bluuebunny/crossref_metadata_2025 huggingface dataset:
Speech reconstruction from a noisy reception signal
Authors: Kazama Michiko , Tohyama Mikio , Morita Akira
Published: July 2002

Noise reduction is a fundamental issue of smart microphone systems or a hearing aid. Noise reduction by spectral subtraction has been investigated for speech signals. However, identifying whether frame is a speech or a silence portion is difficult under nonstationary noisy conditions when using this method. Extracting the desired speech based on the sinusoidal wave model [T. Quatieri and R. Mcaulay, IEEE ASSP 34, 1449–1464 (1986)] was investigated. It was confirmed that intelligible speech sound could be synthesized using only five dominant sinusoidal waves [M. Kazama et al., 5th ICSV 2079–2086 (1997)]. In this article, a new noise reduction method by extracting the dominant sinusoidal waves in each frame (32 ms) according to the energy ratio of the signal to noise was proposed. The signal-to-noise ratio was improved by 10 dB (S/N ratio) when the original S/N ratio was 0 dB. Speech quality could also be improved by reconstructing the higher harmonics from the noisy vowels using the frame-dependent comb filters. This reconstructed speech sound will be demonstrated at the presentation. This method might implement a fundamental technology of the smart microphone systems, including hearing aids. [Work supported by Housou Bunka Fund.]
Envelope filtering of signals in the modulation frequency domain and evaluation of fluctuation strength
Authors: Walter Cord , Weber Reinhard
Published: July 2002

Fluctuation strength assessments with predefined envelope variations are commonly performed with synthesized modulated sounds. The intent of the present study is to change gradually the variability of recorded signals’ envelopes for subsequent fluctuation strength evaluations. Manipulation of a signal’s envelope was achieved by implementing a filter in the modulation frequency domain. Making use of an algorithm developed by R. Koch [B. Kollmeier and R. Koch, J. Acoust. Soc. Am. 95, 1593–1602 (1994)], time signals are transformed into (waterfall-like) bandpass-time signals (bandwidth 86 Hz) by calculating the spectra of successive frames. From the time-dependent envelopes of the bandpasses, modulation spectra are computed and filtered. Time signals with changed envelopes are resynthesized from the filtered modulation spectra by reversing the former processing stages. The fluctuation strength of the original and modified time signals was computed and compared with the subjective assessments. The results of this comparison are used to validate an algorithm for fluctuation strength calculations of recorded signals.
Naturally occurring sources of infrasound
Authors: Bedard Alfred J.
Published: July 2002

There are growing numbers of potential applications for infrasonic observing systems. The evolving International Monitoring System for the nuclear test ban treaty (including 60 infrasonic stations) offers exceptional opportunities to make infrasonic data sets widely available and to explore their uses in geophysical studies. This is especially true because of the ability to perform synergistic studies with seismic and hydroacoustic systems in a processing environment where diverse data sets can be readily melded. Natural infrasound sources such as avalanches, earthquakes, geomagnetic activity, meteors, ocean waves, severe weather, turbulence, and volcanoes offer great resources for international cooperative research programs. Sources of low-frequency sound from civilization processes offer a set of parallel opportunities. This paper will review the broad range of investigations possible using both individual and multiple infrasonic observing systems, as well as infrasonic systems in combination with other remote sensing systems.
Temporal variability in the propagation of infrasonic waves over Hawaii and Alaska
Authors: Garces Milton , Lindquist Kent , Hansen Roger , Drob Douglas , Picone Michael
Published: July 2002

Temporally varying atmospheric temperature and wind velocity data from ground level up to heights of 250 km are used to compute travel time curves and azimuth deviations for acoustic waves propagating over the CTBT infrasonic array sites of Hawaii and Alaska. An enhanced formulation of the tau-p method [Garces et al., Geophys. J. Int. (1998)] permits theoretical estimates of travel times and azimuth deviations for infrasonic waves traveling through a stratified, windy atmosphere. Atmospheric data for the season of Winter is obtained from the Naval Research Laboratory MSISE-90 and HWM-93 models, which include tidal and geomagnetic effects. These data will be supplemented with ground-based and satellite-based atmospheric data. An ensemble of circumstances, encompassing infrasonic wave propagation through anomalous environmental conditions as well as studies on site-specific effects, will be presented. Based on the predicted phases, effective detection and source inversion algorithms will be developed at each array.
High-resolution measurements of the angle-of-arrival of infrasonic signals in the range 0.5–5 Hz
Authors: Liszka Ludwik
Published: July 2002

