bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a suitable PML for an harmonic study of a finite 1D phononic crystal
Authors: Bavencoffe Maxime , Morvan Bruno , Hladky Anne-Christine , Bou Matar Olivier , Izbicki Jean-Louis
Published: May 2008

This paper deals with the interaction of ultrasonic Lamb waves with a 1D phononic crystal. The studied structure is a finite plate with a periodic corrugated surface. Two types of forbidden bands arise in the Lamb wave dispersion curves. The first one is located at the limit of the first Brillouin zone, the second one exists at the crossing of dispersion curves of two different Lamb modes. These forbidden bands lead to conversion phenomena. In order to study accuratly the conversion phenomena in the band gaps, harmonic finite element analysis are performed. Perfect matching layers (PML) on both sides of the plate are then necessary to avoid stationnary waves. PML, adapted for Lamb modes involved at a given frequency, must be designed. By using these PML, the attenuation of Lamb waves propagating in the phononic crystal is clearly shown and is related to the existence of the forbidden band.
Acoustic response of a soniclike crystal within a rigid frame porous plate
Authors: Groby Jean-Philippe , Wirgin Armand , Ogam Erick , De Ryck Laurent , Lauriks Walter , Depollier Claude
Published: May 2008

The acoustic response (in particular, the transmission) of a periodic distribution of macroscopic inclusions within a rigid frame, porous plate (similar to a sonic crystal) is studied by the multipole method. Numerical results show that the addition of grating stacks leads to band gaps within the audible frequency range for a small number of stacks, this being associated with a large decrease of the transmission coefficient of the initial plate. The first band gap is of practical interest for noise suppression. The second band gap enables total acoustic absorption within a narrow frequency range due to the fact that a modified mode of the plate lies within this band gap.
K-dependent polarization of sagittal acoustic waves in phononic crystals
Authors: Ramos-Mendieta Felipe , Manzanares-Martinez Betsabe
Published: May 2008

By calculating the longitudinal and transverse strain energy averages we studied the polarization states of sagittal acoustic waves in one- and two-dimensional phononic crystals. Our theoretical results show the continuous variation of the field displacement components when the Bloch wave vector sweeps the Brillouin zone; thus, the vibrational modes of a same dispersion curve can have different polarization. First we present the polarization map of sagittal waves for an epoxy/Sn superlattice. Then we discuss the band polarization of an array of cylindrical holes in epoxy. As we shall see, the mixed modes can be either predominantly transverse of predominantly longitudinal. For calculations we have used an energy balance criterion.
Omnidirectional phononic reflection and selective transmission in solid/fluid superlattices
Authors: El Boudouti El Houssaine , El Hassouani Youssef , Aynaou Hassan , Djafari-Rouhani Bahram
Published: May 2008

We present a theoretical analysis of the occurrence of omnidirectional reflection in one-dimensional phononic crystal. We discuss the conditions for a one-dimensional layered structure, made of alternating solid and fluid layers, to exhibit total reflection of acoustic incident waves in a given frequency range for all incident angles. In general, this property cannot be fulfilled with a simple finite superlattice if the incident wave is launched from an arbitrary fluid. Therefore, we propose two solutions to obtain such an omnidirectional band gap, namely: (i) cladding of the superlattice with a layer of high acoustic velocities that acts like a barrier for the propagation of phonons, or (ii) the association in tandem of two different superlattices in such a way that the superposition of their band structures exhibits an absolute acoustic band gap. We discuss the appropriate choices of the material and geometrical parameters to realize such structures. The behavior of the transmission coefficients is discussed in relation with the dispersion curves of the finite structure embedded between two fluids. By inserting a defect layer in the structure, we show that selective transmission may occur in the forbidden bands.
Band gaps in a phononic crystal constituted by cylindrical dots on a homogeneous plate
Authors: Djafari-Rouhani Bahram , Pennec Yan , Larabi Hocine , Vasseur Jérôme , Hladky Anne-Christine
Published: May 2008

Using the finite difference time domain (FDTD) and the finite element (FE) methods, we investigate theoretically the band structure of a phononic crystal constituted by a periodic array of cylindrical dots deposited on a thin homogeneous plate. We demonstrate that such a structure can exhibit a very low frequency absolute band gap as compared to the wavelength in the constituent materials. The occurrence of this gap requires an appropriate choice of the geometrical parameters and, in particular, of the thickness of the plate as compared to the period or to the height of the cylinders. However, the same behavior can be obtained for various combinations of the materials constituting the homogeneous plate and the dots. We study in detail the width of this band gap as a function of the geometrical and physical parameters of the structure. On the other hand, the structure can also exhibit one or more higher gaps whose numbers can be increased by increasing the height of the cylinders.
Accelerometer measurements of acoustic-to-seismic coupling above buried objects
Authors: Attenborough Keith
Published: May 2008

