bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of enhanced spectral contrast on the internal representation of vowel-shaped noise
Authors: Sidwell Andrew , Summerfield Quentin
Published: October 2005

Two steady-state noise-excited vowel sounds of 200-ms duration were synthesized: one similar to a naturally produced whispered vowel, the other with energy removed outside a nominal 50-Hz band centered at each formant peak. The threshold for a brief sinusoidal probe tone was measured at frequencies corresponding to the peaks and troughs in the vowel spectra, in both forward and simultaneous masking. The masking functions for a flat-spectrum masker at each frequency were also measured, so that the vowel masking patterns could be expressed in terms of the equivalent broadband masker level. In the first experiment, masking patterns for the two maskers were measured with three normal-hearing subjects. Increasing spectral contrast was effective in increasing peak–valley differences in the masking patterns up to 2.5 kHz. Contrast was greater in forward than in simultaneous masking, suggesting that the internal representation of a vowel may be enhanced by suppression. In a second experiment, masking patterns and flat-spectrum masking functions were measured with three listeners with moderate sensorineural hearing impairments. The enhancement produced by increasing spectral contrast was less than that obtained with normal-hearing listeners, but still present up to 2.5 kHz. A comparison of forward- and simultaneous-masking patterns again revealed an increase in peak–valley differences, suggesting that suppression mechanisms were still effective in these listeners. The ability to enhance the internal representation of speechlike sounds in hearing-impaired listeners may have implications for the design of signal-processing hearing aids.
Intensity difference limens at high frequencies
Authors: Long Glenis R. , Cullen John K.
Published: October 2005

Thresholds for amplitude modulation detection were obtained from four subjects at frequencies of 2, 4, 6, 8, and 10 kHz for sensation levels of 15, 30, 45, and 60 dB and modulation rates of 2, 4, and 8 Hz. High-frequency difference limens calculated from amplitude modulation thresholds were found to change nonmonotonically as a function of sensation level, independent of modulation rate. This nonmonotonic relation stemmed mainly from a gradual reduction of the difference limen at the lowest sensation level with increasing frequency. Difference limens for pulsed tone discrimination were also measured in two of the subjects at 2, 6, and 10 kHz and sensation levels of 15, 30, 45, and 60 dB. The relation between intensity discrimination and sensation level was similar to that found for amplitude modulation detection. These findings are interpreted as indicating that the nonmonotonic relation between sensation level and intensity resolution is a general characteristic of stimulus processing at higher frequencies.
Biochemical and immunochemical approaches to the study of the auditory system
Authors: Wenthold Robert J.
Published: October 2005

In recent years a new arsenal of biochemical and immunological techniques has been developed to probe the biochemical function of the nervous system. This paper describes some of these techniques and indicates how they are being used within the auditory nervous system. These techniques provide the possibility of understanding the generation of neural activity within single neural elements of the auditory system.
Mathematical modeling of cochlear mechanics
Authors: Neely Stephen T.
Published: October 2005

The recent discovery of oto-acoustic emissions [see Zurek, J. Acoust. Soc. Am. 78, 340–344 (1985)] and the newer measures of the micromechanics of the inner ear have generated renewed interest in quantitative descriptions of the biomechanics of the cochlea. Active elements (mechanical force generators) are thought to be essential for producing the high sensitivity and sharp tuning typically associated with normal cochlear function. A mechanical model with active elements is described which can simulate basilar membrane displacements with neural-like tuning and peak amplitudes of about 1 nm at the threshold of hearing. In addition, such models might help explain the source of oto-acoustic emissions. The paper describes the power of the recent attempts at providing quantitative descriptions and predictions of the mechanics of the cochlea.
The owl’s cochlear nuclei process different sound localization cues
Authors: Konishi Masakazu , Sullivan W. Edward , Takahashi Terry
Published: October 2005

This paper discusses how the barn owl’s brain stem auditory pathway is divided into two physiologically and anatomically segregated channels for separate processing of interaural phase and intensity cues for sound localization. The paper also points out the power of the ‘‘downstream’’ approach by which the emergence of a higher-order neuron’s stimulus selectivity can be traced through lower-order stations.
The role of suppression in psychophysical measures of frequency selectivity
Authors: Jesteadt Walt , Norton Susan J.
Published: October 2005

The neural output of the cochlea consists of a structured spectral representation of the input waveform. Psychophysical studies of frequency selectivity provide measures of the quality of this spectral representation based on the detection of a spectrally narrow signal in the presence of competing acoustic inputs. Results are often interpreted in terms of the underlying physiological processes. The present paper begins with a summary of the basic principles and data and a review of recent efforts to extend the theoretical framework to account for a wider range of phenomena. It then discusses and evaluates specific assumptions concerning the role of suppression in psychophysical measures of frequency selectivity, an area of research that has received much attention in recent years. The goal is to provide a summary of current answers to basic questions at a time of rapidly expanding knowledge about both the physiology and psychophysics of frequency selectivity.
Sound diffraction for a spherical microphone
Authors: Peterson Arnold P. G.
Published: October 2005

