bluuebunny/crossref_metadata_2025 huggingface dataset:
The detection of a tone in a narrow band of noise
Authors: Richards Virginia M. , Heller Laurie M. , Green David M.
Published: October 2005

Detection thresholds were obtained for 2000-Hz tones masked by 100-Hz-wide bands of noise centered at 2000 Hz. On each interval of the two-interval, forced choice (21FC) task, the level of the noise or signal-plus-noise waveform was varied over a range of 0 (no variation), 30, or 60 dB. As has been reported previously [Gilkey, in Auditory Processing of Complex Sounds, edited by W. A. Yost and C. S. Watson (Erlbaum, Hillsdale, NJ, 1987); Kidd et al., J. Acoust. Soc. Am. 86, 1310–1317 (1989)], level variation had a negligible effect. Next, thresholds were determined using equal-energy, but uncorrelated, bands of noise. Performance levels in the equal-energy condition were indistinguishable from those obtained using independent noise samples. Thus neither increasing nor decreasing the across-interval variance in stimulus energy altered the detectability of the tone. In a second experiment, equal-energy maskers had bandwidths that varied from 20 to 320 Hz. For this condition, an energy-based ideal detector yields no effect of bandwidth. For bandwidths ranging from 20–80 Hz, human performance was nearly constant. However, thresholds were relatively elevated when the 160- and 320-Hz bandwidths were employed. [Work supported by the National Institutes of Health.]
Auditory-filter shapes at low frequencies in hearing-impaired listeners
Authors: Peters Robert W. , Moore Brian C. J.
Published: October 2005

Auditory-filter shapes were measured for two groups of hearing-impaired subjects, young and elderly, for center frequencies (fc) of 100, 200, 400, and 800 Hz using a modified notched-noise method [B. C. J. Moore et al., J. Acoust. Soc. Am. (in press)]. Two noise bands, each 0.4 fc wide, were used; they were placed both symmetrically and asymmetrically about the signal frequency to allow the measurement of filter asymmetry. The overall noise level was either 77 or 87 dB SPL. Stimuli were delivered monaurally using Sennheiser HD424 earphones. Although auditory filters for the hearing impaired were generally broader than for normally hearing listeners [B. C. J. Moore et al., J. Acoust. Soc. Am. (in press)], some impaired listeners with moderate losses had normal filters. There were not any clear differences in filter characteristics between young and elderly hearing-impaired listeners and processing efficiency (K) values were not different for hearing impaired as compared to normal listeners.
Precedence effect in interaural time difference (IATD) and interaural cross correlation (IACC) perception
Authors: Aoki Shigeaki , Houtgast Tamtoo
Published: October 2005

A series of experiments is performed to investigate the degree of perceptual dominance of dichotic information presented in the initial part of a brief stimulus. Two types of dichotic information, interaural time difference (IATD) and interaural cross correlation (IACC), are considered separately. The experimental approach rests on the principle of estimating the overall sensation of a brief stimulus (20-ms broadband noise) in which the relevant information (IATD or IACC) in the leading part of the stimulus is opposite to that in the trailing part. The “physical” weight of the two parts of the stimulus is manipulated by two parameters: the ratio of the durations of the leading and trailing part (T1/T1, with T1 + T1 = 20 ms) and the ratio of the intensities (I1/I1). In case of equal physical weight (T1 = T1 and I1 = I1), a precedence effect is manifest for both IATD and IACC. The condition for equal subjective weight for the present 20-ms stimuli is well described by the relation 1.5I0.31 T1 = I0.31 T1.
The position of the amplitude peak as an acoustic correlate of stress in English and French
Authors: Behne Dawn M.
Published: October 2005

Early d scussions of the acoustic correlates of stress suggested that stressed syllables are produced with greater amplitude than unstressed syllables [e.g., H. Sweet, A Primer in Phonetics (Clarendon, Oxford, 1890]. More recently, increased fundamental frequency (F0) change and duration have been demonstrated to be more reliable cues of stress than increased amplitude [e.g., D. Fry, Lang. Speech 1, 126–152 (1958)]. Nevertheless, none of these acoustic parameters has been consistently connected with stress, and their relative importance as cues for stress appears to vary across languages. In the present study, English and French monolinguals produced sentences containing sententially stressed and unstressed monosyllabic words. In addition to F0 change, duration, and amplitude, the relative positions of the maximum and minimum amplitude were measured. The results indicate that: (1) increased F0 change, duration and amplitude are associated with stress in English, but not in French; and (2) an early maximum amplitude is associated with stress in both English and French. The present study suggests that early discussions of amplitude as an important acoustic correlate of stress may not have been far off, but that the position—rather than the relative level—of the maximum amplitude is the pertinent parameter.
The articulation of consonant-induced vowel duration changes in English
Authors: deJong Kenneth
Published: October 2005

