bluuebunny/crossref_metadata_2025 huggingface dataset:
Iterative reconstruction for attenuation correction in positron emission tomography: Maximum likelihood for transmission and blank scan
Authors: Glatting G. , Wuchenauer M. , Reske S. N.
Published: July 2002

The quality of the attenuation correction strongly influences the outcome of the reconstructed emission scan in positron emission tomography. The calculation of the attenuation correction factors must take into account the Poisson nature of the radioactive decay process, because—for a reasonable scan duration—the transmission measurements contain lines of response with low count numbers in the case of large attenuation factors. Our purpose in this study is to investigate a maximum likelihood estimator for attenuation correction factor calculation in positron emission tomography, which incorporates the Poisson nature of the radioactive decay into transmission and blank measurement. Therefore, the correct maximum likelihood function is used to derive two estimators for the calculation of the attenuation coefficient image and the corresponding attenuation correction factors depending on the measured blank and transmission data. Log likelihood convergence, mean differences, and the mean of squared differences for the attenuation correction factors of a mathematical thorax phantom were determined and compared. The algorithms yield adequate attenuation correction factors, however, the algorithm taking the noise in the blank scan into account can perform better for noisy blank scans. We conclude that maximum likelihood—including blank likelihood—is advantageous to reconstruct attenuation correction factors for low statistic blank and good statistic transmission data. For normal blank and transmission statistics the implementation of the statistical nature of the blank is not mandatory.
Peer Instruction: Ten years of experience and results
Authors: Crouch Catherine H. , Mazur Eric
Published: July 2002

We report data from ten years of teaching with Peer Instruction (PI) in the calculus- and algebra-based introductory physics courses for nonmajors; our results indicate increased student mastery of both conceptual reasoning and quantitative problem solving upon implementing PI. We also discuss ways we have improved our implementation of PI since introducing it in 1991. Most notably, we have replaced in-class reading quizzes with pre-class written responses to the reading, introduced a research-based mechanics textbook for portions of the course, and incorporated cooperative learning into the discussion sections as well as the lectures. These improvements are intended to help students learn more from pre-class reading and to increase student engagement in the discussion sections, and are accompanied by further increases in student understanding.
Implication of conservative and gyroscopic forces on vibration and stability of an elastically tailored rotating shaft modeled as a composite thin-walled beam
Authors: Song Ohseop , Jeong Nam-Heui , Librescu Liviu
Published: July 2002

Problems related with the implications of conservative and gyroscopic forces on vibration and the stability of a circular cylindrical shaft modeled as a thin-walled composite beam and spinning with constant angular speed about its longitudinal axis are addressed. Taking into account the directionality property of fiber reinforced composite materials, it is shown that for a shaft featuring flapwise-chordwise-bending coupling, a dramatic enhancement of both the vibrational and stability behavior can be reached. In addition, the effects played in the same context by transverse shear, rotatory inertias as well as by the various boundary conditions are discussed and pertinent conclusions are outlined.
Numerical modeling of finite-amplitude sound beams: Shock formation in the near field of a cw plane piston source
Authors: Khokhlova V. A. , Souchon R. , Tavakkoli J. , Sapozhnikov O. A. , Cathignol D.
Published: July 2002

Two theoretical models and the corresponding numerical codes for the description of nonlinear acoustic beams radiated from intense cw sources in water are presented. In the first model, diffraction effects are included using the Rayleigh integral, whereas nonlinearity and thermoviscous absorption are accounted for in a quasi-plane approximation. The simulations are performed in the time domain using the code previously developed for single-pulse propagation in medium having arbitrary frequency-dependent absorption. The second model is based on the Khokhlov–Zabolotskaya–Kuznetsov equation, which, contrary to the first model, accounts for diffraction in the parabolic approximation. The simulations are performed in the frequency domain using a novel algorithm that has been developed. A variable number of harmonics, which follows the nonlinear broadening of the wave spectrum are employed in the algorithm to speed up calculations. In order to prove the validity and the accuracy of the two codes developed, the simulation of diffraction and nonlinear effects in the near field of an intense ultrasound circular piston source in water is performed. The results of modeling obtained by both codes are compared with each other and with known experimental data, and are found to be in a good agreement. Frequency-domain code is then used for detailed study of the strongly nonlinear regime of propagation, when shocks are developed in the waveform close to the source. It is demonstrated that diffraction plays a major role in shock formation. Development of two shocks in each cycle and their further collision is predicted. It is also shown that nonlinear propagation and shock formation result at some distance in the two times excess of peak positive pressure in comparison with the maximum value obtained in the case of linear propagation. The beam total power decay due to formation of shocks as a function of the propagation distance is compared with the intensity in a plane wave propagation without diffraction. It is shown that nonlinear energy decay starts earlier for the beam, but decreases slower over longer distances.
Informational and energetic masking effects in the perception of multiple simultaneous talkers
Authors: Brungart Douglas S. , Simpson Brian D. , Ericson Mark A. , Scott Kimberly R.
Published: July 2002

