bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-, three-, and four-interval forced-choice staircase procedures: Estimator bias and efficiency
Authors: Schlauch Robert S. , Rose Richard M.
Published: October 2005

Threshold estimates for multiple-interval forced-choice staircase procedures were studied using computer simulations. A sigmoidal psychometric function shape governed the hypothetical subject’s responses in the simulations. Parameters varied included the number of trials, the step size for stimulus level change, and decision rules that targeted 70.7% and 79.4% correct performance. Each threshold estimate was calculated by averaging the stimulus levels at which a reversal a stimulus level direction occurred. The results of the simulations suggest that, as the number of alternatives is increased from 2 to 4, the variability of repeated threshold estimates decreases or remains constant, and the accuracy of the estimator, in most cases, improves. A subset of the simulations was compared with data obtained in a detection-in-noise task. The behavioral data were consistent with the simulation results. Two major conclusions were reached. First, 3- and 4-interval forced-choice (IFC) procedures are more efficient than a 2IFC procedure with a decision rule that targets 70.7% correct performance even when the additional time required to complete 3- and 4IFC trials is considered. Second, the accuracy of 2IFC procedures can be improved by fitting the trial history of a staircase run using probit analysis.
Forward masking in patients with cochlear implants
Authors: Shannon Robert V.
Published: October 2005

Forward masking was measured in 12 patients with cochlear implants. The amount of masking (in microamps) decreased linearly as a function of the logarithm of the signal delay from masker offset. Normalized forward-masking recovery functions for cochlear implants were similar to normalized functions of normal-hearing listeners, indicating that the mechanism of psychophysical forward masking is retrocochlear. These results indicate that the logarithm of acoustic amplitude should be mapped to microamps to produce normal forward masking in implanted patients. Despite the fact that the forward-masking recovery functions were similar across all patients, their performance with their speech processor varied widely.
A new version of duplex perception: Evidence for phonetic and nonphonetic fusion
Authors: Nygaard Lynne C. , Eimas Peter D.
Published: October 2005

In a series of experiments, a variant of duplex perception was investigated. In its original form, duplex perception is created by presenting an isolated transition to one ear and the remainder of the syllable, the standard base, to the other ear. Listeners hear a chirp at the ear receiving the isolated transition, and a full syllable at the ear receiving the base. The new version of duplex perception was created by presenting a third-formant transition in isolation to one ear and the same transition electronically mixed with the base to the other ear; the modified base now has all the information necessary for syllabic perception. With the new procedure, listeners reported hearing a chirp centered in the middle of their head and a syllable in the ear presented the modified base that was clearer than that produced by the isolated transition and standard base. They could also reliably choose the patterns that contained the additional transition in the base when attending to either the phonetic or nonphonetic sides of the duplex percept. In addition, when the fundamental frequency, onset time, and intensity of the isolated third-formant transition were varied relative to the base, the phonetic and nonphonetic (lateralization) percepts were differentially affected, although not always reliably. In general, nonphonetic fusion was more affected by large differences in these variables than was phonetic fusion. However, when two isolated third-formant transitions were presented dichotically, fusion and the resulting central location of the chirp failed markedly with relatively small differences in each variable. The results were discussed in terms of the role of fusion in the new version of duplex perception and the nature of the information that undergoes both phonetic and nonphonetic fusion.
Unidirectional magnetostrictive/piezoelectric hybrid transducer
Authors: Butler John L. , Butler Stephen C. , Clark Arthur E.
Published: October 2005

A unidirectional magnetostrictive/piezoelectric hybrid transducer was constructed that produced enhanced motion at one end and canceled motion at the other end. In the simplest form the transducer consists of a quarter wavelength section of piezoelectric material joined to a quarter wavelength section of Terfenol-D rare earth magnetostrictive material. A 3-kHz experimental hybrid transducer with a total length of approximately 18 in. (0.46 m) was constructed with a small central mass and two small identical end piston masses. Measurements and calculations on this device showed an average front-to-back ratio of approximately 17 dB.
Analysis of thermoacoustic wave propagation in elastic media
Authors: Rudgers Anthony J.
Published: October 2005

Wave propagation in a material continuum is a thermodynamic process that is governed, not only by the mechanical character of the propagation medium, but by the thermal character as well. The dispersion relation derived on the basis of linear thermoelastic theory shows that two distinct types of dilatational waves can propagate in an isotropic elastic medium. In each such wave, mechanical and thermal effects are coupled. The behavior of these thermoacoustic waves, in particular, their speeds and absorption coefficients as functions of frequency, is described. Three models of thermoacoustic wave propagation are considered. The classic model, which incorporates the Fourier description of heat conduction, is analyzed first. The shortcomings of this model are pointed out. Two models incorporating the Vernotte hypothesis of heat conduction are examined next—a ‘‘lattice’’ model, which is based upon an idea implicit in the Debye theory of specific heats, and a ‘‘phonon-gas’’ model. Both models incorporating the Vernotte hypothesis are shown to describe linear thermoacoustic wave propagation in a more physically realistic fashion than does the classic model. Thermoacoustic wave propagation is considered from a general phenomenological (i.e., from a macroscopic) standpoint, and only the most general assumptions about the constitution of the propagation medium are made. In the analysis, only the dissipation of energy by heat conduction is considered; the medium is assumed to be elastic in that no purely mechanical mechanisms for energy dissipation (e.g., classic viscosity) are considered to be present.
On the effect of a modified ground plane for a simple source configuration
Authors: Sandström Sven-Erik
Published: October 2005