This reports on an articulatory investigation of acoustic findings that vowels tend to be longer before voiced than voiceless consonants [House and Fairbanks, J. Acoust. Soc. Am. (1953)], before fricatives than stops [Umeda, J. Acoust. Soc. Am. (1975)], and before single consonants than before multiple consonants [Fowler, J. Exp. Psychol. (1983)]. Measurements were taken from tongue movement traces obtained with the Wisconsin microbeam system during vowels in accented and unaccented conditions. Assuming a gestural theory of speech production, three mechanisms for producing these duration differences are considered: The duration of the closing gesture may be stretched, the consonantal gesture may begin later in the vowel, or the production of the entire vowel may be lengthened. One subject's vowel durations were affected by the voicing and manner of the following consonant. Another's were affected only by consonant voicing when the word is accented, and only by consonant duration when the word is unaccented. Moreover, the effect of duration and voicing on the vowel duration was due, in part, to differences in how early the closing gesture for the consonant begins, while the effect of manner of articulation was due entirely to differences in the duration of the closing gesture. [Work supported, in part, by NSF.]
Variations of duration in stressed syllables taken from French read sentences
Authors: Santi S. , Guaitella I.
Published: October 2005

This study deals with the analysis of the relationships between stress and duration in French. The duration of stressed and unstressed syllables, taken from 55 read sentences, has been measured. The results have lead to conclude that, while stress is closely correlated to a modification of duration, the nature of this modification is more complex than expected, according to classical theories. The stressed syllable can be lengthened or shortened with regard to the nearest unstressed syllable and also to the other stressed syllable of the sentence. This choice seems to be allowed and motivated according to perception laws and mechanisms of expressivity.
Word and nonword durations in toddlers
Authors: Robb Michael P. , Bauer Harold R.
Published: October 2005

An issue rarely addressed in developmental acoustic phonetics is the simultaneous occurrence of and relationship between work and nonword forms. The vocalizations of six children were sampled 12 times over a 13-month period. Each child's monthly vocalization sample was examined for the frequency of occurrence and duration of words and nonwords. A child was given credit for a “word” production ifs/he produced a phonetic form that was a recognizable attempt at the adult word. Complete agreement between the caregiver and investigator defined word status. The results compared the duration of word and nonword vocalizations produced by a group of normally developing toddlers. The durations were examined as the occurrence of words increased and nonwords decreased.
Semantic and pragmatic effects in speech production
Authors: Luce Jan Charles
Published: October 2005

This study addresses how semantic information may prime, and thus facilitate, the articulation of a target word. In addition, it addresses how the pragmatic interaction between speaker and listeners may modify speech production. To examine these issues, subjects were presented with a visual prime and target and were asked to name the target aloud. Prime type and neighborhood characteristics of the target were manipulated. Primes were either semantically related or unrelated to the target. Targets occurred in neighborhoods that had either many or few phonetically similar neighbors and these neighbors were either high or low in frequency. Dependent variables were duration and the pitch of stressed vowels. Prefiminary results suggest that vowel duration of the target decreases when it has many neighbors that are high frequency, suggesting facilitation. Pitch is higher on targets with low- versus high-frequency neighbors when preceded by an unrelated prime, suggesting speaker compensation. The results will be discussed in the frameworks of interactive activation and pragmatic compensation.
Real-time adaptive ultrasonic imaging
Authors: Trahey Gregg E.
Published: October 2005

Spatial inhomogeneities in the acoustic velocities of tissues distort propagating wave fronts and degrade the quality of diagnostic ultrasonic images. A real-time adaptive ultrasonic imaging system has been developed that uses image quality factors to iteratively adjust the phasing of transducer elements and restore image quality. This system has been used to evaluate a number of alternative quality factors and iterative algorithms for diffuse reflectors, pointlike targets and clinical targets, and good success with such targets was achieved with image-brightness based quality factors. The results of these experiments agree well with theoretical descriptions of adaptive imaging and with direct measurements of the characteristics of phase aberrations in human tissues.
Internal-wave tomography: From conception to the future
Authors: Flatté Stanley M.
Published: October 2005

In 1982, the idea of measuring statistical properties of the internal-wave field by means of long-range ocean-acoustic propagation was put forward. Since that time, feasibility studies have indicated that the strength, depth dependence, spectral character, and geographical variability of the internal-wave spectrum can be measured with high-quality acoustic experiments. One successful experiment has been completed and analyzed (in the Sargasso Sea area). Several recent experiments have successfully retrieved data and arc in the process of being analyzed. The newer experiments involve very long vertical arrays, which will allow the separation of the spectrum into contributions from different vertical wavenumber. The prospect of analyzing vertical-array data has led to a new global view of broadband, long-range, acoustic-waveguide propagation including a realization that ray theory is useful down to very low frequencies. [Work supported by ONR, Code 1125 OA.]
Statistical descriptions of fine structure and microstructure from propagation experiments
Authors: Duda Timothy F.
Published: October 2005

