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Journal of the Acoustical Society of America

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Jun 1995

Volume 97, Issue 6, pp. 3441-3931

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On automated language acquisition

Allen Gorin

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3441-3461 (1995); (21 pages)

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The purpose of this paper is to review our investigation into devices which automatically acquire spoken language. The principles and mechanisms underlying this research are described and then experimental evaluations for several tasks are reported, involving both spoken and keyboard input. The generic mechanism in these experiments is an information‐theoretic connectionist network embedded in a feedback control system.
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43.10.Ln Surveys and tutorial papers relating to acoustics research; tutorial papers on applied acoustics
43.72.Ne Automatic speech recognition systems

Acoustic multipole logging in transversely isotropic two‐phase medium

Bixing Zhang, Kexie Wang, and Qingde Dong

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3462-3472 (1995); (11 pages)

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An anisotropic reservoir is simulated by a transversely isotropic two‐phase medium, and the acoustic field excited by a multipole source in a fluid‐filled borehole is investigated. The medium outside the borehole is modeled following Biot’s and homogenization theories. Similar work has only be seen in Schmitt’s [J. Acoust. Soc. Am. 86, 2397–2421 (1989)] study, but he focused his attention on the behavior of the mode waves. In this article, not only are the dispersion and excitation of the mode waves analyzed thoroughly, but the propagation mechanism of the critical refracted P and S waves corresponding to the multipole source branch cut integrations is also investigated for the first time. The effect of the vertical and horizontal permeabilities, porosity, radius, stiffnesses, and other factors on the acoustic field is analyzed.
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43.20.Bi Mathematical theory of wave propagation
43.20.Fn Scattering of acoustic waves
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves

Generalized boundary conditions for scalar fields

Thomas B. A. Senior

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3473-3477 (1995); (5 pages)

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Generalized boundary conditions are characterized by the presence of field derivatives higher than the first, and are designed to improve the simulation of the material properties of a surface. A rather general class of conditions is described and the constraints necessary to ensure a unique solution of the boundary‐value problem are then derived. In the case of a planar surface, each boundary condition implies a pair of related transition conditions describing membranes. These are complementary in the sense of Babinet’s principle, and the connection between the total fields in the two problems is shown.
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43.20.Fn Scattering of acoustic waves

Connection between the dynamic bulk modulus of air in a porous medium and the specific surface

Pavel Lemarinier, Michel Henry, Jean‐F. Allard, Jean L. Bonardet, and Antoine Gedeon

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3478-3482 (1995); (5 pages) | Cited 1 time

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A model for the prediction of the frequency dependence of the dynamic bulk modulus of air in a porous medium with one parameter, the thermal characteristic dimension Λ′, was proposed previously by one of the authors. This parameter depends only on the porosity and the area of the surface of porous frame in contact with the air in the material. This area can be evaluated with the standard Brunauer, Emmett, and Teller (BET) method, from krypton adsorption by the frame at liquid–nitrogen temperature. Comparisons between acoustically measured bulk moduli and predictions obtained with values of Λ′ evaluated with the BET method are presented. The BET results provide reasonable agreement with acoustic measurements of thermal dimensions and dynamic bulk moduli.
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43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Jr Velocity and attenuation of elastic and poroelastic waves

Borehole wave propagation in three dimensions

Ningya Cheng, C. H. Cheng, and M. N. Toksöz

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3483-3493 (1995); (11 pages) | Cited 11 times

