bluuebunny/crossref_metadata_2025 huggingface dataset:
A statistical approach to automatic speech recognition using the atomic speech units constructed from overlapping articulatory features
Authors: Deng Li , Sun Don X.
Published: October 2005

In recent years, the development of a feature-based general statistical framework has been pursued for automatic speech recognition via novel designs of minimal or atomic units of speech, aiming at a parsimonious scheme to share the interword and interphone speech data and at a unified way to account for the context-dependent behaviors in speech. The basic design philosophy has been motivated by the theory of distinctive features and by a new form of phonology which argues for use of multidimensional articulatory structures. In this paper, the most recently developed feature-based recognizer is presented, which is capable of operating on all classes of English sounds. Detailed descriptions of the design considerations for the recognizer and of key aspects of the design process are provided. This process, which is called lexicon ‘‘compilation,’’ consists of three elements (1) establishing a feature-specification system; (2) constructing a probabilistic and fractional temporal overlapping pattern across the features; and (3) mapping from the feature-overlap pattern to a state-transition graph. A standard phonetic classification task from the TIMIT database is used as a test bed to evaluate the performance of the recognizer. The experimental results provide preliminary evidence for the effectiveness of the feature-based approach to speech recognition.
Comparison of sonar discrimination: Dolphin and an artificial neural network
Authors: Au Whitlow W. L.
Published: October 2005

The capability of an echolocating dolphin to discriminate differences in the wall thickness of cylinders (3.81 cm o.d. and 12.7 cm length) was determined by Au and Pawloski [J. Comp. Physiol. A 170, 41–47 (1992)]. The dolphin was required to discriminate a standard target from comparison targets of differing wall thicknesses. Performance varied from 96% to 56% correct depending on the wall thickness of the comparison targets. The 75% correct threshold was determined to be wall thickness differences of −0.23 mm for comparison targets with thinner walls and +0.27 mm for comparison targets with thicker walls than the standard. The dolphin performance was unchanged in the presence of artificial broadband masking noise until the echo-energy-to-noise ratio fell below approximately 15 dB. A counterpropagation artificial neural network was used to examine broadband echo features from the same cylinders. Features of the echoes were determined by passing them through a filter bank of constant-Q filters. Echo features of the standard and each comparison target were analyzed in pairs by a neural network having two output nodes. Twenty echoes per target were used in the training set and 30 additional echoes per target were used in the test set. For the noise free condition, the network performed at a comparable level to the dolphin for Q values between 4 and 5. In the presence of noise, Q values between 7 and 8 were needed before the network could perform at a comparable level to the dolphin for echo-energy-to-noise ratios of 10 and 15 dB. Discrimination cues seem to originate from a shift in the spectra of the thinner comparison targets to lower frequencies and to higher frequencies for the thicker comparison targets.
Stroboscopic hearing as a mechanism for prey discrimination in frequency-modulated bats?
Authors: Feng Albert S. , Condon Curtis J. , White Kenneth R.
Published: October 2005

A hypothesis was proposed that bats employing frequency-modulated (FM) echolocation pulses could utilize dynamic information of a flying insect to discriminate prey on the basis of ‘‘stroboscopic hearing.’’ To test this hypothesis, single unit recordings were made from the inferior colliculus (IC) of the little brown bat, Myotis lucifugus. Response characteristics of IC units to trains of modulated and unmodulated sound pulses were analyzed at various pulse repetition rates that corresponded to a bat’s pulse emission rates during the different stages of its target directed flight. The results show that amplitude modulation (AM) across a train of sound pulses was faithfully encoded in the units’ discharge pattern when the pulse repetition rate was different from the AM frequency. When the AM frequency was integer multiples of the pulse repetition rate, the stimulus amplitude was reduced drastically under these conditions. Consequently, the discharge of an IC unit diminished precipitously, or if there was a phase delay between the pulse onset and the modulating sinusoidal waveform the unit fired to each modulation cycle with more or less the same vigor as if the modulation was absent. These data indicate that the across-pulse amplitude modulation becomes undetectable when the AM frequency is integer multiples of the pulse repetition rate. It is interpreted that FM bats can potentially employ a ‘‘stroboscopic hearing’’ strategy for discriminating insects on the basis of the wing-beat frequency of the prey.
Comments on ‘‘Barrier attenuation in terms of A-weighted sound exposure level’’ [J. Acoust. Soc. Am. 91, 1500–1503 (1992)]
Authors: Lane Sam R.
Published: October 2005

In the subject article it could be made more clear that the decrease in A-weighted sound exposure level is assumed as equivalent to the approximated barrier attenuation at the single frequency of 550 Hz. The comments in this Letter consider the differences between the barrier attenuation at 550 Hz as estimated by the FHWA model, the approximated barrier attenuation per the article, and the attenuation of A-weighted noise level that can be calculated using the FHWA data and methodology. Simpler approximations for barrier attenuation with less error are suggested.
The use of C0,α boundary elements in an improved numerical formulation for three-dimensional acoustic radiation problems
Authors: Rêgo Silva J. J. , Power H. , Wrobel L. C.
Published: October 2005

