bluuebunny/crossref_metadata_2025 huggingface dataset:
A large microphone array for outdoor sound propagation studies
Authors: Havelock David I.
Published: October 2005

A sound field propagating outdoors is perturbed by the turbulence in the atmosphere. To study the fluctuations due to turbulence, the sound field is measured simultaneously at a large number of points using a microphone array. The array consists of 64 microphones which can be configured in a variety of geometries ranging from small patches of only a few square meters to an elongated array spanning 700 m. Remote ‘‘satellite’’ arrays are also possible. The data are collected and processed in a mobile equipment trailer. The microphones, electronics, data collection, and processing are described and practical aspects of deploying the array are discussed. The design criteria and example applications of the array are also discussed.
Modeling and analysis of three-dimensional scattering from Arctic Ice features
Authors: Kapoor Tarun K. , Schmidt Henrik
Published: October 2005

Interpretation of low-frequency acoustic scattering data from Arctic Ice is facilitated with realistic models of the large-scale features observed under the ice sheet. Previous analyses have modeled these, for example, as a hemispherical protuberance on an an infinite plane. Here, the under-ice feature is modeled as a solid elastic sphere attached in the center of a thin elastic plate. The sphere is assumed to be completely submerged in water while the plate is assumed to be floating on water. The interaction between the plate and sphere is characterized in terms of equivalent coupling forces and bending moments at the attachment ring which are determined by matching the kinematics of the sphere and the plate at the junction. At our frequencies of interest [ka∼O(1)], the model demonstrates scattering of the sphere modes into the in-plane and out-of-plane motions of the plate. A comparison will be made between the scattered fields from the free and coupled spheres. The analytical results will also be compared with those obtained from the CEAREX89 scattering experiments conducted in the Central Arctic region with 1.8-lb SUS charges detonated at nominal depths of 800 ft. [Work supported by ONR, High Latitude Program.]
The role of segment-internal rate information in the phonetic classification of stop consonants
Authors: Bourgeois Thomas Charles , Green Kerry P.
Published: October 2005

During the course of a normal conversation talkers make frequent and extensive changes in speaking rate which affects the acoustic realization of both consonants and vowels. Previous research has shown that the articulation rate of a syllable influences both the production and phonetic categorization of its segmental components. However, little certainty exists regarding which portions of the syllable carry information about overall articulation rate. The present study investigated this question by editing the burst and aspiration phases from natural /bi/ and /pi/ syllables produced at a fast rate of speech, and cross-splicing them onto the same tokens produced at slow rates of speech (and vice versa). These tokens were presented to subjects for speeded classification of the initial consonant. The results indicate that subjects were sensitive to the mismatch in articulation rate between the initial burst and aspiration of the stop consonant and the remainder of the syllable created by the cross-splicing technique. Further investigation using /bi–pi/ continua created in a similar manner indicates that consonant-internal rate information is used during phonetic categorization of the stimuli. These results are discussed in the context of current issues of rate normalization and speech perception. [Work supported in part by Research and Training Center Grant No. P60 DC-01409 from the National Institute on Deafness and other Communication Disorders.]
Postvocalic consonant clusters in Swedish
Authors: Czigler Peter E. , Behne Dawn M.
Published: October 2005

In Swedish a postvocalic consonant is phonologically long following a distinctively short vowel and phonologically short following a distinctively long vowel. Previous research has demonstrated that this distinction is reflected in the relative durations of the corresponding segments. In addition, it has been shown that a consonant tends to be shorter in duration when it occurs in a consonant cluster than when it is a single consonant. However, when a consonant occurs in a cluster, it becomes less obvious whether it is a short or long consonant. The goal of this project is to determine whether the short–long dichotomy of consonants is acoustically realized in clusters. Target words were identified in which /k/ occured occurred in four different codas structures: C, C:, Cs, and sC. Native speakers of Swedish produced the target words in carrier sentences and the duration of the closure of /k/ and the preceding vowels were measured. The results demonstrate that the structure of a consonant cluster and its neighboring segments can affect the duration of a postvocalic consonant. These findings are discussed in terms of syllable-internal timing and the extent to which consonant duration varies within clusters.
Pitch percepts associated with amplitude-modulated current pulse trains in cochlear implantees
Authors: McKay Colette M. , McDermott Hugh J. , Clark Graeme M.
Published: October 2005