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In this paper the three‐dimensional finite difference method is used to simulate borehole wave propagations in an isotropic as well as an anisotropic formation. The finite difference results agree excellently with the analytic solutions of a point force source in the transversely isotropic medium. The finite difference synthetics are also in very good agreement with the discrete wave‐number solutions for fluid‐filled borehole wave propagation. The finite difference synthetics are compared with ultrasonic lab measurements in a scaled borehole model. The borehole is drilled along the X axis in an orthorhombic phenolite solid. Both monopole and dipole logs agree well. The observations of the shear wave splitting in the dipole logs are confirmed by the finite difference simulations. The 3‐D finite difference method is applied to the fluid‐filled borehole wave propagation in the tilted isotropic formation and in the orthorhombic phenolite formation. In a borehole drilled along the Z axis in a phenolite formation, the monopole log shows the P wave traveling with velocity vzz. There are no shear‐pseudo‐Rayleigh wave arrivals. The dipole log is dominated by the single slow flexural mode. In a borehole drilled along the Y axis in a phenolite formation, the monopole log shows the P wave traveling with velocity vyy. There are shear‐pseudo‐Rayleigh wave arrivals shown on the monopole seismograms between P and Stoneley waves due to the shear wave anisotropy. The anisotropy also causes the shear wave splitting in the dipole log. The two shear wave arrivals correspond to the fast and the slow flexural modes.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Jr Velocity and attenuation of elastic and poroelastic waves

A note on the effect of wall compliance on lowest‐order mode propagation in fluid‐filled/submerged impedance tubes

V. Easwaran and M. L. Munjal

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3494-3501 (1995); (8 pages) | Cited 1 time

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Wave propagation in fluid‐filled/submerged tubes is of interest in large HVAC ducts, and also in understanding and interpreting the experimental results obtained from fluid‐filled impedance tubes. Based on the closed form analytical solution of the coupled wave equations, an eigenequation, which is the determinant of an 8×8 matrix, is derived and solved to obtain the axial wave number of the lowest‐order longitudinal modes for cylindrical ducts of various diameter and wall thickness. The dispersion behavior of the wave motion is analyzed. It is observed that the larger the diameter of the duct and/or the smaller its wall thickness, the more flexible the impedance tube leading to more coupling between the waves in the elastic media. Also, it is shown that the wave motion in water‐filled ducts submerged in water exhibits anomalous dispersion behavior. The axial attenuation characteristics of plane waves along water‐filled tubes submerged in water or air are also investigated. Finally, investigations on the sound intensity level difference characteristics of the wall of the air‐filled tubes are reported.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Tb Interaction of vibrating structures with surrounding medium
43.20.Hq Velocity and attenuation of acoustic waves

Propagation in fluids inside thick viscoelastic cylinders

J. E. Greenspon and E. G. Singer

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3502-3509 (1995); (8 pages) | Cited 5 times

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This paper presents a study of wave propagation in a fluid contained inside a thick viscoelastic cylinder, which is used as a liner inside a rigid pipe to attenuate acoustic waves inside the fluid. Both the axially symmetric (axisymmetric) and nonaxially symmetric (asymmetric) waves are treated. A representative group of pipe sizes was chosen to illustrate the general behavior, and a viscoelastic material was chosen for which the viscoelastic constants have been measured. Velocity and attenuation plots are presented for pipes of various sizes with liners of different thicknesses.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Hq Velocity and attenuation of acoustic waves
43.35.Mr Acoustics of viscoelastic materials

The nonlinear pressure field of plane, rectangular apertures: Experimental and theoretical results

Andrew C. Baker, Aina M. Berg, Ali Sahin, and Jacqueline Naze Tjøtta

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3510-3517 (1995); (8 pages) | Cited 9 times

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The nonlinear sound pressure field from finite amplitude, plane, rectangular apertures, is considered. Experimental measurements on a 2.25‐MHz transducer are presented for various source geometries and excitation levels. These results are compared with simulations based on the transformed beam equation, using a new algorithm which generalizes the Bergen code to treat the case of nonaxisymmetric on‐source boundary conditions.
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43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

Application of a κ‐ϵ turbulence model to the prediction of noise for simple and coaxial free jets

W. Béchara, P. Lafon, C. Bailly, and S. M. Candel

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3518-3531 (1995); (14 pages) | Cited 2 times