The increase in pressure due to diffraction for a point microphone on a sphere is calculated for random incidence. Calculations have shown that for a fixed angle of incidence a significant ripple is present in the diffraction characteristic for a sphere when plotted as a function of frequency. This detail appears to have been ignored in previous theoretical calculations.
Measurements of acoustic ambient noise in shallow water due to breaking surf
Authors: Wilson O. B. , Wolf Stephen N. , Ingenito Frank
Published: October 2005

Horizontal directionality of ambient noise was measured at ranges up to 15 km from the southeastern shore of Monterey Bay, California. Water depths at the sites ranged from 8–175 m. A steerable cardioid receiving pattern was formed using signals telemetered from dipole and omnidirectional hydrophones suspended from tethered buoys. With no nearby shipping, whenever the maximum of the cardioid pattern was directed toward the beach, noise levels in the frequency range 20–700 Hz were greater than those obtained when the maximum was directed seaward. This difference or anisotropy (seaward versus shoreward), which depends on range from the beach, on frequency, and on surf intensity, was 10 dB at 300 Hz at the 9-km site during very heavy surf. Surf beat was clearly audible when the cardioid maximum was steered shoreward at ranges as great as 2 km. The anisotropy effects diminish both in magnitude and frequency range with lower wave height but are still observable during light surf. During heavy surf, the omnidirectional ambient noise levels also increased significantly in the same frequency range at which the anisotropy is evident. The spectrum levels during heavy surf compare reasonably well with data reported by Knudsen et al. [J. Mar. Res. 7, 410–429 (1948)] and by Piggott [J. Acoust. Soc. Am. 36, 2152–2163 (1964)]. We conclude that intense breaking surf can contribute significantly to ambient noise in fairly deep continental shelf waters.
New type transducer for measuring contact compliances of a soft body
Authors: Omata Sadao
Published: October 2005

A new type transducer for measuring a contact compliance or a contact resonance is described. The instrument is very different from conventional electrodynamic vibrometers which consist of a moving coil and a loudspeaker magnet. The old instruments exert a greater influence on the contact resonance of a soft body, because they have a heavy driver unit. In order to minimize elastic deformations of a test material on which the transducer rests, the new transducer is designed to operate with a piezoelectric disk which is employed as the driver unit. Therefore, the piezoelectric transducer proposed here is small, light, and consumes very little electricity. In addition, by using the piezoelectric vibrator technique, experimental investigations are conducted to deduce the characteristics of the contact resonance of a soft body such as foam rubber.
Nonlinear effects in the farfield of a directive sound source
Authors: Hamilton Mark F. , Tjo/tta Jacqueline Naze , Tjo/tta Sigve
Published: October 2005

Nonlinear propagation of a periodic sound beam in a dissipative fluid is considered using Fourier series expansion and numerical methods to solve the governing equation of motion in the parabolic approximation. The nearfield was considered in a previous paper [Aanonsen et al., J. Acoust. Soc. Am. 75, 749–768 (1984)]. The analysis is now extended to the farfield. Numerical and asymptotic results are derived and used to explain the development of the fundamental and harmonic components from the nearfield into the farfield. A discussion is also given of some earlier models for the farfield of directional waves. Emphasis is put on the importance of imposing the proper matching conditions between the nearfield solution and the spherical solution in the farfield in order to obtain a good approximation. Propagation and saturation curves are calculated, as well as beam patterns for various harmonic components. The results are compared with available experimental observations. Nonlinear effects, although generated in the nearfield, are found to be propagated to ranges many tens of Rayleigh distances if the absorption is weak.
F
in the perception of lenis and fortis plosives
Authors: Kohler Klaus J.
Published: October 2005

This paper reviews articulatory data that provide evidence for a backward influence of stop manner production on the F0 of the preceding vowel in German, and it presents results from four experiments that show the relevance of pre-closure F0 for stop manner perception in the German word pair ‘‘leiden’’/‘‘leiten.’’ The results are compared with several perceptual investigations of monotone versus changing F0 on English monosyllables influencing the voiced/voiceless judgment for post-vocalic consonants. The theory that we are here dealing with a general auditory phenomenon instead of a production–perception relationship is refuted on the basis of the production and perception data available for German and for English.
A probabilistic interpretation of the acoustic impulse response and applications to numerical calculations
Authors: Simonds R. M.
Published: October 2005

