on two horizontal arrays lying on the sea floor, each of length 250 m. They each had about 25 elements and were approximately 3.5 km apart [N. O. Booth et al., IEEE, JOE, 25(3), (2000)]. The data on the arrays were produced by a source tow covering ranges of about 1 km to 10 km emitting tones from 50 Hz to 400 Hz. The data were processed using various conventional and adaptive algorithms for all the cases covering incoherent frequency and incoherent inter-array processing to coherent frequency and coherent inter-array processing, as a function of source position relative to the arrays. The results are compared to simulations. [Work supported by ONR.]
Extraction of a backscattered target signature in a shallow water waveguide with decomposition of the time reversal operator method
Authors: Philippe Franck , Prada Claire , de Rosny Julien , Clorennec Dominique , Fink Mathias
Published: September 2008

In a shallow water waveguide, detection and characterization of a target is an active field of research. Retrieving the target signature is extremely difficult due to the complex mode coupling between the incident wave and the backscattered wave. One solution consists of deconvolving the target response from the waveguide impulse response. However this method needs an extensive a priori knowledge of the waveguide geometry [Mignerey et al., JASA 1992 and Yang et al., JASA 1994]. To overcome this difficulty, we propose to apply the DORT method (French acronym for decomposition of the time reversal operator). This method is based on time-reversal invariance. Time reversal is commonly known to be an effective means to focus on a target without any a priori knowledge of the propagation medium. In the same way, here we show that the eigenvalues of the time reversal operator are directly proportional to the backscattered target signatures, and the waveguide geometry only acts on the proportionality factor. A theory based on modal waveguide analysis is presented. Ultrasonic scale experiments prove the effectiveness of this method.
Source localization and interference suppression using mode space estimation
Authors: Kim Kyungseop , Seong Woojae , Kim Seongil
Published: September 2008

Weak target detection and localization in the presence of loud surface ship noise is a critical problem for matched field processing in shallow water. For stationary sources, each signal component of a received signal can be separated, and interference can be suppressed using eigen-space analysis schemes. However, source motion, in realistic cases, causes spreading of signal energies in their subspace. In this case, eigenvalues of target and interference signal components are mixed and hard to be separated with usual phone-space eigenvector decomposition (EVD) approaches. Our technique is based on mode space and utilizes the difference in their physical characteristics of surface and submerged sources. Performing EVD for modal cross-spectral density matrix, interference components in the mode amplitude subspace can be classified and eliminated. This technique is demonstrated with data obtained from an L-shaped (vertical and horizontal) line array during the MAPLE IV experiment conducted in the East Sea, Korea, and results will be discussed.
Depth dependence of planewave beamformed data with a horizontal array in a waveguide
Authors: Cockrell Kevin , Schmidt Henrik
Published: September 2008

Despite extensive effort by the ocean acoustics community to design signal processing techniques that take advantage of the waveguide structure of ocean environments (e.g., matched field processing), planewave beamforming remains the only technique robust enough to be used with autonomous vehicles processing data in real-time. However, the waveguide affects the beamformed data in ways that can degrade the performance of bearing estimation. Precisely how the waveguide affects the beamformed data depends on several parameters: The acoustic source’s range, the acoustic source’s depth, the environmental parameters, and the horizontal array’s depth. All of these parameters are ‘‘out of our control’’ except the depth of the towed array. Thus, numerical simulation is used to determine if there is an optimal depth to tow the horizontal array, which will minimize degradation to bearing estimation. [Work sponsored by ONR.]
Pressure sensitivity kernels applied to time-reversal acoustics
Authors: Raghukumar Kaustubha , Cornuelle Bruce D. , Hodgkiss William S. , Kuperman William A.
Published: September 2008

Time-reversal has been found to be more robust to sound speed perturbations than a one-way transmission. Various explanations have been advanced to account for the lower sensitivity of time-reversal. In this contribution, the robustness of time-reversal is quantitatively examined using sensitivity kernels. A first-order Born approximation is used to obtain the pressure sensitivity of the received signal to small changes in medium sound speed. The pressure perturbation to the received signal caused by medium sound speed changes is expressed as a linear combination of single-frequency sensitivity kernels weighted by the transmit signal in the frequency domain. This formulation can be used to predict the response of a source transmission to sound speed perturbations. The stability of time-reversal is studied and compared to that of a one-way transmission using sensitivity kernels. In the absence of multipath, a reduction in pressure sensitivity using time-reversal is only obtained with multiple sources. This can be attributed both to the presence of independent paths and to cancellations that occur due to the overlap of sensitivity kernels for different source-receiver paths. [Work supported by ONR.]
Straying outside the rehearsal room box
Authors: Conant David , Chu William
Published: September 2008

