bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and evaluation of a German sentence test for objective and subjective speech intelligibility assessment
Authors: Kollmeier Birger , Wesselkamp Matthias
Published: July 2002

A German sentence test was developed which is comprised of 20 test lists of ten sentences each. The test corpus is a selection from sentences for speech quality evaluation recorded with a male unschooled speaker. Performance-intensity curves were measured for each individual sentence in a speech-simulating babble noise with a total of 40 normal-hearing listeners. Based on these data and the phonemic transcription of the 200 sentences selected from the underlying speech corpus, 20 test lists were composed using a numerical optimization process. These 20 test lists are highly equivalent with respect to their performance-intensity curves, the number of words within each test list, the number of phonemes within each test list, and approximately the frequency distribution of the phonemes which approximates the phoneme frequency distribution of the German language. The equivalence of the respective performance-intensity curves was demonstrated in an independent experiment with 20 normal-hearing listeners. In addition, a comparison was performed between the “objective” intelligibility measurements and two “subjective” speech intelligibility rating methods employing the same materials. As a result, both subjective assessment procedures correlate highly with each other and with the “objective” procedure across sentences. This underlines the applicability and validity of the test in combination with time-saving subjective assessment methods. Moreover, the variability in performance across different sentences correlates inversely with the RMS level of the respective sentence. This indicates that an adjustment of sentence material with respect to RMS level already yields reasonably homogeneous test material with respect to intelligibility.
A comparison of quasi-continuous wave and broadband travel time techniques in the prediction of long-range reverberation
Authors: Smith Kevin B. , Cushman Erick B.
Published: July 2002

Previous work has shown that the general structure of deep ocean reverberation can be reasonably modeled using single-frequency propagation techniques. Recent results indicate that secondary, multipath influences can affect reverberation levels significantly. Primarily, these influences are observed in shadow regions of the primary, direct path ensonification. Temporal separation of these paths is required in order to distinguish these effects. This suggests that regions of the reverberation signal may not be well predicted by single-frequency quasi-cw (continuous wave) methods. In this paper, a quasi-cw method of predicting long-range reverberation is compared to an exact, two-way travel time technique. Each model assumes a simple, constant plane-wave scattering strength, thereby emphasizing the influence of propagation. Results from both models are compared to measured reverberation data from an ONR-SRP bottom reverberation experiment conducted near the Mid-Atlantic Ridge. It is shown that the single-frequency method underestimates reverberation levels on the backside of large ridge structures which act as shadow zones for all propagation paths. Returns from multipaths, however, begin to fill in these regions in time and may explain the lack of such dramatic signal drop-outs from measured data.
Analytical solutions for outdoor sound propagation in the presence of wind
Authors: Li Kai Ming , Wang Qiang
Published: July 2002

A theoretical analysis for the sound field due to a point monopole source in a fluid, layered atmospheric environment is described. The analysis has included explicitly the effect of fluid motion in the three-dimensional wave equation. The atmospheric environment is assumed to have sound-speed and vector wind-velocity profiles that either increase or decrease monotonically with height. In addition, the atmosphere is assumed to be vertically stratified. In such an environment, the solution can be expressed analytically in terms of Airy functions but the forms of solution are different for the situations of upward and downward refraction. Some sound-speed and wind-velocity profiles are amenable to exact analyses. Two notable examples are (i) a windless environment with a linear sound-speed profile; and (ii) a medium with a linear wind shear layer and a constant sound speed. These two profiles are studied analytically and compared numerically with other computational schemes. The validity of a heuristic approximation, which replaces the vector wind-velocity profile with an effective sound-speed profile, is also investigated numerically.
High-resolution analysis of the complex wave spectrum in a cylindrical shell containing a viscoelastic medium. Part I. Theory and numerical results
Authors: Vollmann Johannes , Dual Jürg
Published: July 2002

In this study the relation between frequency and complex wave number of axisymmetric wave modes in an isotropic, thin-walled, cylindrical shell containing a linear viscoelastic medium is derived. Shell wall bending and longitudinal motion are coupled in an empty cylindrical shell. When a viscoelastic medium is enclosed, the shell motion is affected by the complex bulk and shear modulus, as well as by the density of the medium enclosed. A Maxwell model is used for both complex Lamé constants λ and μ to describe the constitutive equations of the medium. By varying the complex moduli, the medium can be modeled as an inviscid fluid, an elastic material, or anything between these two extremes. The interaction of the thin-walled linear elastic shell and the viscoelastic medium is discussed numerically by calculating the complex dispersion relation. Numerical results are presented for an empty shell and a shell filled with three types of core material: an inviscid fluid, a shear dissipative fluid, and a shear elastic fluid. In a companion paper [J. Vollmann et al., J. Acoust. Soc. Am. 102, 909–920 (1997)], the experimental setup and the signal processing used to perform the high-resolution measurement of the dispersion relation are described in detail. Theoretical and experimental results are compared.
Binaural modulation detection interference
Authors: Sheft Stanley , Yost William A.
Published: July 2002