One approach used to estimate the radiation fields of acoustic radiators is the convolution method. This procedure evaluates the velocity potential by transforming the Rayleigh integral into the convolution of the radiator velocity profile with the so-called spatial impulse response of the radiator. It is shown that the impulse response is related to the probability density function of the acoustic path lengths and that calculations of the impulse response can proceed either from knowledge of the density or distribution functions of the radiator’s acoustic path lengths. Examples of the use of the method are shown to demonstrate that the approach leads to the same analytical expressions for the impulse response as obtained by traditional methods. It is shown that this probabilistic interpretation of the impulse response leads to readily evaluated numerical methods in the cases of radiator shapes which cannot be evaluated in closed form.
Acoustics of a standing wave tank for studying the hearing capacity of fish
Authors: van den Berg A. V. , Schuijf A.
Published: October 2005

In a standing wave tank responses of fish to sound stimuli used to investigate the hearing capacity of fish may perhaps be affected by unintended stimulation of the lateral line. Uniform oscillatory water flow patterns do not stimulate the lateral line. Departures from uniformity were derived from measurements of acoustic pressure and particle velocity at 5-cm spacings around the center in our standing wave tank containing six transducers suspended along three axes that are perpendicular to one another. These measurements are compared with the results of a model in which negligible influence of the tank wall and an incompressible water column in the tank are assumed. Deviations of computed values from measured values of sound pressure and the principal velocity components are less than 5 dB. The model underestimates velocity components perpendicular to the principal component. However, the model does appear a reliable aid for estimating the spatial function of sound pressure and velocity from the values of p and v̄ measured at the tank center. Upper limits for the relative velocities between the fish body and the water can only approach threshold values for the lateral line stimulation under worst conditions (i.e., a velocity node at the tank center) in this setup.
Diffuse elastic waves at a free surface
Authors: Weaver Richard L.
Published: October 2005

For a diffusely vibrating elastic body, the participation of the surface in the general disturbance is evaluated. It is shown that in the vicinity of a free surface a diffuse acoustic field may legitimately be regarded as a sum of incoherent isotropic and homogeneous independent plane waves incident upon the surface together with their respective outgoing reflected consequences. The work contributes to a conceptual basis for the study of acoustic emission signals on time scales large compared to acoustic travel times across the structure.
A theoretical model of surface-generated noise in a wedge-shaped ocean with pressure-release boundaries
Authors: Buckingham Michael J.
Published: October 2005

A theoretical model of ambient noise in a wedge-shaped domain with pressure-release boundaries is presented. The noise generators are represented as impulsive monopoles located in a narrow wedge-shaped region immediately below the surface. The treatment is analytical, and is based on a solution of the Helmholtz equation for propagation in a (three-dimensional) wedge. This solution, which includes the effects of horizontal refraction, takes the form of a sum of normal modes; this modal structure is also apparent in the general solution derived here for the cross-spectral density of the noise. It is shown from this solution that, as in the case of shallow water, the noise field in the wedge is quasihomogeneous over a substantial region of the water column. Moreover, deep in the water column and many wavelengths from the apex of the wedge, the noise field closely approximates a plane-wave, isotropic noise field.
Application of a new theoretical treatment to an old problem; sinusoidal pressure release boundary scattering
Authors: McCammon Diana F. , McDaniel Suzanne T.
Published: October 2005

The scattering of sound from a sinusoidal pressure release boundary has long been the subject of study among researchers. Recently, R. L. Holford [J. Acoust. Soc. Am. 70, 1116–1128 (1981)] outlined an exact solution to a variant of the Helmholtz integral equation that permits calculation of the unknown velocity potential on the surface by the solution to a matrix equation. Application of this solution is made to the sinusoid to generate plane wave reflection coefficients. The reflection coefficients are then compared with two sets of model tank data as well as with the approximate solutions of Kirchhoff, Eckart, Rayleigh, and Brekhovskikh. The exact solution compares most favorably with the data, particularly on the rougher surfaces. The principal errors produced by the approximate solutions are a shift in the location of the reflection nulls, an inability to correctly predict unity when all side orders are evanescent, and the absence of Rayleigh reflection anomalies. These errors appear regardless of the roughness parameter range or radius of curvature, even when the solution is theoretically within its region of validity. The reflection coefficients are also compared with a previous solution that utilized the same basic method of solution for a different formulation of the scattering problem.
Contextual effects on lingual–mandibular coordination
Authors: Edwards Jan
Published: October 2005

Coordination between intrinsic and jaw-related components of tongue blade movement during the articulation of the alveolar consonant /t/ was examined across changes in phonetic context. Tongue–jaw interactions included compensatory responses of one articulatory component to a contextual effect on the position of the other articulatory component. A similar reciprocity has been observed in studies that introduced artificial perturbation of jaw position and studies of patterns of token-to-token variability. Thus the lingual–mandibular complex seems to respond in a similar manner to at least some natural and artificial perturbations.
Contextual effects on vowel duration, closure duration, and the consonant/vowel ratio in speech production
Authors: Luce Paul A. , Charles-Luce Jan
Published: October 2005

