bluuebunny/crossref_metadata_2025 huggingface dataset:
Cognitive control skills and speech perception after short-term second language experience during infancy
Authors: Conboy Barbara , Sommerville Jessica , Kuhl Patricia K.
Published: May 2008

Previous research has linked increasing cognitive abilities to reductions in sensitivity to nonnative phonemes toward the end of the first year, but found no association between cognitive skills and native speech perception (Conboy et al., 2006; Lalonde & Werker, 1995). The present study examined cognitive abilities and brain activity to second-language (L2) phoneme contrasts in infants who had short-term experience with the L2: we predicted better cognitive skills in infants with better discrimination of the L2 contrast. Seventeen infants from monolingual English homes completed event-related potential (ERP) speech perception testing and nonlinguistic tasks requiring attentional flexibility, memory, and inhibitory control at 11 months, after twelve Spanish play sessions from 9.5 - 10.5 months. An ERP oddball paradigm assessed discrimination of English and Spanish contrasts (English: voiced /da/ vs. voiceless-aspirated [tha]; Spanish: prevoiced /da/ vs. voiceless-unaspirated /ta/). Infants showed broad mismatch negativity (MMN) discriminatory responses to both contrasts. Larger Spanish MMN amplitudes were linked to better performance on cognitive tasks (detour-reaching object-retrieval and the A not B task) (Fisher's exact test, p=.01), suggesting a role for specific cognitive abilities in the early stages of phonetic learning. There was no association between English MMN amplitudes and cognitive skills.
Model based echo processing architectures for sonar target classification
Authors: Zakharia Manell E.
Published: May 2008

The discrimination between man-made and natural targets is faced to the problem of setting up appropriate processing architectures that extract relevant and robust parameters that could be used for classification. To be robust, signal models have to be associated to physical models and echo parameters have to be associated to physical ones. Several models already published are investigated: bright spots, generalized bright spots, resonances. Associated processing architectures are presented: matched filter, bank of filters, AR modeling. Their performance are compared on experimental data set obtained in tank. The discriminating performance are compared in the case of shells (man-made) and solid targets (natural) of the same shape insonified in a random incidence (monostatic). Following a detailed description of echo formation mechanisms in the time-frequency plane, an explicit time-frequency architecture is presented: the time-frequency filtering. Finally a new (all chirp) model based on velocity dispersion of surface waves ,is proposed that could reduce the number of discriminating parameters and be robust to minor changes of shell characteristics.
Automatic Acoustics Measurement of Audible Inspirations in Pathological Voices
Authors: Castilllo-Guerra Eduardo , Lee Williams
Published: May 2008

Audible inspiration (AI) is a type of speech perturbation commonly heard in pathologic voices. This acoustic parameter is used in conjunction with other acoustic observations to assess different types of pathologic conditions of speech associated with neurological or vocal cord disorders. However, the perception of this speech perturbation is often very subjective and difficult to appraise in a quantitative and consistent form. This work reports an algorithm to estimate the severity of this perturbation using time-frequency characteristics. The algorithm is based on a linear combination of the frequency of occurrence, the duration and the intensity of the inspirations. An algorithm to segment the AIs in conversational speech is proposed. The AI index was first evaluated with the Massachusetts Eye and Ear Infirmary Voice Database and then with two other databases containing recording from motor speech disorders. The segmentation algorithms was 90% effective detecting the audible inspirations and the AI index showed a high correlation (80.8%) with respect to the average perceptual judgment obtained from three judges with experience evaluating disordered speech.
Estimation of acoustic directivity from microphone array measurements using parametric models
Authors: Bulté Jean , Fleury Vincent , Davy Renaud
Published: May 2008

In this paper, we are interested in recovering the far-field acoustic pattern of a directive source from signals recorded in the near-field by an array of microphones with a reduced spatial extent. This question is particularly relevant in small test facilities where far-field acoustic measurements can not be carried out. A two-step approach is suggested. Firstly, the characteristics of sources are estimated from near-field measurements. Secondly, these characteristics are used to estimate the far-field radiation pattern. The main difficulty of this problem mainly resides in the first step. Due to the reduced spatial extent of the array, much information is lost about source characteristics, which mathematically leads to solve an ill-posed inverse problem. Our approach consists in using a parametric model based on physical assumptions, which has the virtue of regularizing the estimation problem. The suggested method is firstly evaluated with simulations, and then applied to experimental data recorded during aeroacoustic tests with a subsonic jet in an anechoic wind tunnel. It is shown that comparison between far-field measurements and estimated far-field pattern are in good agreement.
A volumetric interferometric synthetic aperture sonar reconstruction algorithm
Authors: Hayes Michael , Gough Peter T.
Published: May 2008

