bluuebunny/crossref_metadata_2025 huggingface dataset:
Bubble population measurements with a parametric array
Authors: Gensane Marc
Published: October 2005

This paper presents a method that estimates gas bubble density in water versus range. A bubble cloud being insonified with a highly directive acoustic transducer, this method combines backscattering and attenuation measurements. It relies on the linear theory of bubble resonance, and the so-called first-order multiple scattering approximation. Here it is applied to some measurements performed with a parametric array (primary frequency: 210 kHz; secondary: 8 to 40 kHz). The application of this method to the secondary frequencies fails, because the backscattered levels are much higher than the saturation level. This failure is imputed to the nonlinear scattering occurring at the secondary frequencies by the bubbles whose resonance is close to the primary frequency. From this assumption, minimum ranges are deduced under which the measurements of bubbles resonating at the secondary frequencies cannot be stated as reliable.
On determination of orthotropic material moduli from ultrasonic velocity data in nonsymmetry planes
Authors: Chu Y. C. , Degtyar A. D. , Rokhlin S. I.
Published: October 2005

This paper reports analysis of the reconstruction of elastic constants from ultrasonic velocity measurements in nonsymmetry planes of unidirectional composite materials. It is shown that the nonlinear least-square optimization method is stable to initial guess selection and data scatter and can be used routinely to measure the full set of nine elastic constants for orthotropic materials. Simple analytical expressions are derived for phase velocities in arbitrary directions in an orthotropic material with low transverse-to-fiber anisotropy. Using these, coefficients of sensitivity of phase velocities to elastic constants are obtained in closed form and used to find the optimal wave propagation directions for elastic constant measurement. The changes in velocity due to elastic constant variation calculated by the exact theory agree well with the predictions from the sensitivity coefficients. When all nine elastic constants are reconstructed from velocity data in nonsymmetry planes, the inversion is highly dependent on the initial guesses and susceptible to random data scatter. When seven elastic constants are found from velocity data in planes of symmetry, the remaining two (C12 and C66) can be found from nonsymmetry-plane data independently of initial guesses and scatter levels. This is especially important since the elastic constants C12 and C66 cannot be determined from immersion velocity measurements in two accessible planes of symmetry.
Comparative analysis of through-transmission ultrasonic bulk wave methods for phase velocity measurements in anisotropic materials
Authors: Chu Y. C. , Rokhlin S. I.
Published: October 2005

In this paper a critical evaluation of ultrasonic bulk wave velocity measurements by the through-transmission and the recently introduced self-reference methods is reported. The major difference in these two techniques is the reference acoustic path: through-water for the through-transmission method and through-sample at normal incidence for the self-reference method. The error introduced by geometrical imperfection of the sample is compared theoretically and experimentally for two methods. Composite materials with different anisotropies are used in the experiment, including ceramic matrix (SiC/Si3N4) and graphite/epoxy composites. Both analytical and experimental studies show that the self-reference method has advantages over the through-transmission method, which is susceptible to geometrical imperfections in the sample. The effect of temperature fluctuation on the accuracy of ultrasonic phase velocity measurements is discussed and different compensation techniques are proposed.
Acoustic double-reflection and transmission at a rough water–solid interface
Authors: Rose James H. , Bilgen Mehmet , Nagy Peter B.
Published: October 2005

The double interaction of a wave with a rough interface is important in many acoustic measurements. An acoustic beam that reflects twice from a rough water–solid interface is considered. The second reflection from the rough surface is accomplished after the transducer’s buffer rod is used as an acoustic mirror. Changes in the spatially averaged specular reflection are related to the phenomenon of ‘‘enhanced backscatter,’’ previously observed for diffuse scattering. Simple, approximate closed-form analytic formulas for the strength of the specular double reflections are given as a function of frequency and the stand-off distance of the transducer. As one application of the analytic results, a method is proposed for determining the surface correlation function from the specular double reflections. The same physics (and appropriately modified analytic formulas) apply to doubly transmitted waves. Experimental measurements have been made of acoustic double reflection with a normally oriented broadband piezoelectric transducer near a rough water–solid interface. Measurements of (1) the wave reflected once from the rough interface, and (2) the wave reflected twice from the rough interface are given. The strength of the specular reflections was measured as a function of frequency and the transducer’s distance from the surface. It was observed that for large distances between the transducer and the rough surface and at low frequencies the scattering-induced loss of the doubly reflected wave was twice the loss of a singly reflected wave. However, for small distances between the transducer and the surface and at high frequencies the scattering-induced loss of the doubly reflected wave was four times the loss of a singly reflected wave.
Advanced time domain wave-number sensing for structural acoustic systems. II. Active radiation control of a simply supported beam
Authors: Maillard J. P. , Fuller C. R.
Published: October 2005

