bluuebunny/crossref_metadata_2025 huggingface dataset:
Age of learning affects the learning of L2 pronunciation but not morphosyntax
Authors: Flege James E. , Yeni-Komshian Grace , Liu Serena
Published: July 2002

Many studies have shown that performance in a second language (L2) decreases as the age of L2 learning increases, but such findings are difficult to interpret because many factors are confounded with age. Here we assessed the overall degree of foreign accent in English sentences, and scores obtained on a 144-item grammaticality judgment test (GJT). The subjects were 240 Koreans who differed according to their age of arrival (AOA) in the United States (2 to 23 years). As AOA increased, foreign accents grew stronger and the GJT scores decreased steadily. However, when variables confounded with AOA were controlled using a subgroup matching technique, AOA was found to exert a significant effect on the foreign accent ratings but not on the GJT scores. Total years of education in the United States, but not language use or AOA, significantly affected scores for a subset of GJT items that tested rule-based, generalizable aspects of English morphosyntax. Conversely, language use, but not education or AOA, affected the scores for GJT sentences testing lexically based aspects of morphosyntax. Age effects on L2 pronunciation thus appear to be real. However, differences in morphosyntactic knowledge may instead be due to age-related variation in education or English-language use.
Localization in real life and with individual, nonindividual, and artificial head binaural recordings
Authors: Moller Henrik
Published: July 2002

Human sound localization was studied in real life (1), and with binaural recordings made in the ears of the listener him/herself (2), in the ears of other humans (3), and with artificial heads (4). The localization with individual binaural recordings turned out to be identical to that of real life. An increased number of errors was seen for nonindividual binaural recordings, especially in terms of confusions between median plane sources. It proved possible to select human ‘‘recording heads’’ that offered recordings which gave more favorable results than others. The highest number of errors was seen with artificial head recordings. This is surprising, since the artificial heads aim at replicating the acoustics of the ‘‘average’’ human. Measurements of head-related transfer functions confirmed differences between data obtained with artificial heads and those obtained from humans. The paper gives an overview of experiments and measurements carried out at Aalborg University over a number of years.
Relearning sound localization with new ears
Authors: Hofman P. M. , Van Opstal A. J. , Van Riswick J. G. A.
Published: July 2002

Because the inner ear is not organized spatially but tonotopically, sound localization relies on the neural processing of implicit acoustic cues. To determine a sound’s position, the brain must learn and calibrate these individual cues, using accurate spatial feedback from other sensorimotor systems. Experimental evidence for such a system has been demonstrated in barn owls, but not in humans. In this study, the existence of ongoing spatial calibration in the adult human auditory system is demonstrated. The spectral elevation cues of human subjects were disrupted by modifying their outer ears (pinnae) with molds. Although localization of sound elevation was dramatically degraded immediately after the modification, accurate performance was steadily reacquired. Interestingly, learning the new spectral cues did not interfere with the neural representation of the original cues, as subjects could localize sounds with both normal and modified pinnae.
Holophony versus ambisonic: Deriving a hybrid method for 3-D sound reproduction in videoconferencing
Authors: Nicol Rozenn , Emerit Marc
Published: July 2002

Current research in videoconferencing intends to introduce 3-D reproduction methods both for image and sound. This paper will deal only with the problem of 3-D sound reproduction. First, one specific requirement must be borne in mind: in a videoconference, the listening area has to be wide, since it is addressed to several listeners. Two approaches have been considered: Holophony—acoustical equivalent to holography—and ambisonic. In a previous paper, it has been shown that these two methods are based on the same principle, i.e., physical reconstruction of the acoustical 3-D field, which appears as the most relevant solution to obtain an extensive listening area. However, holophony and ambisonic achieve opposite compromises between system complexity (number of signals recorded, number of microphones and loudspeakers) and reconstruction performance (accuracy, size of listening area, implementation opportunities). The two approaches are compared in order to point out a hybrid method, which optimizes the result. First studies focus on sound pick-up and show that ambisonic is more efficient concerning the coding of spatial information. In this paper, this analysis will be completed, first by examining the sound reproduction step, and second by studying the method robustness toward the actual behavior of transducers.
Hydroacoustics in monitoring the comprehensive test ban treaty
Authors: Orcutt John A.
Published: July 2002

