bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection coefficient of a Stonely–Scholte wave: An experimental investigation
Authors: Mouton Edouard , Zakharia Manell E.
Published: July 2002

The Stoneley–Scholte waves are becoming more and more popular in both sediment characterization and nondestructive testing (computation of material and sediment properties, flaw or obstacle detection). When dealing with a 3-D obstacle, the coupling of these evanescent waves with the elastic waves in the target and the continuity conditions may have several definitions. In theoretical papers, some authors choose to impose the continuity of each component of the wave, some others the continuity of the sum vector. A specific tank experiment has been designed and conducted. Its specific goal is to define the continuity conditions that have to be used in future works. A special-purpose mock-up has been built up that contains two different blocks molded in an epoxy resin. One block is ‘‘mechanically hard’’ (duraluminum) and the other one is more ‘‘soft’’ (PVC). The geometry of both blocks has been especially optimized in order to enhance the reflection and refraction phenomena. For each material, two interfaces were considered: a perpendicular one and sloping one (wih respect to the direction of propagation of surface waves). Frequency range is centered around 100 kHz with an investigation thickness of a few centimeters.
Measurements of pulsed velocity field generated by circular and rectangular piezoelectric transducers directly coupled to a block of aluminum
Authors: Ouarradi N. , Piwakowski B.
Published: July 2002

A new computational tool Discrete Representation Acoustic Modelling/Solid (DREAM/S), has been developed for computing the displacement field generated by a pulse-excited transducer, directly coupled to an elastic half-space. It allows the separate determination of different components (shear, compressional, radial, axial) of displacement. This method is based on the spatial pulse response approach and gives directly the transient time-domain field. DREAM/S has already been validated mathematically in regard to analytic and exact methods. The main objective of this paper is to show the experiments performed in order to validate this software. First, a brief presentation of DREAM/S and elementary examples of computing are given. Afterward, the experimental results obtained in the case of circular and rectangular transducers directly coupled to a block of aluminum are presented and compared with the ones obtained by DREAM/S. This comparison displays a good agreement and confirms the high precision of this approach. In order to facilitate the interpretation of multichannel records, including the direct and edge waves and the reverberations from the borders of the model, both computed and recorded signals are displayed in specific format, usually applied in the geophysical imaging.
Dissipation in solids: Thermal oscillations of atoms
Authors: Akay Adnan , Celik Cem
Published: July 2002

Dissipation in a solid is related to the increase in the average kinetic energy of its atoms as a result of external excitation. This paper investigates the relationship between vibration field of a nonlinear lattice of atoms and its energy absorption properties. Numerical results show that a nonlinear lattice accepts energy when excited within its resonance bands. The width of the resonance bands increases with increased nonlinearity, eventually leading to their overlap.
Sonoluminescence: Current status and future perspectives
Authors: Crum Lawrence A. , Matula Thomas J.
Published: July 2002

Considerable recent attention has been directed at the phenomenon of sonoluminescence, especially since the discovery of single-bubble sonoluminescence (SBSL), in which a single, stable, acoustically levitated gas bubble can be made to pulsate with a sufficiently large amplitude to emit light each acoustic cycle. It appears that exciting physics may be associated with this phenomenon. When a sufficiently strong acoustic field is propagated through a liquid containing microscopic cavitation nuclei, similar optical emissions can be observed, although the spectrum of this multiple bubble sonoluminescence (MBSL) often possesses characteristics of the host liquid and its constituents, unlike the spectra of SBSL, which has no discernible bands or lines. Nevertheless, MBSL spectra should be able to shed considerable light on the discipline of sonochemistry. Relevant aspects of the current status of SBSL and MBSL research will be reviewed, some speculations on future directions will be offered. [Work supported in part by the NSF.]
Experimental observations of the effect of ambient pressure on single-bubble sonoluminescence
Authors: Dan M. , Cheeke J. D. N. , Kondic L.
Published: July 2002

The experimental observations of the influence of ambient pressure on single-bubble sonoluminescence will be presented. In the SBSL regime as the ambient pressure was decreased only about 10%, the SL intensity increased significantly as predicted [L. Kondic, C. Yuan, and C. K. Chan, Phys. Rev. E 57(1), R32–R35 (1998)]. There was an increase of about five times in SL intensity as the ambient pressure was decreased by about 10%–12%, at constant driving acoustic pressure. This increment continued until a certain value of the ambient pressure, below which the bubble became unstable and vanished. The equilibrium radius and the maximum radius of the SBSL bubble both incerased with decrease of ambient pressure. This observation provides valuable insight into the mass flow mechanism between the bubble and the liquid, and gives the first direct confirmation of ‘‘argon bubble hypothesis.’’ [Work supported by NSERC and Concordia Seagram Fund for Innovative Research.]
Tone quality and important modal properties of the guitar
Authors: Wright Howard A. K.
Published: July 2002