A real time structural acoustic sensor and associated signal processing is developed and applied to the active control of sound radiated by a simply supported beam. The sensor consists of multiple accelerometers mounted on the structure. An array of FIR filters processes the measured structural information to provide an estimate of the structural wave-number component coupled to acoustic radiation in a prescribed direction. This time domain signal is used as the error information in a feedforward adaptive control approach. The single channel filtered-X LMS algorithm is implemented here. Computer simulations in the discrete time domain demonstrate the ability of the sensor to replace the use of error microphones in the far field. The described sensor represents a significant alternative to the use of distributive structural sensors (for example piezoelectric material) by providing accurate radiation information over a broadband frequency range.
Analytical formulations for annular disk sound radiation using structural modes
Authors: Lee Ming-ran , Singh Rajendra
Published: October 2005

Sound radiation characteristics of an annular disk with application to the computer disk are examined analytically. The far-field and the radiation impedance approaches are employed to calculate radiated sound of a disk vibrating at its elastic or rigid body modes. Modal sound power is formulated by approximating the structural modal functions and is expressed in terms of a power series of the wave number. Predictions show that axisymmetric vibration modes are more efficient radiators compared to those asymmetric disk modes that have the same number of nodal circles. Numerical results obtained by a boundary element program are used to support analytical predictions. Formulations are also extended to include the modal coupling and source rotation effects. The effect of coupling between disk vibration modes on the radiated sound is found to be significant if multimodes are excited. A simple empirical equation has been developed to predict the modal sound radiation efficiency of a rotating disk for selected vibration modes.
Surface and body waves generated by a point traction applied on transversely isotropic solids
Authors: Lin W. , Keer L. M. , Xu Y.
Published: October 2005

This paper derives analytical expressions for the far-field surface waves and body waves generated by a point traction on a semi-infinite, transversely isotropic solid. The closed-form expressions are also analytically and numerically checked with the related problem for isotropic media. Slowness and wave-front curves and decay behavior of the surface waves are plotted for magnesium, cobalt, and a composite.
Generalized modal expansion: A Wiener–Hopf problem
Authors: Haj-Hariri Hossein
Published: October 2005

A method is presented that is suitable for studying linear wave-scattering problems for guided waves in bounded or unbounded domains. The method is developed for the classical wave equation. The generality of the discussions show the promise of the method for studying scattering problems governed by linear equations more complicated than the classical wave equation (e.g., higher-order, nonconstant coefficients). The method allows for modal expansion in cases where the spectrum of the governing operator may not be readily accessible. The well-known example problem of sound propagation and scattering in a plane waveguide in the presence of a semi-infinite splitter plate is studied using this technique. The results are in agreement with the analytical solutions obtained using the Wiener–Hopf and classical modal expansion methods. Whereas these latter two techniques are simple, they cannot be generalized easily; in contrast to the method proposed herewith.
Acoustic coupling from a focused transducer to a flat plate and back to the transducer
Authors: Chen Xucai , Schwarz Karl Q. , Parker Kevin J.
Published: October 2005

An approximate solution for the acoustic coupling factor (the diffraction correction function) from a focused transducer to a flat plate and back to the transducer is provided. This function is useful for system calibrations where a pulse-echo system or transmit–receive system is used. Numerical solutions are provided for the important case where the flat plate is placed near the focal plane of the transducer. The solution for a flat disk transducer is obtained as a limiting case. Experimental evidence for a focused transducer is provided.
Simultaneous measurement of the acoustical properties of a thin-layered medium: The inverse problem
Authors: Kinra V. K. , Jaminet P. T. , Zhu C. , Iyer V. R.
Published: October 2005

This paper presents a frequency-domain ultrasonic technique for a simultaneous determination of the thickness (h) and wave speed (c) of the individual layers comprising a multilayered medium. The layers may be ‘‘thin’’; by thin we mean that the successive reflections of an ultrasonic pulse from the two faces of a layer are nonseparable in the time domain. Plane longitudinal waves which are normally incident upon the medium are considered. A systematic analysis of the sensitivity of the complex-valued transfer function to the acoustical parameters of each layer has been carried out. An inverse algorithm, which utilizes either the Newton–Raphson or the Simplex method in conjunction with the incremental search method, has been developed to reconstruct simultaneously the thickness and phase velocity of each layer by minimizing the difference between the theoretical and the experimental results in the mean-sum-square sense; the entire complex spectrum, i.e., the amplitude as well as the phase spectrum, was used. The technique is fully automated and computer controlled and can be readily used for in situ NDE applications. Results are presented for several three-layer specimens; aluminum/water/aluminum, aluminum/water/titanium, and titanium/water/titanium. Successful inversion was obtained for the following cases (1) simultaneous determination of h and c of any one of the three layers, given h and c of the remaining two layers; (2) simultaneous measurement of the three thicknesses, given the three wave speeds; (3) simultaneous measurement of the three wave speeds, given the three thicknesses; (4) simultaneous determination of all three thicknesses and one wave speed, given the remaining two wave speeds. The precision of our measurements was found to be excellent; typically, ±3 μm in h (for h of the order of 1 mm) and ± one part per thousand in c. The accuracy was found to be about one order of magnitude lower than the precision; typically, ±10 μm in h and ±2% in c.
Nonspecular reflection of two- and three-dimensional acoustic beams from fluid-immersed plane-layered elastic structures
Authors: Zeroug Smaine , Felsen Leopold B.
Published: October 2005

