bluuebunny/crossref_metadata_2025 huggingface dataset:
Historical ambient noise levels in a topographically isolated basin
Authors: Reeder D. Benjamin , Mach Susan M. , Sheffield Edmond S.
Published: May 2008

During the late 1970s and early 1980s, careful measurements of ambient noise were made in the Tongue of the Ocean (TOTO) in the Bahamas. The measurements were made using a vertical array of five omni-directional hydrophones moored in 2200 m water depth with an average hydrophone depth of 122 m. Data were collected within a 20 Hz - 20 kHz band at ten specific 1/3 octave band frequencies, and then reported in spectrum level as a function of surface wind speed. Records contaminated by anthropogenic sources (e.g., local vessel traffic), biological sources (e.g., marine mammal vocalizations) and other sources (e.g., rain) were eliminated to allow analysis of background ocean ambient noise only. TOTO is a deep basin, topographically isolated from the Atlantic Ocean, and therefore largely acoustically decoupled from the Atlantic Ocean deep sound channel. The basin's geographical isolation and the controlled data collection methodology employed over a four-year period make this three-decade-old data set a potential proxy for preindustrial era ocean noise levels. The environmental setting, data collection methodology, analysis methodology and results are presented and discussed within the context of historical ocean ambient noise levels.
Analysis of wind generated shallow water ambient noise
Authors: Poikonen Ari , Madekivi Seppo
Published: May 2008

Underwater ambient noise measurements were carried out in very shallow water (10-20 m) in the archipelago of the Gulf of Finland during the full year. Weather conditions varied from calm sea to near gale winds. The lowest spectral levels were obtained under the ice cover during the coldest winter months. No seasonal effect was observed in the measured spectra. The role of water depth was modeled with several bottom sediments in order to identify possible channel effects at lower frequencies of the noise spectra. The ambient noise spectra are typically bandlimited. A bandpass filter model was thus fitted to the noise spectra. The filter model provides several useful parameters to characterize the effect of wind speed on the noise spectra. The cutoff frequency of the high-pass part of the spectra decreases from ca 400 Hz down to below 200 Hz as wind increases from light breeze to near gale force. The corresponding spectral slopes get steeper with increasing winds saturating to the value of 12 dB/oct already in fresh breeze. The other parameters used in the analysis are high frequency (low-pass) spectral slope, the frequency of maximum spectral level, noise bandwidth and total power in the band.
A review of approaches towards effective underwater sensor networks
Authors: Leonard Michel , Merani Diego , Berni Alessandro
Published: May 2008

The still largely unexplored vastness of the ocean, covering about two-third of the surface of earth, has fascinated humans for as long as we have records for. Its currents, chemical composition, and ecosystems are all highly variable at different locations and times. New paradigms for the monitoring of the undersea environment, based on autonomous underwater sensor nodes organized in ad-hoc coalitions, offer a promising approach towards the development of scalable networks for underwater sensing, monitoring, reconnaissance and surveillance. This promise has however to be balanced against important challenges, which need to properly addressed in order to devise a credible system concept. Some challenges worth mentioning are the difficulty in ensuring a low error-rate end-to-end path between source and destination for the duration of the communications session, the negative impact of communications performance characteristics at applications level, and energy constraints for battery-operated nodes. The requirement is therefore to design new protocols to provide network flexibility and reliability through self-organization and reconfiguration, as well as new energy-efficient routing schemes, including geographic and data-centric routing, to maximize the operational lifespan of autonomous power-constrained nodes. In this paper we will present the state of the art and approaches being investigated at NURC.
Nested Autonomy - Adaptive and collaborative sensing with hybrid sensing networks
Authors: Balasuriya Arjuna , Schmidt Henrik , Benjamin Michael B.
Published: May 2008

Control of undersea sensing networks is restricted by the limited acoustic communication capacity and the need for surfacing “data-mules” for communicating with the operators. Adaptive sampling of episodic events must therefore be performed fully autonomously. Similarly, collaboration between nodes is limited by the communication horizon. These constraints favor the use of a nested operational paradigm, with clusters of highly autonomous nodes capable of detecting, classifying, and localizing episodic events, if possible collaborating with neighboring nodes without operator intervention. Such a Nested Autonomy operational paradigm is being developed for capturing episodic oceanographic events by AUVs and gliders in the NSF ORION ocean observatory. Based on the portable, open-source MOOS-IvP autonomous control framework, the same paradigm is being applied for distributed acoustic surveillance networks in the ONR PLUSNet program. In either case the nested autonomy enables the autononomous exploitation of the environmental and tactical situation, and collaborative tracking of targets or oceanographic events. The operator control is limited to very simple deploy and prosecute commands. The performance of the nested autonomy paradigm is demonstrated by examples using a high-fidelity simulation environment, and by results from recent field experiments. [Work supported by ONR.]
The applicability of a small autonomous vehicle towed array system to ocean acoustic measurements and signal processing
Authors: Carey William M. , Holmes Jason D. , Sullivan Edmund J. , Lynch James F.
Published: May 2008