The ability to detect amplitude modulation (AM) of a tonal probe can be disrupted by the presence of modulated masking tones. Two experiments examined whether a disparity in the interaural parameters of the probe and masker can reduce the amount of interference. In the first experiment, the effects of interaural time and intensity differences were studied in separate sets of conditions. With low-frequency carriers, the detection of 10-Hz probe modulation in the presence of 10-Hz masker modulation was not significantly affected by interaural time differences. With higher-frequency carriers, dichotic stimuli were generated through combinations of diotic, dichotic, or monotic probe and masker presentations in which the probe and masker did not share a common interaural intensity difference. In these conditions, the amount of interference was affected by the interaural configuration. However, monotic level differences between the probe and masker may have contributed to the effect of interaural configuration. In the second experiment, the probe and masker were presented through separate speakers in an enclosed listening environment. Spatial separation between the sources for the probe and masker led to a small reduction in the amount of interference. When the masker modulation rate was varied with the probe AM rate fixed at 10 Hz, the extent of tuning in the modulation domain in the sound-field conditions was similar to that obtained with diotic stimulus presentation over headphones.
Speech reception thresholds in noise with and without spectral and temporal dips for hearing-impaired and normally hearing people
Authors: Peters Robert W. , Moore Brian C. J. , Baer Thomas
Published: July 2002

People with cochlear hearing loss often have considerable difficulty in understanding speech in the presence of background sounds. In this paper the relative importance of spectral and temporal dips in the background sounds is quantified by varying the degree to which they contain such dips. Speech reception thresholds in a 65-dB SPL noise were measured for four groups of subjects: (a) young with normal hearing; (b) elderly with near-normal hearing; (c) young with moderate to severe cochlear hearing loss; and (d) elderly with moderate to severe cochlear hearing loss. The results indicate that both spectral and temporal dips are important. In a background that contained both spectral and temporal dips, groups (c) and (d) performed much more poorly than group (a). The signal-to-background ratio required for 50% intelligibility was about 19 dB higher for group (d) than for group (a). Young hearing-impaired subjects showed a slightly smaller deficit, but still a substantial one. Linear amplification combined with appropriate frequency-response shaping (NAL amplification), as would be provided by a well-fitted “conventional” hearing aid, only partially compensated for these deficits. For example, group (d) still required a speech-to-background ratio that was 15 dB higher than for group (a). Calculations of the articulation index indicated that NAL amplification did not restore audibility of the whole of the speech spectrum when the speech-to-background ratio was low. For unamplified stimuli, the SRTs in background sounds were highly correlated with absolute thresholds, but not with age. For stimuli with NAL amplification, the correlations of SRTs with absolute thresholds were lower, but SRTs in backgrounds with spectral and/or temporal dips were significantly correlated with age. It is proposed that noise with spectral and temporal dips may be especially useful in evaluating possible benefits of multi-channel compression.
Experiments on acoustic streaming in a fluid layer between vibrating surfaces and amplitude-dependent damping of vibrations
Authors: Akay Adnan , Xu Zhaoshun
Published: July 2002

The dynamic behavior of a thin fluid layer between two flat, vibrating surfaces is examined experimentally. The oscillatory motion of the surfaces is shown to generate a continuous flow of fluid within the layer in the form of eddies. Damping induced by the presence of the fluid layer is found to be amplitude-dependent and related to the generation of the steady streams within the layer.
A study of the medium frequency response of sound field in a panel–cavity system
Authors: Sum K. S. , Pan J.
Published: July 2002

Vibration and absorption properties of structures which are used to form an enclosure have significant effects on the acoustical response of the enclosed sound field. Boundary structures such as panels and partitions found in real enclosures like buildings and vehicles are often elastic, thus their perturbational/coupling effect cannot be isolated from the vibrational motion of boundary-induced acoustic modes in the enclosed sound field. The effect of acoustic-structural coupling on the transient and steady-state responses of the sound field has been investigated in both low- and high-frequency ranges. In the medium-frequency range, acoustic–structural coupling problems are not well understood. In this paper, acoustic–structural interactions at medium frequencies are investigated using the modal coupling method and the effect of the coupling on the medium frequency response of the sound field in a panel–cavity system is studied. Features associated with the sound field response are then obtained when modal properties of the boundary structures are varied.
Basilar membrane nonlinearity and loudness
Authors: Schlauch Robert S. , DiGiovanni Jeffrey J. , Ries Dennis T.
Published: July 2002