The surface velocity of sand inside a large PVC container, induced by the sound pressure from either a large loudspeaker radiating into an inverted cone and pipe or a B&K point source loudspeaker mounted with its axis vertical, has been measured using accelerometers. Results of white noise and stepped frequency excitation are presented. Without any buried object the mass loading of an accelerometer creates resonances in the spectral ratio of sand surface velocity to incident acoustic pressure i.e. the acoustic-to-seismic (A/S) admittance spectra. The A/S responses above a buried compliant object are larger and distinctive. The linear A/S admittance spectra in the presence of a buried electronic components box have been studied as a function of burial depth and sand state. The nonlinear responses above the buried box have been studied as a function of depth, sand state and amplitude. Predictions of a modified 1D lumped parameter model have been found to be consistent with the observed nonlinear responses. Also the modified model has been used to explain features of the A/S responses observed when using an accelerometer without any buried object [Work supported by DSTL, UK.]
Acoustic-laser land mine detection: Operationally enabling technologies
Authors: Haupt Robert
Published: May 2008

Reliable and cost effective methods are critically needed to locate the vast number of land mines left behind from military conflicts. Many mine location systems being developed fall short of being operationally practical since they may detect only metal or a specific mine feature, have limited standoff ranges, or have slow search speeds. An approach that may overcome operational issues is the acoustic-laser method. Acoustic waves generated by a noncontact/standoff source and transmitted through air can couple to the ground and induce resonances from a large variety of mines. The vibration field above these mines can be measured remotely using laser Doppler vibrometry. In this paper, enabling technologies that can significantly increase search area speed, improve standoff range, and reduce size in an acoustic-laser system are discussed. We take a novel approach to excite mines by using a high powered parametric acoustic array source developed at MIT Lincoln Laboratory that transmits a highly directive sound beam from a safe distance. The avalanche photo diode (APD) array developed at MIT Lincoln Laboratory will also be discussed as the enabling technology of a proposed 4096 multipixel laser system that can sense a wide vibration field out in front of a moving vehicle.
In-situ monitoring of megasonic cleaning
Authors: Zijlstra Aaldert G. , Janssens Tom , Mertens Paul , Versluis Michel
Published: May 2008

Acoustic agitation is used in ultrasonic cleaning to induce a physical force to remove nanoparticles in semiconductor processing. The performance of cleaning tools is commonly quantified ex-situ by the particle removal efficiency η (i.e. the ratio of the remaining to the original particle concentration). The resulting η -wafer maps often reveal spatial nonuniformities related to tool design. The local study of the cleaning dynamics, quantified by the removal frequency (fR[s-1]) also indicates that the density of cleaning events over a wafer can be strongly non homogeneous. Because the sound frequencies used in industrial tools are in the MHz range, visualization of the cavitating bubbles (resonant size 3 μm) is highly challenging, both in time and in spatial resolution. Considering that the cleaning effect of a cavitating bubble is permanent a method is presented here to determine the acoustic cleaning event size (Aevent[μm2]) and the event flux (φ[μm-2s-1]) through visualization techniques. The method consists of time-resolved imaging of the removal of a nanoparticle layer deposited on a transparent substrate. The microscopic cleaning activity can then be correlated to the actual removal frequencies fR through the relation fR=φAevent to further clarify the cleaning mechanisms in industrial tools.
Ultrasonic cleaning of particle and natural organic matter fouled cross-flow membranes
Authors: Weavers Linda K. , Walker Harold W. , Chen Dong , Lamminen Mikko O.
Published: May 2008

Membrane filtration has arguably been the most significant development in the area of water purification in the past 50 years. It has enabled many processes to become more reliable and to achieve purities that have not been achieved previously. One of the drawbacks of membrane use is fouling. In this research the ultrasonic cleaning of particle-fouled membranes was investigated. Specifically, we have explored the mechanisms responsible for ultrasonic cleaning and how solution conditions, particle conditions, cake layer effects, and ultrasonic conditions affect cleaning using scanning electron microscopy (SEM) and permeate flux measurements. We have investigated continual cleaning during membrane filtration in addition to cleaning after fouling. Results of this work will be discussed for cross-flow system configurations.
Auditory temporal edge detection in human auditory cortex
Authors: Chait Maria
Published: May 2008

Auditory objects are detected if they differ acoustically from the ongoing background. In simple cases, the appearance or disappearance of an object involves a transition in power, or frequency content, of the ongoing sound. However, it is more realistic that the background and object possess substantial nonstationary statistics, and the task is then to detect a transition in the pattern of ongoing statistics. How does the system detect and process such transitions? We use magnetoencephalography (MEG) to measure early auditory cortical responses to transitions between constant tones, regularly alternating, and randomly alternating tone-pip sequences, where the dimension of change is either frequency, loudness, or spatial location. Such transitions embody key characteristics of natural auditory temporal edges. Our data demonstrate that the temporal dynamics and response polarity of the neural temporal-edge-detection processes depend in specific ways on the generalized nature of the edge (the context preceding and following the transition) and suggest that distinct neural substrates in core and noncore auditory cortex are recruited depending on the kind of computation (discovery of a violation of regularity, vs the detection of a new regularity) required to extract the edge from the ongoing fluctuating input entering a listener's ears.
Perception of simultaneous sentences with frequency-shifted voiced excitation
Authors: Roberts Brian , Holmes Stephen D. , Darwin Chris J.
Published: May 2008

