bluuebunny/crossref_metadata_2025 huggingface dataset:
Reply to ’’Comments on ’Sound propagation through an East Australian current eddy’ ’’ by Marshall Hall
Authors: Scully-Power Paul , Browning David , Nysen Paul
Published: October 2005

Hall’s comments constitute a comparison between our experimentally measured results and his theoretically derived results for the particularly interesting case of acoustic coupling between the surface duct and the eddy duct. [AIP]
Echo waveform synthesis in a rapidly varying geometry
Authors: Ricker D. W.
Published: October 2005

The synthesis of an echo waveform when the transmitter–receiver and scatter are stationary or have constant velocity colinear trajectories is a straightforward application of the Doppler principle. If however, the relative geometry is time varying and the variation over the time of echo transit is significant in terms of wavelength, the echo waveform may be a nonlinear distorted version of the transmitted waveform and not easily modeled. In this paper, an algorithm based upon a grahical construction (trajectory diagram) is given which allows the computation of the received echo waveform given a priori knowledge of the geometry, its variation, and the transmitted waveform. The method may easily be generalized for multiple scatters and multiple receivers as long as the geometry is known. The primary areas of application of the method are in air acoustics (bat echolocation) and water acoustics (sonar) where in each case the velocity of the source and scatterer may be appreciable compared to the propagation speed.
Threshold of degradation for frequency-distributed band-limited noise in continuous speech
Authors: Mermelstein Paul
Published: October 2005

Two series of perceptual experiments have been conducted to investigate the level of noise that acts as a threshold of degradation (TOD) when band-limited noise is added to speech such that the noise is either constrained to lie in one subband of the entire speech band or separately introduced into all subbands. In all cases the within-band signal-to-noise ratio is maintained invariant with time to model the encoding of subbands with the aid of adaptive quantizers. Below 1000 Hz, the TOD for 500 Hz wide bands is found to drop with frequency at roughly half the rate of the speech drop. Above 1000 Hz, the TOD for noise in individual subbands is only 10 dB and does not vary significantly with frequency. When noise is introduced simultaneously into all bands, the TOD is some 5 dB lower than when the noise is introduced into one band alone. Additional subdivision of the frequency bands for independent encoding, so as to increase the noise at TOD and thereby reduce the required SNR, is particularly effective at the lower speech frequencies, because it allows one to take advantage of both the rapidly dropping speech spectrum as well as the time incoherence of the speech energy variations within the various bands. The perceptual tolerance appears guided by the extent to which the noise can be masked by the speech energy present. Encoding techniques that take better advantage of this factor are likely to lead to transmission efficiencies while maintaining excellent speech quality.
Differences between psychophysical ‘‘suppression effects’’ under diotic and dichotic listening conditions
Authors: Yama Mark F.
Published: October 2005

A forward-masking paradigm was used in an attempt to measure and compare ‘‘suppression effects’’ under one monaural system condition, NOSO, and two binaural system conditions, NOSM and NOSΠ. The signal was a 500-Hz tone burst of 10-ms duration (measured at the 6-dB down points) and was presented 12.5 ms after the termination of the masker. In the diotic condition, as the masker bandwidth increased, masking at first increased, reached a maximum between bandwidths of 50 and 150 Hz, and then decreased with further increases of the bandwidth. The pattern of results was very different for the dichotic conditions: Here, masking never decreased with increases in the masker bandwidth; unlike the NOSO condition, there was no evidence of a ‘‘suppression effect.’’ These data are used to argue that diotic ‘‘suppression effects’’ obtained with noiseband maskers are actually produced by a combination of off-frequency listening and quality-difference cues.
The T matrix for acoustic and electromagnetic scattering by circular disks
Authors: Kristensson Gerhard , Waterman P. C.
Published: October 2005

The T matrix for scattering of waves by a circular disk is derived. Both the scalar (Dirichlet and Neumann boundary conditions) and the vector (perfectly conducting disk) cases are considered and the use of alternative choices for surface field functions is discussed in detail, and it is found that either type of the surface field representation is equally good for the disk case. Analytic expression of the farfield amplitude and total cross section is given in the low-frequency limit for both plane-wave incidence or a point source. Numerical results are presented for the two scalar cases as well as for the perfectly conducting disk. Finally, we give a computation of scattering from two parallel perfectly conducting disks.
Love waves in granular medium over a half-space under gravity
Authors: Dey S. , Mukherjee S. P.
Published: October 2005

The paper deals with the propagation of Love waves in a granular medium over an elastic half-space under hydrostatic initial stress due to gravity. The model has been considered to fit with earth having the upper part as granular and the interior as an elastic solid under high initial compressive stress due to gravity. The frequency equation has been obtained and also as particular cases (i) the equation for Love waves in a granular medium over an elastic half-space without gravity field and (ii) the equation for Love waves in an elastic medium over an elastic half-space without gravity field have been obtained. The last result has been shown to tally with the result obtained in Ewing et al. [Elastic Waves in Layered Media (McGraw–Hill, New York, 1957)].
Fundamental frequency and vowel perception
Authors: Ryalls John H. , Lieberman Philip
Published: October 2005