Interferometric synthetic aperture sonar (InSAS) bathymetric reconstruction is an inverse problem that is often simplified to a time delay estimation problem. This uses a simple system model of a continuous scattering surface with single scatterer per resolution cell. This model is violated by layover, multiple scattering, occlusions, or sea-surface multipath producing artefacts in the reconstructed image. While some artefacts, such as from occluded shadow regions, can be rejected by using a threshold on the correlation coefficient, this does not work in general. Moreover, since each pixel is reconstructed independently it is difficult to improve the reconstruction by adding prior information. In this paper we propose a reconstruction algorithm using a probabilistic volumetric model; similar to those used for photometric 3-D scene reconstruction from multiple cameras. While significantly slower than time delay estimation methods, the bathymetric reconstruction can be improved due to better scene modelling and the incorporation of priors such as surface continuity. Furthermore, an advantage of a volumetric model is that correction for the footprint shift is implicit. We demonstrate the algorithm using both simulated and real data.
An Overview of Bayesian Computational methods for audio signal processing
Authors: Godsill Simon J. , Cemgil Ali-Taylan T. , Peeling Paul
Published: May 2008

In this talk we describe Bayesian computational models and methods for inference about noisy audio signals, with the aim of performing tasks such as musical trnscription, source separation, automated annotation with content descriptors, noise reduction and object-based coding. The models are structured models of non-stationary sparsity in audio sources, usually expressed in the time-frequeny plane. The computational inference methods are based around Monte Carlo techniques including the particle filter for rapid on-line inference and Markov chain Monte Carlo for batch problems of higher compleixity. Examples will be given from the spheres of source separation, multiresolution noise reduction, denoising and intetrpolation of missing batches from audio. We will also describe their use for acoustical analysis of the properties of a musical instrument, focusing on the parameters of inharmonicity in struck or plucked strings.
Bayesian formant tracking using conditionally linear Gaussian models
Authors: Wolfe Patrick
Published: May 2008

Formants play a central role in the perception and analysis of speech. In this presentation we describe Bayesian approaches to estimating vocal tract resonances from speech waveforms, formulated as a statistical model-based tracking problem. In particular, approaches by Deng and colleagues have shown the promise of an extended Kalman filtering approach based on a robust linearization of the formant-to-cepstrum map. We describe recent extensions to model inter- as well as intra-formant correlation, and detail efficient inference schemes that preserve conditional Gaussianity. A database of formant trajectories provides a notion of ground truth by which estimator performance can be evaluated, and which demonstrates the efficacy of our approach relative to contemporary benchmark tools for formant analysis.
Bayesian tracking and geoacoustic inversion
Authors: Dosso Stan E. , Wilmut Michael J.
Published: May 2008

This paper describes a Bayesian approach to two related inverse problems in underwater acoustics: localizing/tracking an acoustic source when ocean environmental properties are unknown, and determining environmental properties using acoustic data from an unknown (moving) source. The goal of this work is not simply to estimate values for source and/or environmental parameters, but to determine parameter uncertainty distributions, thereby quantifying the state of knowledge and information content of the inversion. A common formulation is applied for both problems in which source parameters (location and spectrum) and environmental parameters are considered unknown random variables constrained by noisy acoustic data and by prior information on parameter values (e.g., physical limits for environmental properties) and on inter-parameter relationships (limits on horizontal and vertical source speed). Given the strong nonlinearity of the inverse problem, marginal posterior probability densities are computed numerically using efficient Markov-chain Monte Carlo importance sampling methods. Source tracking results are represented by joint marginal probability distributions over range and depth, integrated over unknown environmental parameters. The approach is illustrated with two examples representing tracking a quiet submerged source and geoacoustic inversion using noise from an unknown ship-of-opportunity. In both cases, source, seabed, and water-column parameters are unknown.
A nonlinear frequency-domain beamformer for underdetermined speech mixtures
Authors: Davies Michael , Dmour Mohammad
Published: May 2008

Extraction of a target speech source from among multiple interfering speech sources is challenging when there are fewer microphones than sources (the underdetermined case). Existing speech source separation techniques often suffer from artifacts as well as performance deterioration in reverberant environments, and in some cases also need to estimate the number of sources present. This paper introduces a frequency-domain non-linear beamformer that can perform speech source separation of underdetermined mixtures, is reasonably artifact free and does not require prior knowledge of the number of speakers. Our approach models the data via a Gaussian mixture distribution in the observation domain, which can be learned using the expectation maximization (EM) algorithm. A non-linear distortionless beamformer is then developed, based on this model. Simulations of the non-linear beamformer in underdetermined mixtures with room reverberation confirm its capability to successfully separate speech sources with virtually no artifacts.
Bayesian single channel blind speech dereverberation using Monte Carlo methods
Authors: Hopgood James R. , Evers Christine , Bell Judith
Published: May 2008