Identification of key words in one of two simultaneous sentences is substantially improved when the sentences differ in fundamental frequency (F0). When the sentences are constructed to be almost continually voiced, identification can improve from 20% at 0 semitones difference to 80% at 8 semitones difference (J. Bird & C.J. Darwin 1998 in Psychophysical and Physiological Advances in Hearing, Ed A.R. Palmer et al., Whurr, London, pp. 263-269). We recorded the same monotone sentences as Bird and Darwin. These were first resynthesised using PSOLA to give a range of harmonic F0 differences (0, 1, 3, and 10 semitones) and then additionally resynthesised by LPC with the LPC residual frequency shifted by 25% of F0, to give excitation with inharmonic but regularly spaced components. Experiment 1 showed that frequency-shifted sentences gave the same large improvement with nominal F0 difference as did the harmonic sentences, although overall performance was about 10% poorer. Experiment 2 replicated the finding by Bird and Darwin that swapping the F0 difference across spectral regions only reduced the improvement in recognition for large F0 differences, and extended this finding to frequency-shifted voiced excitation. The results extend the range of perceptual phenomena originally attributed to harmonic processing.
Speech in noise and the medial olivo-cochlear efferent system
Authors: Meddis Raymond , Ferry Robert , Brown Guy J.
Published: May 2008

A central question in auditory scene analysis is how we are able to follow speech against a background of interfering noise. The question is particularly acute for artificial speech recognition algorithms and the hearing impaired. The medial efferent system has been suggested as one contributor to our ability to hear speech in noise. We have recently added efferent suppression to our model of the auditory periphery and evaluated it against physiological observations at the level of the basilar membrane and auditory nerve. We have also replicated a study using compound action potentials where a tone in a noise background became more salient when the efferent system was artificially activated. Visual representations of the computed auditory nerve response to speech in noise show considerable improvement when the efferent system is activated. Tests using the auditory model as a front end to a connected-word recognition algorithm also showed improved performance in the presence of noise when efferent effects were included. The benefits of efferent suppression include reduced compression and extension of the dynamic range of individual auditory nerve fibers.
The European starling as a model for understanding mechanisms underlying auditory scene analysis
Authors: Klump Georg
Published: May 2008

The European starling is a songbird that has evolved mechanisms for the analysis of acoustic scenes exhibiting a number of similarities with human perception. Segregation of signals and background noise from different sources is enhanced due to the processing of differences in modulation patterns as is evident in experiments on the comodulation detection difference and and comodulation masking release. Similarly to auditory streaming in human subjects, integration of sequential signals into streams occurs in the European starling and it is affected by spectral and temporal properties of the sounds. The presentation reviews results from psychophysical experiments and compares these to observed neural response patterns of auditory forebrain neurons in starlings.
Effect of channel interactions on sensitivity to binaural timing cues in electrical hearing
Authors: Jones Gary , Litovsky Ruth , Van Hoesel Richard
Published: May 2008

With bilateral cochlear implant (BICI) users it is possible to test sensitivity to interaural timing differences (ITDs) while bypassing peripheral auditory processing. Ongoing work in our lab suggests that at low pulse rates ITD JNDs in the tens of microseconds can be achieved by BICI users with postlingual onset of deafness at single pairs of electrodes at the base, middle or apex of the electrode array. The current project is concerned with channel interactions and, specifically, performance when there is activation of more than one electrode pair and when more than one ITD is presented to the auditory system simultaneously. We examined ITD sensitivity in BICI users with bilateral pairs of pitch-matched electrodes on which unmodulated pulse trains were presented at 100 pulses per second. A probe pulse train and an added pulse train were temporally interleaved. ITD JNDs for the probe train were measured while varying the added train's: a) frequency place, b) level, and c) ITD (matched to probe or fixed at 0 μs). Results suggest that stimulation of multiple electrodes can result in a range of interaction effects that can have either facilitatory or interfering effects on binaural sensitivity. Work supported by NIH-NIDCD (R01 DC003083-09, F31 DC009361).
Development of a general SEA subsystem formulation using FE periodic structure theory
Authors: Cotoni Vincent , Shorter Phil S. , Langley Robin S.
Published: May 2008