The set of nine nondiphthong vowels of American English were synthesized using the male formant values from Peterson and Barney [J. Acoust. Soc. Am. 24, 175–184 (1952)]. These vowels were produced in three conditions of the fundamental frequency: (1) average 135 Hz, (2) low 100 Hz, and (3) high 250 Hz. In forced-choice testing, subjects identified vowels in the average and low condition of the F0 with greater accuracy than the high F0 vowels. A second experiment was conducted using the female formant frequency values from Peterson and Barney and the same conditions of F0. Subjects still performed better on the low and average condition of the F0 for these vowels. These results suggest that the human formant frequency extractor is aided by the denser spectral sampling of the transfer function by a lower fundamental. The pattern of vowel errors was the sense neither across F0 conditions nor across male or female formant values. The point vowels [i] and [u] were the most consistently identified across all conditions.
Sound absorption variation caused by modifications to a standard mounting
Authors: Halliwell R.E.
Published: October 2005

Investigation has shown that the absorption coefficient of a panel with an E400 mounting can be significantly affected by small details of the mounting construction. Recommendations are provided to minimize any contribution to the absorption from the mounting frame.
Limitations to the measurement of sound power by the reference sound source method
Authors: Ballagh K. O.
Published: October 2005

The variation in sound power output with environment of some sources has been studied. The theoretical variation of a monopole and dipole near a reflecting plane was confirmed experimentally. Similar measurements were made on a centrifugal fan, a commonly used reference sound source, in free and diffuse fields. The variation in sound power output of the centrifugal fan was significantly different to the behavior of a monopole or dipole. Errors in estimating sound power level can occur with the reference source method if the source is calibrated in a different environment to that in which it will be used. Universal corrections cannot be applied to all sources to compensate for changes in environment because various types of sources behave differently.
Ultrasonic velocity and absorption in bromoform
Authors: Takagi K.
Published: October 2005

Pulse echo method, HRB (high-resolution Bragg reflection), and Brillouin scattering were used to observe the velocity and absorption spectra in liquid bromoform at 10°, 20°, and 25 °C over the frequency range from 3 MHz–5 GHz. The velocity dispersion shows a typical spectrum with two relaxations, one at 92 MHz and the other at 6.5 GHz at 20 °C. The absorption is exceedingly high at 3 MHz (α/f2≂2000×10−17 s2/cm) but decreases drastically down to 90×10−17 s2/cm at 1.5 GHz. A hypothesis of vibrational double relaxation was successful to describe these results.
Transmission through twin plates
Authors: Sabin Gerald A.
Published: October 2005

The transmission of normally incident sound through a pair of identical parallel plates is analyzed. An expression is derived that gives the transmission coefficient with the separation distance between the plates as a parameter. Computational examples are shown.
Acoustic propagation in the upper sound channel
Authors: Macaskill C. , Uscinski B. J. , Freedman N.
Published: October 2005

This paper deals with acoustic propagation in sound channels occurring naturally in the ocean, allowing for the presence of random scattering irregularities. These irregularities are generally very weak and are often large compared to the acoustic wavelength. The parabolic equations for propagation of the moments of the wave field can be used in these circumstances and an approximate solution has been obtained for the second moment which is valid even in the case of multiple scatter. Although the physical meaning of the solution is clear, the expressions can be difficult to evaluate for most sound channels, and special care must be exercised in the neighborhood of caustics and foci. A detailed description is given of the methods used to evaluate the solution of the second moment equation with a particular discussion of the numerical techniques used. Results are presented for a sound-speed profile modeled by a cubic polynomial corresponding to channeling conditions observed in the North Atlantic. It is found that the presence of scattering irregularities has only a very small effect on the mean intensity in and near the channel and that the present methods are of only limited value at caustics. The spatial coherence of the acoustic field is, however, strongly affected by the irregular structure.
Occurrence and acoustical significance of natural gas hydrates in marine sediments
Authors: Daniels J. M. , Vidmar P. J.
Published: October 2005

This article reviews current knowledge concerning gas hydrates in marine sediments: their chemistry, occurrence, formation conditions, and acoustic properties. In a hydrated sediment the water molecules form an icelike crystalline structure, which traps the gas molecules within it. This structure can greatly increase compressional sound velocity and may alter shear velocity and absorption processes from those expected for typical marine sediment types. The potential impact of hydrates on underwater acoustics is demonstrated through computations of bottom reflection loss for a hypothetical subbottom structure containing a hydrate zone.
Theory of the pulsed optoacoustic technique
Authors: Lai H. M. , Young K.
Published: October 2005