An array was developed to demonstrate, and quantify the performance characteristics of an autonomous-vehicle towed-array system. This technology provides for a cost effective tool for the measurement of coherent signal propagation, depth dependent and directional noise fields and to establish quantitative limits on array performance. The tangential drag on a 40-m length array composed of a reinforced tube with an outer diameter of 2.8 cm is extrapolated to be between 20-28 N for diameter Reynold's number of approximately 4 104. The hydrophone- preamplifier groups have a sensitivity of –174±1.5 dB re 1μPa/V between 100 Hz to 10 kHz. with an adjustable spacing between 0.5 and 1.5 m. The system tow stability enabled the use of the synthetic Hankel transform to estimate the modal horizontal wave number spectrum and the identification of interface wave speeds at frequencies up to 1000 Hz. The formation of synthetic apertures combined with model based extended Kalman filter techniques was found to demonstrate both narrow band and broadband tracking. Finally the system is shown to provide a unique measurement capability for directional noise measurement in shallow water environments.
Several imaging algorithms for synthetic aperture sonar and forward looking gap-filler in real-time and post-processing on IXSEA's “Shadows” sonar
Authors: Jean Frédéric
Published: May 2008

SHADOWS is a new sonar system developed by IXSEA SAS. It is a towed composed of a synthetic aperture side-scan sonar and a forward-looking sonar. The system produces SAS images with a constant resolution 15 cm from 30 m to 300 m on each side. It also fills the nadir gap from 0 to 30 m with images having 40×15 cm resolution. The images are provided in real-time and are georeferenced. The synthetic aperture sonar algorithm uses INS data combined with the Displaced Phase Center Algorithm (DPC). Differences between INS and DPC navigations can be used to compute a topography profile of the ground. The post processing and real-time modes differ on the weight given between INS and DPC, and on the approximations to be done. The real-time beam-forming algorithm used is the time-domain fast factorized back projection which can be pushed to an exact back projection in the post processing mode. The forward-looking sonar uses a patented “sectorized emission” architecture. The images are side-scanlike. The real-time algorithm can be customized to make some incoherent integration on several pings increasing the contrast but slightly decreasing the resolution. A post processing algorithm can also provide an animation on a specific contact on the floor.
Passive synthetic aperture as an experimental tool
Authors: Sullivan Edmund J. , Carey William M. , Holmes Jason D. , Lynch James F.
Published: May 2008

The use of autonomous undersea vehicle towed arrays offer an inexpensive way to carry out oceanographic measurements. Due to the small size and limited power of such vehicles, the physical aperture of the array is necessarily limited and the tow speed is low. However, there is an advantage in that short arrays at low speeds can have no flow noise. In addition the use of passive synthetic aperture (PSA) to provide spatial resolution and gain can play a major role. Here, we describe the use of two forms of passive synthetic array processing used in a shallow-water experiment. A six-element towed array, with 0.75 m spacing, was used to estimate the horizontal wave numbers of a propagation channel. A narrow-band form of PSA will be described which was used to generate coherent spatial gain by generating an aperture hundreds of wavelengths and provided accurate estimates of the horizontal modal wave numbers at frequencies les than 600 Hz. A broadband form of PSA was used to provide bearing estimation of a ferry passing through the area. The ferry's broadband propulsion noise, which was in the 900 Hz region, was used as the source. An overall increase in gain is demonstrated.
Radar and sonar interferometry
Authors: Garello René , Sintes Christophe , Gueriot Didier , Nicolas Jean-Marie
Published: May 2008

This paper is an attempt to compare two interferometric processings. The first one is applied to traditional space-borne radar (SAR) and the second on recent interferometric sonar data. Few comparisons between those tech-niques have already been made, despite the fact that they share many similar principles, only a. Thus, the key idea of this article is to present both techniques with assets, drawbacks and specific “tricks” used in dataprocessing. The first part introduces briefly both sensors and compares signal and processing techniques used for both of them. The second part deals with interferometry, and more precisely with underwater and satellite interferometry. Then a noise-pollution analysis is performed on both techniques followed by bias removal methods for getting interferometric information. The conclusion summarizes the similarities between sonar and radar processing, pointing at the techniques that can applied to both.
Theoretical considerations in the prediction of decay times for the Philharmonie de Paris
Authors: Scelo Thomas , Marshall Harold , Valentine Joanne O.
Published: May 2008

The brief for the Philharmonie de Paris includes the requirement that the hall should combine great clarity with high reverberation. The proposed solution, which won the design competition, consists of two nested chambers: an inner space producing acoustical intimacy and an outer space with its own architectural and acoustical presence. The interaction between these two spaces gives the possibility for the full range of acoustical adaptability required in the acoustical brief. This paper reports on some theoretical modelling work for the hall where the geometry considered is first described in the context of coupled space modelling. The predicted range of the variability achieved in the design by closure of the coupling openings is then presented. Finally, the paper discusses the appropriateness of these models when predicting the decay times in such a complex geometry.
Travel-time sensitivity kernels in long-range propagation
Authors: Skarsoulis Emmanuel , Cornuelle Bruce , Dzieciuch Matthew
Published: May 2008

