bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of quality of speech enhanced by HMM and AR model-based systems
Authors: Yasmin Anisa , Fieguth Paul , Deng Li
Published: July 2002

Speech enhancement algorithms have demonstrated their application potential in a wide variety of speech communication contexts in which the quality or the intelligibility of speech has been degraded by the presence of background noise: hearing aids, cellular phones, public telephones, hands-free telephones, air-ground communications, etc. By far the two most popular choices for model-based speech enhancement are the Wiener-filter-based hidden Markov model (HMM), and the autoregressive (AR) model-based Kalman filter. Although researchers have been studying such enhancement systems for some time, relatively little has been undertaken in comparing the quality of enhanced speech produced by these two systems. This paper studies the Wiener/HMM and AR/KF models and conducts a comprehensive comparative study of the relative quality of enhanced speech, based on utterances from the TIMIT database contaminated by simulated and sampled empirical noises. The Wiener/HMM and AR/KF comparison includes both subjective and qualitative evaluations: subjective assessments are based on mean opinion scores (MOS) and the inspection of temporal and spectrogram plots; objective evaluations are based on average and segmental signal-to-noise ratios. HMM enhanced speech has most of the noise removed, but with interruptions and discontinuities present due to the switched nature of the HMM. AR model-based enhancement possesses more audible background noise in the high-frequency region above 4 kHz, however the speech is smoother, with fewer discontinuities.
Comparative study of F0 extractors for high-quality speech synthesis
Authors: Kawahara Hideki , Zolfaghari Parham S.
Published: July 2002

Performance of a new F0 extraction algorithm based on fixed point analysis of filter center frequency to output instantaneous frequency [Kawahara et al., Eurospeech’99] was compared with numbers of F0 extraction algorithms based on different definitions of fundamental frequency. The proposed method uses partial derivatives of the mapping at fixed points to estimate carrier to noise ratio of F0 information. It also enables integration of distributed F0 cues among harmonic components to provide a reliable F0 estimate. Objective evaluations were conducted using simulations and a speech database with simultaneous EGG (electroglottograph) recording. Subjective evaluations were based on reproduced speech quality assessment by a high-quality speech analysis/modification/synthesis method STRAIGHT [Kawahara et al., Speech Commun. 27, 187–207]. Discussions about the relevance of various F0 definitions for high-quality speech synthesis will be presented based on these test results. It was also indicated that the proposed method is tunable to specific needs.
Improvements to segmentation accuracy using a large speech database
Authors: Conkie Alistair
Published: July 2002

Current text-to-speech (TTS) systems rely increasingly on large speech databases for both the raw speech necessary for concatenative synthesis and for material used for modeling prosody. It is time-consuming to label the databases phonetically so that they can be useful. It is nevertheless important for the quality of the resulting synthesis that the labeling be accurate. One currently used method involves some kind of automatic labeling – usually using hidden Markov modeling (HMM) techniques, followed by manual correction. This is still time-consuming. Recently, work has been done on post-processing the output from an HMM recognizer with a fuzzy logic system [Torre Toledano et al., Third ESCA/COCOSDA Workshop on Speech Synthesis, Australia, November 1998] to improve accuracy. We examine this promising idea by applying post-processing to automatically generated segmentation of the speech signals in our TTS database. The effectiveness of the technique is evaluated both in terms of labeling accuracy in comparison to hand-labeled data, and with informal listening tests for synthesis quality.
Recent progress on nonuniform fast Fourier transform algorithms and their applications
Authors: Liu Q. H. , Tian B. , Xu X. , Zhang Z. Q.
Published: July 2002

Recently, nonuniform fast Fourier transform (NUFFT) algorithms have received significant attention [Dutt and Rokhlin, SIAM J. Sci. Stat. Comput. 14, 1368–1393 (1993)]. Unlike the regular fast Fourier transform (FFT) algorithms, the NUFFT algorithms allow the data to be sampled nonuniformly. The leading order of the number of arithmetic operations for these NUFFT algorithms is O(Nlog2N). Here, we review the recent progress of the NUFFT algorithms using the regular Fourier matrices and conjugate-gradient method for the forward and inverse NUFFT algorithms [Liu and Nguyen, IEEE Microwave Guid. Wave Lett. 8, 18–20 (1998); Liu and Tang, Electron. Lett. 34, 1913–1914 (1998)]. Because of their least-square errors, these NUFFT algorithms are about one order of magnitude more accurate than the previous algorithms. These NUFFT algorithms have been applied to develop the nonuniform fast Hankel transform (NUFHT) and nonuniform fast cosine transform (NUFCT) algorithms. Both NUFFT and NUFHT algorithms have been used to solve integral equations in computational electromagnetics and acoustics; The NUFCT has been used to solve time-dependent wave equations. Numerical examples will demonstrate the efficiency of the fast transform algorithms, and the applications in computational electromagnetics and computational acoustics.
Noncontact ultrasonic imaging for the evaluation of thermal injury
Authors: Jones Joie P.
Published: July 2002