Loudness matching functions for tones for persons with one shifted-threshold ear (hearing loss and noise-shifted thresholds) and one ear within normal limits were used to derive the presumed basilar membrane (BM) input–output (I/O) function in a normal ear. The comparison was made by assuming that the BM I/O function for the ear with the cochlear threshold shift has a slope of one (a linearized cochlea). The function for the normal ear was derived from the loudness matching function based on this assumption. Comparisons were made for archival basilar membrane data [M. A. Ruggero, N. C. Rich, A. Recio, S. S. Narayan, and L. Robles, J. Acoust. Soc. Am. 101, 2151–2163 (1997)] for chinchilla and archival loudness matches for long-duration tones for persons with various degrees of cochlear hearing loss [F. Miskolczy-Fodor, J. Acoust. Soc. Am. 32, 486–492 (1960)]. Comparisons were made also between BM I/O functions and ones derived from loudness matches for persons with unilateral hearing loss simulated by broadband noise. The results show a close resemblance between the basilar membrane I/O function and the function derived from loudness matches for long-duration tones, even though the comparison was between human and chinchilla data. As the degree of threshold shift increases from 40 to 80 dB, the derived BM I/O functions become shallower, with slopes for losses of 60 dB or more falling in the range of values reported for physiological data. Additional measures with short-duration tones in noise show that the slope of the loudness function and the slope of the derived basilar membrane I/O function are associated with the behavioral threshold for the tone. The results for long-duration tones suggest a correspondence between BM displacement and loudness perception in cases of recruitment, but the relation between the degree of loss and the amount of BM compression and the relation between signal duration and compression suggests that other factors, such as the neural population response, may play a role.
New symmetries and conservation laws for lossless KZK equation
Authors: Sapozhnikov Oleg A. , Kudryavtsev Andrei G.
Published: July 2002

The Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation is widely used to describe intense acoustic beams. No general analytical solution has been obtained for this nonlinear equation, so numerical methods are usually employed. Known analytical approaches are associated with various approximations. An additional powerful mathematical tool is group analysis that enables the finding of general symmetrical properties of differential equations. These symmetries help to generalize known analytical and numerical solutions, to derive new solutions, and to obtain conservation laws. In this work, results of group classification of the KZK equation with arbitrary nonlinear term are presented. It is shown that the KZK equation can be written in Euler–Lagrange form. All the classical Lie symmetries (geometric symmetries) are found and some classes of Lie–Backlund symmetries are considered. The largest number of the symmetries corresponds to the cases of quadratic and cubic nonlinearities. Besides scaling and translation groups of symmetries, there exist additional transformation groups which are not evident from the physical point of view. Examples of obtaining new solutions and deriving reduced equations are presented. New conservation laws for intense acoustic beams are obtained using the Noether theorem. [Work supported by RFBR and CRDF.]
Recent acoustical measurements in the Christchurch Town Hall Auditorium
Authors: Marshall A. Harold , Nielsen Johan L. , Halstead M. Miklin
Published: July 2002

Two significant changes have occurred in the Christchurch Town Hall during 1996-97: the original seats have been replaced with a new type and a new Rieger pipe organ has been installed behind the choir seats. A new comprehensive set of acoustic measurements has been made in the unoccupied hall. These are reported and compared in this paper with earlier measurements. A related study on the usefulness of C80 as a clarity measure in concert halls and which makes use of these results is reported in a companion paper. [This work is supported by the Marsden Fund administered by the Royal Society of New Zealand.]
Acoustical renovation of The Opheum Theatre, Vancouver Canada
Authors: O’Keefe John P. , Soulodre Gilbert A. , Bradley John S.
Published: July 2002

The Orpheum Theatre is a 2800 seat vaudeville house that was renovated for the Vancouver Symphony in the 1970s. Funds ran out prior to completion and some problematic conditions remained for the following fifteen years. Perhaps the most significant was an image shift heard on the balcony. Two focused reflections arriving at approximately 50 ms made some source locations on the stage appear to be perched in the ceiling. The efficacy of the plastic reflectors above the stage was also questioned. These and other issues were addressed with a complete set of stage and audience measurements in the full-scale room, experiments with a 1:48 small scale model, and listening tests using anechoic music convolved with the full-scale binaural impulse responses. The latter was particularly important because it allowed for reliable quantification of image shift thresholds that were unique to this room. Small scale modeling proved useful in matching the new convex reflectors’ radii of curvature to the image shift threshold. The renovation work is complete and the image shift has been completely eradicated.
The potential of lithotripter shock waves for gene therapy of tumors
Authors: Miller Douglas L. , Gies Richard A. , Thrall Brian D. , Bao Shiping
Published: July 2002