The method used in the present study is a further development of the threshold filtering technique. Signals are transformed using the Morlet wavelet and a sliding window in the domain of the wavelet coefficient magnitude (spectral density). The procedure results in an ampligram, a graph demonstrating the amplitude and phase of components of the signal corresponding to different spectral densities. The ampligram may be further used to determine the number of independent components of the signal using the principal component analysis. The method offers a possibility to detect the statistical properties of signal components: stochastic and deterministic components may be easily distinguished. The most important applications for infrasound measurements are nonlinear filtering of the signal, extraction of weak deterministic components outside the working range of microphone, extraction of different propagation modes, and high-resolution measurements of the angle-of-arrival. The application described here facilitates measurements of the angle-of-arrival for each propagation mode separately.
On temporal and spatial variations of infrasonic signals at long distances from surface explosions
Authors: Kulichkov Sergey N.
Published: July 2002

Temporal and spatial variations of infrasonic signals at the long distances from surface explosions are discussed. The experiments were performed in different seasons during 1989–1991. Surface explosions with yields of 20–70 tons were realized one to two times in a month in runs of four to ten explosions with 10–20-min intervals between them. The receivers were placed both in the zone of acoustic shadow and in the zone of acoustic audibility at the distances about 300 km from the explosions. Signals from more than 60 explosions were recorded. It was observed that the characteristics of infrasonic signals from similar explosions can vary sufficiently both during one hour and during one day. The variations of those during different seasons were observed too.
Cell noise at the output of a MFP beamformer in shallow water
Authors: Booth Newell O. , Schey Phil W. , Abawi Ahmad T.
Published: July 2002

Measurements of ambient noise in search cells at the output of linear and adaptive beamformers are presented for data from three arrays deployed simultaneously in the SWellEX-96 experiment (200-m water depth off San Diego, CA). Previous papers by the authors have demonstrated the application of matched-field processing (MFP) to the detection and localization of submerged acoustic sources using the SWellEX-96 arrays. In this paper, the arrays (horizontal, vertical, and tilted-vertical lines) were processed to obtain cell noise spectra in noisy and quiet regions of the range, depth, and azimuth search space. Array noise gain measurements quantitatively compare the noise rejection capability of the arrays and processing methods. Frequency, integration time, array orientation, number of elements, and aperture are important parameters. Results are presented for linear and adaptive beamforming methods using plane-wave, focused plane-wave, and MFP steering vectors. [Work sponsored by the Office of Naval Research.]
Objective function particularity for shallow water waveguide parameter estimation procedure
Authors: Pudovkin Alexey A.
Published: July 2002

The acoustic field observable parameter values and its acoustic field model predictions were compared, when one desired to estimate model parameters. The measurement was completed when its error was known. It is a preferred tool for analysis to describe statistically disalignments of the model predictions and experimental observations; then one tries to avoid it by creating a sophisticated physic model. Stochastic description acceptability is checked by stochastic hypotheses test (SHT). One tests the hypothesis which was used for objective function (OF) conformation, for instance, by maximum likelihood (ML) tenet. The more disalignment, the bigger OF value for acceptable OF. The model parameters are estimated by OF minimization. The ML OF modification is proposed by penalty function (PF) method. The PF takes into account hypothesis test results, which implicate an acceptable physical–stochastic model of the waveguide acoustic field. If SHT does not give cause to reject the acoustic field formation model on acceptable significance level, then it is possible to calculate the estimation error with the use of ML OF and PF. The measurement implementation main difficulty provided for the model finding. This model ought to be rather simple to calculate the error, but at the same time rather complete to describe disalignments correctly.
Matched-field depth discrimination with active sonar
Authors: Hickman Granger W. , Krolik Jeffrey L.
Published: July 2002

This paper concerns the problem of estimating target depth in a shallow ocean using multiple pings from a low-frequency active sonar. Although much work on passive range-depth source localization using full-wave propagation models has been published, little attention has been given to the active sonar problem because of the difficulty in modeling target reflection characteristics. In this paper, active MFP is achieved without knowledge of the target’s backscatter coefficients. By assuming the target’s aspect and depth are relatively constant during its track, a MFP range-depth estimate is obtained by modeling the changes in the unresolved coherent multipath returns from ping to ping. The MAP range-depth estimate involves a dynamic programming procedure which uses a Markov model of changes in the target backscatter coefficients from ping to ping. Preliminary simulation results suggest that the target depth can be resolved (after approximately ten pings) to within 10 m in a water column 215 m deep. [Work supported by ONR.]
The evolution of tympanate hearing from proprioceptors in ancient grasshoppers
Authors: Roemer Heiner , van Staaden Moira J.
Published: July 2002