The percepts elicited by electrical stimulation of auditory neurons by trains of amplitude-modulated current pulses were studied in a group of six cochlear implant users. Modulation frequencies of 100, 150, and 200 Hz were studied, with a range of carrier rates up to 1200 Hz. It was found that all but one subject could consistently rank 150- and 200-Hz modulated stimuli by modulation frequency when the carrier rate was more than 800 Hz, but for lower carrier rates the ranking was greatly affected by the harmonic relationship between carrier and modulation frequency. Pitch matching experiments showed that the subjects generally considered the modulated stimuli to be equal in pitch to unmodulated stimuli with rates the same as, or somewhat higher than, the modulation frequency. The results showed that the ‘‘pitch’’ of pulsatile electrical stimulation resulting from periodicities in the time structure of the electrical stimulus has similarities to the ‘‘pitch’’ observed for temporal patterns in acoustic stimulation such as amplitude-modulated noise. There were some differences, however, which may be attributable at least in part to the physiological response differences for electric and acoustic stimulation.
Scattering from flexural waves on a ribbed cylindrical shell
Authors: Photiadis Douglas M. , Bucaro Joseph A. , Houston Brian H.
Published: October 2005

Monostatic scattering measurements over a ka range 2–30 made on two cylindrical shell structures, one with regular internal frames and one without, clearly demonstrate that the periodic discontinuities in the framed shell give rise to distinctive features in the scattering patterns at frequencies much lower than those at which Bragg scattering peaks can exist. These features are found to be even more dominant than those associated with the now well-known scattering from supersonic shear and compressional helical shell waves. When the measured scattering levels are displayed as a function of frequency and aspect, these features manifest themselves as curves suggestive of folded-over dispersion curves of flexural waves. It will be shown that these effects are, in fact, due to scattering from Bloch or Floquet wave packets arising from the frame-induced multiple scattering of the subsonic flexural waves. The measured scattering functions are compared with predictions based on phase matching of the acoustic waves to flexural Bloch waves whose dispersion properties are computed using an approximate model. The simple model predictions agree well with the measured scattering data.
Comparison of the envelope following response in the Mongolian gerbil using two-tone and sinusoidally amplitude-modulated tones
Authors: Dolphin William Ford , Chertoff Mark E. , Burkard Robert
Published: October 2005

Two-tone (TT) and sinusoidally amplitude-modulated (SAM) signals, although differing in spectra, are both periodic; the period corresponds to the difference between the two frequencies (f2,1=f2−f1) in the former and to the frequency of the modulation tone (fmod) in the latter. Here the results of a study comparing the steady-state electrophysiologic responses to TT and SAM stimuli recorded from Nembutal-anesthetized Mongolian gerbils are reported. In the first experiment a modulation rate transfer function (MRTF) was obtained for each stimulus type by setting the SAM carrier frequency (fc) and f1 of the TT signal at the same frequency while fmod and f2,1 were covaried. MRTFs were obtained for f1s and fcs of 1, 3, and 5 kHz, with envelopes which varied between 50 and 500 Hz in 50-Hz increments. Stimuli were presented at 75 dB peak sound-pressure level (pSPL). Responses to the two stimulus types yielded MRTFs which were very similar and generally low pass in shape. In the second experiment responses to the TT and SAM signals were recorded in the presence of a continuous interfering tone of 85-dB pSPL which was varied between 650 Hz and 3 kHz. In these experiments a maximum reduction in the response to the TT and SAM signals, measured at f2,1 and fmod as well as at fc and f1, occurred within a narrow frequency band above the frequency of the probe carrier and a broader region of reduced response extending to higher frequencies. This reduction in response was asymmetrical, spreading more to high than to low frequencies. The similarity of both MRTFs and interference response patterns supports the view that the envelope following responses to TT and SAM stimuli are manifestations of the same nonlinear phenomena.
Multipole sources in a fluid-filled borehole surrounded by a transversely isotropic elastic solid
Authors: Zhang Bixing , Dong Hefeng , Wang Kexie
Published: October 2005

In this paper, the acoustic field excited by multipole sources in a fluid-filled borehole surrounded by a transversely isotropic elastic solid is systematically analyzed and numerically simulated. Not only have the mode waves been analyzed thoroughly, but the propagation mechanism of the critical refracted P and S waves corresponding to the multipole branch cut integration for the transversely isotropic formation has also been investigated for the first time. In the presence of a fast or a slow transversely isotropic elastic solid formation, the component waves excited by a monopole, a dipole, and a quadrupole source have been studied in the time and frequency domains. It is found that the critical refracted arrival of the S wave is a dominant factor, while the mode wave is not in the low-frequency multipole direct shear wave logging. When the formation is changed from isotropic to transversely isotropic, the amplitudes of the component waves vary significantly, but the variation of the cutoff frequencies of the mode waves and the resonant frequencies of the P and S waves is less pronounced.
Effect of sequence delay on the discrimination of temporal patterns
Authors: Sorkin Robert D. , Montgomery DeMaris A. , Sadralodabai Toktam
Published: October 2005