Tissue destruction by lithotripter shock-wave-induced cavitation can be effective for antitumor therapy. Since DNA transfection can be accomplished through cavitation-induced sonoporation, the potential may exist for an advantageous combination of shock wave and gene therapy of tumors. B16 mouse melanoma cells were cultured by standard methods and a luciferase reporter vector was used as the DNA plasmid. The shock-wave generation system, similar to a Dornier HM-3 lithotripter, had peak pressure amplitudes of 24.4 MPa positive and 5.2 MPa negative. In vitro exposures of cell suspensions indicated that results were greatly enhanced by leaving an air space in the exposure chambers to promote cavitation activity. For in vivo exposure, cells were implanted subcutaneously in C57BL/6 mice 10–14 days before treatment. DNA at 0.2 mg/ml and sometimes air at 10% of tumor volume was injected intratumorally before exposure. Exposure to 800 shock waves, followed by culture of isolated tumor cells for one day, yielded 1.1 (0.43 SE) pg luciferase production per 106 cells, increasing to 7.5 (2.5 SE) pg/106 cells for air injection. Significant luciferase production occurred for 200, 400, 800, and 1200 shock waves with air injection. Gene transfer therefore can be induced during lithotripter shock-wave treatment of tumors. [Work supported by NIH Grant No. CA42947.]
Effects of the structural anisotropy and the porosity on ultrasonic wave propagation in bovine cancellous bone
Authors: Otani Takahiko , Hosokawa Atsushi
Published: July 2002

Ultrasonic wave propagation in water-saturated bovine cancellous (spongy) bone has been experimentally studied in vitro by a pulse transmission technique. Fast and slow longitudinal waves have been clearly observed in the earlier investigation when the acoustic wave propagates to the direction of the trabeculae orientation [A. Hosokawa and T. Otani, J. Acoust. Soc. Am. 101, 558–562 (1997)]. In the present study, propagation speeds of the fast and the slow waves were measured as a function of the propagation angle to the trabeculae orientation. Experimental results show that the propagation speed of the fast wave and the amplitude of the slow wave depend greatly on the angle to the trabeculae orientation, and the speed of the slow wave and the amplitude of the fast wave are little affected by the angle of the trabeculae orientation. The propagation speeds of both waves were also experimentally examined as a function of the porosity. Measured results are discussed in relation to the structural anisotropy and the porosity using Biot’s theory.
Wideband acoustics spectroscopy of liquid phantoms of biological tissues
Authors: Andreev Valery G. , Pischalnikov Yury A. , Karabutov Alexander A. , Podymova Natal’ya B.
Published: July 2002

Biological tissues have a specific frequency dependence of the ultrasonic absorption and sound-speed dispersion. It makes fruitful the diagnostics of tissues by studying these parameters. It is necessary to carry out the spectroscopic investigation in a wide frequency band in a real time. Pulsed laser ultrasonic spectroscopy is the most useful technique to solve this problem. The method of wideband acoustic spectroscopy with laser thermo-optical source is proposed. A Q-switched YAG-Nd laser was explored to excite the short acoustic transients (pulse duration 12 ns, amplitude up to 8 MPa) by an especially produced thermo-optical generator. The acoustic transients transmitted through the medium under the testing were detected by a wideband transducer (frequency band 2–350 MHz). The absorption of ultrasound was calculated by FFT. The absorption in glycerol, acetic acid, and butanediol was investigated in a frequency band 2–50 MHz. The spectra of relaxation times were calculated. [Work supported by RFBR and CRDF.]
Noise diagnostic and reduction of a scooter engine motorcycle
Authors: Lu Cho H. , Cheng Jen C.
Published: July 2002

This paper presents an appropriate way to reduce the noise of a scooter engine motorcycle. In order to investigate the noise contribution of each engine component, the lead covering method was used to rank the noise source. With the noise spectra from measuring the pass-by noise and releasing the lead cover on each component sequentially, the correlations between specific frequencies and each component of the engine were found. Furthermore, the noise characteristics of all components were cataloged into the airborne noise and the structure-borne noise. In this research, it was shown that the airborne noise was usually coming from the air cleaner or muffler. Additionally, the power transmission mechanism like CVT or crankcase generated the structure-borne noise. Based on the diagnostic results above, some modifications of the motorcycle had been done, for example, isolating of the CVT-cover and the crankcase-cover, fixing of high density material at the air cleaner box and adding another layer around the exhaust pipe. For the pass-by noise measurement, it was shown that the noise level of the scooter was reduced by 2.5 dB(A). [Submitted For Noise ‘‘Outstanding Young Presenter’’ Paper Award.]
Pulse width and shape in single bubble sonoluminescence
Authors: Gompf Bruno , Nick Gerald , Pecha Rainer , Eisenmenger Wolfgang
Published: July 2002

To test the different theoretical models describing the light emitting process in SBSL measurements of the width and shape of the emitted light pulses are essential. The light pulses have been characterized by two independent methods: with time-correlated single photon counting and with a streak camera. Both methods lead to the same results. The pulse width strongly depends on the parameter’s driving pressure, gas and gas concentration and temperature and varies between 60 ps and more than 300 ps, and there is no difference between the red and uv part of the spectrum. The streak camera results additionally show that the pulse shape is slightly asymmetric with a steeper ascent and a slower descent. This asymmetry increases with decreasing temperature.
Planar backward projection of transient fields obtained from optical imaging methods
Authors: Clement Gregory , Liu Ruiming , Letcher Stephen , Stepanishen Peter
Published: July 2002