The effect of increasing range on the sensitivity of finite-frequency travel-time observables to sound-speed perturbations is studied using the notion of wave-theoretic sensitivity kernels based on the first Born approximation of the Green's function and the notion of peak arrivals. Travel-time sensitivity kernels are examined in a range-independent background ocean environment. While at medium ranges the kernels exhibit zero-sensitivity cores on the eigenrays, these cores shrink and disappear at long ranges due to refraction and the kernels converge in the vertical towards the corresponding eigenrays; this behavior is not observed in free space. On the other hand the kernels expand in the horizontal cross-range direction and attain their maximum extent at the midpoint between source and receiver, similar to the behavior of the Fresnel volume in free space. Thus, stratification affects the shape of the sensitivity kernel in the vertical preventing expansion with increasing range but not in the horizontal such that the sensitivity kernel takes the form of a folded rug expanding the eigenray in the horizontal cross-range direction. [Work supported by ONR.]
Simulated response of the human lung to low-frequency underwater sound using a finite-element-based thoracic model
Authors: Wochner Mark S. , Ilinskii Yurii A. , Hamilton Mark F. , Zabolotskaya Evgenia A.
Published: May 2008

In a previous paper, inhomogeneity within the lungs and its influence on the lung's response to low-frequency underwater sound using a finite-element-based model was discussed [Wochner, et al., J. Acoust. Soc. Am. 122, 2957 (2007)]. Here we report an extension of the previous work that adds surrounding organs to the finite element model. It is hypothesized that the significant damage that can occur at relatively low amplitudes when the lung is in resonance is due primarily to the shear stresses that can occur in the lung through its interactions with surrounding organs. In particular, the heart, diaphragm, and ribs, all of which have considerably different material properties compared to lung, may have a sizable effect on the lung's response to low-frequency underwater sound. This paper will discuss the resonance frequency, motion, and stress and strain fields produced using this new finite-element-based thoracic model. [Work supported by ONR and ARL:UT IR&D.]
Noninvasive monitoring of mesenchymal stem cells by 1.2 GHz acoustic microscopy
Authors: Von Buttlar Moritz , Twerdowski Evgeny , Wannemacher Reinhold , Grill Wolfgang
Published: May 2008

Cell-based therapies can benefit from noninvasive and marker-free monitoring techniques for living cells. For this purpose a phase-sensitive scanning acoustic microscope operating at a frequency of 1.2 GHz was combined with a commercial confocal laser scanning microscope. The system is equipped with a live-support system for the long-term observation of living cells. Confocal acoustic imaging with phase and magnitude contrast and confocal laser scanning microscopy can be performed simultaneously. Both techniques are used in reflection from opposing sides of the object. Time-lapsed acoustic microscope images of ovine mesenchymal stem cells are presented. For this purpose, a pseudo-3D representation is generated by encoding the unwrapped phase in the height and the magnitude in the brightness. In the case of highly reflective substrates and sufficiently low reflection from the interface between the cells and the surrounding fluid the echo from the top of the cells can be neglected and the phase contrast image can be transformed to a time-of-flight image. In the same approximation the magnitude image provides information about the gradual extinction of the echo signal due to absorption in the cells. The two images can be combined to generate a new form of contrast representing the product of the absorption coefficient and the velocity of sound inside the observed cells.
Air-borne and tissue-borne sensitivity of skin-radiation acoustic sensors
Authors: Zanartu Matias , Ho Julio C. , Kraman Steve , Pasterkamp Hans , Huber Jessica E. , Wodicka George R.
Published: May 2008

Measurements of body sounds on the skin surface have been widely used in the medical field and continue to be a topic of current research, ranging from the diagnosis of the respiratory and cardiovascular diseases to the monitoring of voice dosimetry. These measurements are normally acquired by means of light-weight accelerometers and/or air-coupled microphones attached to the skin. Such recordings can be corrupted by air-borne sounds that are generated by the subject or by other sources of background noise. In this project, the sensitivity of various commonly used bioacoustic sensors to airborne sounds was evaluated and compared with their sensitivity to tissue-borne body sounds. To delineate the sensitivity to each pathway, the sensors were first tested in-vitro, and then on human subjects. The results indicated that in many cases the air-borne sensitivity is sufficiently high to significantly corrupt body sound signals. The effectiveness of different air-borne insulation devices was also evaluated. Spectral analysis showed that simple acoustic insulators (e.g., passive hearing protectors) provide significant attenuation within the range of frequencies of interest for most applications, particularly when using air-coupled microphones.
Are classrooms in historical buildings compatible with good acoustics standards
Authors: Maffei Luigi , Iannace Gino , Masullo Massimiliano
Published: May 2008