Although conventional wisdom suggests that ultrasonic imaging of the body cannot be accomplished without direct contact (or at least via water coupling), we have shown that noncontact imaging through air is possible, certainly for superficial body regions, provided judicious choices of piezoelectric materials and matching layers are made. In preliminary experiments and clinical studies reported here, noncontact imaging is demonstrated for the evaluation of thermal injury (including the quantitative measurement of burn-depth), for the assessment of wound healing, and for the examination of assorted skin lesions. Specifically, in the case of thermal injury, reflections from the dermal/fat interface in human skin is clearly seen using a noncontact 5-MHz transducer. Such measurements are sufficient to determine burn-depth which, in turn, are sufficient to provide, for the first time, a quantitative and noninvasive method for burn evaluation and treatment specification. Evaluating over 500 burn sites in some 100 patients, noncontact ultrasound showed a much greater accuracy and sensitivity than standard clinical assessment. Our method is applicable to a conventional clinical environment as well as a battlefield situation and should prove particularly effective for large-scale medical triage.
Acoustics laboratory experiments for all
Authors: Hansen Uwe J. , Rossing Thomas D.
Published: July 2002

For most students, understanding scientific principles requires hands-on experience, and that is the reason for having undergraduate laboratories. This is especially true of acoustics, in which the laboratory experience is important not only to beginning and advanced students in science and engineering but also to students taking a general education course. We will describe some favorite experiments on the introductory, intermediate, and advanced levels. Most of them are based on experiments in Acoustics Laboratory Experiments, a collection of 52 experiments on all levels. Some of them are appropriate for introductory courses in musical acoustics or speech and hearing, others are suitable for physics and engineering students in more advanced courses. Ways to incorporate acoustics experiments into courses not having a scheduled laboratory period will also be discussed.
New acoustics experiments on an old NeXT computer
Authors: Russell Daniel A.
Published: July 2002

The manufacture of NeXT computer hardware was discontinued in 1993. However, the operating system (now known as OPENSTEP and Macintosh OS-X) is still alive and kicking, and refurbished NeXT systems are still available at greatly reduced cost. Coupled with an A/D converter, the NeXT computer is a powerful, and relatively inexpensive, tool for an undergraduate acoustics laboratory. There is a fairly wide selection of free acoustics software available over the internet, including applications for digital sound recording, mixing, and editing; oscilloscopes; FFT analysis; spectrum analysis; MIDI sequencing; sound file conversion; and signal generation. In addition, there are some excellent new commercial software packages which allow the NeXT to act as a professional quality digital function generator and audiometer. This paper will summarize how NeXT computers are used at Kettering University for undergraduate acoustics laboratory experiments involving digital sound recording and manipulation, signal analysis, Fourier synthesis, principles of digital audio, noise, and human hearing.
Spectral characteristics and efficient critical-band-associated group synthesis of piano tones
Authors: Zheng Hua , Beauchamp James W.
Published: July 2002

The physics of piano sound production has been studied extensively, while little has been done to explore its spectral characteristics for efficient and perceptually accurate digital synthesis. Piano tones with a large variety of explicit performance parameters were recorded from a MIDI-controlled acoustic piano, and spectral modeling methods were used for the analysis. A number of features have been concluded: (1) relationship between harmonic structure and pitch for six levels of dynamic; (2) relationship between spectral envelope and dynamic for all pitches; (3) typical amplitude envelopes; (4) effects of the sustain and soft pedals; (5) inharmonicity characteristics; (6) noise characteristics. A multiple-wavetable synthesis algorithm implementing a group synthesis model was developed. Each harmonic group corresponds to one or more consecutive critical bands. Amplitude versus time envelopes of all harmonics within one group share a weighted-average shape with individual weight applied to each harmonic. With appropriate numbers of groups and characteristic noise, convincing results have been obtained for the entire range of pitches and dynamics. The synthesis algorithm has been implemented as a subroutine of an analysis/synthesis software package, as a Music 4C instrument, and as a real-time plug-in for a software sound server.
A hybrid waveguide model of the transverse flute
Authors: Bartsch Mark A.
Published: July 2002

Recent years have seen substantial improvements in the modeling and synthesis of jet-reed instruments such as flutes and organ pipes. Developments in the modeling of woodwinds using so-called digital waveguides have allowed the efficient acoustical modeling of the main body and toneholes of the instrument. Further, a new and more complete model of the jet’s behavior in the presence of the edge and the resonator has been formulated for recorderlike instruments [Verge et al., J. Acoust. Soc. Am. 101, 2925–2939 (1997)]. A new simulation model of the transverse flute is presented which combines the contributions of digital waveguide modeling and the new source model. This new model is defined almost entirely by physical parameters (such as dimensions of the instrument) rather than by the arbitrary adjustment parameters often employed. The model is evaluated by comparing the effects of certain parameters on the model’s operation with their effects on the performance of an actual flute. The model is further evaluated for its tuning characteristics by comparing its frequencies of oscillation with the sounding frequencies of a simple flute with matched physical parameters. [Work supported by the University of Dayton Honors Program.]
Acoustic landmine detection using laser scanning vibrometer
Authors: Sabatier James , Xiang Ning
Published: July 2002

