bluuebunny/crossref_metadata_2025 huggingface dataset:
Masked thresholds and consonant recognition in low-pass maskers for hearing-impaired and normal-hearing listeners
Authors: Dubno Judy R. , Ahlstrom Jayne B.
Published: October 2005

Thresholds and consonant recognition were measured in six low-pass maskers as a function of masker bandwidth for hearing-impaired subjects and for normal-hearing subjects listening in spectrally shaped broadband noise (SSBB). SSBB was adjusted such that thresholds in that masker for a normal-hearing listener were equal to a hearing-impaired listener’s absolute thresholds. Thresholds measured in low-pass maskers were higher for hearing-impaired than for normal-hearing subjects for signal frequencies both within and outside masker passbands, although threshold differences were larger for signal frequencies outside masker passbands. Slopes of functions relating consonant recognition to speech level were not significantly different between groups, due to the presence of SSBB for the normal-hearing listeners. However, 25% of observed scores for hearing-impaired listeners, compared to only 5% of observed scores for normal-hearing listeners, were significantly poorer than predicted by the articulation index (AI), when AIs were computed using subjects’ absolute thresholds. Better correspondence between observed and predicted scores in low-pass maskers was achieved when AIs were derived empirically from thresholds measured in each low-pass masker. Hence poorer-than-predicted consonant recognition scores in low-pass maskers were accounted for by higher-than-normal thresholds in those maskers.
The perception of frequency peaks and troughs in wide frequency modulations. II. Effects of frequency register, stimulus uncertainty, and intensity
Authors: Demany Laurent , Clément Sylvain
Published: October 2005

In widely frequency modulated sine tones, frequency maxima are perceived more accurately than frequency minima: A shift in a local frequency extremum is better detected when the extremum is a maximum than when it is a minimum, even within the same spectral region [L. Demany and K. I. McAnally, J. Acoust. Soc. Am. 96, 706–715 (1994)]. It is reported here that this perceptual asymmetry is about equally strong for frequency extrema near 250 and 1000 Hz, but weaker near 4000 Hz. It was also found that near 1000 Hz, the asymmetry is about equally strong for stimuli with an SPL of 35 and 70 dB, although the neural excitation patterns of a 1000-Hz tone probably have a different shape—and more specifically a different asymmetry—at these two levels. Finally, stimulus uncertainty was found to reduce the perceptual asymmetry: A weaker asymmetry was measured when the standard frequency extremum varied randomly from trial to trial than when it was fixed. The latter result, and the fact that the asymmetry did not decrease with training in the discrimination task, suggest that the asymmetry cannot be counteracted by ‘‘top-down’’ attentional processes and may be a preattentional phenomenon.
Frequency discrimination as a function of frequency, measured in several ways
Authors: Sek Aleksander , Moore Brian C. J.
Published: October 2005

Frequency discrimination was measured for a wide range of center frequencies (0.25–8 kHz) using three different tasks. In the first (difference limens for frequency, DLFs) subjects were required to indicate which of two successive tone pulses was higher in frequency. In the second (difference limens for change, DLCs), two successive pairs of tone pulses were presented; one pair had the same frequency and the other pair differed in frequency. Subjects were required to indicate which pair differed in frequency. In the third (frequency-modulation difference limens, FMDLs), subjects were required to indicate which of two successive tone pulses was frequency modulated. Modulation rates were 2, 5, or 10 Hz. For frequencies up to 2 kHz, DLFs and DLCs were small (less than 0.6% of the center frequency) and were similar to one another. For frequencies of 4 kHz and above, both DLFs and DLCs increased markedly, but the increase was greater for DLFs. Thus the worsening of performance at high frequencies is greater when subjects are required to indicate the direction of a frequency change than when they just have to detect any change. FMDLs, when expressed relative to the carrier frequency, varied much less with frequency than DLFs or DLCs. At 2 kHz and below, FMDLs were larger than DLFs or DLCs. Above 4 kHz, FMDLs were smaller than DLFs or DLCs. At 2 kHz and below, FMDLs usually worsened with increasing modulation frequency. Above 4 kHz, FMDLs improved with increasing modulation frequency. The pattern of results suggests that two mechanisms play a role in frequency discrimination, one based on changes in the excitation pattern (a ‘‘place’’ mechanism) and one based on phase locking in the auditory nerve (a ‘‘temporal’’ mechanism). The temporal mechanism only operates below about 4 kHz and, within this range, it determines DLFs and DLCs. The temporal mechanism is probably sluggish, and it affects FMDLs only for very low modulation rates. The place mechanism dominates for high frequencies, and for lower carrier frequencies when stimuli are frequency modulated at high rates.
Modulation discrimination interference for narrow-band noise modulators
Authors: Moore Brian C. J. , Sek Aleksander , Shailer Michael J.
Published: October 2005