Two methods have been studied and utilized to statistically characterize short vertical wavelength (high-mode) internal waves. One technique uses broadband, low-frequency, simulated pulses transmitted hundreds to thousands of kilometers in conjunction with tomography, the other uses high-frequency signals transmitted less than a few kilometers. In the first technique, the internal waves cause directional fluctuations of the arriving long-range rays, which can also be considered as pulse wave front distortions with time and length scales of hours (or less) and hundreds of meters, respectively. Recent frequently sampled, vertical-array recordings of long-range pulses enable comparison with theoretical numerically calculated predictions. Understanding the long-range acoustic fluctuations is required to enable remote monitoring of volumetrically averaged internal waves. In the second technique, unsaturated theory should describe variations in amplitude and phase. Spectra of the short-range fluctuations can be modeled using ocean sound-speed spectra, and comparisons to observations are made. The Fresnel length determines the sensitivity in the ocean-structure wavenumber domain, and adjusting this from tens of meters to a meter or so (a rough limit imposed by absorption) shifts sensitivity from fine structure to microstructure.
Reconstruction of an incomplete ultrasonic image: Maximum entropy approach
Authors: Krishnan V. , Xu L.
Published: October 2005

The convolution backprojection and the algebraic reconstruction methods are two of the most popular techniques used for the reconstruction of a soft tissue attenuation image by ultrasound. However, where data have been truncated due to physical limitations, these techniques do not produce satisfactory results. One-dimensional linear prediction estimators by which the missing data can be estimated based on known projection information have been developed. In this paper, the missing data are extrapolated using a two-dimensional maximum entropy method, and the backprojection algorithms are applied to reconstruct the completed projection data set. There is a significant improvement in the quality and reliability of the reconstructed image as compared to one-dimensional linear prediction approach. There is also a relative improvement in the computation time as compared to the conventional methods. The techniques are developed based on a soft tissue phantom. Computer simulation results and comparison with conventional methods are presented.
Do listeners hear phase or duration of articulation in judging syllabic structure?
Authors: Harsin C. A. , Porter R. J.
Published: October 2005

Previous work suggests that stabilities in articulator phasing, over changes in speech rate and stress, support the underlying perceptual stability of syllabic structures over such changes [B. Tuller and S. Kelso, J. Acoust. Soc. Am. 76, 1030–1036 (1984)]. Control of articulator phasing may, therefore, be an important part of the communicative act. If this is the case, it might be expected that the acoustic manifestations of articulator phase (i.e., relative duration of acoustic segments) have a more important influence on judgments of syllabic structure than the absolute durations of acoustic events. To investigate this possibility, synthetic waveforms corresponding to the v + c + v sequence /ipi/ were created. The acoustic events manipulated were duration of the initial and final v's and the position of a burst corresponding to a /p release/ in the intervocalic interval. Preliminary results suggest that judgments of syllabic structure (e.g., /i♯pi/ vs /ip♯i/) are, indeed, more affected by relative durations of the acoustic events than by their absolute durations. [Work supported in part by Louisiana Lions' Foundation and UNO Chancellor's Fellowship.] Also at Kresge Hearing Res. Lab., LSU Medical Ctr., New Orleans, LA 70122.
Rate effects in speech and nonspeech
Authors: Fahey Richard
Published: October 2005

A well-documented effect in speech perception is the rate normalization effect. Temporally defined cues are held to be perceived in relation to the prevailing rate of speech. In CV syllables information about rate of speech may be provided by the duration of the vowel. Recently this account has been challenged. The effect of vowel duration on consonant identification disappears if invariant cues are built into stimuli [P. C. Shinn, S. E. Blumstein., and A. Jongman, Percept. Psychophys. 38, 397–407 (1985)]. A rate effect also occurs with nonspeech stimuli, suggesting that it is not entirely phonetic [R. L. Diehl and M. A. Walsh, J. Acoust. Soc. Am. 85, 2154–64 (1989)]. The present experiments show that the rate effect returns when the stimuli of Shinn et al. (1985) are placed into a sentence. Information for rate of speech may be more reliable in sentences than in CV syllables. Another series of experiments addresses the question of whether rate effects occur for nonspeech analogs to voiced-voiceless continua.
Perception of American-English in noise by Greek listeners
Authors: Roussohatzaki Maria , Florentine Mary
Published: October 2005

This study examined the ability of Greek listeners to understand American-English in noise. The speech perception in noise (SPIN) test was administered at 75 dB SPL in the presence of babble noise to 23 Greek and 10 American listeners with normal hearing. The Greek listeners had studied English for an average of 8 yr and lived in the U.S. for an average of 2.5 yr. Noise levels were chosen in 3-db steps to encompass the range from 20% to 90% correct performance. At each noise level, 50 new sentences were presented and the percent correct for 25 high- and 25 low-predictability sentences was measured. Results show (1) the slope of the psychometric functions in terms of Z score per decibel of speech-to-noise ratio was steeper for the native than the Greek listeners, (2) the native listeners could obtain 50% correct performance at significantly higher noise levels (about 3 dB) than the Greek listeners, (3) both groups performed significantly better on the high-predictability sentences than on the low-predictability sentences, and (4) the difference in tolerable noise levels (levels yielding 50% correct) between the high- and low-predictability sentences was the same for both groups. These results corroborate earlier studies with other non-native languages [e.g., Florentine, J. Acoust. Soc. Am. Suppl. 1 77, S106 (1985)].
Noncategorical perception of a voiced-voiceless fricative continuum
Authors: Formby C. , Olson H. L. C. , Childers D. G. , Lalwani A. L. , Raney J. J.
Published: October 2005

