bluuebunny/crossref_metadata_2025 huggingface dataset:
Noise outdoors
Authors: Embleton Tony F. W.
Published: October 2005

Concerns about noise in the community date back to the dawn of recorded history, have continued through Roman times, the Middle Ages, and are still with us. Many of the principal wave-propagation mechanisms involved in the real atmosphere outdoors were understood at least qualitatively by the late 1800’s. Today, a good understanding of all the sound propagation phenomena is of considerable economic and social importance in connection with environmental impact studies. Reality is far more interesting than simple spherical spreading in the space above a hard, flat ground. Some grounds are hard like concrete or soft as snow. Corresponding reflection coefficients are usually less than unity and vary with angle. Grounds may not be flat, leading to shadow zones or alternatively multiple reflected paths. Wind convects sound waves, and gradients of wind or temperature refract waves either upward (temperature lapse) or downward (inversion). The atmosphere is rarely still and turbulence causes fluctuations in the acoustical effects. All these features are frequency dependent, and mutually interact. Measured sound levels outdoors owe as much to near-surface weather and to ground shape as to the obvious acoustical factors to source and receiver heights and their separation. Discussion will emphasize field measurements and simple physical interpretations.
Benchmark comparisons between an NRL, SCC high-frequency shallow water normal mode code and commonly used codes with more detailed explanations of the method
Authors: White E. , Werby Michael F.
Published: October 2005

In the past, a new normal mode code developed at NRL, Stennis Space Center based on a new expansion method was discussed. The expansion functions are solutions of a related iso-velocity profile. The method is discussed in more detail and compared with old perturbation methods, the Galerkin method, and variational methods. Then benchmark comparisons with other codes are presented.
Statistics of shipping noise vertical directionality in shallow water
Authors: Mitchell Stephen K.
Published: October 2005

Even a cursory examination of ambient noise from a region of moderate or high shipping density shows that one of the most important features of noise in the frequency region from approximately 10 to 1000 Hz is its variability. A useful statistical summary of a noise time series n(θ,t), where n(θ,t) is the beam noise level from a vertical array steered in direction θ is the sample distribution function Dn(L). Dn(L) is computed from data as the fraction of time for which the noise n(θ,t) is less than or equal to L. A practical problem is to use known shipping densities for an area, together with a description of the acoustic propagation environment, to predict the distribution, Dn(L). In this paper, an approach is presented for modeling the distribution function of vertical beam noise, and to demonstrate a comparison with experimental data from a shallow-water region. [This work is supported by the Office of Naval Research, Code 23, through Block RL3B.]
Characterizing the performance of acoustic microscopes
Authors: Bond Leonard J. , Lee U. W.
Published: October 2005

The transfer functions for focused and defocused, coherent and confocal imaging systems developed in optics are applied to the equivalent ultrasonic imaging systems. Assuming that both of the two systems are free of attenuation and aberrations except defocus, the ideal complex amplitude line-scan signals across a step edge, with various degrees of defocus, are generated. The scalar magnitude of ideal complex image profiles are differentiated to get the unique theoretical IRF’s and Fourier transformed to obtain the corresponding TF’s. The acoustic system has been operated with a 50-MHz lens-rod design focused transducer. The experimental single frequency and broadband image profiles of a step edge, with varying degree of defocus, are differentiated and Fourier transformed. The experimental IRF’s and TF’s are compared with the corresponding theoretical data. As the initial theoretical analysis is for the wave propagating in an ideal fluid, the effects of attenuation and aberrations are investigated to enable the experimental data to be compared with the theoretical data. The relation between broadband and single frequency acoustic images is described. A practical model for the detection limits for 2-D cracks using the response for a pair of step edges is proposed. The numerical calculations are compared with experimental data. Usually the strong contrast seen in the imaging of cracks is associated with the excitation of Rayleigh waves in surface. In this study, a similar sensitivity to detect cracks is achieved by the defocus effect of pure longitudinal waves, which can be clearly explained by theory.
Time domain causality relations: Results for absorption obeying a power law
Authors: Szabo Thomas L.
Published: October 2005

The Kramers–Kronig relations are used frequently to obtain velocity dispersion from attenuation frequency data and vice versa. For many cases of practical interest, attenuation is described by a power law equation, α(ω)=α0‖ω‖y, where α0 and y are arbitrary real constants and ω is angular frequency. If y≥1, these relations fail because the Paley–Weiner theorem is no longer satisfied. Based on a time domain expression of causality, new time-causal relations, with the aid of generalized functions, provide a way of obtaining dispersion relations for the y≥1 cases. For y≤1, the time-causal relations reduce to the Kramers–Kronig relations. The new results for attenuation of the power law form indicate that dispersion is maximum for y=1, and it falls symmetrically to zero at y=0 and y=2. These results are in contrast to the approximate nearly local Kramers–Kronig theory [M. O’Donnell etal., J. Acoust. Soc. Am. 69, 696–701 (1981)], which predicts dispersion for values of y=0 to y=2. The two theories agree at y=1, but deviate elsewhere. Experimental data confirming the new theory will be given.
The use of cluster methods in complex machine diagnostics
Authors: Ünal A. , Karakasoǧlu A.
Published: October 2005