Many surveys and researches have underlined that the acoustic characteristics of classrooms are strictly connected to performances of students and to the stress of the teachers during lessons. In standard classrooms sound quality can be easily reached without sound amplification but introducing appropriate sound absorbing/scattering materials at the ceiling and/or at the vertical walls. Nevertheless in historical buildings with vaults or trusses, high walls and many architectural restrictions imposed by district superintendent, it could be very difficult to achieve good acoustics standards with widespread solutions. In this paper the acoustic performances of different classrooms in an historical Monastery actually center of the Faculty of Architecture of the Second University of Naples are analysed. After these analysis, compatible architectural and acoustic solutions to improve the sound quality were developed and tested in laboratory measurements and then applied in some classrooms to verify the benefits.
Noise - A stress factor? Acoustic ergonomics at schools
Authors: Tiesler Gerhart , Oberdoerster Markus
Published: May 2008

Description of teaching reality is the main topic of this interdisciplinary examination about “acoustic ergonomics of schools.” In the first step we analyse how different teaching methods affect basic noiselevel and working noise level. Which effect has an altered room acoustics on the sound levels in the context of each teaching method. The data records available as timeseries allows for the first time analysing single phases of lessons, which are characterized by certain pedagogical characteristics or individual instruction phases. Is it correct to speak of “noise stress” or is this stress an emotional reaction to the kind of? Based on recordings of teachers heartrate we analyse in the third step the effects of noise level on the workload of the teachers as a stress reaction. A distinction is made on the subject of different teaching methods, and on the basis the different room acoustic conditions. In one primary school we had four classes with a RT>0.5 s and four further classes with a RT<0.5s. At a second primary school we analysed the effect of the room acoustic refurbishment. Finally we investigate factors of fatigue. Which effect has CO2 in the classroom on all people, and the working noise level?
Subjective evaluation of acoustical quality of lecture rooms with respect to the quality of the sound reinforcement system and the level of background noise
Authors: Grubesa Sanja , Horvat Marko , Domitrovic Hrvoje
Published: May 2008

As a part of a general questionnaire on the quality of lecturing on the Faculty of EE and Computing in Zagreb, Croatia, the students have to grade the acoustical quality of lecture rooms in an indirect way by giving answers to several questions included in that questionnaire. As the sound reinforcement system in two largest lecture halls is in rather bad condition, it is to be replaced in the near future with a new one of significantly better quality. The goal of this paper is to examine whether this change is reflected in the grades of acoustical quality given by the students. In the second part of the paper, the students' grades on acoustical quality of two smaller lecture rooms of identical size and acoustic treatment are compared. The comparison is made with respect to the position of these rooms relative to the nearby street as the source of traffic noise. The overall level and spectral content of noise are measured in those lecture rooms. The correlation is then examined between the results of these measurements and the grades given by the students.
Infrasonic and seismic signals from explosions in Northwestern Europe
Authors: Evers Laeslo G. , Haak Hein
Published: May 2008

Large explosions often generate both seismic and infrasound signals that can be detected over large ranges, i.e., hundreds of kilometers. Ground truth of such explosions is available from direct observations and/or seismic signals and can be used to get insight in the propagation of infrasound. Long range infrasound propagation is controlled by the state of the atmosphere. Tropospheric, stratospheric, and thermospheric ducts might exist and have implications on the signal characteristics and their detectability. In this study, we will show results of studies on explosions in Northwestern Europe using both seismic and infrasound data. These observations are used to derive source characteristics like: location, origin time and yield. Furthermore, the propagation characteristics of infrasound will be addressed.
Deducing ground structure using seismic pulses originating from an outdoor explosive source
Authors: Taherzadeh Shahram , Attenborough Keith
Published: May 2008

Near-surface layering of ground soil can influence propagation of acoustic and seismic pulses originating from above-surface sources. Simultaneous recording of acoustic air pressure and seismic radial and vertical particle velocities resulting from a small, above ground explosion is used to obtain information about soil structure near the surface. Assuming nonlinear effects to be small at the ranges of interest here, a numerical model called Fast Field Program for Layered Air Ground Systems (FFLAGS), developed originally for continuous sound sources above a porous elastic ground is used to model a porous elastic layered ground system. Suitable optimisation methods were used to predict a set of best fit parameters for the near-surface ground structure. It is shown that the model can explain multiple seismic arrivals and give a reasonable prediction of wave speeds and layer depths while the pressure pulse can predict permeability of the surface soil.
Axisymmetrical and nonaxisymmetrical guided waves propagating in a solid elastic cylinder embedded in a solid medium
Authors: Yaacoubi Slah , Laguerre Laurent , Ducasse Eric , Deschamps Marc
Published: May 2008