The discrimination of the depth of amplitude modulation of a signal carrier frequency can be disrupted by the presence of other modulated carriers (maskers), an effect called modulation discrimination interference (MDI). This paper examines whether MDI is influenced by the similarity in the envelope pattern of the signal and masker. A narrow-band noise (centered at 10 Hz) was used as the signal modulator. The first experiment used masker modulators that were narrow-band noises identical in spectral characteristics to the signal modulator. The masker modulators were either identical to the signal modulator, negatively correlated with it, or uncorrelated with it. The amount of MDI was similar for all three cases. In experiment 2, the masker was sinusoidally modulated at rates varying from 2 to 64 Hz. The results showed a broad tuning for modulation rate, comparable to that found for sinusoidal modulation of the signal. The maximum amount of MDI produced by the sinusoidally modulated masker was similar to that produced by the noise-modulated maskers when modulation depths were expressed as their root-mean-square values. It is concluded that similarity of the moment-by-moment envelope pattern of the signal and masker modulators plays only a minor role in MDI, although similarity in modulation rate has some influence.
A nonlinear dynamical systems analysis of fricative consonants
Authors: Narayanan Shrikanth S. , Alwan Abeer A.
Published: October 2005

Acoustic waveforms of the strident fricatives /s/, /z/, /sh/, and /yog/ spoken by two native American English speakers are analyzed using modern chaotic analysis techniques. Fricative data are extracted from both intervocalic and sustained utterances. For comparison, acoustic waveforms of the vowels /a/, /i/, and /u/ are also analyzed. For 44% of the unvoiced fricative tokens in VCV contexts and 59% of the sustained voiced fricatives, indications of low-dimensional dynamics could be found with the given limitations of stationarity. The low-dimensional chaotic behavior is exhibited by a correlation dimension (D2) ranging between 3 and 7.2, and by positive maximum Lyapunov exponents (LEs). For the remaining fricatives, results suggest that the dimensional complexity therein is greater than the maximum D2 value that could be reliably estimated from the available data (about 7.8 for the intervocalic cases and 9 for the sustained cases). Intervocalic voiced fricatives are excluded from the analysis due to stationarity requirements. Analysis of vowels, on the other hand, indicates nonchaotic behavior demonstrated by folded limit cycles and nonpositive maximum LEs; this is consistent with results of previous studies. Findings are interpreted in terms of posited articulatory and aerodynamic parameters of turbulence in the production of fricative consonants.
Minimizing the effect of period determination on the computation of amplitude perturbation in voice
Authors: Qi Yingyong , Weinberg Bernd , Bi Ning , Hess Wolfgang J.
Published: October 2005

Current methods of computing amplitude perturbation present in human voices depend upon being able to accurately determine fundamental period. In this paper, two methods of estimating the amplitude perturbation present in human voices, which do not depend on accurate determination of the boundaries between fundamental periods, are described. In both of these methods, amplitude perturbation is computed as the variance of an ensemble of periods calculated after these periods have been aligned in time. In one method, time alignment is accomplished using zero-phase transformation. In the second method, an unconstrained dynamic programming procedure is used. The accuracy of estimating amplitude perturbation by these two methods is evaluated using synthetic and natural voice signals and is also compared with an estimation using zero-padding based time alignment. The unconstrained dynamic programming method is shown to provide accurate estimation of voice amplitude perturbation over a variety of signal conditions.
Intrinsic F0 of vowels in the babbling of 6-, 9-, and 12-month-old French- and English-learning infants
Authors: Whalen D. H. , Levitt Andrea G. , Hsiao Pai-Ling , Smorodinsky Iris
Published: October 2005

In every language so far examined, high vowels such as [i] and [u] tend to have higher fundamental frequencies (F0s) than low vowels such as [a]. This intrinsic F0 effect (IF0) has been found in the speech of children at various stages of development, except in the one previous study of babbling. The present study is based on a larger set of utterances from more subjects (six French- and six English-learning infants), at the ages 6, 9, and 12 months. It is found, instead, that IF0 appears even in babbling. There is no indication in these data of a developmental trend for the effect, and no indication of a difference due to the target language. These results support the claim that IF0 is an automatic consequence of producing vowels.
The perception of English and Spanish vowels by native English and Spanish listeners: A multidimensional scaling analysis
Authors: Fox Robert Allen , Flege James Emil , Munro Murray J.
Published: October 2005

