bluuebunny/crossref_metadata_2025 huggingface dataset:
A decade of acoustic thermometry in the North Pacific Ocean: Using long-range acoustic travel times to test gyre-scale temperature variability derived from other observations and ocean models
Authors: Worcester Peter , Dushaw Brian D. , Andrew Rex K. , Howe Bruce M. , Mercer James A. , Spindel Robert C. , Cornuelle Bruce , Dzieciuch Matthew , Birdsall Theodore G. , Metzger Kurt , Menemenlis Dimitris
Published: May 2008

Large-scale, range- and depth-averaged temperatures in the North Pacific Ocean were measured by long-range acoustic transmissions over the decade 1996-2006. Acoustic sources off central California and north of Kauai transmitted to receivers throughout the North Pacific. Even though acoustic travel times are spatially integrating, suppressing mesoscale variability and providing a precise measure of large-scale temperature, the travel times sometimes vary significantly on time scales of only a few weeks. The interannual variability is large, with no consistent warming or cooling trends. Comparison of the measured travel times with travel times derived from (i) the World Ocean Atlas 2005 (WOA05), (ii) an upper ocean temperature estimate derived from satellite altimetry and in situ profiles, (iii) an analysis provided by the Estimating the Circulation and Climate of the Ocean (ECCO) project, and (iv) simulation results from a high-resolution configuration of the Parallel Ocean Program (POP) show similarities, but also reveal substantial differences. The differences suggest that the data can provide significant additional constraints for numerical ocean simulations. The acoustic data show that WOA05 is a much better estimate of the time-mean hydrography than either the ECCO or POP estimates and provide significantly better time resolution for large-scale ocean variability than can be derived from satellite altimetry and in situ profiles.
Dual apodization technique for improved contrast
Authors: Yen Jesse , Seo Chi
Published: May 2008

We propose a method to use dual apertures or dual apodization functions to reduce side lobes and clutter for ultrasound imaging. Using a common transmit aperture but different receive apodizations or apertures, we create two point spread functions with very similar main lobes and different sidelobe and clutter signals. Main lobe signals can be distinguished from clutter signals using normalized cross-correlation of the raw radio-frequency data. The normalized cross-correlation coefficient is used as a pixel-by-pixel weighting to pass main-lobe signals and suppress side lobe and clutter signals. Main lobe signals will have a high cross-correlation coefficient near 1 and clutter signals will have coefficients between 0 and -1. Point target simulations show a narrowing of the main beam compared to conventional beamforming at beamwidths -20 dB and lower. Using a 5 MHz 128-element linear array, improvements of contrast-to-noise ratio (CNR) of an anechoic cyst compared to delay and sum beamforming exceed 130% in both simulations and experiments. We also evaluated this method for robustness in the presence of phase aberration. Aberrators ranging from 25-45 ns rms with correlation lengths of 3-5 mm were used. Here, improvements in CNR also exceed 100% in many cases.
Results of acoustical treatments in existing classrooms
Authors: Astolfi Arianna , Griginis Alessia
Published: May 2008

In 2001, 2002, and 2005, the Department of Energetics of the Politecnico di Torino has carried out in-field objective and subjective surveys with the aim of evaluating the acoustical quality in secondary-school classrooms of the Province of Turin (Italy). From the results the following main problems emerged: high reverberation times, high background noise levels caused mainly by low sound insulation between classrooms and corridors and between adjacent classrooms, low façade sound insulation, excessive teachers' vocal efforts. In this work results of acoustical treatments in some of these existing classrooms are reported. Measurements are made before and after the restorations. The case studies are chosen with reference to different building typologies and urban contexts, and consisted of improvements in sound absorption, sound insulation of internal partitions, doors and façades, and acoustic bridges elimination. They are divided in “light” and “heavy” types. The first, less expensive, with the aim to obtain good acoustical conditions, the latter, more expansive, focused to obtain optimal conditions. In fact, mainly in restoration of public schools, a good level of acoustical quality with contained costs is requested. The treatments are carried out with the aim to constitute a repertory of solutions to apply primarily in school restoration.
High-altitude infrasound calibration experiments
Authors: Bass Henry E. , Herrin Eugene T. , Golden Paul , Woodward Robert , Drob Douglas , Hedlin Michael A. , De Groot-Hedlin Catherine , Walker Kris , Garces Milton , Szuberla Curt , Whitaker Rod
Published: May 2008

At the 152nd Meeting of the Acoustical Society of America, Andre and Bass reported an infrasound experiment conducted at White Sands Missile Range during the 2005-2006 time frame. The experiment consisted of exploding a 22.4 kg charge at altitudes from 31.3 km to 49.6 km then recording the waveforms at 30 infrasound arrays (not all at the same time) at distances up to 1200 km from the source. The analysis is not yet complete but some preliminary observations have been reported in the most recent issue of Acoustics Today. This talk will summarize the findings published in Acoustics Today and offer suggestions to others who might want to access and analyze the data.
Infrasound propagation in the zone of silence
Authors: Golden Paul , Negraru Petru , Herrin Eugene T.
Published: May 2008