The ears of modern insects occur on rather different body parts, from head, to thorax, to abdomen, and there is evidence from comparative anatomy and embryology in divergent taxa that they have evolved from proprioreceptors responding to stretch or vibration. Receptor cells of these ears are directly or indirectly coupled to thin cuticular membranes (tympana), which are considered to play important roles in sensitivity and frequency tuning of such ears. This report is on a new set of hearing organs in an ancient grasshopper (Bullacris membracioides) without the typical tympanum, but a sensitivity exceeding most tympanate ears. As a result, males are capable of signaling acoustically over up to two km. In addition, within single individuals of this species, six pairs of serially repeated abdominal ears exist which all respond to biologically relevant frequencies and intensities. Altogether, anatomical comparison and results of neurophysiological and behavioral experiments provide strong evidence for the transition in function from proprioreception to airborne sound reception, and for the selective advantage during the evolutionary development of a complex ear structure. [Work supported by Austrian Science Foundation.]
Wavelet decompositions versus singular value decomposition (SVD) in a fish target strength estimation
Authors: Moszynski Marek , Stepnowski Andrzej
Published: July 2002

The fish target strength estimation when using acoustic echoes from a single-beam echosounder is possible after solving ill-conditioned equations where probability density functions (PDFs) of echo level, target strength, and beam pattern are involved. The modified singular value decomposition (SVD) algorithms are typically used in such cases. Unfortunately, this technique often leads to artifactual modes in solution due to Fourier nature of underlying eigenfunctions. The expectation maximization smoothing (EMS) method is used to improve smoothness of solution but by the cost of increasing the time of computation of estimates. D. L. Donoho (1995) proposed the wavelet-vaguelette decomposition (WVD) as being well suited for solving ill-conditioned equations with inhomogeneous functions. This concept was extended to fish target strength estimation and obtained results were compared to SVD performances.
Thermal effect of ultrasound enhancer for transdermal insulin delivery
Authors: Park E. J. , Yoon S. W.
Published: July 2002

Ultrasound has been known as a good enhancer for transdermal drug delivery. However, major mechanisms in the ultrasound enhancer to improve the transdermal drug delivery were not well understood. In this study a simple experiment was designed to simulate the human skin system with rat back skin. An unfocussed 1-MHz ultrasound transducer and a heating wire loop were used as enhancers. Transmitted amounts of insulin with the ultrasound enhancer were increased ten times more than those without any enhancer. The ultrasound enhancer also improved by 25% the enhancement of insulin transportation compared with that due to thermal effect solely by heating wire loop. It was also observed that rapid temperature increase with ultrasound more efficiently enhanced transdermal transport of insulin. The thermal effect of the ultrasound enhancer is suggested as a most likely mechanism for transdermal insulin delivery.
A new deep-submergence broadband multiport underwater sound transducer
Authors: Butler John L. , Butler Alexander L.
Published: July 2002

The back radiation from a transducer is normally isolated from the front radiation in order to avoid cancellation due to the out-of-phase nature of the back radiation. However, this isolation is difficult to achieve if the transducer is broadband and operated under significant ambient pressure encountered in deep submergence applications. The multiport transducer (U.S. Patent 5,184,332) offers a solution to this problem by using free-flooded resonance chambers on both the front and back surfaces of the transducer. It will be shown that with these chambers the acoustic pressure cancellation is avoided and the pressure now adds at frequencies between the two resonance’s (which set the bandwidth of the system). A multiport design for a coaxial set of cylinders driven by the two surfaces of a piezoelectric ring transducer will be presented. Results from finite element and circuit analysis models will be presented and shown to agree with measured results on the model fabricated by Massa Products Corporation, Hingham, MA. [Work supported in part by an SBIR through NUWC, Newport, RI.]
Recent developments of underwater acoustic transducers in China
Authors: Zhu Houqing
Published: July 2002

Some of the recent developments of underwater acoustic transducers in China, such as the Rare-Earth giant magnetostrictive (Terfenol-D underwater acoustic transducers (including 1-kHz free-flooded modified IV flextensional transducer, the 890-Hz free-flooded Terfenol-D hexagonal transducer, and the 2.7-kHz Tonpilz Terfenol-D transducer), the 500-Hz flexible disk piezoelectric high-power transducer, the 450-kHz 2-2 piezoelectric composite underwater acoustic transmitting transducer, the 1-3 piezoelectric composite hydrophone, the 100–10000-kHz polar glass ceramic hydrophone, the small-size low-frequency narrow beam hydrophone, the acoustic pressure receiver-vibration pick-up compound hydrophone, the large area PVDF hydrophone, etc., are presented in this paper.
Simulation and measurement of wall vibrations of a flue organ pipe
Authors: Kob Malte , Scholz Matthias
Published: July 2002

The question of whether the vibrations of a metal flue organ pipe contribute to the perceived sound or not is still not completely answered. One result of the research done within the GOArt (Göteborg Organ Art Center) project is that, due to the casting process and the need to save material, the baroque flue organ pipe has considerably thinner walls than a modern pipe. According to an organ builder, the pipe under test is likely to vibrate. To demonstrate the influence of the wall vibrations on the perceived sound, recordings of a blown pipe with and without damping of the wall are carried out. An FE model is created and the radiation for the case of coupled air and structural modes are calculated to enable parametric studies of the influence of the wall properties. The simulations are compared to FRF measurements using MLS excitation of a shaker, laser vibrometer velocity measurements, and subsequent modal analysis. The results indicate that some structural modes significantly change the spectral components in the transient spectra of the blown pipe, whereas in the stationary spectrum, the effect is small. [This work was performed at the Department of Applied Acoustics, Chalmers University of Technology, Göteborg, Sweden.]
What is and should be in the area of noise-protection: Make progress a catalog on noise reduction
Authors: Ross Karl
Published: July 2002