Although many researchers have examined the role that binaural cues play in the perception of spatially separated speech signals, relatively little is known about the cues that listeners use to segregate competing speech messages in a monaural or diotic stimulus. This series of experiments examined how variations in the relative levels and voice characteristics of the target and masking talkers influence a listener’s ability to extract information from a target phrase in a 3-talker or 4-talker diotic stimulus. Performance in this speech perception task decreased systematically when the level of the target talker was reduced relative to the masking talkers. Performance also generally decreased when the target and masking talkers had similar voice characteristics: the target phrase was most intelligible when the target and masking phrases were spoken by different-sex talkers, and least intelligible when the target and masking phrases were spoken by the same talker. However, when the target-to-masker ratio was less than 3 dB, overall performance was usually lower with one different-sex masker than with all same-sex maskers. In most of the conditions tested, the listeners performed better when they were exposed to the characteristics of the target voice prior to the presentation of the stimulus. The results of these experiments demonstrate how monaural factors may play an important role in the segregation of speech signals in multitalker environments.
An effective density fluid model for acoustic propagation in sediments derived from Biot theory
Authors: Williams Kevin L.
Published: July 2002

In this paper we present an acoustic propagation model that approximates a porous medium as a fluid with a bulk modulus and effective density derived from Biot theory. Within the framework of Biot theory it is assumed here that the porous medium has low values of frame bulk and shear moduli relative to the other moduli of the medium and these low values are approximated as zero. This leads to an effective density fluid model. It is shown that, for saturated sand sediments, the dispersion, transmission, reflection, and in-water backscattering predicted with this effective density fluid model are in close agreement with the predictions of Biot theory. In this agreement we demonstrate that the frame bulk and shear moduli play only a minor role in determining several aspects of sand acoustics. Thus, for many applications the effective density fluid model is an accurate alternative to full Biot theory and is much simpler to implement.
Interpretation and identification of minimum phase reflection coefficients
Authors: McDaniel J. Gregory , Clarke Cory L.
Published: July 2002

If the acoustic reflection coefficient is minimum phase, then the causality condition can be used to reconstruct its phase from its magnitude. Such reconstructions are useful when environmental conditions obscure the phase, which is vital to understanding the dynamics of the reflecting object. However, the reconstructions are usually impossible because one cannot be sure that the reflection coefficient is minimum phase. The present work addresses this difficulty by formulating a time-domain description of the minimum phase condition and by identifying classes of submerged objects that always create minimum phase reflection coefficients. Numerical examples are used to confirm the analytical findings and to illustrate their applicability to objects that reflect sound with a wide range of magnitudes.
An integrated wave-effects model for an underwater explosion bubble
Authors: Geers Thomas L. , Hunter Kendall S.
Published: July 2002

A model for a moderately deep underwater explosion bubble is developed that integrates the shock wave and oscillation phases of the motion. A hyperacoustic relationship is formulated that relates bubble volume acceleration to far-field pressure profile during the shock-wave phase, thereby providing initial conditions for the subsequent oscillation phase. For the latter, equations for bubble-surface response are derived that include wave effects in both the external liquid and the internal gas. The equations are then specialized to the case of a spherical bubble, and bubble-surface displacement histories are calculated for dilational and translational motion. Agreement between these histories and experimental data is found to be substantially better than that produced by previous models.
American and Swedish children’s acquisition of vowel duration: Effects of vowel identity and final stop voicing
Authors: Buder Eugene H. , Stoel-Gammon Carol
Published: July 2002

Vowel durations typically vary according to both intrinsic (segment-specific) and extrinsic (contextual) specifications. It can be argued that such variations are due to both predisposition and cognitive learning. The present report utilizes acoustic phonetic measurements from Swedish and American children aged 24 and 30 months to investigate the hypothesis that default behaviors may precede language-specific learning effects. The predicted pattern is the presence of final consonant voicing effects in both languages as a default, and subsequent learning of intrinsic effects most notably in the Swedish children. The data, from 443 monosyllabic tokens containing high-front vowels and final stop consonants, are analyzed in statistical frameworks at group and individual levels. The results confirm that Swedish children show an early tendency to vary vowel durations according to final consonant voicing, followed only six months later by a stage at which the intrinsic influence of vowel identity grows relatively more robust. Measures of vowel formant structure from selected 30-month-old children also revealed a tendency for children of this age to focus on particular acoustic contrasts. In conclusion, the results indicate that early acquisition of vowel specifications involves an interaction between language-specific features and articulatory predispositions associated with phonetic context.
Nonlinear propagation applied to the improvement of resolution in diagnostic medical ultrasound
Authors: Ward B. , Baker A. C. , Humphrey V. F.
Published: July 2002