Audio signals in confined spaces exhibit reverberation due to reflections off surrounding obstacles. Moreover, the signal is distorted by noise, usually modeled as an additive signal observed within the room, independent of the microphone's location, and unaffected by the acoustics. Reverberation and noise cause significant deterioration of audio quality and intelligibility to signals recorded in acoustic environments. Bayesian blind dereverberation infers knowledge about the system by exploiting the statistical properties of speech and the acoustic channel. In the Bayesian framework, the reverberant and noisy signal can be enhanced by processing it either sequentially using online methods or in a batch using offline methods. This paper compares several distinct Bayesian approaches for single-channel blind speech dereverberation. These include Markov chain Monte Carlo methods for batch processing, and sequential Monte Carlo (particle filtering) methods for online processing. In the batch method, static parametric models are used for modeling the statistics of the speech and channel. Optimal parameter estimates are then used to enhance the observed signal. In the sequential approach, the clean speech signal is considered itself an unknown state. Various dynamical models and optimal sampling strategies are discussed for state estimation. The results demonstrate the superiority of the sequential method.
Sound intensity variations in the presence of shallow-water internal waves passing through acoustic track
Authors: Luo Jing , Badiey Mohsen , Karjadi Entin A. , Katsnelson Boris , Tshoidze Alexander , Moum James , Lynch James F.
Published: May 2008

Fluctuations of low frequency pulses (LFM signals in 270-330 Hz band) in the presence of internal solitary wave (ISW) packet during the SW06 experiment are analyzed to quantify the interaction of sound with ISW field. Three situations during approximately 2 hours (20:30 - 22:30 GMT of August 17, 2006) are considered: a period when ISW was absent, a period when ISW started to intersect the acoustic track, and a period when ISW occupied the acoustic track. The propagation direction, velocity, and amplitude of the ISW were estimated from the on-board radar images recorded by two research vessels along with temperature records of sensors moored at the source, at the receiver, and between the source-receiver track. Modeal and frequency filtering of received pulses was carried out as well as analysis of temporal variations of the field depth distribution. This analysis allows us to identify two different acoustic fluctuation mechanisms: horizontal refraction and adiabatic variability, and it confirms the previously proposed theory on the sound field fluctuations due to ISW. Work was supported by ONR and RFBR.
Simultaneous nearby measurements of acoustic propagation and high-resolution sound speed structure containing internal waves
Authors: Henyey Frank S. , Williams Kevin L. , Tang Dajun
Published: May 2008

On two occasions during the SW06 experiment, towed CTD chain measurements were made close to an acoustic propagation path. The acoustic path was 1 km long, oriented roughly in the direction of propagation of large nonlinear internal waves. On the first occasion, large nonlinear internal waves were absent, and on the second occasion, they were present. The CTD chain was towed in loops around the acoustic path, roughly 200 m on either side of the path. On the first occasion, 17 loops were made in about 5.5 hr, and on the second occasion, 7 loops were made in about 2.5 hr. Throughout these time periods, acoustic transmissions between 2 kHz and 10 kHz were carried out. The acoustic environment on the path is estimated by space and time interpolation between the tows on the two sides of the path. The acoustic data is compared with propagation modeling in this environment.
Spatial and temporal coherence of low-frequency acoustic field in shallow water: Experimental results
Authors: Guo Lianghao , Gong Zaixiao , Wu Lixin , Li Xilu
Published: May 2008

Spatial and temporal coherence of acoustic field has very important effects on applications of underwater acoustics. In this paper, recent experimental results of low-frequency signal coherence in shallow water are presented. For signals with low frequencies of 100∼500Hz in shallow water, the vertical correlation has no distinct depth dependence, but it has obvious range dependence. The horizontal correlation length is greater than 40 wavelengths, the temporal correlation length is greater than 510s at frequency of 475Hz and greater than 1800s at frequency of 150Hz. These experimental results show that low-frequency acoustic field has strong spatial coherence and temporal stability in shallow water. [Work supported by the National Natural Science Foundation of China under Grant No.10734100]
Observations of noise generated by nonlinear internal waves on the continental shelf during the SW06 experiment
Authors: Serebryany Andrey N. , Newhall Arthur , Lynch James F.
Published: May 2008

As part of the Shallow Water 2006 (SW06) experiment, simultaneous measurements of coastal internal wave oceanography and ocean acoustics were made over a two month period in late summer. The generation of noise by nonlinear internal waves propagating on the shelf during the SW06 experiment was observed, and is reported upon here. Three main types of noise were observed: bed noise, mid-column noise and noise from the sea surface. Surface noise is created due to an enhancement of surface wave breaking in the convergence zone created by the internal waves. Strong broadband bed noise was observed during the moments of internal wave passage above a horizontal array of hydrophones lying on the bottom. Appearance of bed noise in the form of several spikes we observed coinciding with the strongest bottom currents created by internal wave orbital currents. For the case of breaking internal waves, the near-bed spike-like noise disappeared and mid-column noise of a different character was seen instead. Mechanisms of the various types noise generation will be discussed. Work sponsored by ONR.
Acoustic propagation modeling in the presence of environmental uncertainty
Authors: Khine Yu Yu , Finette Steven , Oba Roger
Published: May 2008