Noise has a harmful effect on health. Also, More than 10000 deaths every year in the ecological domain, for example, are said to be caused indirectly in this way in Germany. In the area of the industrial safety, the following applies: the regulation governing accident prevention under the title ‘‘Noise’’ has been in existence since 1975. Annually, more than four million persons are at noisy workplaces and two million hearing screening tests are being carried out. Yet, noise-related illnesses still occur (1996: 11724 reported illnesses/1252 pension-cases receiving compensation for the first time). The costs of these were over 500 million German Marks altogether. However, company practicians are often not able to plan/carry out noise reduction without intensive support. Therefore, there had been checked more than 200000 pages for the keynotes ‘‘noise reduction’’ or something similar. A new catalog on noise reduction is introduced at this point. It contains more than 400 examples. In it are listed in alphabetical order: the noise-problem with its dB(A) values before and after the decrease, the approximate cost of material, a short description of noise reduction, and a guide to the literature pertaining to special cases. Providing nonbinding advice in the area of industrial safety, the catalog is used at this time as a prototype free of charge. The costs, the protected area, or volume are partly estimated.
Variable-volume/coupled-volume response at Sala Julio Prestes
Authors: Blair Christopher N. , Nepomuceno José Augusto
Published: July 2002

Sala Julio Prestes (opening in early 1999) is an adaptive conversion of a railway station in São Paulo, Brazil into a traditional ‘‘shoe-box’’ concert hall. A unique feature of this 1600-seat room is the ceiling, formed in 15 large, tightly spaced, coffered panels. The nine central panels can be raised or lowered independently, while the six edge panels move in symmetric pairs. When the ceiling pieces move together, the room volume can be incrementally adjusted, from a minimum of approximately 12000 m3 to a maximum of about 28000 m3. When the pieces are placed at different levels, various coupled-volume conditions between the lower audience chamber and the volume above the ceiling are also possible. The coupled response is further tunable by provision of absorptive banners which can be deployed in the space above the ceiling panels. Acoustic measurements and binaural recordings of orchestral excerpts in this room with an audience are planned for late 1998 and early 1999. This paper presents preliminary results of these efforts, including recorded musical examples played with various ceiling configurations.
Four protectors in search of a rating system
Authors: Murphy William J. , Franks John R. , Harris Dave A. , Johnson Jennifer L.
Published: July 2002

The EAR Classic, V-51R, Howard Leight Max-1 and EAR Express Pod insert earplug hearing protection devices (HPDs) were tested at the NIOSH Hearing Protector Laboratory using real-ear attenuation at threshold (REAT) according to ANSI S12.6-1997 Method B subject-fit (SF) and ANSI S3.19-1974 experimenter-fit (EF) methods. Several subject panels were created from the NIOSH subject pool which permitted comparisons to the manufacturer’s REAT data published on the device’s label. For the Classic, NIOSH data agreed with the manufacturer’s data. However, for the other devices, the manufacturer’s data typically produced higher noise reduction ratings (NRRs) than the NIOSH data. The subject-fit NRR, NRR(SF), results were 17, 1, 12, and 10 dB for the Classic, V-51R, Max and Express, respectively. The REAT variances for the Bilsom V-51R data and the Howard Leight Max were significantly smaller than the NIOSH variances. The NIOSH recommendation that SF data, measured according to ANSI S12.6-1997, be used to rate the performance of a hearing protector, is supported by these results. Application of the NIOSH and OSHA derating schemes to EF NRR either overestimated or underestimated the NRR(SF). [Portions of work supported by the U.S. EPA IA 75090527.]
Effects of cup, cushion, headband force, and foam lining on the attenuation of earmuffs
Authors: Zannin Paulo Henrique T.
Published: July 2002

The essays were undertaken using an artificial head and a diffuse sound field, according to DIN ISO 4869-1. Increasing the cup mass improved the noise attenuation by 17 dB at 100–300 Hz. The coherence function between cup vibration and sound pressure inside the cup has shown that a great amount of sound energy is transmitted to the inside of the cup, at low frequencies. The foam lining of the cup clearly attenuated the sound in the frequency between 2000 and 8000 Hz. Increasing absorbent mass improved attenuation because resonances could be damped. The attenuation measured with a complete earmuff, and the same without the cushion, have shown that sound leakage occurs at frequencies ranging from 100–2000 Hz. The vaseline coating between the skin and the cushion improve the attenuation by less than 5 dB (100–200 Hz). As the headband force increases to a maximal deformation of the cushion, attenuation reaches 20 dB at 200 Hz. The increase in the headband force is, however, a limiting factor in the use of the earmuff, as it becomes too uncomfortable. The same conclusion applied to the increase in the mass of the cup.
Experiences with high-speed algorithms for full-field predictions of long-range sound propagation in the atmosphere
Authors: West Martin , Sack Robert A.
Published: July 2002