Medical B-mode scanners operating under conditions typically encountered during clinical work produce ultrasonic wave fields that undergo nonlinear distortion. In general, the resulting harmonic beams are narrower and have lower sidelobe levels than the fundamental beam, making them ideal for imaging purposes. This work demonstrates the feasibility of nonlinear harmonic imaging in medical scanners using a simple broadband imaging arrangement in water. The ultrasonic system comprises a 2.25-MHz circular transducer with a diameter of 38 mm, a membrane hydrophone, also with a diameter of 38 mm, and a polymer lens with a focal length of 262 mm. These components are arranged coaxially giving an imaging geometry similar to that used in many commercial B-scanners, but with a receiver bandwidth sufficient to record the first four harmonics. A series of continuous wave and pulse-echo measurements are performed on a wire phantom to give 1-D transverse pressure profiles and 2-D B-mode images, respectively. The reflected beamwidths wn decrease as wn/w1=1/n0.78, where n is the harmonic number, and the reflected sidelobe levels fall off quickly with increasing n. In imaging terms, these effects correspond to a large improvement in lateral resolution and signal-to-clutter ratio for the higher harmonics.
Articulatory strengthening at edges of prosodic domains
Authors: Fougeron Cécile , Keating Patricia A.
Published: July 2002

In this paper it is shown that at the edges of prosodic domains, initial consonant and final vowels have more extreme (less reduced) lingual articulations, which are called articulatory strengthening. Linguopalatal contact for consonants and vowels in different prosodic positions was compared, using reiterant-speech versions of sentences with a variety of phrasings read by three speakers of American English. Four prosodic domains were considered: the phonological word, the phonological (or intermediate) phrase, the intonational phrase, and the utterance. Domain-initial consonants show more linguopalatal contact than domain-medial or domain-final consonants, at three prosodic levels. Most vowels, on the other hand, show less linguopalatal contact in domain-final syllables compared to domain-initial and domain-medial. As a result, the articulatory difference between segments is greater around a prosodic boundary, increasing the articulatory contrast between consonant and vowels, and prosodic domains are marked at both edges. Furthermore, the consonant initial strengthening is generally cumulative, i.e., the higher the prosodic domain, the more linguopalatal contact the consonant has. However, speakers differed in how many and which levels were distinguished in this way. It is suggested that this initial strengthening could provide an alternative account for previously observed supralaryngeal declination of consonants. Acoustic duration of the consonants is also affected by prosodic position, and this lengthening is cumulative like linguopalatal contact, but the two measures are only weakly correlated.
Measurements of coupled Rayleigh wave propagation in an elastic plate
Authors: Ti Boon Wee , O’Brien William D. , Harris John G.
Published: July 2002

At frequencies where the thickness of an elastic plate is more than a wavelength, the propagation of the two lowest Rayleigh–Lamb modes in an elastic plate can be viewed as the propagation of a Rayleigh surface wave over two weakly coupled, surface-wave waveguides. That is, a Rayleigh wave launched on one surface gradually transfers to the other and then back. It does so in a length we call the beatlength. Measurements of the beatlength for brass plates are reported as a function of frequency and thickness. This phenomenon is readily excited and persists over a wide range of thicknesses and frequencies
Coupled phase theory for sound propagation in emulsions
Authors: Evans J. M. , Attenborough K.
Published: July 2002

The coupled phase approach is extended to model sound propagation in an emulsion of two compressible, thermoviscous liquids. This provides an alternative to scattering theory for modeling sound propagation in emulsions in the low-acoustic radius regime. Predictions of the new theory are compared with predictions of multiple-scattering theory and experimental results for ultrasonic velocity and attenuation in an emulsion. For the particular set of experimental data used here, the coupled phase theory gives predictions close to the scattering theory predictions, and a better prediction of the dependence of the attenuation on volume fraction. A similar difference between the two theoretical approaches has been found in earlier work on coupled phase models for sound propagation in suspensions.
Efferently mediated changes in the quadratic distortion product (f2−f1)
Authors: Chang Kay W. , Norton Susan J.
Published: July 2002