A nine-token synthetic VOT continuum for /feɪl/-veɪl/ was constructed with 10-ms steps in fricative voicing. Perceptual studies revealed better-than-chance discrimination between pairs of tokens labeled /feɪl/, chance discrimination between pairs of tokens labeled /veɪl/, and a slight peak in the discrimination function at the labeling boundary between /feɪl/ and /veɪl/. To better understand the noncategorical discrimination data, relative onset time (ROT) difference limens were measured for a range of durations of a 100-Hz sawtooth waveform, which served as the analog for voicing in the speech continuum. ROT difference limens increased systematically with increasing duration of the standard sawtooth waveform. The ROT data suggest that better-than-chance discrimination near the /feɪl/-endpoint and chance discrimination near the /veil/-end-point reflect larger absolute difference limens for onset of voicing as voicing duration was increased from /feɪl/ to /veɪl/. Traditional phonetic processes presumably account for the slight peak in the discrimination function at the labeling boundary between the /feɪl/ and /veɪl/categories. [Research supported by NIH.]
The effects of temporal structure on infant cry categorization
Authors: Tsukamoto Taeko , Tohkura Yoh'ichi , Tenpaku Seiichi
Published: October 2005

Two perceptual experiments were performed to examine the effects of temporal structure on the categorization of infant cry stimuli using three labels: hunger, anger, and call cries (i.e., calling for infant-mother interaction). In both experiments, subjects were instructed to make a forced choice among the three cry categories in labeling the cry stimuli. In the first experiment, the temporal structures of cry stimuli were changed using a linear time-scale conversion method. It was found that the call cry stimuli, when the time-scale was compressed, tended to be perceived as the anger or hunger cries. These results show that the whole temporal organization, including spectral and melodic patterns of the cry stimuli, is very important in the cry category identification. In the second experiment, pause durations in the cry stimuli were changed. In contrast with the first experiment, results from the second one showed that use is not made of pause durations as a perceptual cue for cry category. This indicates that the temporal structure of acoustic features within cry vocalization units is one of the reliable cues for the cry category identification.
Two fast methods for the calculation of sound radiation: Multipol radiator synthesis and boundary element multigrid method
Authors: Ochmann Martin
Published: October 2005

The sound radiation of oscillating structures of arbitrary shape into three-dimensional space will be calculated by representing the normal velocity on the surface as a superposition of multipoles. Depending on the geometry of the radiator, one or more source locations in the interior volume are selected. Different variants of this technique (null field method, weighted residual methods, etc.) and their interdependence will be discussed. The advantage of the method is a strongly reduced calculation time for complex structures. A disadvantage is the presently still incomplete investigation of the convergence behavior. For this reason a boundery element method will alternatively be applied to the discretized Kirchhoff-Helmholtz integral equation, which will be solved on grids of varying size (multigrid method). Both methods will be used to calculate the radiation from spheres, cylinders, cubes, etc. Results will be compared to analytical solutions, numerical results obtained by other techniques, and experimental data. [Work supported by the Department of Research and Technology of the Federal Republic of Germany (BMFT).]
An in vacuo modal method to analyze fluid-loaded shells of revolution
Authors: Chen Huo-Wang , Stepanishen Peter R.
Published: October 2005

A general approach is presented to evaluate the acoustic field and vibratory response of harmonically excited fluid-loaded shells of revolution. The excitation force and velocity of shells of revolution are expressed as a modal sum of the in vacuo eigenvectors. The eigenvectors for shells of interest are evaluated by the finite element method. A new method is presented to determine the acoustic loading on the shells. This method is based on the use of internal source distributions to obtain acoustic radiation impedances. In the present study, the modal velocity coefficients are obtained from a set of algebraic equations and the Helmholtz integral equation is used to evaluate the acoustic pressure in the fluid. Numerical results for spherical and spheroidal shells will be presented and discussed. [Work supported by ONR.]
Acoustical observations of zooplankton distributions near physical, chemical, and biological boundaries in the sea
Authors: Holliday D. V. , Pieper R. E.
Published: October 2005

A multifrequency acoustic profiling system (MAPS) was used to collect quantitative data on zooplankton distributions in relation to the physical (temperature, density, currents), chemical (salinity), and food (phytoplankton) environment in the sea. The sea surface, the bottom, the pycnocline, and both salinity and chlorophyll maxima, as well as oceanographic fronts and current boundaries, often appear in MAPS data as either biologically active surfaces or as apparent boundaries for plankton distributions. Volume scattering strength data as well as acoustically derived size-specific zooplankton abundances are used to illustrate coherencies between ocean physics and zooplankton distributions. The challenge of the 1980s was to develop the technology to observe these associations. The challenge of the 1990s is to determine the advantages gained by plankton communities from their proximity to and association with such oceanographic features. [Work supported by ONR Oceanic Biology and NSF Biological Oceanography.]
Role of thermal fronts in structuring acoustical scattering patterns
Authors: Brandt Stephen B.
Published: October 2005