Real-life examples will be given to assess the efficiency of the cluster techniques and artificial neural network-based methods in complex machine diagnostics.
An issue (sediment volume fluctuations) and a nonissue (shear wave propagation) in shallow water acoustics
Authors: Tappert Fredrick D. , Yamamoto T.
Published: October 2005

A two-way full-wave PE reverberation model has been developed that provides predictions of mean reverberation levels in shallow water to long ranges (hundreds of water depths) due to sediment volume fluctuations as well as bottom and basement interface roughnesses. Using T. Yamamoto’s tomographically measured sediment volume fluctuation spectra as one of the inputs, the PE reverberation model has been exercised at several locations on the shelf in the East China Sea over a broad range of frequencies. It has been found that predicted reverberation levels due to both mechanisms are generally comparable in magnitude, and that absolute levels are controlled mainly by total field ensonification of the sediment volume and boundaries, i.e., forward transmission losses. The question whether it is necessary to include shear wave propagation in shallow water acoustic models has been resolved: the answer is definitely negative, and this is no longer an issue. Measured shallow water transmission loss data over a broad range of frequencies with source and receiver in the water column has been successfully modeled using a full-wave range-dependent PE model that includes rough bottom forward scattering (necessary for good agreement), but treats shear wave effects as an equivalent fluid by augmenting the volume attenuation of compressional waves in the sediment layers. The conclusion that it is not necessary to include shear wave propagation when sources and receivers are in the water column has been further confirmed by inter-model and intra-model comparisons using realistic geoacoustic sediment properties as measured by T. Yamamoto’s BSMP system [J. Acoust. Soc. Am. 90, 441–456 (1991)]. [Work supported by ONR, 1125OA.]
Modeling acoustic propagation in shallow range-dependent environments
Authors: Stephen R. A.
Published: October 2005

‘‘Shallow’’ water means water depth less than an acoustic wavelength and implies by definition strong interaction with the bottom. However since most ocean bottoms are rough and laterally heterogeneous many of the assumptions used to simplify the elastodynamic equations are invalid. On the other hand, since the depths and ranges of interest are considerably less (in terms of wavelengths) than deep water problems, direct numerical solutions of shallow water problems are quite tractable. Finite difference approaches, for example, have the following advantages over alternative methods: (a) They include all shear wave (rigidity) effects in the bottom including body and interface waves. (b) They can be applied to pulse beams at low grazing angles (less than 20°). (Methods based on ‘‘infinite plane waves’’ have conceptual problems at low angles.) (c) Both forward scatter and backscatter are included in the solutions. (d) Multiple interactions between scatterers are included. (e) Arbitrary range-dependent topography and volume heterogeneity, can be treated simultaneously in the same formulation. (f) Problems are scaled to wavelengths and periods so that the results are applicable to a wide range of frequencies. (g) The method considers scattering from structures with length scales on the order of acoustic wavelengths.
Shallow water acoustic channel monitoring with selective mode excitation
Authors: Preisig James C. , Catipovic Josko A.
Published: October 2005

The shallow water environment is characterized by multiple processes that cover a wide range of temporal and spatial scales and that have a significant effect on the propagation of acoustic signals [G. V. Frisk, ‘‘Report on the Office of Naval Research Shallow Water Acoustics Workshop,’’ 24–26 April 1991, WHOI-92-06]. The coupling between the modes of acoustic signals is potentially an effective means of monitoring these processes. Traditionally, a signal source is used to excite the acoustic medium. A receiver array is used to sort out the modes of the propagating signal and the coupling between particular modes is inferred from travel time differences. This approach provides relatively little control of the distribution of transmitted energy among the modes and adds uncertainty to the estimation of the coupling between particular modes. An alternative approach is proposed to use an array of sources to selectively excite modes of the medium. There are several advantages and challenges of using such an approach. First, this will improve the ability to estimate the actual coupling between different modes. Second, it is well known that propagation of and coupling between particular modes is most sensitive to environmental perturbations having particular spatial scales. [B. Cornuelle and B. M. Howe, ‘‘High Spatial Resolution in Vertical Slice Ocean Acoustic Tomography,’’ J. Geophys. Res. 92, No. C11 (15 October 1987)]. Therefore, by exciting particular modes and not exciting other modes, the emitted signal can be tuned to be most sensitive to environmental fluctuations on a particular spatial scale. A major challenge in this approach is the tuning of the source array to ensure that only the desired modes are excited.
Effects of measurement procedure and equipment on average room acoustic measurements
Authors: Gade A. C. , Bradley John S. , Siebein Gary W.
Published: October 2005