Two controlled source experiments were conducted in Nevada in 2006 and 2007 to study infrasound signal propagation at distances less than 300 km from the source. In 2006 three temporary infrasound arrays were deployed at distances of 76, 108, and 157 from the source. In 2007 the site at 157 km was reoccupied, and data was also recorded at 288 km from the source. Interesting results were derived from the travel time analysis. In 2006 the site at 76 km recorded both tropospheric and stratospheric arrivals, while at 108 and 157 km only stratospheric arrivals were recorded. In 2007 the site at 157 km recorded both tropospheric and stratospheric arrivals, while at 288 km both stratospheric and thermospheric arrivals were recorded. Atmospheric modeling with the InfraMAP software failed to predict returning rays or pressure levels similar to the observed data. Because of the large amplitude variations we attempt to estimate the yields of the explosions using the predominant frequency content of the signals. The physical basis for such a method is found in an increased acoustic transit time of the explosion blast radius with increased yield. Preliminary results suggest this is possible.
Ground effects on sound and vibration from explosions
Authors: Madshus Christian , Lo/vholt Finn , Cleave Ra , Rothschild Karin , Cetina-Medina Zenon
Published: May 2008

Low frequency sound from military activity and explosions do propagate over large distances. The sound pressure may induce substantial vibration in the ground and particularly in buildings. Such vibrations turn out to be a major cause of complaints among neighbouring communities around training fields and blast sites. We will present investigations on long range propagation of low frequency sound and sound-induced vibration, based on a substantial amount of data collected during a series of full scale tests performed in Norway over the last 14 years. All data are assembled in the NORTRIAL database, which is now publicly available. Meteorology and ground interaction largely influence the sound propagation and vibration response. At low frequency meteorological- and ground effects may intricately interact and lead to large, apparently random variability in sound pressure at large distances. Statistically based investigations on the sound propagation and its variability will be presented. Particular focus will be on the ground interaction effects, and a new and more extensive system for ground classification, based on cartographic data, empirical and numerical modeling will be introduced. Findings on building response to outdoor low frequency sound and transfer mechanisms from outdoor pressure to indoor sound and vibration will be presented.
Predictions for the influence of the nocturnal jet on the long range propagation of impulsive signals
Authors: Waxler Roger , Gilbert Kenneth E , Talmadge Carrick L. , Di Xiao
Published: May 2008

On clear nights, inland over flat ground, one generally finds a temperature inversion in the first hundred meters or so of the atmosphere. Near the ground, winds tend to be light, increasing with altitude. Above the temperature inversion one finds a stiff geostrophic wind known as the nocturnal jet. Theoretical predictions, based on ray theory and expansions in vertical modes, for the effect of the nocturnal jet on the long range propagation of impulsive signals are presented. For sufficiently short ranges, less than 3 km or so, the nocturnal jet has no effect. At these ranges only the temperature inversion and the light winds in the inversion play a role. At longer ranges the nocturnal jet significantly alters the arrival structure of the propagated signal. It is predicted that, due to coincident arrivals from the inversion and from the nocturnal jet, there is a segment of ranges about 1 km long, beginning at about 4 km, in which the amplitude of the first arrival becomes anomalously large and then splits into two distinct arrivals.
The physics of pulse propagation in the nocturnal atmospheric boundary layer: measurement and theory
Authors: Talmadge Carrick L. , Waxler Roger , Gilbert Kenneth E , So Jin , Stribling Rommel , Di Xiao
Published: May 2008

A series of experiments designed to probe the effect of the nocturnal atmosphere on low-frequency (10- 500 Hz) sound propagation will be discussed, and their ramifications explored. These experiments involve detecting arrivals from a propane cannon on a vertical array of microphones 1-3 km from the source, which were collected simultaneously with meteorological experiments designed to measure the vertical temperature and horizontal wind velocity profiles. Chief among the results of these experiments is the observation of a nocturnal model structure that has a significant surface wave component at frequencies below 150 Hz. At higher frequencies and longer propagation distances (>1.5 km), the surface wave is not observed due to attenuation from its interaction with the ground. At higher frequencies, the model structure displays a characteristic “quiet height” first described in Waxler et al. (2006). The potential application of these results for remote sensing the atmospheric boundary layer are discussed, and contrasted with other methods of measurement of the atmospheric profile.
Road traffic noise from viaducts in mountainous areas
Authors: Defrance Jérôme , Beyret Matthieu , Baulac Marine , Jean Philippe A.
Published: May 2008