Examples of high-frequency (38-, 120-, and 420-kHz) acoustical scattering in small (e.g., 12-ha) lakes, the Great Lakes, the Chesapeake Bay Estuary, and the Atlantic Ocean show striking similarity in the coherence of thermal structure and patterns in acoustical scattering, despite the differences in spatial scale and biological composition of the acoustic targets. Biological scatterers are not distributed randomly but are often aggregated in layers at or near thermal fronts and biological variance is generally greater across thermal gradients than within uniform thermal zones. Patterns of biological patchiness also respond to long-term (e.g., seasonal thermal stratification) and short-term (upwelling, weather events, meanders) physical dynamics. It is argued that thermal scales (°C, °C m−1) may be more useful than spatial scales per se in describing acoustical scattering patterns and inferring the biological mechanisms that may have caused the observed distributions.
Vibrotactile thresholds as measures of peripheral nerve dysfunction in occupational epidemiology
Authors: Letz Richard , Gerr Fredric
Published: October 2005

Measurement of vibrotactile threshold (VT) has been proposed as a rapid, nonaversive method of assessing the functional integrity of large myelinated peripheral nerve fibers. Current methods of assessing peripheral nerve function include physical examination and electrophysiologic evaluation. Physical examination is of unknown reliability and results in categorical outcomes. Electrodiagnostic procedures are sensitive and yield quantitative results, however, their aversive nature may discourage voluntary participation in epidemiologic studies. In order to justify the substitution of VT measurement for nerve conduction study in field investigations of neurologic dysfunction, we have initialed a comprehensive evaluation of methods suitable for such applications. The elements of this program include (1) comparison of psychophysical procedures, (2) determination of threshold reliability, (3) comparison of VT with electrophysiologic evaluation and physical examination, (4) development of age- and height-standardized nonnative values, and (5) measurement of VTs in groups at risk of peripheral nerve dysfunction. Group studies include workers exposed to mercury, solvents, industrial chemicals, and hand-arm vibration. The utility of VT measurement in occupational neuroepidemiology will be discussed.
Tactile motion perception in neurologically normal and nerve-injured individuals
Authors: Essick Greg K.
Published: October 2005

Cutaneous low-threshold mechanoreceptors transmit information about innocuous deformations of the skin that occur duing contact with stimulus objects as well as during normal motoric behaviors. Movement across the skin not only elicits motion-sensitive responses in individual mechanoreceptors, but sequentially activates different spatially adjacent populations of mechanoreceptors to sites along the path of motion. Psychophysical tests of subject's capacity to distinguish opposing direction to tactile motion across the skin (i.e., of directional sensitivity) provide quantitative indices of the integrity of peripheral mechanoreceptors, as well as of central neural mechanisms to which they project. It will be shown that in neurologically normal subjects, directional sensitivity (i) is a curvilinear function of the velocity of stimulus movement, (ii) increases linearly with the length of skin transversed, and (iii) varies grossly in proportion to the innervation density of the fast and slowly adapting type I mechanoreceptors. Since injury to peripheral sensory nerves results in alterations in the mechanoreceptors' spatial- and temporal-encoding properties, directional sensitivity is often impaired. The degree of impairment can be quantitatively characterized by alterations in the slope and x intercept of the relationship between directional sensitivity (d′ units) and the length of skin traversed.
Assessment of peripheral neuropathies by mechanoreceptor-specific vibrotactile thresholds
Authors: Piercy J. E. , Brammer A. J. , Nohara S. , Nakamura H. , Auger P. L. , Haines A. T. , Lawrence M. , Brubaker R. L. , van Netten C.
Published: October 2005

Mechanoreceptor-specific vibrotactile perception thresholds have been determined at the fingertips of 79 workers who regularly operate pulpwood chain saws (in Ontario), large-timber chain saws (in coastal British Columbia), or rock drills. The measurement procedure, which involves establishing the sensitivity of three receptor populations (types SAI, FAI, and FAII) from thresholds determined at up to six frequencies from 4 to 200 Hz, has been described elsewhere (A. J. Brammer and J. E. Piercy, Proceedings of the 5th International Conference on Hand-Arm Vibration, Kanazawa, 1989). Even after repeated screening to exclude peripheral neuropathies unrelated to work, and neuropathies confined to either the median or ulnar nerve, the results continue to reveal two patterns of abnormality. Within the group, 21% of hands exhibit similarly elevated thresholds at all frequencies, which is consistent with peripheral nerve degeneration. Thirty-seven hands (26%) exhibit elevated thresholds at frequencies mediated by only one or two receptor populations (almost always SAI and/or FAII types), which is suggestive of receptor-specific degeneration at or near the nerve endings. Seventy-one hands (50%) possess thresholds within the limits of normality.
Radiated flow noise
Authors: Skudrzyk Eugen J.
Published: October 2005