This paper reports the results of a measurement tour of nine U.S. concert halls. Three measurements teams, from the University of Florida, the National Research Council of Canada, and the Technical University of Denmark, made parallel sets of measurements using their own equipment and procedures. In some of the halls measurements were repeated using the procedures of the other teams to make it possible to separate the effects of different equipment and different procedures. The paper will present position-averaged results from the three teams and will discuss reasons for the differences observed. [Work partially supported by the Concert Hall Research Group.]
F0 turning point as an F0 cue to tonal contrast: A case study of Mandarin tones 2 and 3
Authors: Shen Xiaonan Susan , Lin Mascan , Yan Jingzhu
Published: October 2005

This study first replicated Shen and Lin’s [Lang. Speech 34(2), 145–156 (1991)] experiment with improved stimuli to confirm their claim that the F0 turning point was a perceptual cue to Mandarin tones 2 and 3, and further investigated the relative importance between the timing of the turning point and F0 height. The results indicated that, indeed, the distinction between these two tones was cued by the timing of the turning point, and that F0 height had little effect on the labeling.
Alteration of central auditory processing of brief stimuli: A review and a neural model
Authors: Gerken George M.
Published: October 2005

There is evidence that the manner in which the central auditory system processes transient signals can be altered by either of two seemingly unrelated experimental factors, namely, hearing loss, or the presence of a continuous tone of moderate intensity. In particular, altered processing of brief signals in the central auditory system is indicated by either: (i) lower (better) behaviorally measured thresholds for pulsate electrical stimulation of brain-stem auditory nuclei, or (ii) an increased amplitude of some components of the brain stem or cortical potentials evoked by brief acoustic stimuli. A simple two-neuron model which evolved from the above findings and related visual system phenomena was used to evaluate the effects produced by hearing loss or continuous tone. In the model, a ‘‘hearing loss’’ condition, which was represented by less spontaneous neural activity (and, hence, reduced inhibition) relative to a ‘‘normal hearing’’ condition, yielded both increased gain for steady-state stimuli and increased responsiveness for transient stimuli. Thus the model provides two possible, and simultaneously operable, explanations of reduced electrical stimulation thresholds and increased evoked potential amplitude: one based on increased steady-state gain and the other based on increased responsiveness to transient stimuli. A third condition, ‘‘normal hearing with a longer excitatory time constant,’’ yielded effects that were similar to those produced by reduced inhibition, thereby suggesting a physiological basis for alteration of psychophysically measured time constants.
Audiometric and histological differences between the effects of continuous and impulsive noise exposures
Authors: Hamernik Roger P. , Ahroon William A. , Hsueh Keng D. , Lei Sheau-Fang , Davis Robert I.
Published: October 2005

An experiment was designed to determine if, for equal SPL and power spectrum, the effects on hearing of high-kurtosis noise exposures and a Gaussian noise exposure are different and the extent to which any differences measured in terms of audiometric and histological variables are frequency specific. Three groups of chinchillas with 10 animals/group were exposed for 5 days at 90 dB SPL to one of three types of noise, each with the same power spectrum. The impulsiveness, defined by the kurtosis, and the region of the spectrum from which the impulsive components of the noise were created differed for two of the noises, while the third was a continuous Gaussian noise. The results show that the most impulsive noise produced up to 20 dB greater permanent threshold shift at the high frequencies than did the Gaussian noise exposure. However, these audiometric results were difficult to reconcile with the pattern of sensory cell losses that showed statistically significant larger losses of outer hair cells for the impulsive exposure in the 0.25-kHz region. When the impacts in a high-kurtosis noise were created from the energy in the 1-through 6-kHz region of the spectrum, the audiometric profile of hearing loss was similar to that produced by the Gaussian noise; however, inner hair cell losses were significantly greater in the 4-kHz octave band region of the cochlea.
The use of inhomogeneous waves in the reflection–transmission problem at a plane interface between two anisotropic media
Authors: Lanceleur Patrick , Ribeiro Helder , De Belleval Jean-François
Published: October 2005

A mathematical form is proposed for the study of the problem of reflection–transmission of monochromatic ultrasonic plane waves at the interface between two arbitrary anisotropic semi-infinite media. The method used leads to a complete determination of all characteristics of the studied waves for all possible configurations, i.e., their directions of propagation, polarizations, and magnitudes. In particular, cases are taken into account where the waves generated by the existence of the interface are evanescent or more generally inhomogeneous. Applying this method to the calculation of several practical cases typically encountered in ultrasonic nondestructive evaluation fields, this paper points out the existence of phenomena that cannot be interpreted by classical methods usually used for the resolution of this kind of problem.
The flexural wave-number response of a string and a beam subjected to a moving harmonic force
Authors: Pierucci Mauro
Published: October 2005

