bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal prediction of the acoustic radiation of vibrating structures: subjective evaluation of a simplified approach
Authors: Hamzaoui Nacer , Pierangelo Juliette , Levy Antoine
Published: May 2008

The goal of the approach presented in this paper is to predict the noise radiated by vibrating structures with acquired vibratory measurements, in the temporal field, on their surface. In the frequential field this prediction is based on the resolution of the Kirchhoff integral equation, which requires a lot of computing time and is thus limited to low and intermediate frequencies; the boundary element method (BEM) is used for the resolution. Simplifications were already brought to low (< Flim1) and to high (> Flim2) frequencies, leading to a simple calculation of a fast integral. The limiting frequencies (Flim1 and Flim2) depend on the structure dimensions and its position towards the observation point. In this paper we will present an approach developed in the temporal field in which a complete calculation (BEM) is avoided by choosing a minimal distance in order to have Flim1 = Flim2 and use only the simplified calculations. The vibratory data is measured in the temporal field and the studied structure is a parallelepipedic box excited by two mechanical excitation pots which excite one or two faces. The acoustic pressures calculated in the temporal field will be confronted with measurements, by using similarity subjective tests and integrating a variation of the principal parameters intervening in this approach.
Modelling of the hydro and aero acoustic sources in piping
Authors: Villouvier Véronique
Published: May 2008

In the industrial piping networks, various components are crossed by flows, generally in air or in water. The pressure fluctuations generated locally close to these singularities are propagated then in all the network and can lead to important vibrations of the structures. A research program based on many laboratory tests made it possible to highlight a hydroacoustic modelling of the butterfly valves in the low frequencies domain. The model, which describes the acoustic sources, generated by the turbulence, has a general applicability. In this paper, one presents the application of this model to orifices (openings and slits) working in air and in water. These various orifices were studied from an acoustic point of view on different test loops and for several hydraulic conditions (flow rate and head loss). These experimental cases were then simulated using the source model of turbulence noise, associated to the transfer matrix of each singularity, which is determined by another way. The comparison between these calculations and the corresponding measurements makes it possible to consolidate the general character of the model of turbulence noise for singularities in piping.
Use of noise and vibration signal for detection and monitoring of cavitation in kinetic pumps
Authors: Černetič Jan , Prezelj Jurij , Čudina Mirko
Published: May 2008

Cavitation in kinetic pumps causes lowering performance, mechanical damage and increase of vibrations and noise. Therefore, it is important to detect inception and development of cavitation phenomenon in the pump. This paper deals with signals of vibrations and noise, which will be used for detection and monitoring of cavitation in kinetic pumps, and also to prevent the effect of cavitation in the pump and pumping system. When the cavitation is increasing, the flowing conditions are changing, which leads to an increase of vibrations of the pump and emitted noise in the surroundings. Because vibrations and noise are transferred from the pump through its casing, the signal is non-uniformly distorted due to transfer losses and structure of the casing surfaces. Even so, it is possible to determine development of cavitation phenomena from the measured signal. Noise and vibrations are increasing steadily, but in some specific frequency ranges the signal is more pronounced than in other part of the spectrum. Experimental results have shown that when the cavitation is fully developed, the measured signals at a characteristic frequency or range of frequencies start to decrease. This characteristic frequency or band of frequency is discussed in this paper, and also comparison between theoretical expectations and measurement results was performed.
Experimental investigation of the acoustic black hole effect for vibration damping in elliptical plates
Authors: Gautier François , Cuenca Jacques , Krylov Victor V. , Simon Laurent
Published: May 2008

It is well known that flexural waves in beams or plates slow down if their thickness decreases. A beam or a plate with a decreasing thickness in the vicinity of one of their boundaries can be designed so that the travel time needed for a wave to reach the edge becomes infinite. Thus, the reflection coefficient associated with the corresponding region is zero. This effect is referred to as the acoustic black hole effect. The use of 'acoustic black holes' in combination with thin damping layers for wedges of power-law profile has been theoretically and experimentally studied by V.V. Krylov and R.E.T.B. Winward (JSV 300 (2007) 43-49). The aim of this paper is to show experimentally the acoustic black hole effect in a two-dimensional configuration comprising an elliptical plate with a pit of power-law profile placed in one of its focuses. The elliptical shape of the plate induces a focalization of waves towards the black hole, which is observed by means of scanning laser vibrometry. Comparison of input mobility measurements for plates with and without black hole shows the reduction in vibrational level induced by the black hole effect.
Cue switching in the perception of approximants: Evidence from two English dialects
Authors: Knight Rachael-Anne , Villafana Dalcher Christina , Jones Mark J.
Published: May 2008