Due to incomplete knowledge of ocean environments, this research incorporates environmental uncertainty into an acoustic model representing wave propagation in order to quantitatively represent the uncertainty of the acoustic field. The waveguide considered here has a spatially varying, uncertain sound speed distribution with a known correlation length. Karhunen-Loeve and polynomial chaos expansions are used to represent the uncertainty in the environment and acoustic field, respectively, in a narrow- angle parabolic wave equation. In this two-dimensional model, the water depth is 150 m and propagation is over a range of 20 km. The environmental uncertainty term in the wave equation is assumed to vary randomly in the range direction, and is characterized by an exponentially decaying correlation function. An implicit finite difference scheme is used to solve a set of coupled differential equations for the stochastic envelope function at different source frequencies in the range of a few hundred Hz. The simulated results will include probability density functions at selected spatial locations in the waveguide, first and second moments of the field, and these results will be compared with those obtained independently from Monte Carlo samplings from the same ocean environment. Work supported by ONR.
Comparisons of the dynamic moduli of various polymers
Authors: Smith John
Published: May 2008

To fully characterise the elastic properties of a homogeneous, isotropic material, two independent elastic constants are needed, usually the bulk and shear moduli. For the types of polymers used in sonar applications, these moduli are typically both frequency and temperature dependent. Of particular interest is the position (in frequency and temperature) of peak loss tangent, which is related to the glass transition temperature through the free volume concept. Although there exists in the literature a lot of data on the dynamic shear (and Young's) modulus for various polymers, data on dynamic bulk modulus is scarcer, due to the difficulty of the measurement. This paper reviews the current literature on the dynamic moduli of various polymers, with particular regard to the relationship between the peak loss tangents of the bulk and shear moduli. Simple relaxation models are studied to give insight on the factors affecting the peak of the loss tangent and new measurements on a nitrile-butadiene rubber compound are presented.
Measuring grain roughness for the purpose of high-frequency acoustic modeling
Authors: Briggs Kevin , Reed Allen , Ray Richard , Richardson Michael
Published: May 2008

Grain roughness and packing may be important sediment properties for newer acoustic models. We present Scanning Electron Stereomicroscopic imagery of natural sand grains of varying shape and roughness for evaluation of potential grain interactions of individual grains. The grain shape and presence of microasperities will determine the probability of the contact with surrounding grains being a point or a broader area. Moreover, the use of a micro-roughness power spectrum in characterizing the sand grain roughness may be appropriate. Grain contact information is an essential starting point for developing and evaluating acoustic models that address acoustic losses at high frequencies. This information provides the basis to understand contact mechanics, such as grain slip and frame dilation, during insonification. Because media frame stiffness depends, at the grain scale, on the number and type of grain-to-grain contacts, ultimately we would like to characterize sand sediments with imagery identifying such grain contact information. The natural shapes of grains, their variations, and their packing density present a variety of non-ideal (point) contacts. X-ray micro-focus Computed Tomography shows great promise for documenting of the number and size (area) of grain contacts within grain aggregations, and a demonstration of these data will also be presented.
Estimating sediment speed and attenuation with sub-bottom reflections
Authors: Yang Kunde , Chapman Ross , Ma Yuanliang
Published: May 2008

An inversion method based on sub-bottom reflection is investigated using LFM data collected by a Vertical Linear Array from the SW06 experiment. The distance between the LFM source and the array is about 230m. After extracting the impulse response with matched filter from the received signal, the sub-bottom reflections were found to be strong. The chirp sonar survey nearby the experiment site showed that there is a prominent shallow sub-bottom R reflector with about 20 m depth (based on 1500 m/s). The relative arrival time and amplitude of the sub-bottom reflection signals were used to estimate the sound speed and the attenuation of the sediment. Because the direct arrivals in the water were influenced strongly by the internal wave, the first bottom reflection was applied as the reference path to calculate the relative arrival time and absorption loss in sediment. The sediment attenuation was estimated by assuming that it had linear frequency dependence. The estimated values of the sediment sound speed and attenuation were compared with matched field geoacoustic inversion results published by other research group.
What is the spatial volume involved for wave reflection from flat and curved interfaces
Authors: Cristini Paul , Favretto-Cristini Nathalie , De Bazelaire Eric
Published: May 2008