The effect of a moving harmonic force that acts upon either a string or a beam is analyzed according to its spectral wave-number components and the decaying components of the flexural vibrations. The speed of motion of the force is nondimensionalized with respect to the wave flexural speed. For a string, the wave number of the right traveling disturbance increases monotonically at subsonic speeds; at supersonic speeds both wave numbers lead to left traveling waves which decrease as a function of Mach number. For a beam, the effect of the motion is to produce one right traveling wave, with an everincreasing wave number, and three disturbances which propagate and decay behind the forcing function. The decaying modes, at a Mach number of two, become traveling modes. The critical Mach number of two corresponds to a speed of the force equal to the group velocity at that frequency.
Interwell seismic transmission and reflection through a dipping low-velocity layer
Authors: Parra Jorge O. , Sturdivant Vernon R. , Xu Pei-cheng
Published: October 2005

A dipping fractured layer zone has a characteristic seismic signature in interwell seismic data. A fracture zone is simulated as a dipping low-velocity layer in an unbounded medium using the elastodynamic Green’s function for layered earth to include absorption and dispersion effects. The vector wave displacement solution is developed for a point force at an arbitrary angle with respect to the axis of symmetry of a horizontal layer. The source and detector boreholes are rotated such that the new boreholes are perpendicular to the force to form a new plane which contains a dipping layer and horizontal force. To simulate interwell seismic responses, a modified Clenshaw–Curtis quadrature method for wave-number integrals of the Bessel function type is developed to evaluate the wave displacement vector in the frequency-space domain. The model results demonstrate that the presence of a dipping low-velocity layer produces seismic signatures associated with the attitude of the low-velocity layer and the angle of the layer with respect to the source. Also, the results suggest that the amplitudes of shear wave events associated with the presence of a dipping low-velocity layer diminish and their hyperbolic moveout patterns are modified as the dipping layer becomes horizontal.
Efficient evaluation of narrow-band spatial ambiguity functions
Authors: Johnson Robert K. , Harris David B. , Hedstrom Gerald W.
Published: October 2005

The evaluation of spatial ambiguity functions is required for several acoustical signal processing applications including matched-field processing (MFP) and computing bounds on array localization error. In both of these applications, the ambiguity function is usually evaluated repeatedly over a region of interest for a specific acoustic array. When either the region or the array is large, computational efficiency is an issue. In this paper, two algorithms are presented for efficiently evaluating the spatial ambiguity function over weakly range-dependent regions utilizing an adiabatic normal mode signal model. The algorithms are referred to as the direct method and the indirect method. The direct method involves a recursive update in range of the so-called replicant vector. The computational complexity of the direct method for each range step is proportional to the product of the number of array sensors and the number of modes. In contrast, the indirect method recursively updates the entire ambiguity function and has an incremental computational complexity proportional to the number of modes squared. Thus, for low-frequency operation with a large array, the indirect method is more efficient. Computational results are presented in which the relative efficiency of the two algorithms is compared.
A unified approach to acoustical reflection imaging. I: The forward model
Authors: Berkhout A. J.
Published: October 2005

A discrete theory is proposed that represents acoustical reflection measurements in terms of a so-called data matrix. One column of the data matrix is related to one source position; one row is related to one detector position. In the proposed theory the data matrix is expressed in a sequence of matrix operators. These matrix operators quantify the physical processes of emission, downward propagation, reflection, upward propagation, and detection in inhomogeneous media. The important concept of optimum ‘‘illumination’’ is introduced. Using the matrix formulation, it is shown how to design an experiment that is optimum for a specific target area. The proposed theory is pre-eminently suited to relate and derive current and new imaging technology.
Acoustic scattering from elemental Arctic ice features: Numerical modeling results
Authors: Fricke J. Robert
Published: October 2005

In this paper acoustic scattering from Arctic ice is considered. No analytic scattering theories are able to explain the observed loss at low frequency (10–100 Hz) in long-range propagation experiments. A finite difference method is used to solve the heterogeneous elastodynamic equations in two dimensions; this technique permits arbitrary roughness, unrestricted in slope, displacement, or radius of curvature and provides direct, physical insight into the rough ice scattering mechanism. Broadband numerical scattering simulations are conducted on pressure ridges. The specular loss due to a ridge is affected by three parameters: cross-sectional area or mass of the ridge, excitation of plate waves, and a material-dependent power law. The first two affect the magnitude of the loss, while the last affects the frequency dependence. Multi-year ridges are completely frozen and are best modeled as elastic structures yielding a loss frequency dependence of ≊f9/2. Observed loss in field data, with a frequency dependence of ≊f3/2, is not explained by scatter from multi-year ridges. In contrast, young pressure ridges are modeled as fluid structures since they are loose aggregations of ice blocks and cannot support shear strain. Scatter from fluid ridges has a loss frequency dependence of ≊f3/2 and yields a good match to the observed frequency dependence in field data. These results suggest that observed long-range propagation loss is best explained by scatter from large, young pressure ridges.
Demonstration of the power-handling capability of Terfenol-D
Authors: Moffett Mark B. , Clay William L.
Published: October 2005