In this study, a preparation was developed which continuously monitored the f2−f1, 2 f1−f2, and 3f1−2 f2 distortion products in guinea pigs, in response to various contralateral and ipsilateral tones and broadband noise. A consistent decline over time in the quadratic distortion product, f2−f1, with continuous ipsilateral stimulation was observed, confirming previous findings by Kirk and Johnstone [Hearing Res. 67, 20–34 (1993)]. Broadband noise applied to the contralateral ear simultaneously increased both the magnitude and the rate of decline. This effect was shown for primaries across all frequencies tested (f2 from 2–16 kHz, f2/f1 ratio of 1.26), though a maximal effect was found for f2 of 4 kHz. Experiments using contralateral tones demonstrated a half-octave shift in the frequency specificity of this effect. A more “immediate” suppression effect on 2 f1−f2 (0.6 dB) was found in animals awakening from anesthesia, though this was even larger for f2−f1 (5.1 dB). Extended ipsilateral stimulation with contralateral noise results in completely diminishing f2−f1 to the noise floor. These findings suggest an adaptive process within the cochlea that may be modulated by efferent stimulation. A model relating the various even- and odd-order distortion products to outer hair cell receptor potentials is presented.
A model of ultrasonic nondestructive testing for internal and subsurface cracks
Authors: Bövik Peter , Boström Anders
Published: July 2002

The scattering of elastic waves in a half-space containing a striplike crack is investigated. As a special case it seems that the crack may be surface breaking. A surface integral equation with the half-space Green tensor is employed. The key point of the method is the expansion of the Green tensor in Fourier representations with the free part of the Green tensor expanded in the crack coordinate system and the half-space part in the half-space coordinate system. The integral equation is discretized by expanding the crack opening displacement in terms of Chebyshew functions having the correct square root behavior along the crack edges. The incident field is emitted from an ultrasonic probe and a recent model for this is employed. The signal response in another (or the same) probe is modeled by a reciprocity argument and the stationary phase approximation is employed to simplify the final answer, which is thus only valid in the far field of the probes (yielding essentially a spherical wave). Numerical results are given and are compared with both other methods and with available experiments.
Simulating the effect of cochlear-implant electrode insertion depth on speech understanding
Authors: Dorman Michael F. , Loizou Philipos C. , Rainey Dawne
Published: July 2002

Normally hearing listeners were presented with vowels, consonants, and sentences for identification through an acoustic simulation of a five-channel cochlear implant with electrodes separated by 4 mm (as in the Ineraid implant). The aim of the experiment was to simulate the effect of depth of electrode insertion on identification accuracy. Insertion depth was simulated by outputing sine waves from each channel of the processor at a frequency determined by the cochlear place of electrodes inserted 22–25 mm into the cochlea. The results indicate that simulated insertion depth had a significant effect on performance. Performance at 22- and 23-mm simulated insertion depths was always poorer than normal, and performance at 25-mm simulated insertion depth was, most generally, the same as normal. It is inferred from these results that, if insertion depth could be unconfounded from other coexisting factors in implant patients, then insertion depth would be found to affect speech identification performance significantly.
Feedback vibration control of a flexible plate at audio frequencies by using a physical state-space approach
Authors: Seto Kazuto , Ren Mingzhang , Doi Fumio
Published: July 2002

A study on feedback control of the vibration of a clamped elastic plate in the audio frequency range is presented in this paper. The study is specified by a discretization method based on an inverse modal analysis approach, through which a new lumped parameter system can be established to represent the dynamics of the low-order modes of the actual structure. With the discrete model the standard linear quadratic optimal control theory can be formulated in physical state space to design a controller, that will be later implemented in experiments to control the real structure. As an illustration, a lumped parameter model with 9DOFs has been created for the clamped plate. It is demonstrated by experiments under both impulse excitation and stationary random excitation that the corresponding nine vibration modes of the plate are quite well controlled with a collocation of two electromagnetic actuators and five sensors.
Validation of a multidimensional distance model for perceptual dissimilarities among musical timbres
Authors: Misdariis Nicolas , Smith Bennett , Presssnitzer Daniel , Susini Patrick , McAdams Stephen
Published: July 2002

Several studies dealing with the perception of musical timbre have found significant correlations between acoustical parameters of sounds and their subjective dimensions. Using the conclusions of some of these studies, a calculation method of the perceptual distance between two sounds has been developed. Initially, four parameters are considered: spectral centroid, irregularity of the spectral envelope, attack time, and degree of variation of the spectral envelope over time. For each of these, a transformation factor between the physical axis and the corresponding subjective dimension is obtained by linear regression. After a normalization of the data, the four coefficients then found are those of a linear combination that gives the final distance values. Since this model is based on numerical results derived from experiments that mostly used synthesized sounds, the application to a database of recorded musical instrument sounds needs a strong validation procedure. This procedure involves the adjustment of the coefficients of the first four parameters as well as the eventual introduction of new ones to attain a perceptually relevant distance between two musical sounds. The progress of this research and the results of the database search engine built on this similarity model will be presented and discussed.
The development of the multibeam echosounder: An historical account
Authors: Vilming Ståle
Published: July 2002