The main function of a string instrument’s body is to convert string vibrations into radiated sound that is detected by the listener. The coupling between string and body modes determines the vibrational response of the instrument to a plucking/bowing force applied to the string, and therefore has a crucial influence on the instrument’s sound. The nature of this coupling depends on the body’s modal properties as detected at the bridge. An interesting question arises: how do changes to the body modes affect the perceived tone quality of the instrument? The use of numerical models permits independent control of an instrument’s modal properties. By performing psychoacoustical tests with sounds synthesized from these models one can examine the effect on perceived tone of changes to individual body modes. In relation to the guitar, this approach has shown that mode shapes, and, in particular, the positions of nodal lines in relation to the bridge, have a powerful influence on tone quality. This paper reviews the current understanding of the links between the guitar’s modal properties and its sound, and highlights the need for further numerical and psychoacoustical work as a means of extending our knowledge in this area.
Acoustic quality of musical instruments and categorization
Authors: Castellengo Michele , Besnainou Charles , Dubois Daniele
Published: July 2002

The qualitative evaluation of high vintage musical instruments gives rise to several theoretical as well as technical questions. Depending on the experts, either instrument makers trained in various technologies or variously skilled and styled interpreters, the judgments rely on different criteria, regarding the object itself, its manipulations, as well as acoustic or aesthetic properties of the sounds it produces. Various experiments were run with classical guitars (Montchalin, 1993), harpsichords (Guyot, Castellengo, and Dumoulin, 1997), and violin bows (Saint-Loubry and Besnainou, 1997). The judgments were processed in free categorization tasks of musical (listened or performed) sequences, followed by verbal comments on the partitions realized. The analysis of the psychological judgments of similarity and difference, and the linguistic processing of the verbal comments, led to the identification of the relevance of various perceptual modalities (not only acoustic but also kinaesthetic, haptic, and even visual) as well as symbolic associations constructed through experience and training. Physical correlates of the psychologically relevant parameters were transformed by sound synthesis. These experiments allow further theoretical and practical conclusions.
Vibrato and portamento, hypotheses and tests
Authors: Desain Peter
Published: July 2002

As Seashore already pointed out, continuous aspects in music performance, which happen during and in between notes, can be a relevant means for expression. These modulations, like vibrato and portamento, are very consistently controlled and seem to exhibit striking regularities. However, there are many conflicting hypotheses in the literature about these regularities, especially concerning the relation between vibrato and global tempo. To investigate these more systematically, experiments were conducted in which different instruments perform the same piece at different tempi. The results, relating vibrato rate, extent, and phase to tempo and timing will be presented. Apart from understanding the process of music performance better, they may be applied in the design of synthesizers and software for the music studio.
Collection data of noise emissions from building construction sites
Authors: Becker Stefan , Schaffert Edelbert
Published: July 2002

Until now, construction noise has mainly been looked at in terms of machinery. Several publications deal with the noise emission of construction machinery such as excavators, saws, etc. Government noise limits are normally given as average levels for daytime or night time. Thus (especially during the construction of the walls) noise predictions cannot be made on the basis of information of single tools only. Therefore a new study was initiated by the German Umweltbundesamt to collect data describing the total noise emission during the construction of buildings. The integrated approach has to be used, especially during the construction of the walls, because of the variety of simultaneous working processes. The study will determine the average sound-power level, information on sound impulses, and time information during each construction phase depending on the method used (e.g., prefabricated or cast concrete). The emission data have been obtained from measurements at several construction sites, observation of the construction works, and discussions with construction-site managers.
Characterization of an ultrasound system
Authors: Vervik Steinar , Vestrheim Magne
Published: July 2002

Frequency responses of an ultrasound system consisting of sender electronics, sender transducer, air as coupling medium, receiver transducer, and receiver electronics are measured and theoretically regenerated in the range 170 to 270 kHz. Magnitude and phase of the sender and receiver sensitivities are estimated by utilizing the reciprocity principle in combination with models and measurements of the transducer–transducer coupling function and the frequency response and loading effects of the electronics. Voltage-to-particle velocity frequency responses and electrical input admittances of the transducers are theoretically regenerated by the use of experimental modal analysis methods. The sound speed and absorption coefficient are estimated with diffraction corrections through spectral analysis methods. Simulated and measured waveforms are compared. Using time-frequency analysis, mode effects are studied and the waveforms and delays are related to the different functional blocks of the system. Differences between the measured and simulated transit times are found to be of the order of 10 ns in the range considered. The results are of interest in the analyses of zero-flow performance of ultrasound flow meters, in, for example, the study of signal detection criteria and in analyses of delays caused by nonfluid parts of the measurement system.
Laser Doppler anemometry applied to airborne acoustics: Influence of the signal processing parameters
Authors: Poggi Sylvain , Gazengel Bruno , Valière Jean-Christophe , Bruneau Anne-Marie
Published: July 2002