The exact flow noise [M. J. Lighthill, Proc. R. Soc. London Set. A 211, 564–587 (1952); 221, 1032 (1954)] equation for the pressure or the density does not contain viscous terms. Only the loss factor of the elastic constant is affected by viscosity. An exact solution for the radiated noise is obtained with the aid of Green's theorem, integrating it over infinite space. Boundaries then do not contribute. The boundary layer is simulated by introducing image sources. Because viscous forces have no effect on the sound pressure, no conditions need be ascribed for the flow tangential to the boundary. The solution can then be simplified for the radiated farfield. By performing the tensor contraction for the eddy terms on the right-hand side of the Lighthill equation, a very simple, almost trivial, result can be obtained. The numerical evaluation then is based on the Willmarth-Roose correlation measurements of the cross-spectral density. For a nonintermittent boundary layer, the farfield power spectrum increases with the seventh power of the velocity and proportionately to the frequency. It is a simple function of the pressure spectrum measured with a flush-mounted receiver.
The cell structure (standing waves) of underexpanded noncircular supersonic jets
Authors: Powell Alan
Published: October 2005

The quasiperiodic structure of a slightly underexpanded supersonic jet issuing from a round nozzle was first treated by Prandtl (1904). Rayleigh (1916) viewed the structure as due to propagating sound waves in a cylinder, with an axis change to yield the standing wave pattern. He indicated an analogy with the vibrations of a membrane of the shape of the jet cross section, so that the results in his 1877 book for the fundamental period of membranes of various shape related directly to the cell length, Rayleigh's principle being applicable to “nearly circular” geometries. A discussion of the cell length for various geometries is presented, e.g., an approximation (error < 1%) for an elliptic nozzle (for which an exact solution has been given recently by Tam) is that the cell length is increased relative to the square geometry by the factor [4 − 1.378 (short side/long side)], while that for an annular one corresponds to a straight infinite strip of the same width, with < 1% error for an annulus of 50% radius, and < 2 12% for 75%.
Effects of air injection upon cavitation noise in condensing two-phase flow
Authors: Piacsek Andrew A.
Published: October 2005

A discussion is given of some recent noise measurements on an apparatus where condensation occurs in an annular region. The possible dominant noise sources are discussed and assessed with the aid of data. The primary cause of noise is argued to be the unsteady flow in the condenser and this is attributed to large-scale cavitation effects. In the turbulent two-phase region of the condenser, where the liquid is at its vapor pressure, local pressure fluctuations cause voids to form. These voids, when convected to a cooler or higher pressure region, rapidly collapse. A means of reducing this noise is to inject a noncondensing gas, such as air, into the flow. The presence of such a gas prevents the complete collapse of bubbles, thereby reducing the radiated sound. In addition, since dissolved gas promotes cavitation, its presence causes many smaller bubbles to be formed rather than a single large bubble. The loud transients associated with collapse of larger bubbles will consequently be eliminated.
Acoustic resonance in a solid fuel combustion chamber
Authors: Schouten Gerrit
Published: October 2005

The resonance frequencies of a solid fuel comb are predicted by a model, including part of the piping system and diffuser. Visual observations of the flow in the transparent combustion chamber by a high-speed movie camera reveal that a large vortex structure periodically moves down the flow. The large-amplitude velocity oscillations eventually lead to extinction of the combustion process. The driving terms in the acoustic equations are of fluid-dynamic and thermodynamic origin. This analysis is concentrated on the investigation of the role of the fluid-dynamic terms. Making use of the method devised by Howe, the strength of the source term due to the periodically generated vortex system is computed. The response of the model to this source term leads to the conclusion that its magnitude is too small to play a role of importance. As an acoustic source it yields a response in counterphase with the occurring oscillations, so in this configuration its role is a damping one.
A new HMM/LVQ hybrid algorithm for speech recognition
Authors: Katagiri Shigeru , Lee Chin-Hui
Published: October 2005

A new HMM/LVQ hybrid algorithm for speech recognition is proposed. The motivations are: (1) to expand the capability of learning vector quantization (LVQ) for handling dynamic speech patterns and (2) to improve the performance of an HMM-based system. It is shown that, by combining both the discriminative power of LVQ and the capability of modeling temporal variations of speech of an HMM into a hybrid algorithm, the performance of the original HMM-based speech recognition algorithm is significantly improved. The proposed recognition algorithm uses HMM to segment speech utterances and then adopts a novel classifier in place of the conventional HMM likelihood comparison for recognition. Since the parameters of the classifier can be estimated through adaptive learning rules, the discriminative power of the recognizer is greatly enhanced. Any learnable classifier, such as an artificial neural network (ANN), can be used for the discriminative classifier. By way of example, an LVQ-based multicategory classifier is used in this study. The LVQ codebook is obtained through a probabilistic descent method using segmented and normalized speech tokens as training samples. The evaluation was conducted using a multispeaker, isolated English E-set letter database. The average word accuracy for the original HMM-based system was 61.7%. When the LVQ classifier was incorporated into the hybrid algorithm, the word accuracy increased to 81.3%.
Continuous multiple similarity method using stable and dynamic phonetic feature vectors for continuous speech recognition
Authors: Tsuboi Hiroyuki , Sadamoto Yoichi , Takebayashi Yoichi
Published: October 2005