Algorithms based on a parabolic equation (PE) solution of the Helmholtz equation have in the last few years become popular because of their precision and robustness, as well as their flexibility in dealing with a wide range of ground boundary conditions and meteorological conditions. PE solutions previously had to be performed on powerful workstations, but with recent advances in personal computer (PC) hardware it is possible to obtain limited predictions on more modest computers. The new algorithms being developed by this group have the potential to increase computational speeds of standard PE algorithms by up to two orders.
Track dispersion in aircraft noise modeling
Authors: Buetikofer Rudolf , Pluess Stefan
Published: July 2002

Aircraft noise calculations based on clusters of single flight events are compared to results from a set of average flight paths. For the situation of Zurich airport, the aircraft noise was calculated with two different methods for the data input to the noise calculation program. The traditional method consists of defining a main track and several side tracks, each associated with a specific percentage of traffic. Further, an average climb profile was defined for each aircraft type. The definition of these average flight paths is based on the analysis of radar information from the airport. The new method selects for a given aircraft and departure (or landing) procedure from all available radar data sets a representative sample of, e.g., 100 flights, including different seasons, different companies, and different take-off weights. For each individual (real) flight the aircraft noise is calculated and the results are summed up according to the flight statistics. The price is an increase of computation load by a factor of 20, the benefit is a more representative result especially for regions with curved flights where the tracks diverge over a large area.
Computational methods for designing a silator—A low-frequency resonator element
Authors: Kalus Norbert
Published: July 2002

The silator is a vacuum bubble resonator element which is used as a noise control device and has a low-frequency performance. It consists of an evacuated, lens-shaped, convex cap of sheet metal. The capsule volume can be made as small as desired, since, because of the vacuum inside, there is no air stiffness. The effect of a silator is comparable to that of a Helmholtz resonator, but only a hundredth of the latter’s installation volume is needed. Broadband noise control can be achieved by a set of silators tuned to different frequencies. The principles of this silator technology in aeroacoustics were established by Bschorr and Laudien in 1992. The resonant characteristics of such a device are very sensitive to its geometrical properties. The plasticity of the material, the metal forming, and the remaining stresses in the convex cap also influence its effectiveness. The major development problem lies in the extremely small manufacturing tolerances. The tolerances decrease with increasing size and frequency. In this paper, computational methods and results are presented to yield the final design of the silator’s shape with a very low resonant frequency. The calculations were performed using the finite-element program MSC/NASTRAN for Windows.
Measurements of sound radiated by turbulent wall jets past singularities
Authors: Jacob Marc C. , Louisot Alain , Guerrand Sylvie
Published: July 2002

Sound radiated by high-speed turbulent wall jets past backward facing steps or shallow cavities is investigated experimentally. Both aerodynamic (laser Doppler and hot wire anemometry) and acoustic measurements (far-field directivity, spectra, and source localizations) are performed. Source localizations show that a backward facing step is a major sound source. Far-field measurements show that it has a strong upstream directivity and radiates in the medium frequency range. Aerodynamical results and an acoustic parametric study suggest that the source is due to the diffraction of the separated shear layer eddies by the sharp edge of the step: this is qualitatively confirmed by existing diffraction models. A shallow cavity (with length exceeding seven times the depth) has a strong downstream and upstream directivity: it can be regarded as a superposition of two acoustically independent sources, a backward facing and an upward facing step. In particular for such cavities and for Reynolds numbers (based on cavity depth) ranging from 40000 to 470000 no feedback mechanism and no cavity resonances are observed. [Work supported by the French Ministère des transports.]
An analytical model for upstream and downstream sound power from swept blade rows
Authors: Glegg Stewart A. L.
Published: July 2002

This paper will describe an analytical approach which can be used to calculate the upstream or downstream sound power generated by a swept blade row. The blade row is modeled using a linear cascade of flat plates with finite chord. The correct allowance for spanwise loading and gust convection is included. The value of this approach is that it can be used at very high reduced frequencies which are typically found in broadband fan noise applications. Results will be given which show the problems associated with only considering the noise sources at the leading edges of the blades and ignoring the trailing edges. The effects of blade sweep will also be illustrated by showing the radiated modal sound power as a function of blade sweep. [Work supported by NASA.]
Sound transmission in a slowly varying flow duct with lossless liner
Authors: Rienstra Sjoerd W.
Published: July 2002