This paper presents an integral equation formulation for acoustic radiation problems that allows for the use of higher-order boundary elements with C0,α continuity. This formulation, originally proposed by Panich [Usp. Mat. Nauk. 20 (1), 221–226 (1965)], has theoretical proofs of existence and uniqueness of solution for all values of frequency. The computational advantages of the formulation are verified by numerical applications.
Finite amplitude acoustic propagation modeling using the extended angular spectrum method
Authors: Vecchio Christopher J. , Lewin Peter A.
Published: October 2005

The angular spectrum method is a technique for modeling the propagation of acoustic fields between parallel planes. The technique may be used to predict an acoustic pressure field distribution over a plane, based upon a known pressure field contour at a parallel plane. In addition to the modeling of diffractive phenomena, the technique has been extended to include the effects of attenuation, dispersion, refraction, and phase distortion. Recently, the ability to predict the effects of finite amplitude acoustic propagation through nonlinear media has also been incorporated into the model. This paper focuses on the incorporation of the latter effect. The motivation behind this research and the theory upon which the model is based are summarized, and comparisons between experimental data and extended angular spectrum predictions are presented. The experimental results verify the ability of the model to predict nonlinear acoustic phenomena and demonstrate the importance of including nonlinear effects when making field predictions. No other model currently exists that can predict the propagation of wideband acoustic fields produced by sources of arbitrary geometry including all of the above-mentioned propagation effects.
Thermodynamic consideration of the cavitation mechanism in homogeneous liquids
Authors: Endo Harumi
Published: October 2005

The object of this study is to understand the mechanism of the growth of a cavity in homogeneous liquids. The cavitation intensity obtained by Niemczewski [Ultrasonics 18, 107–110 (1980)] was elucidated on the basis of the theory of fluctuations proposed by Landau and Lifshitz [Statistical Physics (Pergamon, Oxford, 1980), 3rd ed.]. It was proved that the cavitation can be realized by both fluctuations of bulk and a vapor bubble, respectively. This conclusion was obtained by the relationship between the tensile strength of liquids and the fluctuations in bulk. The resulting cavitation probability is expressible in terms of both fluctuations probabilities, respectively. Although it is very difficult to distinguish between the nuclei of vapor and gas in real cavitation systems, it is emphasized that the fluctuations in liquids play an important role in real cavitation processes.
Numerical analysis of a gas bubble near a rigid boundary in an oscillatory pressure field
Authors: Sato Kotaro , Tomita Yukio , Shima Akira
Published: October 2005

The behavior of a gas bubble near a rigid boundary in an oscillatory pressure field is numerically investigated by means of two kinds of methods. The boundary integral method is utilized to simulate the bubble profiles at various times, and the image theory is also applied for solving the differential equations describing the nonlinear oscillations and migrations of a spherical gas bubble. Both calculations are performed, assuming that the liquid around a bubble is inviscid, incompressible, and irrotational and that the gas inside the bubble follows a polytropic gas law. The influence of the boundary proximity on the bubble motion is characterized by the bubble migration and the deformation of the bubble shape, especially by the liquid microjet formation. It is found that the period and the amplitude of the bubble oscillation are related not only to the nature of the time-dependent pressure in the liquid but also to the bubble location from a rigid wall. Furthermore, the influence of the boundary proximity on the frequency response curve associated with the bubble oscillation is examined on the supposition that the surrounding pressure oscillates with small amplitude and a rigid boundary is relatively far from a bubble.
Downwind propagation of sound in an atmosphere with a realistic sound-speed profile: A semianalytical ray model
Authors: Salomons Erik M.
Published: October 2005

A ray model is presented for downwind propagation of sound in a layered atmosphere, with a logarithmic or a power profile of the sound speed. The model employs a new method to compute ray paths, which takes advantage of the fact that ray paths are ordered in groups of four. The paths are obtained from an iterative solution of an integral equation. This solution requires a very small computation time, compared with computation times of numerical ray models and wave models. Ground reflections are taken into account by either the plane wave reflection coefficient or the spherical wave reflection coefficient (a pseudoreflection coefficient for a point source above a ground surface). At high frequency both coefficients yield good agreement with numerical solutions of the Helmholtz equation. An empirical reflection coefficient is introduced to obtain good agreement at low frequency. The ray model is used to compute effects of atmospheric turbulence on the received sound spectrum. It is found that these effects are rather small for downwind sound propagation. The ray model is used further to compute the flow of acoustical energy along the different rays through the atmosphere. It is found that much of the energy flows along the highest rays, in particular at high frequency.
A simple 3-D Gaussian beam sound propagation model for shallow water
Authors: Bucker Homer P.
Published: October 2005