A theory of the pulsed optoacoustic effect for a weakly absorbing liquid is presented for all ratios of pulse time τp to acoustical transit time across the beam radius τa . The behavior in different regimes of τa and τp is studied and attention is drawn to possible dependence on details of the temporal and radial profiles of optical intensity. The limit to the sensitivity of this technique due to electrostriction is analyzed.
A signal-detection-theory measure of pitch shifts in sinusoids as a function of intensity
Authors: Jesteadt Walt , Neff Donna L.
Published: October 2005

Pitch shifts in sinusoids as a function of intensity result in systematic response biases and differences in performance in forced-choice frequency-discrimination tasks. Two approaches are described for converting these effects to a measure of pitch shift in Hz using standard signal-detection-theory assumptions. To illustrate these approaches, forced-choice frequency-discrimination data were obtained for three listeners at 250 and 4000 Hz, with six intensities from 40 to 90 dB SPL. The resulting pitch-shift estimates are in good agreement with adjustment data obtained from the same listeners. Collection and analysis of the forced-choice data can be greatly simplified by using an adaptive procedure. Pitch-shift estimates obtained in this way for two of the three listeners are in good agreement with the other estimates.
Time-delay triangulation ranging using beta density measurement error statistics
Authors: Hilliard E. J. , Perruzzi Joseph J.
Published: October 2005

A beta-type density function is used to model time-delay measurement errors associated with sensors used in triangulation ranging applications. The range density function together with the mean and standard deviation are derived. Maximum positive and negative time-delay error limits over which these statistics are valid are also determined. Bounds on the time-delay standard deviation for the square-law approximation are established as well as length requirements on the effective baseline to achieve reliable range estimates.
Spectral analysis of impulse noise for hearing conservation purposes
Authors: Stevin Guy O.
Published: October 2005

Damage-risk criteria for impulse noise does not presently take the spectrum of the impulse into account; however, it is known that the human auditory system is spectrally tuned. The present paper advocates the extension to impulse noise of the noise dose concept which is widely used for continuous noise. This approach is based upon sound exposure instead of sound pressure. An A-weighting filter or an octave band analysis can then be used to take the spectral content of the impulses into account. The equipment needed for applying these procedures for impulse noise is an integrating sound level meter or a digital Fourier processor. Generalized spectral methods have been evaluated by means of an impulse simulation applied to a mathematical model of the human hearing mechanism. The results of this simulation agree with the most recent experiments on impulse noise and fully support the proposed rating methods. This conclusion must be emphasized as it leads the derivation of a uniform procedure for predicting loudness and damage risk for hearing which is applicable for continuous noise as well as for impulse noise.
Sound velocities at hypersonic frequencies in molten alkali chlorides
Authors: Aronsson R. , Knape H. E. G. , Torell L. M.
Published: October 2005

Measurements of the hypersonic velocity were made in a number of molten alkali chlorides by using Brillouin spectroscopy. The data indicate that no dispersion appears between the two different hypersonic frequencies studied for any of the molten salts. Furthermore, a comparison with corresponding ultrasonic velocities implies that any relaxation frequency must be higher than the investigated frequencies.
Comparison of the measured covariance of surface reverberation for horizontal and vertical arrays
Authors: Wilson Gary R.
Published: October 2005

An experimental study of the scattering of sound from the surface of a freshwater lake was performed. The study utilized nine staves in a vertical receiving array and four staves in a horizontal receiving array to examine the spatial and temporal covariance of the reverberation for both orientations simultaneously. The reverberation returns were generated by repetitively projecting a 100-μs cw pulse centered at 80 kHz at the wind-roughened surface of the freshwater lake at a 10.5° grazing angle. The returns were digitized and the covariance was estimated on a general purpose computer by ensemble averaging over 500 pings. Significant differences were observed between the covariances of the vertical and horizontal arrays. The envelope of the covariance between the vertical staves maintained a significant level at much larger separations than the horizontal array. The normalized covariance of the horizontal array was constant with time, while the normalized covariance of the vertical array slowly oscillated with time because the phase of the vertical covariance changed linearly with time. Thus the joint reverberation process measured by the horizontal staves was reducible to joint wide-sense stationarity while the joint reverberation process measured by the vertical staves was not. The vertical covariance was also found to depend on the location of the staves on the array for a fixed separation.
An analysis of intrinsic noise for a class of digital beamformers
Authors: Lockhart Clayton M. , Pitre Richard , Miller Max K.
Published: October 2005

The performance of a digital beamformer is analyzed in order to study harmonic distortion caused by the quantization and roundoff error intrinsic to the system. The analysis is limited to a first-order sampling, low-pass beamformer. The noise (distortion) sources discussed here are those generated by A/D conversion, interpolation beamforming (including digital filtering), and a fast Fourier transform. Additional degradation factors related to the sampling, time-delay quantization, and amplitude estimation are also included. Both clipping and nonclipping cases of the A/D process are discussed. The nonclipping analysis is based on computer simulation of the quantization and is compared to the actual quantization of sine waves performed by an A/D converter. The nonvanishing components of the noise spectrum are found to be uniform for both simulated and real data, and the noise levels are nearly equal to those predicted by the standard statistical model. For the clipping case, we characterize the placements and amplitudes of the harmonics as functions of percent clipping. The beamformer performance is analyzed by means of the statistical model of roundoff noise and by computer simulation of a finite bit beamformer for two particular beamformers.
Deconvolution applied to a near-bottom seismic profiler
Authors: Marchisio G. B. , Hodgkiss W. S.
Published: October 2005