Two barrel-stave flextensional underwater acoustic projectors, one with a lead zirconate titanate (PZT) ring-stack (longitudinal, 33) driver and one with a permanent-magnet-biased Terfenol-D driver, were driven at high power levels. The PZT transducer, driven to its electric-field limit of 390 kV/m rms, produced a source level of 194.7 dB//1μPa⋅m at 1.56 kHz. The Terfenol-D (Tb0.3Dy0.7Fe1.93) projector power was limited by the stave-attachment method used in the two transducers to 202.9 dB//1μPa⋅m at 1.48 kHz.
Temporary threshold and loudness shifts: Frequency patterns and correlations
Authors: Botte M. C. , Charron S. , Bouayad H.
Published: October 2005

Two experiments studied the frequency pattern of TLS (temporary loudness shift) as a function of the level and frequency of the fatiguing sound. In experiment 1, the fatiguing tones were intermittent 375-, 1500-, or 3000-Hz tones (10 s on/10 s off) at 75, 80, 85, 90, or 95 dB SPL. The TLS patterns were established for a continuous, 60-phon test tone at different frequencies presented simultaneously with the intermittent fatiguing tone. In experiment 2, a 1000-Hz exposure tone with an intermittency of 10 s on/20 s off was used with a continuous 60-dB test tone at different frequencies. In both experiments, the total exposure duration was 60 s; TLS was measured 5 s after the exposure ended. For the lowest two exposure levels, the TLS pattern had one peak centered on the exposure frequency. As the exposure level increased, a two-peak pattern became evident, with the second peak at higher test frequencies. This finding could be interpreted as psychoacoustical evidence for the double (passive and active) mode of displacement of the basilar membrane. In experiment 2, a TTS (temporary threshold shift) measurement after exposure to a 45-min, 1000-Hz tone at 90 dB was added to the TLS sessions. The correlations between maximum TTS after a 45-min exposure and the TLS obtained after a 60-s exposure were calculated for each of the exposure levels and test frequencies used in TLS measurements. The correlation reached as high as 0.9 for TLSs measured at 1120 Hz after a 90-dB exposure; it was smaller but significant for TLSs at the exposure frequency. Despite these correlations, differences in the overall patterns of TTS and TLS suggest that they stem from two different mechanisms.
Detection of temporal gaps in sinusoids: Effects of frequency and level
Authors: Moore Brian C. J. , Peters Robert W. , Glasberg Brian R.
Published: October 2005

Thresholds for the detection of gaps in sinusoidal signals were measured as a function of frequency (100–2000 Hz) and level (25–85 dB SPL) in 11 normally hearing subjects. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the gap. In a separate experiment, auditory filter shapes and detection efficiency were estimated for the same 11 subjects using the notched-noise method, at center frequencies of 100, 200, 400, and 800 Hz. Gap thresholds varied only slightly with frequency over the range 400–2000 Hz, but increased markedly at 200 and 100 Hz. At all center frequencies, gap thresholds were almost invariant with level for levels above 55 dB SPL. Gap thesholds increased at low levels, reaching values about 50% greater than their asymptotic values at a sensation level of about 20 dB. The decrease in auditory filter bandwidth with decreasing center frequency does not seem sufficient to account for the increase in gap thresholds. Also, individual gap thresholds at a given center frequency were not significantly correlated with the bandwidth of the auditory filter at that center frequency, as would be expected if the auditory filter played a role in limiting gap detection. Detection efficiency decreased with decreasing center frequency. Individual differences in detection efficiency were significantly correlated with gap thresholds. However, changes in detection efficiency with frequency do not seem to be of the right form to account for the increase in gap thresholds at low frequencies. It seems likely that there is a central sliding temporal integrator which integrates over longer times at lower center frequencies.
Extracting dynamic parameters from speech movement data
Authors: Smith Caroline L. , Browman Catherine P. , McGowan Richard S. , Kay Bruce
Published: October 2005

A quantitative characterization of articulatory movements, using the parameter values of a linear second-order dynamical system, was developed in order to compare classes of movements, in particular, classes defined by linguistic factors such as syllable position, stress, and vowel quality. Movements of the lower lip in utterances such as [′bibEbib] and [babE′bab] were partitioned into sections (‘‘windows’’) in two ways: at successive displacement peaks and valleys, and at the right edge of plateau regions around such extreme values. The linguistic factors affected natural frequency in similar ways regardless of whether damping ratio was permitted to vary or held fixed at one of several different values. Damping ratio was generally unaffected by the linguistic factors. For the most part, the type of partition or window did not affect the patterns of the results, with the exception of the closing gesture out of the reduced syllable.
Gap detection in a narrow band of noise in the presence of a flanking band of noise
Authors: Grose John H. , Hall Joseph W.
Published: October 2005