A simple 3-D Gaussian beam propagation model has been developed for the calculation of acoustic fields in shallow water where variation of bottom depth in range and bearing has a significant effect. The algorithm traces beams in appropriate directions and determines when there is a close approach of a beam to a receiver. When this happens, there is a coherent contribution to the sound field at the receiver that depends upon the history of the beam and the closeness of approach. Examples are given showing reasonable agreement with exact solutions for a negative gradient shallow water channel and two difficult wedge cases.
Application of a maximum likelihood processor to acoustic backscatter for the estimation of seafloor roughness parameters
Authors: Michalopoulou Zoi-Heleni , Alexandrou Dimitri , de Moustier Christian
Published: October 2005

Maximum likelihood (ML) estimation is used to extract seafloor roughness parameters from records of acoustic backscatter. The method relies on the Helmholtz–Kirchhoff approximation under the assumption of a power-law roughness spectrum and on the statistical modeling of bottom reverberation. The result is a globally optimum, highly automated technique that is a useful tool in the context of seafloor classification via remote acoustic sensing. The general geometry of the Sea Beam bathymetric system is incorporated into the design of the ML processor in order to make it applicable to real acoustic data collected by this system. The processor is initially tested on simulated backscatter data and is shown to be very effective in estimating the seafloor parameters of interest. The simulated data are also used to study the effect of data averaging and normalization in the absence of system calibration information. The same estimation procedure is applied to real data collected over two central North Pacific seamounts, Horizon Guyot and Magellan Rise. The Horizon Guyot results are very close to estimates obtained through a curve-fitting procedure presented by de Moustier and Alexandrou [J. Acoust. Soc. Am. 90, 522–531 (1991)]. In the case of Magellan Rise, discrepancies are observed between the results of ML estimation and curve fitting.
Time domain dynamic response functions of elastically anisotropic solids
Authors: Every A. G. , Kim K. Y.
Published: October 2005

A method is described for calculating the displacement response function tensor for an infinite anisotropic elastic continuum subjected to a concentrated point force with Heaviside step function time dependence, and examples of computed response functions for zinc, diamond, and silicon are provided. Particular attention is given to the singularities of various orders that travel outward from the point of excitation on the wave surface. The commonly occurring forms that these wave arrival singularities take are described, and explanation provided of how they arise. Some of the singularity types mentioned here have not previously been noted in the literature. Computed response functions for silicon and zinc are compared with waveforms measured in these crystals using the capillary fracture technique.
High-temperature pulsed photoacoustic studies of surface waves on solids
Authors: Schindel D. W. , Hutchins D. A. , Smith S. T. , Farahbakhsh B.
Published: October 2005

A noncontact laser system has been designed that employs a pulsed photoacoustic source and an interferometric detector for the measurement of absolute velocity of surface waves. This can be achieved accurately at high temperatures without the need for thermal expansion corrections. Studies have been carried out on polycrystalline aluminum and single-crystal silicon and results have been presented for both at temperatures up to 800 °C. The angular dependence of surface wave velocities for propagation in the (001) plane of silicon has also been investigated, and has confirmed the system’s 0.5% room temperature accuracy.
A finite element method for estimating the effective coupling coefficient of magnetostrictive transducers
Authors: Butler John L. , Moffett Mark B. , Rolt Kenneth D.
Published: October 2005

A simple finite element method for determining the effective coupling coefficient of magnetostrictive transducers that includes the effects of both the mechanical and magnetic structure is presented. The method uses two finite element programs that are separately dedicated to mechanical and magnetic structures. An example based on a Terfenol-D driven barrel stave flextensional transducer is evaluated using the method.
Low-frequency incoherent scattering from Biot’s theory
Authors: Purcell Anthony
Published: October 2005

The low-frequency theory of surface scattering, as suggested by Biot for a nonuniform distribution of bosses, predicts both specular and nonspecular scattering and permits a calculation of the (incoherent) scattering strength. It is found that the scattering strength predicted by this variant of the standard Biot theory is independent of frequency for sufficiently low grazing angles. This is to be compared with the low-frequency limit of perturbation theory that predicts a f4 dependence for all grazing angles. It is a well-known empirical observation that the scattering strength for the seabed is independent of frequency (or weakly dependent on frequency) for low-grazing angles. This leads to the postulate that scattering from the seabed at low-grazing angles may be due to small-height, large-slope roughness elements, such as considered in Biot’s theory of surface scattering.
Method of superposition applied to scattering from a target in shallow water
Authors: Sarkissian Angie
Published: October 2005