Statistical Energy Analysis (SEA) represents a field of study in which statistical descriptions of a system are employed in order to simplify the analysis of complicated vibro-acoustic problems. In SEA, a vibro-acoustic system is represented by a collection of subsystems that can receive, store, dissipate and transmit vibro-acoustic energy. Traditionally, the SEA parameters for a given subsystem are formulated analytically based on consideration of wave propagation through the subsystem. While such analytical algorithms can be readily applied to the majority of systems encountered in practical problems, there are certain types of sections that are difficult to describe using existing analytical formulations. Examples include: isogrid in launch vehicle fairings, extruded aluminum sections in train floors and modern corrugated aircraft fuselage constructions. This paper describes the development of a generic SEA subsystem formulation based on the use of finite element (FE) periodic structure theory. A small unit cell of the section is created and computationally efficient algorithms are developed to calculate wave propagation through a large array of such cells. The resulting algorithms are used to calculate the SEA parameters for the section. The approach is described and a number of numerical validation examples are presented.
Structure/cavity coupling using Statistical Energy Analysis: Coupling loss factors and energy maps into subsystems
Authors: Totaro Nicolas , Guyader Jean-Louis
Published: May 2008

Prediction of interior noise is one of the most concerning issues of vehicle industry. Statistical Energy Analysis theoretically allows to determine energy spread over a structure divided into subsystems when one subsystem is submitted to a rain-on-the-roof excitation. Subsystems can be either a part of the structure or a cavity. Recently, a method (SmEdA) based on modal bases of uncoupled subsystems have been derived. This method permits to compute CLF using standard FEM software. This method has been successfully applied on structure/structure coupling and is extended to estimation of CLF between a structure and a cavity in the present article. In addition, in the case of interior noise, SEA can only provide a global energy into the cavity on frequency bands. No information on energy repartition into the subsystem is given. In the present article, an extension of SmEdA method is proposed to quickly estimate energy repartition into subsystems (structure or cavity).
Spherical harmonic analysis of the field radiated by a source embedded in a two-layer coating of a spherical shell
Authors: Ginsberg Jerry H.
Published: May 2008

The acoustic field generated by a small source embedded in a viscoelastic layer encapsulating a spherical shell was modeled previously by treating each layer as a dissipative fluid [J. H. Ginsberg, JASA, 122, 3067 (2007)]. Using spherical harmonic series for each layer was shown to lead to profoundly ill-conditioned equations because of the enormous differences of scale of the spherical Bessel functions having complex argument and high order. Mie series is not directly applicable because the present source is embedded in a layer. Scaling of the spherical Bessel functions and the alternatives of using Bessel and Neumann or two Hankel functions are examined for their efficacy in addressing ill-conditioning. The specfic system that is analyzed consists of a soft inner layer that coats the shell, covered by an outer layer that encapsulates the source. The impedance of the outer layer nominally matches the surrounding water, so reflection of the source from the soft inner layer might seem to have the effect of creating a dipole. However, depending on the wavelength in the inner layer, it might seem that the source “sees” the shell, in which case one would expect the behavior to be like a simple source whose strength is doubled.
Comparison of numerical techniques for the vibro-acoustic behaviour of a flexible structure
Authors: Goth Yvon
Published: May 2008

The tractors bonnets are large flexible parts that radiate noise under the excitation of the forces exerted on the contact points and the sound pressure fluctuations coming from the engine. The vibro-acoustic behaviour of such a bonnet, excited by local forces or a diffuse pressure field, has been computed using various techniques: - In the low frequency domain, the finite element method has been used to compute the structural behaviour, while the acoustic radiation has been computed by using the boundary element method and the finite element method with approximated boundary conditions to simulate the free field conditions. - In the high frequency domain, the computation has been made using the SEA method, with an approximation of the radiation coefficients. -In the medium frequency domain, both techniques have been used and compared. Software used where VA-One, from ESI, and Code-Aster, from EDF. The paper presents the numerical results obtained, associated to the computing time. Approximated methods can be largely faster than 'exact' ones (finite elements associated with boundary elements) and, for engineering use, represent a good compromise between quality and efficiency.
Particular analysis of vibration energy transmission in connections of thin plates
Authors: Cieslik Jacek
Published: May 2008

Analyses of energy balance in the mechanical systems are done by the quantitative and qualitative assessment. Qualitative assessment is possibly by the use of energy flow descriptors and observation of energy density distribution in the mechanical structure. The work presents the results of investigation of welded connections of rectangular steel plates. The aim of the analysis was the quantitative estimation of vibrational energy transmitted though the welded connection depending on the inclination angle of plates. The structural intensity was used as the parameter for the analysis. Method of structural intensity evaluation enabled the elaboration of intensity vector field. Unification of shape and size of finite elements made possible the summation of only the magnitude of intensity. Summation was performed in the plate's cross sections far from the places of excitation and the damping. The detailed information on vibration energy flow was achieved. The obtained results of calculation give the quantitative information on amount of energy transmitted, reflected and the damped in welded joints of plates. The analyzed case was intentional to show the utility of intensity method in diagnostics of joints in mechanical constructions. The calculation results were verified experimentally with application of thermograph measurements of stress and vibration velocity.
Active modal control in rooms - practical approach
Authors: Rene Pierre-Jean , Lissek Hervé
Published: May 2008