Acoustic measurements were conducted to determine the degree to which vowel duration, closure duration, and their ratio distinguish voicing of word-final stop consonants across variations in sentential and phonetic environments. Subjects read CVC test words containing three different vowels and ending in stops of three different places of articulation. The test words were produced either in nonphrase-final or phrase-final position and in several local phonetic environments within each of these sentence positions. Our measurements revealed that vowel duration most consistently distinguished voicing categories for the test words. Closure duration failed to consistently distinguish voicing categories across the contextual variables manipulated, as did the ratio of closure and vowel duration. Our results suggest that vowel duration is the most reliable correlate of voicing for word-final stops in connected speech.
Stimulus parameters governing confusion effects in forward masking
Authors: Neff Donna L.
Published: October 2005

In forward masking, performance may be affected by confusion, that is, by the difficulty of discriminating a suprathreshold signal from the preceding masker. This study investigated confusion effects for forward maskers composed of repeated bursts of a 1000-Hz sinusoid followed by sinusoidal signals; such ‘‘pulsing’’ maskers produce confusion when the properties of the signal are identical to those of an individual masker ‘‘pulse.’’ The level, frequency, and duration of the signal relative to an individual masker pulse, as well as offset–onset delay, were varied to determine the minimum change necessary to eliminate confusion. For maskers composed of 20-ms pulses, confusion was eliminated by changes in signal level of 5 dB or changes in signal frequency of 30 to 40 Hz. For maskers composed of 10-, 20-, or 40-ms pulses, confusion was eliminated by signal delays of 8 to 16 ms or by signal durations less than half or greater than twice the masker-pulse duration. Results with adaptive procedures designed to measure confusion-free or confusion-determined thresholds suggest that confusion effects can be minimized or avoided by extensive listener training with a procedure in which the signal and masker are not presented at similar intensities.
Ultrasonic background noise in industrial environments
Authors: Bass Henry E. , Bolen Lee N.
Published: October 2005

Ultrasonic noise associated with various manufacturing operations has been measured in the frequency range 0–1 MHz in order to evaluate typical noise environments for ultrasonically controlled robots. Industrial operations studied include impact, bending, grinding and drilling, laser etching, and high-velocity fluid or air sprays. The first three operations provide little ultrasonic energy above 100 kHz. For these processes, ultrasonic sensors operating above 100 kHz should have an advantage since signal and noise will both fall off with increasing frequency. Ultrasonic emission from laser etching was found to be quite broadband, making such processes less suitable for ultrasonic control. High-velocity fluid or air sprays are the most prevalent sources of ultrasonic noise. The noise from these sources rolls off slowly with frequency, and no frequency bands without noise exist for ultrasonic sensing below several hundred kHz. For applications requiring ultrasonic sensing, aerodynamic noise should be reduced.
A simple shallow water propagation model including shear wave effects
Authors: Ellis Dale D. , Chapman D. M. F.
Published: October 2005

The Pekeris model has proved to be very useful in describing some features of acoustic propagation in shallow water, and as a simple test of ideas in normal mode theory. The basic model consists of a homogeneous layer of fluid overlying an infinite homogeneous fluid half-space of greater sound speed. Here, we extend the Pekeris model to handle the case of a fluid overlying an elastic basement in which the shear speed is less than the (compressional) speed of sound in the fluid. This gives rise to leaky modes in which both the mode eigenfunctions and eigenvalues are complex. The model predictions are compared to some measured propagation losses for a shallow water site overlying a chalk bottom, where compressional to shear wave conversion at the water–chalk interface causes large losses. The predictions of the simple model explain the very high losses measured at frequencies less than 200 Hz. At higher frequencies the sound-speed profile, absorption of sound by the water, and the effects of a thin sediment layer become important, but then an all-fluid normal mode model is in agreement with the measured results.
Rectified heat transfer in vapor bubbles
Authors: Patel G. M. , Nicholas R. E. , Finch R. D.
Published: October 2005

Some experimental findings on the dynamics of vapor bubbles in ultrasonic fields are reviewed. In particular, attention is drawn to a phenomenon which might be described as ultrasonically stimulated boiling. There is also a summary of certain pertinent facts about the threshold of cavitation in liquids with low foreign gas content, such as liquid nitrogen or liquid helium. It is emphasized that threshold pressure amplitudes can be less than the static pressure. It is proposed that an explanation of these observations could lie in a net positive heat transfer into a pulsating bubble. The minimum amplitude required to cause such a ‘‘rectified’’ heat transfer is calculated.
Binaural analysis in forward masking: Effects of signal frequency
Authors: Yama Mark F.
Published: October 2005