A polarimetric fiber-optic detection system is used to reconstruct the field in front of a planar source. The field is then back-projected toward the source using a filtered wave vector/frequency domain method. This method is compared with a second temporal projection technique that records data over space at a specific time and projects the field to an earlier time. Numerical results will be presented to illustrate the two methods. Experimental results from a pulsed ultrasonic transducer will be presented and discussed.
Minimum bandwidth required for speech-reception by normal-hearing and hearing-impaired listeners
Authors: Noordhoek Ingrid M. , Houtgast Tammo , Festen Joost M.
Published: July 2002

A new adaptive test has been developed to determine the bandwidth of speech (with a center frequency of 1 kHz) required for 50% intelligibility. Measuring this speech-reception bandwidth threshold (SRBT), in addition to the more common speech-reception threshold (SRT) in noise, may be useful in investigating the factors underlying impaired suprathreshold speech perception. A wider-than-normal SRBT points to a deterioration in suprathreshold sound processing in the 1-kHz frequency region. Both the SRT in noise and the SRBT were measured for 10 normal-hearing and 34 hearing-impaired listeners. To keep the speech signal above hearing threshold for all frequencies, speech and noise spectra were shaped to fit in the dynamic range of individual listeners. The average SRBT of the normal-hearing listeners was 1.4 oct. Most hearing-impaired listeners needed a wider bandwidth to reach 50% intelligibility. Some wider SRBTs were predicted by the SII model (speech intelligibility index) from a high presentation level or narrow dynamic range. The remaining differences between the performance of normal-hearing and hearing-impaired listeners are probably caused by an impaired suprathreshold sound processing in the 1-kHz frequency region. [Work supported by the Foundation ‘‘Heinsius-Houbolt Fonds.’’]
Acoustic properties of English fricatives
Authors: Jongman Allard , Sereno Joan , Wayland Ratree , Wong Serena
Published: July 2002

A fundamental issue in speech research concerns whether distinctions in terms of place of articulation are more succesfully captured by local (static) or global (and/or dynamic) properties of the speech signal. While most studies of place of articulation have investigated stop consonants, it is uncertain whether these properties can successfully classify fricatives. In the present study, both static and dynamic metrics were used to investigate place of articulation in fricatives. Static metrics include spectral peak location, noise duration, and noise amplitude; dynamic metrics include relative amplitude, locus equations, and spectral moments. Twenty speakers produced the fricatives /f, v, θ, ð, s, z, ∫, ȝ/ followed by the vowels /i, e, æ, ɑ, o, u/. Preliminary results based on ANOVA and discriminant analysis suggest that all metrics could distinguish nonsibilant /f, v, θ, ð/ from sibilant /s, z, ∫, ȝ/. In addition, spectral moments separated /s, z/ from /∫, ȝ/ with about 95% accuracy and /f, v/ from /θ, ð/ with about 65% accuracy while locus equations only served to separate labiodental /f, v/ from all other fricatives. Accuracy of the metrics will also be compared to human perception data. [Work supported by NIH.]
Auditory scene analysis by European starlings (Sturnus vulgaris): Perceptual segregation of tone sequences
Authors: MacDougall-Shackleton Scott A. , Hulse Stewart H. , Gentner Timothy Q. , White Wesley
Published: July 2002

Like humans, animals that use acoustic stimuli to perceive their world ought to be able to parse the auditory scene into functionally significant sounds. The ability to do so ought to have significant adaptive value when, for example, an animal can identify the sounds of a predator among other natural noises. In earlier work it was shown that a species of songbird, the European starling, can identify excerpts of both its own song and songs from other avian species when the songs are mixed concurrently with other natural signals. In this experiment it is demonstrated that starlings can segregate two synthetic pure-tone sequences when the sequences differ in frequency. Taken together, the experiments show that at least one nonhuman species is capable of auditory scene analysis both for natural and for non-natural acoustic stimuli. This suggests in turn that auditory scene analysis may be a general perceptual process that occurs in many species that make use of acoustic information.
Enhancement of the transient-evoked otoacoustic emission produced by the addition of a pure tone in the guinea pig
Authors: Withnell Robert H. , Yates Graeme K.
Published: July 2002

This study examined the transient-evoked otoacoustic emission obtained in response to a click stimulus presented in combination with a pure tone in the guinea pig. Low-pass filtered click waveforms were digitally generated using a sin(t)/t function windowed over 3 ms with an elevated cosine envelope. Transient-evoked otoacoustic emissions were obtained using the nonlinear derived response technique. Phase locked pure tones of various frequencies at ∼70 dB SPL were electrically mixed with electrical clicks, with the pure tone present only for the three lower level stimuli in the train of four stimuli. Enhancement in the amplitude of the response spectrum at frequencies which corresponded to regions of the basilar membrane apical to the tone was observed with the addition of the tone. This finding is inconsistent with the transient-evoked otoacoustic emission being the result of independent generators. It suggests that intermodulation distortion energy may contribute to the transient-evoked otoacoustic emission, the enhancement in the emission response spectrum at frequencies below the pure tone being a result of a complex interaction on the basilar membrane of intermodulation distortion products.
Extracting in-plane bistatic scattering information from a monostatic experiment
Authors: Hines Paul C. , Crowe D. Vance , Ellis Dale D.
Published: July 2002