A surprising dissimilarity is attested in the perception of approximants by speakers of American and Standard Southern British English. Eighteen subjects (6 AE and 12 SSBE) performed an identification task in which they judged whether stimuli were more like /r/ or /w/. The stimuli comprised five sounds, copy-synthesised from a source /r/, where the values of F2 and F3 we adjusted to fall between the frequencies typical for ["turned r"] and [w]. The only significant difference between the two dialect groups' performance occurred with a token in which F3 was at a frequency typical for /r/ and F2 was lowered to that of /w/. AE and SSBE speakers identified this token as /r/ 90% and 59% of the time, respectively. This is unexpected as /r/ in both dialects is characterised by a low F3. However, the difference may be due to the existence of the 'labiodental' variant of /r/ in SSBE. As this variant does not have a low F3, SSBE speakers must tolerate a wider diversity of /r/-types than AE speakers. Therefore, the /r/ category in SSBE may be becoming increasingly defined by F2, rather than F3, which also has implications for the future production of /r/ in this accent
Statistical identification of critical, dependent and redundant articulators
Authors: Jackson Philip J. , Singampalli Veena D.
Published: May 2008

An automatic method for identifying critical, dependent and redundant roles in speech articulation is presented. Critical articulators are identified using the Kullback-Leibler divergence between phone-specific and model pdfs, which are initialised to the grand pdfs for each articulator. Model pdfs of critical and dependent articulators, those significantly correlated with the critical ones, are updated accordingly for both 1D and 2D cases, as long as the divergence exceeds the threshold. Those unaffected are termed redundant. Algorithm performance is evaluated on the MOCHA-TIMIT database by comparison with phonetic features. Results are also given for an exhaustive search, and principal component analysis of articulatory fleshpoints. Implications of being able to extract phonetic constraints automatically from articulatory recordings are discussed.
The effect of facal dynamics on infant perception of adult-directed speech in noise
Authors: Polka Linda , Panneton Robin , Versele Jessica
Published: May 2008

Recently Polka and Rvachew (in press) found that 6- to 8-month-old infants discriminated a native contrast("bu" - "gu") when familiarized and tested with syllables presented in quiet, but not when familiarized with syllables mixed with a competing noise, even when testing was conducted in quiet. Because the competing noise (segments of cricket and bird song) did not create energetic masking, infant failure to encode the familiarization syllable was due to a disruption in attention to the speech stream. Importantly, in this study, infants watched a checkerboard while listening to syllables spoken in an adult-directed (AD) style. The current study investigated if the addition of a dynamic face facilitates infants' speech processing in the same task. Six-month-olds were habituated to repetitions of the native syllable "ba" mixed with the same noise but these infants saw and heard syllables produced in AD style. Following habituation, infants were presented familiar (repetitions of "ba") and novel test trials (repetitions of "ga"). Infants failed to show syllable discrimination as indexed by a reliable preference for the novel test trials. These findings show that a dynamic face producing AD speech does not engage infant attention to speech enough to support syllable discrimination in noise.
Magnetic Resonance investigation of palatalized stop consonants and spirants in Russian
Authors: Kedrova Galina Y. , Anisimov Nikolay V. , Zaharov Leonid M. , Pirogov Yurij A.
Published: May 2008

The research in question is aimed at the experimental MRI-investigation of articulatory gestures corresponding to the palatalized Russian stop consonants [p'], [t'], [k'], [b'], [d'], [g'] and spirants [s'], [z'] [h'] countered with their non-palatalized counterparts [p], [t], [k], [b], [d], [g], [s], [z] [h] in Russian speech production. An experimental dataset was based upon 2D MR-images, audio- and video recordings taken from 4 native speakers of Russian (3 males and 1 female) producing VCCV sequencies (Russian pseudo-words with the second vowel stressed) containing Russian consonants under investigation in the vocalic contexts [a]_[a] and [a]_[i]. All speaking subjects had standard pronunciation and were without any perceptible articulation disease. MRI investigation of the Russian consonantal phonemes was based upon admitted procedures and techniques though expanded with several new original methods elaborated by the Russian team of experimentalists. Experimental data was collected through several MRI sessions (done in a month and in a year with participation of the same speaking subjects), ensuring thereby credibility and robustness of the experimental results. A detailed analysis of the whole dataset of MR-images of palatalised Russian consonants countered with their non-palatalized counterparts revealed special articulatory pattern of palatalisation in Russian.
Neighbors as competitors: Phonological analysis of spoken word recognition errors
Authors: Buchwald Adam , Felty Robert A. , Pisoni David B.
Published: May 2008

Theories of speech perception and spoken word recognition widely assume that phonetically similar words compete for selection during lexical access. These competitors - called lexical neighbors - are classically defined as differing by a single segment, with little attention paid to other levels of phonological structure such as featural content or syllabic structure. This paper reports on analyses of over 15,000 word recognition errors made on a representative sample of the lexicon (N=1428) that includes the same variety of syllable structures, lengths, and lexical frequencies that exists in the English lexicon. The analyses reveal that competitors share segmental information as has been previously suggested, but that the classic definition of neighbor cannot capture the level at which featural and syllabic properties of the target constrain the error responses. We will discuss several analyses on these issues and discuss the implications for our understanding of the organization of the lexicon. [Work supported by NIH-NIDCD R01 00111 and T32 00012]
The prosody of second position clitic placement and focus in Croatian
Authors: Yu Kristine
Published: May 2008