The present study investigates the relationship between signal frequency and size of the MLD in forward masking for the two binaural conditions NoSM and NoSπ. For both conditions, the largest MLDs were produced for signal frequencies between 200 and 500 Hz, and as signal frequency was increased above these values, the MLD progressively diminished. This pattern of frequency dependence, and the similarity of the results for the NoSM and NoSπ conditions, are consistent with data obtained in simultaneous masking experiments and are compatible with a vectorial description of the stimulus processed by the binaural system.
Optical method for measurement of ear canal length
Authors: Zemplenyi Jan , Gilman Samuel , Dirks Donald
Published: October 2005

A noninvasive optical method using an operating microscope was developed to measure the length of an ear canal under both open and occluded conditions. The method is based on the optical measurement of the distance between a reference point at the eardrum and a second point on the lateral aspect of an earmold-occluded ear canal. To estimate the occluded canal length, the length of the earmold is then subtracted from results of the previous measurement. The method was also used to determine the open ear canal length (the lateral reference point was the ear canal entrance), and averaged results agreed closely with previously reported data.
Viscoelastic modeling of canine vocalis muscle in relaxation
Authors: Alipour-Haghighi Fariborz , Titze Ingo R.
Published: October 2005

Analysis of vocal fold vibration requires information on the viscoelastic properties of the vocalis muscle. The force response of two canine vocalis muscles was measured in one-dimensional, stepwise elongation of the tissue as a function of time with a computer-controlled ergometer. The viscoelastic behavior of the muscle in its passive state was demonstrated through the relaxation test. A quasilinear viscoelastic model was used to parametrize the relaxation function, and results are reported for various levels of strain. Furthermore, a model was used to obtain theoretical time-dependent stress–strain curves to compare with experimental data.
Coupled thickness–shear and thickness–twist vibrations of unelectroded AT-cut quartz plates
Authors: Tiersten H. F. , Smythe R. C.
Published: October 2005

The equation of coupled thickness–shear and thickness–twist vibrations for rotated Y-cut quartz plates is applied in the analysis of unelectroded rectangular and circular AT-cut quartz plates with free edges. In the case of the rectangular plate, the appropriate edge conditions are found and the solutions are obtained. In the case of the circular plate, the two coefficients appearing in the planar differential operator are written as a sum of an isotropic part plus a deviation. The eigensolutions for the nearby isotropic case are found and the resonant frequencies for the actual anisotropic case are obtained from the equation for the perturbation of the eigenfrequency from the isotropic solution. For the circular plate, the results have been compared with measurements of the fundamental and the third harmonic overtone, and the agreement is quite good.
Ray transmissions over a sloping bottom in shallow water
Authors: Rousseau T. H. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

The effects of a sloping bottom on acoustic transmissions, between a source and receiver at arbitrary but fixed locations, are investigated using ray theory. An isospeed channel is assumed, and bottom angles up to about 3° are considered. Sloping bottom influence on per-ray quantities, including travel time and transmission loss, are examined for cw transmissions. Significant variations are shown to occur, such as travel time changes of more than 200 ms over ranges of about 6 km. Per-ray transmission loss is found to be influenced strongly by bottom slope, the amount of influence depending upon source–receiver bearing and the bottom loss model used. Variations of more than 20 dB are demonstrated. Effects of a sloping bottom on the total acoustic field are examined also, and the results compared with those for a horizontal bottom. Finally, a simple model of a shallow water front is superposed over the sloping bottom, and travel time is investigated. The sloping bottom effect can induce travel-time changes more than 300% larger than the frontal effect for different source–receiver geometries and bottom inclinations.
On the theory of sound scattering and viscous absorption in aqueous suspensions at medium and short wavelengths
Authors: Hay Alex E. , Mercer Douglas G.
Published: October 2005

An explicit expression is derived for the phase shifts of the partial waves scattered by a solid elastic sphere, incorporating the effects of the viscosity of the ambient fluid. The solution is applicable to frequencies and scatterer sizes for which the viscous boundary layer thickness is much less than the radius of the sphere. For particle sizes in the sand-size range (30 μm<a< 1 mm) or larger, this requires that the wavelength be comparable to or smaller than the scatterer circumference. Expressions for the phase shifts in the rigid and immobile, rigid limits, including viscous effects, are also obtained, as is an approximate expression for the viscous absorption coefficient in the rigid, immobile limit. These results are used to calculate the backscatter amplitudes and the viscous and scattering attenuation coefficients for tungsten carbide, aluminum, and quartz spheres in water. It is found that the viscous absorption coefficient is a slowly increasing function of frequency, except for sharp peaks at the frequencies of the whispering gallery wave resonances. Rayleigh wave resonances have little effect. In contrast, the Rayleigh wave resonances cause the largest departures from the rigid sphere form of the scattering attenuation coefficient.
Acoustic measurements of the anatomy of fish at 220 kHz
Authors: Sun Ying , Nash Richard , Clay C. S.
Published: October 2005