The spatial region in the vicinity of the interface which actually affects the interface response, and hence the reflected wavefield, is of particular interest for the characterization of reflectors. This region represents a volume of integration of properties above and beyond the interface whose maximum lateral extent corresponds to the lateral extent of the Interface Fresnel Zone (IFZ), and whose maximum vertical extent is equal to a thickness we evaluate approximately for subcritical incidence angles and for the case of a plane homogeneous interface. The maximum vertical extent may be greater than the seismic wavelengths for subcritical incidence angles close to the critical angle and for strong impedance contrast at the interface. The whole part of reflector which actually affects the reflected wavefield is then larger than described by previous estimates which considered only the spatial region beyond the interface. In addition to the case of a flat interface, we also discuss the change in the characteristics of this part of the reflector as a function of the interface curvature.
Specific features of surface reverberation in shallow water with focused sound field
Authors: Petnikov Valeriy G. , Pereselkov Sergey A.
Published: May 2008

The specific features of long-range low-frequency (230 Hz) surface reverberation using vertical radiating array are studied in the framework of numerical experiment. We assume that the array focuses a sound field at different distances from ruffled surface in shallow water. Focusing is carried out by using a time-reversal mirror at a distance 10 - 30 km from radiating array. We consider sound focusing and surface reverberation in the presence of developed wind waves for acoustic waveguide common to shallow water for different seasons. The feasibility of surface reverberation suppression is estimated by sound focusing in the central region of the waveguide including the region located below thermocline. The results of numerical modeling are compared with the similar results obtained before for bottom reverberation. The work was supported by RFBR Project 05-02-16842.
Equivalence of the waveguide invariant and two path ray theory methods for range prediction based on Lloyd's mirror patterns
Authors: Kapolka Daphne
Published: May 2008

For shallow, range-independent environments where the sound is dominated by low-order modes, the constant which characterizes the modal interference pattern, the waveguide invariant, is approximately equal to one. The speed of a contact which maintains a constant course and speed as it passes through its closest point of approach (CPA) can be determined from the asymptotic behavior of its tonal frequencies from the Doppler shift. This information can be used along with the change in broadband striation frequencies in a Lloyd's mirror pattern over time to extract the range of the contact as it transits through CPA. If instead of using normal mode theory, the Lloyd's mirror pattern is derived as the coherent interference between a straight-line direct and surface-reflected path, a relationship between the striation frequencies and time of a crossing contact can also be derived. This relationship can be shown to be identical to the result obtained from the normal mode approach when the value of the waveguide invariant is equal to one. Thus, the same equations can be used to extract range information from a Lloyd's mirror pattern regardless of contact range as long as the environmental conditions support a waveguide invariant close to one.
Parabolic Wavelet Technique to Numerical Modelling of Sallow Water Acoustic
Authors: Bakhoday Paskyabi Mostafa , Mortazavi Seyed Taha
Published: May 2008

In this paper, parabolic equation (PE) model is applied for environment of slowly varying with range and azimuth in a region of Persian Golf. This method is currently the most used to study propagation in non-stratified media. Due to required accuracy for a gridding step comparable with the wavelength, the computation load is very heavy. To overcome this disadvantage, we develop the weak form of PE formulation by the use of Deslauier-Daubuc interpolating wavelet (DDW) basis functions. The formulation is similar to combination of conventional Finite Element Method (FEM) and split step technique except that, here DDW basis is used for approximating in depth to reduce the cost of computations and to increase the accuracy of method by the use of multi-resolution structure of wavelets. The localized and circulant representations of depth differential operators based on DDW connection coefficients allow efficient imposition of boundary values and circumvent some disadvantages of the traditional PE. Furthermore, details of bottom boundary imposing and some disadvantages of approach are presented. Numerical experiments are performed to study two layers water-bottom environment with none-smooth sediment interface to some canonical standard test problems in comparison with solutions obtained by conventional PE method.
Studying converted waves in shallow marine environment
Authors: El Allouche Nihed , Drijkoningen Guy G. , Versteeg Willem , Simons Dick G.
Published: May 2008

For many years, waves converted from compressional to shear mode have been successfully applied in hydrocarbon exploration to image and characterize the subsurface. Since shear-waves propagate with a velocity that is dependent on the shear modulus and are thus directly related to the shear strength of the sediment, they are very useful for geotechnical purposes. Generally, P-wave reflection amplitudes contain S-wave information but Riedel et al. (2001) showed that these reflections are not very sensitive to this. An alternative approach is to obtain S-wave information directly from converted waves. However, it is not clear whether these waves can be applied for geotechnical aims. The main focus will be on understanding the dependence of mode conversion on the seismic properties. In this study, we investigate the possibility of acquiring converted waves in marine unconsolidated sediments. From our numerical experiments we found that the conversion is maximal at two angles where the smallest angle appears to be more favorable in the environment of interest. Furthermore, we show how and where converted waves can be observed on a seismogram and the optimum field configuration to acquire them.
Tank experiment: The ultrasonic approach to ocean physics
Authors: Roux Philippe
Published: May 2008