Recent work attempting to relate the characteristics of the acoustic return from a near-bottom seismic profiler and the physical properties of sediment core samples motivated this study. The energy envelope of the seismogram does not reproduce the detailed structure of the underlying stratigraphy and in fact, can be misleading. Accordingly, we have modeled the physics of the process in terms of a convolution system and undertaken a comparison of the tradeoffs between three deconvolution techniques: (1) deterministic, (2) linear predition, and (3) homomorphic. The resolution and stability of each technique as a function of signal-to-noise ratio are illustrated for recovery of an underlying reflection coefficient sequence. Further, since the signals returned by significantly different stratigraphic columns may be strikingly similar in appearance, we have assessed the reliability of each processing scheme by pursuing two reflection coefficient sequences in parallel. The first, derived from physical properties of the core samples, contained no prominent features. The second was identical to the first with the addition of four large reflectors placed such that the energy envelopes of the two resulting seismograms were identical.
Reflection and scattering of sound by correlated rough surfaces
Authors: Twersky Victor
Published: October 2005

Pair correlations and the effects of dense packing are included to extend existing results on reflection and scattering by distributions of protuberances (bosses) on rigid or free base planes. The earlier energy conserving forms for the specularly reflected wave, the surface impedance, and the differential scattering cross section per unit area, are obtained in terms of a transform of the scattering amplitude of an isolated boss. Low-frequency approximations are developed with emphasis on the roles of the packing density and multipole coupling effects, and explicit results are given for semi-elliptic cylinders and hemi-ellipsoids. For lossless bosses, the reflection coefficient has a minimum, and the incoherent scattering a maximum, at the packing density corresponding to maximum fluctuations in the number of bosses per unit area. Multipole coupling effects may be misinterpreted in data inversion programs as changes in boss shape; if such effects are not included, then, e.g., hemispheres may be mistaken for hemiellipsoids broadened along the base plane and shortened along the normal.
Time-varying features as correlates of place of articulation in stop consonants
Authors: Kewley-Port Diane
Published: October 2005

Running spectral displays derived from linear prediction analysis were used to examine the initial 40 ms of stop-vowel CV syllables for possible acoustic correlates to place of articulation. Known spectral and temporal properties associated with the stop consonant release gesture were used to define a set of three-time-varying features observable in the visual displays. Judges identified place of articulation using these proposed features from running spectra of the syllables /b,d,g/ paired with eight vowels produced by three talkers. Average correct identification of place was 88%; identification was better for the male talkers (92%) than the one female talker (78%). Post hoc analyses suggested, however, that simple rules could be incorporated in the feature definitions to account for differences in vocal tract size. The nature of the information contained in linear prediction running spectra was analyzed further to take account of known properties of the peripheral auditory system. The three proposed time-varying features were shown to be displayed robustly in auditory filtered running spectra. The advantages of describing acoustic correlates for place from the dynamically varying temporal and spectral information in running spectra is dicussed with regard to the static template matching approach advocated recently by Blumstein and Stevens [J. Acoust. Soc. Am. 66, 1001–1017 (1979)].
An ordering principle for elastic wave propagation velocities
Authors: Sutcliffe Samuel
Published: October 2005

An elastic solid has, in general, three distinct wave propagation velocities in a given direction. According to a theorem of Fedorov, however, there are only two distinct velocities of propagation associated with an axis of material symmetry greater than binary symmetry. The converse of this theorem is proved herein, namely, that it is only in directions of material symmetry greater than binary symmetry that two distinct velocities occur. This leads to an ordering principle for elastic wave propagation velocities, that is, that the order of the velocities, regarded as functions of the direction of propagation, is invariant.
On caustics in a moving medium
Authors: Gorman A. D. , Wells R.
Published: October 2005

The extended Lagrange manifold (JWKB) technique is presented to illustrate how it reduces to a straightforward exercise the problem of locating the caustic curve and determining the asymptotic series solution on the caustic formed near a fixed source in a stratified medium moving with a uniform horizontal velocity. The case where the horizontal motion is depth dependent is also discussed. [AIP]
Scattering from a corrugated surface: Comparison between experiment, Helmholtz–Kirchhoff theory, and the facet-ensemble method
Authors: Kinney Wayne A. , Clay C. S. , Sandness Gerald A.
Published: October 2005