Acoustic backscatter data were collected from the ocean bottom at four sites on the Sohm Abyssal Plain. The bottom sediment at the four sites varied from mud/clay to silt/gravel. Using a simple array consisting of a free-flooding-ring projector which was omnidirectional in azimuth, and an omnidirectional hydrophone, data were collected over the frequency range of 800–2400 Hz [Hines and Barry, J. Acoust. Soc. Am. 92, 315–323 (1992)]. To obtain sufficient signal-to-noise ratio without impairing spatial resolution, 200-Hz-wide linear FM pulses were employed. By deploying the array at a height of 500 m above the seabed, bottom backscatter data were obtained at grazing angles down to 4 degrees before the onset of the first surface return. For data arriving after the first-bottom–first-surface interaction, the geometry approximates an in-plane bistatic experiment. Estimates of the in-plane bistatic scattering strength were obtained for pairs of incident and scattered grazing angles (φi,φs)<(50 degrees,88 degrees), at frequencies of 900, 1200, and 1600 Hz. At one site the grazing angle dependence matched Lambert’s rule; at all other sites the data exhibited a steeper slope than that of Lambert’s rule. There was insufficient data to extract the frequency dependence. The fathometer returns were used to estimate the normal-incidence bottom loss at the four sites. The measured bottom loss ranged from a low of 2 dB to a high of 16 dB. The in-plane bistatic data and the monostatic data were compared to examine the validity of the separable and half-angle approximations [Ellis and Crowe, J. Acoust. Soc. Am. 89, 2207–2214 (1991)]. The separable approximation provided a reasonable fit to the data at three of the four sites; the half-angle approximation did not match the data well at any of the sites.
The influence of broadband noise on the precedence effect
Authors: Chiang Yuan-Chuan , Freyman Richard L.
Published: July 2002

This study examined the influence of background noise on the localization of lead-lag noise-burst pairs and on echo threshold for the same stimuli. Experiments were conducted in an anechoic chamber with a leading stimulus delivered from a loudspeaker at 45° to the right of center and a lagging stimulus from 45° left. Lead and lag stimuli were 4-ms bursts of Gaussian noise. In experiment 1, with lead and lag at equal levels and the lag delay fixed at 2 ms, the perceived location of the image produced by the lead-lag stimulus was estimated from subjects’ left/right judgments relative to bursts from a “comparitor” loudspeaker whose position could be adjusted. In experiment 2, the dominance of the leading burst on perceived location was measured by determining the increase in level of the lagging burst necessary to produce an image estimated to be centered at 0° azimuth. Experiment 3 was concerned with echo threshold. Subjects reported whether or not they heard a sound in the vicinity of the lagging loudspeaker as the lag-burst delay was varied. In all three experiments, data were obtained for four to five stimulus levels in quiet and for three levels of background white noise from a loudspeaker at 180°. The results revealed a substantial weakening effect of background noise on the precedence effect in experiments 2 and 3, and a nonsignificant effect in experiment 1.
A least-squares spectral element method for sound propagation in acoustic ducts
Authors: Lin Wen H.
Published: July 2002

This letter presents a novel numerical method and results for sound waves propagating in two-dimensional acoustic ducts without a flow. The method is based on a least-squares finite-element formulation to solve the two-dimensional Helmholtz equation with acoustic boundary conditions. Numerical calculations were obtained for sound waves propagating in an acoustically lined duct and in a rigid duct with a 90-deg bend. The exact solution and the boundary element solution of the acoustically lined duct were also obtained to validate the proposed numerical algorithm. Sound pressures computed by the present method agree very well with the exact and BEM solutions.
Long-range acoustic detection and localization of blue whale calls in the northeast Pacific Ocean
Authors: Stafford Kathleen M. , Fox Christopher G. , Clark David S.
Published: July 2002

Analysis of acoustic signals recorded from the U.S. Navy’s SOund SUrveillance System (SOSUS) was used to detect and locate blue whale (Balaenoptera musculus) calls offshore in the northeast Pacific. The long, low-frequency components of these calls are characteristic of calls recorded in the presence of blue whales elsewhere in the world. Mean values for frequency and time characteristics from field-recorded blue whale calls were used to develop a simple matched filter for detecting such calls in noisy time series. The matched filter was applied to signals from three different SOSUS arrays off the coast of the Pacific Northwest to detect and associate individual calls from the same animal on the different arrays. A U.S. Navy maritime patrol aircraft was directed to an area where blue whale calls had been detected on SOSUS using these methods, and the presence of a vocalizing blue whale was confirmed at the site with field recordings from sonobuoys.
Ultrasonic interferences in polymer plates
Authors: Juliac Etienne , Arman Jacques , Harran Daniel
Published: July 2002