This paper treats the interaction of two- and three-dimensional acoustic quasi-Gaussian beams with plane-layered elastic configurations. Emphasis is placed on the regime of nonspecular reflection, which is characterized by strong coupling between the specularly reflected beam and leaky waves supported by the structure. The present analysis generalizes previously published studies of these phenomena by allowing for arbitrarily collimated two- and three-dimensional beams as well as simultaneous excitation of multiple leaky waves. The substantially enriched range of nonspecular phenomena encountered under these generalized conditions is explained by examining the spectral content of the reflected and leaky wave constituents that participate in the interaction. By use of the complex source point (CSP) method for modeling quasi-Gaussian beams, the reflection problems are solved rigorously by wave-number spectral decomposition. Subsequent reduction by uniform asymptotic techniques yields physically meaningful wave-field contributions, which explain the phenomenology and also allow efficient computation. The accuracy of the CSP asymptotic algorithms is assessed by comparison with purely numerically generated reference data. The results establish the accuracy and versatility of the CSP strategy for a broad range of beam-interface conditions.
Direct measurements of edge diffraction from soft underwater acoustic panels
Authors: Piquette Jean C.
Published: October 2005

Direct measurements of edge diffraction arising from the interaction of an acoustic wave with an underwater panel that satisfies soft-body boundary conditions are reported. The measurements were obtained by utilizing a specially fabricated ‘‘airbox’’ sample, which is literally a ‘‘box of air,’’ fabricated using thin polycarbonate walls. The airbox theoretically would exhibit a typical insertion loss in excess of 60 dB (in the absence of edge diffraction), thus avoiding interference of the directly transmitted wave with the edge-diffracted wave of interest. The validity of the edge-diffraction measurements was established by demonstrating that the performance of a small sample panel fabricated from a closed-cell foam material can be deduced by adding (frequency-by-frequency) measurements obtained from an airbox to diffraction-free measurements obtained from a large sample of the same closed-cell foam. This procedure simulates (from direct experimental measurements) the combined edge-diffracted plus transmitted wave field that is present in the transmission region of the small sample. The results reported include the edge diffraction caused by the interaction of a spherically symmetric source with a soft sample panel and the edge diffraction caused by the interaction of an acoustic array with a soft sample panel. The frequency interval considered is 1–21 kHz.
Wiener kernel analysis of inner ear function in the American bullfrog
Authors: van Dijk Pim , Wit Hero P. , Segenhout Johannes M. , Tubis Arnold
Published: October 2005

The response of 17 primary auditory nerve fibers in the American bullfrog (Rana catesbeiana) to acoustic noise stimulation of the tympanic membrane was recorded. For each fiber, the first- and second-order Wiener kernels, k1(τ1) and k2(τ1,τ2), were computed by cross correlation of the stimulus and the response. The kernels revealed amplitude and phase characteristics of auditory filters of both phase-locking and non-phase-locking fibers. Wiener kernels of high- and midfrequency fibers (best frequency, BF≳500 Hz), implied a simple sandwich model, consisting of a cascade of a linear bandpass filter, a static nonlinearity, a linear low-pass filter, and a spike generator. The bandpass filter was at least of order 7, and had a linear phase response, for both the high- and the midfrequency fibers. Averaged across fibers, filter order 2, and cutoff frequency 451 Hz for the second filter in the model was observed. The responses of low-frequency fibers (BF<500 Hz) could not be fit with the sandwich model, because the Fourier transform K2(f1,f2) of the second-order Wiener kernel showed significant components at off-diagonal frequencies f1≠±f2. The presence of these off-diagonal components shows that, in addition to the phase and gain characteristics of auditory filters, the Wiener kernel analysis reveals nonlinear two-tone interactions.
Detection of unexpected tones with short and long durations
Authors: Wright Beverly A. , Dai Huanping
Published: October 2005

The detectability of short and long unexpected tones masked by a continuous wideband noise was assessed using a probe-signal method. This method leads the listener to expect a target frequency by presenting the signal most often at that frequency, and only occasionally at other unexpected probe frequencies. The probe-signal contour (percent correct as a function of probe frequency) was considerably broader with 5-ms than with 295-ms signals. However, auditory filter shapes measured using the notched-noise technique were very similar for those two signal durations, indicating that the results obtained in the probe-signal conditions do not simply reflect peripheral frequency selectivity. Further supporting this interpretation, probe tones having the same frequency but a different duration from the target were poorly detected. It is proposed that the subject listens through a time-frequency window whose location and shape in the time-frequency plane is determined by the duration and frequency of the target.
Detecting pitch-pulse asynchronies and differences in fundamental frequency
Authors: Carlyon Robert P.
Published: October 2005