Airborne acoustic waves that couple into the surface of the ground excite Biot compressional and shear waves. If a minelike target is present below the surface, the ground surface vibrational velocity will show distinct changes due to reflection and scattering of these waves. Taking advantage of a noncontact measurement technique, the surface vibrational velocity is detected with a laser Doppler vibrometer. Sound waves with a wavelength comparable to the object size are suitable for recognizing geometrical shapes of targets, while true wavelike acoustic scattering phenomena can be observed with a shorter acoustic wavelength. In the present contribution, both shape/size recognition and scattering phenomena of buried mines detected by the laser Doppler based acoustic detection will be visualized in terms of a number of 2-D and 3-D animations. [The work is supported by U. S. Army Communications-Electronics Command.]
Effect of BM compression on masking period patterns (MPPs)
Authors: Wojtczak Magdalena , Schroder Anna C. , Kong Ying-Yee , Nelson David A.
Published: July 2002

MPPs were measured in listeners with normal and impaired hearing using tonal 4-Hz SAM maskers and short tonal probes with frequencies that were either identical to or higher than the carrier frequency of the masker. The probe frequencies were 500, 1200, and 3000 Hz for on-frequency masking, and 1200, 2400, and 6000 Hz for off-frequency masking. In normal-hearing listeners MPPs measured with off-frequency probes had valleys that were much longer and deeper than valleys observed with on-frequency probes. A similar result was observed in hearing-impaired listeners in the frequency region of mild hearing losses, where significant residual compression was presumably operating. However, in the frequency region with substantial hearing loss where compression is substantially reduced or absent, MPPs measured with the on- and off-frequency probes were very similar. A model consisting of peripheral filtering, compressive nonlinearity, and a sliding temporal window was used in an attempt to predict the data and to estimate the compression index. The results suggest that the similarity of on- and off-frequency temporal resolution in hearing-impaired listeners may be due in part to the lack of the compressive nonlinearity that is evident at the level of the basilar membrane in normal-hearing listeners. [Work supported by NIH-NIDCD DC00149.]
Estimation of psychometric functions using a hybrid up–down maximum likelihood procedure
Authors: Yuan He , Levitt Harry , Miller James D.
Published: July 2002

Rapid, efficient, and reliable estimation of psychometric functions is a much sought after goal in psychophysics. Adaptive techniques of the up–down type have many advantages in this regard, but they are not without their limitations. An alternative approach is the use of maximum likelihood estimation in placing observations. Whereas the maximum likelihood method is as efficient if not more efficient than any other method of estimation, this property only holds for very large samples. The use of maximum likelihood estimation in adaptive testing has significant limitations when the sample size is very small. In this study, a hybrid adaptive procedure was developed using an up–down technique initially and then converting to a maximum likelihood procedure once sufficient samples have been obtained for reliable estimation using the latter technique. The up–down technique that is used reduces the step size systematically employing a rule analogous to that used in analog-to-digial converters and is referred to as the AD procedure. Monte Carlo simulations of experiments using the hybrid adaptive technique showed promising results in comparison with other adaptive procedures. [Research supported by Grant 5P50DC00178 from NIDCD.]
Using resynthesized speech in /r/–/l/ production and perception training
Authors: Kubo Rieko , Akahane-Yamada Reiko , Kawahara Hideki
Published: July 2002

To find effective speech stimuli for second-language (L2) training, we generated resynthesized speech using the STRAIGHT algorithm developed by Kawahara (1997). First, Japanese speakers were trained to produce English /r/ and /l/ in a reproduction task. Training proceeded by first using model words which were artificially lengthened by STRAIGHT, and then gradually introducing words at a natural speed. Spectrograms of the model speech and the learner’s speech were given as feedback. Subjects improved significantly from pretest to post-test in their production ability as evaluated by human judges. Second, resynthesized speech was used in perception training. Previous perceptual training studies using synthetic speech have not always been successful. However, training based on resynthesized speech from STRAIGHT led to the same amount of improvement as training based on the original natural tokens, suggesting the potential for using STRAIGHT in L2 perception training. We then manipulated certain acoustic parameters of the stimuli, namely, lengthening and/or enhancement of the third formant. The training effect using these stimuli did not differ significantly from the effect found with the unmodified synthetic stimuli. These results suggest that resynthesized speech from STRAIGHT is suitable for L2 training, but further effort is necessary to find more effective stimulus manipulations.
Listeners’ representations of within-word structure of native and nonnative words by Japanese speakers
Authors: Otake Takashi , Yoneyama Kiyoko
Published: July 2002