Since Browne 1974, the placement of second position clitics in Bosnian/Croatian/Serbian has inspired debate about interaction at the syntax-phonology interface. The placement of these clitics can alternate quite freely: either after the first phonological word or after the first syntactic constituent. While it's generally agreed that prosodic phonology, in addition to morphosyntax, plays a role in clitic placement in Bosnian/Croatian/Serbian, the prosodic patterns for the different placements have not been studied acoustically. In addition, it has been suggested that clitic placement and pragmatic focus may interact (Bošković 2001), but this has not been systematically studied. We recorded adult Zagreb Croatian speakers producing subject noun phrases with initially stressed trisyllabic adjectives and nouns in transitive sentences. We varied clitic placement (after the first word or first constituent) and focus domain (broad focus, and narrow focus on adjective, noun, both the adjective and the noun, or the entire noun phrase) and controlled for dialect and pitch accents. Preliminary results from three speakers indicate that gross differences in prosodic patterns occur only as a function of focus domain but not clitic placement. Further work will confirm if these patterns hold for more speakers and if clitic placement is correlated with finer-grained prosodic differences.
Acoustic consequences of gestural intrusion errors
Authors: Marin Stefania , Pouplier Marianne , Harrington Jonathan , Waltl Susanne
Published: May 2008

An increasing number of studies have elicited speech errors in articulatory experiments, and thus evaluated errors on the basis of their articulatory properties, yet there has been no study that relates the articulatory variability observed in errors to the acoustic consequences. The present study aims to evaluate the acoustic properties of errorful/error-free [k] and [t] stimuli with known articulatory configurations (and articulatorily categorized as errorful/error-free), and determine the extent to which articulatory errors have acoustically observable consequences. The most frequent error observed in the articulatory data is an intrusion of a second gesture, resulting in a simultaneous presence of both tongue tip and tongue body gestures during production of [k] or [t]. Spectral analysis of these stimulis' bursts shows that [k] and [t] are differently affected by intrusion gestures: intrusion errors during intended [k] tokens are more robustly grouped with error-free [k] across speakers, while intrusion errors during intended [t] tokens are more variable, some being acoustically like [t], some like [k], and some like neither category, matching previous perceptual results (Pouplier & Goldstein 2004, Journal of Phonetics). These results will be discussed in the context of different timing patterns between the two co-occurring gestures during intrusion errors.
Investigating the perception of noise-vocoded speech - an individual differences approach
Authors: McGettigan Carolyn , Rosen Stuart , Scott Sophie K.
Published: May 2008

We used a cochlear implant simulation (noise-vocoded speech) to investigate speech recognition and perceptual learning in normal-hearing adult speakers of English. In two separate sessions (1-2 weeks apart), 28 listeners were tested on recognition of noise-vocoded Sentences, Words, and isolated segments (Consonants and Vowels). There was evidence of significant perceptual learning that survived until Session 2 for all tasks. An individual differences analysis of Session 1 data suggested two independently-varying 'levels' of processing at work in the initial perception of the distorted speech stimuli - a 'top-down' listening mode making use of contextual and lexical information, and a 'bottom-up' mode focussed on acoustic-phonetic discriminations. By Session 2, a more generalised listening mode emerged, reflecting listeners' consolidation of basic sound-to-representation mappings. Further exploration of Consonant and Vowel confusion data (using Information Transfer analyses) suggested that better speech recognition performance may be achieved through more efficient use of the preserved cues to duration and voicing in noise-vocoded stimuli, but that listeners failed to take full advantage of such information. We conclude that training regimes involving directed attention to specific features, such as vowel length, may help to improve performance with noise-vocoded speech.
Vowel spaces in Swedish children with cochlear implants
Authors: Ibertsson Tina , Sahlén Birgitta , Lofqvist Anders
Published: May 2008

This study analyzed vowel productions of Swedish children with cochlear implants, capitalizing on the rich vowel system of Swedish with nine vowels. Minimal word pairs were used as linguistic material. A group of 12 children with CI (mean age 184 months, range 144-229 months), and a group of children with normal hearing (mean age 105 months, range 103-118 months) were recruited. The age at implantation of the CI was 79 months (range 31-155 months). The first two formants were measured for each vowel. To estimate the vowel space, the average Euclidean distance in the F1-F2 plane between each vowel and the mean first and second formant frequencies of all the vowels was calculated for each child. The results show a significantly smaller vowel space for the children with a cochlear implant. However, there was no overall significant correlations between the vowel space and measures of speech recognition and vowel production in the CI group. Although the present results show that speech recognition ability affects intelligibility and vowel production, the vowel space may not be a suitable measure for assessing speech production in this population. [Work supported by the Sunnderdahl Disability Foundation.]
Detection of obstruent consonant landmark for knowledge based speech recgonition system
Authors: Lee Jung-In , Choi Jeung-Yoon
Published: May 2008