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A numerical solution of a κ‐ϵ turbulence model is used to provide local and statistical properties throughout simple and coaxial round jets. These are inserted into predictive formulas for jet noise based on Lighthill’s theory: Ribner’s formalism postulates locally isotropic turbulence superposed on mean flow; Goldstein and Rosenbaum’s formalism generalizes this to accommodate the more realistic assumption of axisymmetry. Numerical jet noise predictions via the Ribner/κ‐ϵ model (designated Ra) and the Goldstein/κ‐ϵ model (designated Ga), and some variants, are compared with experiment. Only a single empirical factor is used. The Ga model, with its threefold longer axial scale, shows closer agreement with experiment than the Ra model. The predictive capacity of the Ga model is demonstrated by further calculations for coaxial jets. The results confirm the experimental observation of a minimum of acoustic radiation when the outer flow has 0.4 the velocity of the inner flow. An advantage of the κ‐ϵ method is that it yields information on the spatial and spectral distribution of the acoustic sources.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.50.Nm Aerodynamic and jet noise

A numerical study of seafloor scattering

Johan O. A. Robertsson and Alan Levander

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3532-3546 (1995); (15 pages) | Cited 2 times

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The processes which result in backscattered acoustic energy from the seafloor are of primary interest for interpreting sonar signals measured in the deep ocean basins. This complex problem can be approached from a realistic perspective with the employment of modern high‐resolution seafloor bathymetry measurements and viscoelastic wave simulation techniques capable of modeling highly heterogeneous anelastic media. A numerical study of low‐frequency (100–200 Hz) backscattering processes from rough seafloor models is presented and several scattering hypotheses are proposed. In particular the effects that low‐Q sediments have on the backscattered field from a rough seafloor and the effects that perturbations in the different material properties have on the backscattered energy are investigated. The principal conclusions reached are that anelastic sediments on the seafloor can have a significant impact on the backscattered field from low grazing angle scattering experiments, and that small perturbations in the compressional sediment velocity can dramatically alter the backscattered field.
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43.30.Hw Rough interface scattering
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

Deterministic reverberation from ocean ridges

Nicholas C. Makris, Lilimar Z. Avelino, and Richard Menis

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3547-3574 (1995); (28 pages) | Cited 17 times

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The deterministic relationship between low‐frequency reverberation and detailed geomorphology is documented for wide‐area insonifications of the western Mid‐Atlantic Ridge. Charted reverberation registers precisely with extended ridges and has a high correlation with negative transmission loss, confirming previous analysis with lower resolution data [J. Acoust. Soc. Am. 95, 1865–1881 (1993)]. For a given ridge, prominent returns come from steep escarpments and cliffs that face the bistatic source and receiving arrays. This was hypothesized in the above reference, but could not be proven without the higher resolution waveforms and more sophisticated charting procedures of the present analysis. Monostatic and bistatic returns from the same lineated ridge at 1/2, 11/2, and 21/2 convergence‐zone ranges are used to thoroughly document the registration with steep scarps. A decrease in resolution of the scattering site is also documented for increasing measurement range. Ambiguity from the horizontal receiving array is resolved by two independent methods that show close agreement for prominent returns. The first is an environmental symmetry breaking (ESB) technique that requires detailed knowledge of bathymetry to be incorporated into a range‐dependent propagation model. The second is a global inversion of reverberation charts obtained from differing receiving‐array locations and orientations. The global inversion requires no a priori environmental information and has not been previously applied to field data.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Vh Active sonar systems
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

Arrival‐time perturbations of broadband tomographic signals due to sound‐speed disturbances. A wave‐theoretic approach

G. A. Athanassoulis and E. K. Skarsoulis

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3575-3588 (1995); (14 pages) | Cited 9 times