The facet-ensemble method is used to compute the complex field scattered by a corrugated surface with large roughness. The method employs in part the frequency transform of an asymptotic approximation to the exact impulse solution for diffraction from a rigid (or pressure release, if desired) ridge or trough [M. A. Biot and I. Tolstoy, J. Acoust. Soc. Am. 29, 381–391 (1957); A. D. Pierce, Acoustics (McGraw–Hill, New York, 1981), pp. 489–490.] In the method, the scattering surface is approximated by joining edge to edge long plane strips (facets). Each adjacent pair of facets makes up a ridge or trough. Theoretical scattered acoustic pressure amplitude values are then obtained by superposing the diffracted and reflected contributions from individual ridges and troughs. A similar method was introduced by Novarini and Medwin [J. C. Novarini and H. Medwin, J. Acosut. Soc. Am. 64, 260–268 (1978); H. Medwin and J. C. Novarini, J. Acoust. Soc. Am. 69, 108–111 (1981)]. A comparison is provided here between amplitude values measured in a water-tank, scattering experiment [G. A. Sandness, Ph.D. thesis, Univ. of Wisconsin, Madison (1971)] and values predicted using the facet-ensemble method. Agreement is good in general and remains so when the number of approximating facets per spatial wavelength of the surface is changed. Also provided is a comparison (for the experimental geometry) between the facet-ensemble method and numerical evaluation of the Helmholtz–Kirchhoff integral. Most of the scattering occurred near the normal direction, and the Helmholtz–Kirchhoff integral is accurate for that direction. Agreement in this case between the integral solution and the facet-ensemble method, therefore, is good. The facet-ensemble method shows promise for estimating accurately the complex field scattered from a rough rigid (or pressure release) surface for any number of receivers at any number of locations.
Nonlinearity acoustical parameter and its relation with Rao’s acoustical parameter of liquid state
Authors: Sharma B. K.
Published: October 2005

Sound-speed properties of liquids are calculated in terms of the easily measurable parameters on the assumption that the isochoric temperature derivative of the sound speed is the dominant factor with significant contribution to influencing the thermo-acoustic properties. Using this simple model it is shown that Beyer’s parameter of nonlinearity, Rao’s exponent, Carnevale and Litovitz’s exponent, molecular constant relating internal pressure and cohesive energy density, the microscopic Grüneisen parameter, and the thermodynamic or pseudo-Grüneisen parameter are all simply related to each other. The parameter of nonlinearity has been shown to depend on both Rao’s exponent and that of Carnevale and Litovitz. The calculated results are in reasonably good agreement with both the empirical and experimental results for various liquids.
Radiation from a double layer jet
Authors: Dash R.
Published: October 2005

The paper deals with the radiation of aerodynamic sound due to two symmetrically placed point sources on either side of a double layer jet flow. These sources are regarded as the driving forces in the acoustic medium. In consequence, the illumination due to a point source on one side is supplemented by the transmission due to the point source on the other side, which results in an enhanced radiation on each side. The analysis provides an expression for the reflexion coefficient which is valid at an interface that separates a fluid at rest from a fluid in motion [which is in perfect agreement with the one obtained by Miles, J. Acoust. Soc. Am. 29, 226–228 (1957), Ffowcs Williams, J. Fluid Mech. 66, 791–816 (1974), and Dash, J. Sound Vib. 49, 365–377; 379–392 (1976)] and predicts an aerodynamic zone of silence, also known as the valley of relative silence, which prevails parallel to the vortex interface off the source locations and appears in the form of sharp clefts around the jet axis. This deep valley in the directivity pattern deepens as the jet velocity or the ambient-to-jet density ratio ( ρ0/ρ1) increases. Marked by the conspicuous absence of highly directional beams, the formation of symmetric directivity patterns around the jet axis resembling a kidney-shaped, lung-shaped, or heart-shaped structure has been vividly illustrated in Figs. 5–8. The emergence of these structures depends on the jet speed and the ambient-to-jet density ratio ( ρ0/ρ1). This investigation also suggests that the sharp, steep, dual dimples formed in the directivity pattern are characteristics to the transonic and supersonic flows at ρ0/ρ1=1 whereas the balloon-type, puffed-up, dual loops formed symmetrically at close angles to the jet axis in the forward flow direction are solely characteristics to the supersonic flows at all values of the ambient-to-jet density ratio, ρ0/ρ1≥1.
Scattering by spherical elastic layers: Exact solution and interpretation for a scalar field
Authors: Gerard Alain
Published: October 2005

We consider an infinite space with a given set of concentric elastic spheres which are solicited by SH waves emitted by an external point source. The exact solution for the wave propagation in every zone of this pattern is determined. It is shown that the ratios of determinants which define the solution of this problem can be expanded in series of which each term can be explicit in terms of reflection and refraction coefficients. This second expression of the exact solution allows one to give an accurate interpretation of all terms to describe the excitation of resonance of a multilayered spherical structure and to facilitate the study of miscellaneous physical phenomena (resonance, diffusion, and interference spectra).
Laser-generated high-frequency sound waves in water
Authors: Emmony D. C. , Geerken T. , Klein-Baltink H.
Published: October 2005