The explicit multiple-scales solution, presented in AIAA-No 98-2311, for modal sound transmission through slowly varying ducts with mean flow and acoustic lining, is extended to include the case of a (nominally) lossless liner (Z=0). Especially the hydrodynamic or vortical mode is examined since this contains, in cooperation with higher order modes, the possibility of sound production or absorption by transfer of acoustic energy to and from the vorticity layer.
Nonlinear standing waves in the two-tube structure
Authors: Liu Ke , Maa Dah-You
Published: July 2002

Nonlinear standing waves have been studied in a structure consisting of two lengths of tubing with different diameters. Preliminary theory of this structure is proposed. The measurement system of experiment is presented. A 100-W loudspeaker driver is used as a sound source to excite the larger tube of 45-mm diameter through a 10-mm hole near one end, which is closed. The properties of the output at the end of the smaller tube, as well as their relation to the intput were investigated, and a resonance diagram of the two-tube structure is completed. The experimental results agree well with the predicted values. At the end of the smaller tube of 13-mm diameter, a sound pressure level (SPL) of 176.5 dB has been obtained with low distortion. Emphases are placed on the analysis of fundamental SPL. It is possible to drive the structure directly with a modern high power loudspeaker to produce high sound intensity in a more extended space. Further research is in progress. [Work supported by the National Science Foundation of China.]
Control of nonlinear bubble dynamics
Authors: Szeri Andrew J. , Wyczalkowski Matthew A.
Published: July 2002

Bubbles, either free or encapsulated, are valuable as contrast agents in diagnostic ultrasound in medicine. In this capacity, the compressibility of microbubbles is exploited to increase the acoustic backscatter from internal vessels and cavities of interest after injection into the patient. The scattering cross section of the contrast agent is further increased by driving resonant radial pulsations of the microbubbles with the ultrasound field. Recent derivatives of this basic technique rely on nonlinear aspects of the bubble response to reduce clutter and thereby to extend imaging capability to new areas. Unlike the surrounding tissue, these nonlinear bubble oscillations have a backscatter signature at a different frequency than the forcing, and so are especially useful in distinguishing the area to be imaged. New control capabilities are described for changing the architecture of the bubble dynamics phase portrait and response diagram so as to enhance their utility in imaging applications. [Work supported by NSF.]
Modeling of inhomogeneous monochromatic plane wave at the interface between two arbitrary homogeneous anisotropic absorbent media
Authors: Roge Bruno , Lanceleur Patrick , de Belleval Jean-Francois
Published: July 2002

This work aims to model the interaction of an inhomogeneous monochromatic oblique plane wave with a plane interface separating two semi-infinite homogeneous media. These media can be either isotropic or anisotropic, absorbent or not. A numerical method is proposed to generalize previously developed procedures, which were restricted to the case of incident homogeneous waves, interacting with absorbing materials. In this case the waves propagating are always inhomogeneous. Due to this inhomogeneity of the waves, the choice of compatible parameter for the incident wave is to be done on an energy criterion and not necessarily on a radiation one. The computation of all the parameters of all the involved waves makes several unexpected phenomena or behaviors to arise. For instance, by applying the study to the case of a water/nickel monocrystal interface, incident directions for which the energy flow vector is directed toward the transmission medium, whereas the slowness vector is directed toward the incident medium, are observed. The appearance of leaps in the reflection coefficient will then be explained by an orientation change of the slowness vector, which results from a forward/return of the energy flow vector through the interface.
Further examination of the relationship between overshoot and filtering
Authors: Strickland Elizabeth A.
Published: July 2002

In a previous experiment, threshold was measured for a brief duration probe positioned temporally at the onset of a broadband masker, with and without a broadband precursor, to determine the amount of overshoot. The probe level was then fixed 10 dB above the threshold levels determined in the overshoot experiment, and a notched-noise masker was varied in level to estimate filter shape, with and without a precursor. In general, filters were broader and the signal-to-noise ratio at threshold, k, was lower following a precursor, but there was not a clear relationship between the amount of change in the filters and overshoot. In the present study, filter shapes were measured with the probe level set at the threshold from the overshoot experiment, rather than 10 dB above. Results revealed that the change in k is in general closely related to the amount of overshoot (which would be expected) and also that there is at least some relationship between the change in filter width and the amount of overshoot. The study was also extended to look at possible filtering changes with decrease in overshoot, and to look at effects of overshoot from off-frequency precursors and maskers. [Work supported by NIH (NIDCD).]
Spectral integration of auditory temporal information
Authors: Eddins David A.
Published: July 2002