An algorithm is developed to compute the field scattered from a target placed in shallow water. The method of superposition is applied where the scattered field is approximated to be equivalent to the field produced by a large number of point sources placed on a surface inside the target. The source strengths are determined by minimizing the least-squares error of the normal velocity on the surface of the target. This algorithm is applicable even when the source or the receiver is close to the target as well as in the case where the target is close to the surface. Scattering computations are made for a cylinder with hemispherical endcaps in an isovelocity fluid with soft boundary conditions on top and rigid boundary conditions on the bottom. They are compared to the scattered field computed by using an algorithm discussed by Ingenito [F. Ingenito, J. Acoust. Soc. Am. 82, 2051–2059 (1987)] for the case when both the source and the receiver are distant from the target and when the target is distant from the surface. Results from both methods agree in the range of applicability of Ingenito’s method.
High-frequency diffraction by nonconvex obstacles
Authors: Sumbatyan Mezhlum A. , Boyev Nickolaj V.
Published: October 2005

The paper is devoted to the development of ray diffraction theory for arbitrary nonconvex smooth obstacles both for the scalar and elastic case. The consideration is restricted to two-dimensional problems. An exact expression for the ray amplitude with an arbitrary number of reflections is derived from repeated Kirchhoff integrals using the stationary phase method. It is shown that the difference between scalar and elastic cases consists of the reflection coefficients that are present for the second case. Some examples are considered as a demonstration of the theory.
A new representation of a scalar wave field diffracted by solid obstacles that satisfies both the wave equation and hard or soft boundary conditions
Authors: Ueda Mitsuhiro
Published: October 2005

A new diffraction principle formulated by assuming a hypothetical observer at a point of interest in the sound field and considering the wave propagation in a space seen by the observer virtually is proposed in this paper. This new approach allows one to grasp a simple concept of diffraction by solid obstacles and to formulate the representation of diffracted waves that satisfies both the wave equation and hard or soft boundary conditions. Thus the diffraction problem for the scalar wave equation is solved in principle by this approach. Heuristic derivation of the new principle of diffraction, followed by the theoretical analysis, is presented and the meaning and limitation of the conventional representations of diffracted waves are analyzed in the light of the new principle.
Localized and propagating modes in acoustical waveguides with variable cross section
Authors: Razavy M.
Published: October 2005

A method of determining the propagating and the localized modes in an acoustic waveguide with continuously varying cross section is studied. For the rectangular and circular waveguides where the area of the cross section is dependent on the distance from the center of the waveguide, the wave equation with Dirichlet (pressure release) boundary condition can be transformed into an infinite set of coupled ordinary differential equations with variable coefficients. This set of differential equations has a first integral which is the flux of the wave and is constant along the length of the waveguide. If the cross section approaches a constant value at the two ends of the waveguide, then there are a finite number of propagating modes plus a number of localized modes. A technique for the numerical integration of the stiff ordinary differential equations resulting from the partial wave projection is discussed and applied to different examples.
Interpretation of biomechanical simulations of normal and chaotic vocal fold oscillations with empirical eigenfunctions
Authors: Berry David A. , Herzel Hanspeter , Titze Ingo R. , Krischer Katharina
Published: October 2005

Empirical orthogonal eigenfunctions are extracted from biomechanical simulations of normal and chaotic vocal fold oscillations. For normal phonation, two dominant empirical eigenfunctions capture the vibration patterns of the folds and exhibit a 1:1 entrainment. The eigenfunctions show some correspondence to theoretical low-order normal modes of a simplified, three-dimensional elastic continuum, and to the normal modes of a linearized two-mass model. The eigenfunctions also facilitate a physical interpretation of energy transfer mechanisms in vocal fold dynamics. Subharmonic regimes and chaotic oscillations are observed during simulations of a lax cover, in which case at least three empirical eigenfunctions are necessary to capture the resulting vocal fold oscillations. These chaotic oscillations might be understood in terms of a desynchronization of a few of the low-order modes, and may be related to mechanisms of creaky voice or vocal fry. Furthermore, some of the empirical eigenfunctions captured during complex oscillations correspond to higher-order normal modes described in earlier theoretical work. The empirical eigenfunctions may also be useful in the design of lower-order models (valid over the range for which the empirical eigenfunctions remain more or less constant), and may help facilitate bifurcation analyses of the biomechanical simulation.
A note on using the fast field program
Authors: Li Y. L. , White Michael J.
Published: October 2005

The fast field program is a numerically efficient algorithm for computation of the sound pressure due to a time harmonic point source above a general boundary in a layered medium. In this method, the inverse Hankel transform for obtaining the pressure is approximated by two Fourier integrals. One of the Fourier integrals was treated as the incoming wave term and neglected in the computation of sound pressure. Actually, no one has theoretically proven that one of the Fourier integrals can be neglected. In this paper, it is shown that the neglected integral is necessary for the computation of low-frequency sound pressure when a pressure-release boundary is involved.
A computational approach to analyzing sentential speech perception: Phoneme-to-phoneme stimulus–response alignment
Authors: Bernstein Lynne E. , Demorest Marilyn E. , Eberhardt Silvio P.
Published: October 2005