The interaction of pulsed carbon dioxide laser radiation with the free surface of water gives rise to shock waves in the water and in the air above the surface. In addition a train of high-frequency, ∼20 MHz, oscillations in the water have been observed using ultra-high-speed photography by means of a nitrogen laser with a pulse duration of ∼1 ns. Confirmation that the oscillations are not due to diffraction effects in the shadowgraphs has been obtained by direct pressure transducer measurements in the water.
Estimation of the area function of human ear canals by sound pressure measurements
Authors: Hudde Herbert
Published: October 2005

A method to determine the ‘‘area function’’ of a duct, i.e., the variation of the cross section along the middle axis of the duct is described. It is shown that it is sufficient to measure the sound pressure at three locations in the duct to get knowledge of the area function. The calculated approximation fits the true area function the better the broader the bandwidth of the sound pressure signals is chosen. The bandwidth is bounded by the condition that no higher modes of sound propagation must be excited. In principle, the area function can be determined by solving a linear system of equations and executing a simple iterative algorithm. Some more work however is necessary to stabilize the computation against unavoidable small measuring errors. The calculated area function reproduces the acoustical transformation characteristics with good precision. In spite of this the calculated area function may disagree with the real area function in some regions, especially at the edges. Such errors occur, if the deviations of the area function from constant cross section correspond to frequencies outside the range of measurement. The method was applied to determine the area function of human ear canals and the results are presented.
ABR measurements in the cat using a forward-masking paradigm
Authors: Gorga Michael P. , McGee JoAnn , Walsh Edward J. , Javel Eric , Farley Glenn R.
Published: October 2005

Probe-elicited wave V amplitudes of the auditory brainstem response (ABR) were measured using a forward-masking paradigm. Subjects were anesthetized cats. For individual experiments, probe frequency and intensity were fixed and masker frequencies and intensities were varied. For each masker frequency, the extent to which the probe-elicited wave V amplitude was reduced by the preceding masker was plotted as a function of masker intensity. The rising segments of the masking functions were fitted with straight lines, using a least-squares procedure, to obtain estimates of their slopes. Masking grew most rapidly for masker frequencies below probe frequency, becoming progressively less steep as masker frequency increased. ABR tuning curves were constructed by using the linear fits to define the masker intensity that caused a 50% reduction in probe-elicited wave V amplitude. The shapes of these tuning curves were comparable to whole-nerve action potential (AP) tuning curves obtained under similar stimulus conditions. These results indicate that ABR amplitude measurements in a forward-masking paradigm can be used to estimate the growth of response to masking stimuli and frequency selectivity in a manner similar to AP amplitude measurments.
Inverse ray tracing in elastic solids with unknown anisotropy
Authors: Norris A. N.
Published: October 2005

The problem of inverse ray tracing in a homogeneous anisotropic elastic solid is considered. The wave speeds in the solid are assumed unknown, and must be obtained in the course of the inversion. The specific problem of locating a crack tip in a two-dimensional geometry is investigated. The data are assumed to be in the form of travel times of diffracted ultrasonic signals between transducers positioned on an exterior surface of the solid. Both pulse–echo and pitch–catch data are considered. It is found that travel-time data on the exterior surface suffices to locate the crack tip only if the material is isotropic. If the material is anisotropic, we must be able to move the source and/or receiver in the direction normal to the surface. The same problem is considered with the source and receiver positioned in a surrounding isotropic material, e.g., a water bath. It is shown that the ray inversion is now possible only if the solid is isotropic, the problem being underdetermined for an anisotropic solid. This indicates that the problem of inverse ray tracing, in the context of crack sizing, is not possible in a medium which is both inhomogeneous and anisotropic. Numerical results are presented for a synthetic experiment in which a finite crack is present in some transversely isotropic homogeneous elastic solids. It is demonstrated that an initial presumption of isotropy can lead to very erroneous results.
Anomalous infrasound from Space Shuttle II and Skylab I
Authors: Tahira Makoto , Donn William L.
Published: October 2005

Infrasound from Space Shuttle II and Skylab I recorded at Palisades, New York had characteristics strikingly different from all previous signals recorded from large rockets launched at Cape Canaveral. In the case of Space Shuttle, the reentry signal is unusually weak and lacking normal low frequency components. This anomaly is traced to the horizontal attitude of the reentry boosters and their slower speed. In the case of Skylab, the reentry signal arrives unusually early and the ratio of launch to reentry signal amplitude is inverted from past values. A combination of a different launch direction and weak stratospheric sound channel is responsible for the signal anomalies.
Time of day noise adjustments or ‘‘penalties’’
Authors: Schomer Paul D.
Published: October 2005