This experiment tested listeners’ ability to discriminate between two temporal patterns as a function of the time interval between the pattern onsets. The listener’s task was to decide whether two arrhythmic sequences of nine tones had the same or different temporal patterns; the patterns were defined by the time intervals between the tones. According to the temporal pattern correlation model [R. D. Sorkin, J. Acoust. Soc. Am. 87, 1695–1701 (1990)], listeners extract information about the series of time intervals in each sequence and then compute the correlation between the two series. In the present experiment, the tones in the second sequence were presented at a different frequency than the tones in the first sequence. In one condition, all time intervals in the second sequence were compressed or expanded by a factor that varied randomly over trials. Performance was very good when the sequences did not overlap in time, but was poor when the sequences overlapped. Performance was generally consistent with a discrimination mechanism that cannot process more than one pattern at a time.
Design of active structural acoustic control systems by eigenproperty assignment
Authors: Burdisso Ricardo A. , Fuller Chris R.
Published: October 2005

The traditional design approach of feedforward control systems involves the selection of number and location of the actuators and sensors based on some physical understanding of the system. This empirical methodology yields satisfactory results for simple structures and sinusoidal inputs. However, such a heuristic approach can easily result in an inefficient control system with an unnecessarily large number of control channels for complex structures and more realistic disturbances. In this work an efficient formulation is presented for the design of actuators and sensors for structurally radiated sound reduction. The technique is based on the modification of the eigenstructure such that the system responds with the weakest set of modal radiators. The technique is applicable to both narrow-band and broadband excitations. The formulation is demonstrated for controlling the odd–odd modes of a simply supported plate driven by a point force located at the center of the plate. The radiation due to the first three odd–odd modes is reduced with a single-input, single-output (SISO) controller. The control actuator and error sensor are implemented with piezoelectric (PZT) ceramics and polyvinylidene fluoride (PVDF) films, respectively. It is shown that the design approach yields excellent global sound reduction.
Sound localization precision under conditions of the precedence effect: Effects of azimuth and standard stimuli
Authors: Litovsky Ruth Y. , Macmillan Neil A.
Published: October 2005

Minimum audible angles (MAAs) were estimated for single noise bursts, and for burst pairs that satisfied the conditions of the precedence effect (that is, produced fused images). In one burst-pair condition, the bursts to be discriminated differed in lead location; in the other, they differed in lag location. Sounds were presented over loudspeakers. MAAs were lowest for single bursts, slightly higher for lead discrimination, and much higher for lag discrimination. Presence of a standard reference burst had no reliable effect on performance. The data are interpreted using a model of Shinn-Cunningham et al. [J. Acoust. Soc. Am. 93, 2923–2932 (1993)] in which discrimination of precedence-effect burst pairs is based on the lateral position of the auditory image, which is a weighted average of the positions of the leading and lagging bursts.
Ultrasonic pressure fields due to rectangular apertures
Authors: Sahin Ali , Baker Andrew C.
Published: October 2005

The linear pressure fields generated by rectangular apertures at ultrasonic frequencies are considered, experimental results and theoretical predictions are presented both for focused and unfocused cases. Measurements were made in water using a circular transducer (38 mm in diameter) with various rectangular apertures in front of it. Focusing was achieved by the addition of perspex lenses. The aperture dimensions and focal lengths were chosen to be comparable with those encountered in medical ultrasound systems. The pressure field generated by the aperture was sampled using a 1-mm-diam bilaminar polyvinylidene difluoride (pvdf) hydrophone. Predictions for diffraction losses due to a rectangular transmitter and a circular receiver of finite size are also shown. The general behavior of the pressure field of a rectangular aperture is discussed and good agreement is shown between experimental measurements and theoretical predictions within the known limitations of both.
Bending A wave in the scattering by a circular cylindrical shell: Its relation with the bending free modes
Authors: Veksler N. D. , Izbicki J. L. , Conoir J. M.
Published: October 2005

The steady-state problem of a plane acoustic wave scattered by an elastic circular cylindrical shell is considered. The standard resonance scattering theory (RST) procedure is used for the analysis of modal resonances. The bending waves, namely A and A0 waves, are investigated in detail. At a fixed order of modal resonance n, it is possible to obtain either the A wave resonance, or the A0 wave resonance, but never both of them together. The relation between the modal resonances of the peripheral waves A and A0 and the free modes of vibration of the shell is studied by means of the variation of the density ρ of the ambient liquid. When the density of the ambient liquid tends toward zero (at unchanged sound velocity in it), the resonance frequency approaches the one of the free vibration in two different ways. If the wave associated with the free mode has a velocity greater than the sound velocity in the fluid, the A0 wave resonance frequency tends to that of the free mode. If the wave associated with the free mode has a velocity lower than the sound velocity in the fluid, the A wave resonance frequency tends to that of the free mode. The A wave, which was up to now considered as an external wave, is rather internal at a low frequency and becomes more external when the frequency increases.
Single-mode excitation in a laboratory waveguide using feedback control
Authors: Buck John R. , Johnson Mark , Preisig James C. , Catipovic Josko
Published: October 2005