A solution to the following problem is presented: Obtain a principled approach to studying error patterns in sentence-length responses obtained from subjects who were instructed to simply report what a talker had said. The solution is a sequence comparator that performs phoneme-to-phoneme alignment on transcribed stimulus and response sentences. Data for developing and testing the sequence comparator were obtained from 139 normal-hearing subjects who lipread (speechread) 100 sentences and from 15 different subjects who identified nonsense syllables by lipreading. Development of the sequence comparator involved testing two different costs metrics (visemes versus Euclidean distances) and two related comparison algorithms. After alignments with face validity were achieved, a validation experiment was conducted for which measures from random versus true stimulus–response sentence pairs were compared. Measures of phonemes correct and substitution uncertainty were found to be sensitive to the nature of the sentence pairs. In particular, correct phoneme matches were extremely rare in random pairings in comparison with true pairs. Also, an information-theoretic measure of uncertainty for substitutions in true versus random pairings showed that uncertainty was always higher for random than for true pairs.
A measure of the reasonableness of equal-tempered musical scales
Authors: Krantz Richard J. , Douthett Jack
Published: October 2005

Using three criteria a desirability function is developed which allows comparison of the reasonableness of equal-tempered musical scales to approximate just musical intervals. Unlike most other measurements, this scale is not dominated by very fine octave divisions. This feature allows for comparison of systems with few divisions to the octave with those with many divisions to the octave. Based on our measure, an equal-tempered scale which must best represent the pure fifth requires 12, 41, or 53 notes to the octave. If the major third is to be well represented, equal-tempered scales of 28 or 59 notes are required. Best representation of the minor third occurs for a 19-note equal-tempered scale. These results are shown to be in accordance with previously cited continued fraction results and other published evaluation criteria. The method is generalized to assess the reasonableness of equal-tempered scales to approximate multiple just intervals simultaneously as well as to account for numerical weighting of intervals. Our results show that an equal-tempered scale required to approximate the pure fifth, major third, and minor third equally requires 12, 19, 34, or 53 notes. This result is contrary to previously cited results in which 34 notes to the octave is relegated to a relatively minor role.
On measures to increase sound-field diffuseness and the applicability of diffuse-field theory
Authors: Hodgson Murray
Published: October 2005

This letter discusses the definition of a diffuse sound field, two measures (diffuse surface reflection and volume scatterers) proposed to increase sound field diffuseness, and the applicability of diffuse-field theory. It is shown that the two proposed measures increase diffuseness, and the applicability of diffuse-field theory, with respect to sound decay/reverberation time. However, they decrease diffuseness, and the applicability of diffuse-field theory, with respect to steady-state sound-pressure level. The implications of these results for the definition of a diffuse sound field are discussed.
Successful ray modeling of acoustic multipaths over a 3000-km section in the Pacific
Authors: Spiesberger John L. , Terray Eugene , Prada Ken
Published: October 2005

A new ray model is compared with tomographic data from basin-scale transmissions in the northeast Pacific (250 Hz, 0.016-ms resolution, ∼3000 km). Model calculations resemble the arrival pattern of the acoustic multipaths quite well. To date, this is the longest distance in the ocean over which ray theory has been shown to accurately predict the acoustic impulse response of the ocean. The new ray model confirms previous analysis that basin-scale tomography is feasible and that the international algorithm for the speed of sound in seawater is too fast. However, the new ray model looks much more like the data than the previous ray model because the new model has a more realistic bottom and a more realistic sound-speed field. At 3000 km, there is no evidence that ray theory suffers from any lack of predictability due to chaotic behavior in this particular experiment. The new model is suitable for automating the identification of acoustic multipaths over basin scales.
Fundamental frequency and perceived prominence of accented syllables. II. Nonfinal accents
Authors: Terken Jacques
Published: October 2005

An experiment is described addressing the question of whether two accented syllables in a phrase should have equal pitch maxima in order to be perceived as equally prominent, or whether the second accented syllable should have lower pitch. The latter alternative was found to apply to the last accented syllable in an utterance by Terken [‘‘Fundamental frequency and perceived prominence of accented syllables,’’ J. Acoust. Soc. Am. 89, 1768–1776 (1991)]. The current results show that the earlier findings also apply to nonfinal accented syllables, thereby ruling out an explanation in terms of final lowering. The results are discussed in relation to listeners’ expectation about the application of downstep.
A numerically stable global matrix method for cylindrically layered shells excited by ring forces
Authors: Ricks David C. , Schmidt Henrik
Published: October 2005

This paper defines a numerically stable method for modeling cylindrical shells that can have multiple viscoelastic layers and external compliant coatings. The method is numerically stable over a wide range of axial wavenumbers and circumferential orders because it uses a ‘‘global matrix’’ approach with appropriately defined coefficients. The excitations used here are time-harmonic ring forces that can push on the shell in the radial, circumferential, and axial directions. The ring forces can have a linear phase shift around the circumference of the shell, so helical waves can be excited and studied for any circumferential order. Analytically, the order can be complex, although the software is presently implemented for real orders. The method is verified by modeling a thin cylindrical shell surrounded by fluid. To provide a very demanding test of the numerical stability, the drive point response of the shell is computed. This computation demonstrates the numerical stability of the method over a wide range of axial wavenumbers and circumferential orders.
A new tool for predicting rapidly and rigorously the radiation efficiency of plate-like structures
Authors: Atalla Noureddine , Nicolas Jean
Published: October 2005