Mountainous zones in Europe, such as the Alps, represent huge areas where many viaducts are built, most of them for motorways. The way the sound grazes the asphalt surface from the low and high traffic equivalent sources up to the road edges, and how it then diffracts towards dwellings is a complex mechanism. The standard approaches are suited to plain situations but fail in predicting finely sound propagation behaviour for such geometries. In this paper, one gives the main trends of received noise levels from viaducts as a function of both their geometry and the receiver location. A 2D Boundary Element Method is used for predictions since meteorological effects can be neglected for the short propagation (a few hundreds meters). This assumption makes sense since the viaduct considered in this work is sufficiently high (20 m) and the ground effect is weakly affected by refraction. Different configurations are then simulated in order to address and discuss several geometrical effects, such as: platform elevation, low height barriers addition, complex shape barriers and presence of a central gap in the platform.
Intermodal coupling in a dissipative fluid filling a rough-walled waveguide
Authors: Valier-Brasier Tony , Potel Catherine , Bruneau Michel , Depollier Claude
Published: May 2008

The present study follows recent works dealing with the analytical model of an acoustic field in fluid-filled waveguides with rough walls. In these works, the acoustic field is obtained from the coupling between Neumann eigenmodes of the regularly shaped waveguide which bounds outwardly the rough walls of the waveguide considered, using integral formulation with suitable Green function. The effect of the roughness is expressed in such a way that two intermodal coupling mechanisms are highlighted: a bulk coupling and a surface coupling, the first one depending on the depth of the roughness and the second one depending in addition on the local slope. Moreover, a phonon relation is involved when the rough profile is periodic. The aim of the present study is to account for the thermo-viscous boundary layer effects through eigenmodes which satisfy appropriate mixed boundary conditions, leading to a better understanding of the physical mechanisms when resonances and phonon relationship are involved.
Evaluation of the lined duct performances based on a 3D two port scattering matrix
Authors: Taktak Mohamed , Ville Jean Michel , Haddar Mohamed , Foucart Félix
Published: May 2008

The scattering matrix constitutes a good tool to characterize a lined duct. In fact, this matrix relates the incoming modal pressures to the out coming ones and contains detailed information and per mode about the transmission, reflection, and conversion properties of the duct. It depends only on the geometric and acoustic properties of the duct. The two port acoustic dissipation and attenuation interest the designers of lined duct like aircraft engine manufacturers to evaluate the duct performances. These values can be deduced from the two port scattering matrix and from the vector of incoming modal pressures. In this work, a study about the two port acoustic dissipation and attenuation computed from the scattering matrix and for different cases of incoming modal pressures are presented. Scattering matrices used in this study are measured by an experimental procedure developed at the University of Technology of Compiègne based upon the experimental setup realized during the European Project DUCAT. The experimental acoustic power dissipation and attenuation are computed for different cases of modal structure on the both side of the duct. Then, these results were confronted with ones given by a theorical study of the problem based on the finite element method.
Coupling transfer matrix method to finite element method for the analysis of hollow body networks with passive or reactive elements
Authors: Chevillotte Fabien , Panneton Raymond , Bougrab Hakim , Chaut Christophe , Wojtowicki Jean-Luc
Published: May 2008

This work shows how to couple transfer matrix method to finite element method with a view to analyze the acoustic response of hollow body structures with a minimum of memory requirements and computational time. An hollow body structure is made up from a series of elongated rigid-walled fluid partitions (i.e., waveguides). These fluid partitions are separated by any passive (e.g., multilayered sound barrier) or reactive elements (e.g., expansion chamber). In the proposed hybrid model, the elongated fluid partitions are modeled using 1D fluid finite elements, and the passive or reactive elements using transfer matrices. From the weak integral formulation of the acoustic problem, it is shown how the coupling with the transfer matrix is taken into account through a mixed boundary condition. After discretization of the acoustic pressure and application of the variational principle, the finite element matrix system is obtained, where only the nodal pressures in the fluid partitions remain. The transfer matrix has been converted into a kind of admittance matrix, where no additional degrees of freedom are necessary to account for the passive or reactive elements. The method is used to predict the acoustic response of a real hollow body structure. Good correlations are obtained with experimentations.
Gigahertz ultrasonic interferometry at high pressure and temperature: Geophysical implications
Authors: Kantor Anastasia P. , Jacobsen Steven D. , Kantor Innokenty Y. , Dubrovinsky Leonid S. , Reichmann Hans Josef
Published: May 2008

High-frequency acoustic interferometry is widely used to penetrate a medium and measure the reflection signature, which can reveal details about the inner structure of the medium. It is a very helpful and one of the most accurate techniques for determination elastic properties of different materials being capable to measure sound wave velocities in very small samples under high pressures. The ultrasonic interferometry system operating at 0.6-2.1 gigahertz (GHz) frequencies was developed in the Bavarian Geoinstitute of the University of Bayreuth for in situ high pressure and temperature experiments. High pressures are reached by using diamond anvil cell, and a Pt-resistive heater allows reaching high temperatures. The experimental setup is equipped with a laser system, which allows measuring a shift of ruby fluorescence line at every given temperature.
Estimation of thermophysical properties of fluids under high pressure from speed of sound measurements
Authors: Daridon Jean Luc
Published: May 2008