Previous work formulated an adaptive algorithm for exciting a single mode in a shallow-water waveguide using feedback control [Buck etal., J. Acoust. Soc. Am. 95, 2927(A) (1994)]. This paper presents results obtained using this algorithm in a laboratory waveguide experiment under a variety of conditions. Unlike previous laboratory single-mode excitation experiments [Clay and Huang, J. Acoust. Soc. Am. 67, 792–794 (1980); Gazanhes and Garnier, ibid. 69, 963–969 (1981)], our algorithm does not require apriori environmental knowledge, but only the sound-speed profile at the feedback array. The experiment results to be presented demonstrate the algorithm’s convergence behavior and robustness to environmental mismatch. If time permits, present experimental results illustrating the ability of the algorithm to track time variations in the channel will also be presented. [Work supported by ONR and ARPA.]
Perceptual centers are affected by stress location in English disyllables
Authors: Bell Alan , Biasca Debra Halperin
Published: October 2005

The perceptual centers of English disyllables were investigated in two experiments. Six subjects participated in the first experiment, and five in the second. The first experiment compared initially stressed disyllables with five onsets whose duration varied from 4 (batter) to 180 ms (flatter). Its results demonstrated that initially stressed disyllables with longer onsets have perceptual centers that are displaced relatively further from the acoustic beginning of the word by about the same amount as the difference in the onset durations, in agreement with earlier research on English monosyllables [e.g., A. Cooper, D. Whalen, and C. Fowler, Percept. Psychophys. 39, 187–196 (1986)]. The second experiment compared initially stressed disyllables with disyllables composed of a reduced first syllable and a stressed second syllable, e.g., com’mute vs ’comet, holding the total duration of all items constant. Again, longer onsets produced later perceptual centers for both stress locations, but the perceptual centers of finally stressed disyllables were later than those of initially stressed ones by about 50 ms, or roughly half the duration from the beginning of the unstressed vowel to the beginning of the stressed vowel.
Acoustic scintillation and random focusing effects in the ocean
Authors: Potter John R.
Published: October 2005

Small-scale oceanographic variability becomes increasingly relevant to acoustic propagation as the frequency of interest exceeds a few kHz. The intensity effects are generally unspectacular at very close or distant ranges; little scattering has yet occurred in the near field and stochastic limits apply in the far field. At intermediate ranges random focusing can greatly enhance the intensity in small volumetric regions. These predicted high-intensity ‘‘ribbons’’ result from an accrual of multiple forward scattering of individual wavefronts and appear in addition to multipath effects. An experiment was performed in the eastern Mediterranean during 1986 using 3.6-kHz pulses transmitted over ranges of 11–23 km to investigate this effect. Observations were made over vertical and horizontal apertures of 200–250 m and 4–4.5 km, respectively. The experiment is described and the random focusing is confirmed. The acoustic signals traveling along individual ray paths are observed to develop randomly focussed regions 6–18 dB above normal levels over regions some 1 km long and 20 m deep. The strength and size of these anomalies are consistent with predictions from multiple scattering theory. Understanding these features creates the possibility of inversion for a statistical description of the small-scale oceanography in addition to permitting constructive tactical use and improved quantitative estimates of system performance. [Work supported by ONR.]
Pulsed nonlinear Rayleigh waves
Authors: Knight E. Yu. , Hamilton M. F. , Zabolotskaya E. A.
Published: October 2005

Pulsed, plane, nonlinear Rayleigh waves in isotropic solids are investigated with numerical solutions of the coupled spectral equations derived by Zabolotskaya [J. Acoust. Soc. Am. 91, 2569 (1992)]. Calculations of waveform evolution are presented as functions of distance from the source and depth within the solid. For the case of weak nonlinearity (characteristic absorption length on the order of the shock formation distance), self-demodulation of tone bursts is investigated. Self-demodulation refers to the nonlinear generation of a low-frequency waveform by a high-frequency pulse. Comparisons are made with the analogous process in fluids. Whereas demodulated Rayleigh and acoustic waveforms have similar shapes, the demodulated Rayleigh waveforms have substantially smaller relative amplitudes. The difference in amplitude is due to the frequency dependence of the nonlinearity coefficient matrix for Rayleigh waves. For the case of strong nonlinearity, shock formation is investigated in a variety of transient waveforms. Via comparison with acoustic waveform evolution in fluids, precursors generated by certain Rayleigh waveforms are identified as consequences of nonlocal nonlinearity. [Work supported by DOE, ONR, and NSF.]
Vocalization tracking of blue and fin whales in the North Pacific
Authors: McDonald Mark A. , Hildebrand John A. , Webb Spahr C.
Published: October 2005

Arrays of seafloor seismometers provide the ability to track vocalizing marine mammals in the deep ocean over a radius of 20 km or more with position accuracy as good as several hundred meters. These tracking data can be used to infer swimming speed and apparent respiration rate, as measured by position change and by repeated pauses in the vocalization sequence. Speed and respiration rate can be compared during times of relative quiet, during the passage of large merchant vessels, and during times of man-made acoustic transmissions to evaluate possible effects of low-frequency noise. Seafloor seismometer arrays also allow study of fin whale call sequences, which often are interactions between multiple whales located several kilometers apart. That these fin whales are interacting, rather than calling independently, is suggested by: (1) consistent spacing between calls with rarely overlapping calls, (2) a distinctive spectral signature for each whale, and (3) synchronization of respiration among vocalizing whales.
On crack identification and characterization in a beam by nonlinear vibration analysis
Authors: Sundermeyer Jeffry N. , Weaver Richard L.
Published: October 2005