Obstruent consonant landmarks are detected using spectral energy difference profiles. This study expands upon previous work by Liu. A[J. Acoust. Soc. Am. 100, 3417-3430, 1996]. The proposed algorithm detects four types of landmarks : [stop closure], [stop release], [fricative closure] and [fricative release], where affricates are detected by combining [stop closure], [fricative closure] and [fricative release]. In addition to finding abrupt changes in energy differences, we use energy contours, relative energy and spectral center of gravity differences. This method results in improved performance particularly for CV obstruents. Overall detection rates for stop closure and release are 76.9% and 85.7% for obstruent landmarks in TIMIT, and fricatives yield 82.2% and 83.6% respectively. For strident fricatives, the figures are 94.7% and 93.6%.
Visual Influences on Alignment to Voice Onset Time
Authors: Sanchez Kauyumari , Miller Rachel M. , Rosenblum Lawrence D.
Published: May 2008

In speech alignment, interlocutors inadvertently imitate aspects of each others utterances. Alignment also occurs when talkers are asked to shadow (identify out loud) recorded words heard over headphones. For example, the voice onset time (VOT) of consonants produced by subjects will be greater when shadowing heard words whose consonants have been modified to have extended VOTs [K. Shockley, et al., Percept. Psychophys. 66, 422 (2004)]. An experiment was conducted to test whether alignment to VOT has a purely acoustic basis. For this purpose, visual speech tokens composed of a face articulating /ba/ syllables at three different rates, were each dubbed onto a series of seven audio /ba/ syllables varying in VOT. Subjects were asked to simply shadow the audiovisual /ba/s. Results revealed that both the visible syllable rate and audio VOT of the stimuli influenced the VOTs of the shadowers' produced syllables. The implications of these results for theories of alignment, audiovisual integration, and the perceptual primitives of speech are discussed.
Identification of place of articulation and voicing in white and babble noise
Authors: Alm Magnus , Behne Dawn
Published: May 2008

Previous research shows that white noise influences the degree auditory and visual modalities are used in audio-visual (AV) speech perception. This study assesses identification of voicing and place of articulation (POA) in the infrequently studied natural babble noise. Incongruent monosyllabic AV stimuli were presented to 15 young adults in white and babble noise at 0 and -12 dB SNR where voicing stimuli differed in voicing and voicing structure and POA stimuli differed in POA and POA structure. In white noise POA stimuli received fewer audio responses than in babble whereas voicing stimuli received more audio responses in white noise than in babble. Voiced syllables received more audio responses than voiceless. Findings suggest that differences in noise type for POA and voicing identification are attributable to discrepancies in acoustical attributes of noise and target stimuli. In voicing identification, the spectral transition between aspiration (stabile signal) and voicing (fluctuating signal) is less distinct in the fluctuating babble noise than in the flat power white noise. Voiceless consonants are more spectrally similar to white noise than voiced consonants, making the latter more auditorily accessible. Visual cues aid voicing identification, but only when POA is visually salient and auditorily susceptible to the noise type.
Evaluation of a simplified phonetic annotation scheme for disordered speech
Authors: Murray Kathleen , Graff David , Heman-Ackah Yolanda D. , Sataloff Robert T.
Published: May 2008

Attempts to train a computer to mimic a vocal pathology expert's perception of perceivable voice problems have had limited success. A recent study successfully used a Cepstrum-based calculation (CPPs) to detect dysphonic speech, but it made significant false negative and false positive errors [1]. Appropriate training data could improve calculation accuracy, but logistical and legal issues from the medical domain render large amounts of detailed, consistent training data difficult to produce. A simple scheme has been developed based on labeling one point in time for each of a few vowels in a read statement. Calculations from [1] and [2], centered on neighborhoods of these vowels will augment the CPPs classifier. The annotation scheme will be evaluated with respect to its ability to assist a classifier to automatically predict perceptual labels [1] from data, and practicalities such as inter/intra-annotator agreement. 1. Heman-Ackah, Y.D., Heuer, R.J., Michael, D.D., Ostrowski, R., Horman, M., Baroody, M., Hillenbrand, J.M., and Sataloff, R.T. (2003). "Cepstral peak prominence: A more reliable measure of dysphonia," Annals of Otology, Rhinology, and Laryngology, 112, 324-333. 2. "Perceived Level of Noise by Mark VII and Decibels (E)" S. S. Stevens, J. Acoustical Soc. Am. v. 51(2, part 2) 1972. pp. 575-602.
Analytical prediction of sample eigenvector quality deterioration in large arrays due to SNR or sample size constraints
Authors: Nadakuditi Raj , Baggeroer Arthur B.
Published: May 2008