The thermophysical properties of pure substances in fluid state as functions of temperature and pressure are of great interest not only for industrial applications (for example in the oil and gas industry), but also for fundamental aspects in view of developing models for an accurate representation of dense fluids. Now these measurements are difficult to perform under pressure, particularly for non single-phase systems, at atmospheric pressure. An interesting alternative consists in using the ultrasonic velocity which can be determined experimentally with a high degree of accuracy including at high pressures and high temperatures, and which presents the advantage of giving access to various derived properties. This potential, which is specific to ultrasonic velocity in fluids, has been the starting point for the investigation of a large number of pure liquids and gases as well as of several types of mixtures by ultrasonic measurements. In this work we will review the procedures used to evaluate thermophysical properties as a function of pressure from speed of sound measurements. The validity of the different approaches will be checked by comparison to several thermophysical properties measured in an extended pressure range. The accuracy reached for each property by the different procedures will be bring out.
Measurements under high pressure of ultrasonic velocity in glycerol
Authors: Khelladi Hassina , Plantier Frédéric , Daridon Jean Luc , Djelouah Hakim
Published: May 2008

Glycerol has been the subject of significant scientist interest. Indeed, glycerol is a polyalcohol and the presence of three hydroxyl groups per molecule makes glycerol a complex system to explore. The purpose of this investigation is to measure under high pressure the ultrasonic wave velocity in glycerol, from which a number of important thermodynamic properties could be derived and determined as a function of pressure and temperature. Pressure and temperature ranges exploited in this experimental investigation of various glycerol properties, are extended respectively from 0.1 MPa to 100 MPa and from 10 °C to 100 °C. A high pressure measurement cell equipped with temperature and pressure monitoring and control instrumentation was used. A time of flight method was exploited to measure, under high pressure, the ultrasonic wave velocity at different temperatures. The resulting experimental data of ultrasonic wave velocity in glycerol combined with measurements at atmospheric pressure, of density, specific heat and thermal expansion coefficient were used to derive density at elevated pressures. As isentropic compressibility is linked to ultrasonic wave velocity and density by means of the Newton-Laplace equation, this intrinsic physical property is easily deduced. These results led to the behavior of each physical property as a function of temperature and pressure.
Ultrasonic exploration at extreme shallow underground in submerged soil
Authors: Seo Kunihiko , Shirakawa Takashi , Sugimoto Tsuneyoshi
Published: May 2008

Now a lot of land mines remain buried in the world, so that the clearance of them is required. As a tool of removing land mines, equipments using electromagnetic radiation are often employed. However, there is a problem that the land mines in the flooded soil such as in Southeast Asia cannot be detected in the rainy season. Therefore, the new way using sound waves will be profitable to detect the land mines in the flooded soil. In this research, the acoustic exploration at very shallow area in submerged sand is examined at a water tank in the lab. First we measure the propagation property of ultrasound of 120 kHz in the shallow submerged sand, and examine underground imaging. As a result, the acoustic velocity is measured at about 1500 m/s and the attenuation is measured at about -19 dB/m. And next, shallow underground exploring by using acoustic shielding boards is carried out. As a result, underground images in the water tank simulating the submerged soil are obtained. Then acoustic shielding boards can block wave which propagates specific route. This will make another exploration method possible.
Acoustic field in a spherical resonator: effect of modal coupling due to small perturbations
Authors: Guianvarc'H Cécile , Pitre Laurent , Guillou Arnaud , Bruneau Michel , Bruneau Anne-Marie
Published: May 2008

The international community recently recommended a re-definition of the kelvin referring to the value of the Boltzmann constant k, which must thus be known with a relative uncertainty of 10-6. The measurement of the acoustic resonance properties of a gas filled spherical or quasi-spherical resonator is an appropriate method to do this with these requirements. Actually, a detailed modeling of the acoustic field in the resonator is required for the determination of k. Several phenomena must be taken into account including heat conduction, shear and bulk viscosity of the gas, the real shape of the resonator, the acoustic input impedance of small acoustic elements flush-mounted on the wall (tubes, transducers)... . Significant theoretical studies have already been done in which these perturbations are accounted for separately, the coupling between them being neglected. The scope here is thus to provide a unified model for the acoustic field in the cavity including all these perturbations and the resulting modal coupling, and applying it on a simple practical configuration: a spherical resonator filled with argon, acoustic transducers being flush-mounted on the wall.
Convergence of correlations in multiply scattering media
Authors: Larose Eric , Derode Arnaud , Roux Philippe , Campillo Michel
Published: May 2008