Laser Doppler anemometry (LDA) is widely used for fluid mechanics but may also provide measurements of the acoustic particle velocity. The validation of its use in acoustics, which is being achieved, requires knowledge of the appropriate data processing parameters. In order to understand their effects, an experiment is conducted in which LDA measures structural velocities. In this experiment, the velocity of a shaker tip measured by LDA is compared with the velocity measured by a laser vibrometer. The LDA signal is a sinusoidal frequency modulation whose instantaneous frequency is proportional to the measured velocity. LDA-measured velocities are estimated using either spectrum analysis or time-frequency analysis. These comparisons point out three major results. Even if the velocity is small, which corresponds to a narrow bandwidth of the measured signal, oversampling should be preferred. Time windows should be chosen as short as possible despite the poor estimation of the instantaneous frequency. These first two results lead to a precise temporal description of the measured velocity but a rough one in the amplitude domain. However, the a priori knowledge of the excitation signal frequency enables the precise estimation of the velocity amplitude by means of a least-square method.
Review of the method of reduced variables for the dynamic mechanical properties of viscoelastic materials
Authors: Hartmann Bruce , Lee Gilbert F.
Published: July 2002

Under certain conditions, a change in temperature is equivalent to a change in frequency for dynamic mechanical measurements in viscoelastic materials. This property allows one to extend the effective frequency range of the measurements by shifting isotherms along the log frequency axis using the method of reduced variables, also known as time–temperature superposition. The most commonly used analytical equations describing the required shift are the WLF equation and the Arrhenius equation, but shifting can be implemented without the necessity of an analytical representation. This review will consider the physical basis for this property, known as thermorheological simplicity, the limitations of its applicability, and the advantages and disadvantages of various shifting procedures. Techniques that have been used include shifting the real part of the modulus, the imaginary part of the modulus, the loss factor, and the use of complex compliance rather than complex modulus. Other important issues are the choice of reference temperature and the use of a vertical shift in addition to a horizontal shift. [Work supported by the Carderock Division of the Naval Surface Warface Center’s In-house Laboratory Independent Research Program sponsored by the Office of Naval Research.]
Estimates of the instantaneous versus overall loudness of noise emissions
Authors: Filippou Thomas , Fastl Hugo
Published: July 2002

Usually when comparing the relations between instantaneous and overall loudness judgments of noise emmissions, the overall loudness is larger than the average of the instantaneous loudness judgments. Obviously, the prominent parts of a noise emmission play a crucial part in overall loudness judgment. Two models were proposed to describe the overall loudness on the basis of the instantaneous loudness judgments [Fastl, DAGA 97]. The merits of the different models in predicting the overall loudness of noise emissions with a different number of events were studied. For emissions with 2 up to 11 events within 15 min, a simple percentile of the instantaneous loudness judgments cannot predict overall loudness. However, when the events are prolonged by an exponential decay with 30-s time constant, the judgment of overall loudness can be predicted with an average accuracy of 6%.
On the use of auditory information in human movement control
Authors: Hellmann Andreas , Guski Rainer
Published: July 2002

A human acting and moving in the environment often produces sounds, which are related to his or her body movements. Movement control requires the continuous use of perceptual information about the ongoing movement. It was investigated whether humans can and do use sound produced by their movements as auditory information for the control of their movements. In the experiments the movements or tasks required from the subjects were varied, as well as the available auditory and visual information. The success in the movement tasks was measured. The results obtained so far show that auditory information is used for movement control by the subjects, especially with complicated movements.
Normal mode oscillation of a sphere with solid–gas–solid structure
Authors: Oda H. , Suzuki I.
Published: July 2002

A free oscillation study was made for a heterogeneous sphere with three-layered spherical shell structure composed of an inner spherical sample, middle gas, and outer solid layers in order to apply resonant sphere technique (RST) to elasticity measurements at high pressures. The spheroidal modes of the sphere are classified into “sample,” “gas,” and “container” modes, whose strain energy distributions are localized in the sample, gas, and outer layers, respectively. The sample modes, whose frequencies provide information about the elastic constants of the spherical sample, are more strongly excited than the gas and container modes when putting a vibrational source on the surface of spherical sample in the three-layered sphere and measuring the resonance spectrum on the sample sphere. The localization of strain energy is due to a large difference in acoustic impedance between gas and solid layers. All the resonant frequencies increase with increasing pressure in the gas layer, but the pressure derivatives of resonant frequencies of gas modes are larger than those of sample and container modes. Thus the pressure curves of gas modes frequently intersect those of sample and container modes. At pressures where the sample or container modes intersect the gas modes, modal interchange takes place only between spheroidal modes of Sln and Sl′n′ satisfying the conditions of l=l′ and n−n′=±1. To avoid such an interchange, the gas layer should be kept thin.
The new Konzertsaal of the KKL Center, Lucerne, Switzerland. II. Preliminary acoustical measurements
Authors: Kahle Eckhard , Johnson Russell , Katz Brian
Published: July 2002