A group of Spanish- and English-speaking listeners participated in a multidimensional scaling (MDS) study examining perceptual responses to three Spanish and seven English vowels. The vowel stimuli represented tokens of Spanish /i/, /e/, and /a/ and English /i/, /i/, /ei/, /ε/, /æ/, /inverted vee/, and /ɑ/. Each vowel had been spoken by three monolingual talkers of Spanish or English and all possible vowel pairs (405 pairs) were presented to listeners (excluding pairs representing the same vowel category). Thirty monolingual English listeners and thirty native Spanish listeners who had learned English as a second language rated these vowel pairs on a nine-point dissimilarity scale. These perceptual distances were then analyzed using the individual-differences version of ALSCAL. Results demonstrated that the English monolinguals used three underlying dimensions in rating vowels while the Spanish–English bilinguals used just two. The most salient perceptual dimension for both groups distinguished vowel height. However, for the English listeners, this dimension was most significantly correlated with duration and indicated a language-dependent sensitivity to this phonetic feature. The second dimension for the English listeners represented a front–back distinction, while the third reflected a central/noncentral distinction. For the Spanish listeners, the second dimension was less easily interpreted. However, the perceptual data for the Spanish listeners was more interpretable in terms of the distribution of the vowels in the two-dimensional perceptual plane. The vowels were distributed in terms of three separate vowel clusters, each cluster near the location of a Spanish vowel. Separate MDS analyses were carried out for subgroups of Spanish listeners who were relatively proficient or nonproficient in English. The vowel space of the proficient Spanish listeners was more Englishlike than that of the nonproficient Spanish listeners, suggesting that the perceptual dimensions used by listeners in identifying vowels may be gradually modified as proficiency in the second language improves.
An algorithm for forward and inverse scattering in time domain
Authors: Poovendran Raadhakrishnan , Dorband John E. , Yagle Andrew E.
Published: October 2005

This paper presents an alternative numerical scheme for a class of forward and inverse scattering problems based on invariant imbedding method [Corones et al., J. Acoust. Soc. Am. 74, 1535–1541 (1983)]. The algorithm presented in this paper is decoupled more than the previous implementations and hence, readily amenable to parallel processing. It is also shown that the effect of this decoupling on error can be expressed in terms of the estimated reflection coefficients, facilitating the decision to accept or reject any computed parameter.
Observation of two longitudinal and two transverse waves in a frozen porous medium
Authors: Leclaire P. , Cohen-Ténoudji F. , Aguirre-Puente J.
Published: October 2005

Experimental results on the transmission of elastic waves in a water-saturated sample of glass powder are presented. Both longitudinal and transverse waves are studied in a temperature range of [−30, 0 °C]. Two longitudinal and two transverse waves are detected. For a temperature of −28 °C and a frequency of 500 kHz, the measured velocities are of the order of 4000 and 2300 m/s for the two longitudinal waves and of 2400 and 1400 m/s for the two transverse waves. The two supplementary signals detected (one longitudinal and one transverse) are very unlikely the result of spurious reflections or electromagnetic coupling since such phenomena were not observed when replacing the porous sample by water. The values of the experimental velocities are in good agreement with the predictions of the extension of Biot’s theory to frozen porous media developed by Leclaire et al. [J. Acoust. Soc. Am. 96, 3753–3768 (1994)].
Ultrasonic plate waves in three-dimensional braided composites
Authors: Nayfeh Adnan H. , Chimenti D. E.
Published: October 2005

This paper reports on a study of ultrasonic wave propagation in three-dimensional braided composites; an extensive experimental survey is compared to the results of an approximate analytical model. The model describes the average elastic behavior of composites having continuous fiber weaving in three spatial dimensions. The approximation rests upon the treatment of the composite as a homogeneous medium that possesses the average directional stiffnesses implied by the fiber placement and braid angles. The model is compared to the results of experimental ultrasonic guided wave studies in 3-D woven AS4/PEEK. This composite has the structure of a three-dimensional braided fabric infiltrated with thermoplastic polyether ether ketone matrix. Its unit-cell size dimensions are approximately 8 by 2.5 by 1.2 mm. Some 90% of the fibers are braided in the ±20° directions, with the balance being laid-in fibers in the warp (0°) direction. It is found that the approximate model yields an acceptably good description of the measurements. The observed disparities likely arise from the geometrical structuring of the 3-D braid, which is generally larger than the acoustic wavelengths of interest, and not yet included in the model. Comparisons between measurements at low and intermediate acoustic frequencies using relatively wide beams and the approximate calculations are presented.
Acoustic and membrane wave interaction at plate junctions
Authors: Norris Andrew N. , Rebinsky Douglas A.
Published: October 2005

The interaction of an acoustic wave with two joined flat plates results in a diffracted acoustic wave emanating from the junction. The plates are assumed, for simplicity, to have different masses but no stiffness, and the exact solution of the two-dimensional diffraction problem is derived as a Fourier integral. The diffraction coefficient for a plane acoustic wave is found to depend in a simple manner upon the product of the total acoustic pressures at the junction for waves incident from the source and receiver directions. Also, the diffraction coefficient displays a maximum as a function of frequency, which is interpreted as a quasiresonance phenomenon. The results for the flat, massive plates are extended by perturbation methods to consider the acoustic interaction with longitudinal (membrane) waves originating from the junction of two curved shells, joined so that their tangent is continuous. Relatively simple results are found for the acoustic-to-membrane coupling coefficients, and these again show strong dependence on frequency. The related problem of membrane-to-acoustic diffraction is analyzed, and the diffraction coefficients obey simple reciprocity relations with the acoustic-to-membrane coefficients.
An investigation of the small slope approximation for scattering from rough surfaces. Part I. Theory
Authors: Thorsos Eric I. , Broschat Shira Lynn
Published: October 2005