It is well-known that subspace-based estimation methods in adaptive array processing suffer a rapid degradation in performance as either the signal-to-noise ratio (SNR) or the number of available snapshots drops below a certain threshold value. In the large system, relative large sample size limit, one can use random matrix theory to analytically predict this threshold and the degradation in the ''quality'' of the corresponding subspace estimates. In certain settings, one observes a "phase transition" phenonemon so that if the signals are too weak or there are insufficient number of snapshots or both, the subspace estimates are, statistically speaking, noise-like. We discuss the implication of these results for the subspace based detection of signals in white and colored noise using large arrays and illustrate the accuracy of the predictions with numerical simulations.
Particles filter applied in the real-time bearings-only tracking problem of a sonar target
Authors: Rodrigues Cleide V. , Soares-Filho William
Published: May 2008

The development of a passive sonar tracking system in real-time needs algorithms each time more accurate and that can be able to follow rapid changes in the signal characteristics. In a bearings-only tracking problem, the bearing model is a nonlinear function of the target states. Nowadays, methods that deal with nonlinear and non-Gaussian estimation are receiving great attention. Particles filter is one of these methods. Particles filters are Sequential Monte Carlo methods that represent the required probability density function as a set of random samples. This present paper describes the particles filter application in the bearings-only tracking problem. Real data of targets are displayed in energy versus bearing graphics obtained in an operational naval environment. These data were used with the Sampling Importance Resampling algorithm (SIR). The particles filter is formulated in the Cartesian coordinates and then are transformed to modified polar coordinates. Results are compared with Kalman Extended Filter and the effectiveness and limitations of SIR algorithm for tracking target using a bearing/time record are examined.
Robust beamforming and beamspace DOA estimation using measured array manifold of arbitrary geometry acoustic array
Authors: Yang Yixin , Sun Chao
Published: May 2008

The acoustic diffraction of array supporting structure will result in the large difference of the amplitude and phase response of each hydrophone, which leads to the distortion of beampattern. A method for obtaining the array manifold of arbitrary geometry acoustic array is proposed in this paper. We measured the array response vector in many directions with a fixed angular step in anechoic water tank. The array response vectors were smoothed to eliminate the measurement system error. Using these smoothed array response vectors, the robust beampattern of arbitrary geometry array is obtained via beam synthesis method. A 16 element volumetric acoustic array was constructed and tested in an anechoic water tank. Robust low sidelobe beampatterns based on the measured manifold were formed, and then the beamouputs were used to apply to beamspace high resolution DOA estimation methods. The experimental results show that our method can suppress noise and interferences outside the beam coverage regions, and get high resolution DOA estimation results. When the array geometry has some distortion, the weighting vectors of beamforming can still work well to form good beampatterns, and then get accurate DOA estimation results. This verifies the effectiveness of our proposed method.
A sequential Bayesian approach to vertical slice tomography of a shallow water environment
Authors: Carrière Olivier , Hermand Jean-Pierre
Published: May 2008

A major challenge of acoustic tomography in shallow water environments is to track physical features that are highly variable in time and space and to properly account for sound interaction with the subbottom. In a previous work an extended Kalman filter (EKF) scheme was proposed to track the sound-speed field variations in a vertical slice of the water column for known bottom geoacoustic parameters. Although the results were encouraging, it was shown that some biases were encountered when using the standard EKF, principally because of the high nonlinearity between the observations (the multi-frequency pressure field) and the environmental parameters (here the sound-speed field). In this paper, we show that Ensemble Kalman or sequential Monte Carlo filtering significantly enhance the estimation of the sound-speed field, for both range-independent and range-dependent cases. Reproducible results show that the temporal variations are well tracked, even in presence of measurement noise and model uncertainty. Furthermore the sampling approach allows to increase the time interval between successive measurements, which is an advantage from an operational viewpoint. The performances of the different nonlinear filters are also discussed.
The role of reproducing densities in a joint likelihood approach to multi-sensor detection and estimation
Authors: Roan Michael , Hoppe Elizabeth
Published: May 2008