Acoustic/elastic waves ranging from a few kHz to a few MHz are nowadays easy to emit/receive through the use of "key in hands" multi-channel systems. These systems provide the instantaneous amplitude and phase of the deterministic wave propagating in the medium with a dynamic larger than 90 dB in some cases (16-bit amplitude sampling). The use of a large number of channels (at least 64) is mandatory to simultaneously investigate the spatial and temporal aspect of wave propagation in complex media. The advantage of a laboratory-scaled ocean model relies in the ease with which it can be build, modified, and/or controlled over time. Finally, the trend in ocean wave physics is now to study the dynamics of such medium (internal waves, turbulent flow, sensor motion) that requires the use of a real-time acquisition system. Examples of the types of analog experiments that could be carried out with a laboratory-scaled system are the study of nonuniform doppler shifted fields in reverberant environments, ocean acoustic tomography and similar inverse problems, coherent communications in complex moving environments, etc. After the description of the equipment, we give more specific examples of potential experiments to illustrate the versatility of the laboratory set-up.
Laboratory investigations of the detection and characterization of buried targets by iterative, single-channel time reversal
Authors: Waters Zachary J. , Dzikowicz Benjamin R. , Holt R. Glynn , Roy Ronald A.
Published: May 2008

Due to the dynamic nature of the shallow water environment, targets are often buried beneath the seafloor, hindering their detection and identification by acoustic methods. Using iterative time reversal with a single channel transducer [Waters et al., J. Acoust. Soc. Am. 122, 3023 (2007)], the monostatic return from a buried resonant target is enhanced, yielding convergence to a narrowband waveform characteristic of the dominant mode in the target's scattering response. Scaled laboratory experiments are performed with a broadband (Q̃2) transducer operating in the 0.5-2 MHz frequency range. Solid and evacuated metallic spheres used as targets are buried beneath a layer of simulated sediment. Images generated by scanning the transducer laterally in two dimensions over an area of sediment containing multiple targets show enhancement of different modes in a single target's scattering response and test the selectivity between targets of differing type. Experiments with the transducer positioned at normal and non-normal incidence, quantify the enhancement in the signal-to-noise ratio of target returns as a function of window size and position. [Work supported by The Office of Naval Research and the Center for Subsurface Sensing and Imaging Systems (NSF ERC Award No. EEC-9986821).]
Inverse problems in sound radiation of complex structures from measurements in a large acoustic tank
Authors: Williams Earl G. , Houston Brian H. , Valdivia Nicolas , Herdic Peter C.
Published: May 2008

The Laboratory for Structural Acoustics (LSA) at NRL consists of an indoor cylindrical tank (17 m dia. by 15 m deep) filled with ̃ 1 million gallons of deionized water. Key features include: 1) vibration isolation, 2) active temperature control, and 3) anechoic materials. This unique laboratory is instrumented with sophisticated mechanical, electronic and optical systems, that include large workspace in-water robotic scanners to generate nearfield acoustical holography (NAH) databases. We discuss such a database consisting of the underwater near-field pressure measured on a two-dimensional surface conformal to an internally driven complex structure floating at the air-water interface. Various inverse approaches are discussed to image the normal velocity and intensity of the structure at its interface to the fluid, as well as the total power radiated, revealing mechanisms of radiation related to the internal structure. These inverse approaches consist of the equivalent source method compared with the well established Fourier acoustics methods of NAH. This work was supported by the US Office of Naval Research.
Estimation of some geoacoustic parameters of a tank experiment by match field processing
Authors: Papadakis Panagiotis , Taroudakis Michael , Sessarego Jean-Pierre , Sanchez Patrick
Published: May 2008

The work deals with an inversion procedure for the estimation of geometrical and environmental parameters of a simulated shallow water environment. Two of the most significant parameters in a shallow water environment affecting the acoustic field in long range acoustic propagation are the sound speed of the sediment and the depth of the water column. The accurate estimation of these parameters is perhaps the most important task in scaled laboratory experiments. Therefore, the calibration phase of such an experiment involves the estimation of these parameters, preferably using acoustical techniques, regardless the final scope of the experiment. The present work describes an inversion procedure based on standard match field processing. The acoustic signal used was a short gaussian shaped pulse and it was recorded at a certain distance from the source and for several depths in the water column. The spectrum of the recorded signal was obtained using FFT and the complex acoustic field at the central frequency was calculated. The estimated values of the water depth and the sound speed in the sand which was used to simulate the sea-bed, were found in accordance with the observed modal structure of the acoustic field.
The Broadband In-Water Structural Acoustics of Unexploded Ordinance
Authors: Simpson Harry J. , Houston Brian H. , Saniga Michael L. , Bucaro Joseph A.
Published: May 2008