The small slope approximation (SSA) of Voronovich [Sov. Phys. JETP 62, 65–70 (1985)] is a promising method for application to scattering from many natural surfaces. The theory gives a systematic expansion that can be interpreted as a series in generalized surface slope. The SSA series for the T matrix satisfies the appropriate reciprocity condition at each order and reduces to the standard perturbation series for small surface roughness. In this paper we examine in detail the derivation of the SSA for surfaces subject to the Dirichlet (zero field) boundary condition. A number of points are discussed, including the requirements for determining the series terms. In addition, questions have been raised recently about the SSA: It has been argued that (1) an assumption in the derivation contradicts the exact formulation of the problem and (2) there is an arbitrariness in determining the series terms. These two points are refuted and the assumptions needed to determine the series terms unambiguously are clarified. The meaning of slope orders in the SSA series expansion are examined and the concept of generalized slope is discussed. A future companion paper (Part II. Numerical studies) will present an investigation of the accuracy of the SSA through comparison with exact results.
Diffusion of ultrasound in a glass bead slurry
Authors: Weaver Richard L. , Sachse Wolfgang
Published: October 2005

The ultrasonic energy density in a close-packed disordered assemblage of glass beads immersed in water is shown to evolve in accordance with a diffusion equation. The diffusion and dissipation rates which parametrize the evolution equation are shown to be recoverable from the observed energy densities. The recovered diffusivity exhibits a frequency dependence which characterizes the microscale length and is in qualitative accord with theory. The recovered diffusivity also shows a slight dependence on source/receiver separation which is inconsistent with the hypothesized diffusion model; potential causes for this behavior are discussed. The recovered dissipation rate is greater than predicted by a model of viscous shear loss at solid/fluid interfaces. An estimate for the proximity of the Anderson transition is constructed.
Guided plate waves in piezoelectrics immersed in a dielectric fluid. II. Experiments
Authors: Yang C.-H. , Chimenti D. E.
Published: October 2005

Detailed ultrasonic reflection measurements in piezoelectric LiNbO3 are reported which are compared to the results of the theoretical analysis of the previous paper, part I. Differences in mode coupling and behavior are illustrated in several calculated examples. The calculated numerical results are demonstrated in a full image format. It is shown how dielectric fluid loading influences the reflection behavior and how strong piezoelectric coupling can lead to unexpected dispersion in the fundamental symmetric mode. The data confirms in each case the predictions of an exact partial-wave analysis of the problem, including the dielectric influence of the fluid. These phenomena play a role in the design and performance of piezoelectric sensing devices.
The propagation of sound waves in drill strings
Authors: Drumheller Douglas S. , Knudsen Steven D.
Published: October 2005

Deep wells are commonly drilled while steering the drill bit. The steering process is completely controlled by the drilling-rig operator. A key element of this procedure is the measurement and communication of navigation information from the bottom of the well to the operator. Pressure pulses modulated onto the flow of the drill fluid are now employed in some cases to communicate this information. However, data rates are only a few binary bits per second with this method. This drastically limits the quantity of data available to the operator. As an alternative method, elastic waves generated within the steel drill string can be used as a carrier signal to transmit data. The drill string is commonly assembled from 10-m segments of threaded pipe and forms a periodic structure. The elastic wavelengths of interest are shorter than this periodic length. Consequently, these waves undergo significant dispersion. This paper presents new data for the propagation of elastic waves in a 2-km drill string. The influence of aperiodicity in the drill string, rotation of the drill string, and noise levels are studied in detail. The data verify a method for reducing the attenuation of a carrier signal by a factor of 2.
Equilibrium shape of an acoustically levitated bubble driven above resonance
Authors: Asaki Thomas J. , Marston Philip L.
Published: October 2005

The equilibrium shapes of stably levitated bubbles on the Earth in an ultrasonic standing wave have been measured and calculated for bubbles larger than resonance size. The shape and equilibrium position are sensitive to the acoustic field used for levitation. Measured static oblate shapes are in good agreement with predictions based upon the quadrupole projection of the radiation pressure on a compressible sphere taking into account the monopole response of the bubble. For the size range of bubbles considered, the monopole response is limited by inertia and radiation damping. A simplified theory (based on the deformation resulting from the Bernoulli pressure of incompressible potential flow around a sphere) is generally consistent with the measurements for the smaller of the bubbles observed.
Estimation and correction of quadrature signal error for high-resolution acoustic microscopy
Authors: Chiao Richard Y. , Lee Hua
Published: October 2005