Acoustical considerations are seldom the singular driving factor in rehearsal room design. The desire in academia, to maximize use of precious construction footprint by accommodating an increasing variety of programs, while simultaneously adjusting to ever-decreasing budgets, has resulted in the emergence of hybrid rehearsal spaces that defy conventional classification. The described spaces by MCB serve musical groups with divergent acoustical demands and are variously, yet successfully, pressed into service for lectures, recitals, recording studios, and even experimental theater.
Remedial acoustical design of a college band instrument rehearsal room modified because of asbestos treatment
Authors: Pettyjohn Steven D.
Published: September 2008

Removal of asbestos material from an instrument rehearsal room at CSU, Sacramento, including acoustical treatment led to a new design. The fix dramatically altered the characteristics of the room and resulted in unacceptable conditions. Temporary installation of heavy velour curtains made the room tolerable, but a permanent fix was sought. The room has nonparallel surfaces, large and long, barrel-shaped diffuser panels, hard walls and floor, and a mostly hard ceiling. Field measurements were made under three conditions to quantify the room’s acoustical conditions, including reverberation time and background sound levels. One-third octave band measurements were made from 12.5 to 10,000 Hz to cover all instruments and background sources. The 1-inch acoustical treatment first added to the room was not adequate to attenuate sound below 500 Hz, and insufficient to handle the high acoustical energy produced by the band. The echo between the floor and ceiling was very distinct, as neither surface had any treatment. Calculations using two different methods showed that substantial low-frequency sound absorption was required to reduce the sound at all frequencies to the design goal. The room is currently undergoing the modification, and results may be available at the time of the presentation.
Negative radiation forces on spheres illuminated by Bessel beams: Modeling using finite elements
Authors: Thiessen David B. , Marston Philip L.
Published: September 2008

An analytical solution for the scattering of an acoustic Bessel beam by a sphere centered on the beam [P. L. Marston, J. Acoust. Soc. Am. 121, 753–758 (2007)] has made it possible to explore the way the acoustic radiation force on elastic and fluid spheres depends on beam and material parameters. Situations have been previously noted where, even in the absence of absorption, the radiation force of the beam on the sphere is opposite the direction of beam propagation [P. L. Marston, J. Acoust. Soc. Am. 120, 3518–3524 (2006); J. Acoust. Soc. Am. 121, 3109 (2007)]. In the case of solid spheres, the interpretation is simplified using an analysis of the scattering [P. L. Marston, J. Acoust. Soc. Am. 122, 247–252 (2007)]. In the present research, the finite-element method (FEM) is used to evaluate the total acoustic field in the region near the sphere. This makes it possible to evaluate the radiation force from numerical integration of an appropriate projection of the Brillouin radiation stress tensor. The result agrees with analytical results for plane wave and Bessel beam illumination. The FEM result predicts negative radiation forces for appropriate beam, material, and frequency parameters. [Supported in part by NASA.]
Vibro-acoustography of thyroid
Authors: Allizad Azra , Mitri Farid G. , Kinnick Randall R. , Greenleaf James F. , Fatemi Mostafa
Published: September 2008

Thyroid imaging with conventional ultrasound scanners does not always lead to conclusive results. Furthermore, current ultrasound imaging technology has difficulty in detecting important microcalcifications. Ambiguities in ultrasound and other thyroid imaging methods lead to a large number of unnecessary biopsies. For these reasons, alternative imaging methods capable of detecting both microcalcifications and lesions in thyroid are of great interest. This paper describes recent results on imaging human thyroids with vibro-acoustography. Experiments were conducted on eight excised human thyroids from autopsy. The specimens were each imbedded in a block of gel to simulate the surrounding tissue and to facilitate scanning. Three types of images were acquired from each specimen: X-ray, B-mode ultrasound, and vibro-acoustography. Anatomical details seen in the images were correlated and image quality was compared. X-ray images displayed calcifications with high contrast, but did not show anatomical details of soft tissue. B-mode displayed some soft tissue structures; however, the speckle masked the details and reduced the contrast. Vibro-acoustography displayed calcifications, anatomical details, and some nodules where they existed. Furthermore, vibro-acoustography images displayed tissue structures with high contrast and free from speckle. It is concluded that vibro-acoustography may be a suitable technique for thyroid imaging.
Acoustic radiation force biorheology
Authors: Orescanin Marko , Mahr David , Kalyanam Sureshkumar , Insana Michael
Published: September 2008