For NDT of rods and pipes, fundamental characteristics of guided waves are to be known, especially dispersion relations between frequency and wave number. A necessary step before detecting defects is to be able to calculate the propagated elastodynamical field in healthy waveguides. Thus, the goal of this work is the calculation of this field propagating in a cylindrical stratified waveguide. The incident field is generated at the end of the cylinder by a force or velocity source which is off-axis and Gaussian distributed. First, Vector Hankel transform and Fourier series are combined to decompose this field with respect to the angular position. Second, each component is decomposed into an infinite sum of rays, i.e., elementary generalized conical waves. These waves undergo multiple reflections with the guiding surface of the waveguide. Third, we use Generalized Debye Series (GDS) for calculating the global reflection coefficients resulting from these multiple reflections. Finally, the total field is synthesized by the summation of the incident and reflected rays. Many outputs of this code can be exploited like velocity field, stress field, energy field in 2D or 3D spatiotemporal or frequential simulations. Diagrams obtained by this code are compared with results from DISPERSE software.
New results on the sound velocity measurements under extreme conditions using time-resolved picosecond acoustic technique
Authors: Decremps Frédéric , Belliard Laurent , Perrin Bernard , Gauthier Michel
Published: May 2008

In this presentation, recent works on the pressure and temperature dependence of the sound velocity will be discussed. We have used a newly developed method combining the time-resolved picosecond optical technique and a diamond anvil cell [1]. This setup makes possible accurate measurements of the attenuation and velocity of longitudinal waves in the Ghz range, and opens the elastic investigations of all materials (opaque, transparent, single- or polycrystal, liquids) up to several Mbar and thousands of K. The experimental method will be first described, with a discussion of the factors limiting the possibilities and the technique accuracy. [1] F. Decremps, L. Belliard, B. Perrin, and M. Gauthier, Phys. Rev. Lett, to be pubished in January 2008.
Elastic moduli at high temperatures with two different ultrasonic methods
Authors: Bourgeois Ludivine
Published: May 2008

“The elastic moduli and specially the shear modulus G is one of the parameters needed to implement the constitutive relations. These mechanical properties can be measured for a solid or a liquid with different ultrasonic methods. This paper deals with the determination of G(T) with two different methods: a contact delay-line ultrasonic device which has been developed to measure the shear and compression waves velocities up to 1000 K on cylindrical specimens and a contactless (laser) ultrasonic device which can measure surface acoustic waves velocities in metals up to the melting point. Results on metals such as Al without phase transition and for Co through the phase transition will be presented.”
Absorption and velocity of acoustical waves in binary solutions of poly (ethylene glycol) and water
Authors: Singh Rajendra Kumar , Singh Manish Pratap , Singh Rishi Pal
Published: May 2008

A resonator technique has been devoleped to measure ultrasonic velocity and absorption for aqueous solutions of PEG of different molecular weights. The velocity has been measured at different frequencies and the concentrations (by weight) ranged from 1% to 10% of poly (ethylene glycol) in water. Adiabatic compressibility has been obtained at different temperatures, using experimental value of velocity and density. Viscocity has also been measured in wide temperature range . Ultrasonic absorption has been measured in the frequency range 400 KHz-50 MHz, using resonator technique and pulse technique in temperature range 400-650 °C. Observations showed that the ultrasonic absorption decreases with increasing temperature at a given concentration and also increases with concentration at a given temperature. The velocity increases with increasing temperature and concentration. Shear viscosity has been found to decrease with temperature but increases with concentration. Velocity studies show that as the polymer concentration increases a more rigid molecular structure is formed by bonding between the large polymer molecules.
V(z) oscillations in acoustic microscope at upward defocusing
Authors: Kozlov Anton V. , Mozhaev Vladimir G.
Published: May 2008

Acoustic microscopy is widely used for imaging and study of elastic properties of transparent and opaque materials. As a rule, multiple periodic oscillations in the output signal V of a reflection acoustic microscope can be observed in the case of negative defocusing of the wide-angle acoustic lens, i.e., when its focus is a distance z below the solid sample surface. The main well-known mechanism for V(z) oscillations is the interference of radiation reflected perpendicularly from the sample surface and re-radiation of leaky Rayleigh waves generated on the sample by the lens. This effect explains high contrast imaging in reflection scanning acoustic microscopy, and it is a popular method to study properties of solids by measuring Rayleigh wave speeds. As it is shown in this work, bulk acoustic waves in the sample can also give rise to V(z) oscillations. A new mechanism of such oscillations is predicted in the case of positive defocusing (focusing above the sample surface) in acoustic microscopy of anisotropic plates exhibiting negative acoustic refraction. The ray model of this effect shows a possibility to find a relationship between extrema of V(z) curve and separate points on the acoustic slowness surface of the sample.
A global search tool for the equivalent source method and its applications to the scattering problem
Authors: Gounot Yves J.r. , Musafir Ricardo E.
Published: May 2008