A series of experiments investigated the detection of pitch-pulse asynchronies (PPAs) and of differences in fundamental frequency (ΔF0’s) between two simultaneous ‘‘formants,’’ each of which consisted of a group of sinusoidal components spaced sufficiently closely in frequency to be incompletely resolved by the peripheral auditory system. For such stimuli, introducing a ΔF0 caused the pitch pulses of the two groups to become progressively more asynchronous at later and later parts of the stimulus. A comparison of the psychometric functions for the detection of ΔF0’s and of (constant) PPAs suggested that listeners could, under some circumstances, detect ΔF0’s from the resulting asynchrony. Using an adaptive procedure, it was also shown that, for a range of F0’s from 20 to 125 Hz, the threshold PPA was constant at about 2.5 ms. This relationship between PPA threshold and F0 differs from that previously reported for the detection of envelope asynchronies between pairs of sinusoidally modulated tones [e.g., Strickland et al., J. Acoust. Soc. Am. 86, 2160–2166 (1989)], which remain constant in degrees, rather than in ms. Further experiments investigated the rôle of onset asynchronies in the detection of PPAs and showed that, although an asynchrony between the first pitch pulse in each formant was sufficient for near-asymptotic performance, listeners could still do the task when this cue was removed. For the detection of ΔF0’s, onset asynchronies also aided, but were not necessary for, discrimination.
Vowel identification in mixed-speaker silent-center syllables
Authors: Jenkins James J. , Strange Winifred , Miranda Salvatore
Published: October 2005

Strange [J. Acoust. Soc. Am. 85, 2135–2153 (1989b)] has demonstrated that there is sufficient information in the onsets and offsets of syllables, spoken in sentence context, to provide accurate identification of the vowel in the syllable. Verbrugge and Rakerd [Language Speech 29, 39–57 (1986)] and Andruski and Nearey [J. Acoust. Soc. Am. 91, 390–490 (1992)] have shown that such information is present in citation-form syllables even when the syllables begin with one speaker and end with another. These studies of ‘‘hybrid syllables,’’ however, reported relatively high error rates. In a perceptual experiment using /dVd/ syllables spoken in sentence context by a male and a female speaker, relatively low error rates were obtained for both ‘‘silent-center’’ syllables and ‘‘hybrid silent-center’’ syllables. It was concluded that the information specified over syllable onsets and offsets together for identification of vowels is speaker independent and that it was sufficient in most cases to specify the vowel. The acoustic patterns, represented as functions of log(F2/F1) over time, revealed potentially useful dynamic acoustic characteristics of coarticulated vowels.
Intensity resolution and loudness in high-pass noise
Authors: Schlauch Robert S.
Published: October 2005

Intensity resolution and loudness growth for a 1000-Hz tone were studied in the presence of high-pass noise (cutoff: 1800 Hz). Intensity resolution was measured for gated and continuous standards using a three-interval forced-choice (3-IFC) adaptive procedure. Loudness matches were obtained using an adaptive, alternate binaural loudness balance procedure. Three subjects listened in three conditions (1) quiet; (2) high-pass noise with a spectrum level of 32 dB SPL; and (3) high-pass noise with a spectrum level of 42 dB SPL. Noise levels were selected so that detection thresholds were minimally affected at the test frequency; however, for frequencies in the noise passband, thresholds were shifted to either 50 or 60 dB SPL, depending on the spectrum level of the noise. On average, loudness growth and intensity resolution were unaltered by the presence of the noise for tonal levels below 40 dB SPL; above 40 dB SPL the following was generally true: (1) intensity resolution for gated standards was well described by Weber’s law except at the highest levels where the Weber fraction decreased; (2) intensity resolution for continuous standards showed a ‘‘near-miss’’ to Weber’s law, but just-noticeable differences (jnd’s) were slightly larger than those in quiet for the same SPL; (3) loudness was reduced. A comparison of jnd’s for equally loud tones showed that loudness is less dependent on excitation spread than the jnd. That is, jnd’s in the threshold-shifted ear were larger than the ones in quiet when the comparison was made for tones judged to be equally loud. This finding is qualitatively consistent with excitation-pattern models of these phenomena. The results were also evaluated in terms of the proportional-jnd theory, which yielded more accurate predictions of loudness growth with gated-standard resolution than with continuous-standard resolution for most comparisons.
Detecting mistuning in the presence of synchronous and asynchronous interfering sounds
Authors: Carlyon Robert P.
Published: October 2005