Community response descriptors, such as Day-Night Average Sound Level (DNL), have included a nighttime adjustment or ‘‘penalty’’ in their formulation. Typically this nighttime penalty has been 10 dB. Some models incorporate an evening penalty in addition to the nighttime penalty. The basis for these penalties is examined in this paper. This analysis is based on results from a community attitudinal survey conducted in the vicinity of a large Army base. The survey sought to compare blast noise (e.g., artillery) and helicopters in the context of all noise such as airplane, traffic, and children. The analysis shows that there are at least two factors which contribute to a ‘‘penalty’’ during any time period. One factor occurs when individual events are intrinsically more bothersome or annoying during one period of time than during another time period. The second factor occurs because a greater percentage of events are most likely to be noticed and found bothersome during one period of time as compared with another. The results show that single bothersome events are more or less equally annoying during all time periods of the day. There is only a small growth in annoyance during the night and this growth occurs primarily with the more impulsive sources such as artillery and helicopters. The results indicate that the second factor described above is more important in contributing to a total nighttime adjustment of penalty. That is, for a given number of available events, respondents are more likely to notice and be bothered by events during the night than during the day. This factor appears to be a primary contributor to any nighttime adjustment. The nighttime penalty indicated by these two factors is of the order of 5 to 10 dB. These results tend to support retention of a nighttime penalty in descriptors such as DNL. Based on the results, one would not be tempted to depart from the long-established 10-dB value for the penalty.
Power amplification in an active model of the cochlea—Short-wave case
Authors: de Boer E.
Published: October 2005

To account for the most recent experimental results on cochlear mechanics, a mathematical model should include an active source of vibrational energy. In this note the energy gain of such a model is computed, for the case that only short waves are supported. It is shown how, via a so-called criterion function, the required energy gain can be found from the basilar-membrane velocity response.
Masking patterns for synthetic vowels in simultaneous and forward masking
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

Two synthetic vowels /i/ and /æ/ with a fundamental frequency of 100 Hz served as maskers for brief (5 or 15 ms) sinusoidal signals. Threshold was measured as a function of signal frequency, for signals presented immediately following the masker (forward masking, FM) or just before the cessation of the masker (simultaneous masking, SM). Three different overall masker levels were used: 50, 70, and 90 dB SPL. In order to compare the data from simultaneous and forward masking, and to compensate for the nonlinear characteristics of forward masking, each signal threshold was expressed as the level of a flat-spectrum noise which would give the same masking. The internal representation of the formant structure of the vowels, as inferred from the transformed masking patterns, was enhanced in FM and ‘‘blurred’’ in SM in comparison to the physical spectra, suggesting that suppression plays a role in enhancing spectral contrasts. The first two or three formants were usually visible in the masking patterns and the representation of the formant structure was impaired only slightly at high masker levels. For high levels, filtering out the relatively intense low-frequency components enhanced the representation of the higher formants in FM but not in SM, indicating a broadly tuned remote suppression from lower formants towards higher ones. The relative phase of the components in the masker had no effect on thresholds in forward masking, indicating that the detailed temporal structure of the masker waveform is not important.
Detecting a repeated tone burst in repeated noise
Authors: Patterson Roy D. , Milroy Robert , Lutfi Robert A.
Published: October 2005

Samples of wideband noise 0.05, 0.1, 0.2, or 0.4 s in duration were digitized and then replayed cyclically to produce repeated-noise maskers. The signal was a repeating tone burst (0.4 or 1.6 kHz). It was half the duration of the noise sample, centered in the noise temporally, and it was repeated at the same point in each repetition of the noise. In the antiphasic conditions of the experiment, either the noise sample or the tone burst was inverted in alternate repetitions of the masker; in the homophasic conditions both the tone burst and noise, or neither, were inverted in alternative repetitions. If the auditory system were capable of storing detailed waveforms of sufficient length, alternate repetitions could be added or subtracted and we might expect a release from masking in the antiphasic conditions. The results show a small but significant advantage for the antiphasic conditions when the signal frequency was 0.4 kHz, but no difference with the 1.6-kHz signal.
The inverse problem for the vocal tract: Numerical methods, acoustical experiments, and speech synthesis
Authors: Sondhi Man Mohan , Resnick J. R.
Published: October 2005

In this article we will describe our recent experiments on the estimation of vocal tract area functions from transient acoustical measurements at the lips. Since the theoretical basis for such measurements has been discussed in several earlier publications we will concentrate on the measurement technique and the numerical procedures used to estimate the area functions from the measurements. The two main accomplishments we will report on are (1) We are now able to make measurements and compute and display the area function about 18 times per second. Such a display, which has not been possible before, allow one to visualize the shape of one’s vocal tract as one changes the position of one’s articulators. This display could form the basis of a visual aid for the improvement of the speech of profoundly deaf persons. (2) We have synthesized intelligible though not yet high quality speech from several sentence-length sequences of measured area functions. To the best of our knowledge, this is the first instance of continuous speech synthesized from direct measurements of area functions.
Bistatic low-frequency inverse scattering
Authors: Bojarski Norbert N.
Published: October 2005