This study examined gap detection in a narrow band of noise in the presence of a flanking band of noise which did not carry the gap. The study was motivated by the phenomenon of comodulation masking release (CMR) where coherent amplitude modulation at a distal frequency facilitates the detection of a signal at a target frequency. The results showed that gap detection in the target band of noise was disrupted by the presence of a flanking narrow band of noise, particularly if the flanking band was gated on and off synchronously with the target band. The disruption was greater for a comodulated flanking band. It was concluded that a necessary condition for the interference was either the presence of modulation or the occurrence of synchronous gating, since the interference did not occur for a continuous pure tone of equal energy. The findings were interpreted in terms of modulation detection interference (MDI).
A high resolution fundamental frequency determination based on phase changes of the Fourier transform
Authors: Brown Judith C. , Puckette Miller S.
Published: October 2005

The constant Q transform described recently [J. C. Brown and M. S. Puckette, ‘‘An efficient algorithm for the calculation of a constant Q transform,’’ J. Acoust. Soc. Am. 92, 2698–2701 (1992)] has been adapted so that it is suitable for tracking the fundamental frequency of extremely rapid musical passages. For this purpose the calculation described previously has been modified so that it is constant frequency resolution rather than constant Q for lower frequency bins. This modified calculation serves as the input for a fundamental frequency tracker similar to that described by Brown [J. C. Brown, ‘‘Musical fundamental frequency tracking using a pattern recognition method,’’ J. Acoust. Soc. Am. 92, 1394–1402 (1992)]. Once the fast Fourier transform (FFT) bin corresponding to the fundamental frequency is chosen by the frequency tracker, an approximation is used for the phase change in the FFT for a time advance of one sample to obtain an extremely precise value for this frequency. Graphical examples are given for musical passages by a violin executing vibrato and glissando where the fundamental frequency changes are rapid and continuous.
Identification of steady-state vowels synthesized from the Peterson and Barney measurements
Authors: Hillenbrand James , Gayvert Robert T.
Published: October 2005

The purpose of this study was to determine how well listeners can identify vowels based exclusively on static spectral cues. This was done by asking listeners to identify steady-state synthesized versions of 1520 vowels (76 talkers×10 vowels×2 repetitions) using Peterson and Barney’s measured values of F0 and F1–F3 [J. Acoust. Soc. Am. 24, 175–184 (1952)]. The values for all control parameters remained constant throughout the 300-ms duration of each stimulus. A second set of 1520 signals was identical to these stimuli except that a falling pitch contour was used. The identification error rate for the flat-formant, flat-pitch signals was 27.3%, several times greater than the 5.6% error rate shown by Peterson and Barney’s listeners. The introduction of a falling pitch contour resulted in a small but statistically reliable reduction in the error rate. The implications of these results for interpreting pattern recognition studies using the Peterson and Barney database are discussed. Results are also discussed in relation to the role of dynamic cues in vowel identification.
Vowel boundaries for steady-state and linear formant trajectories
Authors: Nábělek Anna K. , Czyzewski Zbigniew , Crowley Hilary J.
Published: October 2005

Locations of boundaries and slopes of identification functions were tested for iε vowel continua with steady-state and linearly changing formant trajectories. In experiment 1, the boundaries and slopes for arbitrarily selected trajectory directions were determined for ten normal-hearing and ten hearing-impaired subjects in three listening conditions: Quiet, noise, and reverberation. The boundaries did not depend upon the group of subjects or the listening condition. A boundary shift was found for stimuli with F1 changing in a downward direction relative to boundaries for stimuli with either only F1 or with both F1 and F2 changing in an upward direction. The slope of the identification function for stimuli with F1 changing in a downward direction was shallower than the slopes for stimuli with steady-state formants or stimuli with F1 changing in an upward direction. The slopes obtained from the hearing-impaired subjects were shallower than those of the normal-hearing subjects and were shallower in noise than in either quiet or reverberation. In experiment 2, boundaries and slopes for the trajectory directions found in the natural vowels iε and iε, F1 changing in an upward direction and F2 in a downward direction, were determined for nine normal-hearing subjects in two listening conditions, quiet and reverberation. The boundary for stimuli with both F1 and F2 changing in directions characteristic for natural vowels was shifted relative to the boundary for stimuli with steady-state formants. The directions of the boundary shifts in experiments 1 and 2 indicated a perceptual emphasis on the initial sections of changing F1 and F2. Sound quality of the end-point /i/ and /ε/ stimuli depended upon F1 and F2 trajectories. For both vowels, the best quality judgments were found for the stimuli with natural F1 and F2 trajectory directions. The quality judgments were weakly correlated with the slopes of identification functions, with better quality judgments being associated with steeper slopes.
Low-frequency Arctic reverberation. III: Measurement of ice and bottom backscattering strengths from medium-range bottom-bounce returns
Authors: Yang T. C. , Hayward T. J.
Published: October 2005