Listeners were presented with the first seven harmonics of a 500-Hz fundamental (the ‘‘test complex’’), and were required to detect a mistuning imposed on its fourth harmonic (the ‘‘target’’), which had a nominal frequency of 2000 Hz. All components were frequency modulated by a 5-Hz sinusoid, and, in the signal interval of each 2IFC trial, a 180° phase delay was imposed on the modulation applied to the target. This led to a mistuning proportional to the depth of FM, which was varied adaptively to obtain thresholds. When an unmodulated 2000-Hz ‘‘interfering’’ sinusoid was gated on and off together with the test complex, thresholds were largely unaffected, provided the level of the interferer was more than 3 dB below that of the target. However, when the interferer started before and ended after the test complex there was a substantial elevation in threshold, even at low interferer levels. The elevation was mainly due to the portion of the interferer preceding the test complex, but the part following the complex also had some effect. When the offset asynchrony between the interferer and the test complex was held constant at 100 ms and the onset asynchrony varied, the highest thresholds occurred at an onset asynchrony of 200 ms. A threshold elevation could also be achieved by replacing the interferer with a narrow-band noise centered on 2000 Hz, or by preceding the test complex with an interferer consisting of all components except 2000 Hz. The elevation could be reduced by presenting the leading portion of the 2000-Hz interferer as part of a harmonic complex with an F0 of 333 Hz, or even by presenting it as part of a complex with which it did not form a harmonic series. It is concluded that the effect of the asynchronous interferer was to pull the target component into a separate perceptual stream from the rest of the test complex, and that this prevented listeners from detecting mistuning by comparing its frequency to that of the remaining components. Implications of these findings for theories of perceptual streaming and of mistuning detection are discussed.
Vibration of two concentric submerged cylindrical shells coupled by the entrained fluid
Authors: Yoshikawa Shigeru , Williams Earl G. , Washburn Karl B.
Published: October 2005

The vibrational characteristics of a point-driven ‘‘double shell’’ (two concentric submerged cylindrical shells coupled by the entrained fluid) are investigated theoretically and experimentally. Of particular interest are the shielding effects, if any, of the outer shell upon the inner shell. The theory on the double shell is based on Flügge’s infinite-shell equations, the Helmholtz wave equation, and boundary conditions at the fluid–structure interfaces. This theory is used to model a finite double-shell structure in wave number-frequency space. Experiments are carried out in which generalized near-field acoustical holography (GENAH) is employed to provide the experimental vibration characteristics in wave number-frequency space of the finite double shell. It is confirmed theoretically and experimentally that the outer shell of the double shell exhibits two separate dispersion curves: A higher-frequency dispersion curve exhibits in-phase vibrations with respect to the inner shell, and a second lower-frequency curve, out-of-phase vibration. The higher-frequency dispersion curve of the double shell is very similar to the dispersion curve of the single shell (the inner shell without the outer shell), and thus is identified as a forced wave number response. The lower-frequency curve seems to be dependent on the free wave number response of the outer shell alone of the double shell. A double-shell structure can usually reduce its vibrational amplitudes by splitting the response of single-shell’s forced vibration into the responses of inner-shell’s forced vibration and outer-shell’s induced vibration. However, it radiates low-frequency underwater sounds inevitably according to the lower-frequency dispersion curve. Furthermore, the appearance of the inner shell’s dispersion curve on the outer shell seems to indicate that the shielding influence of the outer shell is not completely effective.
Otoacoustic emissions and quinine sulfate
Authors: McFadden Dennis , Pasanen Edward G.
Published: October 2005

A moderate dose of quinine sulfate, administered to three young adult males, reduced or eliminated various forms of otoacoustic emission (OAE). The individual differences in response to the drug were substantial, but a number of generalizations did emerge. The time courses of onset and recovery were considerably more rapid than for the parallel effects produced by aspirin. Most spontaneous otoacoustic emissions (SOAEs) were eliminated within 7 h of the first 325-mg dose (about 3 h after the second dose). Most SOAEs showed partial or complete recovery about 24 h after the last dose, although considerable instability often remained. The functions relating the magnitude of a distortion-product OAE (DPOAE) to the sound-pressure level (SPL) of the primary tones producing it were displaced toward higher primary levels and became lower sloped following quinine administration. The magnitudes of SOAEs, DPOAEs, and nonlinear peaks in the click-evoked spectra declined and recovered with grossly similar time courses, but there were some partial dissociations. The ability of a DPOAE to suppress an SOAE lying about 50 Hz below it either increased slightly or remained about constant through the drug episode, even though the magnitudes of both DPOAE and SOAE were changing. On several occasions, increases in SOAE magnitude of as much as 10–20 dB were observed during the first 15–30 min of an SOAE measurement period (an initializing effect). Psychophysical measures revealed hearing losses of as much as 20 dB at some frequencies in some subjects. Several short-lived ‘‘enhancements’’ of OAEs are discussed relative to similar quinine-induced effects reported in an animal model.
Correlation-based analysis of a generalized target description
Authors: Delaney P. A. , Marshall D. F.
Published: October 2005