The newly opened Concert Hall in Lucerne is the home of the International Music Festival with its extremely varied programs. Furthermore, the remainder of the year requires this hall to provide an appropriate acoustic environment for an even wider range of performances, ranging from conferences and other speech events to symphony orchestra, amplified popular music, ethnic music, and organ recitals. In a town with a population of 60000, it will also be necessary to accommodate a varying number of audience members. For all these reasons, several elements of acoustic variability have been included in the design of the hall. During the first months of the inaugural season, the settings of the variable acoustics features of the hall were documented for each individual performance in the form of a logbook. This paper will discuss the use of the acoustical elements for selected performances taken from the ongoing log. The results of preliminary acoustical measurements and subjective listening impressions for the selected performances will be given. Furthermore, objective measurements were recorded in the hall at various stages of construction.
The acoustics evolution of Chicago’s Orchestra Hall: A case study
Authors: Kirkegaard R. Lawrence
Published: July 2002

Originally opened in 1904, Chicago’s Orchestra Hall was immediately recognized as acoustically flawed due to low reverberation times, poor bass response, a crowded stage, and poor on-stage hearing conditions. In 1991, the Orchestral Association of Chicago decided to renovate and expand Orchestra Hall into a comprehensive Symphony Center for music in Chicago. The core of the project was a commitment to improve the acoustics to the extent feasible within the constraints of the site and the historic beauty of the hall. The Association contracted directly with Kirkegaard and Associates as acoustical consultants to work in parallel with the architects, Skidmore Owings and Merrill. The renovated hall reopened in the fall of 1997, with completion of acoustics work delayed until summer of 1998. The renovated hall is beautiful architecturally, and its acoustics has been gratifyingly improved. This paper describes the history and results of the remodeling. Test data as well as subjective assessments will be discussed and important acoustics lessons shared.
Orchestra shells: Acoustical and practical design considerations
Authors: Commins Daniel E.
Published: July 2002

A hall or an outdoor facility is rarely used for a single type of artistic program. Often, it is necessary to design an orchestra shell that transforms theoretically a theatre or an opera house into a concert hall. The acoustical criteria for opera or concerts are quite different; the design of an orchestra shell that would create proper acoustical conditions on stage for the musicians and in the hall for the audience can be quite complex. The larger the hall and the proscenium opening, the harder it is to come up with an adequate solution. The major problems are the following: architecture and aesthetics, acoustical efficiency, ensemble conditions, acoustic response, diffusion, size, weight, transformation time, and storage. Some progress has been made over the last few years, but the problem remains complex. This paper will attempt to explain the design and construction process and will provide recent examples of small and large shells: Ravinia, Lille concert hall, Gradignan, Porto Teatro S. João, Opera Garnier in Paris, Staatsoper in Munich, and Serralves auditorium in Porto.
‘‘Internal spectra’’ in the dolphin’s auditory system obtained by a minimal-masking technique
Authors: Supin Alexander Ya. , Popov Vladimir V.
Published: July 2002

To understand signal processing in the auditory system, it is of importance to know the ‘‘internal spectrum’’ representations of test stimuli, i.e., profiles of excitation along the frequency-representation axis. Such profiles may be obtained using a ‘‘minimal-masking’’ technique: An excitation profile is reflected by a masking curve (masker level dependence on frequency) when a masking criterion is not the threshold response to the probe stimulus but the threshold masking effect—a very small standard decrease of the probe response. The dolphin’s auditory system provides good opportunities for such measurements because of the large amplitude and high consistency of the auditory brain-stem-evoked potentials (ABR). Minimal-masking curves were obtained in bottlenosed dolphins for various probe stimuli: narrow-band, rectangular, and rippled spectrum stimuli. At low stimulus levels, the profiles reproduced the stimulus spectrum well, except for a little wider bandwidth; this widening corresponded to the bandwidth of peripheral auditory filters. Stimuli with rectangular spectra evoked excitation profiles with enhanced edges, thus indicating enhancement of spectral contrast by lateral effects. Stimuli with rippled spectra evoked profiles reproducing ripples; however, edge ripples were also markedly enhanced. At high stimulus levels, all stimulus types evoked excitation profiles markedly expanded to high frequencies, far beyond the stimulus bandwidth.
Effect of removing physiologically relevant sound-localization parameters on tuning properties of barn owl tectal neurons
Authors: Wagner Hermann , Poganiatz Iris , Nelken Israel , Jacobson Gilad
Published: July 2002