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The problem of arrival‐time perturbations due to perturbations of the sound‐speed profile is studied on the basis of full‐wave equation modeling of the direct problem. Arrival times are analytically modeled as the time instants corresponding to the significant maxima (peaks) of the arrival pattern, in full agreement with measurement practice. In this framework the identification of actual (measured) arrivals as ray or modal ones is not required. An elegant perturbation formula is derived for the arrival times, containing the background arrival times, time derivatives of quantities associated with the background field, and also the functional derivative of the background field with respect to the sound‐speed profile. This formula is of a system‐theoretic nature and can be applied to any kind of environment, either range‐dependent or range‐independent. The restriction to the range‐independent environment permits further elaboration of the perturbation formula since, in this case, the functional derivative of the acoustic‐channel transfer function can be analytically expressed, e.g., in terms of normal modes. The performance of the proposed approach is demonstrated by studying two test cases: the linear‐ and the canonical‐profile waveguide. The agreement between actual arrival times, obtained by numerically solving the direct propagation problem, and the arrival times predicted by means of the perturbation formula is very satisfactory. Since the proposed scheme can predict arrival‐time perturbations even in cases that the arrival times cannot be identified as ray or modal ones, it is expected to be helpful in extending the applicability of ocean acoustic tomography.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Bp Normal mode propagation of sound in water
43.20.Bi Mathematical theory of wave propagation

Inversion for geometric and geoacoustic parameters in shallow water: Experimental results

Donald F. Gingras and Peter Gerstoft

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3589-3598 (1995); (10 pages) | Cited 29 times

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Experimental results on the estimation of both geometric and geoacoustic parameters in shallow water are presented. Genetic algorithms are used for estimation of the forward model parameters; the estimated parameters are then used by a standard Bartlett processor for source localization. A stationary source at a range of 5.6 km and a moving source at ranges from 5.8–7.7 km were successfully localized in range and depth using a single frequency Bartlett processor. The results indicate that global estimation of the forward model parameters significantly improves source localization performance.
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43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.60.Pt Signal processing techniques for acoustic inverse problems

Coupled vibration in hollow cylinders of longitudinally polarized piezoelectric ceramics

Lin Shuyu

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3599-3604 (1995); (6 pages) | Cited 1 time

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Longitudinally polarized piezoelectric ceramic disks with central holes have been the most commonly used elements in underwater acoustics and ultrasonics. However, their vibrational characteristics and frequency spectra have not been thoroughly studied. In this paper, when the mechanical coupling coefficient is introduced and the shearing strain is ignored, an analytic method is presented. The coupled vibration of the longitudinally polarized piezoelectric ceramic disks with central holes is studied and the resonance frequency equations are derived. Based on the frequency equations, the longitudinal and radial resonance frequencies can be obtained when the dimensions and the material parameters are given. Compared with one‐dimensional theory, the computed resonance frequencies in this paper are in good agreement with the measured results. Compared with the numerical methods, the analytic method presented in this paper is simple in computing the longitudinal and radial resonance frequencies and in analyzing the coupled vibrational modes of the piezoelectric ceramic disks with central holes.
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43.38.Fx Piezoelectric and ferroelectric transducers

High‐temperature fiber‐optic lever microphone

Allan J. Zuckerwar, Frank W. Cuomo, Trung D. Nguyen, Stephen A. Rizzi, and Sherman A. Clevenson

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3605-3616 (1995); (12 pages) | Cited 2 times

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The design and construction of a fiber‐optic lever microphone, capable of operating continuously at temperatures up to 538 °C (1000 °F), are described. The design is based on the theoretical sensitivities of each of the microphone system components, namely, a cartridge containing a stretched membrane, an optical fiber probe, and an optoelectronic amplifier. Laboratory calibrations include the pistonphone sensitivity and harmonic distortion at ambient temperature, and frequency response, background noise, and optical power transmission at both ambient and elevated temperatures. A field test in the Thermal Acoustic Fatigue Apparatus at Langley Research Center, in which the microphone was subjected to overall sound‐pressure levels in the range of 130–160 dB and at temperatures from ambient to 538 °C, revealed good agreement with a standard probe microphone.
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43.38.Kb Microphones and their calibration
43.38.Zp Acoustooptic and photoacoustic transducers
43.58.Vb Calibration of acoustical devices and systems