This study further explored how Japanese represented within-word structure of native and nonnative spoken words in terms of two phonological units, morae and syllables, using a new task. The main question addressed in this study was to investigate which phonological unit was preferred to represent nonnative and native words. Three experiments were conducted with Japanese college students, using a tapping task. In experiment 1, 42 syllable Japanese materials which included a CVN syllable in the first syllable and fillers were presented to 20 Japanese college students to identify the number of chunks. The result showed that they preferred morae to syllables. In experiments 2 and 3, 42 syllable English and Spanish materials which included exactly the same syllable structure and fillers were presented to the same number of students, respectively. The results showed that the preference was around 50% each, respectively. These results obviously contradicted to the previous findings in which morae were preferred to nonnative words. The results in this study may suggest that the previous findings using an explicit segmentation task may have been influenced by orthography and that Japanese may be able to suppress morae to represent nonnative words. [Work supported by IFC and Ministry of Education.]
Effect of linguistic background on accuracy of discrimination task and reaction time
Authors: Kumar Aman
Published: July 2002

This study examines how American English (AE) speakers categorize Hindi laryngeal and place of articulation contrasts. These results are interpreted with respect to the Perceptual Assimilation Model (PAM) [Best, ‘‘A direct realist view of cross-language speech perception,’’ in Speech Perception and Linguistic Experience: Issues in Cross Language Research (York Press, Inc., 1995), pp. 171–204]. Accuracy and reaction time data were obtained for discrimination and identification of Hindi bilabial and dental phonation contrasts and the retroflex-dental place contrast. Subjects included both AE speakers and a control Hindi speaker group. Discrimination accuracy averaged across the subjects for the phonation contrasts was nativelike while accuracy for the retroflex-dental contrast was significantly lower but above chance. Overall, the reaction time was inversely proportional to discrimination accuracy. For some subjects discrimination performance for the retroflex-dental contrast was nativelike. However, the reaction time for those subjects was significantly higher than that of other speakers. In general, the reaction time was higher for the retroflex-dental contrast than for the other contrasts.
Articulatory effects of contrastive emphasis on the Accentual Phrase in French
Authors: Loevenbruck Helene
Published: July 2002

Recent works (Beckman, 1996) show that prosody is itself a complex linguistic structure, and it is imperative to better describe its phonological and phonetic (acoustic and articulatory) characteristics. Articulatory studies of French prosody provide variable conclusions. The irregularities could come from the fact that prosodic structure is rarely considered and that different phenomena (‘‘accents primaires,’’ ‘‘secondaires’’) are examined together. Articulatory correlates of a prosodic entity, the Accentual Phrase (AP), are studied here, using a model of French prosody (Fougeron and Jun, 1998). The AP features an initial high tone Hi, also called ‘‘accent secondaire,’’ a final high tone H* (‘‘primaire’’), and two low L tones preceding them. Sentences containing four-syllable words (APs), were recorded for two French speakers (one male, one female), using EMA. The position of the AP in the sentence varied, several speaking conditions were elicited. Displacement, peak velocity, and movement duration are analyzed for the tongue-middle vertical position. The results suggest that LHi could be related to hyper-articulation of the first or second syllable, and LH* to even stronger hyper-articulation of the last syllable. With contrastive emphasis on the AP, the initial hyper-articulation can become as strong as, and even stronger than, the final one.
Taiwanese final stops and following initial voiced stops and nasals
Authors: Pan Ho-hsien
Published: July 2002

The places of articulation of unreleased Taiwanese final stops, e.g., /p,t,k/ and glottal stop, have been known to assimilate into that of initial voiceless stops in following a syllable, depending on the speed of articulation (Peng, 1997). Besides assimilation in place of articulation, nasalization can be observed across syllables between voiced stops and nasals (Pan, 1999). However, little is known about the assimilation in place of articulation, voicing, and nasalization between Taiwanese final stops, and following voiced stops and nasals across different prosodic boundaries. This study uses EPG, airflow, and acoustical data to investigate the coarticulation between Taiwanese final stops, and initial nasals, initial voiced stops, across syllable boundary, morpheme boundary, phrase boundary of narrow focus, and intonation boundary. Preliminary results showed that Taiwanese final stops are lost in certain contexts. There is assimilation in place of articulation between unreleased final stops and initial voiced stops and nasals. No progressive nasalization is observed between final stops and initial nasals. Taiwanese final stops are easily coarticulated with following segments. Though the presence of final stops and short syllable duration are both vital cues to Taiwanese entering tones syllables, duration is a more invariant cue than the presence of final stops. [Project supported by NSC 87-2411-H-009-008.]
A cross-gender examination of the breathy tone in Green Mong
Authors: Andruski Jean E. , Ratliff Martha
Published: July 2002