Engineers dealing with noise reduction in habitations close to transportation traffic or industrial facilities encounter several problems to decrease noise level in rooms at low frequencies. Passive materials and current building construction knowledge enable to avoid noise transmission in habitations at medium and high frequencies and the regulations based on the dBA scale can often be respected. But these regulations do not take into account the real unpleasantness of noise for the inhabitants who are still disturbed by low frequency noise. Because of the modal behavior of rooms, air-borne and structure-borne noise generate high sound pressure level at the first modal frequencies, even with small amount of energy. The aim of this work is to decrease noise level in rooms at these specific and most annoying frequencies. Usual techniques of room acoustics and acoustic insulation reach their limits and cannot be improved due to cost and volume constraints. To reach our goal, active modal control seems to be the best way. The principle of the AMC is to decrease only the 2 or 3 first modal frequencies with a unique microphone-controller-loudspeaker system. Several results are presented for different excitations and room configurations. The controller setup has to be the more autonomous and flexible system as possible.
Resonant frequencies of a cantilevered timoshenko beam with an attached general point-connected vibratory system
Authors: Koch Robert M.
Published: May 2008

The literature is full of technical papers that have examined the free vibration of cantilevered Bernoulli-Euler beams with both rigidly and elastically-attached point masses at the free end. Additionally, much work has been published in the last ten years on cantilevered Timoshenko beams (which includes the effects of shear deformation and rotatory inertia) with a similar, yet more restricted, set of free end boundary conditions. Rossit and Laura published in the Journal of the Acoustical Society of America in 2001 a formulation for a Timoshenko beam with a simple single DOF spring-mass system attached to the free end. The present paper extends Rossit and Laura's mathematical formulation to account for a general, damped, multi-DOF system point-connected to a cantilevered Timoshenko beam's free end. To demonstrate the formulation, mathematical relations and numerical results for a single DOF damped system and both damped/undamped 2DOF vibration absorbers are presented.
Low-dimensional, auditory feature vectors that improve vocal-tract-length normalization in automatic speech recognition
Authors: Monaghan Jessica J. , Feldbauer Christian , Walters Tom C. , Patterson Roy D.
Published: May 2008

Human speech recognition is robust to large changes in vocal tract length (VTL) but automatic speech recognition is not. In an effort to improve VTL normalization, an auditory model was used to derive formant-like features from syllables. The robustness supported by these auditory features was compared to the robustness provided by traditional MFCCs (Mel-Frequency Cepstral Coefficients), using a standard HMM recognizer (Hidden-Markov-Model). The speech database consisted of 180 syllables, each scaled with the vocoder STRAIGHT to have a wide range VTLs and glottal pulse rates. Training took place with syllables from a small, central range of scale values. When tested on the full range of scaled syllables, average performance for MFCC-based recognition was 73.5%, with performance falling close to 0% for syllables with extreme VTL values. The feature vectors constructed with the auditory model led to much better performance; the average for the full range of scaled syllables was 91%, and performance never fell below 65% even for extreme combinations of VTL and GPR. Moreover the auditory feature vectors contain just 12 features whereas the standard MFCC vectors contain 39 features. Research supported by the UK-MRC (G0500221) and EOARD (FA8655-05-1-3043).
Ambiguity in the recognition of phonetic vowels when using a bone conduction microphone
Authors: Zimpfer Véronique , Buck Karl
Published: May 2008

When speaking, not only air conducted noise is generated, but also vibrations can be recorded at different places on the head using accelerometers. The bone conduction microphones are less sensitive to noise than regular acoustical microphones, they are usable in harsh environments and they are compatible with head equipment such as NBC protection devices. This paper reports the first results of a study designed to evaluate the differences in perception between speech recorded via a acoustic microphone and speech recorded using bone conduction. These differences may cause of a bad intelligibility of bone conduction communication, even if presented in an undisturbed environment. We study the recognition of ten French phonetic vowels recorded by a bone conduction microphone. A listening test is designed to show the confusions of phonetic vowels when listening to speech picked up by an air or bone conduction microphone. The tests show confusion between the vowels [i] [y] [u]. All of these have the frequency of their first formant in common. The sonograms are distinctly different when recorded with an aero-acoustic microphone, become almost identical if the bone conducted speech is analyzed. Moreover, the confusions of the phonetic vowels depend on the speaker.
Analysing cockpit and laboratory recordings to determine fatigue levels in pilots' voices
Authors: Legros Claude , Ruiz Robert , Plantin De Hugues Philippe
Published: May 2008