Reflection and transmission of an ultrasonic beam by a homogeneous polymer plate (PMMA) immersed in water are studied experimentally and theoretically by the interference method. The elementary waves which emerge from the plate after 0, 1, or 2 internal reflections on the lower interface are considered individually, and their amplitude and phase shift are calculated. The interferences between these elementary waves provide the resulting waves reflected and transmitted by the plate. This method is valid because only a small number of these elementary waves have a significant amplitude when they emerge, due to the relatively high wave attenuation of polymer materials. For a 2-mm-thick PMMA plate, for example, only two internal reflections on the lower face must be taken into account for the reflection by the plate, and one for transmission. Perfect agreement with results from the classical global method confirms the validity of the interference method. This treatment enables us to better understand the physical significance of the reflection and transmission curves by the plates. Moreover, this method facilitates the calculation of accurate ultrasonic parameter values of the plate (velocities and attenuation coefficients of the longitudinal and transverse waves), by adjustment of the theoretical to the experimental reflection and transmission curves.
Initial evaluation of the dominant mode rejection beamformer
Authors: Redheendran Tina M. , Gramann Richard A.
Published: July 2002

Long integration times are needed to give accurate cross-spectral matrix (CSM) estimates; however, integration times must be short enough so that the dynamic behavior of the noise described by the CSM is captured. The dominant mode rejection (DMR) beamformer, described by Owsley and Abraham, calculates adaptive weights based on a reduced rank (CSM) estimate, where the CSM estimate is formed with a subset of the eigenvalues containing the largest eigenvalues and their eigenvectors. Thus the integration time required to obtain this CSM estimate is reduced, as the largest eigenvalue/eigenvector pairs are estimated much more rapidly than the smaller ones. The purpose of this study was to determine whether performance comparable to a fully adaptive beamformer could be achieved with the DMR beamformer, without the potential penalties associated with requiring the increased integration time for the CSM. Data acquired with bottom-mounted horizontal line arrays, in both deep- and shallow-water environments, were used to test the dominant mode rejection beamformer performance. Appropriate DMR parameters were found using the deep-water data so that the DMR performance emulated the performance of a fully adaptive beamformer with a white-noise gain constraint. Additional processing performed on the shallow-water data showed that the DMR beamformer had equivalent performance to a robust fully adaptive beamformer, but with much less output power bias at small integration times.
Reflection and diffraction in room-acoustic modeling
Authors: Baan Jan , de Vries Diemer
Published: July 2002

Many programs for room-acoustic modeling are based on the mirror image source concept. This way, only specular reflections are taken into account such that the resulting wave field is incomplete. Nonspecular reflections, or diffraction phenomena, can be added using an algorithm based on Pierce’s theory. Then, the true wave field is significantly better approximated. However, comparison of both results reveals that, averaged over time and space, the energy is equal in both cases: the added diffraction field so strongly interferes with (i.e., is so strongly correlated with) the specular reflections that no energy is added. This intuitively surprising result can be argued with a thought experiment. In this context, taking into account that acoustic perception is described with energetic criteria (clarity, definition, lateral energy fraction, etc.), it should be critically reconsidered as to how far the physically incomplete mirror image source programs are adequate for the prediction of the global acoustic quality of a hall.
A Helmholtz resonator with elongated orifice
Authors: Randeberg Rolf T. , Kristiansen Ulf R. , Vigran Tor E.
Published: July 2002

For panel absorbers there is an increasing trend toward a design not utilizing fibrous components. For the distributed Helmholtz type of resonator absorbers, the challenge is to increase the natural losses, making the absorbers reasonably broadbanded. In this paper a new type of distributed resonators is investigated. Using a double-plate construction, the resonator necks have been substantially elongated in the lateral direction, while their widths have been kept small. Thus the viscous losses in the resonator necks have been increased compared to traditional resonators. Measurements are compared with a theoretical model using analytic solutions for the slit impedances, the end corrections, and the resistance of the inner and outer surfaces. For the volume between the plates, a finite-difference approach is used. The results show a high dependency on the plate separation, and to attain high absorption over a broad frequency range, this separation should be on the order of one boundary layer.
A seamless absorbing ceiling with a smooth surface: Álvaro
Authors: Commins Daniel E. , Wilhelmi Frank H.
Published: July 2002

The use of absorbing ceilings is generalized. Contemporary architecture, in many cases, does not relish the use of ‘‘classical’’ absorbing ceilings of the perforated or slit type. Some manufacturers have developed smooth absorbing ceilings that can cover large areas without seams. Until today, the finish of these ceilings was unacceptable wherever a perfectly smooth surface was required. Improving on existing technology has led to a new type of ceiling: its surface is quite similar to a stucco or plasterboard finish, but its absorption coefficient is of the order of 0.5 over the full frequency range. The quality of the finished surface depends on the material itself and the quality of construction. Examples will be shown. In addition, this new type of ceiling has been mixed with other materials such as stucco, wood, fiberglass, and even loudspeakers. It has been shown in a full-size test model that it is possible to apply the same finish to all these materials, thus making the transition between the various components invisible. The absorptive and reflective parts of a wall or ceiling become undistinguishable. This ceiling has been named Álvaro since it was developed with the active input of Architect Álvaro Siza.
Approximation of dummy-head recording technique by a multimicrophone arrangement
Authors: Tohtuyeva Nataliya , Mellert Volker
Published: July 2002