Tone is generally thought of as a pitch difference that carries information regarding word meaning, but tone often correlates with phonation type as well as pitch. This paper presents the acoustic portion of a cross-gender study on acoustic and perceptual correlates of the breathy tone in Green Mong. Three male and three female native speakers of Green Mong residing in the Detroit area were asked to produce a series of target words containing the breathy tone and comparison tones in sentence context. Target words were minimal sets in which only tone varied. Each speaker produced a sequence of minimal sets containing each possible voiceless stop and voiced fricative onset of Green Mong. Vowel identity also varied across minimal sets. Four acoustic correlates of tone (fundamental frequency or F0, F0 contour, duration, and breathiness) were measured in each target word. Degree of breathiness was measured by subtracting the amplitude of F0 from the amplitude of the second harmonic at the durational midpoint of the vowel. Each of these four acoustic correlates will be examined in the breathy tone and the comparison tones, and a cross-gender comparison of the results will be presented.
Phonological representation in Japanese and American rap music: Further evidence for mora timing
Authors: Iwai Atsuko , Otake Takashi
Published: July 2002

This paper investigated how words in Japanese and American rap music were represented in terms of two phonological units, morae and syllables. The main question addressed in this study was to find out which unit was preferred to represent words in Japanese and American rap music. One hundred CVN syllables in two or multi-syllable words were identified from 9 pieces of 2 Japanese musical bands and 27 pieces of 3 American musical bands. Then, the first author set these syllables to music one by one, using a Japanese computer music software to determine how these syllables were assigned to notes. The analysis showed that 73% of the CVN syllables in Japanese rap music were assigned to a note which was two times longer than that of the following note and 27% were assigned to two separate equivalent notes, while 93% of the CVN syllables in American rap music were assigned to a single note which was equivalent to the following note. In other words, the computation of duration was considered to choose notes in the former, while it was not in the latter, suggesting that words in Japanese and American rap music were represented in terms of morae and syllables, respectively.
Vowel epenthesis in productions of English consonant clusters by Japanese
Authors: Tajima Keiichi , Kubo Rieko
Published: July 2002

Phonotactic contraints on syllable structure vary across languages. Japanese has a more restricted set of consonant clusters (e.g., ‘‘honda’’) than English (e.g., ‘‘instruct’’). This presents a problem for Japanese learners of English, who often avoid consonant clusters by inserting epenthetic vowels between consonants. This study examines how often Japanese speakers produce epenthetic vowels in English and the phonetic environments in which they commonly occur. A group of native Japanese speakers, and a control group of native English speakers, read English words embedded in a sentence, and isolated words spoken at normal and slow rates. Measurements were made from spectrograms of the duration of the target clusters, including any epenthetic vowels produced. Preliminary results suggest that Japanese speakers show more instances of epenthetic vowels than do English speakers, and that such vowels are more commonly observed in slow, careful speech than in normal-rate speech. Also, in the absence of vowel epenthesis, Japanese speakers’ productions of consonant clusters differ from those of native speakers in the durational characteristics of component segments. Thus, Japanese speakers’ difficulties in producing English consonant clusters are reflected not just through frequent vowel epenthesis, but also through differences in durational properties in the clusters.
Validity of the sonar equation and Babinet’s principle for object scattering in a shallow water waveguide
Authors: Makris Nicholas C. , Ratilal Purnima , Lai Yisan
Published: July 2002

It has recently been shown that the sonar equation can provide a reasonable approximation to nonforward scattering from a noncompact (ka>1) sphere submerged in an ocean waveguide. The omnidirectional scattering characteristics of the sphere in nonforward directions enables the sphere’s far-field plane wave scattering function to be factored in the single-scatter waveguide solution just as it is in free space. The highly directional nature of the sphere’s scattering in the forward direction, however, prevents this factorization and leads to significant departures from sonar equation predictions in the forward direction. By Babinet’s principle, the forward scattered field from a noncompact sphere subject to an incident plane wave in free space will be nearly the same as that of a disk of the same projected area. Accordingly, it is shown that the sonar equation can significantly overestimate the field scattered from an upright plate or disk submerged in an ocean waveguide. These flat objects yield some of the most directional scattering possible from a finite body. It is also shown that in an ocean waveguide the upright disk and an equivalently located sphere with the same great circle area can have nearly identical forward scattered fields, just as in free space.
Scattering enhancements for penetrable tilted circular cylinders in water: The computed evolution away from the meridional plane
Authors: Marston Philip L. , Blonigen Florian J.
Published: July 2002

Significant contributions to the high-frequency backscattering by penetrable bluntly truncated solid circular cylinders include meridional leaky Rayleigh waves [K. Gipson, Ph.D. thesis, Washington State University (1998)] and the caustic merging transition [F. J. Blonigen and P. L. Marston, J. Acoust. Soc. Am. 102, 3088 (1997)]. The latter is important for plastic objects (where Rayleigh waves become subsonic relative to water) and is associated with merging transmitted and internally reflected rainbow rays. One way to explore the dependence of these processes on tilt is to compute the exact scattering by infinite circular cylinders away from the meridional plane. The meridional Rayleigh-wave feature for infinite metallic cylinders is a dip in the total scattering and a peak in the background-subtracted scattering [P. L. Marston, J. Acoust. Soc. Am. 102, 358–369 (1997)]. We find it evolves in a way bounded by the locus of those rays reflected with their local angle of incidence matching the Rayleigh-wave coupling angle. In the caustic merging case, the evolution of the rainbow enhancement is similar to optical observations [Mount et al., Appl. Opt. 37, 1534–1539 (1998)]. [Supported by the Office of Naval Research.]
An efficient parabolic equation solution based on the method of undetermined coefficients
Authors: Dacol Dalcio K. , Collins Michael D. , Lingevitch Joseph F.
Published: July 2002