Backscattering strength measurements are usually extracted from short-range reverberation data using direct-path returns or from long-range reverberation data for which the dominant source of reverberation (e.g., a bottom seamount) is known. The small area ensonified by short-range direct paths provides only a relatively small data sample for backscattering strength estimates. While long-range data cover a much larger area, the returns from the surface and bottom are not always easily identified in the data. In the Arctic both the surface (ice) and bottom contribute significantly to the reverberation at low frequencies. The contributions of ice and bottom must be separated by signal processing means before their backscattering strengths can be measured separately. In this paper a method to separately measure the surface and bottom backscattering strengths using medium-range (5- to 20-km) reverberation data is investigated. The method of separation is based on the time versus vertical arrival angle contours associated with bottom-bounce propagation paths. Separation of surface and the bottom backscattering returns is most straightforward for a vertical array. It is noted that a (low tilt) vertical array has been shown to be a practical tool for collecting reverberation data in the Arctic. By extending analysis to medium-range reverberation data, backscattering data samples can be significantly increased. The ice backscattering strengths are estimated at 23 Hz from the CEAREX 89 reverberation data and the results are compared with the Burke–Twersky model, in which surface roughness is modeled by elliptic half-cylindrical protuberances on a pressure-release surface. Bottom backscattering strengths are also obtained at 23 Hz, and are found to be consistent with Lambert’s law within the experimental errors.
Predictability of acoustic intensity and horizontal wave numbers in shallow water at low frequencies using parabolic approximations
Authors: Cederberg R. J. , Siegmann W. L. , Jacobson M. J. , Carey W. M.
Published: October 2005

Accuracy of relative intensity and horizontal wave-number predictions from parabolic approximation models of shallow water, low-frequency (less than 100 Hz) acoustic propagation problems is examined. Effects of input parameter uncertainties and basic approximations in parabolic equation models are investigated. Environmental parameters and uncertainties considered correspond generally to those from a recent New Jersey Shelf experiment. Parameter uncertainties are found to impose the greatest limitations on prediction accuracy, with sediment sound-speed uncertainties causing the largest restrictions. Issues associated with modeling the sediment sound speed, such as using isospeed layers to approximate sound-speed variations, are also resolved. Weak range dependence in the channel depth and sound speed, of similar type as at the experiment site, is found to be well approximated by range-independent models. Comparisons of the experimental results with model predictions illustrate how parameter uncertainties may have significant effects.
Effects of sea ice cover on acoustic ray travel times, with applications to the Greenland Sea tomography experiment
Authors: Jin Guoliang , Lynch J. F. , Pawlowicz R. , Wadhams P.
Published: October 2005

The travel-time effects of a sea ice cover on an acoustic pulse are estimated using generalized ray theory. This expands upon the previous work done by Jin and Wadhams [Prog. Oceanogr. 22, 249–275 (1989)] by including the effects of frequency dispersion and different sets of ice parameters. Travel-time changes due to single reflections are approximated by plane wave reflection theory, and compared to the generalized ray theory results. Statistical effects for multiple reflections, such as the ice thickness probability distribution function, Fresnel zone averaging, and shadowing are considered. Finally, the effects of ice-induced travel-time changes on tomographic inversions for water column oceanography are considered. The implications of this work on the 1988–89 Greenland Sea tomography experiment are considered in detail.
Wave scattering from a ground with a Gaussian bump or trough in an inhomogeneous medium
Authors: Li Y. L. , Franke S. J. , Liu C. H.
Published: October 2005

A closed-form solution of the Helmholtz equation is obtained for the case of a time-harmonic line source embedded in a medium with the linear sound-speed profile. Substituting the closed-form expression of the Green’s function into the Helmholtz–Kirchhoff integral equation, the exact solution of the scattered fields from a ground with a Gaussian shaped bump or trough in such a medium is obtained. An extension of the method of moments, which can solve the Helmholtz–Kirchhoff integral equation for sound scattering in the inhomogeneous medium, has been developed. Using these new tools, the effects of scattering in the region beyond a bump or trough are studied for situations when the background medium is upward refracting. Numerical results show that a soft ground with a bump or a hard ground with a trough in the upward refracting medium may cause some enhanced field regions beyond the bump or trough. The phenomenon is not observed when the background medium is homogeneous. Numerical results also show that a hard ground with a bump or a soft ground with a trough in the inhomogeneous medium may not cause any major difference when compared with results from the case using the homogeneous medium as the background medium.
An experimental investigation of the nonlinear pressure field produced by a plane circular piston
Authors: TenCate James A.
Published: October 2005

An experimental investigation of the nonlinearly generated harmonics in the sound beam of a plane circular piston in water has been carried out. Special attention was paid to the higher harmonic sidelobes called fingers. All experiments were performed using a high precision, computer-controlled tank facility where movement resolution is better than 50 μm. Harmonic beam patterns generated by a 1-MHz, 12-mm radius plane circular piston driven with a face sound pressure level of 223 dB (re: 1 μPa) were measured. Beam patterns of the first ten harmonics (out to the first sidelobe of the fundamental beam pattern) are shown. The first four harmonic beam pattern data are compared with results produced by a numerical solution of the Khokhlov–Zabolotskaya–Kuznetzov (KZK) equation. Agreement between experiment and theory is excellent. Finally, careful measurements of the decay of the fingers were made. The decay of the first finger in the second harmonic beam pattern generated by a 2.2-MHz, 3-mm radius circular piston [217 dB (re: 1 μPa)] out to 30 Rayleigh distances was measured. As predicted by Naze Tjo/tta and Tjo/tta [J. Acoust. Soc. Am. 83, 487–495 (1988)], the finger decays as 1/z (neglecting absorption).
Relaxation-matched modeling of propagation through porous media, including fractal pore structure
Authors: Wilson D. Keith
Published: October 2005