Analysis of pilots' voices was undertaken under controlled laboratory conditions, using aeronautical terminology, standard professional equipment, and a standardized recording environment. The aim of the experiment was to determine the way the acoustic characteristics of the voice are modified after a phase of sleep. The results, which are presented in this paper, show very significant variations in the dispersion parameters, like jitters, associated with the fundamental frequency. In an aircraft cockpit, the electro-acoustic and environmental conditions are not so good. Therefore, it is essential to improve and adapt voice analysis methods to achieve reliable results. Cockpit Voice Recorder recordings have poor acoustic characteristics due to microphone quality and the signal to noise ratio, in addition to the non-predetermined vocabulary range. This paper will outline the modifications made to the laboratory methodology and the comparative results obtained, to improve the analysis of CVR recordings. Comparisons of the test recordings meant that it was feasible to determine, via voice analysis, the state of drowsiness of a pilot and, made possible the study of CVR recordings from accidents using new analytical techniques.
Segmental and supra-segmental contributions to cross-language speech intelligibility
Authors: Preece-Pinet Melanie , Iverson Paul
Published: May 2008

Non-native accents affect speech recognition in noise, and previous work has shown that intelligibility is modulated by listener-talker interaction; a matched linguistic background between the two seems to maximise intelligibility. The present study examined the contribution of segmental and supra-segmental cues, as well as how the degree of L2 experience affects non-native speech perception. A group of monolingual native English listeners and two groups of French native listeners with different amounts of L2 experience were presented with English sentences produced by native and non-native (French) speakers in noise. The stimuli were digitally processed to swap the pitch and segment durations between recordings of the same sentences produced by different speakers (e.g., imposing a French-accented prosody onto recordings made from English speakers). The results revealed that English listeners were more accurate at recognizing speech with English segments but were little affected by prosody; low proficiency French listeners were more accurate when the speech had both French-accented segments and prosody; and high proficiency French listeners varied in the cues that they used depending on the noise level. The use of segmental and supra-segmental cues thus appears to vary with language experience and listening context.
A multidimensional acoustic analysis of vowels in two Polish dialects
Authors: Cholewa Wieslawa , Karypidis Charalampos
Published: May 2008

In this paper, we attempt to examine the acoustic (oral) vowel spaces of two main Polish dialects: the Polish spoken in Cracow and that spoken in the wider region of Warsaw. A semi-spontaneous corpus consisting of four speakers (two male, two female) of each dialect was recorded with approximately 2000 vowel occurrences for each speaker. The segmentation was performed manually and was subsequently corrected with an intensity-based algorithm. The tokens were submitted to acoustic analyses, and two multidimensional representations were then prepared, one based on formants (accompanied with bandwidths and amplitudes) and the other on critical bands. Both representations included measurements for duration, F0, spectral center of gravity, skewness, and kurtosis. These values served as input for discriminant and principal component analysis which allowed us: (a) to compare the relative weight of each cue, (b) to isolate those parameters that allow a differentiation of the members of a vowel system (in a language such as Polish, F1 and F2 are traditionally the sole cues regarded as relevant), and (c) to detect any (dis)similarities between the two dialects in the three aforementioned aspects.
Do Japanese speakers perceive nonexistent vowels in non-native consonant clusters
Authors: Funatsu Seiya , Imaizumi Satoshi , Fujimoto Masako , Hashizume Akira , Kurisu Kaoru
Published: May 2008

Vowel epenthesis is a well known phenomenon that non-native speakers insert epenthetic vowels inside non-native consonant clusters. Vowel epenthesis is assumed as perceptual "illusory vowels" (Dupoux et al. 1999). We analyzed vowel epenthesis shown by native Japanese speakers during reading and repetition tasks for non-native consonant clusters, and analyzed their brain responses using magnetoencephalographic methods. Under the reading task, in which subjects read English words and nonsense words, native Japanese speakers (eight females) inserted vowel /o/ after /t/ and /d/ in consonant clusters, and vowel /u/ after other consonants. Under the repetition task, in which subjects repeated utterances of a native English speaker, native Japanese speakers did not produce epenthetic vowels with few exceptions. The length of exceptional epenthetic vowels found under the repetition task was shorter than those under the reading task. The magnetoencephalographic mismatch responses were elicited by epenthetic vowels, suggesting that the native Japanese detected epenthetic vowels as real segments. Based on these results, we conclude that vowel epenthesis by native Japanese speakers did not arise from "illusory vowels", but rather from the difficulty of articulating consonant clusters which are not found in Japanese and/or Japanese phonological rules.
Fine-phonetic variation in a computational model of word recognition
Authors: Scharenborg Odette
Published: May 2008