The Comprehensive Test Ban Treaty was signed by the U. S. in 1996 and many other nations have since joined in supporting the treaty. On a planet which is more than 70% covered by oceans, only 11 sites will monitor acoustic propagation in the oceans. The capabilities of the system are further limited through the avoidance of any directionality capability at the sites and five of the sites are simply seismometers located on islands. Several research projects become very important in developing understanding to the level needed to remove some of the more substantial problems introduced by this limited capability. In particular, the coupling of acoustic to seismic wave propagation in the vicinity of islands is an important issue. Research has demonstrated that the efficiency of coupling, for example, is highly dependent on azimuth and, hence, the offshore morphology. Additional work is required to develop a predictive capability for coupling. Typically hydrophones in the ocean detect far more events than seismometers on land. This, coupled with the slow speed of propagation, makes location of events difficult. Research involving the joint location of events using hydrophones and seismometers will be reviewed.
Normal-mode composition of earthquake T phases recorded in the deep ocean
Authors: D’Spain Gerald L. , Berger Lewis P. , Kuperman William A. , Stevens Jeff L. , Baker G. Eli
Published: July 2002

For upslope propagation in an ocean environment, the place(s) where underwater acoustic field energy couples into the land seismic field is determined by the local water depth and the normal-mode composition of the acoustic energy, to first approximation. Therefore, the use of earthquake-generated T phases as natural probes of water-to-land coupling characteristics is aided by knowledge of their modal makeup. During the 1989 VAST experiment, conducted in 5000-m-deep water in the midlatitude Northeast Pacific Ocean (34.0 deg N, 140.0 deg W), the Marine Physical Lab deployed a 200-element, 3000-m-aperture vertical hydrophone array from R/P FLIP. Several earthquakes generated detectable T phases during the 11-day recording period and the modal composition of five such events, including one on land, have been determined. Because of the extended nature of the T-phase source region, the individual modes are uncorrelated, permitting an eigenanalysis of the data cross spectral matrix at a given frequency to provide approximate mode amplitude and eigenfunction information. Results indicate that for the predominant T-phase energy around 5 Hz, the first four or five modes are important, with the mode having largest amplitude often not being the lowest one. [Work supported by ONR and DSWA.]
Rapid assessment of bottom backscattering
Authors: Akal Tuncay , Lyons Anthony P.
Published: July 2002

There is a strong need to obtain information about the expected acoustic reverberation environment that will be encountered in various shallow-water sites to aid in planning and evaluating the effectiveness of operational systems. A new technique is being developed at the SACLANT Undersea Research Centre to quickly sense the mean reverberation levels of a shallow-water area. A prototype device and analysis algorithms have been developed and used as part of rapid response operations. The system transmits and receives acoustic signals from an 80-kHz transducer and simultaneously calculates the quantitative acoustic response of the seafloor. The reverberation measurements made so far have concentrated on mapping the mean seafloor scattering level (backscattering strength) and amplitude statistics over an area for various grazing angle regimes. Differences in scattering strength between high and low reverberation zones within an operational area were significant, with differences in mean level reaching 10–12 dB. Additionally, the reverberation measurements were compared with other techniques to verify relevant bottom-type classification. The experimental technique and data obtained from different areas are presented.
The ancient Greek theater and its acoustical quality for contemporary performances
Authors: Schubert Gottfried , Tzekakis Emmanuel G.
Published: July 2002

The acoustical quality of the ancient Greek theater is often described as a phenomenon with mythical dimensions. According to recent experiences with contemporary theater performances at famous historical ancient Greek theaters, the acoustical situation is much more simple and even more problematic than described. To understand the real situation, it is helpful to review the evolution of the ancient theater in terms of construction as well as the theater play as a religious and cultural event. The Dionysus Theater of Athens is one of the most important examples to base this review on. Modern theater festivals also take place in the ancient theater of Epidaurus, which compared to many others, is in a remarkably good condition especially after its restoration. Nevertheless, the scene building is missing and this leads to several acoustical problems. The Epidaurus Theatre is used as an example for the description of the experiences with contemporary performances in ancient Greek theaters.
An evaluation of scattered reflections in sound fields
Authors: Suzumura Y. , Ando Y. , Oowaki M. , Iizuka Toshiki , Yamamoto I.
Published: July 2002

Although a large number of studies have been made on a theory of scattering, no studies have been attempted to evaluate the scattered sound fields in a concert hall. This paper will show an evaluation method of sound fields that involve scattered reflection by a circular-columns array installed in front of both side walls. Measurements were performed by use of a 1/10 scale model of the concert hall. Here, scattered sound fields are evaluated by four acoustic factors (SPL, DT1, Tsub; IACC, and in addition WIACC and tauIACC). It is found that the IACC and Dt1 of the sound fields of the concert hall are improved with use of the circular columns array.
Effect of closely spaced high-frequency reflections on perception of music
Authors: Calamia Paul T. , Pfeiffer Scott D.
Published: July 2002

Experience in three concert halls with complaints about harsh high-frequency response led to the investigation of acoustic effects in these halls. The use of wall treatments intended to be acoustically diffusive or transparent, or intended to make a fan-plan more similar to a shoe-box hall, resulted in repetitive, closely spaced, high-frequency reflections. Effects have been measured in place and in laboratory simulations. Examples of the wall treatments and corresponding measurements will be discussed, as will recommendations for achieving a more desirable frequency response.
Middle ear frequency characteristics of Norwegian cattle
Authors: Kringlebotn Magne
Published: July 2002