In this letter, an approach to the estimation and correction of quadrature data-acquisition error in acoustic microscopy is presented. Prior methods modeled the signal error mainly as phase perturbations. Because the amplitude error was not included in the model, the prior approach was not as effective as expected for some experiments of which amplitude error was significant. Here the technique is extended and modified by including the amplitude error as a component of the perturbation, and subsequently a matrix operation is formulated for the error correction process. This improvement enables one to perform estimation and correction of the signal errors effectively without additional iterations. An experimental data set from the scanning laser acoustic microscope is utilized to demonstrate the effectiveness of the algorithm.
Planar fiber optic acoustic velocity sensor
Authors: Lagakos Nicholas , Bucaro Joseph A.
Published: October 2005

The design and fabrication of a large area, planar fiber optic acoustic velocity sensor is reported. The device is based upon exploiting the optical fiber’s response to acceleration induced strains and by designing specific jackets which suppress the fiber sensor’s response to acoustic pressure. The broadband response to acceleration and the response to pseudostatic pressure changes were measured. These results confirm the efficacy of the concept and design.
Transient response of refined cross-ply laminated plates for various boundary conditions
Authors: Khdeir A. A.
Published: October 2005

An analytical procedure to investigate the dynamic response of cross-ply laminated composite plates is presented. The solution is applicable to rectangular plates whose parallel edges are simply supported and the remaining ones can have arbitrary combinations of clamped, simply supported, and free-boundary conditions. A generalized modal approach is used to obtain these solutions. The equations of motion of the third-order, first-order, and classical theories are converted into a single-order system of equations by using state variables. The biorthogonality conditions of principal modes of the original and adjoint eigenfunctions are used to decouple the state space equation. The closed-form solutions developed are illustrated in a number of figures revealing the influences of the transverse shear deformation, of the degree of anisotropy, and of the character of boundary conditions on the response and the normal stress of the plate.
Detection of the depth of a surface-breaking crack using transient elastic waves
Authors: Wu T. -T. , Fang J. -S. , Liu P. -L.
Published: October 2005

This paper presents a method for the detection of a normal surface-breaking crack in a plate using impact-induced transient elastic waves. First, the forward simulations of the transient diffracted wave propagations in a plate with a normal surface-breaking crack are made by using a heterogeneous finite difference formulation. The important characteristics of the initial part of the waveforms are addressed. Second, experimental studies on the crack-induced transient diffracted waves are also made and the results are in accordance with the numerical results. Finally, a nonlinear optimization algorithm based on the simplex method is developed to recover the depth of the normal surface-breaking crack in a plate. The recovered crack depths from the measured transient diffracted wave signals are in very good agreements with the true crack depth.
On the prediction of propeller tone sound levels and gradients in an airplane cabin (benchmark utility)
Authors: Pope Larry D.
Published: October 2005

An advanced version of the propeller airplane interior noise (PAIN) model [L. D. Pope, J. Acoust. Soc. Am. 88, 2755–2765 (1990)] can generate a prediction of the variation of the cabin cross-section average sound-pressure level of a transmitted propeller tone. The prediction can then be averaged along the length of the cabin to obtain the cabin volume average sound-pressure level, the latter being the only quantity that the original version of the PAIN model [L. D. Pope, E. G. Wilby, and J. F. Wilby, J. Sound Vib. 118, 449–467 (1987); L. D. Pope, C. M. Willis, and W. H. Mayes, ibid. 118, 469–493 (1987)] calculated. Of considerable interest is a comparison of the two volume average predictions because the advanced and original models are based on fundamentally different types of analyses. The original model predicts the response of each individual acoustic mode caused by each structural mode, leading to the average sound-pressure level within the cabin volume. The advanced version predicts the response of the entire complement of acoustic modes having a common cross mode index for each exciting structural mode. The average sound level in cabin cross section is obtained, as well as the cabin volume average. Close agreement in the two predictions of the average cabin level yields a higher level of confidence in both prediction results, compared to the independent predictions, particularly in circumstances where comparisons with flight measurements are minimal or nonexistent. Recently, during parametric studies, modifications were made to the advanced model to obtain better agreement between the two average predictions. This paper presents the revisions (upgrades) that were found to be necessary for consistency in the cabin trim absorption models. A demonstration is given of the present prediction capability through example benchmark calculations for two representative airplanes. Finally, the general usefulness of benchmark calculations and necessity of validation efforts in the development of interior noise prediction software are discussed.
Active damping of enclosed sound fields through direct rate feedback control
Authors: Clark Robert L. , Cole Daniel G.
Published: October 2005