The first paper on narrow-beam echosounding was published in 1960. Since then, the advantages of the principle of multibeam swath bathymetry for seabed mapping has been recognized by many institutions working in the field of area mapping underwater. We intend to review the development the multibeam echosounder has undergone from the ‘‘beginning’’ until the present in order to better understand the challenges facing the field today. It can safely be said that the field of area mapping has diversified into many directions since the 1960s. At that time most of the development was related to the mechanical and electronic system components, whereas present research focuses on: better algorithms for more precise mapping, seabed classification, image processing, acoustical modeling of the backscattering process from seafloor and volume, and high-resolution methods for direction finding of plane waves. Multibeam echosounding thus encompasses many scientific disciplines, and we consider it important to summarize the state of the art in these disciplines as far as they are related to seabed characterization. This could help scientists to better understand the requirements for further research.
Vibratory gyro-sensor using a trident tuning fork resonator with lateral width set in parallel with a rotationary axis
Authors: Tomikawa Yoshiro , Ogasawara Toshiharu , Ishida Norikazu
Published: July 2002

This paper deals with a new type of piezoelectric vibratory gyro-sensor using a trident tuning fork resonator, which is supported laterally at its base portion, the width direction of which is in parallel with a rotationary axis. The vibratory gyro-sensor is an important and attractive device as an angular velocity sensor, especially, in the vehicle stability control (VSC) system schemed for a practical use in the not so far future. Therefore, many researchers have been engaged in development of such a key device in the VSC system. Some types of piezoelectric vibratory gyro-sensors have also been investigated; for example, two types of vibratory gyro-sensors have been studied using a trident tuning fork resonator: one of them was vertically supported at its base portion and the other was flatly supported at the same portion. The gyro-sensor dealt with here is one of such types of gyro-sensors; however, its operation principle is different from theirs. That is, this new gyro-sensor is aimed at being constructed using two-mode coupling of flexural and torsional vibrations in tuning fork arms. In this paper, the structure and operation principle of such a new trident tuning fork resonator gyro-sensor are described, with simulated results of vibrational characteristics for designing the resonator, and moreover, experimental results to confirm its operation principle are shown.
Auditory-visual speech recognition by hearing-impaired subjects: Consonant recognition, sentence recognition, and auditory-visual integration
Authors: Grant Ken W. , Walden Brian E. , Seitz Philip F.
Published: July 2002

Factors leading to variability in auditory-visual (AV) speech recognition include the subject’s ability to extract auditory (A) and visual (V) signal-related cues, the integration of A and V cues, and the use of phonological, syntactic, and semantic context. In this study, measures of A, V, and AV recognition of medial consonants in isolated nonsense syllables and of words in sentences were obtained in a group of 29 hearing-impaired subjects. The test materials were presented in a background of speech-shaped noise at 0-dB signal-to-noise ratio. Most subjects achieved substantial AV benefit for both sets of materials relative to A-alone recognition performance. However, there was considerable variability in AV speech recognition both in terms of the overall recognition score achieved and in the amount of audiovisual gain. To account for this variability, consonant confusions were analyzed in terms of phonetic features to determine the degree of redundancy between A and V sources of information. In addition, a measure of integration ability was derived for each subject using recently developed models of AV integration. The results indicated that (1) AV feature reception was determined primarily by visual place cues and auditory voicing+manner cues, (2) the ability to integrate A and V consonant cues varied significantly across subjects, with better integrators achieving more AV benefit, and (3) significant intra-modality correlations were found between consonant measures and sentence measures, with AV consonant scores accounting for approximately 54% of the variability observed for AV sentence recognition. Integration modeling results suggested that speechreading and AV integration training could be useful for some individuals, potentially providing as much as 26% improvement in AV consonant recognition.
Heterogeneous structure of modes and Kramers–Kronig relationship in anisotropic viscoelastic materials
Authors: Hosten Bernard
Published: July 2002

Composite materials made of fibers and a viscoelastic matrix, exhibit an orthotropic viscoelastic behavior that is described by a tensor with nine independent complex viscoelastic moduli. This tensor makes it possible to compute the velocity and attenuation of heterogeneous or homogeneous modes in any direction. In experiments, the immersion method of a plate shaped sample insonified by plane ultrasonic waves is used to measure this complex tensor. The liquid/solid interface generates heterogeneous quasilongitudinal and quasishear bulk modes that propagate through the plate with velocities and attenuations that depend on the frequency. In a viscoelastic material, velocity and attenuation are linked by the Kramers–Kronig relations. For heterogeneous modes, the attenuation that needs to be used is the projection of the damping vector on the wave vector. This paper shows that these relations limited to a “local” frequency band can be experimentally verified and permit one to link anisotropic velocity and attenuation dispersion of quasilongitudinal and quasishear modes only if their heterogeneous structure is taken into account. The extrapolation of the material properties determined by ultrasonic measurements, towards low frequencies, relies on this feature in combination with a model of the attenuation evolution versus frequency.
Speech intelligibility and localization in a multi-source environment
Authors: Hawley Monica L. , Litovsky Ruth Y. , Colburn H. Steven
Published: July 2002