There is now considerable evidence from psycholinguistic and phonetic research that fine-phonetic variation in the speech signal modulates human speech processing (HSP), and helps the listener segment a speech signal into syllables and words [e.g., Salverda et al., Cognition 90, 51-89 (2003)]. This kind of information also appears to help the human perceptual system distinguish short words (like 'ham') from the longer words in which they are embedded (like 'hamster'). Salverda et al. showed that the lexical interpretation of an embedded sequence is related to its duration; a longer sequence tends to be interpreted as a monosyllabic word more often than a shorter one. Until recently, no computational models of HSP existed that are able to model this fine-phonetic variation [Hawkins, J. of Phonetics 31, 373-405 (2003)]. In this paper, we present Fine-Tracker, a novel computational model of human word recognition that it is able to capture and use this fine-grained acoustic-phonetic variation during speech recognition. Simulations using the recordings from the listener experiments by Salverda et al. show that Fine-Tracker is able to capture and use duration variation in the speech signal to distinguish short words from the longer words in which they are embedded. [Research supported by NWO.]
Lombard speech: effects of task and noise type
Authors: Lu Youyi , Cooke Martin
Published: May 2008

An analysis of the effect of noise on speech production requires material recorded while undertaking realistic tasks in the presence of realistic noise backgrounds. This study examined speech produced in a number of types of "noise" in tasks with and without a communication factor. In one task, individual speakers were asked to speak aloud while solving "sudoku" puzzles, while in another task pairs of speakers solved these puzzles cooperatively. In both cases the background was quiet or contained one of three types of noise: competing talker, babble-modulated noise and speech-shaped noise. Individual digit words "one" to "nine" and speech/nonspeech sections were manually segmented for acoustic analysis. Both tasks produced Lombard effects observed in previous studies: increases in duration, energy, F0 and spectral centre of gravity. Relative to the non-communicative task, the presence of a communication factor led to words with shorter duration, more overall energy and higher spectral centre of gravity. Speakers actively avoided overlapping with the competing speech masker, with a stronger effect in the communicative task. These results suggest that speakers can, to some extent, compensate for both energetic and informational masking at the ears of the interlocutor.
Production of Parisian French front rounded vowels by second-language learners
Authors: Levy Erika S. , Law Franzo
Published: May 2008

This study examined the effects of language experience and consonantal context on the production of Parisian French (PF) vowels by American English (AE) learners of French. A repetition task was performed, involving French vowels /y-œ-i-a-u/ uttered by a native speaker of Parisian French (PF) in bilabial /bVp/ and alveolar /dVt/ contexts embedded in the nonsense word/phrase /raCVCa/. Three groups of native AE speakers participated: speakers without French experience (NoExp), speakers with formal French experience (ModExp), and speakers with formal and extensive immersion experience (HiExp). Production accuracy was assessed by native PF listeners' judgments and by acoustic analysis. Native PF listeners identified second-language (L2) learners' productions more accurately as a function of speakers' increased language experience, although /u/, /y/ and /œ/, even produced by the HiExp group, were frequently misidentified. A consonantal context effect was revealed, including /u/ being misidentified more often in alveolar context than in bilabial context by all three groups. Overall, all groups distinguished front rounded /y/ from /u/ in production, but often in a non-native manner, e.g., producing /y/ as /ju/. Individual differences, interactions between consonantal context and vowels, as well as implications for the perception-production link in L2 learning, are discussed.
Cortical mechanisms of speech perception in noise in elderly listeners
Authors: Lee Edward R. , Wong Patrick C. , Dhar Sumitrajit , Gunesekera Geshri M. , Abel Rebekah A.
Published: May 2008

The present study examines the cerebral hemodynamics (measured by fMRI) associated with listening to speech in noise in elderly listeners with relatively normal peripheral hearing. We asked subjects to identify single words in quiet and in two multi-talker babble noise conditions (+20 and -5 dB SNRs). The behavioral results indicated that subjects performed similarly between the Quiet and +20 SNR conditions, both in accuracy and reaction time, but were less accurate and responded slower in the -5 SNR condition. There were performance-independent and SNR-dependent effects in the brain. A contrast of the +20 SNR and Quiet conditions revealed bilateral (especially left) auditory and prefrontal activation in noise despite equal behavioral performance (performance-independent but noise-dependent activations). As noise increased and behavioral performance decreased (as in the -5 SNR condition), activation in these regions increased. These results reveal a cortical network involving acoustic analysis, working memory, and auditory attention associated with speech perception in noise by the elderly. [Work supported by NIH.]
Computer simulations of intraoral pressure patterns during voiced stop consonant production
Authors: Lucero Jorge C. , Koenig Laura L.
Published: May 2008