Preliminary results indicate that for a constant sound pressure to the tympanic membrane, the mean low-frequency asymptote value for the volume displacement in the inner ear windows of Norwegian cattle as compared to human ears is less by about 8 dB, while above about 2 kHz the volume displacement becomes increasingly larger than in the human ear. If mean amplitude responses are roughly approximated by straight lines above 1 kHz, the slope for cattle ears is about −4 dB/oct as compared to an earlier measured value of −16 dB/oct for the human ear. Mean resonance frequencies are nearly equal, both about 0.8 kHz. The phase of the windows volume displacement relative to the sound pressure at the tympanic membrane is close to zero below 0.2 kHz, and falls to about −4π at 20 kHz. Earlier phase measurements in human ears indicating a phase change of less than 2π are believed to be in error.
A simple method to estimate the absorption coefficient of porous absorbers
Authors: Ackermann Ulrich
Published: July 2002

To estimate the attenuation D of silencers under practical conditions, the formula of Piening is used: D=1.5αCL/A (C is the circumference, L the length, and A the cross-sectional area of the absorbing duct). For most of the porous absorbers the absorption coefficient α can be estimated by the very simple relation α=0.9 log(fd)−X (0≤α≤1), where f is the frequency in Hz and d the thickness of the absorber in cm. For different porous absorbers the constant X can be derived from measurements in small test rigs, where only a few materials are needed. For mineral wool with a density between 20 and 40 kg/m3, X=2,4, and for snow with a density of 270 kg/m3, X=2,65, e.g., the Piening formula together with the relation for α gives a simple method to calculate the space for splitter- or tube-silencers in ducts, e.g., without knowing the acoustical performance of the porous absorber exactly.
Teaching musical acoustics
Authors: Ayers R. Dean , Rossing Thomas D.
Published: July 2002

Although designed particularly for music students, musical acoustics courses at American universities generally draw a ‘‘mixed bag’’ of students with a rather wide variety of backgrounds. This presents some real challenges but also some real rewards. Some of the problems in teaching musical acoustics to heterogenous classes and some of the ways these problems can be dealt with are discussed. Readable textbooks, demonstration experiments, and videotapes help to challenge and motivate the students, but the best way of all to learn the subject is by doing hands-on experiments.
Noise annoyance by freight trains
Authors: Steenbekkers Anja H. M. , de Jong Ronald G.
Published: July 2002

In The Netherlands a new freight-only railway route, the ‘‘Betuweroute,’’ is being planned to carry freight traffic from Rotterdam harbor east into Germany. Inhabitants of areas near the future route are concerned about noise and vibration, and question the relevance of current legislation for a ‘‘freight-only’’ line. Results of analyses on existing data show no consistent differences in exposure–response relations between routes with a small or high proportion of freight trains, once the effects of different noise levels are removed. Thus these results do not support the need for special legislative provisions for freight-only lines. However, hardly any freight-only train route was included in the analyses, and concern remains. The most western part of the future Betuweroute is an existing freight-only line, the ‘‘Harbour line.’’ Some 109 inhabitants living near this line were interviewed in order to pretest the questionnaire for a social survey in areas along the future Betuweroute. For most homes accurate noise data are available. This offers another opportunity to test the hypothesis that, once the effects of different noise levels are removed, freight trains do not cause more annoyance than passenger trains. The results of this test will be presented.
Scale model experiments on new types of noise barriers
Authors: Ouis Djamel
Published: July 2002

This paper is concerned with the results of experiments conducted on some new types of noise barriers. The experiments were conducted in the anechoic chamber at a scale model level and the barriers have different profiles with focus on the so-called forklike topped barrier. The quantity of interest is the sound-pressure level in the zone shadowed by the barrier. The arms of the barrier top were combined in several different ways and angles as well as also being mounted by either hard or soft cylinders to predict the effect of these latter on the edge diffraction phenomenon. The ground is taken either as hard on both sides of the barrier or a combination of hard and soft ground on, respectively, the source and receiver sides. [This work was supported by a grant from TeknikBrostiftelsen in Lund, which is gratefully acknowledged.]
Noise exposure, hearing loss, and hearing conservation in the construction industry
Authors: Suter Alice H.
Published: July 2002

Workers in certain sectors of the construction industry incur more noise-induced hearing loss than in most other trades. This paper reviews data on noise exposure and hearing loss in the construction industry, gathered mainly in Washington State, British Columbia, Canada, and Sweden. The problem of worker mobility, where temporary employment is typical even for unionized workers, has hampered the implementation of effective hearing conservation programs in the construction industry. Solutions to this problem include a central repository for audiometric test results and information on training and noise control programs. Multiemployer benefit programs concerning health insurance and pensions provide models in the United States. A hearing conservation program specific to construction noise has been successfully implemented in British Columbia, with a resulting decrease in the incidence of noise-induced hearing loss.
Noise control case studies
Authors: Broughton Keith A.
Published: July 2002