Natural environments typically contain sound sources other than the source of interest that may interfere with the ability of listeners to extract information about the primary source. Studies of speech intelligibility and localization by normal-hearing listeners in the presence of competing speech are reported on in this work. One, two or three competing sentences [IEEE Trans. Audio Electroacoust. 17(3), 225–246 (1969)] were presented from various locations in the horizontal plane in several spatial configurations relative to a target sentence. Target and competing sentences were spoken by the same male talker and at the same level. All experiments were conducted both in an actual sound field and in a virtual sound field. In the virtual sound field, both binaural and monaural conditions were tested. In the speech intelligibility experiment, there were significant improvements in performance when the target and competing sentences were spatially separated. Performance was similar in the actual sound-field and virtual sound-field binaural listening conditions for speech intelligibility. Although most of these improvements are evident monaurally when using the better ear, binaural listening was necessary for large improvements in some situations. In the localization experiment, target source identification was measured in a seven-alternative absolute identification paradigm with the same competing sentence configurations as for the speech study. Performance in the localization experiment was significantly better in the actual sound-field than in the virtual sound-field binaural listening conditions. Under binaural conditions, localization performance was very good, even in the presence of three competing sentences. Under monaural conditions, performance was much worse. For the localization experiment, there was no significant effect of the number or configuration of the competing sentences tested. For these experiments, the performance in the speech intelligibility experiment was not limited by localization ability.
Identification of resynthesized /hVd/ utterances: Effects of formant contour
Authors: Hillenbrand James M. , Nearey Terrance M.
Published: July 2002

The purpose of this study was to examine the role of formant frequency movements in vowel recognition. Measurements of vowel duration, fundamental frequency, and formant contours were taken from a database of acoustic measurements of 1668 /hVd/ utterances spoken by 45 men, 48 women, and 46 children [Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099–3111 (1995)]. A 300-utterance subset was selected from this database, representing equal numbers of 12 vowels and approximately equal numbers of tokens produced by men, women, and children. Listeners were asked to identify the original, naturally produced signals and two formant-synthesized versions. One set of “original formant” (OF) synthetic signals was generated using the measured formant contours, and a second set of “flat formant” (FF) signals was synthesized with formant frequencies fixed at the values measured at the steadiest portion of the vowel. Results included: (a) the OF synthetic signals were identified with substantially greater accuracy than the FF signals; and (b) the naturally produced signals were identified with greater accuracy than the OF synthetic signals. Pattern recognition results showed that a simple approach to vowel specification based on duration, steady-state F0, and formant frequency measurements at 20% and 80% of vowel duration accounts for much but by no means all of the variation in listeners’ labeling of the three types of stimuli.
Predicting the sound reduction of building elements from material data
Authors: Gerretsen Eddy
Published: July 2002

The airborne and impact sound reduction of building elements are important quantities to compare the acoustic performance of products and to use as input for prediction models for the acoustic performance of buildings. Besides the excising measurement methods, it can be very useful to have also calculation models to predict these quantities for various types of elements from data on the design and materials used. Such models provide a quick and easy way to estimate the effect of changes in an element and to check for anomalies in measurement results. For homogeneous elements a calculation model is given in an annex to EN 12354-1. That model will be discussed and possible extensions to layered, stiffened, or double elements will be presented. For more or less homogeneous elements, various so-called mass-law predictions are in use. Some of these will be discussed in relation to the theoretical mass-law which can be deduced from the mentioned model.
A hybrid method for the vibration analysis of complex structural-acoustic systems
Authors: Langley R. S. , Bremner P.
Published: July 2002

A new method is presented for the analysis of complex dynamic systems which is based on partitioning the system degrees of freedom into a “global” set and a “local” set. The global equations of motion are formulated and solved in a standard deterministic manner, although due account is taken of the presence of the local degrees of freedom via an approach which is analogous to fuzzy structure theory. The local equations of motion are formulated and solved by using statistical energy analysis (SEA) with due account being taken of power input from the global degrees of freedom. The method can be considered to encompass a number of existing analysis techniques and to form a flexible framework within which a number of detailed modeling strategies can be devised. A simple rod system provides an initial application, and it is shown that the method yields very good results from low to high frequency excitation.
Modeling of an electrohydraulic lithotripter with the KZK equation
Authors: Averkiou Michalakis A. , Cleveland Robin O.
Published: July 2002