The weakly nonlinear character of a cracked vibrating beam is exploited for the purpose of determining crack location, depth, and opening load. The approach is motivated by examining the response of a bilinear spring-mass system to excitation at two frequencies, such that the difference between the two frequencies is the resonant frequency of the system. The numerically generated steady-state response of the system clearly betrays the presence of the bilinear spring, even if the difference between the compressive and tensile stiffness is very small. The same idea is applied to a cracked beam forced at two frequencies, with the crack providing a local bilinear stiffness in the beam. The numerically generated steady-state response shows the effect of the opening and closing of the crack. The prominence of this nonlinear effect is then correlated with crack position and depth. It is shown that the nonlinear effect is maximized if a static load is also placed on the beam that would cause the crack to be on the verge of opening, thus determining the opening load. A perturbation analysis is applied to the problem, and some preliminary experimental results are discussed. [Work supported by the Army Research Office.]
Abiotic controls on elephant communication
Authors: Larom David , Garstang Michael , Raspet Richard , Lindeque Malan
Published: October 2005

Atmospheric conditions conducive to long-range transmission of low-frequency sound as used by elephants are found to exist in the Etosha National Park in Namibia during the late dry season. Meteorological measurements show that strong temperature inversions form at the surface before sunset and decay with sunrise, often accompanied by calm wind conditions during the early evening. These observations are used in an acoustic model to determine the sensitivity of infrasound to the effects of (a) the strength, thickness, and elevation of temperature inversions, and (b) the growth and decay of an inversion typical of dry, elevated African savannas. The results suggest that elephant communication range more than doubles at night. Optimum conditions occur 1–2 h after sunset on clear, relatively cold, calm nights. At these times ranges of over 10 km are likely, with greatest amplification occurring at the lowest frequency tested. This strong diurnal cycle in communication range may be reflected in longer period changes in weather and may exert a significant influence on elephant behavior on time scales from days to many years.
Limitation on labial anticipation in [i] in a language with an [i]–[y] contrast
Authors: Fougeron Cécile
Published: October 2005

In French, the acoustic effects of anticipation of a final high front rounded vowel, [y], can be observed in a preceding [i]. This labial anticipation induces a lowering of the formants being measured (F2,F3,F4) both in the middle and, to a greater extent, at the end of the [i] in [iCny] sequences. Although significant, this contextual influence does not jeopardize the acoustic contrast between [i] and [y]. To understand the articulatory basis of these results, acoustic consequences of the gestures involved in the so-called rounding contrast between [i] and [y] are investigated through articulatory modeling. An [i]-like area function is simulated with different degrees and combinations of anticipatory lipprotrusion, reductionoftheareaatthelips, and larynxlowering. [i] allows little variation in lip gestures; beyond a limited range of coarticulation [i] shifts acoustically to the region occupied by [y]. While [i] appears to be quantal when we consider variation in tongue constriction, it shows a sensitive response to lip perturbation. In the [iCy] sequences observed, it seems that constraints on distinctiveness prevent a greater labial anticipation.
The effect of removing the fundamental component on the perception of vowel height in stimuli with varying F0
Authors: Diehl Randy L. , Fahey Richard P.
Published: October 2005

Using front vowels, Hoemeke and Diehl [J. Acoust. Soc. Am. 93, 2422(A) (1993)] found that F1−F0 Bark distance is a correlate of perceived vowel height. This finding is consistent with a suggestion that perceived vowel quality depends on the pattern of the neural ‘‘place’’ representation, rather than the absolute position of spectral peaks [Potter and Steinberg, J. Acoust. Soc. Am. 22, 807–820 (1950)]. On this view, vowel perception should be disrupted if a critical component of the place pattern is removed. In the current study, listeners identified synthetic vowels varying between /i/ and /eh/, with F0 varied orthogonally, in three conditions: in quiet, in quiet with the fundamental component removed, and in low-pass noise with the fundamental component removed. The results reported by Hoemeke and Diehl were replicated in all three conditions: Increasing F0 shifted the phoneme boundary towards the /ε/ end point. There was no apparent decrease in the size of this effect in the conditions where the fundamental component was absent. Thus the role of F0 in vowel height perception is not as a formantlike peak in the place representation of the spectrum. [Work supported by NIDCD.]
Relations between the apparent source width (ASW) of the sound field in a concert hall and its sound pressure level at low frequencies (GL), and its inter-aural cross correlation coefficient (IACC)
Authors: Okano Toshiyuki , Hidaka Takayuki , Beranek Leo L.
Published: October 2005