Correlations of ambient seismic or acoustic noise are now widely used to reconstruct the impulse response between two passive receivers as if a source was placed at on of them. Applications include terrestrial and solar seismology, underwater acoustics and structural health monitoring. Nevertheless, for a given set of data, correlations do not only yield automatically the Green function between the sensors, but also contains residual fluctuations that might "blur" the images. [Gizon et al, Astrophys. J. 614 (2004); Weaver and Lobkis, J. Acoust. Soc. Am. 117 (2005); Sabra et al., J. Acoust. Soc. Am. 118 (2005)]. We propose a model to describe the “signal-to-fluctuations” ratio in the correlations in the case of nonstationary wavefields, and more particularly in the case of scattering media. The work includes theoretical derivations and numerical simulations. The role of multiple scattering in the rate of convergence of the correlations toward the Green function is quantitatively evaluated [Larose et al, (submitted 2008)].
Reflection and transmission coefficients of a fluid slablike region containing a depth-varying random distribution of cylinders
Authors: Conoir Jean-Marc , Robert Sébastien , El Mouhtadi Abdelhak , Luppé Francine
Published: May 2008

This work deals with multiple scattering by a random distribution of parallel elastic cylinders immersed in a fluid slablike region. The concentration of scatterers inside the slab is supposed to vary slowly with depth, and the WKB method is used to calculate the reflection and transmission coefficients of the slab. In order to do so, the continuity conditions on the boundaries between the slab and the surrounding fluid are needed. They follow from the application of Twersky's theory to the case of a slab with a given constant concentration of scatterers, which shows that both pressure and normal displacement are continuous, provided an effective mass density of the slab is correctly defined. The results of the WKB are successfully compared to those obtained from the discretization of the slab into layers of constant concentrations of cylinders and the use of Twersky's theory.
Reception of phonetic features in fluctuating background noise maskers
Authors: Lorenzi Christian
Published: May 2008

We will review recent studies investigating the reception of phonetic features (voicing, manner and place of articulation) in nonstationary background maskers. In each study, consonant identification was assessed in steady and amplitude-modulated speech-shaped noise at signal-to-noise ratios yielding about 50% correct in steady noise. The rate and depth of amplitude modulation applied to the noise masker were either fixed or systematically varied. Confusion matrices were compiled across listeners and the amount of release from masking (percent information received in nonsteady minus steady noise) was calculated for each phonetic feature and experimental condition. Speech and noise mixtures were (i) left intact (unfiltered), (ii) lowpass filtered (<1.5 kHz), or iii) processed in order to degrade spectral (place of excitation in the cochlea) and/or temporal fine structure cues. Overall, the results indicate that release from masking typically reported in normal-hearing listeners (i.e., the substantial improvement in speech reception in fluctuating noise compared to steady noise) is not identical across phonetic features. This suggests that the ability to “glimpse” into background noise valleys involves multiple auditory processes constrained by both peripheral and central factors.
Understanding the complex modulation spectrum for consonants and consonant features
Authors: Grant Kenneth W. , Phatak Sandeep A. , Grassi Elena
Published: May 2008

Speech intelligibility is highly dependent on the magnitude and phase characteristics of the low-frequency modulation spectrum. However, unlike more traditional representations of speech, such as the spectrogram, associating details of the modulation spectrum to specific phonemes and subphonemic units of speech has not been readily forthcoming. In the present study we used local time reversals of the speech waveform between 20-160 ms to selectively distort portions of the complex modulation spectrum. Normal-hearing subjects were tested on a consonant recognition task and a detailed analysis of the perceptual confusions was performed. Consistent with earlier results using sentence-length materials, average consonant intelligibility declined as the length of the time reversal segment increased. Further analyses were conducted to determine the effect of time-reversal segment duration on the amount of information transmitted for individual consonants (including specific consonant productions) and acoustic features for voicing, manner of articulation, and place of articulation. An acoustic analysis using a biologically motivated auditory processing model was also performed to determine the effect of time reversals on cochlear and cortical representations of speech. The relations between changes to the complex modulation spectrum and the percent information transmission of selected speech segments and features are discussed.
The role of the cochlear processing in human speech recognition
Authors: Allen Jont B. , Regnier Marion , Phatak Sandeep , Li Feipeng
Published: May 2008