An alternative approach to the control of enclosed sound fields subjected to impulsive or broadband disturbances is presented based upon direct rate-feedback control. Results from this preliminary study suggest that if a pressure transducer is collocated with a volumetric source in an enclosed sound field and rate-feedback control is employed, then the global properties of the sound field can be modified, specifically the modal damping ratio of the acoustic modes. Guaranteed asymptotic stability of the control approach was demonstrated for positive feedback gains, making it model insensitive and thus ideal for actively tuning the transient characteristics (i.e., the reverberation time) of the enclosure. Significant levels of global reduction in the acoustic potential energy can be achieved with the proposed control approach for stationary random disturbances or impulsive disturbances.
Development and validation of a criterion for assessing the acoustic performance of industrial rooms
Authors: Ondet A. M. , Sueur J.
Published: October 2005

This paper presents a criterion for assessing the acoustic performance of industrial rooms. This criterion has been defined from numerical simulations by using the Rayscat predictive acoustic software. It allows a distinction between reverberant industrial halls and those for which an efficient acoustic treatment has been performed. The criterion has been validated on the basis of experimental data obtained in more than 200 industrial rooms.
Use of large bandwidth-duration binary phase shift keying signals for bearing measurements in active sonar classification
Authors: Henrioux J. P. , Jourdain G.
Published: October 2005

Presented in this paper is a new method for spatial localization in active sonar using large bandwidth-duration binary phase shift keying signals. The very good time and frequency resolution power and the large process gain of such signals allow the use of the phase of the cross-ambiguity function. When using a sensors array, the differential phase measured on two homolog peaks is related to the target azimuth. So a global localization and classification can be made. This new spatial localization method is proposed to improve the classical beamforming being used in passive sonars as well for multiple targets (far field) as for a single target exhibiting multiple highlight points (near field).
Performance analysis of the holographic array processing algorithm
Authors: Al-Kurd Azmi A. , Porter Robert P.
Published: October 2005

This paper provides detailed analysis and performance evaluation of the holographic array processing (HAP) algorithm. The HAP is a source localization method that is based on medium calibration. Conventional array processing algorithms, such as matched-field processing (MFP), require precise knowledge of the medium between the source and the receiving array, but the HAP method relaxes this stiff requirement. It calibrates the integrated effect of a great portion of the medium, and geoacoustic parameter estimation is needed only for a small portion of the ocean between the unknown source and the virtual array. The virtual array is constructed by moving a reference source to incremental depths of the water column near the target. Theoretical analysis is provided using the WKB approximation for a range dependent ocean. The numerical simulation is performed using a high-order parabolic equation (PE) code for a range-dependent analytical sound-speed profile (SSP), and measured sound-speed data from the North Pacific ocean. The results of the analysis and simulation show the possibility of localizing a source at large distance with great accuracy.
‘‘Say–stay’’ identification and psychoacoustic performance of hearing-impaired listeners
Authors: Nelson Peggy B. , Nittrouer Susan , Norton Susan J.
Published: October 2005

Controversy exists over the extent to which psychoacoustic abilities explain speech perception. The present study addressed this issue by assessing the contribution of psychoacoustic abilities to speech identification by hearing-impaired listeners. Speech stimuli and nonspeech analogs were presented to normal-hearing and hearing-impaired listeners with varying degrees of hearing loss. Phonemic judgments for synthetic versions of ‘‘say–stay’’ stimuli were evaluated as a function of first formant onset frequency and of silence duration between the /s/ noise and the vocalic portion. Three psychoacoustic measures were obtained: glide onset frequency discrimination, gap detection in noise, and gap detection in speechlike composite signals. Although the resulting difference limens increased with increasing hearing loss, the acoustic cues to the speech contrast were available to all listeners. Nonetheless, the response patterns to the speech stimuli varied among groups in a manner that was not explained by the psychoacoustic results. Thus, although hearing-impaired listeners were able to detect and discriminate essential acoustic cues for speech, the perceptual organization of speech stimuli appeared to differ with degree of loss. Alternative explanations for the findings are considered, including the possible effect of hearing loss on auditory/linguistic experience.
Effects of combining maskers in modulation detection interference
Authors: Bacon Sid P. , Moore Brian C. J. , Shailer Michael J. , Jorasz Urszula
Published: October 2005

The threshold for detecting 10-Hz amplitude modulation of a 2000-Hz carrier was measured in quiet, in the presence of an unmodulated masker, and in the presence of an amplitude-modulated masker. Two experiments were run; in each, the masker consisted of one or two sinusoidal carriers (chosen from among the frequencies of 800, 1600, 2400, and 3200 Hz). In experiment 1, the modulation rate of the masker ranged from 2 to 80 Hz. The ‘‘tuning’’ in the modulation domain was not affected much by the masker carrier frequency or the increase from one to two carriers. The amount of interference, however, was sometimes greater in the two-carrier condition, although this resulted primarily from the presence of the carriers and not from their modulation. In experiment 2, the modulation rate of each single-carrier masker ranged from 2 to 80 Hz (as in experiment 1), but for the two-carrier conditions, all possible combinations of two carriers (2400 and 3200 Hz) and three masker rates (5, 10, and 20 Hz) were evaluated. In general, the combination of two modulated carriers did not produce more interference than that produced by the more interfering carrier presented alone. Thus the results from both experiments provide little evidence for an additivity of modulation detection interference.
The strong/weak syllable distinction in English
Authors: Fear Beverley D. , Cutler Anne , Butterfield Sally
Published: October 2005