An implementation of the self-starter based on the method of undetermined coefficients is described and tested. For many problems, this parabolic equation technique for solving short range propagation problems provides an efficiency gain of an order of magnitude or more over the finite difference solution. With this forward model, it is possible to solve geoacoustic inverse problems in seconds on the current generation of desktop computers. The approach can be implemented for the inverse problem so that efficiency is essentially independent of the depth of the water column.
Internal waves and sound-speed distributions in the Yellow Sea
Authors: Wang Tao , Gao Tian-fu , Zhang Yun-peng , Jiang De-jun
Published: July 2002

The theory of resonant scattering of sound by internal solitons in the Yellow Sea is well known [Zhou et al., J. Acoust. Soc. Am. 90, 2042–2054 (1991)]. However, the oceanographic measurements made were rather sparse. In this paper, the time dependencies and the vertical structures of the internal waves and the resulting sound speeds over a period of 49 h 49 min in a strong seasonal thermocline of the Yellow Sea are presented. A temperature chain, sampling once per 6.42 s and consisting of 32 sensors spaced 0.4 m apart, provides the data. It is found that the volume sound speeds are significantly perturbed in the presence of the internal waves. At a fixed depth, the sound-speed perturbations may exceed 45 ms−1. The mean sound-speed gradient is −8.3 s−1, but the gradient becomes −25 s−1 when the thermocline is the strongest. The sound-speed distributions show the diurnal periodicity of the internal wave activity. The 6-h component, with high-frequency fluctuations riding on top of it, is also clearly seen. However, the data give no evidence of the presence of solitons although the internal waves are indeed nonlinear. [Work supported by NSFC.]
Models of uncertainty in structural dynamics
Authors: Langley Robin S.
Published: July 2002

At medium to high frequencies small changes in the properties of a structure can have a significant effect on the vibrational response. The theoretical methods which are currently available to assess the influence of structural uncertainties are either probabilistic (for example, Monte Carlo simulations, FORM and SORM reliability methods, and asymptotic analysis of probability integrals) or possibilistic (for example, convex modeling, interval analysis, and fuzzy set theory). The interrelationships between these methods are far from clear, and research in each area tends to progress independently of the others. It is shown here that there is a very close relationship between asymptotic analysis, FORM, SORM, and the full range of possibilistic techniques: in fact, a single algorithm can encompass all the methods. This means that software developed for FORM and SORM can be applied to convex modeling (for example) providing the input variables and output quantities are reinterpreted in an appropriate way. It then becomes straightforward to select and implement the analysis method most suited to the available data. The theoretical developments are illustrated here by application to an example dynamic system.
Midfrequency acoustical modeling of a coated plate
Authors: Norris Andrew
Published: July 2002

A steel plate with an attached thick viscoelastic layer exhibits ‘‘midfrequency’’ characteristics at relatively low frequencies, certainly below 1 kHz for a 1-in. steel plate with thicker coating. The low-shear stiffness of the coating leads to a cut-on frequency associated with a shear thickness resonance. Classical plate theory or composite plate theory cannot capture this phenomenon. Although it is not difficult to compute the exact dispersion and modal properties of this system, an approximate plate theory is required in order to examine how the coated plate interacts dynamically with uncoated regions (reflection, transmission), and for modeling scattering from structure incorporating these elements. A hybrid plate theory is presented, based on a classical Kirchhoff assumption for the steel, and a Timoshenko/Mindlin model for the coating. This leads to a three degrees of freedom model, which exhibits the same dispersive properties as the exact theory. Comparisons and differences are discussed. The effects of fluid loading are also presented. [Work supported by ONR.]
Basic development of a hybrid finite element method for mid-frequency computations of structural vibrations
Authors: Zhao Xi , Vlahopoulos Nickolas
Published: July 2002

In the past it has been demonstrated that energy finite element analysis (EFEA) allows computation of high-frequency structural vibration in complex marine structures and produces results similar to statistical energy analysis (SEA) predictions [Vlahopoulos et al., ‘‘Numerical implementation, validation, and marine applications of an energy finite element formulation,’’ accepted by the Journal of Ship Research]. In this paper a basic theoretical development of a hybrid finite element method is presented. Conventional finite element analysis (FEA) is combined with EFEA in order to achieve solution to mid-frequency vibrations. The new formulation is based on deriving appropriate interface conditions at the joints between members modeled by the FEA and the EFEA methods. Effects of strong coupling, power re-radiation, and power re-injection can be accounted in the analysis. Examples of systems of co-linear beams will be presented. Analytical solutions are compared to the hybrid solution in order to validate the theoretical developments. [Research supported by Automated Analysis Corporation.]
The fundamental mechanisms and control of power flow to cylindrical shells in the midfrequency range
Authors: McDaniel J. Gregory
Published: July 2002