Little is know about how the auditory system decodes speech. We may think of speech communication re Shannon's source-channel model, thus viewed, the most complex part of the speech communication channel is the auditory system (the receiver). In my speech-perception research, I have attempted to limit the assumptions, and have thus fallen back on Shannon's basic source-channel model. The basic tool is the confusion matrix (CM) for isolated natural consonant and vowels (CV), as a function of the speech to noise ratio (SNR), with several types of masking noise. We have used large numbers of talkers and listeners (i.e., 20). In a second experiment we selectively remove islands of speech in time-frequency, and then correlate the resulting modified speech against subject scores. Our most important conclusions are: (1) The across-frequency onset transient portion of the signal is typically the most important. (2) The spectral regions of these transient are used to code different consonants. (3) While the frequency regions for a given consonant are correlated to the following vowel, this may not be important for perception. (4) Compact spectral-temporal amplitude modulations components (e.g., a 10 Hz modulation) do not seem to play a significant role, at least above 1-2 kHz.
A model with compression for estimating speech intelligibility in quiet and in noise
Authors: Rhebergen Koenraad S. , Lyzenga Johannes
Published: May 2008

For speech reception thresholds (SRTs), measured in normally-hearing listeners using various types of stationary noise, the Speech Intelligibility Index (SII, ANSI S3.5-1997) model predicts a fairly constant speech proportion (of about 0.3) necessary for sentence intelligibility. For SRTs in quiet, the estimated speech proportions are often lower, and show a larger inter-subject variability, than found for speech in noise near normal speech levels. This might be related to the fact that cochlear compression is larger at normal speech levels than near the threshold for speech in quiet. The SII model does not take this into account. The present model attempts to alleviate this problem by including cochlear compression. It is based on a loudness model for normally-hearing and hearing-impaired listeners [ANSI S3.4-2007]. It estimates internal excitation levels of the speech, accounts for the compressed effective dynamic range of the internal speech signal, and calculates the proportion of speech above threshold using similar spectral weighting as used in the standard SII. The present model and the standard SII were used to predict SRTs in quiet and noise for both normally-hearing and hearing-impaired listeners. The present model predicted speech intelligibility with less variability than the standard SII.
Externalization in binaural synthesis: effects of recording environment and measurement procedure
Authors: Völk Florian , Heinemann Fabian , Fastl Hugo
Published: May 2008

Databases of head related impulse responses (HRIRs) for binaural synthesis can be measured either in anechoic or reflective environments. If high synthesis quality is needed, miniature microphone measurements are performed in the ear canals of each individual user (individual measurement). Sometimes impulse responses measured in the ear canals of one individual are used for synthesis for other persons (nonindividual measurement). In most other cases artificial head measurements are used. This paper considers the dependence of the perceived distance of auditory images (externalization) on the measurement procedure (individual, nonindividual, artificial head) and on the recording environment (anechoic, reflective). For each measurement the same system and the same setup, especially the same geometric parameters, are used. Differences in the corresponding impulse response databases are determined and related to the subjective relative externalization differences in the front, in the back, and to both sides. For each direction a seven point rating scale was used. Statistical analysis suggests that the measurement parameters applied influence the externalization of auditory images.
Real-time auralization system based on beam-tracing and mixed-order Ambisonics
Authors: Noisternig Markus , Savioja Lauri , Katz Brian F.
Published: May 2008

Auralization, the final step in computational room acoustic simulations, aims to make audible the acoustics of complex virtual architectural spaces in a realistic and accurate manner. This paper presents a novel real-time auralization system comprising a geometry engine, a beam-tracer, and an audio renderer. The computation of early reflection paths is based on an efficient beam-tracing algorithm capable of real-time detection of specular reflection paths in a static geometry with one or several moving listener(s). For simpler rooms, the real-time performance is maintained even with dynamic geometries and sources. Results of the beam-tracer, sent to the audio renderer, consist of visible reflection paths and their accumulated material attenuation. From this geometrical and acoustical data, listener position-related 3D room impulse responses are generated applying a higher-order virtual Ambisonics approach. Final rendering of the binaural room impulse response (BRIR) is made taking into account the listener's head-orientation. As higher order reflections are more diffuse in nature, they may be encoded using lower Ambisonic orders, thereby reducing computational load. The environment combines high quality audio with visual rendering realized using the open source platforms Pure Data and VirChor respectively. This auralization framework provides direct audio-visual feedback in real-time for VR environments.
Real-time auralization of modifiable rooms
Authors: Schröder Dirk , Assenmacher Ingo
Published: May 2008

Immersive virtual environments are a powerful tool for acousticians and architects to design buildings if the virtual reality system provides an interactive imaging of virtual sound sources with respect to the rooms' physical aspects. Current implementations using hybrid room acoustic simulation methods (e.g., combining image sources and ray tracing) enable the user to walk freely in such virtual architectural spaces, whereby the position/orientation of sound sources are interactively manipulable to detect possible acoustic defects, e.g., flutter echoes. In the case of coupled rooms, sound transmission effects must be included into the real-time simulation in order to identify deficient airborne sound insulation, whereby current implementations only support a change of state (open/closed) of fixed room-connecting elements, e.g., doors and windows. However, in scenarios like an architectural planning stage, it is convenient to manipulate the room geometry more freely, e.g., via the interactive positioning of stage reflector panels, but common spatial data structures, e.g., BSP- or Octrees do not efficiently support these operations. For this purpose, the concept of Spatial Hashing, which originates from computer graphics for collision detection of deformable objects, is applied to the simulation process. This adaptation also features an efficient identification and update process of image sources.
Comparison of auralisation results betwee measurements and simulations of line arrays with high resolution modeling data
Authors: Ahnert Wolfgang , Feistel Stefan , Bauer-Diefenbach Ralph
Published: May 2008