Giving advice to owners and employers on how they can introduce methods of controling noise in industrial situations is often difficult. Many years ago the noise specialist inspectors built up a database of successful control methods they witnessed in their normal duties in visiting factories. These were collated into a case study book and sold. Recently this exercise was repeated and the second book, Sound Solutions, was issued. Aimed specifically at employers, it gives examples from a wide range of industries of noise problems which have been successfully overcome. It outlines the original problem, gives the solution, and indicates an approximate cost, and gives advice on where such control can be obtained. In the introduction advice is given so that the employer can ask a consultant or engineer questions on the method to be employed to solve a problem, so that they have a better understanding of the control process involved. The guidance is published by the HSE, a department of government.
Remarks on acoustical descriptors for explosions in air
Authors: Hirsch Karl-Wilhelm
Published: July 2002

Currently, ISO/TC43/SC1/WG51 is collecting ‘‘experiences’’ with measuring and predicting shooting noise. One goal of this working group is to write a guideline for the measurement of source data of shooting noise, taking into account the special characteristics of these high energy, impulsive blasts. There are three special aspects with shooting noise: First, there are nonlinear effects close to the source. Second, the strong directivity of blast sources plays a very important role. Third, in contrast to most of the continuous noise sources, blasts are single events which involve coherence effects during source and receiver measurements. Therefore, a dedicated set of emission data has to be introduced to describe a blast source with respect to sound propagation models. The presentation will discuss the definition of a set of appropriate source descriptors for muzzle blasts. The source will be treated as a linear spherical source with directivity. Its intensity will be defined in the far field and its directivity pattern will describe the acoustical strength. The radius of this artificial source depends on the blast energy and is an important parameter when determining the appropriate measurement distance for source measurements.
Standardization efforts in Germany on the quality of software products for the prediction of environmental sound emission
Authors: Kurze Ulrich J.
Published: July 2002

Based on ISO/IEC 12119 for quality requirements and testing of software packages, a special standard has been drafted for software products designed for noise mapping and related tasks of environmental noise control. The most important aspects are related to the definition and testing of software precision and to an interface suitable for data exchange between various programs. In a first step, the potential consistency of the software calculation procedures with standarized procedures is checked by test cases. Since switches can be set in most programs to accelerate calculation procedures for complex and extended situations, a second step is required to control the precision obtainable by the user for his special application. This is done on a statistical basis. Most of the effort is generally spent with the collection, adjustment, and input of geometrical data. In order to simplify repeated runs for modified situations and to allow for maximum flexibility of users, a common interface has been defined for all acoustically relevant data determined for a first run. This helps avoid errors and allows for data exchange suitable for comparison of different programs and situations.
Aircraft noise model corrected by operational and propagation effects
Authors: Zaporozhets Oleksander I. , Tokarev Vadim I. , Attenborough Keith , Li Kai M.
Published: July 2002

Although there are mathematical models for predicting aircraft noise, the requirements on their accuracy have recently increased. Possibilities for model improvements are reviewed with respect to both noise source generation characteristics and noise propagation effects. The review indicates that the required corrections are not standard since they depend on the physical model of the noise source. The results of aircraft noise assessment for different types of aircraft and for different models of noise propagation are discussed. Recommendations for their use in computational schemes are made. The most rational method generates the required corrections for each type of aircraft according to the operational and noise propagation conditions in a given situation.
FLULA2: Aircraft noise prediction and measurements
Authors: Thomann Georg , Buetikofer Rudolf
Published: July 2002

Aircraft noise predictions of the program FLULA2 are compared with airport noise monitor measurements and with single flight events. Further, the versatility of using a point source model for simulation is discussed and the implications of accurate noise predictions on land use planning are outlined. The aircraft noise simulation program FLULA2, developed at EMPA, uses a point source with a directivity characteristic in contrast to many other models which use line segments and correction terms. With the powerful model of a moving point source, the level-time history of a single flight can be reconstructed. Thus all acoustic effects (topography, spectral air absorption, ground effects,...) may be included and any noise metrics can be calculated. The program is validated by comparing single events (the level-time history of measurements and of calculations) and by comparing the yearly average of measurements at monitoring stations around airports with the Leq predictions. There are variations, but there is no systematic under- or overestimation of the noise calculations compared with the monitors.
Direct computation of sound generation and radiation from a ‘‘Singing Wire’’ (or direct computation of Aeolian tone)
Authors: Lee Duck Joo , Kim Jae Wook
Published: July 2002