This presentation will survey the fundamental mechanisms of midfrequency power flow to cylindrical shells from point excitations and, based on these mechanisms, propose approaches to controlling power flow. The mechanisms derive from an analytical expression for the shell velocity that involves a Fourier series about the shell’s circumference. Each Fourier coefficient is a sum of four waves that propagate in the axial coordinate. At high frequencies, these four waves resemble the flexural, evanescent, shear, and longitudinal waves that propagate in a flat plate and each has an associated cutoff frequency, below which it becomes spatially attenuated. When a wave is excited near its cutoff frequency, its amplitude rises dramatically and, therefore, the total power delivered to the shell is dominated by that wave. This view suggests an approach to controlling power flow in the midfrequency range by constraining the shell from responding in circumferential harmonics whose waves are excited near cutoff. In this context, the attachment of a reinforcing structure that is axially coincident with the excitation but circumferentially distributed is explored. Using a genetic algorithm to optimize structural parameters, an example will illustrate that a circumferentially distributed structure controls power much more effectively than a circumferentially compact structure.
An approximation to the frequency-average radiation efficiency of rectangular flat plates
Authors: Bonilha Murilo W. , Fahy Frank J.
Published: July 2002

The average radiation efficiency of plate modes which are resonant in a given frequency band is termed the frequency-average radiation efficiency and it is an extremely useful quantity in applications of Statistical Energy Analysis to interior or exterior noise control. In the present work, computation of the frequency-average radiation efficiency of flat plates is made on the basis of the vibration field correlation of randomly excited flat plate structures [M. W. Bonilha and F. J. Fahy, J. Sound Vib. 214, 443–467 (1998)]. The advantage of this representation is that the radiation efficiency can be economically computed for simply-supported, free, clamped, guided and spring-supported boundary conditions. In addition, corrections to account for the presence of stiffeners and plate curvature can also be incorporated in the computation. Furthermore, the current representation also allows the use of FEA-derived spatial correlation results for the case of plates with complex boundary conditions and accommodate spatially varying materials or geometric properties. Radiation efficiency results for various boundary conditions are presented. It is shown that results for simply-supported boundary conditions agree well with those obtained by Leppington et al. [F. G. Leppington, E. G. Broadbent, and K. H. Heron, Proc. R. Soc. London, Ser. A 382, 245–271 (1982)].
Midfrequency structural acoustics by the dynamic direct stiffness method. II. Plate-like structures
Authors: Miller Russel D.
Published: July 2002

The use of the dynamic direct stiffness method (DDSM) for the harmonic analysis of beam structures is well known. In this paper the development of a harmonic plate element with similar characteristics is discussed. Whereas the finite-element method requires approximately six nodes per wavelength, the harmonic plate element requires nodes only at element connections, terminations, and load points. The governing equations are used in the variational form to derive the direct stiffness matrix. The matrix form of the element derived is compatible with those of the FEM and may be used for the harmonic analysis of general FEM/DDSM structures. The motivation for this development is the need for computationally efficient evaluation of the midfrequency range for general structures where the FEM method requires a large number of degrees of freedom and statistical energy analysis (SEA) does not provide sufficient accuracy. A number of examples are provided to establish verification of the DDSM plate element. Examples include the response of harmonically driven plates, plates with beam stiffeners, and plate/beam truss structures.
Sub-optimal adaptive matched-field processing of a three-dimensional array in a changing environment
Authors: Lee Yung P.
Published: July 2002

The major problem in adaptively processing data from a large array is inversion of the covariance matrix. The matrix must be well-conditioned to be inverted. The number of independent samples that is needed to form a well-conditioned matrix is at least twice the number of array elements. The integration time to form a well-conditioned large array covariance matrix may then be unreasonably long relative to the coherent time of signal in a changing environment. A sub-optimal subarray processing has been developed. The adaptive weight vectors are calculated for each subarray. These weight vectors are linearly combined to form a full-array adaptive weight vector and are applied to the full-array covariance matrix. The required integration time is reduced to that which is needed to form the well-conditioned subarray covariance matrices. In a recent shallow water experiment, a three-dimensional array had been deployed. The array consisted of 5 VLAs each with 30-element spaced evenly on a circular baseline of a radius of 200 m. The subarray processing approach had been used to localize a moving source that had a fast range/bearing change relative to the baseline.
Results of environment inversion using modes extracted from vertical line array data
Authors: Neilsen Tracianne B. , Westwood Evan K.
Published: July 2002