Measures of temporal acuity reveal a remarkable ability to integrate temporal information across frequency throughout most of the audible spectrum. This apparent trading of spectral bandwidth and temporal resolution was investigated in three different experiments measuring amplitude-modulation detection, temporal gap detection, and intensity discrimination. Each experiment included six spectral conditions: a single band of noise 1600-Hz wide centered at 3000 Hz; a set of four noise bands 400-Hz wide having center frequencies separated by 1200 Hz (1200, 2400, 3600, 4800 Hz); and four conditions composed of only one of the four 400-Hz bands. The form of the modulation transfer functions did not depend upon total bandwidth or frequency region. Sensitivity to modulation was inversely related to total noise bandwidth. Temporal gap detection thresholds and intensity discrimination were strongly dependent upon total noise bandwidth but were independent of the spectral proximity and the center frequency of the noise bands. Analysis of the three experiments revealed that the inverse relation between intensity discrimination and noise bandwidth may be used to predict the variation in amplitude modulation and temporal gap detection thresholds with noise bandwidth.
Experiments on active control of sound radiation around double-wall resonance frequency
Authors: Pietrzko S. J.
Published: July 2002

The first part of this paper will be focused on identified modal shapes and sound power measurements of a double-wall panel in the low-frequency range around the double-wall resonance frequency. New experimental results show that for a double-wall panel with one laminated pane (asymmetric panel) around the predicted double-wall resonance frequency, there exist three natural frequencies, respectively three modes. One of these modes is highly complex and the other two are real. It is characteristic that at one of these real modes both planes of the panel move exactly in phase and at the second they move precisely out of phase. The second part of the paper will be focused on the design of control system to minimize the radiated sound power from the double-wall panel and efficiency of the proposed control. The radiation efficiency for each of the identified modes was estimated with goal to define the optimal position for the piezoactuators used to minimize the radiated sound power around the double-wall resonance frequency. Different control schemes will be presented. The efficiency of proposed control schemes will be compared and illustrated by means of laser scanned vibratory patterns of the panel.
A comparison of active control strategies for the reduction of sound transmission through double panels
Authors: Gardonio Paolo , Elliott Stephen J.
Published: July 2002

A theoretical study of the active isolation of air-borne and structure-borne sound transmission through a double panel system is presented. The reductions in the radiated sound are investigated for three different families of control approaches. The first and the second families are based on the minimization of total sound power radiation or the minimization of the weighted sum of the square values of the sound pressure at a set of positions between the two panels and the square values of the velocities at a set of positions of the radiating panel using either active mounts or/and control loudspeakers. The third family considers: first, the cancellation of out-of-plane velocities underneath the mounts using active mounts; second, the cancellation of sound pressure near each loudspeaker using loudspeakers; and third, the cancellation of both velocities and the sound pressure using both loudspeakers and mounts. The third family does not give good performances except at low frequencies. Alternatively, the minimization of weighted square values of plate velocities and cavity pressures gives good results which are comparable with those obtained with the optimal control approach of total sound power minimization. In general, the control loudspeakers give better control in all control approaches considered.
Intensity error sensing in the active control of sound
Authors: Koehler Robert , Snyder Scott D.
Published: July 2002

In the active control of radiated sound fields, the use of intensity as an error signal has intuitive appeal, due to the fact that the measure is directly related to the sound power radiated from the source. To date, examinations of this proposition have been restricted largely to theoretical studies. This work to be presented here extends previously derived theoretical results, and presents experimental results from the use of intensity-based error measures in a practical adaptive active noise control system. It is found that while minimization of an acoustic pressure-based error signal does not guarantee a satisfactory global result, the use of an intensity-based error signal may not improve the situation. In fact, there are many instances where the use of a pressure-based error signal in the active noise control system may be preferable. This includes instances where the error signal is measured in the near field of the sound source, at locations where it was hoped that minimization of intensity-based error signals would deliver superior overall active control system performance.
Simulations of the feedback control of sound transmission through a plate using measured data
Authors: Sors Thomas C. , Elliott Stephen J.
Published: July 2002

This paper describes a simulation of active structural acoustic control (ASAC) based on experimentally measured frequency response functions. An experimental arrangement consisting of a plate mounted between two rooms and equipped with integrated actuators and sensors is described. The aim of the experiment is to use these transducers mounted on the plate to reduce the transmission of an acoustic disturbance generated by a loudspeaker in one room to the other. Frequency response functions are measured from the loudspeaker and the actuators to the integrated sensors and also to a number of far-field error microphones. These measurements are used to predict the performance of various feedback controllers on the sound transmission. It is found that, provided there is only a small amount of delay inherent to the control process, significant reductions can be made for periodic disturbances and also some reductions can be made for broadband disturbances. [Work supported by the TNO Institute of Applied Physics, Delft, The Netherlands.]
The profile of interaural decorrelation across frequency: A binaural representation of pitch and timbre
Authors: Summerfield A. Quentin , Culling John F. , Akeroyd Michael A.
Published: July 2002