Low computational-cost solutions to the acoustic scattering problem can be obtained with the equivalent source method (ESM), provided the sources are adequately positioned. Because this last point represents often a complicated task - mainly responsible for the not much widespread use of the method - a technique that hurdles this difficulty, called ESGA, has been previously proposed (Gounot and Musafir, Internoise 2004). Based on a combination of genetic algorithm with ESM, the ESGA is a global search tool that provides, given a set of monopoles, their 'optimal' positioning and complex amplitudes. The technique efficiency is here shown through a number of three-dimensional scattering problems. The algorithm is also used in order to identify, for each of the different cases considered, typical geometrical arrangements of monopoles which provide good solutions.
Identification of intervocalic consonants in stationary and nonstationary noise
Authors: Cooke Martin , Scharenborg Odette
Published: May 2008

The factors which underlie the perception of consonants in noise remain poorly understood. In this study, native listeners identified 24 English consonants spoken by eight talkers presented in nine intervocalic contexts with varying stress position. Listeners were tested in 5 noise conditions: tokens were masked by stationary speech-shaped noise, a competing talker, three and eight speaker babble and speech-modulated noise, all of which have the long-term spectrum of speech. The rank ordering of consonant identification scores in stationary noise was highly-correlated (r=0.9, p<0.0001) with a similar condition reported by Phatak and Allen [JASA 121: 2312-2326, 2007], but less so in the four nonstationary noise backgrounds (r=0.74, p<0.001). In particular, /y/, /r/, /l/, /f/, /ch/, /sh/, /m/ and most of the plosives showed a wide variation in ranking. These findings suggest that, in addition to the long-term spectrum of the masker, consonant identification is noise is affected by other factors such as temporal fluctuations in the masker, misallocation of foreground/background components and attention.
The interaction of glimpsing, pitch and vocal tract length in the recognition of concurrent syllables
Authors: Vestergaard Martin D. , Fyson Nicolas R. , Patterson Roy D.
Published: May 2008

In multispeaker environments, human listeners use the temporal misalignment of competing speech signals to improve recognition- an effect referred to as “glimpsing.” When the temporal envelopes of concurrent syllables pairs are carefully matched to preclude glimpsing, listeners were observed to use vocal tract length (VTL) and glottal pulse rate (GPR) cues to improve recognition. This paper reports an investigation of the interaction between glimpsing and these vocal cues. Syllables were synthesized with a vocoder to simulate speakers with widely different combinations of GPR and VTL. Recognition of one syllable in the presence of a concurrent syllable was measured as the vocal cues and the temporal alignment of the syllables were varied. The effect of glimpsing was most pronounced when the vocal cue differences between the target and distracter syllables were small. Furthermore, there was a strong effect of consonant type (stops, fricatives, or sonorants) and an asymmetry between consonant-vowel (CV) and vowel-consonant (VC) syllables. The lowest recognition rate was observed, not at perfect temporal alignment but rather at a distracter lag of -50 ms for CVs and 100 ms for VCs. The results are analyzed with confusion matrices. Research supported by the UK MRC [G0500221, G9900369].
Smart sound environments: merging intentional soundscapes, nonspeech audio cues and ambient intelligence
Authors: Jung Ralf
Published: May 2008

We introduce an intelligent audio notification system for multiuser environments that provides users with information about events (e.g., important emails) in a more discreet and non-distracting way. The peripheral awareness of individual-related events is done by using nonspeech audio cues which can be seamlessly integrated into artificial background soundscapes. These ambient soundscapes are self-composed with respect to well-known perceptual constraints such as auditive Gestalt laws as well as music psychological findings. To follow a hierarchical approach for the notification sounds we use notification instruments, ambient noises and traditional alert signals that are grouped by their level of intrusiveness. Since the notification system also follows a human-centered approach it takes parameters like user preferences, his/her current position in the environment and the type of event into consideration to decide which notification is the appropriate at this time. In the paper, we will describe the architecture of the personalized ambient audio notification service, compositional constraints as well as some findings of a user study in which we tested successfully the efficiency of our system with 25 subjects.
Recording of anechoic symphony music
Authors: Lokki Tapio , Pätynen Jukka , Pulkki Ville
Published: May 2008

When designing the acoustics of a concert hall, it would be beneficial to be able to use real recording of a symphony orchestra in auralization. The technical constraints for such recordings are high. First, the instruments have to be recorded separately, as in simultaneous recording the cross talk between microphones could not be avoided. Second, the recording room should be anechoic. Third, the instruments have different sound radiation patterns, thus they should be recorded with multiple microphones around them. Therefore, we end up recording each instrument individually in an anechoic chamber with multiple microphones. The remaining problem is to achieve a common timing as an ensemble between the individually recorded instruments. This was solved by first recording a video of a conductor conducting a pianist playing the whole score. The players in an anechoic chamber then followed the conductor in a monitor while listening the pianist on headphones. Four short passages, from two to four minutes, from different music styles were recorded. The recordings were made with 20 low-self-noise microphones, mounted on the shape of a dodecahedron. Finally, we discuss the musical and technical quality of recorded sound, and the response by the musicians, who were professional orchestra players.
Multimodal control of talking heads
Authors: Bailly Gerard , Govokhina Oxana , Breton Gaspard
Published: May 2008