Sound from a singing wire, known as ‘‘Aeolian Tone,’’ is simulated by directly solving unsteady compressible Navier–Stokes equations. The surface pressure on the surface of the wire in the presence of wind fluctuates periodically and the pressure near the surface radiates as a ‘‘dipole sound.’’ The mechanisms of the surface pressure fluctuation are closely related to vortex shedding from the wire. An OHOC (optimized high-order compact) scheme is used to have high resolutions of the flow and the sound. A new formalism of characteristic boundary conditions in the body-fitted generalized coordinates is presented. Extended kinds of numerical boundary conditions for simulating subsonic inflow, nonreflecting outflow, and solid wall are formulated on the basis of characteristics and applied to computational aeroacoustics (CAA). The boundary conditions are applied to actual computation of 2-D wire having a cylindrical cross section on nonuniform and nonrectangular grid meshes. Far-field acoustic pressures due to Karman vortex streets are measured and the Strouhal number is evaluated correctly. The feasibility of using the generalized characteristic boundary conditions is investigated for sound generation owing to an unsteady flow around a body.
An error analysis for the lattice gas time domain (LGTD) method in CAA
Authors: Sparrow Victor W.
Published: July 2002

One of the most important requirements in computational aeroacoustics (CAA) is that a numerical method have excellent dispersion characteristics. The new lattice gas time domain (LGTD) method has better dispersion characteristics than any other scheme encountered by the author. This talk will first review LGTD in comparison with the better known finite difference time domain (FDTD) method. Then quantitative error estimates will be provided for a benchmark problem from ICASE/LaRC Workshop on Benchmark Problems in CAA [NASA Conf. Pub. 3300, 143–147 (1995)], showing the spectacular performance of the LGTD method. The present work answers some questions raised and extends the findings presented in CEAS/AIAA-95-115 [in Proc. 1st Joint CEAS/AIAA Aeroacoustics Conference, 12–15 June 1995, Munich, Germany, pp. 813–817] and in J. Comp. Acoust. 1, 423–454 (1994).
Uncertainty in dosage-annoyance relations
Authors: Botteldooren Dick B. , Gjestland Truls
Published: July 2002

Dosage-annoyance relations have traditionally been derived by fitting analytical curves through data gathered from large numbers of field studies. Information on the uncertainty of the relation thus derived is not often given. In this paper the same data set will be examined in several different ways and how this can influence conclusions will be demonstrated. The data set used is taken from Fidell and Barber [J. Acoust. Soc. Am. 89, 221–233 (1991)]. Transformations of annoyance scales and sound-level measures are assumed to be suitable and are not redone in this work. It is assumed that the average annoyance response of Man is searched and that the dosage-response curves will be used to integrate exposure levels to a single figure that can be used to compare noise impact to a community. This goal is totally different, with respect to uncertainty, from predicting noise annoyance in a particular exposure situation. In this work, individual data are combined, taking into account the different number of data points at different exposure levels and the uncertainty in results from individual studies. Each study is treated as an observation made by an independent expert. Differences to dosage-annoyance relations derived in a more traditional way are discussed. The obvious conclusion is that dosage response relations must be used with caution and that this can well be expressed by taking into account calculation uncertainty accurately.
A new test of the validity of a maximum single-event-level model in the prediction of the community response to artillery sounds
Authors: Buchta Edmund
Published: July 2002

It is common, for many environmental sounds, to predict the community response from acoustic measures (such as Leq or Ldn) that take the yearly energy-average sound level into account. According to Rylander and colleagues, however, the annoyance is determined mainly by the level of the noisiest events [e.g., see J. Sound Vib. 127(3), 555–563 (1988); 192(1), 199–206 (1996)]. The number of those events is less important: the annoyance increases with the number of events up to a saturation point (e.g., for large firearms 1000 shots/year with LCE>90 dB) above which a further increase in number does not affect the annoyance. In the present paper, the usefulness of Rylander’s model was tested with the help of data from a German field survey on the subjective effects of artillery sounds [J. Acoust. Soc. Am. (in press)]. The analyses showed that (1) application of a threshold to CSEL results in the loss of important information from residential areas without events above threshold, and (2) saturation, if any, might be observed only from about 70000 shots/year. It is concluded that for several reasons Rylander’s model is inferior to models in which total exchangeability of single-event levels and number of events is assumed.
Modulation of distortion product otoacoustic emissions (DPOAE) by low-frequency masker tones in human ears
Authors: Marquardt Torsten , Hensel Johannes , Scholz Günther , Mrowinski Dieter
Published: July 2002