Placing small constrained layer damping patches on a plate to attain global or local velocity changes

Amy B. Spalding and J. Adin Mann, III

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3617-3624 (1995); (8 pages) | Cited 5 times

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Experimental results show how structural intensity can predict where to locate small constrained layer damping patches to attain either local or global velocity changes on a plate. If damping is applied to a region of low shearing reactive structural intensity magnitude, a local velocity change is seen. If damping is applied to a region of high shearing reactive structural intensity magnitude, a global velocity change is seen. In addition, the researchers noted that large damping patches produce global velocity changes. The filtering process needed to calculate the structural intensity was partially automated to reduce computational time.
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43.40.Dx Vibrations of membranes and plates
43.40.Tm Vibration isolators, attenuators, and dampers

Mechanical impedance of a cracked cantilever beam

G. Bamnios and A. Trochidis

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3625-3635 (1995); (11 pages) | Cited 2 times

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In this paper the influence of a transverse surface crack on the mechanical impedance of a cantilever beam is investigated both analytically and experimentally. Modeling the flexibility induced by the crack by a linear spring constant, relations linking the changes of the mechanical impedance to the location and size of the crack are obtained for both longitudinal and flexural vibrations. The results show that the mechanical impedance changes substantially due to the presence of the crack in case of flexural vibrations. The changes follow definite trends depending upon the location and size of the crack and consequently the impedance can be used as an additional defect information carrier for crack appearance and possible estimation of crack location.
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43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission

Choice of frequency weighting for the evaluation of weapon noise

Tommaso Meloni and Allan Rosenheck

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3636-3641 (1995); (6 pages) | Cited 5 times

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This paper describes a laboratory study to choose an appropriate frequency weighting network for predicting the annoyance caused by the noise from small, medium, and large weapons. The results indicate that the annoyance of all three weapon types is the same if the blasts are heard at identical A‐weighted SEL’s. On the other hand, equal C‐weighted SEL’s result in large differences in annoyance between the weapon types. The implications of these results for outdoor noise criteria depend on the assumption concerning window condition. If one assumes that people hear the blasts predominantly through open windows, then A‐weighted criteria should be appropriate for all the weapon types without any correction (penalty or bonus) for weapon type. On the other hand, if the blasts are heard predominantly through closed windows a penalty of about 5 dB should be applied to the outdoor levels of the large weapons to account for the poorer low‐frequency attenuation of the windows.
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43.50.Ba Noisiness: rating methods and criteria
43.50.Pn Impulse noise and noise due to impact
43.50.Qp Effects of noise on man and society

Mechanical modeling of palatal snoring

Lixi Huang

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3642-3648 (1995); (7 pages) | Cited 1 time

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The mechanism of human snoring caused by vibration of the soft palate and the characteristics of the noise are investigated. The soft palate becomes unstable and vibrates violently once the inspiratory flow exceeds a critical speed. The physiological phenomenon is modeled by studying flow over a flexible plate. In determining the stability of this flow, the trailing edge conditions are crucial. It is found that the noise generated in the simple experimental configuration has distinct characteristics found in human snores. For example, there is an antiphase relation between unsteady pressures from the oral and nasal channels and this provides a feature that distinguishes snoring by vibration of the soft palate from that caused by other parts of the human airway.
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43.50.Ed Noise generation
43.50.Nm Aerodynamic and jet noise
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics

Identification and synthesis of acoustic scattering components via the wavelet transform

D. M. Drumheller, D. H. Hughes, B. T. O’Connor, and C. F. Gaumond

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3649-3656 (1995); (8 pages) | Cited 3 times