The influence of GL (amplifier gain the low-frequency range below 355 Hz) and IACC on ASW was determined by psychoacoustic experiments with simulated concert-hall sound fields using anechoic symphonic music presented to subjects by multiple loudspeakers. ‘‘Equal ASW curves’’ were determined for 1/1 octave band filtered source signals with mid-frequencies from 125 to 4000 Hz. The ASW’s for the upper four bands are found to be equal for the same IACC and SPL band values, indicating equal importance of those bands in determining overall ASW’s. Combinations of GL’s and IACCE3’s (average of IACC’s in the 500, 1 and 2 kHz bands) for wide-band musical source signals were determined that produced the same ASW’s. The early sound was comprised of 2 to 11 early ‘‘reflections’’ and judgments were made with and without later reverberation. It was found that both larger values of GL and smaller values of IACCE3 result in larger values of the subjectively determined ASW’s. It is shown that GL and IACCE3 jointly are physical measures of spatial impression in a concert hall and that, combined, they cover the frequency range from low to high frequencies.
High-frequency acoustic penetration of ocean sediments
Authors: Chotiros Nicholas P. , Altenburg Robert A. , Stanic Stephen J.
Published: October 2005

Two experiments were conducted to investigate acoustic penetration of ocean sediments: one in a muddy site in the Baltic Sea and the other in a sandy site in the Gulf of Mexico. In both experiments, acoustic sensors were placed in the sediment to measure the acoustic signals. The signals are processed coherently to give direction and speed of the acoustic waves. The data from the two sites give very different results. In the muddy site, the sediment sound speed is very close to that of the water, the situation in the sandy site is more complicated. The medium is treated as a poro-elastic solid governed by Biot’s theory of acoustic propagation. For the sandy site, the theory predicts two acoustic waves, one faster than the sound speed in water, and the other slower. Comparisons are made between theory and experiment. [Work supported by Office of Naval Research, under the Coastal Benthic Boundary Layer (CBBL) Special Research Program.]
Localizing broadband noise in a reverberation room
Authors: VanderVelde Timothy J. , Ow Millicent M. , Thorpe Wendy R. , Hartmann William Morris , Rakerd Brad
Published: October 2005

Sound localization experiments were performed to determine the relative importance of steady-state information and onset-transient information to the localization of broadband noise in a reverberant environment. Experiments used a source identification method with an array of 24 speakers, separated by 2 deg of azimuth, in a reverberation room (RT60≊4 s). Noise signal onsets were either abrupt, or slowly ramped, or entirely masked by other noise. The ratio of direct to reverberant sound was controlled by positioning the listener with respect to the speakers. Data showed that (1) localization of sound with abrupt onsets is particularly insensitive to direct/reverberant ratio. (2) Slowly ramped onsets allow listeners to use localization information in the weak direct sound before the reverberant field has fully formed. (3) Some listeners (all young) have remarkable ability to extract localization cues from apparently overwhelming reverberated noise when onsets are masked. Further experiments suggested that these listeners make use of cues at high frequencies where reverberated sound is minimized by wall absorption; performance for these listeners decreased dramatically when the noise was lowpassed at 5 kHz. [Work supported by the NIDCD.]
Developments in the ‘‘chopper’’ theory of rotating diffuser sideband production
Authors: Lubman David
Published: October 2005

Periodic motion of a sound reflector in a tonally excited reverberant sound field results in a multitonal reverberant spectrum consisting of symmetrical ‘‘sidebands’’ centered around the forcing frequency. This surprising and useful phenomenon does not violate linear system theory! It was first reported in 1968, late in the history of what some consider to be the ‘‘mature’’ field of architectural acoustics. It was discovered in connection with the invention of rotating diffusers (RDs), which were themselves a surprise. (Moving diffusers were shown to be the only class of diffuser that can improve spatial uniformity of reverberant sound.) Interest in RDs was spurred by their ability to improve the precision of tonal sound power determination in reverberation rooms. But neither the reason for multitonal ‘‘sidebands’’ nor their role in improving spatial uniformity was understood. Some workers pronounced sidebands to be trivial doppler shifts. Others denied their very existence, dismissing data as mere illusions of reactive sound. At the recent Sabine Centennial, this writer proposed a new ‘‘chopper’’ hypothesis to account for RD sidebands. More physically compelling than the doppler hypothesis, it shows strong potential for analytical development, and may facilitate RD design optimization. Chopper theory is reviewed and recent developments are reported.
Influence of rib resonances on the acoustic scattering from rib reinforced elastic plates
Authors: Karali Angela K. , Hayek Sabih I.
Published: October 2005