Biasing of the basilar membrane displacement by a loud low-frequency tone causes changes of the DPOAEs depending on the phase of the masker. A corresponding model helps to understand the nonlinear behavior of the cochlea and to improve the diagnosis of inner ear diseases. Up to now, short time Fourier transform has been used to measure the DPOAE suppression pattern. This method has inherent time and frequency resolution limits. Therefore a new approach is presented, where the primaries and all frequencies generated by the process are harmonics of the masker. A rectangular time window with length according to the masker period is used. The part of the spectrum representing the DPOAE signal is regarded as modulated tone, consisting of a DPOAE frequency (2f1−f2) and spectral side frequencies. The time course of the DPOAE suppression pattern is computed by superposition of these complex components. The results are compared with a simulation of the distortions of the outer hair cells’ mechano-electrical transfer function. In addition, a cochlear impedance model is verified. Variation of masker frequency results in the expected phase shift of the DPOAE modulation pattern and allows the assessment of the lower cutoff frequency of the human cochlear impedance.
Excitation and inhibition in the dorsal nucleus of the lateral lemniscus influence binaural response properties of neurons in the rat’s inferior colliculus
Authors: Kelly Jack B.
Published: July 2002

In vitro brain slice studies have shown that neurons in the rat’s dorsal nucleus of the lateral lemniscus (DNLL) are affected by both NMDA and non-NMDA receptor-mediated excitation and glycineric inhibition evoked by electrical stimulation of ascending afferent fibers in the lateral lemniscus and GABAergic inhibition evoked by stimulation of the commissure of Probst [Wu and Kelly, 1996]. The effects of excitatory and inhibitory events in the DNLL on binaural responses in the rat’s inferior colliculus are reported here for in vivo experiments. Receptor specific antagonists were injected locally into the DNLL before and after recording extracellular single-neuron responses from the contralateral inferior colliculus. Binaural responses were evoked by paired clicks delivered to the two ears. Both NMDA and non-NMDA excitatory amino acid antatonists (NBQX and CPP) produced a release from binaural inhibition and glycinergic and GABAergic antagonists (strychnine and bicuculline) resulted in enhanced binaural inhibition. The results support the idea that the DNLL plays a role in binaural processing through an inhibitory (GABAergic) influence on the contralateral central nucleus of the inferior colliculus. [Research supported by NSERC of Canada.]
On the acoustic Zeeman effect
Authors: Kauffmann Christiaan
Published: July 2002

Thin, square plates subject to uniform boundary conditions vibrating in flexural motion have an enumerable set of resonances, some of them having multiple resonant modes. This holds for plates vibrating in vacuo. If the plate motion is subject to fluid loading, the resonant properties modify. Fluid loading induces all resonances to shift downwards (added mass effect), while acoustic radiation contributes to the damping of the modes. These features are well known and understood, although the actual calculation requires considerable computational effort. A perturbation method is presented for dealing with the effect of light fluid loading on the degenerate resonances. Removal of degeneracy is found for repeated modes having different coefficients for added mass and radiation damping. Symmetry is preserved for degenerate resonances that are modified by fluid loading in an identical way. Numerical results are presented that show how resonances split for the modes umn±unm of simply supported plates, where m and n have the same parity, i.e., m+n is even. Simple physical arguments, like equivalent multipole sources of the mode shapes and their spatial modulation, are used to interpret the results. Mode shapes with the highest degree of symmetry show the largest shift in frequency.
Finite element and boundary elements for underground input to SEA calculations
Authors: Jean Philippe
Published: July 2002

In order to study underground structures with a SEA model, special care must be given to ground loading which affects the behavior of the walls. The use of more precise techniques such as finite elements and boundary element techniques enables a description of complex phenomena and the computation of input to the SEA model. Therefore, several aspects have been analyzed: effect of type and position of source, type of ground, size and shape of the foundation, influence of the superstructure (size and type). Applications to the case of railway type situations are given. The source can be either on the surface or in the ground resulting in the generation of different types of waves.
Designing structures for noise and vibration control with statistical energy analysis
Authors: Huang Liangyu , Raju P. K.
Published: July 2002

Statistical energy analysis (SEA) was initially developed for predicting noise and vibration levels in interior spaces and structures at audio frequencies. The methodology developed in this paper extends traditional statistical energy analysis beyond the prediction of mean-rms vibroacoustic response. An SEA response sensitivity algorithm was formulated to relate variability of design parameters to SEA response variation. The method can be used to sort the design parameters which have the greatest effect on the sound-pressure levels in acoustic spaces. The SEA response variance analysis relates response variance directly to variances in design parameters. This methodology is important for acoustic design of aircraft, ship, and automotive vehicles because it enables the user to qualitatively and quantitatively determine the rank and variations of vehicle interior sound-pressure level with respect to changes in design parameters. When fully developed, this methodology can be a powerful tool for identifying the design changes that would be most effective for controlling noise and vibration from structures.
Development of an active exhaust silencer for combustion engines
Authors: Boonen Rene , Sas Paul
Published: July 2002