In this work, a Bayesian, joint estimation-detection approach is used for computation of sufficient statistics and development of a general multi-sensor information fusion architecture. An approach borrowed from sequential Bayesian processing is used to compute prior densities for joint Bayesian estimation-detection. In this approach, a posteriori densities calculated at one sensor become priors at the next sensor after a coordinate transformation that transforms the outputs of each sensor to a common reference frame for all sensors. Reproducing prior densities are used to simplify the Bayesian iteration scheme and reduce communications requirements. The framework that is developed is equally applicable to networks where all sensors communicate with a centralized detection and estimation processor as well as those networks where sensors relay information from point to point. We anticipate using Bayesian iteration to convert posterior information into prior information on the next data gather cycle, iterate on estimates by exchanging information between sensors, i.e., "turbo likelihood fusion," and having the central decision maker decide when sensors should or should not communicate, depending on a cost criterion which combines information gain versus communication energy expenditure. Simulation are used to show detection and estimation performance under various conditions of sensor position and orientation uncertainty.
Reconstruction of temporal invariants of the time-reversal operator for communication in shallow water
Authors: Philippe Franck D. , Folégot Thomas , Prada Claire , Fink Mathias
Published: May 2008

Time-reversal techniques allow focusing in waveguides with application for detection or telecommunication (Kupperman et al., J. Acoust. Soc. Am. 103(1), 25-40, (1998)). It has been shown that the DORT method (French acronym for Decomposition of the Time Reversal Operator) can be used to achieve detection and selective focusing on pointlike scatterers in a waveguide (Mordant et al., J. Acoust. Soc. Am. 105, 2634-2642 (1999)). However, the decomposition is done in frequency domain providing eigenvectors V(ω) of undetermined phase. In order to achieve temporal focusing, it is necessary to built 'temporal eigenvectors' V(t) as an appropriate combination of the eigenvectors V(ω). Due to dispersion, the reconstruction of the temporal eigenvectors is difficult in waveguides. One solution was proposed by Mordant et al., using the symmetry of the array response matrix and assuming continuous frequency dependence of the invariants. However this method does not work if eigenvalues crossings occur. Furthermore, it cannot be applied to distinct arrays of transmitters and receivers. We propose a simple method to reconstruct the temporal invariants by using the back propagation of eigenvector in free space. Application to data from a laboratory experiment and from the DOREV 2005 shallow water experiment are presented.
Modeling time-reversal focusing in a multiple scattering medium
Authors: Haworth Kevin J. , Fowlkes Jeffrey B. , Carson Paul L. , Kripfgans Oliver D.
Published: May 2008

Time-reversal acoustics has been shown to be effective at focusing sound through high-order multiple-scattering media. In addition to signals being refocused, large amplitudes via pulse compression have also been observed. Previously, a statistical model was developed to simulate a time-reversal experiment where an impulse is sent into the scattering medium and the entire response is time-reversed [A. Derode et al., J. App. Phys. 85, 6343-6352 (1999)]. The high-order multiple-scattering process is modeled as a shot noise process. Again postulating a shot noise process the model has been extended to allow for arbitrary input functions and arbitrary windowing before time-reversal. The model has been shown to accurately predict the variance and expectation value of ensembles of simulated data. The analytical model is also tied directly to the governing physical processes, which is useful in attempting to optimize refocused signals. This extension is motivated by a desire to achieve high-amplitude long-pulse focusing, as would be useful in thermal therapies and radiation force experiments. However, the model can find application beyond this specific end-point. The model, it's physical implications, and several time-reversal simulations will be presented.
Similarity-Based Perceptual Feature Identification for Active Sonar Signal Classification
Authors: Philips Scott M. , Pitton James W.
Published: May 2008

In many acoustic signal processing applications human listeners are able to outperform automated processing techniques, particularly in the identification and classification of acoustic events. This paper develops a framework for employing perceptual information from human listening experiments to improve automatic classification of active sonar signals. We focus on the identification of new signal features that are able to predict the human performance observed in formal listening experiments. Using this framework, our newly identified features have the ability to elevate automatic classification performance closer to the level of human listeners. We develop several new methods for learning a perceptual feature transform from human similarity measures. In addition to providing a more fundamental basis for uncovering perceptual features than previous approaches, these methods also lead to a greater insight into how humans perceive sounds in a dataset. We also develop a new approach for learning a perceptual distance metric. This metric is shown to be applicable to modern kernel-based techniques used in machine learning and provides a connection between the fields of psychoacoustics and machine learning.
Auditory-motivated techniques for detection and classification of passive sonar signals
Authors: Brown Guy J. , Mill Robert W. , Tucker Simon
Published: May 2008

Hydrophone arrays used to make passive sonar recordings are becoming increasingly complex, thus placing great demands on sonar operators who are required to identify transient and tonal events. Machine hearing systems can mitigate this problem, by performing initial classification and detection of passive sonar signals based on perceptually relevant principles. We describe two such systems. In the first system, transient sounds are characterised using measures of timbre and acoustic pattern. Acoustic features relating to timbre were identified by a multidimensional scaling study, in which human listeners judged the similarity of transient sonar sounds. The perceptual features give improved classification performance compared to commonly-used statistical measures derived from the power spectrum. The second system is an auditory-motivated approach to narrowband detection, which is based on information in zero-crossing intervals rather than signal power. This is motivated by the observation that the fine time structure of an acoustic stimulus is preserved by the phase locking of auditory nerve fibres. We show that a power detector outperforms the interval detector when the signal is centred on the analysis filter. However, when the signal frequency deviates from the centre of the analysis band, interval-based detection improves and power-based detection worsens.
What it is like to be a bat: A sonar system for humans
Authors: Morland Cameron , Mountain David
Published: May 2008