In a previous paper [A. K. Karali and S. I. Hayek, J. Acoust. Soc. Am. 95, 2805 (1994)] the analytic model for the prediction of the acoustic scattered field by infinite elastic plates reinforced with periodic arrays of line discontinuities was presented. In this paper the analysis is extended to infinite elastic plates reinforced with periodic arrays of ribs. If actual ribs are attached to a plate, instead of line discontinuities, their impedances are frequency dependent. The ribs are modeled as Timoshenko beams attached to an elastic plate, whose flexural vibrations are modeled using Mindlin’s plate theory. Analytic expressions for the rib impedances are obtained and plotted against the normalized frequency of an incoming plane acoustic wave. The rib impedances show resonances and antiresonances in the frequency range of 1 to 15 times the classical coincidence frequency of the plate. The influence of the rib impedance resonances and antiresonances on the nonspecularly reflected field is demonstrated by direct calculation of the acoustic scattered field at several critical frequencies of the ribs.
Matched-field inversion of multifrequency data
Authors: Gerstoft Peter , Hannay Dave , Gingras Don
Published: October 2005

Geoacoustic inversion using single-frequency data measured on a vertical array has become a popular method for estimating sub-bottom parameters. Inclusion of multiple frequencies in the inversions allows exploitation of both the waveguide dispersion and the different penetration into the sub-bottom at different frequencies. This is achieved, however, at the expense of greater required computing time, and more complicated processing schemes. Several approaches exist for defining a broadband object function, i.e., coherent or incoherent addition across frequencies and hydrophones. Each approach has specific requirements with regard to the recording geometry and the source spectrum. For coherent addition across frequencies not only the source spectrum but also the absolute propagation time must be estimated. When a useful object function has been defined it is optimized using genetic algorithms [P. Gerstoft, J. Acoust. Soc. Am. 95, 770–782 (1994)] for both the sediment and the geometric parameters. Different approaches are illustrated on broadband data from the Mediterranean North Elba site with center frequencies of 170 and 330 Hz. The water depth was 130 m and the source range was 5.5 km. The normal-mode code snap was used as the forward model.
Relationships between the variability of magnitude matching and the slope of magnitude level functions
Authors: Cefaratti Lisa K. , Zwislocki Jozef J.
Published: October 2005

Binaural loudness matching and intermodal magnitude matching experiments were performed to test systematically the origins of the phenomenon observed earlier that the variability of binaural loudness matches was larger when sound intensity was varied in the normal ear than when it was varied in the contralateral ear with raised threshold and loudness recruitment. In the experiments, the raised threshold and loudness recruitment were produced by masking a 1-kHz tone with narrow-band random noise. In intermodal experiments, magnitude matches were performed between the masked tone and the length of lines projected on a translucent window pan. The results are consistent with the earlier observations. They show in addition that the variability depends on the slope of the matching functions in a complicated, not previously anticipated way, irrespective of whether the functions are intra- or intermodal. More specifically, for moderate slopes, the variability in the ear with loudness recruitment decreased as the slope increased. The reverse was true for the unmasked ear or the line length—when the slope was large, the variability increased with the slope. Since the variability decreased in one ear and increased in the other, the ratio of the variabilities increased as the slope increased. When the slope was equal to one, both variabilities tended to be the same.
Observation of a reversible, medication-induced change in pitch perception
Authors: Chaloupka Vladimir , Mitchell Stephen , Muirhead Richard
Published: October 2005

This paper reports a study of an absolute pitch possessor who, upon administration of the psychoactive drug Tegratol (carbamazepine), experienced a significant change in her pitch perception. The subject’s performance both in producing, as well as in identifying, random-frequency tones was measured, covering the period of administration of the drug, as well as control periods before and after. The main effect of the drug was a downward shift of the perceived pitch as compared to the two control periods. The magnitude of the shift was observed to increase with increasing fundamental frequency of the stimulus; the average shift was about one semitone. Detailed results on the frequency dependence and time dependence of the pitch shifts are presented. This may be the first documented report of a significant, reversible change of pitch perception caused by a medication.
Active isolation of vibration with adaptive structures
Authors: Guigou C. , Fuller C. R. , Wagstaff P. R.
Published: October 2005

The problem of actively isolating the periodic vibrations of a rigid machine mounted on a supporting flexible structure is usually approached by applying the active inputs in parallel or series with the passive inputs. This has a number of disadvantages which are related to the development of a high power, compact yet stiff/active isolation unit. In this experimental work, a new approach in which the receiving structure is considered to have adaptive properties is studied. The aim is to control the transmitted vibrations by distributed arrays of piezoelectric transducers bonded to the receiving structure. The experimental rig consists of a rigid thick plate (the machine) supported at the corners by four elastic springs mounted on a thin clamped-free elastic steel plate (the receiving structure). The thick plate is driven by a harmonic force input. Response in the receiving panel is measured with a scanning laser vibrometer. Active inputs to the receiving structure are induced by three pairs of piezoceramic actuators bonded to the surface and configured to induce bending. The error sensors consist of up to two polyvinylidene fluoride (PVDF) strips attached to the panel surface in various positions. The control approach uses a two channel feedforward adaptive LMS algorithm implemented on a TMS320C25. The results show that the first three modes of the system can be controlled efficiently when driven ‘‘on resonance,’’ thus effectively isolating the vibrating structure from the ‘‘machine’’ raft input. However, when the system is driven ‘‘off resonance,’’ the vibrations of the receiving structure proved more difficult to reduce effectively. The paper presents vibration distribution of the receiving plate with and without control for a number of input frequencies as well as a variety of control transducer configurations.
Auditory facilitation: Procedural or sensory effect?
Authors: Miśkiewicz Andrzej , Buus So/ren , Florentine Mary
Published: October 2005