Multimodal speech synthesis has been devoted for years to the rendering of linguistic or paralinguistic content - i.e., parametrized but discrete information - by continuous audible and visible consequences of speech articulation, eventually complemented by facial expressions, gaze and other body gestures including head, hand, and arm movements. Articulatory synthesizers (producing sounds from gestures) intrinsically compute coherent audiovisual signals but do not presently compete with data-driven techniques: most talking heads are nowadays controlled by models built using human audiovisual data. These control models should replicate the laws governing the coherence of observed multimodal signals and the correct phasing relations between salient events of the multimodal stream. We will report on two comparative evaluations of various lip-sync models (dealing with post-synchronization between speech sounds and articulatory movements) and present a trainable control model that learns automatically phasing relations between acoustic and gestural events. This model can be further extended to capture the fine temporal structure of multimodal scores and a first application to the synchronization between speech and head, face and hand movements during cued speech production will be presented.
A comparison of visual features for audiovisual automatic speech recognition
Authors: Ahmad Nasir , Datta Sekharjit , Mulvaney David , Farooq Omar
Published: May 2008

The use of visual information from speaker's mouth region have shown to improve the performance of automatic speech recognition (ASR) systems. This is particularly important in presence of noise which even in moderate form severely degrades the speech recognition performance of systems using only audio information. Various sets of features extracted from speaker's mouth region have been used to improve upon the performance of an ASR system in such challenging conditions and have met many successes. To the best of authors knowledge, the effect of using these techniques on recognition performance on the basis of phonemes have not been investigated yet. This paper presents a comparison of phoneme recognition performance using visual features extracted from mouth region-of-interest using discrete cosine transform (DCT) and discrete wavelet transform (DWT). New DCT and DWT features have also been extracted and compared with the previously used one. These features were used along with audio features based on Mel frequency cepstral coefficients (MFCC). This work will help in selecting suitable features for different application and identify the limitations of these methods in recognition of individual phonemes.
Spatial rendering of audiovisual synthetic speech use for immersive environments
Authors: Noisternig Markus , Katz Brian F. , D'Alessandro Christophe
Published: May 2008

Synthetic speech is usually delivered as a mono audio signal. In this project, audiovisual speech synthesis is attributed to a virtual agent moving in a virtual three-dimensional scene. More realistic acoustic rendering is achieved by taking into account the position of the agent in the scene, the acoustics of the room depicted in the scene, and the orientation of the virtual character's head relative. 3D phoneme dependant radiation patterns have been measured for two speakers and a singer. These data are integrated into a Text-To-Speech system using a phoneme to directivity pattern transcription module which also includes a phoneme to viseme model for the agent. In addition to the effects related to agent's head orientation for the direct sound, a room acoustics model allows for realistic rendering of the room effect as well as the apparent distance as depicted in the virtual scene. Real-time synthesis is implemented in a 3D audio rendering system.
Stability of wavefronts at sound propagation in highly structured three-dimensional environments
Authors: Godin Oleg A.
Published: May 2008

Extensive numerical modeling of long-range propagation of sound and seismic waves as well as observations of underwater acoustic fields with line arrays reveal that wavefronts are often much more stable and predictable than the rays comprising these wavefronts. This paper considers multiple scattering of sound by environmental inhomogeneities with spatial scales small compared to the propagation range but large compared to the wavelength. These inhomogeneities include 3D variations in sound speed and current velocity that are small compared to the average sound speed, can be either random or deterministic, and are superimposed on an arbitrary slowly-varying background. A theoretical explanation of wavefront stability in highly-structured environments is achieved by demonstrating that end points of rays launched from a point source and having a given eikonal (phase) are scattered primarily along the wavefront corresponding to the same eikonal in the unperturbed environment. The ratio of displacements of the ray end points along and across the unperturbed wavefront is proportional to the number of uncorrelated scattering events. The results apply to conventional rays and to horizontal rays describing propagation of adiabatic normal modes in almost-layered media. The origin of relative stability of wavefronts compared to rays is traced back to Fermat's principle.
Depth-dependent resonant target strength analysis of a dense Atlantic Herring school from wide-area OAWRS and localized 3D morphology sensing
Authors: Cocuzzo Daniel , Gong Zheng , Andrews Mark , Bertsatos Ioannis , Chen Tianrun , Pena Hector , Weber Thomas C. , Makris Nicholas , Ratilal Purnima
Published: May 2008