Barn owls use the interaural time difference (ITD) for locating sounds in azimuth and the interaural level difference (ILD) for locating sounds in elevation. Neurons in the optic tectum have spatially restricted receptive fields. Recently, Keller et al. [Hearing Res. 118, 13–34 (1998)] have demonstrated that the spatial patterns of responses were almost indistinguishable in response to virtual [stimuli filtered with head-related transfer functions (HRTFs)] and to free-field stimulation in neurons of the inferior colliculus. The inferior colliculus provides input to the optic tectum. The spatial restriction of tectal neurons is mainly due to their sensitivity to ITD and ILD. This paper deals with the effect of removing ITD and/or ILD from the virtual stimuli on the tuning of tectal neurons. HRTFs of two barn owls were recorded, and noise stimuli with ITDs, ILDs, filtered with HRTFs, filtered with HRTFs but containing no ITDs, and filtered with HRTFs but without ILDs were used in the experiments. Preliminary results suggest that removal of ITDs or ILDs caused a substantial loss of spatial tuning in tectal neurons. These results support earlier findings that suggested an essential role of the tectal neurons in sound-localization behavior. [Work supported by GIF.]
The motion of air-driven free reeds
Authors: Cottingham James P. , Lilly C. Joseph , Reed Christopher H.
Published: July 2002

An earlier study on free reeds from reed organs [P. D. Koopman and J. P. Cottingham, Reed Organ Soc. Bull. 15, No. 3–4, 17–23 (1997)] yielded information about the variation in amplitude of reed vibration with pressure, but few further details on the reed motion. A more thorough set of measurements of the motion of these reeds has been done, including the use of a variable impedance transducer to measure reed displacement and a laser vibrometer system to measure reed velocity. For reeds from reed organs, at low to moderate blowing pressures, the reed motion at each point is nearly sinusoidal and the reed profile at maximum amplitude closely approximates that calculated for a cantilevered beam vibrating in the first mode. At blowing pressures considerably higher than normal playing pressure, strong indications of the presence of the second beam mode are observed. The nearly sinusoidal reed motion at normal pressure contrasts with the sound pressure waveform near the reed which, as a result of the valve action of the reed, roughly resembles a pulse wave. Similar measurements on accordion reeds yield somewhat contrasting results.
A new algorithm to simulate nonlinear propagation in a tube of any shape. Application to a real-time physical model of trumpetlike instruments
Authors: Vergez Christophe , Rodet Xavier
Published: July 2002

When air pressure is low enough, wave propagation in a pipe can be considered linear to a reasonable degree. When the pressure level increases, this simplification becomes more and more inaccurate since high pressure values travel faster than low pressure values. The speed of propagation is thus a function of the pressure level. A new time-domain approach is proposed to simulate nonlinear propagation of a sound wave in a tube of any shape. This constraint-based algorithm does not prevent the derivative of the signal from breaking, as it happens when a shock wave occurs. Moreover, the algorithm allows the carrying out of nonlinear propagation even once a shock has occured. Thus, as expected the distorsion of a sinusoidal wave into a N-wave of progressively decreasing amplitude was observed. Moreover, without any additional computational cost, this technique provides fractional delay variation as needed for continuous tube’s variations in length. The nonlinear propagation algorithm is included in the real-time high-quality physical model of trumpetlike instruments. Simulation shows a great improvement in the sound quality since this algorithm allows subtle nuances in the timbre as well as hard brassy effects.
Spectral integration in binaural processing
Authors: Saberi Kourosh , Takahashi Yoshifumi , Farahbod Haleh
Published: July 2002

Results are reported from human psychophysical and animal neurobehavioral experiments that examined the ability of the binaural system to integrate information across frequency channels. The psychophysical experiments measured the lateralization of low-frequency (<1200 Hz) multitone complexes as a function of number of components (five or fewer) and frequency spacing between these components (25 to 400 Hz). A pointing task was used to match the perceived lateral position of a broadband noise burst to that of the complex. The complex contained a fixed interaural delay of 1500 μs leading to the left, and the pointer’s perceived lateral position was adjusted by varying its interaural level difference. Parallel neurophysiological experiments were conducted in the optic tectum (superior colliculus) of the barn owl, using narrow-band dichotic noise bursts and multitone stimuli; the localization behavior of the owl in response to these same stimuli was also measured. Results show complex patterns of responses with implications for models of frequency interaction in the binaural system. Linear multiplicative or additive models customarily used in cross-correlation analysis do not explain the entire data set. [Work supported by NIH.]
A priori knowledge of the sound source spectrum in median plane localization
Authors: Iida Kazuhiro , Morimoto Masayuki
Published: July 2002

The previous papers [e.g., J. Hebrank and D. Wright, J. Acoust. Soc. Am. 56, 935–938 (1974); F. L. Wightman and D. C. Kistler, J. Acoust. Soc. Am. 101, 1050–1063 (1997)] indicated that the median plane localization mechanism requires a priori knowledge of the source spectrum. Listeners, however, localize a sound image accurately for various sound sources on the median plane, such as music, voice, and noise. Since these sources differ from each other in spectrum, it is inferred that listeners have acquired the knowledge of the source spectrum for each sound source. This paper clarifies whether a priori knowledge of the sound source spectrum is classified by the kinds of source or not in the median plane localization mechanism.
Localization experiments with saccadic responses in virtual auditory environments
Authors: Heuermann-Mehmood Heike , Colonius Hans
Published: July 2002