The Laboratory for Structural Acoustics (LSA) at the Naval Research Laboratory consists of a 1 million gallon, deionized water, indoor cylindrical tank (17m diameter by 15m deep). The key features include: 1) vibration and temperature isolation, 2) feedback controlled heating and adiabatic materials (temperature variability <0.01°C), and 3) reverberation reducing anechoic materials. This laboratory has computer controlled robotic scanners and manipulators used for precision freefield measurements including nearfield acoustic holography and compact range scattering. The precision robotics, environmental control, and painstaking measures to insure homogeneity and stability result in a high fidelity, versatile, and unique underwater acoustic measurement laboratory. The LSA also contains an indoor rectangular tank (10m by 8m) laboratory, with a 3m deep sand bottom and 4m of water column. In a similar fashion to the freefield laboratory, this laboratory is used to study target scattering in a marine bottom environment. We discuss such databases focused on the challenging problem of unexploded ordinance (UXO) in water where we use the structural acoustic response measured in a series of laboratory experiments to detect and identify several common UXOs. The 360 degree broadband (1-140 kHz) compact range monostatic and bistatic measurements taken in both laboratories will be discussed.
"Acoustics vases in ancient theatres: disposition, analysis from the ancient tetracordal musical system"
Authors: Barba Sevillano Arturo , Lacatis Radu , Giménez Alicia , Romero José
Published: May 2008

The acoustics of the ancient Greek and Roman theatres has always been rated as excellent by experts, without discussion. Beyond the purely architectural aspects, in this kind of outdoor theatres some mechanisms were used in order to improve the acoustics. In this paper we have studied the texts about "theatre's vases" of the famous book "On Architecture" by Vitruvius. Different interpretations and illustrations of these vases, that several translators carried out in the sixteenth to the eighteenth centuries, have been researched. From the wide bibliography consulted in this regard we have developed a plane with the disposition of the bronze vases in the theatres. In this plane we have specified the frequency of each one of them, and explained their disposition from the tetracordal musical system acquired from the Greek culture. Finally, an analysis of the disposition of the vases has been made. We have studied and looked for the musical intervals and harmonic relations among adjacent vases.
History and acoustics of the Asian free-reed mouth organs
Authors: Cottingham James
Published: May 2008

Mouth-blown instruments employing a free reed coupled to a pipe resonator have long been known and used throughout East and Southeast Asia. Details of the origin and development of these instruments are not known, but are closely connected with the history and prehistory of a multitude of ethnic groups. Free reed instruments have been employed in a variety of ways, from simple signaling devices to use in the court music of Japan and China. The pipe resonators vary from the buffalo horn to bamboo pipes of nearly cylindrical cross section. The instruments exemplify a pipe-resonator coupling significantly different from that of the standard wind instruments of European origin. In some cases the reed is at or near one end of an open or closed pipe resonator, but in other examples the reed is mounted in the side of the resonator away from the ends. A summary of recent experimental investigations of these instruments will be presented, along with musical examples.
Effects of spatial factors of speech, noise, and reverberation sounds on listening difficulty
Authors: Sato Hayato , Takaoka Tomoyasu , Morimoto Masayuki
Published: May 2008

It is well known that the amount of auditory masking in binaural listening is affected by spatial factors of signal and masking sounds such as the degree of interaural cross-correlation and the arriving direction. The amount of auditory masking for speech signal are usually measured using speech intelligibility tests. However, in the sound fields that appears in everyday life, speech intelligibility are usually close to 100%. Therefore, it was unclear how much the effects of spatial factors on speech communication in everyday life are. Listening tests were performed to clarify the effects of spatial factors on listening difficulty ratings [M. Morimoto et al., J. Acoust. Soc. Am. 116, 1607-1613 (2004)] focussing on the degree of interaural cross-correlations of speech, noise, and reverberation sounds, and on the arriving direction of speech signal. The two spatial factors were controlled by several loudspeakers which are horizontally installed in an anechoic room. The results of listening tests showed that the effects of the two spatial factors on listening difficulty ratings decreased with improving listening conditions, and the effects can be ignored in the sound fields that often appears in everyday life.
On the use of a corrugated ceiling for noise reduction in rooms
Authors: Declercq Nico F. , Vanderhaeghe Katelijn , Dewijngaert Katrien , Verleysen Patricia
Published: May 2008

In certain halls the acoustics is dominated by distinct frequencies having disturbingly high intensities caused by yelling children, such as in an indoor swimming pool, or by industrial production processes. The use of damping materials to cover the ceiling, floor and side walls is not always permitted because of esthetic reasons or because of safety grounds or even humidity. The current study shows that in those cases the use of a corrugated surface is possible and is actually more effective in filtering out very distinct frequencies. An example is presented for frequencies at 3 to 4 kHz and numerical results are obtained in support of the use of a corrugated structure rather than classic damping materials such as baffles.
Musicians' Adjustment of Performance to Room Acoustics, Part III: Understanding the Variations in Musical Expressions
Authors: Kato Kosuke , Ueno Kanako , Kawai Keiji
Published: May 2008