The depth-dependent target strength of Atlantic Herring is estimated at several distinct bandwidths close to their resonance frequency for a localized, highly dense school observed during the NOPP-sponsored Gulf of Maine Experiment on September 22, 2006. An ocean acoustics waveguide remote sensing (OAWRS) system was deployed near George's Bank to investigate the migration and spawning behavior of fish over wide areas. In conjunction with OAWRS, a Simrad EK60 conventional fish-finding echosounder (CFFS) and a Reson Seabat 7125 multibeam sonar system were deployed to provide local depth extent and 3D volume morphology of the dense herring school. The calibration of low-frequency target strength derived from OAWRS data using localized CFFS density and multibeam 3D volume estimates as inputs is discussed. The correlation between the mean depth of the vertically migrating herring school and its resonance frequency is investigated. The results are compared with a theoretical model for 3D resonance scattering from fish swimbladder modeled as a spheroidal bubble. This analysis may allow inference of fish depth and species classification based on the scattered frequency response of targets imaged by OAWRS. Implications for classifying general localized targets, biological or man-made, are discussed further.
Application of the matrix Rytov method to the calculation of the coherence function of a sound field in an oceanic waveguide
Authors: Voronovich Alex G. , Ostashev Vladimir E.
Published: May 2008

Closed equations for the coherence function of a monochromatic sound field propagating in a statistically inhomogeneous 3D oceanic waveguide have high dimensions and are difficult to solve even with the use of modern computers. Significant reduction of the dimension of the problem was achieved by assuming that sound speed fluctuations are statistically isotropic in a horizontal plane. However, even in this case calculation of the coherence function for a megameter range takes about a day. In this paper, we develop an approximate solution of the closed equations for the coherence function which is similar to a matrix version of the Rytov method. An explicit expression for the coherence function is obtained which contains exponent of an "interaction" matrix. This matrix is determined in terms of the acoustic and internal wave modes and spatial spectrum of the sound speed fluctuations. It is shown that the matrix Rytov method provides an accurate solution for the coherence function which coincides with the solution of the closed equations within a few percent. Calculation of the coherence function now takes only about an hour. This allows us to study in detail the dependence of the coherence function on parameters of the problem.
Measurements of 3D propagation in the shelf environment
Authors: Heaney Kevin D.
Published: May 2008

In the Fall of 2007 measurements were made to calibrate the acoustic environment on the shallow water shelf off the coast of Florida. The continental shelf is quite flat (less than 1 degree slope) for a region approximately 10 km wide. Transmissions to a cross-shelf 900 m horizontal line array were made from a source transiting along the shelf. The signal transmissions include broadband LFM (20-420 Hz) and a comb of narrow band frequencies spanning the same range. Narrowband beamforming results show the clearly identified source. The arrival angle for the source is as expected until a distance of approximately 30-40 km when there is an apparent bearing shift in-shore of up to 25 degrees. This behavior is expected in propagation on a shelf (of greater slope) but its behavior is surprising. The phenomenon was observed for several runs at various source and water depths. In order to explain the phenomenon, a hybrid adiabatic normal mode-Parabolic Equation method will be applied to the environment. This model computes the vertical modes and phase speeds at each location and then uses the PE to propagate each mode individually using it's spatially varying phase speed and attenuation. Comparisons of theory and data will be made.
Effects of solitons on acoustic energy flow in three dimensions
Authors: Smith Kevin B. , Colosi John A.
Published: May 2008

The impact of a train of nonlinear solitons on the propagation of acoustic energy in shallow water is examined. The soliton perturbations are based on an analytic formulation that produces a train of five soliton waves. Each wave front is parallel and has infinite extent in the horizontal direction. The acoustic field is modeled using a three-dimensional (3D) split-step Fourier parabolic equation (SSF/PE) approach defined in Cartesian coordinates. The standard PE approximation is employed in both depth and cross-range directions. Both pressure and particle velocity fields are computed in a self-consistent manner, allowing a full description of the 3D acoustic intensity field which describes the flow of energy in the presence of the solitons. Individual, low-order modes are extracted from the propagating field so that the impact on specific modes may be examined. The analysis is performed at various frequencies and for various source-receiver geometries relative to the soliton train. Emphasis is placed on the focusing and defocusing of acoustic energy between the various soliton waves. The impact of such soliton perturbations on signal variability and bearing resolution at the receiver will be quantified. [Work supported by ONR 321OA.]
Full field modeling of multiaspect scattering from buried objects
Authors: Karasalo Ilkka
Published: May 2008

Results are presented from a computational study of imaging of objects buried in the seabed under shallow water, using a rail-mounted active sonar and synthetic aperture processing. The medium is modeled as range independent, composed of a shallow water layer above a seabed of a muddy sediment containing the objects, and deeper subbottom layers. The objects have simple shape and structure, with diameters in the range 15-195 cm. From selected positions along the rail, the sonar insonifies the objects by LFM pulses from a directive transmitter, and records the backscattered echoes with a horizontal uniform line array (ULA), or optionally a pair of vertically separated ULAs. The signals from all sonar positions are integrated coherently by synthetic aperture processing for enhanced azimuthal resolution in the images of the objects. The parameters of the models of the medium, the objects and the experimental geometry are chosen to approximate those of a sea trial conducted in the Stockholm archipelago in 2004. The model-predicted scattered field is computed using the XFEM-S code, based on a frequency-domain boundary integral equation (BIE) formulation of scattering from a smooth object in a layered fluid-solid medium. Comparisons of model predictions with experimental results are presented.