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An acoustic scatterer can be described in the time domain by its impulse response function, or in the frequency domain by its form function. Both functions will contain several complementary and distinct components, none of which is fully separable in either the time or frequency domain. This renders Fourier based methods ineffective in identifying and extracting one component from all the others. However, it is possible to do this using the wavelet transform, a transform that yields a two‐dimensional (two‐parameter) representation of a signal. In this paper, this transform is used to identify and extract the acoustic components from physical model data.
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43.60.Gk Space-time signal processing, other than matched field processing
43.20.Px Transient radiation and scattering

Subjective evaluation of four low‐complexity audio coding schemes

Stella M. Joseph and Robert C. Maher

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3657-3662 (1995); (6 pages)

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In this study the subjective performance of four low‐complexity audio data compression methods are compared, operating at nominal bit rates of 2, 3, 4, and 5 bits per sample, applied to four 20‐kHz bandwidth, 16‐bits per sample digitized musical signals. The simple compression schemes compared were elementary differential pulse‐code modulation (DPCM), noise feedback coding DPCM (NFC‐DPCM), adaptive quantizer DPCM (DPCM‐AQB), and a recently proposed method known as recursively indexed quantizer DPCM (RIQ‐DPCM). Pairs consisting of a reconstructed signal and a reference signal were presented in a two‐interval preference experiment. The reference signals were processed for specified levels of modulated noise reference unit (MNRU) in order to estimate the equality threshold rating (ETR) of the reconstructed audio stimuli. The subjective MNRU values were found to increase by 2–5 dB for each increment in bits per sample. The DPCM‐AQB scores were found to be 8–10 dB higher than for DPCM and NFC‐DPCM. RIQ‐DPCM was rated highest, exceeding the DPCM‐AQB results by 2–5 dB in all tests. Objective measurements of segmental signal‐to‐noise ratio (SNRSEG) for the reconstructed signals predicted a performance level 2–5 dB lower than was actually found in the subjective results, particularly for SNRSEG values below 25 dB.
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43.60.Dh Signal processing for communications: telephony and telemetry, sound pickup and reproduction, multimedia
43.60.Cg Statistical properties of signals and noise

Processing of prosthetic heart valve sounds for single leg separation classification

J. V. Candy and H. E. Jones

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3663-3673 (1995); (11 pages)

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People with serious heart conditions have had their expected life span extended considerably with the development of the prosthetic heart valve especially with the great strides made in valve design. Even though the designs are extremely reliable, the valves are mechanical and operating continuously over a long period; therefore structural failures can occur due to fatigue. In this paper acoustical signal processing techniques developed to process noisy heart valve sounds measured by a sensitive, surface contact microphone are discussed. Measuring heart sounds noninvasively in a noisy environment puts more demands on the signal processing to extract the desired signals from the noise. Heart valve sounds are short‐duration (10–20 ms) transients and therefore nonstationary, requiring more sophisticated processing algorithms to achieve the desired signal‐to‐noise ratios. In this paper the preclassification signal processing is concentrated on exclusively. That is, the signal processing operations performed on the heart valve sounds prior to classification are discussed—a subject that will be developed in a future paper.
Efforts are concentrated on the sounds corresponding to the heart valve opening cycle. Valve opening and closing acoustics present additional information about the outlet strut condition—the structural component implicated in valve failure. The importance of the opening sound for single leg separation detection/classification is based on the fact that as the valve opens, the disk passively hits the outlet strut. The opening sounds thus yield direct information about outlet strut condition with minimal amount of disturbance caused by the energy radiated from the disk. Hence the opening sound is a very desirable acoustic signal to extract. Unfortunately, the opening sounds have much lower signal levels relative to the closing sounds and therefore noise plays a more significant role than during the closing event. Because of this it is necessary to screen the sounds for outliers in order to insure a high sensitivity of classification. Because of the sharp resonances appearing in the corresponding spectrum, a parametric processing approach is developed based on an autoregressive model which was selected to characterize the sounds emitted by the Bjork–Shiley convexo–concave (BSCC) valve during opening cycle. First the basic signals and the extraction process used to create an ensemble of heart valve sounds are briefly discussed. Next, a beat monitor capable of rejecting beats that fail to meet an acceptance criteria based on their spectral content is developed. Various approaches that have been utilized to enhance the screened data and produce a reliable heart valve spectrogram which displays the individual sounds (power) as a function of beat number and temporal frequency are discussed. Once estimated, the spectrogram and associated parameters are used to develop features supplied to the various classification schemes. Finally, future work aimed at even further signal enhancement and improved classifier performance is discussed.
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43.60.Gk Space-time signal processing, other than matched field processing
43.60.Pt Signal processing techniques for acoustic inverse problems
43.80.Vj Acoustical medical instrumentation and measurement techniques