Head-related recording and reproduction systems rely on the two-ear microphones of a dummy head. However, the dummy head is sometimes difficult to use, e.g., due to size and weight. Additionally, its geometry, which gives the important diffraction pattern information for sound localization, is fixed. A microphone array, which approximates the head-related transfer functions, has fewer restrictions. Theoretical evaluation of a simple microphone array, which takes psychoacoustic-determined frequency weights for phase and magnitude into account, is presented. Results of practical sound localization test with this array are reported for sound sources in the horizontal plane. [Work supported by the German Science Foundation (DFG).]
Electrical compensation of the microphone sensitivities in a dual microphone directional hearing aid
Authors: Thompson Stephen C.
Published: July 2002

Hearing aids with directional sensitivity have shown enhanced user satisfaction for their improved performance in noisy environments. One way to achieve the directional response patterns is to use two omnidirectional microphones with the necessary beamforming electronics to form a beam with the desired directionality. Proper operation of the beamforming circuitry requires that the frequency-dependent sensitivities of the two microphones be accurately matched, or corrected, in both magnitude and phase. This paper presents a method of electrically compensating the response of the two microphones to provide an accurate match for beamforming without the need for special sorting of the pairs for matched response. The circuit is suitable for field recalibration if aging causes the sensitivities to vary, and can also be implemented as an adaptive circuit to update the compensation parameters with time for any slow drift with time.
Contributions of spectral resolution to speech recognition in noise
Authors: Shannon Robert V. , Fu Qian-Jie
Published: July 2002

Plomp’s model of the speech recognition threshold (SRT) provides a remarkably good description for normal-hearing and hearing-impaired listeners. According to the model, an attenuation factor (A) and a distortion factor (D) can account for the changes in SRT with increasing noise levels. In a recent series of studies, phoneme recognition under conditions of reduced spectral representation and varying signal-to-noise conditions has been measured in both normal-hearing listeners and cochlear implant listeners. Plomp’s basic frameworks were adapted to account for these new data. Results from normal-hearing listeners showed that the reduction in spectral resolution and other spectral manipulations could be well quantified in terms of the D factor. The performance of the best cochlear implant user was similar to that of normal-hearing subjects listening to a similar level of spectral reduction, indicating that the D factor in the spectral domain alone could be used to account for the performance in noise of these cochlear implant users. However, some of the cochlear implant listeners had poorer performance than processor-matched normal-hearing subjects, suggesting that the distortion factor in the amplitude domain, such as distorted loudness growth introduced by acoustic-to-electric amplitude mapping, should also be considered. [Work supported by NIH.]
A complete energy conservation correction for the elastic parabolic equation
Authors: Collins Michael D. , Siegmann William L.
Published: July 2002

A complete energy conservation correction is derived to improve the accuracy of the elastic parabolic equation for range-dependent problems. The correction is complete in the sense that it is valid for problems involving a broad spectrum of horizontal wave numbers. It is a linear condition that associates the incident and transmitted fields on a vertical interface with arrays of point sources having the appropriate energy flux densities. It is a generalization of a complete energy conservation correction for the acoustic parabolic equation [J. Acoust. Soc. Am. 94, 975–982 (1993)].
Can macaques perceive place of articulation from formant transition information?
Authors: Sinnott Joan M. , Williamson Trina L.
Published: July 2002

An important problem in speech perception is to determine how humans extract the perceptually invariant place of articulation information in the speech wave across variable acoustic contexts. Although analyses have been developed that attempted to classify the voiced stops /b/ versus /d/ from stimulus onset information, most of the human perceptual research to date suggests that formant transition information is more important than onset information. The purpose of the present study was to determine if animal subjects, specifically Japanese macaque monkeys, are capable of categorizing /b/ versus /d/ in synthesized consonant–vowel (CV) syllables using only formant transition information. Three monkeys were trained to differentiate CV syllables with a “go-left” versus a “go-right” label. All monkeys first learned to differentiate a /zɑ/ versus /dɑ/ manner contrast and easily transferred to three new vowel contexts /ɔ, ɛ, ɪ/. Next, two of the three monkeys learned to differentiate a /bɑ/ versus /dɑ/ stop place contrast, but were unable to transfer it to the different vowel contexts. These results suggest that animals may not use the same mechanisms as humans do for classifying place contrasts, and call for further investigation of animal perception of formant transition information versus stimulus onset information in place contrasts.