Many measurements of sound backscattered by fish have been made, but most of these are farfield measurements from whole fish. Some of the acoustic properties of a fish can be inferred from the dependence of scattering on aspect and removal of organs such as the swim bladder. However, farfield measurements do not give the detailed structure needed to construct a Huygen’s scatterer acoustic model of a fish. We built a 220-kHz focused sonic scanner. The focal distance was 10 cm and the axis of the fish was placed at 10 cm from the transducer for measurements. We measured the peak amplitudes of backscatter sound along the length of yellow perch (Perca flavescens) (12–14 cm) and hog sucker (Hypenteeium nigricans) (30 cm). Repeatability of results was examined in three different yellow perch and gave a good agreement between the resulting backscattering curves. Preservation (freezing) of the fish resulted in approximately 30% reduction of the overall backscatter but did not affect the shape of the backscattering curve. The measurements showed that the swim bladder gave about 80% of the scattered energy for the yellow perch. The swim bladder gave only about 20% of the scattered energy for the hog sucker. Vertebrae, head, and flesh were distributed scatterers. We observed a gross dependence of the distribution of scatterers on the species of fish. These differences should be observable in measurements of the probability density functions of fish echoes.
Low-frequency reflection and scattering by ellipsoidally embossed surfaces
Authors: Lucas R. J. , Twersky V.
Published: October 2005

Earlier low-frequency results for scattering and reflection by random distributions of relatively arbitrary bosses on rigid or free base planes are applied numerically to completely rigid or free ellipsoidally embossed isotropic and anisotropic surfaces. Illustrative curves exhibit the effects of boss shape and orientation, and of their statistical distribution (pair correlated as well as uncorrelated) on the coherent power reflection coefficient and the reflected phase, and on the incoherent differential scattering cross section per unit area versus angles. In addition, for rigid surfaces, simple approximations are included for the location and magnitude of the pseudo-Brewster minimum in the reflected power and for the extrema of the forward (specular) and backscattered cross sections, as well as for the location of the zero of the phase change on reflection. We emphasize anisotropic forward and backscattered differential cross sections near grazing for applications to sea–air, sea–bottom, and sea–ice programs.
Density estimates of biological sound scatterers using sonar echo peak PDFs
Authors: Stanton T. K.
Published: October 2005

Studies of marine animals such as fish and plankton require knowledge of their density (number of animals per unit volume). Standard acoustical techniques, such as echo integration, give accurate estimates of density, but only with a carefully calibrated system. We have found the statistical nature of the echo useful in making rough estimates of density without a calibrated system. In particular, we are studying the probability density function (PDF) of the maximum (peak) value of the echo achieved in a time gate. One useful property of this PDF is that for the two extremes in which the echoes from the individual scatterers overlap and do not overlap, the PDFs take on drastically different shapes. The difference is so great that one can visually judge from the PDF whether or not the echoes were overlapping. For a given ping duration and sonar beamwidth, there is a critical density above which the echoes overlap (or conversely below which the echoes do not). We use this property to estimate densities of animals. Examples are given in this paper of order of magnitude estimates of the density of fish in Trout Lake, Wisconsin and Lake Michigan, and a lower bound estimate of 1-cm-size plankton density in the Gulf Stream Boundary near Cape Hatteras, North Carolina. The technique is shown to be simple and robust. It was quickly implemented without calibration of the system. The technique is good for fast preliminary results and is a good check on the accurate, more involved techniques.
Multiple scattering of elastic waves by cylinders of arbitrary cross section. II. Pair-correlated cylinders
Authors: Varadan V. K. , Varadan V. V. , Ma Y.
Published: October 2005

Multiple scattering of elastic waves by randomly distributed cylinders of arbitrary cross section has been considered. Because the pair-correlation function, as well as the quasicrystalline approximation, has been incorporated in the presented formalism, the effective phase velocity, as well as the coherent attenuation in dense systems, has been investigated. A more efficient scattering formalism (SF) has been employed rather than the exciting field formalism (EF) used earlier by the authors. Closed form expressions for the phase velocity and the attenuation are given in the Rayleigh limit, and numerical results are presented for a wide range of frequencies and concentrations.
Comparison of electromyographic signals from different electrode placements in the palatoglossus muscle
Authors: Cooper Donald S. , Folkins John W.
Published: October 2005

It is a general practice to insert a single electrode pair per muscle for electromyographic recording. The location of electrode insertion influences the character of the signal obtained. The objective of the experiment was to study the relationships between electromyographic signals recorded simultaneously from different locations in an anatomically simple muscle involved in speech production. Signals from three pairs of fine wire electrodes placed high, middle, and low in the palatoglossus muscle of five speakers of American English were amplified, rectified, and integrated. The data were analyzed statistically to determine the patterns of similarity and degree of independence among simultaneous signals from different sites in the muscle for a given speaker. The middle signal was most often the best, and the low signal was most often the poorest representative of the group of signals. The greatest similarity was found between the high and middle signals; next most similar were the middle and low signals. Similarity between signals varied with utterance. In some cases, the relationship between two signals varied over time. This variation may be due to change in interelectrode distance during anisometric contraction or to different motor unit firing patterns.
Glottal source–vocal tract interaction
Authors: Koizumi Takuya , Taniguchi Shuji , Hiromitsu Seijiro
Published: October 2005