In a concert hall a direct comparison of several line arrays for a new sound system has been made. At different locations the binaural impulse response has been measured and used for auralisation. In a computer model of the hall the measured line array was implemented. The single array sources have been modeled in different modes like far-field cluster, simple module array or as a high-resolution loudspeaker array. By means of the new developed SpeakerLab Module these source simulators have been created and afterwards used to calculate binaural impulse responses at the corresponding seats equal to the measurements. After that an auralisation routine has been used. The results are compared for the different degrees of source resolution and with the measurements. Beside acoustic measures the subjective sound quality of the different auralisation results is reported.
Uni-Verse Acoustic Simulation System: interactive real-time room acoustic simulation is dynamic 3D environments
Authors: Lundén Peter
Published: May 2008

Uni-Verse Acoustic Simulation System (UVAS) is a newly developed interactive room acoustic simulation system that can handle dynamically changing 3D geometric models in real-time. The system can share such models with other application, such as visual renderers or 3D modeling tools, over a network using the Verse protocol. UVAS is implemented using the beam-tracing method. It is build as two separate but highly integrated parts. The first part is handling the geometry, it's responsibility is to find audible sound sources and relevant reflection paths in the simulated environment. The second part is handling the audio rendering, producing the audible result of the simulation based on information given by the first part. This paper will focusing on the first part
Case study of measurements and computer modeling auralization results for medium-sized multipurpose halls
Authors: Savitala Hari V. , Duty Jason , Peltier Christopher
Published: May 2008

This case study focuses on auralizations and their accuracy in modeling medium-sized multipurpose halls (400-600 seats). Within each hall, impulse response measurements were taken with drapes deployed and retracted. The same configurations were modeled in the room acoustics program ODEON. Acoustical parameters, such as T20, T30, C50, C80, were used to check the agreement of the model to the measurements. A systematic approach was then used to adjust model parameters to match the real-world measurements. The modified and unmodified auralizations were then used to determine if any differences could be perceived in an informal listening evaluation. The auralizations and listening evaluation results are presented to better understand how to accurately auralize medium-sized multipurpose halls.
Real-time 3D audio for digital cinema
Authors: Arumi Pau , Garcia David , Mateos Toni , Garriga Adan , Durany Jaume
Published: May 2008

We present a real-time 3D audio system with a number of nice features: it is suited for plausible reference with the visual environment, it is real-time capable, it can process multiple moving sound sources and listeners in a normal CPU. In our approach, a database of pressure and velocities impulse-responses (IRs) is computed offline for each (architectural) environment using physically based ray-tracing techniques. During playback, the real-time system retrieves IRs corresponding to the sources and target positions, performs a low-latency partitioned convolution and smoothes IR transitions with cross-fades. Finally, the system is flexible enough to decode to any surround exhibition setup. The software has been developed within the CLAM open-source audio framework. We present a real scenario where these techniques were successfully applied: an augmented-reality film with 3D audio within the context of the IP-RACINE project for digital cinema. The shooting was done with a high-end prototype camera with zoom and position tracking which enabled the real-time motion of a subjective listener within the scene. Our technology enabled the film director to both pre-hear surround audio of an augmented-reality scene shooting and fine-tune audio rendering in post-production.
An ultrasound-based silent speech interface
Authors: Hueber Thomas , Chollet Gerard , Denby Bruce , Dreyfus Gerard , Stone Maureen
Published: May 2008

The paper proposes the use of ultrasound scans of tongue movement and video sequences of the lips to synthesize speech. A speech synthesizer driven only by video acquisitions may be qualified as a “silent speech interface,” which could be used by laryngectomyzed patient as an alternative to tracheo-esophageal speech, for voice communication where silence must be maintained, or in very noisy environments. Our system is based on the building of a one-hour audiovisual corpus of phonetic units, which associates visual features extracted from video with acoustic observations. The ultrasound and optical images are interpreted as a linear combination of standard configurations obtained by principal components analysis (PCA) from a phonetically balanced subset of typical frames. HMM-based stochastic models trained on these visual features sequences are subsequently used to predict phonetic targets from video-only data. Finally, a Viterbi unit selection algorithm is used to find the optimal sequence of acoustic units given both this phonetic prediction and the sequence of visual features. The system is able to perform phonetic transcription from video-only speech data with over 55% correct recognition, on continuous speech, using neither phonotactic nor linguistic constraints.
Range and cross-range propagation effects in a liquid wedge overlaying an elastic bottom
Authors: Borejko Piotr
Published: May 2008