Recently, a generalized target model was proposed in the literature. The objective of this work was to determine if the added complexity of the generalized model would allow substantially better performance, in terms of the mean-square-error and the average radius estimate, than that which could be achieved using the conventional target model. The scattering target was selected to be a hard acoustic sphere. The experimental results indicate that the order of the generalized model is dependent on the structure of the transmitted signal. Further, the generalized model results in a lower mean-square-error and a more accurate estimate of the sphere radius than the conventional model in the noise-free case. When white Gaussian noise was added to the echo, the generalized model still retained the advantage of a lower average mean-square-error than the conventional model for all signal-to-noise ratios that were tested. The generalized model produces a better radius estimate than the conventional model at high signal-to-noise levels, but at low levels, the insensitivity of the conventional model to noise resulted in a better radius estimate.
Lateralization of bands of noise as a function of combinations of interaural intensitive differences, interaural temporal differences, and bandwidth
Authors: Buell Thomas N. , Trahiotis Constantine , Bernstein Leslie R.
Published: October 2005

Listeners indicated the intracranial position of bands of noise (from 50 to 400 Hz in width) for several combinations of interaural intensitive differences (IID), and interaural temporal differences (ITD), and/or interaural phase differences (IPD). All ITD and IPD combinations produced an interaural delay of 1500 μs at the center frequency of the noise. The interaural phase spectra were constructed to produce several patterns of putative cross-correlation functions. Potency of IIDs depended greatly on particular combinations of bandwidth, ITD and IPD. For some combinations, changing the IID by only 3 dB resulted in large shifts in laterality (sometimes moving the image from near one ear to near the other). The complex interactions observed make the results incompatible with the traditional notion that IIDs simply act as weights or scalars. Rather, IIDs act in two distinct manners: (1) as independent scalar quantities and (2) by interacting with specific combinations of bandwidth and ITD/IPD, which is believed to reflect an action within the cross correlation surface.
An artificial neural network for sound localization using binaural cues
Authors: Datum Michael S. , Palmieri Francesco , Moiseff Andrew
Published: October 2005

A three-layer neural network is used to estimate the direction of a sound source from the signals detected by two directional, spatially separate receivers. Although the implemented system does not require any specific knowledge about acoustical parameters or propagation properties, a model of the acoustical environment is used to generate simulated data for training the network. The neural network is trained according to the multiple extended Kalman algorithm (MEKA), which provides fast convergence and does not require intervention for adjustment of the learning parameters. Lower bounds on estimation are computed and compared with simulations using the neural network.
Single-reference calibration technique for multiple-element array sonar imaging systems
Authors: Douglas Brett L. , Silkaitis John M. , Lee Hua
Published: October 2005

The most recent advancement of sonar imaging has been focusing on the capability of high-resolution imaging, especially for multiple-element arrays and synthetic aperture systems. Consequently, modeling and correction of data acquisition error has become an important subject in high-performance imaging. High-accuracy array calibration techniques are crucial to the performance of sonar systems. However, the fundamental analysis and functions of calibration procedures have not been fully studied in a complete and detailed manner. This paper presents a simple and systematic calibration technique for multiple-element array sonar systems. The presentation includes mathematical and physical modeling, theoretical analysis, and full-scale experiment with the Sonatech SLS-10 array system.
Sound transmission to and within the human ear canal
Authors: Hammersho/i Dorte , Mo/ller Henrik
Published: October 2005

Sound transmission to the eardrum from various points in the external ear was measured by means of probe microphone technique. Twelve human subjects participated, and three directions of sound incidence were included. For the major part of the audio frequency range the transmission to the eardrum proved independent of direction from points at the centerline of the ear canal, including the entrance (open or blocked). The results further suggested that the region with independent transmission extends some millimeters outside the entrance plane. The transmission from the free field to the eardrum was divided into a directional-dependent part and two directional-independent parts: (1) the transmission from the free field to the blocked entrance, (2) a pressure division between the radiation impedance and the ear-canal input impedance, and (3) the transmission along the ear canal. All parts of the transmission were seen to be highly individual. The first part was shown to be uncorrelated with any of the other parts, whereas mutual dependence of parts (2) and (3) resulted in a smaller variation in the combined transmission than for the parts in separate. The standard deviation between subjects for head-related transfer functions (HRTFs) measured at the eardrum, the open entrance, and the blocked entrance was studied, and the lowest values were found for the blocked-entrance HRTFs. It is concluded, that the blocked entrance is the most suitable point for measurements of HRTFs and for binaural recordings, since sound at this point includes the complete spatial information, and in addition to that the minimum amount of individual information.
Variable effects of click polarity on auditory brain-stem response latencies: Analyses of narrow-band ABRs suggest possible explanations
Authors: Don Manuel , Vermiglio Andrew J. , Ponton Curtis W. , Eggermont Jos J. , Masuda Ann
Published: October 2005