In this study, subjects had to localize sound sources in free-field listening conditions and in virtual environments. Under virtual listening conditions, three auditory displays with distinct degrees of individualization were used. In contrast to previous studies using verbal reports or pointing techniques, the participants indicated the perceived location of a sound source by turning their eyes toward it. Localization performance under virtual conditions was comparable to free-field conditions for all subjects, at least if individual HRTFs were used. In general, judgments turned out to be more accurate than in previous studies, especially with regard to dispersion of single judgments. This may be due to a close link between the auditory and the oculomotor system, leading to a quasiautomatic saccade toward an auditory stimulus, even without a corresponding visual target.
The modulation direct field radius: Model
Authors: Lindblad Sven , Lundberg Karl-Ola
Published: July 2002

When experimentally estimating reverberant field parameters, it is important to be positioned outside the ‘‘direct field.’’ In an often used model the total energy density is considered to be a sum of two terms, associated with the direct field and the reverberant field, respectively. The first term is diminishing with increasing source–receiver distance, while the second is receiver position independent. At a certain distance the magnitudes of the two terms are equal. In an extended model which allows fluctuating input power, the modulation direct field radius is monotonically increasing with the modulation frequency. As the modulation frequency goes to zero, the radius diminishes to the usual steady-state direct field radius. The reason is that the reverberant field smears out the modulation, especially above a certain modulation frequency, while the modulation in the direct field is maintained. Damping is often estimated by measuring decay times when a constant input power is suddenly switched off. The modulating signal is then one unit step. The magnitude spectrum of such a signal, though falling, has components at all frequencies. The implication of this is that no sufficiently large measuring source–receiver distance exists, using this method.
The modulation direct field radius: Experiments
Authors: Lundberg Karl-Ola , Lindblad Sven
Published: July 2002

The modulation transfer function, CMTF, of a linear system can be derived by post processing the impulse-response by band-pass filtering and squaring followed by a Fourier transform. Experiments were carried out in a reverberation chamber of 5.6×6.4×6.1 m. The source was a small loudspeaker with an approximately omnidirectional radiation. The impulse-responses were measured on axis by means of a microphone along a straight line at 16 different source-receiver distances in the range 0.4–4 m. The corresponding free-field impulse-response was measured in a nonechoic chamber, also on axis at the distance 1.00 m. The postprocessing was performed computationally. The direct field contribution in the reverberation chamber impulse-responses was excluded by subtracting the response by the adjusted free-field impulse-response. The adjustment consisted of amplitude scaling and left or right shifting, depending on the actual source–receiver distance. The CMTFs were computed for the adjusted impulse-response and for the adjusted free-field impulse-response. For a selected modulation frequency, the magnitudes of the two derived CMTFs were equal at a certain source–receiver distance, here named modulation direct field radius. The results agree very well with the proposed model.
Robust design of a sensorless bass-enhanced moving-coil ANC actuator
Authors: Bai Mingsian R. , Chu Kwangmor
Published: July 2002

Loudspeakers have been employed by far as the major ANC actuators. However, the responses of moving-coil loudspeakers are generally poor in low-frequency range because the diaphragms are unable to produce sufficient volume velocity. To alleviate the problem, this study focuses on enhancing the low-frequency performance of loudspeakers by means of modern control techniques. Both magnitude and phase of the frequency response are optimally compensated. A self-sensing velocity observer is utilized for producing the cone velocity signal required by the controller. Feedback H∞ robust control and feedforward H2 model matching control are employed to simultaneously achieve robust stabilization and tracking performance. The proposed controller is implemented using a combined digital signal processor and operational amplifier circuitry.
Vowel recognition from harmonic spectra
Authors: Hillenbrand James M. , Houde Robert A. , Nearey Terrance M. , Clark Michael J.
Published: July 2002

Vowel classification methods based on either formant representations or overall spectral shape nearly always begin with the calculation of a smoothed, pitch-independent spectrum. In this report, a method is described for the classification of vowels directly from high-resolution spectra that retain harmonics of the voice source. Recordings were made of ten sustained vowels spoken by 20 men and 20 women. Smoothed spectral-shape templates for each of the vowels from a random half of the talkers were constructed as the average of the normalized spectra of like vowels spoken by different talkers. The key steps in the normalization procedure consist of: (1) removal of spectral tilt by the subtraction of a running average of spectral amplitudes, (2) dynamic range compression of the tilt-adjusted spectrum, and (3) smoothing across frequency. High-resolution harmonic spectra from the remaining half of the talkers were then classified by computing the bin-for-bin difference between the harmonic spectrum and each of the smoothed spectral-shape templates.
Production and perception of acoustic cues to gender and individual talker identity
Authors: Bachorowski Jo-Anne , Owren Michael
Published: July 2002