The problem of glottal source–vocal tract interaction is treated. The effect of the first formant load on the waveform of glottal volume flow is investigated by solving a nonlinear differential equation which describes the variation of pressure drop across the first formant load. The glottal volume flow is calculated under the influence of supraglottal and subglottal formant loads. The estimation of the glottal area function is discussed as an application of the theory developed.
On the loudness of complex stimuli and its relationship to cochlear excitation
Authors: Cacace Anthony T. , Margolis Robert H.
Published: October 2005

Two experiments were conducted to reexamine the relation between loudness and the bandwidth of complex stimuli. In experiment 1, experimental stimuli consisting of a 2000-Hz pure tone and ten computer-generated multitonal complexes ranging in bandwidth from 0.26–3.16 oct, logarithmically centered at 2000 Hz, were matched in loudness to a 2000-Hz comparison pure tone presented at 90, 70, and 30 dB SPL. The SPL of the experimental stimuli required for equal loudness was linearly related to bandwidth (in octaves) for each of the three comparison stimulus levels. In experiment 2, the loudness behavior of narrow-bandwidth stimuli within the previously reported critical band region was examined. The results indicated a linear relation similar to that obtained in experiment 1. These results are consistent with an auditory filter concept in which frequency is continuously encoded along the basilar membrane and in which loudness of complex stimuli is linearly related to area of excitation.
Speech processing in the auditory system II: Lateral inhibition and the central processing of speech evoked activity in the auditory nerve
Authors: Shamma Shihab A.
Published: October 2005

A biologically realistic model of a uniform lateral inhibitory network (LIN) is shown capable of extracting from the complex spatio-temporal firing patterns of the cat’s auditory nerve the formants and low-order harmonics of synthetic voiced speech stimuli. The model provides a realistic mechanism to utilize the temporal aspects of the firing and thus supports the hypothesis that the neural coding of complex sounds in terms of average rates can be supplemented by the information coded in the synchronous firing. At low levels of intensity the LIN can sharpen the average rate profiles. At moderate and high levels the LIN uses the cues available in the distribution of phases of the synchronous activity which exhibit rapid relative phase shifts at specific characteristic frequency (CF) locations (corresponding to the frequencies of the low-order harmonics in the stimulus). These temporal phase shifts manifest themselves at the input of the LIN as steep and localized spatial discontinuities in the instantaneous pattern of activity across the fiber array. The LIN enhances its ouput from these spatially steep input regions while suppressing its output from spatially smooth input regions (where little phase shifts occur). In this manner the LIN recreates from the response patterns a representation of the stimulus spectrum using the temporal cues as spatial markers of the stimulus components rather than as absolute measures of their frequencies. Similar results are obtained with various lateral inhibitory topologies, e.g., recurrent versus nonrecurrent, single versus double layer, and linear versus nonlinear.
On the weighting of time delay measurements for improved direction finding
Authors: Hassab J. C.
Published: October 2005

The present paper derives the statistical measures on the bearing estimates (bias, variance, Cramer–Rao bound) for unequally separated clusters of hydrophones and also unequal variances on the time delay estimates. The present results reduce to those found in the literature for direction-finding systems that presume equally separated clusters of hydrophones and equal time delay variances. The derivation takes into account those differences in spatial and temporal characteristics in the direction-finding system to design a minimum least-square-error weighting filter. When applied, the filter is shown to lead to improved direction-finding estimates through reduction of both bias and variance. The relative influence of other approaches on the quality of the bearing estimates is identified.
Coherent active methods for applications in room acoustics
Authors: Guicking Dieter , Karcher Käthe , Rollwage Mathias
Published: October 2005

An adjustment of reverberation time in rooms is often desired, even for low frequencies where passive absorbers fail. Among the active (electroacoustic) systems, incoherent ones permit lengthening of reverberation time only, whereas coherent active methods will allow sound absorption as well. A coherent-active wall lining consists of loudspeakers with microphones in front and adjustable control electronics. The microphones pick up the incident sound and drive the speakers in such a way that the reflection coefficient takes on prescribed values. An experimental device for the one-dimensional case allows reflection coefficients between almost zero and about 1.5 to be realized below 1000 Hz. The extension to three dimensions presents problems, especially by nearfield effects. Experiments with a 3×3 loudspeaker array and computer simulations proved that the amplitude reflection coefficient can be adjusted between 10% and 200% for sinusoidal waves at normal and oblique incidence. Future developments have to make the system work with broadband excitation and in more diffuse sound fields. It is also planned to combine the active reverberation control with active diffusion control.
Colony differences in auditory thresholds in the canary (S
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Authors: Okanoya Kazuo , Dooling Robert J.
Published: October 2005