Echolocation is a method of perceiving the world by emitting noises then listening to the reflections of these noises off objects in the world. It is used by animals for hunting and navigation. Some visually impaired humans use echolocation as part of their orienting repertoire. This work describes a device designed to enhanced one's existing echolocation ability. The device repeatedly emits an inaudible, ultrasonic ''click", several times per second. Each click reflects off surfaces; this reflection is detected by head-mounted microphones. Computer processing converts the signals into audible signals, which are presented to the user over custom open-ear earphones. ILD, ITD, HRTF, and Doppler shifts in the reflections allow the user to distinguish the location and size/surface properties of objects. The spatial cues presented by our device match those used to localize ordinary audible objects. The auditory ''image" generated in this way causes objects in the world to seem to emit sounds, and for objects with different shapes/textures to have subtly different sounds. A prototype has been constructed. Simple detection of objects and open spaces is readily possible, as well as Doppler-based gross surface texture. Further refinement in the areas of emission design, spectral spatialization, externalization, and miniaturization is required.
The sonar equations: definitions, dimensions and units of individual terms
Authors: Ainslie Michael A.
Published: May 2008

The passive and active sonar equations are reviewed with regard to the definitions of individual terms and their units. It is shown on the one hand that ambiguities exist in conventional definitions that can lead to misinterpretation, and on the other that under special conditions correction terms are needed that are not included in the standard equations. Revised definitions are proposed that remove the need for some of the correction terms and reduce the likelihood of misunderstanding. Particular emphasis is placed on the terms 'propagation loss' and 'source level' for both active and passive sonar. For example, the effect on changes in impedance between the source and receiver of the sound is considered in the case of passive sonar, and between the source, receiver and scatterer of sound in the case of active sonar.
Validation of primary hydrophone calibrations by inter-laboratory comparisons and by independent calibration methods
Authors: Robinson Stephen P. , Theobald Peter D.
Published: May 2008

A description is presented of two approaches which may be used to validate primary calibration methods for hydrophones and transducers. Firstly, a comparison may be made with another independent absolute calibration method, preferably one based on a different physical principle (and therefore with few common sources of uncertainty). Secondly, an inter-laboratory comparison of calibrations may be undertaken between different institutes operating at a similar level. This paper describes the results of such exercises for free-field calibration of hydrophones in the range from 1 kHz to 500 kHz. Firstly, two independent calibration methods are compared: the three-transducer reciprocity method and a method based on optical interferometry. The differences observed in the results are typically less than 0.5 dB, which is of the same order as the overall uncertainties of each of the methods. Secondly, the results are shown of a recent international comparison of hydrophone calibrations involving institutes from Canada, China, Germany, Russia, South Africa, UK, and USA. Here, the agreement was generally within quoted uncertainties, the results generally lying within a ±0.5 dB band for frequencies up to 300 kHz. A discussion is given of the general sources of uncertainties in the calibrations.
A method for calibrating hydrophones immersed in sandy sediment
Authors: Robb Gary B. , Hayman Gary , Theobald Peter D. , Humphrey Victor F. , Robinson Stephen P. , Leighton Timothy G. , Dix Justin K. , Best Angus I.
Published: May 2008

Hydrophones are frequently used as receivers for in situ sediment acoustic experiments. At present, processing techniques use receiver sensitivities measured from water-based calibrations. It is, however, accepted that the receive sensitivity will depend on the medium surrounding the hydrophone, particularly at frequencies close to the transducer's resonance frequency. To assess this affect, a series of calibrations were performed over the frequency range of 10 to 200 kHz on two types of hydrophones (with cylindrical and spherical elements) inserted into degassed sandy sediment. Sensitivities were measured using a modified three-transducer reciprocity technique, which uses a co-linear arrangement to allow the sediment attenuation to be omitted from the sensitivity calculation. The insertion of the hydrophones into the sediment reduced the measured receive sensitivities by a maximum value of 3.8 dB with respect to the equivalent water-based calibrations. The co-linear arrangement adopted allowed the transmission between the outer devices to be recorded with and without the central hydrophone present. Repeat measurements indicated that the sediment disturbance associated with the removal of the central hydrophone caused sensitivity differences of less than 1.2 dB, while the inclusion of the central hydrophone caused a shadowing effect which increased sensitivities by between 1.3 to 4.0 dB.
Underwater low frequency sound field simulation with the digital waveguide mesh method
Authors: Piao Shengchun , Tian Lingai , Yang Jing
Published: May 2008