The monostatic acoustic and electromagnetic low-frequency inverse scattering solutions of this author [Office of Naval Research Contract N00014-76-C-0082 Report (25 July 1982); IEEE Trans. Antennas Propag. AP-30 (4), 775–778 (July 1982)] are generalized to the bistatic case. Specifically, derived are bistatic acoustic and electromagnetic low-frequency direct scattering approximations in terms of the characteristic function of a scatterer. These bistatic approximations satisfy the principle of reciprocity, and consist of a generalization of the monostatic–bistatic equivalence theorem, valid for wide bistatic angles. Unlike the monostatic case, for which the acoustic and electromagnetic low-frequency direct scattering approximations are identical, and for which the electromagnetic low-frequency direct scattering approximation fails to yield depolarization information, the bistatic acoustic and electromagnetic low-frequency direct scattering approximations are different, and the electromagnetic bistatic low-frequency direct scattering approximation does yield depolarization information. An inverse scattering solution for the complete set of moments tensors of this characteristic function is obtained. It is shown that this bistatic inverse scattering solution is a bistatic generalization of Rayleigh’s monostatic volume law, yielding the Rayleigh volume of the scatterer for the moments tensor of rank zero. The moments tensors of rank one and two are shown to be the spatial position centroid and the principal dimensions (and their spatial orientation) of the scatterer, respectively. It is shown that the inverse scattering solution can be implemented with one transmitting and one receiving location, and a modest spatial spread in one, the other, or both locations.
Optimum frequency of propagation in shallow water environments
Authors: Jensen F. B. , Kuperman W. A.
Published: October 2005

The optimum frequency of propagation in shallow-water environments is the result of competing propagation and attenuation mechanisms at high and low frequencies. It is shown that the optimum frequency is strongly dependent on water depth, that it has some dependence on the sound-speed profile, while it is only weakly dependent on the bottom type. A comparison between experimental data and normal-mode theory indicates the importance of shear waves in the bottom, both in determining the optimum frequency of propagation and in determining the actual propagation-loss levels at lower frequencies.
Transmission of a pulsed acoustic signal at a two-fluid interface
Authors: Tjo/tta Jacqueline Naze , Tjo/tta Sigve
Published: October 2005

The transmission of an acoustic pulse with a plane front at a two-fluid interface is considered. An exact solution is obtained and several properties are derived. Numerical examples are given, showing patterns of the transmitted signal for different pulse shapes and incident angles. It appears that penetration at angles above the critical incidence (according to Snell’s Law) is indeed possible, depending on how the incident pulse is shaped. This happens at the cost of a self-demodulation of the signal.
Description of regular twelve-tone musical tunings
Authors: Rasch Rudolf A.
Published: October 2005

A framework is presented for the systematic description of musical tunings, based on the music-theoretical and on the frequency-ratio concept of musical intervals. All intervals are described as sums of octaves and fifths. Since the octave is always pure (2:1) knowledge of the sizes of the fifths is sufficient to determine the sizes of other intervals. In regular 12-tone tunings, 11 out of the 12 fifths are equal in size, either pure or tempered. Rules are given by which the size of the consonant intervals, and other intervals, can be derived from a single variable, the main fifth. Tunings are evaluated with the help of mean temperings of the consonant intervals in the major triads, mean temperings of all the triads in a tuning, and mean temperings of triads weighted with respect to a certain key. This is a theoretical study, which should be supplemented by observations from practice and perceptual experiments.
High-frequency sound attenuation caused by the wind-generated bubble layer in the open sea
Authors: Bruno Daniel R. O. , Novarini Jorge C.
Published: October 2005

Sound attenuation along vertical paths for high-frequency beams is calculated using a semi-empirical formula for the distribution of wind-generated bubbles in the open sea [Novarini and Bruno, J. Acoust. Soc. Am. 72, 510–514 (1982)]. These calculations are carried out numerically for frequencies between 70 and 150 kHz, wind speeds up to 30 kn and different transducer depths. The results are fitted with a simple formula.
Reiterant speech: An acoustic and perceptual validation
Authors: Larkey Leah S.
Published: October 2005

Reiterant speech, or nonsense syllable mimicry, has been proposed as a way to study prosody, particularly syllable and word durations, unconfounded by segmental influences. Researchers have shown that segmental influences on durations can be neutralized in reiterant speech. If it is to be a useful tool in the study of prosody, it must also be shown that reiterant speech preserves the suprasegmental duration and intonation differences relevant to perception. In the present study, syllable durations for nonreiterant and reiterant ambiguous sentences were measured to seek evidence of the duration differences which can enable listeners to resolve surface structure ambiguities in nonreiterant speech. These duration patterns were found in both nonreiterant and reiterant speech. A perceptual study tested listeners’ perception of these ambiguous sentences as spoken by four ‘‘good’’ speakers—speakers who neutralized intrinsic duration differences and whose sentences were independently rated by skilled listeners as good imitations of normal speech. The listeners were able to choose the correct interpretation when the ambiguous sentences were in reiterant form as well as they did when the sentences were spoken normally. These results support the notion that reiterant speech is like nonreiterant speech in aspects which are important in the study of prosody.