Strong and weak syllables in English can be distinguished on the basis of vowel quality, of stress, or of both factors. Critical for deciding between these factors are syllables containing unstressed unreduced vowels, such as the first syllable of automata. In this study 12 speakers produced sentences containing matched sets of words with initial vowels ranging from stressed to reduced, at normal and at fast speech rates. Measurements of the duration, intensity, F0, and spectral characteristics of the word-initial vowels showed that unstressed unreduced vowels differed significantly from both stressed and reduced vowels. This result held true across speaker sex and dialect. The vowels produced by one speaker were then cross-spliced across the words within each set, and the resulting words’ acceptability was rated by listeners. In general, cross-spliced words were only rated significantly less acceptable than unspliced words when reduced vowels interchanged with any other vowel. Correlations between rated acceptability and acoustic characteristics of the cross-spliced words demonstrated that listeners were attending to duration, intensity, and spectral characteristics. Together these results suggest that unstressed unreduced vowels in English pattern differently from both stressed and reduced vowels, so that no acoustic support for a binary categorical distinction exists; nevertheless, listeners make such a distinction, grouping unstressed unreduced vowels by preference with stressed vowels.
A comparative acoustic study of English and Spanish vowels
Authors: Bradlow Ann R.
Published: October 2005

Languages differ widely in the size of their vowel inventories; however, cross-linguistic surveys indicate that certain vowels and vowel system configurations are preferred. A cross-linguistic comparison of the acoustic vowel categories of two languages that differ in vowel inventory size, namely, English and Spanish, was performed in order to reveal some of the language-specific and/or universal principles that determine the acoustic realization of the vowels of these two languages. This comparison shows that the precise location in the acoustic space of similar vowel categories across the two languages is determined, in part, by a language-specific base-of-articulation property. These data also suggest that the relatively crowded acoustic vowel space of English may be expanded with respect to the relatively uncrowded acoustic vowel space of Spanish; however, this effect is variable depending on the syllable context of the English vowels. Finally, the data indicate no difference in the tightness of within-category clustering for the large versus the small vowel inventory.
Time-domain deconvolution to measure reflection functions for discontinuities in waveguides
Authors: Agulló J. , Cardona S. , Keefe D. H.
Published: October 2005

An experimental method to measure the reflection functions for discontinuities in cylindroconical waveguides is presented. It involves a single discontinuity and uses a pulselike incident signal. FIR techniques are used to design the incident signal and signal processing is made in the time domain. Two methods to stabilize the numerical deconvolution are considered, those based on singular value decomposition, and the conjugated gradient method. Results presented are related to taper discontinuities, but the method can be applied to other discontinuities as well.
Flow-induced noise on a bluff body
Authors: McEachern James F. , Lauchle Gerald C.
Published: October 2005

Flow noise measurements were made on inertial type pressure gradient hydrophones, configured as three-dimensional cylinders in cross flow, over a diameter-based Reynolds number range of 4×103 to 1.8×104. The measurements were made at frequencies from 4.2 to 50 Hz as the bodies were towed in a quiescent body of water. Systematic changes were made in the cylinder geometry as to affect the flow noise level and to aid in the identification of dominant flow noise sources. The cylinder aspect ratio was varied from 0.5 to 2.5, and the endcap geometry was altered by relieving the 90° edge with radii that ranged from 0.0315D to 0.5D, where D is the diameter of the cylinder. The data from these (and other flow visualization) experiments shows that the presence of a radius at the corner between the endcap and the cylinder results in a significant reduction of the separated flow over the endcap, and that the flow noise levels decrease accordingly. The flow noise levels are also observed to decrease as the body aspect ratio increases which suggests that when three-dimensional effects (endcap flow) are suppressed, unsteady forces will be reduced and the cylinder self-noise will decrease. Thus the dominant source of flow noise on short cylinders in cross flow is attributed to the unsteady separation and turbulent flow over the cylinder endcaps.
Plane-wave reflection and transmission coefficients for a three-layered elastic medium
Authors: Ainslie Michael A.
Published: October 2005

Simple expressions are derived for the (p and s) plane-wave reflection and transmission coefficients for a three-layered elastic medium comprising a homogeneous transition layer between two half-spaces. The result, presented as a function of the well-known coefficients for a two-layered (solid–solid) medium, is in a simple explicit form, and is entirely equivalent to the implicit relationships obtained by conventional matrix methods. Reflection of sound from the seabed with a thin sediment layer is considered as an illustrative example.
Generalization of the k-space formulation to elastodynamic scattering problems
Authors: Liu Qing-Huo
Published: October 2005