The penetrable-wedge model, a constant density isospeed layer of fluid with a pressure-release horizontal surface and a sloping elastic bottom, provides an extensive insight into the role of the ocean bottom in acoustic propagation from an underwater source. In particular, it is a realistic model of a rock-bottom ocean near a shoreline that accounts for horizontal refraction and allows for a ground wave. This paper discusses some new results for small and large range propagation for two penetrable-wedge models: one where the shear wave speed in the bottom is lower than the sound speed in the fluid and the other where the shear wave speed is higher. The operational representation of the ray-integral solution for the acoustic field from a point source in a penetrable wedge of fluid is further developed to the stage at which one can compute the exact, other than the omission of diffraction at the wedge apex, pressure response curve, as recorded at a receiver, due to an arbitrary time variation of the pressure at the source in a 3° wedge. The three-dimensional propagation effects are examined for range transmission when the receivers are located up-slope and down-slope of the source, and for cross-range transmission when the receivers are located cross-slope of the source.
Investigation of 3D benchmark problems in underwater acoustics: a uniform approach
Authors: Sturm Frederic
Published: May 2008

In underwater acoustics, most of the three-dimensional effects on sound wave propagation are usually described by modelers considering one of the following shallow-water benchmark problems: a wedge-shaped waveguide, a canyon, a seamount, and a sinusoidal (corrugated) bottom. These test cases have been thoroughly analyzed individually considering both harmonic point sources (emitting at very low frequencies, for some obvious problems of CPU time and memory limitation) and broadband source pulses (with also very-low central frequencies). In the present work, we report numerical results corresponding to the propagation of broadband pulses in the four above-mentioned test cases. The numerical simulations are performed using a fully 3D parabolic equation based model coupled with a Fourier synthesis technique to handle the time dependence of the source signal. The objective is to propose a uniform representation of the numerical results so as to facilitate the comparison of the 3D effects present in each of the four benchmarks. Snapshots of the propagating pulses at very close successive times are compared with 2D results. In addition, movies of the propagating pulses are shown for each test case and compared to each other. Movies strongly facilitate the observation and thus the understanding of the 3D effects experienced by all the propagating waves.
Synthetic aperture sonar imaging of simple finite targets near a sediment-water interface
Authors: Kargl Steven , Williams Kevin L. , Thorsos Eric , Jackson Darrell R. , Tang Dajun
Published: May 2008

Synthetic aperture sonar (SAS) is used often to detect targets that are either proud or buried below a sandy sediment interface where the nominal grazing angle of incidence from the SAS to the point above a buried target is below the critical grazing angle. A numerical model for scattering from simple targets in a shallow water environment will be described, and can be used to generate pings suitable for SAS processing. For buried targets, the model includes reverberation from the rough seafloor, penetration through the interface, target scattering, and propagation back to the SAS. The reverberation and penetration components are derived from first order perturbation theory where small-scale roughness and superimposed ripple can be accommodated. For proud targets, the simulations include the scattering from the target where interaction with the seafloor is included through simple acoustic ray models. The interaction of the target with an incident field is based on a free field scattering model. Simulations will be compared to both benchmark problems and measurements over a frequency range of 10-30 kHz. These comparisons further support sediment ripple structure as the dominant mechanism for subcritical penetration in this frequency range. [Work supported by the US Office of Naval Research.]
Experiments and numerical modeling of low to midfrequency scattering from elastic objects near the sea floor
Authors: Zampolli Mario , Tesei Alessandra , Jensen Finn B. , Canepa Gaetano
Published: May 2008

The scattering of low to mid-frequency sound (1-10's of kHz) from submerged elastic structures of size O(1m) is a topic of interest to the underwater acoustics community. In the first part of the presentation, a brief description of the relevant components of the EVA experiment is given. The purpose of the sea trial was the acquisition of high-fidelity echoes from submerged spherical and cylindrical targets, made of composite materials with internal layered structure. The second part of the presentation is focused on the finite-element modeling technique developed at NURC for investigating the scattering from axially symmetric submerged elastic objects. Particular attention is dedicated to the computation of the far field at a distance from the target via the Helmholtz-Kirchhoff integral, using the near field sampled on the target surface, together with Green's functions capable of describing a two-layered water-sediment fluid medium. Those geometries, for which the overall axial symmetry is broken by the presence of the water-sediment boundary, can be treated approximately by taking into account the boundary-reflected incident field, as well as the first order interaction between the target-scattered echo and the sea floor. The numerical technique is validated by comparison with data collected during the EVA trial.