Acoustic radiation force techniques are being developed to image rheological properties of engineered tissues and cell cultures. An embedded sphere couples an acoustic source field to the medium, while induced deformations are imaged dynamically via Doppler methods. We conducted three experiments. First, we modeled the response to a step force as a second-order differential equation. Fitting Doppler data to the model, we estimated shear modulus (G) and coefficient of viscosity (ν) for a broad range of tissue-like hydrogels. Measuring a 2% hydrogel over 8d, we estimated G=450–800 Pa, ν=0.26–0.4 Pas, in close agreement with measurements using a cone-plate viscometer. In the second experiment, we applied harmonic acoustic radiation force stimuli and measured the complex modulus of the gels over a very broad bandwidth. The advantage obtained is significantly higher SNR. Finally, spatial variations in gel rheological properties were mapped from shear waves radiating from the harmonically-driven embedded sphere. The wavelength of the shear wave indicates the shear modulus. These three methods describe spatiotemporal variations in scaffolds designed for tissue engineering and cancer cell cultures, all without physically touching the samples. Acoustic radiation force rheometry is being developed as a tool for basic biological research.
Songs my students sang to me
Authors: Blackstock David T.
Published: September 2008

Does the professor teach his/her students? Or do they teach the professor? While the answer to both questions is probably a qualified yes, in looking back, I see that what I know now is largely what they taught me. After a review of the research areas in which my students and I have worked, a few examples are highlighted that show that what I had expected is not how things turned out.
Speech-to-music ratio estimation using wavelets and hidden Markov models
Authors: Smolenski Brett
Published: September 2008

In this paper, a system capable of estimating the long-term, on the order of an utterance, speech-to-music energy ratio (SMR) is developed. The approach uses frame-based Teager energy values at the output of a seven-band wavelet decomposition as features. The features are then modeled using a two-state hidden Markov model (HMM), with each state producing observations having a 64-component Gaussian mixture. Using this approach, estimation of the long-term SMR with a standard error of less then 5% was obtained. In addition, accurate classification of music and speech with these models was still possible when both music and speech were simultaneously present, assuming one had a higher energy than the other.
Effects of several consonant environments on vowel formants
Authors: Kiefte Michael
Published: September 2008

A large body of evidence has shown that relative change in spectral pattern possesses some invariant properties for vowels across speakers in /hVd/ environment. While formant frequency plots from vowel steady-states result in categories with large overlap, better separation of vowel categories is obtained using onset and offset formant frequencies [e.g., Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099–3111 (1995)]. To a large extent, this invariance was also shown in other /CVC/ contexts using all combinations of /h,b,d,g,p,t,k/ [Hillenbrand et al., J. Acoust. Soc. Am. 109, 748–763 (2001)]. The present study explored spectral change in vowels produced in environments where larger differences might be expected across contexts. Nineteen men and 39 women were asked to produce fourteen Canadian English vowels in /hV/, /hVd/, /hVt/, /hVl/, /hVr/, /hVnd/, /hVg/, and /dVd/. Subjects read standard English orthographic representations of the target words which were embedded both in a sentence which indicated the rhyme of the target word—e.g., ‘‘Swooned rhymes with hoond’’ as well as in a sentence which indicated the pronunciation of onset and vowel—e.g., ‘‘Hood sounds like hoog.’’ Formant frequencies were measured and tracked for each token and differences across consonant contexts were analyzed. [Work supported by SSHRC.]
Speaker normalization using cortical strip maps: A neural model for steady state vowel identification
Authors: Ames Heather , Grossberg Stephen
Published: September 2008