Digital waveguide mesh method has been widely used to model musical instruments and simulation for room acoustics. In this paper, this method was applied to calculation the acoustic vector fields in the Pekeris waveguide. After introducing a boundary condition treatment method for the ocean bottom in the digital waveguide mesh, the acoustic pressure and particle velocity fields are calculated in spatial and temporal dimensions. Using these calculation results, the waveforms for the received signals and distribution of acoustic intensity in the underwater sound channel can also be obtained. Numerical simulation shows that the digital waveguide mesh method can be used to simulate the low frequency two-dimensional acoustic vector fields in shallow water and this method is easy to applied to three-dimensional acoustic fields calculation.
Acoustic and audience response analyses of eleven Venetian churches
Authors: Bonsi Davide , Longair Malcolm , Garsed Philip , Orlowski Raf
Published: May 2008

A research project has been carried out by the University of Cambridge (UK), Arup Acoustics (Cambridge, UK) and the Fondazione Scuola di San Giorgio-CNR (Venice, Italy) with the purpose of investigating the relationship between music and the architectural spaces within which it was performed in the context of Venetian vocal polyphony during the 16th century. The most representative churches (San Marco, Parish churches, hospitals and monasteries) were selected for this study and the music was performed within them by the Choir of St John's College of Cambridge University. Members of the audience completed questionnaires assessing the acoustic qualities of the spaces. The results of the audience and expert scores were then statistically analyzed and correlated with a set of room acoustic indices which had been measured in the same locations. In the present paper technical aspects of the experiments and the data analysis will be illustrated. The principal conclusions were as follows: 1. There is a strong correlation between the subjective impression of reverberance with EDT and T30 and musical clarity with C80; 2. A grouping of the churches by typology was found by analysing the reverberation times; 3. The poor quality of clarity was assessed for churches with longest EDT for the performance of music involving polyphony.
A Comparative Study of Four Concert Halls in Istanbul: Correlation of Subjective Evaluation with Objective Acoustic Parameters
Authors: Bayazit Tamer Nurgun , Vural Anil
Published: May 2008

In the studies of room acoustics, the parameters that are taken into consideration while evaluating the acoustic performance of a hall are examined in two sections: objective acoustic parameters which can be measured and calculated and, subjective acoustic parameters which define the impacts of a hall's acoustical qualities over the audiences. During the first half of the century, the reverberation time was considered to be the most important objective acoustic parameter which defined the acoustic quality of a hall. But, the later studies indicated that this parameter wasn't sufficient alone to define a subjective evaluation. Consequently, studies have been made to define the subjective influence on people from the acoustic performance of a hall. In this study, it has been attempted to define the statistical correlation between the subjective evaluation of the acoustic characteristics of the four concert halls, which was done by the members of orchestra together with the ordinary concert-goers, and their objective acoustic parameters are explained. The detailed objective acoustic parameters are presented for measurements in four concert halls in Istanbul. The halls are used by many different performances, from concerts to ballet or opera. The measured octave band quantities are RT, EDT, G,C80 and D50.
The influence of the scattering coefficient on the reverberation time
Authors: Huber Franz , Bednar Thomas
Published: May 2008

The reverberation time is still seen as an important measure of quality in architectural acoustic. The absorption coefficient is to be considered as the largest influencing factor on the reverberation time. The formulas after Sabine and Eyring give us the opportunity to calculate the reverberation time, when the absorption coefficients are known. In contrast to this, is the investigation of the influence of the scattering coefficient on the reverberation time a relatively new field for research. In this study the reverberation time for a "shoebox" was simulated, where the parameters were the values of the absorptions coefficient and the scattering coefficient and the even and uneven distribution of the absorption coefficient. The results of the simulation were compared with the results from the formulas by Sabine and Eyring. The simulations indicate a significant influence of the scattering coefficient on the reverberation time especially at low absorption coefficients. You can see by comparing the results of the simulation with the results of the formulas by Sabine and Eyring, that the theoretical formulas assume a minimum of scattering coefficient. It shows that the variation of the scattering coefficient is a possibly way to influence the reverberation time.
Vibration of a rib-reinforced floor/ceiling structures with irregularities
Authors: Chung Hyuck , Fox Colin
Published: May 2008

This paper describes mathematical modelling procedure of the rib-reinforced floor/ceiling structures, which are made up of components with irregular shapes and physical parameters. Exact determination of the vibration of a composite structure becomes impossible beyond the low-frequency range because one cannot determine all the necessary parameters of the components. Even if every possible parameter of the structure is known, the results from such deterministic model would not represent the real behaviour of the structure. Therefore, the prediction model in the mid- to high-frequency range must include the effects of the irregularities. We show how the power spectra of the irregular features of each component can be included in the model. The model gives statistical estimates of the solutions, which can give appropriate mean and variance of the vibration of the structure for the given severity of the irregularities.