A silencer is developed to attenuate engine exhaust noise using active control. The device consists of an electrically driven valve, combined with a buffer volume. Using the mean flow through the valve and the pressure fluctuations in the volume, the valve regulates the flow such that only the mean flow passes the tail pipe outlet. The flow fluctuations are temporally buffered in the volume. A cold engine simulator is developed to experiment with exhaust systems. This device generates realistic exhaust noise and the matching gas flow using compressed air. It allows quick and reliable acoustic and fluid dynamic experiments on exhaust prototypes. The valve is controlled using a nonadaptive feed-forward algorithm. The active silencer reduces the exhaust noise 13 dBA. However, the nonlinear relation between valve stroke and pressure drop limits the performance of the controller. Currently, a feedback controller is being implemented. It improves the performance, but is now limited by the time delay between control valve and the error pressure sensor. Future developments are now focused to compensate the time delay, using a Smith compensator, or repetitive control. Adaptive feed-forward is in consideration also, but this probably will not be ready when the workshop is held. [Work supported by BOSAL International.]
Active control of pulsating flows in transitory conditions
Authors: Tartarin J. , Carimantran F.
Published: July 2002

The active control in a duct in the presence of hot and/or corrosive gasses (e.g., exhaust system) or even heavy fluids (oil, fuel, water,...) needs an actuator that is particularly resistant. That’s why the LEA designed an original auxiliary source [Hardouin et al., Acta Acustica 1, 189–198 (1993)]: an oscillating flap which acts in a flow as an aeroacoustic source. Its high efficiency in very low frequencies associated with its little bulk is also another major interest. For active control, because it is a source connected in series with the primary source, an online identification is preferable for better adaptive character. Therefore specific algorithms were developed in frequency domain for command strategies of feedback synchronous type. Other time-frequency domain algorithms were implemented. In view of industrial applications, these different algorithms were experimentally compared, particularly in transitory conditions. Jointly, simulations were led to allow the development and the optimization of exhaust mufflers including the flap and passive devices.
Intelligibility enhancement of synthetic speech heard via telephone in a noisy environment
Authors: Köster Stefanie , Mersdorf Joachim
Published: July 2002

The intelligibility of synthetic speech, like the intelligibility of natural speech, decreases if it is transmitted via telephone and/or heard in a noisy environment. A natural speaker adapts his speaking style to these hard speaking conditions in order to restore intelligibility. With new applications for speech synthesis, e.g., navigation systems for cars, the need for adapting synthetic speech to hard speaking conditions arises. Here, the results of intelligibility tests for German databased synthetic speech in comparison to natural speech are presented, and first methods of intelligibility enhancement for synthetic speech are given. It is shown that under the conditions mentioned above unadapted synthetic speech has a lower segmental intelligibility for all phonemes or phoneme clusters than natural speech. For that reason the methods applied affected all speech sounds equally. They are based on prevoius studies of natural speech produced under stress conditions like a noise afflicted environment [Summers et al., J. Acoust. Soc. Am. 84, 917–928 (1988)]. It is shown that the intelligibility of synthetic speech is improved significantly by these enhancement methods. The results give evidence to an individual adaptation for phonemes or phoneme clusters in future.
Russian vowels in mothers’ speech to infants and adults
Authors: Andruski Jean E. , Kuhl Patricia K. , Chistovich L. A. , Kozhevnikova E. V. , Ryskina V. L. , Stolyarova E. I.
Published: July 2002

Cross-linguistically, when mothers address their infants they produce acoustically more extreme point vowels (/i/, /u/, and /a/) than they produce when speaking to another adult [Kuhl et al., Science 277, 684–686 (1997)]. This study examines three nonpoint vowels in Russian (/e/, /o/, /’i/) and compares their acoustics in infant-directed (ID) and adult-directed (AD) speech with the acoustics of Russian point vowels in AD and ID speech. Six target words containing the nonpoint vowels in stressed syllables were recorded while ten mothers conversed with their infant and another adult. F1, F2, and F0 were measured at vowel onset, center, and offset. As with the point vowels, the acoustic structure of all three vowels differs significantly in ID and AD speech. F2 tends to move to an acoustically more extreme position in each case. In addition, nonpoint ID vowels show more vowel-inherent formant movement across the course of the vowel. Formant movement may provide an important cue to vowel identity, and its exaggeration in ID speech may increase the likelihood that infants incorporate formant movement into their mental representation of a vowel. Significant differences in formant structure were found for vowels in one-, two-, and three-syllable words, including vowels with short mean durations.
Integrating acoustic echo cancellation with adaptive beamforming microphone arrays
Authors: Kellermann Walter
Published: July 2002