Adult canaries (Serinus canarius) from a closebred colony of the Belgian ‘‘Waterslager’’ strain were trained with operant techniques to respond to pure tones. A psychophysical tracking procedure was used to measure absolute auditory thresholds in quiet and in noise. Absolute thresholds in the middle- to high-frequency region of the audiogram were between 30 and 40 dB higher (4–5 standard deviations) than those typically reported for other song birds including canaries of other strains and Waterslagers tested some years ago from another colony. Thus the Millbrook colony of domestic canary—an oscine songbird which learns its vocalizations by reference to auditory information—shows unusually high absolute thresholds for pure tones.
Effects of masker waveform and signal-to-masker phase relation on diotic and dichotic masking by reproducible noise
Authors: Gilkey Robert H. , Robinson Donald E. , Hanna Thomas E.
Published: October 2005

The proportions of hits and false alarms were estimated for the detection of a 500-Hz sinusoidal signal in each of 25, reproducible samples of wideband, white, Gaussian noise. The effects of signal phase were investigated under diotic (MoSo) and dichotic (MoSπ) conditions and compared to the predictions of two major models of binaural hearing. Averaging the data over samples obscured important across-sample and across-subject differences in performance. The proportions of hits and false alarms for individual noise samples presented under the MoSo condition were highly correlated with those for the same noise samples under the dichotic MoSπ condition, suggesting that the cues determining performance under these conditions are related. Signal-to-masker phase had a large effect on the proportion of hits under the MoSo condition, but only a small effect under the MoSπ condition. The Vector model predicts a large effect of signal phase under the MoSπ condition, and is, therefore, imcompatible with this aspect of the data. The expected value of the decision variable of the EC model is independent of signal phase. However, when the variance of the decision variable is also considered, the EC model does predict changes in the proportion of hits with the phase of the signal, comparable to those observed here. Further, it was shown that, if minor changes in the form of the EC model’s decision variable or in the distribution of the internal noise parameters are assumed, the expected value of the decision variable also changes with the phase of the signal.
Cancellation level and phase of the ( f2−f1) distortion product
Authors: Humes Larry E.
Published: October 2005

The cancellation level and phase were measured for the (f2−f1) distortion product in six normal-hearing ears as a function of input level (L1,L2) and the frequency separation of the two input signals (f1, f2, where f2>f1). The effects of input level were examined for L1 and L2, varied together (L1=L2) and separately. Typically, f1 was 1500 Hz while f2/f1 was either 1.16, 1.32, 1.44, or 1.68. For L1=L2, the median data indicate that the (f2−f1) level grows at a rate of approximately 1.1 dB/dB when averaged across all stimulus conditions. This slope tended to be higher (∼1.6 dB/dB) for L1=L2>80 dB. Slopes for some subjects also increase as f2/f1 increases. The cancellation phase increases slightly (50°–100°) with an increase in L1=L2. With L1 at 75 to 80 dB, L2 ranging from 65 to 95 dB, and f2/f1=1.16, (f2−f1) increases monotonically with L2 up to L1=L2. As L2 increases further (L2>L1), the slopes for the growth of (f2−f1) decrease. For f2/f1=1.44, on the other hand, (f2−f1) appears to grow monotonically at a rate of approximately 0.5 dB/dB throughout the range of L2 values. The cancellation phase increases with L2 (approximately 100°) only for the wider frequency separation of the two input signals (f2/f1=1.44). There are, however, sizable individual differences in the behavior of the (f2−f1) distortion product.
Relations among some psychoacoustic parameters in normal and cochlearly impaired listeners
Authors: Ludvigsen Carl
Published: October 2005

Frequency resolution (viz., masking by low-pass-filtered noise and broadband noise) and temporal resolution (viz., masking by interrupted noise) were compared with hearing thresholds and acoustic reflex thresholds for four normally hearing and 13 cochlearly impaired subjects. Two models, one for frequency resolution (model I) and one for temporal resolution (model II), were introduced, and these provided a means of predicting individual frequency and temporal resolution from hearing thresholds for both normal-hearing and hearing-impaired listeners. Model I is based on the assumption that the upward spread of masking increases in cochlearly impaired hearing with an amount proportional to the hearing threshold in dB HL. Model II is based on the assumption that the poststimulatory masked thresholds return to the level of the hearing threshold within a duration of 200 ms, independent of the level of the masker and the amount of cochlear hearing loss. Model parameters were determined from results from other studies. Although some discrepancies between measured and predicted values were observed, the model predictions generally agree with measurements. Thus, to a first-order approximation, it seems possible to predict individual frequency and temporal resolution of cochlearly hearing-impaired listeners solely on the basis of their hearing thresholds.