Tones can be detected in noise at lower signal-to-noise ratios (SNRs) when they possess different interaural timing to the noise. One account, equalization-cancellation (E-C), suggests that the left- and right-ear signals are adjusted in time and amplitude to maximize their similarity, and are then cancelled by subtraction. At low SNRs, E-C improves the SNR of the tone by cancelling the noise. E-C is also a method for measuring interaural decorrelation, because the remainder after subtraction is a measure of the extent to which the tone reduces the interaural correlation of the noise. Applying E-C independently in each frequency channel reveals the profile of interaural decorrelation across frequency induced by a complex signal in noise. The profile is a place representation akin to an excitation pattern. It has three properties. (i) It displays the spectrum of speech at low SNRs. (ii) Listeners can integrate it perceptually with the conventional profile of spectral amplitude. (iii) Its spectral structure is compatible with a subset of the dichotic pitches phenomena in which tonal percepts are induced by introducing interaural phase changes into broadband noises. Finally, the profile can be recast in a form compatible with temporal accounts of pitch and timbre based on autocorrelation.
Fluid dynamic effects in speech
Authors: Krane Michael
Published: July 2002

A summary of fluid dynamic effects in speech are outlined using concepts from duct flow aerodynamics and aeroacoustics. A physical picture of fluid motion which produces both voiced and unvoiced sounds is presented, with emphasis on how movement of the acoustic medium affects both the generation and propagation of sound. Particular attention is given to the concept of vorticity (roughly, fluid particle rotational motion) as a means to characterize turbulent flow and as the means by which airflow produces or absorbs sound. First, it is shown how vorticity production by steady flow at the end of an open pipe may act as an absorber of sound, affecting the acoustic impedance of the open end. Unvoiced sound production is then discussed in terms of the formation of a jet by flow separation, the structure of jet vorticity, and how convection of jet vorticity through a nonuniform vocal tract produces sound. Order-of-magnitude estimates of these effects are presented. Finally, the role of these effects in voice production are detailed through a discussion of the modulation of glottal volume flow by movement of the glottal flow separation point and production of sound by the glottal jet.
Turbulent glottal flow during phonation
Authors: Alipour Fariborz
Published: July 2002

Human phonation is the flow-induced oscillation of the vocal folds, producing pulsatile jet through the glottis, which may become turbulent. This turbulent jet was investigated in an excised canine larynx model with simultaneous recordings of air particle velocity, subglottal pressure, airflow rate, and EGG signal for various conditions of phonation. Canine larynges were mounted on a plastic air tube and sustained oscillations were established and maintained by mechanically manipulating the cartilages to mimic the function of laryngeal muscles. The major control parameters were the airflow rate and the glottal adduction. The velocity was measured with a constant-temperature hot-wire anemometer system. To separate the turbulence from the periodic component of the velocity signal, the technique of phase shift averaging was employed. Results suggest that subglottal inlet flow to the larynx is pulsatile but mostly laminar, while the exiting jet is nonuniform and turbulent. The Reynolds number based on the mean glottal velocity and glottal hydraulic diameter varied between 1600 and 7000, the Strouhal number varied between 0.002 and 0.032, and the Womersley number ranged from 2.6 to 15.9. These results help define the conditions required for computational models of laryngeal flow. [This work was supported by NIDCD Grant No. DC03566-01.]
Computational aeroacoustics of subsonic jets for application to speech production
Authors: Frankel S. H. , Zhao W. , Mongeau L. , Scherer R. C.
Published: July 2002

Computational aeroacoustics calculations, based on direct numerical simulations, were performed in order to predict the near-field and far-field sound radiated by a forced, round, unconfined, subsonic jet. The jet Mach number was around Ma=0.4, and the Reynolds number based on the jet velocity and diameter was approximately Re=103. The compressible Navier–Stokes equations were integrated using a high-order finite-difference scheme. A two-dimensional, axisymmetric, nonuniform grid was used. Both direct computations and acoustic analogies were used to compute the far-field sound. Of interest is the role of large-scale vortical flow structures and vortex pairing in the production of sound. The results were used to assess the validity and limitations of the computational approach through comparisons to previously published numerical results. The ultimate goal is to perform large eddy simulations of pulsating jets in a range of flow conditions more relevant to speech production, e.g., approximately Ma=0.1, Re=105, to establish the radiation efficiency and the physical origin of the aeroacoustic sources involved. [Work sponsored by NIH.]
Determination of optimal HRTFs for binaural synthesis
Authors: Christensen Flemming , Moeller Henrik , Olesen Soeren K. , Minnaar Pauli
Published: July 2002

Earlier studies have shown that a carefully selected human substituting an artificial head can minimize the amount of localization errors for a group of people in a listening experiment, thus indicating that a set of head-related transfer functions (HRTFs) can be found, which to some extent fits a population. This study aims at exploring ways of designing such general sets of HRTFs suitable for larger populations. An effort is put into considering the importance of, e.g., different frequency regions of the transfer functions in order to focus on the most general characteristics and avoid focusing attention on highly individual features. The physical origin of the different parts of the HRTFs will be taken into consideration, and HRTF design methods using parameters derived through signal analysis will be studied.