Although listeners routinely identify both gender and individual identity of talkers from their speech, explanations of these abilities remain problematic. Integrating source-filter theory with knowledge regarding variation in vocal production-related anatomy, predictions concerning gender and talker indexical cueing were tested using ‘‘point,’’ /e/, and schwa vowels that were extracted from the naturally produced speech of 40 male and 40 female talkers. Very high rates of gender classification were obtained using F0 and an estimate of vocal tract length, the two measures that best reflect sexual dimorphism in vocal-production-related anatomy. In contrast, individual talker classification depends primarily on the various cues associated with vocal tract filtering. Ongoing perceptual studies are being conducted to evaluate the perceptual importance of these findings to listeners. [Work supported by NSF.]
Articulatory discriminability of vowels: Articulator and corpus effects
Authors: Hoole Philip
Published: July 2002

The principal aim of this work was to compare the potency of different sources of articulatory information for differentiating the vowels of German in discriminant analyses. The secondary aim was to determine whether results depended on the corpus analyzed. Articulatory data (electromagnetic articulography; seven speakers) was available for tongue, lower-lip, and jaw position. Three corpora were compared. The first two used highly controlled nonsense-word material but differed in speech rate (normal versus fast). The third corpus embedded the vowels in a wide variety of real words and sentences. Using as a baseline the classification accuracy obtained with tongue-position data only, the increase in accuracy was about 9% with jaw data, 14% with lip data, and 17% with both jaw and lip. A further noticeable improvement (23% re. baseline) resulted from adding in velocity or acceleration data. Classification patterns were remarkably similar over the three corpora; the real-word corpus was simply, but consistently, about 10% worse than the ‘‘nonsense-normal’’ corpus, with ‘‘nonsense-fast’’ in between. Results will be related to the structure of the German vowel system. Corpus effects on articulatory behavior will be further discussed by comparing PARAFAC factor analysis of tongue configuration for the nonsense versus the real corpora. [Work supported by DFG Ti69/29.]
Loudness and prominence in front vowels
Authors: Gooding Frank G.
Published: July 2002

The perception of the high front vowels such as [i] is known to be dominated by the upper formant (UF) region, as is shown by the fact that [i] can be elicited by a single formant positioned there [P. Delattre et al., Word 8, 195–210 (1952)]. The basis of this dominance remains unclear, however, and is investigated by the present study. The simplest explanation would be that the UF region dominates F1 in terms of peak or total loudness. However, this is not reflected in current auditory models [e.g., B. Moore and B. Glasberg, Acustica 82, 335–345 (1996)]. The representations of [i]-like vowels produced by this model, for instance, whether expressed as dB, phons, or sones, all show F1 strongly dominating the UF region in terms of excitation level or loudness. Two possible explanations for this discrepancy come to mind: first, that the model is inaccurate; or second, that the perceptual dominance reflects mechanisms more central to the modeled excitation patterns. In the first case, the inaccuracy is likely to lie in the equal loudness data used by the model. An experiment was designed to test between these possibilities. Two formant versions of [i] and other front vowels were presented to subjects, who could control the amplitude of F2. The F2 threshold and equal loudness point was determined for each subject. Results indicate that the equal loudness point of F2 occurs at an intensity far below, and hence reflects a sensitivity far greater, than that predicted by the model. This implies that central mechanisms are not required to explain the perceptual dominance, and that the equal loudness data probably needs to be revised.
Internal wave inversions for one year of Pioneer–Hawaii ATOC transmissions
Authors: Heaney Kevin D. ,   ATOC Group
Published: July 2002

The ATOC experiment transmitted 75-Hz signals from Pioneer Seamount off the coast of California to a vertical line array (VLA) off Hawaii. The combination of VLA and long-range propagation provides the opportunity to perform mode-based internal wave tomography. Each arrival is mode-filtered and the statistics of the mode arrivals are tabulated. These individual mode arrival time (centroid) and spread are then compared with calculated mode statistics from broadband PE modeling of the propagation path. In this manner a statistically robust inversion for the internal wave strength is performed. The weakness of the inversion is the sensitivity to the bottom scattering near the source. Results for one year of data will be presented for two different bottom types. The long-scale time series may indicate possible sources of internal waves in the ocean. Small time scale variations may be attributable to internal tides. a)The ATOC Group: A. B. Baggeroer, D. Menememlis, and C. Wunsch (MIT); T. Birdsall, K. Metzger (Univ. of Michigan); C. Clark (Cornell Univ.); J. Colosi (WHOI); B. D. Corneulle, M. Dzieciuch, W. Munk, P. F. Worcester (SIO); D. Costa (Univ. of California, Santa Cruz, CA); B. D. Dushaw, B. M. Howe, J. A. Mercer, and R. C. Spindel (APL-U Wash.); A. M. G. Forbes (CSIRO, Hobart).
General perturbative solution to wave scattering from a soft random cylindrical surface
Authors: Skaropoulos Nikolaos C. , Chrissoulidis Dimitrios P.
Published: July 2002