The auditory brain-stem responses (ABRs) to rarefaction and condensation clicks were obtained for 12 normal-hearing subjects in quiet, and high-pass masking at 8, 4, 2, 1, and 0.5 kHz. Derived narrow-band wave V latency differences were analyzed with respect to (1) stimulus polarity, (2) absolute differences irrespective of polarity. The analyses revealed no significant stimulus polarity effects on latency for the derived bands. Absolute latency differences regardless of polarity tended to be greater for those derived bands having lower characteristic frequencies (CFs). However, these differences were smaller than the expected half-period of the theoretical CF. Further analyses in three additional subjects using repeated runs of the same polarity indicate that this increase in absolute latency difference with lower derived band CF does not reflect a simple half-period change owing to polarity, but rather to the increase variability in measuring the peak latency of the lower CF derived bands. The variability is consistent with variability of eighth nerve PST histograms behavior observed in animal work [Kiang et al., ‘‘Discharge patterns of single fibers in the cat’s auditory nerve,’’ Research Monograph No. 35 (MIT, Cambridge, MA, 1965)]. Thus claimed polarity effects observed in other ABR work using absolute values may have been affected by this variability. It appears from these current data that half-period latency shifts of wave V owing to stimulus polarity differences are not observed in derived bands responses initiated from frequency specific regions of the cochlea.
The lack of frequency dependence of thresholds for short tones in continuous broadband noise
Authors: Dai Huanping , Wright Beverly A.
Published: October 2005

The threshold for detecting a tonal signal in a continuous broadband noise increases with increasing signal frequency for long, but not for short signal durations. This is revealed by an analysis of previous studies, and confirmed with three subjects in the present experiment using signals covering a frequency range from 125 to 4000 Hz and a duration range from 2 to 1000 ms. The relationship between threshold and signal frequency for a wide range of signal durations is explained by an energy-detector model in which the time window is assumed to match the signal duration and the predicted signal level is adjusted to compensate for the loss of signal energy due to spectral spread at short durations.
Recalibrating the perception of loudness: Interaural transfer
Authors: Marks Lawrence E.
Published: October 2005

Previous research, using both magnitude-scaling and direct-comparison methods, has shown the perception of loudness to be contingent on the distribution of tonal stimuli varying in sound frequency as well as SPL: When a low-frequency signal, f1, is presented at low SPLs and a high-frequency signal, f2, at high SPLs, loudness at f1 is great relative to that at f2; reversing the association of SPL with frequency reverses the loudness relation. These shifts in relative loudness, recently termed ‘‘recalibration’’ [Marks, J. Exp. Psychol. 19, 227–249 (1994)], are consistent with the operation of frequency-specific, fatiguelike processes at f1 and f2. Experiment 1 combined both scaling (magnitude estimation) and matching (direct-comparison) methods and showed that exposing one ear to recalibrating stimuli (500 and 2500 Hz) led to substantial shifts not only in the ipsilateral ear but also in the contralateral ear (albeit smaller ones). Experiment 2 used a selective-exposure procedure and gave similar results. Thus the processes underlying recalibration of loudness appear to involve central mediation; consequently, it is possible that processes of auditory fatigue rely on central as well as peripheral mechanisms.
Binaural masking level differences in the inferior colliculus of the guinea pig
Authors: McAlpine David , Jiang Dan , Palmer Alan R.
Published: October 2005

The binaural masking level difference (BMLD) is a striking and well-documented psychophysical effect which relates to the ability to use the phase of low-frequency sounds to dissociate them from masking noise. When identical tones and noise are presented to both ears, detectability is improved by up to 15 dB simply by inverting the phase of either the tone or noise in one ear. Measurements of BMLDs were made in single delay-sensitive neurones in the inferior colliculus of the guinea pig. These have confirmed and extended an earlier report [D. M. Caird, A. R. Palmer, and A. Rees, Hear. Res. 57, 91–106 (1991)] by demonstrating that when signals are optimized for the frequency, level, and interaural delay sensitivities of each neurone, BMLDs can be measured which are in a direction, and of a magnitude, consistent with appropriate psychophysical observations in human subjects. In addition, BMLDs were found to be consistent with the delay sensitivities of the neurones to the signal and masker, the major determinant of the masked threshold for optimized signals being the activity evoked in the neurone by the masking noise. Within-channel signal-to-noise (S/N) ratios at masked threshold for single neurones varied from +20 to −7 dB, depending on the binaural configuration and the units’ delay sensitivities. In single neurones, the size of the BMLD for optimized signals increased with the level of the noise. The BMLD increased by 5 dB over a 40-dB range of noise, consistent with psychophysical observations. This came about because as noise level increased, masked threshold for optimized tones increased more slowly in Nπ noise than in N0 noise. For all binaural comparisons, both positive (π signals more detectable, as in the psychophysics) and negative BMLDs were observed, often in the same neurone, a result entirely consistent with the sensitivity to the interaural delay of the noise and tone signals. For 500-Hz signals in zero and π phase masked by identical noise the majority of BMLDs determined with the PEST procedure was negative, a result which is taken to indicate that increases in spike rate may not be an appropriate cue for masked threshold under these conditions.
Adaptive psychophysical procedures and imbalance in the psychometric function
Authors: Saberi Kourosh , Green David M.
Published: October 2005