This paper describes the continuous multiple similarity method (CMSM) that utilizes stable and dynamic phoentic feature vectors to achieve continuous speech recognition. The phonetic feature vector to represent the time-varying characteristics of both stable and dynamic segments is constructed by a fixed dimensional time-frequency spectrum. Stable phonetic segments correspond to the stable portion of five vowels, fricatives and nasals. Dynamic phonetic segments correspond to the time-variant portion of stops, semivowels, and liquids. The stable phonetic segments are represented by a time-series of the time-frequency spectrum, whereas the dynamic phonetic segments are represented by a single typical time-frequency spectrum. The multiple similarity (MS) values corresponding to the particular phone class are time-continuously computed. The time sequence of the MS values are then used for word matching with word graphs by dynamic programming. An experiment was carried out on 6596 phonetic segments of 492-word vocabulary spoken by four Japanese males to evaluate phone recognition performance based on the CMSM. A recognition score of 73.5% for 23 phone classes was obtained using 224-dimensional phonetic feature vectors.
Development of a female synthetic voice using concatenative synthesis
Authors: Syrdal Ann K.
Published: October 2005

Although there is considerable demand for synthetic female voices in text-to-speech applications, current analysis and synthesis algorithms are more successful for male than for female speech. Difficulties include voice source characteristics and other acoustic differences between female and male speech. Telephone bandwidth constraints present an additional disadvantage for the female voice, because relatively more phonetically relevant high-frequency acoustic information is filtered out of the telephone signal for female speakers than for males. A synthetic female voice is currently being developed for use with an experimental AT&T concatenative text-to-speech system for which only male voices have been available previously [J.P. Olive, Proc. ICASSP, 568–570 (1977); J.P. Olive and M. Y. Liberman, J. Acoust. Soc. Am. Suppl. 1 78, S6 (1985)]. In this synthesis-by-rule system, segments used for synthesis are obtained from natural speech and concatenated to synthesize any arbitrary English utterance. Issues such as speaker selection, preparation and recording of speech materials, inventor? of concatenative units, and analysis and synthesis methods will be discussed. Diagnostic use of intelligibility test results and preliminary evaluations also will be described.
Perceptual evaluation of the naturalness of synthetic speech
Authors: Gow Merrilyn L.
Published: October 2005

This paper reports an investigation that assessed the naturalness of speech produced by several text-to-speech (TTS) systems. Using a 9-point subjective rating scale of naturalness, a group of listeners assigned ratings to speech produced by DECtalk 2.0, three versions of STL's system, and a software system. Each system produced 12 short paragraphs, two of which were repeated in order to assess reliability. These 60 paragraphs were used as the speech stimuli. The paragraphs were recorded in random order onto digital audio tape. Listeners made judgments based on how natural they perceived the speech to be, and assigned a rating accordingly. The reliability with which listeners assigned naturalness ratings was assessed by comparing their judgments on the paragraphs that were repeated. The listeners performed the task with satisfactory levels of intralistener agreement. The results showed that the average naturalness ratings obtained for these TTS systems fell within the predicted range, but outside the range expected for natural human speech. These findings suggest that this procedure may be a reliable tool for perceptually evaluating the naturalness of synthetic speech. The limitations and implications will be discussed.
Finite-difference methods for low-angle seafloor scatter
Authors: Stephen R. A. , Dougherty M.
Published: October 2005

Finite-difference methods applied to the two-way elastic wave equation are the most promising approach to understanding scattering from both surface irregularities and volume heterogeneities. A finite-difference code appropriate for low-angle scatter (less than 20° grazing angle) has been developed. The incident wave field is a Gaussian pulse beam. It has a Gaussian amplitude profile normal to the propagation direction with a time dependence (in pressure) that is the third derivative of a Gaussian. The peak frequency of the pulse is 50 Hz. The pulse beam can be “shone” on a 2-D representation of the seafloor including volume heterogeneities and rough water-sediment and sediment-basement interfaces. Time series of the combined incident and scattered fields are obtained on vertical and horizontal profiles around the scattering region. The incident field can be computed separately and removed from the observed field to give just the scattered field. The rms energy in the scattered field is plotted as a function of angle and includes forward and backscattered energy and energy scattered into the bottom as well as into the water. Time spread of the scattered energy can also be investigated. These concepts will be demonstrated using three models: a flat, laterally homogeneous reference structure, a similar model with surface irregularities, and a similar model with volume heterogeneities.
Relative backscattering strengths from DTAGS data
Authors: Ioup Juliette W. , Rowe Mary M. , Gettrust Joseph F. , Slater Richard R. , Ioup George E. , Rayborn Grayson H.
Published: October 2005

Analysis of data from the 1989 Blake-Bahama Basin Deep Towed Acoustics-Geophysics System (DTAGS) experiment has yielded normal incidence backscattering strengths for the sea bottom. Interesting features are found over the escarpment. The horizontal DTAGS streamer of 24 receiver groups permits relative scattering strengths to be obtained as a function of grazing angle. The DTAGS chirp source covers a range of frequencies from 250–550 Hz, and relative scattering strengths are also presented as a function of frequency. [Work supported by NOARL, the Office of Naval Tech., and the Navy/ASEE Summer Faculty Fellowship Program.]
Measurements of acoustic backscatter from the Sohm Abyssal Plain: Preliminary results
Authors: Hines Paul C. , Barry Patrick J.
Published: October 2005