The results are presented for geoacoustic inversion using the depth-dependent normal modes extracted from vertical line array (VLA) data. The normal modes for multiple frequencies are obtained by performing a singular value decomposition (SVD) on VLA data recorded as a source moves outward in range. The data-extracted mode functions are then used to invert for the environmental parameters. The Levenberg–Marquardt nonlinear optimization method is used to adjust the environmental parameters to find the best fit between the data-extracted modes and modes modeled by the ORCA normal mode model. The method is useful for determining the sound speed profile and the characteristics of the uppermost bottom layers [T. B. Neilsen and E. K. Westwood, J. Acoust. Soc. Am. 104, 1741 (1998)]. Mode extraction and geoacoustic inversion results for a range-independent track during the ACTII experiment will be presented. Extension of the theory for mode extraction (and preliminary results for inversion using simulated data) in a range-dependent environment using the adiabatic approximation will also be presented. [Work supported by ONR.]
Prediction of cutoff noise in centrifugal fans
Authors: Zhu Zhichi , Li Song , Huang Dongtao
Published: July 2002

The most important noise in centrifugal fans is aerodynamic noise, in which cutoff noise is the most main component. Cutoff noise is mainly caused by the fluctuating pressure on the cutoff in the volute impacted by the nonuniform flow from the exit of the rotating impeller. A numerical method is presented for prediction of cutoff noise in centrifugal fans. The contents of the method are mainly the following. (1) The fluctuating pressure serving as the source of cutoff noise is given out by using the existing computation software of 3D viscous flow in centrifugal fans and the time-frozen hypothesis. (2) The sound field in the volute of a centrifugal fan and the sound power levels of cutoff noise are computed by using the forth-order MacCormack scheme and making some important numerical measures. The sound field in the volute and the sound power levels of cutoff noise for three practical volutes with different cutoff clearance have been computed and the acoustic pressure distribution in space and change with time are discussed. Finally, the sound power levels of cutoff noise have been measured. The errors between the predicted and the tested sound power levels of cutoff noise are less than 3 dB. [Work supported by NSF.]
Coupling of velocity dispersion curves of leaky Lamb waves on a fluid-loaded plate
Authors: Toda Kohji , Motegi Kenji
Published: July 2002

The coupling of velocity dispersion curves of leaky Lamb waves is studied based on analytical calculations to clarify the problem of repulsion and crossing of the curves. Two curves, corresponding to the 4th and 5th modes, are closely observed while artificially varying the properties of virtual materials, in the combination of piezoelectric ceramic and glass. The imaginary part of the Lamb-wave velocity is essential for distinguishing the coupling phenomena. The behaviors of the velocity values as functions of two variables, material property and the product of frequency and thickness of the plate, are analogous to the Riemann sphere defined by a mathematical function of ω=z(1/2) (both z and ω are complex) inside the domain containing the point z=0 on the complex plane.
On the decline in overshoot at high masker levels
Authors: Bacon Sid P. , Liu Li
Published: July 2002

The purpose of the present study was to determine whether the decline in overshoot at high masker levels might be due to the slow recovery of the onset response of low-spontaneous rate (sr) fibers. Overshoot was measured for a 4000-Hz signal at a relatively low (20 or 30 dB) and at a relatively high (50 dB) masker spectrum level in both an adaptive, two-interval forced-choice (2IFC) paradigm and in a fixed-level, yes–no paradigm. In the 2IFC paradigm, there was only 500 ms of silence between the two masker bursts of a trial; in the yes–no paradigm, there was 4 s of silence between each burst (i.e., between each trial). The timing of the trial sequences of these two paradigms was such that the 2IFC paradigm probably would not ensure complete recovery of the onset response of low-sr fibers, whereas the yes–no paradigm would. Nevertheless, for both paradigms, there was an average of about 9 dB of overshoot at the lower masker level and 2 dB at the higher masker level. These results suggest that the decline in overshoot at high masker levels is not due to the protracted recovery from adaptation of the onset response of low-sr fibers.
Acoustical design of the opera house of the New National Theatre, Tokyo, Japan
Authors: Beranek Leo L. , Hidaka Takayuki , Masuda Sadahiro
Published: July 2002

Architect Takahiko Yanagisawa’s preface explains his approach to the design. The NNT opera house seats 1810, its volume is 14 500 m3, and its reverberation time, with audience, is 1.5 s (proscenium curtain open). Measurements on CAD computer and 1:10 wooden models and full-sized materials samples were conducted over a 7-yr. period. The main floor is almost rectangular, the three balconies have modest fan shape in plan, although the balcony facia at each level create a rectangular shape. The unique design has a large curved reflector in front of and above the proscenium and six curved reflecting surfaces at the front ends of the three side balconies to form, in combination, an “acoustic trumpet.” These surfaces, along with the balcony faces and the shaped ceiling, distribute the singers’ voices uniformly over the seating areas from a large portion of the large stage at sound levels that easily override the orchestra in the pit.