Classification of prosthetic heart valve sounds: A parametric approach

J. V. Candy and H. E. Jones

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3675-3687 (1995); (13 pages)

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People with heart problems have had their lives extended considerably with the development of the prosthetic heart valve. Great strides have been made in the development of the valves through the use of improved materials as well as efficient mechanical designs. However, since the valves operate continuously over a long period, structural failures can occur—even though they are relatively uncommon. Here the development of techniques to classify the valve either as having intact struts or as having a separated strut, commonly called single leg separation, is discussed. In this paper the signal processing techniques employed to extract the required signals/parameters are briefly reviewed and then it is shown how they can be used to simulate a synthetic heart valve database for eventual Monte Carlo testing. Next, the optimal classifier is developed under assumed conditions and its performance is compared to that of an adaptive‐type classifier implemented with a probabilistic neural network. Finally, the adaptive classifier is applied to a data set and its performance is analyzed. Based on synthetic data it is shown that excellent performance of the classifiers can be achieved implying a potentially robust solution to this classification problem.
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43.60.Gk Space-time signal processing, other than matched field processing
43.60.Pt Signal processing techniques for acoustic inverse problems
43.80.Vj Acoustical medical instrumentation and measurement techniques
87.80.-y Biophysical techniques (research methods)

Discrete wavelet analysis of blade vortex interaction noise

W. Constantine, C. Pezeshki, R. Bamberger, and M. Mosher

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3688-3693 (1995); (6 pages)

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The discrete wavelet transform, implemented in a multirate filter bank scheme using conjugate quadrature filters, is used to analyze blade vortex interaction (BVI) noise from helicopter rotors in different environments. The discrete wavelet transform successfully isolates the bursty, nonstationary nature of this impulsive noise source. The sub‐band coding scheme is then used for signal reconstruction of only the portion of helicopter noise related to blade vortex interaction by filtering in the frequency and time domains. By eliminating extraneous noise sources, the wavelet analysis can produce a more direct comparison between BVI noise generated in flight and in other environments such as a wind tunnel.
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43.60.Gk Space-time signal processing, other than matched field processing
43.50.Pn Impulse noise and noise due to impact

Aeroacoustic measurements in wind tunnels using adaptive beamforming methods

Richard A. Gramann and James W. Mocio

J. Acoust. Soc. Am. Volume 97, Issue 6, pp. 3694-3701 (1995); (8 pages) | Cited 3 times

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Tests have been performed in a conventional low speed wind tunnel using a linear array of microphones to measure the received source level of a speaker projecting within the test section. Conventional, or delay and sum beamforming (CBF), and adaptive beamforming (ABF) have been employed to determine the source bearing and the received source level. Both narrow‐band and broadband sources were used, with two different array configurations and several array orientations. The results show that ABF can be used in such an environment and that it rejects much of the multipath. Consequently more accurate broadband measurements are obtained with ABF than with CBF.
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43.60.Gk Space-time signal processing, other than matched field processing
43.58.Ta Computers and computer programs in acoustics
43.38.Hz Transducer arrays, acoustic interaction effects in arrays
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