This paper attempts to investigate the acoustic variations in the musical sound signals produced by professional performers under different room acoustic conditions. The sound signals produced by four professional instrumentalists and an operatic baritone singer under simulated concert hall sound fields were recorded by placing a unidirectional microphone close to either the instruments or the mouth of the opera singer. In order to quantify the extent of the variations in the resulting sound signals due to the adjustment of the musical expressions, an acoustic analysis was conducted. The results indicated that the "note-on ratio," defined as the ratio of tone duration and inter-onset interval, of several staccato tones was decreased in reverberant halls. The higher harmonics of tones of an oboist and a flutist were suppressed in reverberant sound fields, while the vibrato extent of a violinist was considerably varied as was reported in our previous study (Part II). Based on the results of the interviews with the performers during the recordings, it was inferred that the variations in the musical sound signals were produced by the performers to adjust to the room acoustic conditions.
In situ measurement of acoustic parameters with smart devices
Authors: Van Nieuwenhuyse Karl , Guillaume Patrick , Van Landuit Steve , Vuye Cedric , De Sitter Gert
Published: May 2008

Instruments for in situ analysis of the acoustic parameters of a room are, due to their high prime cost, not widely accessible. In an effort to change this, new software was developed to enable these measurements by use of highly portable consumer electronics such as PDA's and Smart phones. The newly developed software calculates the reverberation time using the impulse method and aims at delivering accurate results using the built-in microphone or an external one. This paper will discuss the accuracy of the new software in comparison with professional equipment through several case studies, even as the different techniques used to overcome the inherent problems forthcoming the equipment used, i.e. microphone quality and automatic gain control.
Correlation between architectural and acoustical parameters in Catholic churches of the colonial era in Ayacucho, Peru
Authors: Jimenez Carlos R.
Published: May 2008

The paper reports the analysis of the results of an acoustic survey carried out on several Catholic Churches in the city of Ayacucho, a southern city in the Peruvian Andes, built during the colonial era through centuries XVI to XVIII. The study is performed taking into account both room-average values and individual position values of many acoustical parameters measured according to ISO 3382. Effects among architectural characteristics of each church as lenght, height, room volume, interior surfaces area, total absorbing area, mean absorption coefficient, and some objective acoustical parameters as reverberation time, early decay time, clarity, definition and center time, are investigated.
Determination of unknown parameters in impervious layers by inverse method
Authors: Escuder Silla Eva , Alba Fernandez Jesús , Ramis Soriano Jaime , Del Rey Tormos Romina
Published: May 2008

In this work, a novel procedure is shown for the determination of unknown parameters in impervious layers used in multilayer structures by inverse method and using scale models. Experimental pressure and velocity data are obtained by Nearfield Acoustic Holography (NAH) for the calculation of the transmission loss of the different multilayer structures mounted on the window of a wooden box designed for that end. These data are used as input data in the inverse method. The forecast model of acoustic insulation in multilayered structures used in this work was Trochidis&Kalaroutis model based on Spatial Fourier Transform (SFT). By applying Trochidis&Kalaroutis model and adjusting by numerical methods the variables that define the impervious layers of the system, the values of the unknown magnitudes of the layers are calculated. For validation purposes the results are compared to those obtained with Ookura&Saito model.
Effect of the estimation of the wall/floor junction type on the acoustic isolation
Authors: Alba Fernandez Jesús , Ramis Soriano Jaime , Escuder Silla Eva , Del Rey Tormos Romina
Published: May 2008

Deviations between the laboratory measurement and the final in situ measurement, are common in the acoustic isolation. A fundamental difference between both cases is the effect of the lateral flanks. This effect produce that the global acoustic insulation changes substantially. With the standard UNE-EN-12354-1, it can be estimated the effect of the flank, obtaining the vibration reduction indexes and evaluating the insulation of every way. It is also possible to carried out a measurement procedure with the Standard ISO 10848, in it the index is measured and then the index is calculated. This paper shows the differences of results of airborne sound insulation and impact insulation with in situ measurements of the vibration reduction index and the different estimations that the Standard allow. Different unions are studied, and the influence of these in the global result of the insulation is evaluated.
Study in the measurement of noise air insulation in laboratory of the effect in the diffuse field
Authors: Del Rey Tormos Romina , Alba Fernandez Jesús , Ramis Soriano Jaime , Escuder Silla Eva
Published: May 2008

We can obtain, in a transmission chamber, the air transmitted noise insulation. In the standard 140-1 the characteristics of these chambers are described. One of these characteristics tries to ensure diffuse field inside these chambers. Nevertheless, we cannot assure an incident angle between 0° and 90° on the test wall, there is a limit angle lower than 90°. In this paper, we study the valuation of the committed mistake by limit angle in transmission chambers. Expressions used for calculating the insulation in transmission chambers are obtained from transmission description in diffuse field, in which case the angle is 90°. In this work, for different materials commonly used in transmission chambers tests, the influence of the indetermination of a mistake and the global mistake evolution with limit angle is studied.