The objectives of this paper are twofold. Firstly, to present a comparison of several models used to evaluate the radiation efficiency of plate-like radiators. The models compared ranged from very simple ones based on modal average expressions, to refined calculations of the radiation impedance matrix with cross modal coupling. It will be seen in particular that simple models, such as Ver and Holmer’s model, give useful guidelines especially for broadband excitations, spatially distributed forces, and thick plates. Expensive methods, such as the far-field approach and BEM are normally used when the hypothesis made in simple models are violated (such as with thin plates and situations where cross modal coupling is important). Secondly, to present a new alternative approach allowing a quick and rigorous evaluation of the radiation efficiency of plate like radiators. This new approach, based on a Taylor’s expansion of the Green’s function, has several advantages over the classical approaches which will be discussed in the paper. This approach represents a step towards answering the accuracy versus computation time problematic currently brought up by some engineers.
Constraint filtered-x and filtered-u least-mean-square algorithms for the active control of noise in ducts
Authors: Kim In-Soo , Na Hee-Seung , Kim Kwang-Joon , Park Youngjin
Published: October 2005

In the active control of noise in ducts, it is common practice to locate an error microphone far from the control source to avoid the near-field effects by evanescent waves. Such a distance between the control source and the error microphone makes a certain level of time delay inevitable and, hence, may yield undesirable effects on the convergence properties of control algorithms such as filtered-x and filtered-u least-mean-square (LMS). This paper discusses the dependence of the convergence rate on the acoustic error path in these popular algorithms and introduces new algorithms ‘‘constraint filtered-x and constraint filtered-u LMS,’’ which increase the convergence region regardless of the time delay in the acoustic error path. In the algorithms, coefficients of the controller are adapted using modified residuals that are defined in such a way that the control process become stationary. Performances of the new LMS algorithms are presented in comparison with those by the conventional algorithms based on computer simulations.
Constrained optimization of active noise control systems in enclosures
Authors: Yang T. C. , Tseng C. H. , Ling S. F.
Published: October 2005

An effective software design tool is proposed for solving active noise control problems associated with constraints in which the complex strength and location of the secondary source of an active noise control system in an enclosed space are simultaneously optimized. The boundary element method is adopted to evaluate the sound field in enclosures. Furthermore, the boundary used could be of pressure, velocity, or impedance; in addition, the primary source may be at an arbitrary position. An optimizer based on sequential quadratic programming is selected for its accuracy, efficiency, and reliability. Bounds for design variables and proper constraints on the sound field and secondary source can be specified as required. The powerfulness of the proposed tool is demonstrated by optimizing an active control system for an enclosure. For a rectangular cavity, the optimal location of the secondary source is confirmed by observed simulations as always forming a dipole with the primary source situated at off-resonance excitations and subsequently approaching a mirror image position of the primary source at resonance excitations. The optimal location of the controller is found to change with varied upper bounds of the strength of the secondary source. These findings show a discrepancy from those reported in previous researches based on an unconstrained formulation. Sensitivity analysis at the optimum is also included to provide information of practical concern for implementing optimized active noise control systems.
Robust sequential MIPA array processor with dependent sampling
Authors: Ketel Mohammed , Kurz Ludwik
Published: October 2005

The problem of detecting small stochastic signals in poorly specified noise environments, often encountered in underwater acoustics, is considered. The array processing detectors are designed to exhibit a near-optimum performance for nominal distributions and maintain high efficiency to changing noise environments by adapting their optimum nonlinearities using an m-interval polynomial approximation (MIPA) of them. Sequential operation of the detectors is used to reduce the average time to decision. Furthermore, the assumption of independent samples is relaxed while temporal and spatial noise dependences are considered separately. A formulation is given that predicts the thresholds under the time-dependent sampling in order to maintain the same error probabilities as in the independent sampling case. For the space-dependent noise process, the thresholds remain constant for fixed error probabilities. Instead, the cross-scores need to be adjusted to compensate for space dependence. The performance of these detectors is compared to that of the corresponding independent noise. It is concluded that improved performance is achieved with a slight increase in structural complexity.
Effects of refraction on synthetic aperture sonar imaging
Authors: Rolt Kenneth D. , Schmidt Henrik
Published: October 2005