The viscous and thermal dissipation of an acoustic wave propagating through a porous medium is shown to be characteristic of a relaxation process. Based on this interpretation, a new model for the complex density (dynamic permeability) and bulk modulus, which describe the viscous and thermal processes, respectively, is proposed. The model is based on approximating the relaxational characteristic, as opposed to previous models based on matching low- and high-frequency asymptotic behavior. An advantage of the relaxation model is that one fewer parameter is required. The relaxation model is also simpler than the commonly used Zwikker/Kosten/Attenborough or Biot/Allard models, in the sense that it contains no Bessel or Kelvin functions, and is not a modified form of the solution for uniform, circular pores. And unlike the Delany/Bazley empirical equations, the relaxation model is physically realistic for all frequencies. Extension of the relaxation model to fractal pore surfaces is also discussed.
Training listeners to perceive novel phonetic categories: How do we know what is learned?
Authors: Logan John S. , Lively Scott E. , Pisoni David B.
Published: October 2005

Logan et al. [J. Acoust. Soc. Am. 89, 874–886 (1991)] carried out a perceptual learning experiment in which Japanese listeners were trained to identify English words containing /r/ and /l/. Pruitt [J. Acoust. Soc. Am. 94 (1993)] has criticized several aspects of the procedures and conclusions. First, he argues that the lack of appropriate control groups make interpretation of the results problematic. Second, he asserts that the generalization test was methodologically flawed. Although Pruitt raises some important issues that are worth pursuing in future research, it is argued that the methodology that was employed and the conclusions that were drawn were valid.
Statistical study of spectral parameters in musical instrument tones
Authors: Ando Shigeo , Yamaguchi Kiminori
Published: October 2005

Methods for short-time spectral analysis [improved over J. Acoust. Soc. Jpn. 33, 233–241 (1977)] and for extracting time-varying amplitude levels and frequencies of partials from musical instrument tones are described. The accuracy of the combined method is examined by applying the method to a synthetic tone having 32 harmonics. Statistical presentations used include histograms and graphs of average sound pressure level spectra, arithmetic mean sound pressure levels, and standard deviations of frequencies and amplitude levels, as well as autocorrelation and cross-correlation functions for various parameters. Seven tones produced by a violin, a flute, an oboe (with and without vibrato), and by a trumpet (nonvibrato) were analyzed. Characteristic features of the time-varying spectral parameters of each musical instrument tone were obtained. Applications of the results to the synthesis of musical instrument tones are considered. As a result, it is suggested that it will be possible to synthesize good synthetic musical instrument tones by realizing the statistical nature of the extracted spectral parameters.
Scanning acoustic imaging of stress in the interior of solid materials
Authors: Drescher-Krasicka Eva
Published: October 2005

A new acoustic, stress-scanning technique is based on the sensitivity of polarized acoustic modes to local elastic anisotropy induced by stress. In samples subjected to load the amplitude of polarized waves varies with the applied stress. The broad range of wavelengths applicable in acoustic imaging makes this technique feasible to many practical applications in metals, ceramics, polymers, and other materials. A few examples: a disc under diametral concentrated load, a disc with a circular hole under diametral compression, polymer and aluminum samples under compression, and metal and ceramic samples with residual stresses will illustrate the advantages and limitations of this technique. The acoustic images show significant patterns caused by the differences of the amplitude values in the stressed and stress free areas, often enhanced by interference effects. Observed intensity variations are related to acoustic trirefringence and birefringence.
Green’s solution of the acoustic wave equation for a circular expansion chamber with arbitrary locations of inlet, outlet port, and termination impedance
Authors: Kim Yang-Hann , Kang Seong-Woo
Published: October 2005

The acoustic characteristics of a circular expansion chamber whose inlet and outlet are situated on arbitrary locations of the chamber, i.e., the side wall or the face of the chamber, are analyzed based on the Green’s function of a chamber with homogeneous boundary conditions. The Green’s function is found by considering the boundary condition of the walls as rigid except at the location of the source, which is assumed to be a uniform volumetric acoustic source. The complete solution that determines the sound pressure distribution, intensity, and sound power pattern inside of the chamber are found. The solutions are compared with those based on the modal expansion techniques for the aforementioned cases. To verify the solutions, experiments were also performed, which determines the transmission loss of the expansion chamber. Side-inlet/side-outlet, face-inlet/side-outlet chambers were tested. A two-microphone method was used to accurately determine the transmission losses of the chambers. The Green’s solutions are verified by comparison with the experimental results and the solutions based on the modal expansion techniques.