Acoustic backscatter data were collected from the ocean bottom at four sites on the Sohm Abyssal Plain. The bottom topography of the sites varies from mud/clay to silt/gravel. Using a simple array consisting of a free-flooding ring projector, which was omnidirectional in azimuth, and an omnidirectional hydrophone, data were collected over the frequency range of 800–2400 Hz in 200-Hz bandwidths. By deploying the array to a depth of 5000-m bottom backscatter, data were obtained at grazing angles down to 3° before the onset of the first surface return. To obtain sufficient signal-to-noise ratio without impairing spatial resolution, linear FM pulses were employed. In this paper the experiment and the bottom topography of the four sites are described, and the preliminary results of the acoustic analysis are presented.
Roughness versus volume inhomogeneity—A discussion on ocean bottom scattering
Authors: Tang Dajun , Frisk George V.
Published: October 2005

Ocean bottom scattering is a research area in which there is considerable current interest. Although some theories have been developed to model the bottom scattering process, there is little quantitative understanding of the nature of the dominant scattering mechanism. At high frequencies, because of bottom absorption, the rough water-bottom interface is considered to be the main contributor to scattering. However, at low frequencies, where considerable bottom penetration exists, it is clear that scattering by volume inhomogeneities cannot be ignored. In order to assess quantitatively the relative importance of these two scattering mechanisms, perturbation methods are used to model the scattering process for an incident plane wave, where the interface roughness and the volume randomness are assumed to be uncorrelated. Both the scattering strength and the spatial correlation of the scattered field are obtained for various values of the parameters characterizing the interface and the volume. The relative importance of the two scattering mechanisms is discussed. [Work supported by ONR.]
Acoustic wave scattering from two solid boundaries at ocean bottom
Authors: Kuo Edward Y. T.
Published: October 2005

An acoustic wave scattering model with three homogeneous layers consisting of a thin solid sediment layer sandwiched by semi-infinite water and solid basalt media is formulated, solved, and analyzed for effects of physical parameters and interface roughness scattering on the reflection loss. Preliminary results are discussed. A dominant mechanism of reflection loss is the combined effects of attenuation of the sediment layer, especially or S waves and conversion and scattering processes of the basalt interface. The scattering process is found not only to produce the well-known acoustic energy loss from specular to nonspecular directions, but also to alter the conversion efficiency between P and S with the resulting loss or gain.
Seafloor sediments and their influence on low-angle acoustic backscatter from the ocean bottom
Authors: Dougherty Martin E. , Stephen Ralph A.
Published: October 2005

Acoustic energy incident upon an elastic seafloor can be backscattered from both a rough water-solid interface and/or heterogeneities within the upper crust or sediments. The strong impedance contrast present at most areas of the ocean floor causes roughness to be a major source for scattering of seismo/acoustic energy. When flat-lying, homogeneous sediments are covering a rough basaltic interface, the scattering can be significantly dampened. However, if heterogeneities exist within the upper sediments, seismo/acoustic energy that is transmitted into the seafloor will be backscattered in these sedimented, flat-seafloor environments as well. In an elastic seafloor medium with no topography, there are at least two mechanisms by which low-grazing-angle acoustic energy can enter the sediments and be scattered by heterogeneities or buried roughness. These are the presence of a direct wave root (an evanescent mode) associated with the direct wave, and conversion of the incident compressional wave into sub-seafloor shear energy phases with low-phase velocity. Two-dimensional, full-elastic, finite-difference models with a low-grazing-angle plane-wave source will be presented which quantify the influence of sediments on the acoustic reverberation problem. [Work supported by ONR.]
Assessment of insert earphones for the use in occupational hearing conservation program monitoring audiometry
Authors: Doswell Royster Julia , Berger Elliott H. , Royster Larry H.
Published: October 2005

The application of insert earphones for annual audiometry was evaluated in an on-going occupational hearing conservation program. For four consecutive years employees were given an extra left-ear audiogram using a 3A-type insert earphone immediately after completing their standard annual audiograms using TDH-49 earphones in supra-aural cushions. For the final 3 yr an additional left-ear audiogram using the TDH-49 earphone was given last, to control for order effects. Sixty employees participated all 4 yr. Analysis of thresholds obtained each year using each earphone indicated that small threshold correction factors for the insert earphone are necessary at each frequency (not just at 6 and 8 kHz) to allow results to be compared directly to supra-aural earphone thresholds. The manufacturer's suggested 10-dB correction factor at 8 kHz appeared too small for the particular combination of TDH-49 and insert earphones used. Standard deviations of thresholds between individuals were similar for both earphones. Year-to-year repeatability of thresholds within individuals was equivalent with both earphones. As long as absolute calibration is accounted for, insert earphones are a viable alternative transducer for audiometry in hearing conservation.