One class of adaptive psychophysical procedures was studied, using simulated and human observers. These procedures are those which require an increase in stimulus intensity after an incorrect response, and a decrease after k successive correct responses. This paper analyzes how step size and the value of k affect the mean and standard deviation of threshold estimates based on a k-down 1-up adaptive procedure. Computer simulations are used to study the bias in threshold estimates, which are most evident when larger step size and small values of k are used. The adaptive procedure can be characterized by a function called the imbalance of the track, the relative probability of adjusting the stimulus either up or down at equal stimulus distances from the equilibrium point. These imbalance functions can be used to understand the threshold biases obtained in the computer simulations. The computer simulations also show that the average number of reversals obtained per trial is dependent on different values of k, but are largely independent of step size. The standard error of the threshold estimates, however, varies systematically with step size, but are nearly independent of k. Finally, we compare the stability of threshold estimates for human listeners using two very different sets of parameters: a very large step size (approximately half the range of the psychometric function) with k=4, and the conventional k=3 with an initial 4-dB and a final 2-dB step size.
Internal structure of phonetic categories: Evidence for within-category trading relations
Authors: Hodgson Philip , Miller Joanne L.
Published: October 2005

Phonetically relevant acoustic properties perceptually trade against each other at phonetic category boundaries. The present investigation used a category goodness judgment task to examine whether such properties also trade against each other in specifying the best exemplars of phonetic categories. The experiments focused on the say–stay distinction, specified by F1 onset frequency and silence duration preceding F1 onset. The main experiment demonstrated a within-category trading relation, such that as F1 onset frequency increased from 230 to 430 Hz a longer silence was required for stimuli to be judged the best exemplars of stay. Two follow-up experiments explored the robustness of this effect. Taken together, the findings underscore the importance of multiple acoustic properties in specifying the internal structure of phonetic categories.
One-tone suppression in the frog auditory nerve
Authors: Christensen-Dalsgaard Jakob , Jo/rgensen Morten Buhl
Published: October 2005

Sixty-seven fibers of a sample of 401 in the auditory nerve of grassfrogs (Rana temporaria) showed one-tone suppression, i.e., their spontaneous activity was suppressed by tones. All fibers were afferents from the amphibian papilla with best frequencies between 100 and 400 Hz. Best suppression frequencies ranged from 700 to 1200 Hz. Spontaneous activities for the fibers showing one-tone suppression ranged from 3 to 75 spikes/s. Spontaneous activities above 40 spikes/s and the phenomenon of one-tone suppression itself has not been reported previously for frogs. The population of fibers showing one-tone suppression comprises 81% of all fibers with best frequencies below 400 Hz and spontaneous activities higher than 3 spikes/s, indicating that the mechanism underlying the suppression is quite general.
The frequency band-averaged wave transmission coefficient of a periodic structure
Authors: Langley R. S.
Published: October 2005

It is well known that an undamped periodic structure displays passbands and stop bands, which are frequency bands over which wave motion, respectively, can and cannot propagate. For narrow-band excitation the response of the structure will be minimized by a design which places the excitation band within a stop band. For wideband excitation the effect of the structural periodicity is not obvious, as the response will be enhanced within a passband and suppressed within a stop band. The wideband performance of a periodic structure is investigated here by considering the wave transmission coefficient of an N-bay embedded periodic system. Simple closed-form expressions are derived for the passband and wideband-averaged transmission coefficient in the absence of damping; these expressions depend only upon the amplitude of the transmission coefficient of a single joint within the system. Damping is then considered and it is shown that the wideband efficacy of a damping treatment can be significantly enhanced by structural periodicity, and a simple approximate formula for the effect of damping is derived. The analytical results are illustrated by application to an example system which represents a beam on multiple rotational spring supports.
A probability distribution for the complex field of waves propagating in random media
Authors: Ritcey James A. , Gordon Scot D. , Ewart Terry E.
Published: October 2005

A model for the joint probability density function is proposed for the quadrature components of waves propagating in random media (WPRM). The model is based on a further generalization of the model for the intensity distribution for WPRM proposed by Ewart [J. Acoust. Soc. Am. 86, 1490–1498 (1989)]. Both this distribution model and the intensity distribution model apply to the full range of scattering strengths and ranges. That is, from short ranges where the intensity probability density function (pdf) is lognormal, through the region of the medium focus, where the intensity moments 〈Iq〉 can be well above q!, to the saturation regime, where the moments approach exponential. Simulation of the complex fields used to test the model was accomplished by parabolic wave equation marching of the field through a medium with a fourth-order power law transverse spectrum (usually termed the modified exponential). The fourth moment of the fields are accurately predicted using parabolic fourth moment theory—giving some confidence in the higher moments. The resulting joint pdf’s are parametrized in terms of the scattering strength γ and the scaled range X that parametrize the simulations. This work provides a necessary first step in the important quest to include highly non-Gaussian quadrature component statistics in signal processing formulations.