The acoustic pressure field of an electrohydraulic extracorporeal shock wave lithotripter is modeled with a nonlinear parabolic wave equation (the KZK equation). The model accounts for diffraction, nonlinearity, and thermoviscous absorption. A numerical algorithm for solving the KZK equation in the time domain is used to model sound propagation from the mouth of the ellipsoidal reflector of the lithotripter. Propagation within the reflector is modeled with geometrical acoustics. It is shown that nonlinear distortion within the ellipsoidal reflector can play an important role for certain parameters. Calculated waveforms are compared with waveforms measured in a clinical lithotripter and good agreement is found. It is shown that the spatial location of the maximum negative pressure occurs pre-focally which suggests that the strongest cavitation activity will also be in front of the focus. Propagation of shock waves from a lithotripter with a pressure release reflector is considered and because of nonlinear propagation the focal waveform is not the inverse of the rigid reflector. Results from propagation through tissue are presented; waveforms are similar to those predicted in water except that the higher absorption in the tissue decreases the peak amplitude and lengthens the rise time of the shock.
Accurate estimation of the mean sound pressure level in enclosures
Authors: Schaffner Albert
Published: July 2002

The accurate determination of the mean sound pressure level is the basis for the determination of the sound power of a source in enclosures. The relation between the sound power of the source under investigation and the mean sound pressure level to be measured in the room can be derived either by means of wave theory or statistical room acoustics. It is shown that both models yield the same relation in the limiting case of high frequencies. Taking this relation as a starting point, it is first possible to include the modal behavior into the statistical model which is important in order to extend the validity of the statistical model to the low-frequency range. Second, the correction term for the potential energy stored near the room boundaries, which is known as the Waterhouse correction, is improved by taking into account the absorption characteristic of the room walls. The improved relation gives a higher accuracy for the determination of the mean sound pressure level in enclosures especially in the low-frequency range. Experimental data is given to verify the theoretical results.
Locating animals from their sounds and tomography of the atmosphere: Experimental demonstration
Authors: Spiesberger John L.
Published: July 2002

Calling animals are located using widely distributed receivers, and the sounds from the animals are used to map the sound speed and wind fields by means of tomography. In particular, two Red-Winged Blackbirds Agelaius phoeniceus are correctly located within a meter using recordings from five receivers spread over a 20 by 30 m region. The demonstration hinges on two new developments. First, a new algorithm for blindly estimating the impulse response of the channel is shown capable of estimating the differences in the time of first arrivals at two receivers. Since it is known that the first arrivals travel along nearly straight paths, the difference in time constrains the animal’s location to a hyperboloid, and the animal is located by intersecting hyperboloids from many pairs of receivers. Second, in order to accurately find the intersection point and map the sound speed and wind fields using tomography, a nonlinear equation is solved. The new algorithm for blindly estimating the impulse response of a channel offers a new way for locating sounds and making tomographic maps of the environment without any requirement for a model for the propagation of sound such as is needed for focalization and matched field processing.
The stabilized self-starter
Authors: Collins Michael D.
Published: July 2002

A stability problem is eliminated from the self-starter, which is a parabolic equation technique for generating initial conditions. The stability problem is associated with evanescent modes that correspond to nearly vertical propagation. It causes the solution to break down at certain frequencies for problems involving relatively low attenuation. The error is restricted to relatively short ranges unless the medium is strongly range dependent near the source. The stability problem is eliminated by placing the pole of the smoothing operator in the self-starter away from the eigenvalues of the depth operator.
Speech recognition meets bird song: A comparison of statistics-based and template-based techniques
Authors: Anderson Sven E.
Published: July 2002

Pattern recognition technology that has been developed for recognizing units of human speech can often be adapted for both recognition and analysis of animal vocalizations. This paper discusses two types of speech recognition algorithms, template based and statistics based, with respect to their ease of deployment and potential application to the objective, quantitative analysis of animal vocalizations. Implementations of the two types of algorithms have been compared using a large database of song units recorded from two song bird species. The algorithms exhibit different strengths and weaknesses. The template-based dynamic time-warping algorithm provides quantitative sound comparisons that are directly useful to a researcher, but selection of training materials depends on expert knowledge. The statistics-based hidden Markov model algorithm requires more training data, but usually performs better in noisy environments and with more variable vocalizations. While both algorithms are accurate in restricted domains, recognition performance could be improved if it were based on species-specific features extracted from the acoustic input. [Work supported by NIH 1-F32-MH10525 and ARO DACA88-95-C-0016.]
Native Italian speakers’ perception and production of English vowels
Authors: Flege James Emil , MacKay Ian R. A. , Meador Diane
Published: July 2002