Auditory signals of speech are speaker-dependent, but representations of language meaning are much more speaker-independent. Such a speaker normalization transformation enables speech to be learned and understood from different speakers. A neural model is presented that performs speaker normalization to generate a pitch-independent representation of speech sounds, while also preserving information about speaker identity. This speaker-invariant representation is categorized into unitized speech items, which input to sequential working memories whose distributed patterns can be categorized, or chunked, into syllable and word representations. The proposed model circuits fit into an emerging theory of auditory streaming and speech categorization in which auditory streaming and speaker normalization both use similar neural designs; namely, multiple cortical strip map representations of auditory signals. This design homology may clarify how speaker normalization circuits evolved from more primitive streaming mechanisms. Simulations with synthesized steady-state vowels from the Peterson and Barney (1952) vowel database achieve accuracy rates similar to those achieved by human listeners. These results are compared to behavioral data and other speaker normalization models. [Work supported in part by NSF and ONR.]
Vowel space and formant dynamics of vowels produced by monolingual and bilingual talkers in conversational and clear speech styles
Authors: Bianchi Michelle , Rogers Catherine L. , Frisch Stefan A. , Krause Jean C.
Published: September 2008

Formant frequency characteristics of vowels produced by monolingual and bilingual talkers were compared. Ten monolingual, 15 early Spanish-English bilingual (age of onset of immersion is 12 or earlier), and ten late Spanish-English bilingual (age of onset of immersion of age 15 or later) talkers produced the target words ‘‘bead, bid, bayed, bed, bad,’’ and ‘‘bod’’ in conversational and clear speech styles. Measurements of F1 and F2 were made at 20%, 50%, and 80% of vowel duration. Significant group effects for F1 and F2 at 50% of vowel duration showed similar locations and distances between the vowels for the monolingual and early bilingual talkers, except that F2 values were significantly higher for the early bilingual than for the monolingual talkers for the vowels in the target words ‘‘bead, bid,’’ and ‘‘bed.’’ Smaller between-vowel distances were found for both F1 and F2 for the late bilingual talkers, especially for the vowels in the target words ‘‘bead, bid, bayed,’’ and ‘‘bed.’’ Changes observed in clear speech were relatively modest for all three groups. Comparisons between formant dynamic vectors and angles across groups and style and between talkers showing large versus small degrees of clear speech intelligibility benefit will be presented. [Work supported by NIH-NIDCD No. 5R03DC005561.]
MRI study of coarticulation in European Portuguese
Authors: Martins Paula , Carbone Inês , Silva Augusto , Teixeira António
Published: September 2008

For this study, a small part of a recently acquired MRI database for European Portuguese (EP) was used. The sounds studied were the 12 EP voiced and unvoiced fricatives and stop consonants, produced in a symmetric VCV context. The vowels chosen were the cardinal vowels [i, a, u]. The speaker sustained the fricative sounds and maintained stop articulation during the 5.6 s of the acquisition time (T1 TSE sequence). The contours were obtained using the seeded region growing method. The influence of the seed placement was evaluated through the generation of 100 contours, with random seeds, for each sound. It was possible to verify, for the EP, some facts already reported by other authors relative to coarticulation in other languages. In general, EP stops are less resistant to coarticulatory effects than fricatives. The EP sounds presenting the highest resistance to coarticulation are the unvoiced postalveolar fricative [∫] and corresponding voiced fricative. As an example of other relevant results, for stops [t], [d] and fricative [s] there is no significant effect of the vowel in the region tongue blade region, being the influence evident in the production of the stops [k] and [g]. [Work supported by FCT, Portuguese Research Agency, by Project HERON POSC/PLP/57680/2004.]
The contributions of global spectral and amplitude structure to speech perception by English-speaking adults and children and Mandarin-speaking adults
Authors: Nittrouer Susan , Lowenstein Joanna H.
Published: September 2008

Two studies examined the recognition of signals preserving only the global spectral or amplitude structure of speech by three groups of listeners: Native English-speaking adults, native English-speaking 7-year-olds, and native Mandarin-speaking adults who learned English as a second language. Stimuli consisted of sine wave (SW) replicas and amplitude-modulated (AM) noise bands derived from semantically anomalous four-word sentences (Experiment 1) and semantically rich five-word sentences (Experiment 2). In both experiments, children demonstrated recognition scores comparable to those of the English-speaking adults for the SW sentences, but scores comparable to those of the Mandarin-speaking adults for the AM sentences. In both experiments, native Mandarin-speaking adults were much worse at understanding either kind of stimulus than were the English-speaking adults. Use of linguistic constraints was similar across listener groups, diminishing the possibility that results could be attributed to differences in ‘‘top-down’’ effects. Results were used to support three main conclusions: (1) Global spectral and amplitude structure varies across languages; (2) native speakers use this information for speech perception; and (3) in learning a native language, children discover global spectral before global amplitude structure. [Work supported by NIDCD Grant No. DC-00633.]