Synthetic aperture sonar (SAS) imaging in a refracting environment requires that refraction be accounted for in the image processing to avoid blurring of the images. In deep water, e.g., this requires some knowledge of the refraction sound-speed profile c(z). Ideally a ‘‘local’’ c(z) profile could be measured, but the measurement may only be valid for one platform position (not necessarily valid across the full synthetic aperture length) and at that one particular time. Historical data for c(z) may also be used for the region being imaged, but these data will not necessarily match the actual c(z) present during sonar data collection. This paper shows that SAS imagery in a refracting environment requires knowledge of the refraction for successful imaging, and that the refraction profile c(z) is a necessary part of matched-filter image processing. For a deep water example where the exact c(z) profile is unknown, the use of historical c(z) data and reduced Doppler bandwidth, reduced-resolution processing leads to useful sharp images that suffer only from incorrect bottom registration.
Transfer characteristic of the inner hair cell synapse: Steady-state analysis
Authors: Zagaeski Mark , Cody Alan R. , Russell Ian J. , Mountain David C.
Published: October 2005

Inner hair cells (IHC) transduce mechanical to electrical energy in the mammalian cochlea producing a receptor potential which is a rectified, filtered representation of the mechanical input to the hair cell. The IHC synapse transfers the information in the receptor potential to the fibers of the auditory nerve (whose cell bodies form the spiral ganglion) where it is encoded as a pattern of action potentials. That transfer was investigated by comparing the steady-state responses in pre- and post-synaptic cells. A nonlinear transfer characteristic describing the synapse was generated by plotting the spiral ganglion cell firing rate as a function of the IHC receptor potential. For each spiral ganglion unit, the operating range maps onto a different portion of the nonlinear inner hair cell operating range, dependent on the neural unit’s threshold. Units whose rate-level functions exhibit similar slopes but different thresholds can have dramatically differing sensitivities to changes in the IHC potential. This threshold-dependent mapping supports the concept that information may be distributed amongst nerve fibers according to their threshold.
Measuring the human head-related transfer functions: A novel method for the construction and calibration of a miniature ‘‘in-ear’’ recording system
Authors: Pralong Danièle , Carlile Simon
Published: October 2005

A method for the construction of a small ‘‘in-ear’’ system for recording the human-free field-to-eardrum and headphone-to-eardrum transfer functions is described. Customized in-ear inserts were obtained by a simple ear printing and electroplating method, resulting in a thin (<0.25 mm) outer shell that minimized obstruction of the entrance at the ear canal. The insert can be used to position a microphone probe tube deep within the auditory canal. The effects of this recording system on the sound field in the ear canal were calibrated using a model head equipped with a second internal microphone close to the eardrum. Transfer functions were recorded for 343 different stimulus locations in free space and for a headphone sound source. For the free-field stimuli the presence of the recording system resulted in a small attenuation with maximum effects around 3.5 and 12.5 kHz (−1.5 and −2.0 dB, respectively). Passing the data through an auditory filter model reduced the averaged attenuation to less than −1.4 dB. Phase was undistorted up to 2.5 kHz. These results suggests that the perturbations produced by the insert are unlikely to be perceptually relevant.
The location-dependent nature of perceptually salient features of the human head-related transfer functions
Authors: Carlile Simon , Pralong Danièle
Published: October 2005

The human head-related transfer function (HRTF) has been recorded binaurally from eight subjects using an ‘‘in-ear’’ recording system, for 343 stimulus locations around the head. There are a number of systematic changes in the HRTF as a function of horizontal location and elevation, on and off the median plane, that could be used as cues to sound location. To identify which components of the HRTF might provide perceptually salient cues to sound location, the HRTFs were transformed using an auditory filter model which accounts for the frequency dependence of auditory sensitivity and the frequency and level-dependent characteristics of the auditory filters. These transformations indicated a systematic variation in the frequency of the peak excitation as a function of the horizontal location of a broad band stimulus. Furthermore, there were differences in the frequency range over which elevation-dependent changes in the excitation patterns varied as a function of the vertical meridian. Interaural level differences were also estimated using the excitation patterns. The across frequency pattern of ILDs were roughly symmetrical about the interaural axis, although there were substantial differences between each ear in the magnitude of the ILDs generated for ipsilateral sounds locations.
Experiments related to the detection of a tone masked by another tone
Authors: Richards Virginia M.
Published: October 2005

Five experiments were completed in an effort to determine which cues allow the detection of a tone in the presence of another tone of a different frequency. Four cues associated with the added tone were examined (a) changes in overall level, (b) changes in envelope modulation (beats), (c) changes in pitch, and (d) changes in phase (frequency) modulation. Detection thresholds were measured using a two-interval, forced choice paradigm, and for maskers of 400 and 3000 Hz. The data suggest that the presence of beats acts as a cue for detection when the signal and masker frequencies are within ten percent of one another. For larger frequency separations the data did not support any of the detection models examined [(a)–(d) above]. Based on limited direct observations and on the failure of the single-channel models tested, it appears that the detection of a tone in the presence of another tone depends on the detection of changes in the pattern of intensity and/or the pattern of temporal synchrony across frequency.
Detection and discrimination of amplitude-modulated signals by macaque monkeys
Authors: Moody David B.
Published: October 2005