In hands-free and untethered man–machine speed communication, acoustic echo control (AEC) is widely acknowledged as a critical issue determining, e.g., the quality of a full-duplex dialogue, or the speech recognition performance of voice control applications. In comparison to single microphones, microphone arrays (MAs) allow for an improved acoustic front-end by increased spatial selectivity and the flexibility to track moving sources. It is argued that in most cases, however, this will not suffice to eliminate the need for AEC. The most effective solution to AEC is provided by echo cancellation systems, which model the acoustic echo path from the source to the receiver by an adaptive digital filter. While the echo path for a time-invariant MA can be modeled by a single adaptive filter, adaptive beamforming MAs require a time-variant filter capable of tracking the change of the beamforming characteristic instantaneously or, alternatively, one echo canceller for each sensor of the array. Given the considerable computational load for acoustic echo cancelers, a concept is proposed here that limits the beamforming to several fixed beams and foresees one echo canceler for each beam. In addition to computational efficiency, this system provides synergies enhancing the control of the acoustic echo canceler as well as source finding for beamforming.
A method for echo cancellation in audio signals using the genetic algorithm
Authors: Zielinski Slawomir K.
Published: July 2002

A new method for echo cancellation is proposed. This method is based on inverse models of systems causing the echo in transmission channels. Parameters of these models are optimized using the genetic algorithm. In general, the inverse models that are used for echo cancellation can be divided into several categories according to their complexity. In the simplest case, the models consist of digital delay lines, scalers, and adders. The more complex models use also a nonlinear filtration, which in the general case may be a nonstationary one. The experiments and informal subjective listening tests showed that the proposed method allows for the perceptually efficient suppression of echo which was caused by multiple reflections providing delayed and scaled copies of the original signal. An additional preprocessing employing a calculation of the correlation function of the input signal can diminish the computational complexity of the proposed algorithm. Some examples of echo cancellation results obtained with the use of the proposed method are presented and illustrated with sound examples.
Blind source separation
Authors: Frikel Miloud , Barroso Victor , Xavier Joao
Published: July 2002

In signal processing the received data can be modeled as a superposition of a finite number of elementary source signals and an additive noise. Generally, in a multi-sensor environment application, such as underwater acoustics, the principal objective is estimating the number and directions of radiating sources. In the last decade, eigenstructure-based methods yielding resolution have been proposed. However, these methods need the model of sources. In many cases, this model is not available, indeed, there is the appearance of the blind methods. Blind technique refers to lack of knowledge about the mixing system. It assumes very weak assumptions either for signals or mixtures. Blind source separation consists in identifying the sensors/sources transfer matrix and retrieving the source signals without resorting a priori information about the above matrix. It exploits only the information carried by the received signals themselves. The potential benefit of such a blind approach is that source separation is essentially unaffected by errors in the propagation model or in array calibration whereas the classical array processing methods assume that the array geometry is known and the sources are in the far field of the array. This contribution deals with blind source separation using second-order statistics. [This work was partially funded by FEDER and PRAXIS XXI, under Contract No. PRAXIS/3/3.1/TPR/23/94.]
Surveying infrasonic noise on oceanic islands
Authors: Hedlin Michael A. H. , Vernon Frank L. , Berger Jon , Orcutt John A.
Published: July 2002

An essential step in the establishment of an international monitoring system (IMS) infrasound station is the site survey. The Provisional Technical Secretariat recommends infrasonic noise be recorded with meteorological data at four separate, promising, locations in the vicinity of the nominal station location to identify a secure site which would give the good signal-to-noise while offering easy access to power and telecommu-nications. A good infrasound station should be sheltered from the prevailing winds by gentle topography, trees, and ground cover and located as far as possible from other natural and cultural noise sources. As the IMS network has been designed to give uniform global coverage, some of the stations will be located on oceanic islands. Noise surveys are being conducted at three locations in the Atlantic: Sao Miguel, Azores; Santiago, Cape Verde; and Ascension Island. These island locations are very important as they provide coverage in a region of great monitoring interest. However, they also offer a range of meteorological, topographical, and habitation conditions which result in few suitable locations to deploy an infrasound array. This paper describes preliminary efforts to characterize infrasonic noise levels on these islands and find locations with the necessary practical requirements.
A high-resolution algorithm for wave number inversion using a holographic technique
Authors: Roux Philippe , McArthur Megan , Hursky Paul , Kuperman William A.
Published: July 2002

The aim of this work is to perform a high-resolution wave number inversion in a noisy shallow water waveguide. A single-frequency source is towed at a constant speed relative to a vertical array. No a priori knowledge of the waveguide characteristics is required. The inversion algorithm starts from the holographic representation of the field received from the source on the array. Then, using the recorded field along the source track, a newly modified eigen-matrix pencil was performed to extract the wave numbers. The accuracy of the method is compared to the Cramer–Rao lower bounds. The dependence of the results on the length of the source track, the number of receivers in the array, the signal-to-noise ratio, and the sound velocity profile in the waveguide are discussed. Both experimental and simulated data are reported.