This study examined the production and perception of English vowels by highly experienced native Italian speakers of English. The subjects were selected on the basis of the age at which they arrived in Canada and began to learn English, and how much they continued to use Italian. Vowel production accuracy was assessed through an intelligibility test in which native English-speaking listeners attempted to identify vowels spoken by the native Italian subjects. Vowel perception was assessed using a categorial discrimination test. The later in life the native Italian subjects began to learn English, the less accurately they produced and perceived English vowels. Neither of two groups of early Italian/English bilinguals differed significantly from native speakers of English either for production or perception. This finding is consistent with the hypothesis of the speech learning model [Flege, in Speech Perception and Linguistic Experience: Theoretical and Methodological Issues (York, Timonium, MD, 1995)] that early bilinguals establish new categories for vowels found in the second language (L2). The significant correlation observed to exist between the measures of L2 vowel production and perception is consistent with another hypothesis of the speech learning model, viz., that the accuracy with which L2 vowels are produced is limited by how accurately they are perceived.
Application of waveguide invariants to analysis of spectrograms from shallow water environments that vary in range and azimuth
Authors: D’Spain G. L. , Kuperman W. A.
Published: July 2002

The waveguide invariant summarizes in a single scalar parameter the dispersive propagation characteristics for a given environment. In this paper, an expression is derived for the invariant in shallow water environments where the bottom bathymetry varies with range and azimuth. It then is applied to the interpretation of broadband, single-element spectrograms collected during SWellEx-3, a shallow water acoustics experiment off the coast of San Diego. The unusual behavior of the interference patterns seen in the spectrograms from this experiment during the transmission of a 75–150-Hz pseudo-random noise sequence by a source towed over range-varying bottom bathymetry is well matched by the model predictions.
Voice onset times and burst frequencies of four velar stop consonants in Gujarati
Authors: Rami Manish K. , Kalinowski Joseph , Stuart Andrew , Rastatter Michael P.
Published: July 2002

Voice onset times (VOT) and burst frequencies of two aspirated (i.e., /kh/, /gh/) and two unaspirated (i.e., /k/, /g/) Gujarati velar stop consonants were investigated in an effort to provide characteristic acoustic information. Stop consonants in a monosyllabic vowel–consonant–vowel (VCV) production were obtained from eight native speakers of Gujarati. Differences in mean VOT and burst frequency as a function of voicing and aspiration were examined. A significant voicing by aspiration effect was found for VOT (p=0.026). The two voiced stops, while not significantly different from each other (p=0.278), had significantly shorter VOTs than voiceless stops. The aspirated /kh/ had a significantly longer VOT than the unaspirated /k/ (p=0.0013). With respect to burst frequency, voiced stops had significantly higher burst frequencies than voiceless stops (p=0.002). There was no significant difference between mean burst frequencies of aspirated and unaspirated stops (p=0.058).
Auditory brainstem responses with optimized chirp signals compensating basilar-membrane dispersion
Authors: Dau Torsten , Wegner Oliver , Mellert Volker , Kollmeier Birger
Published: July 2002

This study examines auditory brainstem responses (ABR) elicited by rising frequency chirps. The time course of frequency change for the chirp theoretically produces simultaneous displacement maxima by compensating for travel-time differences along the cochlear partition. This broadband chirp was derived on the basis of a linear cochlea model [de Boer, “Auditory physics. Physical principles in hearing theory I,” Phys. Rep. 62, 87–174 (1980)]. Responses elicited by the broadband chirp show a larger wave-V amplitude than do click-evoked responses for most stimulation levels tested. This result is in contrast to the general hypothesis that the ABR is an electrophysiological event most effectively evoked by the onset or offset of an acoustic stimulus, and unaffected by further stimulation. The use of this rising frequency chirp enables the inclusion of activity from lower frequency regions, whereas with a click, synchrony is decreased in accordance with decreasing traveling velocity in the apical region. The use of a temporally reversed (falling) chirp leads to a further decrease in synchrony as reflected in ABR responses that are smaller than those from a click. These results are compatible with earlier experimental results from recordings of compound action potentials (CAP) [Shore and Nuttall, “High synchrony compound action potentials evoked by rising frequency-swept tonebursts,” J. Acoust. Soc. Am. 78, 1286–1295 (1985)] reflecting activity at the level of the auditory nerve. Since the ABR components considered here presumably reflect neural response from the brainstem, the effect of an optimized synchronization at the peripheral level can also be observed at the brainstem level. The rising chirp may therefore be of clinical use in assessing the integrity of the entire peripheral organ and not just its basal end.