A few studies have reported that, under certain conditions, thresholds following exposure to a sound may be lower than those measured without prior stimulation. For example, Rubin [J. Acoust. Soc. Am. 32, 670–681 (1960)] found a 7-dB negative shift in threshold, for a 20-ms tone presented 160 ms after termination of a low-level cue tone. This ‘‘auditory facilitation’’ was obtained with an up-and-down psychophysical method. In the present study, auditory facilitation was reexamined using an adaptive, two-interval, two-alternative-forced-choice (2I, 2AFC) procedure. Thresholds were measured for 20-ms tones at 1 and 5 kHz, preceded by a 15-dB SL 80-ms cue tone of the same frequency. In addition, thresholds were measured with the cue absent. The results show that thresholds can be lower in the presence of the cue than in its absence, but the effect averages 0.5 dB or less and seems to be independent of cue-signal delay between 80 and 640 ms. Because this finding contrasts with the 7-dB facilitation, which Rubin obtained using an up-and-down method, part of his experiment was replicated and the results were essentially the same as his. The failure to find a pronounced facilitation effect with a 2I, 2AFC procedure indicates that the poststimulatory lowering of threshold found by Rubin primarily resulted from biases and criterion shifts.
Discrimination of envelope frequency in one spectral region in the presence of modulation in another
Authors: Buus So/ren , Pan Chi
Published: October 2005

This paper examines how discrimination of envelope frequency in one spectral region is affected by the presence of either correlated or uncorrelated modulation in another spectral region. Envelope-frequency discrimination thresholds, Δfe’s, for a 60-dB SPL two-tone complex centered at 2 kHz were measured in the presence or absence of an auxiliary two-tone complex at another frequency. When present, the auxiliary complex had either the same envelope as the standard signal or an envelope that was uncorrelated with both the standard and variable signal. The results show that listeners can take advantage of correlation between simultaneous envelopes in different frequency regions to improve discrimination of a small change in envelope frequency, whereas the presence of uncorrelated envelopes causes interference with discrimination. Except when the auxiliary complex and the signal are close together in frequency, the discrimination advantage afforded by the correlated auxiliaries appears to reflect across-channel envelope processing. The discrimination interference caused by the uncorrelated auxiliaries, on the other hand, may reflect primarily within-channel interaction such as peripheral masking, although a small amount of across-channel masking also is apparent.
Vocal-tract computation: How to make it robust and fast
Authors: Lin Qiguang
Published: October 2005

Numerical methods are described to speed up the frequency-domain calculation of the vocal-tract response and effectively determine the associated pole/zero patterns. These methods include algorithms to properly decompose the numerator and the denominator of the transfer function, to estimate formant patterns of a lossy vocal-tract system from its lossless counterpart by means of linear interpolation, to recover a heavily damped spectral peak by removing its neighboring formant from the true transfer function, and to utilize the information of residues at the system poles to ensure that no pole/zero is missed.
Comodulation masking release for elderly listeners with relatively normal audiograms
Authors: Peters Robert W. , Hall Joseph W.
Published: October 2005

Thresholds for the detection of a 1.0-kHz pure tone were measured in modulated and unmodulated noise for a group of nine elderly listeners, aged 62–83, with normal or near-normal audiograms, and a reference group of seven younger normal-hearing listeners. The masker was either a band of noise 128 Hz wide [approximately one equivalent rectangular bandwidth (ERB) centered at 1.0 kHz], or a band of noise 1505 Hz wide (approximately five ERBs above and five ERBs below 1.0 kHz). The noise was either unmodulated or was square-wave modulated at rates of 10, 20, 30, 40, and 50 Hz. A measure of comodulation masking release (CMR) was derived from the masking data. Because wider filters have been found to be associated with reduced CMR, auditory filter shapes were also estimated for the elderly listeners. The filters were found to be normal at the center frequencies of 800, 1000, and 2000 Hz ruling out possible confounding effects of impaired auditory filters on CMR. Masked detection thresholds were generally significantly higher for the elderly as compared to the younger listeners for both unmodulated and modulated noise. Thresholds were lower in modulated as compared to unmodulated noise masking for both elderly and young listeners. For both groups of listeners and for both narrow- and wideband masking, detection thresholds continued to increase as modulation rates were increased. CMR was not different for the elderly and young listeners and it was similarly decreased, for both groups, at higher rates of modulation.