Behavioral thresholds were determined from macaque monkeys for detection of amplitude modulation (AM) and for discrimination of increases in AM frequency. A positive-reinforcement, go/no-go behavioral paradigm was used with a two-down/one-up psychophysical procedure for all determinations. In the first set of experiments, temporal modulation transfer functions (TMTFs) were determined at two different stimulus levels, for both gated and continuous noise carriers. In the second set of experiments, difference limens for AM frequency were determined using modulated noise and pure-tone carrier signals. TMTFs for gated carriers exhibited a bandpasslike characteristic as has been previously shown. The high-frequency cutoff determined from the average of the gated-carrier TMTFs obtained at 58 dB SPL was 198 Hz, higher than that shown with wideband carriers for other species. With a continuous carrier, there was less of a low-frequency cutoff in the TMTF, again corresponding to previous results. Unlike previous results, however, the present TMTFs showed an effect of stimulus level. Difference limens for AM frequency increased as a function of standard modulation frequency and then leveled off or decreased slightly with further increases in AM frequency. Taken together, the AM discrimination data, coupled with the high cutoff frequency of the TMTF, suggest that detection and discrimination of rapid temporal events may play an important role in the acoustic world of primates.
Effects of harmonicity, modulator phase, and number of masker components on modulation discrimination interference
Authors: Moore Brian C. J. , Shailer Michael J.
Published: October 2005

The discrimination of the depth of amplitude modulation (AM) of a signal carrier frequency can be disrupted by the presence of other modulated carriers, an effect called modulation discrimination interference (MDI). MDI may be caused partly by perceptual grouping of the signal and masker carriers. If this is so, then MDI may be greater when the masker carriers are harmonically related to the signal carrier (promoting perceptual fusion) than when they are nonharmonically related. These experiments examine whether this is the case. They also examine the effect of the number of masker carriers, the proximity of the masker carriers to the signal carrier frequency, and the relative modulator phase of the masker and signal. Thresholds for discriminating the depth of 10-Hz AM of a 1000-Hz signal carrier were measured in the presence of a masker that consisted of two to six carrier frequencies, with an equal number of carriers above and below the signal carrier frequency. The masker was either unmodulated or amplitude modulated with a modulation index of 0.5 and a frequency of 10 Hz, and the masker carrier frequencies were either harmonically related to the signal carrier frequency or were nonharmonically related. There was little difference in the size of the interference effect between the harmonic and inharmonic maskers. There was also little effect of the number of masker carriers. For the maskers with harmonically spaced carriers, the interference effect was slightly larger when all carriers were modulated in phase with the signal carrier than when the modulator phase was shifted by 90° for each successive carrier. The results suggest that harmonicity does not play an important role in MDI.
A comparison of measured and predicted broadband acoustic arrival patterns in travel time–depth coordinates at 1000-km range
Authors: Worcester Peter F. , Cornuelle Bruce D. , Hildebrand John A. , Hodgkiss William S. , Duda Timothy F. , Boyd Janice , Howe Bruce M. , Mercer James A. , Spindel Robert C.
Published: October 2005

Broadband acoustic signals were transmitted from a moored 250-Hz source to a 3-km-long vertical line array of hydrophones 1000 km distant in the eastern North Pacific Ocean during July 1989. The sound-speed field along the great circle path connecting the source and receiver was measured directly by nearly 300 expendable bathythermograph (XBT), conductivity-temperature-depth (CTD), and air-launched expendable bathythermograph (AXBT) casts while the transmissions were in progress. This experiment is unique in combining a vertical receiving array that extends over much of the water column, extensive concurrent environmental measurements, and broadband signals designed to measure acoustic travel times with 1-ms precision. The time-mean travel times of the early raylike arrivals, which are evident as wave fronts sweeping across the receiving array, and the time-mean of the times at which the acoustic reception ends (the final cutoffs) for hydrophones near the sound channel axis, are consistent with ray predictions based on the direct measurements of temperature and salinity, within measurement uncertainty. The comparisons show that subinertial oceanic variability with horizontal wavelengths shorter than 50 km, which is not resolved by the direct measurements, significantly (25 ms peak-to-peak) affects the time-mean ray travel times. The final cutoffs occur significantly later than predicted using ray theory for hydrophones more than 100–200 m off the sound channel axis. Nongeometric effects, such as diffraction at caustics, partially account for this observation.
Overcoming ray chaos
Authors: Collins Michael D. , Kuperman W. A.
Published: October 2005

Computational difficulties associated with chaos may be overcome by solving eigenray problems with boundary-value techniques rather than the initial-value technique of shooting. The nonlinear differential equation for the ray paths is therefore somewhat analogous to stiff linear differential equations. The boundary-value problem is solved using the bending method and simulated annealing. Numerical results are presented for problems that are ill-posed as initial-value problems but well posed as boundary-value problems.