A perturbative solution to the problem of plane-wave scattering from a soft, randomly rough, cylindrical surface is obtained by use of the Rayleigh hypothesis and the assumption that coupled radiation modes can be present in the scattered wave. The wave amplitudes of the cylindrical-wave expansion of the scattered field are expressed as an asymptotic series in the root-mean-square of surface irregularities. The end result of the analysis is a concise recursive formula for the coefficients of that series. The solution is energy consistent up to fourth-order in the smallness parameter. Specific information about the validity and applicability of the solution is given by use of the mean boundary condition error, which is defined in this paper with a view to assessing the conformity of near-field results with the boundary condition. The numerical results show that the fourth-order approximation is more accurate than the second-order one, but it may, under certain conditions, exhibit higher mean boundary condition error.
A new method for an almost-on-the-fly estimation of the instantaneous frequency and of the amplitude of a signal
Authors: Girolami Gerard , Rossi Lucile
Published: July 2002

The instantaneous frequency (IF) of a signal is a parameter whose estimation is of prime importance in a number of domains ranging from musical acoustics to seismics and astronomy. Its determination is usually based on one of the following three general methods: the derivation of the phase of the associated analytic signal, the Wigner–Ville transform and others Cohen’s class transforms, or the three-point algorithms like the Teager–Kaiser ‘‘energy operator.’’ A new three-point method is described which is simple, fast, precise, robust to noise, and estimates the IF and the amplitude with a very small delay. This method gives excellent results on almost any kind of chirps (polynomials, hyperbolics, exponentials, etc.) and frequency modulations (sinusoidal, FSK, Gaussian pulse, etc.), whether or not associated with amplitude modulation (sinusoidal, Gaussian, etc.). The relative errors on the amplitude and on the IF are usually around 1% in the no-noise case, and increase to about 5% for a 20-dB signal-to-noise ratio, even when these different modulations are associated.
Signal processing techniques for passive acoustic location and tracking of animals
Authors: Clark Christopher W. , Fristrup Kurt M.
Published: July 2002

Passive acoustic location and tracking of free-ranging animals has high value for propulation abundance estimation, mitigation of man-made activities, and understanding the biological significance of acoustic behavior. Applications have had limited success: e.g., in the Arctic for long-term study of an endangered bowhead population, in temperate waters with deep-diving sperm whales, and for behavioral studies on birds, dolphins, and seals. The Arctic situation is fairly unique, the whales produce discrete FM signals in the 100–400-Hz band, the water is isothermic, and propagation is relatively coherent. The task of locating and tracking marine animals in environments with more complex propagation conditions is more challenging, and different combinations of environment and species demand slightly different signal-processing solutions. Methods developed for fin, humpback, and sperm whales; elephants; and birds will be presented, and their relative merits will be discussed.
Individuality of advertisement calls in the Australian frog Pseudophryne bibroni: Potential for identification of individuals
Authors: Rogers Daniel J.
Published: July 2002

Pseudophryne bibroni is a small terrestrial frog inhabiting southeast Australia, the males of which call from burrows, both to attract females and maintain territories. This study investigates the capacity for using advertisement calls of P. bibroni to census and monitor frog individuals, through analysis of individually distinct call features. Discriminant analyses revealed that, for 40 individuals, 80% of individual calls were correctly classified, with the analysis of call bouts producing even higher resolution. Given the high level of call individuality in P. bibroni, the potential exists for advertisement calls to be used to identify frog individuals. A system based upon these results is currently being developed, which should provide a practical, field-based method of individual frog identification based on call, allowing the long-term monitoring of frog populations without the necessity for more invasive identification techniques. [I thank David Paton for assistance with supervision, and Nicki Mitchell for assistance with collection of data. This research received financial support from the Department of Environmental Biology Research Fund.]
Shell resonance responses from ultrasound contrast agents
Authors: Allen John , Kruse Dustin , Ferrara Kathy , Jones Jeffrey
Published: July 2002

Ultrasound contrast agents are used to increase the scattered signal from regions containing blood in order to differentiate them from tissue. These agents are microbubbles, 1–10 μm in diameter, encapsulated by an elastic shell 10–250 nm thick. The agents are modeled as air-filled spherical shells and the scattered acoustic field is computed from a modal series representation of the solution. Reflectivity and angular scattering characteristics are computed for various shell thickness and material parameters. In addition to the monopole response, it is demonstrated that other resonance responses exist for agents of sufficient thickness. These additional responses are attributed to Lamb waves in the shell. A large dipole peak in the 15–40 MHz range for 2.5−3.5 μm radius agents occurs for thick shell agents with elastic properties approximating albumin. The relative reflectivity from these dipole responses is comparable to the monopole response of a gas bubble in water. Potential clinical ultrasound applications for this work, including improved tissue perfusion studies, are discussed. [Work supported by NIH CA76062 and EY11468.]