Several past studies have used laryngeal and/or upper vocal tract models to explore aerodynamic control during production of obstruent consonants, yet many aspects of such control remain unclear. Of particular interest in this work is how varying laryngeal and vocal tract dimensions such as occur among men, women, and children influence phonatory behavior and the time course of intraoral pressure (Pio) increase during voiced stop consonant production. To maintain phonation during a voiced stop closure, Pio must remain below the subglottal pressure. Physiological and modeling studies indicate that adult speakers actively increase supraglottal volumes during voiced stops, which slows the rate of Pio increase. Speakers with smaller vocal tracts may either be less successful in slowing the rate of Pio buildup, or else may perform more extreme volumetric changes to achieve similar end results. The current study uses data recently collected on voicing and Pio during stop production in men, women, and children. We use a modified two-mass model of the vocal folds coupled to a model of the upper vocal tract to reproduce the observed Pio patterns, and explore how the behavior of the system reflects differences in anatomical and physiological dimensions. [Work supported by MCT/CNPq-Brazil.]
Enhancement of voiced and voiceless stop categories in infant-directed speech to 11-month-old infants
Authors: Cardillo Gina C. , Perry Jennifer R. , Kuhl Patricia K.
Published: May 2008

It has been proposed that infant-directed speech (IDS) increases the discriminability of phonetic categories by exaggerating the acoustic differences between phonetic units (Kuhl et al., 1997, Science). However, reports show conflicting results on whether this principle holds for consonants. The current study measured English /p/ /b/ /t/ /d/ in both IDS and adult-directed speech (ADS) from connected speech in 27 mothers addressing their 11-month-old infants. Findings supported the exaggeration hypothesis. The mean VOT of /p/ was longer in IDS than ADS, and approached significance for /t/. The mean VOT difference between /p/ and /b/ was greater in IDS than in ADS. Similarly, when phonemes were grouped into voiceless and voiced categories, the difference between categories was significantly greater in IDS than ADS. We will discuss ways to measure AD-ID differences. [Work supported by NIH HD37954.]
Using sets of combs to control pitch estimation errors
Authors: Lienard Jean-Sylvain , Barras Claude , Signol Francois
Published: May 2008

We analyze the errors of a Pitch Estimation Algorithm using the Pitch Function (response of the periodicity estimator as a function of the frequency parameter Fc). The estimator's maximum response for a single signal of fundamental frequency F0 is expected to occur for Fc=F0. Actually the pitch function exhibits many secondary peaks which occasionally cause the errors. When several signals are mixed, secondary peaks of a signal may take over the main peak of the other. By taking as periodicity estimator the correlation of the spectrum module with a uniform infinite spectral comb of fundamental frequency Fc we show that each peak corresponds to a particular value of the ratio Fc/F0=p/q (p and q integers ⩾1). It follows that some secondary peaks can be canceled either by augmenting the comb with intermediary negative teeth, or by setting to zero some of its teeth. These modified combs can be viewed as linear combinations of uniform combs of different Fcs. The present study aims at precisely defining and combining the modified combs so that the main peaks of the new Pitch Function reliably indicate the F0s of the components. Examples are given on mixtures of voiced segments extracted from natural speech.
Inter-speaker variability and the articulatory-acoustic relations in German and English /sh/
Authors: Fuchs Susanne , Toda Martine
Published: May 2008

The aim of this study is to investigate speaker-specific articulatory-acoustic relations and their potential causes in the realisation of /sh/. By means of electropalatographic and acoustic data for 12 German and 12 English native speakers (6 males and 6 females for each language), we obtained the following results: 1) relatively invariant COG values of the frication noise among the subjects, 2) huge inter-speaker variability in the articulatory place of articulation, especially for the males. We suggest that in the realisation of /sh/ motor equivalence principles can be used speaker-dependently. In particular, the length of palatal channel, the size of the front cavity (including its sublingual portion) as well as lip protrusion are the relevant articulatory parameters involved in the adjustment of the frication noise. Speaker-specific articulatory strategies will be discussed in the light of the formant transition characteristics, palatal morphology, and the prototypical articulatory patterns will be illustrated by means of acoustic modelling.
Is there a sensitive period for representation of phoneme sequences
Authors: Welton Mary Anne , Cohen Annabel J.
Published: May 2008

A key issue in development of speech perception and production concerns the possible existence of an early sensitive period that facilitates language acquisition. Spoken language acquisition entails representation of grammatical sequences of phonemes. In a two-phase experiment, 120 participants in three age groups (pre-adolescents, adolescents, young adults) were presented with 64 words, 16 each of English, English pronounceable non-words, Spanish, and Mandarin. The task was to determine if the word was English. All age groups performed well, indicating that the words had been attended. A subsequent surprise recognition phase presented 64 words again, one half of which were old and one half new. Participants judged whether each word had previously been presented. Here performance overall was poorest for Spanish and Mandarin, and children performed relatively more poorly on English non-words as compared to the older groups, but showed no age-relative disadvantage for Chinese. Arguing that evidence for a sensitive period arises if children perform relatively better than older participants on foreign words as compared to English words or English non-words, the recognition results are consistent with the proposal of a sensitive period for phoneme sequence representation. The paradigm provides a new way of examining the sensitive period hypothesis. (supported by NSERC)