A generalized k-space (GKS) formulation is presented for vectorial elastodynamic scattering problems. It represents a generalization of Bojarski’s scalar k-space formulation. From the basic second-order partial differential equation or its integral representation in the space-frequency (r-f) domain, a local equation is derived for the displacement field in the spectral-frequency (k-f) domain. This equation, together with the constitutive equation in the r-f domain, reduces the original scattering problem into two simultaneous local equations with two unknowns (displacement field and the induced source), which are then solved by the conjugate-gradient (CG) method. The connection between the k-f domain and r-f domain is obtained by the spatial fast Fourier transform (FFT) algorithm. The number of complex multiply-add operations per CG iteration is O(N log2 N), and the storage requirement is only O(N), where N is the number of spatial discretization points. This is much more efficient than the conventional method of moment combined with the CG procedures which requires O(N2) operations per iteration and O(N2) storage. In the spectral-time (k-t) domain, however, it is found that four simultaneous local equations have to be used to formulate the k-space algorithm because of the existence of two wave speeds. By virtue of the causality, a new local time-stepping algorithm is derived with the aid of two temporal propagators, i.e., the compressional and shear propagators. The connection between the r-t domain and k-t domain is again obtained by the spatial FFT algorithm. Therefore, in each time step, the number of complex multiply–add operations is O(N log2 N), and the storage requirement is O(N). Most importantly, for the same accuracy, N can be much smaller than that for the conventional finite-difference method.
Determination of structural impedance from scattering data
Authors: Gaumond Charles F. , Yoder Tim
Published: October 2005

Knowledge of the structural impedance is significantly important in the computation of acoustic scattering and radiation because it contains all the information about the structure which is necessary for the evaluation of the scattered or radiated field in any fluid medium. The inverse problem of determining, or reconstructing, the structural impedance from scattering measurements is treated. An algorithm is developed for the reconstruction of the structural impedance from knowledge of scattered field for a set of incident plane wave directions. An intermediate step includes the reconstruction of the surface pressure and normal velocity fields using acoustical holography. The resolution limit of the reconstruction is found in the case of the infinite cylinder and the sphere. The case of the sphere is generalizable to other finite shapes. Problems caused by noise in the inversion of the data are discussed. Alternative reconstructions of wet impedance and wet admittance which can be performed for any scattering data are defined.
Numerical simulation of elastic wave propagation in granular rock with the boundary integral equation method
Authors: Nihei Kurt T. , Myer Larry R. , Cook Neville G. W.
Published: October 2005

To better understand the effects of the microstructural properties of granular rocks such as grain packing geometry, grain shape and size, grain contact properties, and grain scale heterogeneity on the velocities and amplitudes of seismic waves, a numerical approach for modeling elastic wave propagation in granular rock has been developed. The numerical approach employs the boundary integral equation method to model the complete dynamic response of a packing of arbitrarily shaped grains. The effects of dry, fluid-filled, and clay-filled grain contacts are incorporated into the numerical formulation using a discontinuity boundary condition with a complex stiffness parameter. Numerical simulations for SH-wave propagation in an idealized grain packing illustrate the applicability of this technique for investigating the effects of grain contact properties and source frequency on the amplitudes and velocities of elastic waves.
An impulse response function for a fuzzy structure
Authors: Maidanik G. , Dickey J.
Published: October 2005

The authors are employing some of their previous works in structural acoustics to define, investigate, and interpret the response behaviors of so called fuzzy structures. A formalism is developed to describe the response behavior of a master structure to which an ensemble of appendages are attached. The impulse response function for the master structure is, ad hoc, assumed to be proper and known. The appendages are assumed to be described by an impedance operator composed of individual impedances that are localized; each impedance is stated in terms of a singular position and an associated impedance. An impulse response function is then derived and is shown to be proper. The propriety of the impulse response function demands that it be dependent only on quantities and parameters that describe the appended master structure; it needs to be independent of the in situ response of the structure and the external drive that generates the response. Models of naturally interacting and artificially noninteracting appendages on a master structure yield impulse response functions that obey the Le Chatelier’s principle. A model based on the Born approximation violates this principle and, therefore, its use is highly limited. All three models are employed to explain the notion of a configuration for the disposition of an ensemble of appendages. A configuration is shown to require the specification of a two-vector set comprising the positions and impedances of the appendages. The notion of an ensemble of configurations is then proposed to define deviations from a prime configuration. Configurational averages of the equation of motion of the appended master structure can then be performed exposing the averaged response behavior for this structure. An ensemble of appendages that can be assigned an ensemble of configurational deviations that are defined statistically is dubbed fuzzy (structural fuzzy). In turn, a statistical ensemble of configurations about a prime configuration of appendages on a master structure defines a fuzzily appended master structure.