The far field is computed in two dimensions for an acoustic system radiating into the upper half-plane. A small source region is situated on the boundary and in the neighborhood of a rectangular trough. An eigenfunction expansion is used to obtain an additional relation necessary for the solution of the integral equation provided by Green’s theorem. The normal derivative on the trough interface is expanded in a scaled Fourier series. A matrix equation is obtained that yields the expansion coefficients and, via the asymptotic form of the Green’s function, also the far field. Various scalings are investigated with respect to numerical efficiency.
Acoustic scattering from a ‘‘Pierson–Moskowitz’’ sea surface
Authors: Thorsos Eric I.
Published: October 2005

The validity of the Kirchhoff and perturbation approximations for scattering from ‘‘Pierson–Moskowitz’’ sea surfaces has been examined through comparison with exact results obtained by solving an integral equation. The height of the surfaces used varies in only one direction. All results are for an acoustic frequency of 200 Hz and for incident grazing angles of 10°–20°. The Kirchhoff approximation accurately predicts incoherent scattering near the specular direction. First-order perturbation theory yields bistatic backscattering levels that are 1–3 dB low for the examples studied. When the scattering cross section is calculated to order (kh)4 using perturbation theory, the accuracy for bistatic backscattering is excellent, even when kh is as large as 1.79. Here k is the acoustic wave number and h is the root-mean-square (rms) surface height. An easily evaluated approximation to the scattering cross section to order (kh)4 has also been obtained. The Kirchhoff approximation for the coherent reflection loss is more accurate than second-order perturbation theory when the reflection loss exceeds about 1 dB. For lower losses, the perturbation result is more accurate. The composite-roughness model has been examined for monostatic backscattering. The model is accurate at a grazing angle of 20° but predicts a scattering level that is higher than the exact result at a grazing angle of 10°.
Woodwind air column models
Authors: Keefe Douglas H.
Published: October 2005

Woodwind air column models can be used to analyze the acoustical properties of existing instruments, in designing new air columns or modifying historical or contemporary instruments, and in constructing time-domain simulations of woodwinds either for testing theories of woodwind acoustics or as a method of music synthesis. Two types of models and their applications are described, both using a highly accurate representation of each tonehole. The first model generalizes the Benade lattice model, which admits of an analytical solution, and experimental data confirming important features of the model are described. The second model is a computational model based upon a transfer-matrix formulation. It is well suited to generating a number of important air column response functions and is simple to alter for a variety of air column configurations. An example illustrating the use of this transfer-matrix model is presented for a cylindrical bore flute air column. The Hilbert transform applied to the reflection function assists in the interpretation of the response of the air column, when viewed in the time domain.
Control of sound radiation from submerged plates
Authors: Meirovitch Leonard , Thangjitham Surot
Published: October 2005

In many applications, the radiation pressure is an undesirable effect, so that the object is to suppress it. This paper is concerned with radiation pressure suppression through active control. The general idea of active control of a structure is to suppress the vibration by applying suitable feedback control forces, which requires sensors capable of measuring the state of the system and actuators capable of applying control forces. A control technique capable of suppressing the far-field radiation pressure is developed.
Impact and bubble sound from raindrops at normal and oblique incidence
Authors: Medwin Herman , Kurgan Armagan , Nystuen Jeffrey A.
Published: October 2005

The sound generated by rainfall at sea is caused by drops of a wide range of sizes that fall at their terminal velocities and strike the water at various angles of incidence. The purpose of this laboratory research has been to make complete acoustical measurements of the sound generated by single water drops striking the water surface at their terminal velocities for normal and oblique incidence. The measurements have included the total acoustic energy, peak axial pressure, frequency spectrum, polar radiation pattern, and probability of bubble creation. When bubbles are created, they radiate more energy than the impact. However, as the angle of incidence becomes more oblique, the probability of formation of a bubble drops rapidly. For example, a 1-mm drop that always creates a bubble at normal incidence and terminal velocity does so only 10% of the tests at incidence 20° away from normal. These results provide specific reasons for the previously unexplained broadening, frequency increase, and magnitude reduction of the 15-kHz spectral peak of rain noise in the presence of winds at sea.
Remote sensing of ocean flows by spatial filtering of acoustic scintillations: Theory
Authors: Crawford G. B. , Lataitis R. J. , Clifford S. F.
Published: October 2005

Space-time acoustic scintillation analysis has proved to be a valuable technique for probing ocean flows over short (≲2 km) acoustic paths. Measurements of the amplitude and phase perturbations in a distant receiving plane are used to infer the intervening fine-scale variability and transverse current. Observations made using one transmitter and two receivers yield path-integrated measurements that are almost uniformly weighted along the propagation path. Higher resolution measurements can be obtained using multiple sources and receivers. By combining the signals from each transmitter–receiver pair in different ways, a number of different path positions can be probed and profiles of the fine-scale variability and transverse current along the propagation path retrieved. A theory describing the performance characteristics of such a system is presented. The case of linear transmitting and receiving arrays of equally spaced elements is considered in detail. The theory predicts a potential path resolution of up to L/[(N′t+Nr)/2], where N′t≫1 and Nr≫1 are the number of transmitters and receivers, respectively, and L is the propagation path length. The specific case of four-element transmitting and receiving arrays is also considered, and some simulations of profile retrievals are presented. A future paper [D. M. Farmer and G. B. Crawford, J. Acoust. Soc. Am. (in preparation)] will present results of an experiment to test such a system.
Creeping-wave theory applied to impulse propagation around a meteorological shadow boundary
Authors: Cramond A. J. , Don C. G.
Published: October 2005

Detailed experimental impulse-propagation results measured in a refractive atmosphere over grassland at distances up to 200 m from the source are compared with two residue-series forms of creeping-wave theory. Results are compared both prior to and inside the meteorological shadow zone. Although the theory, derived assuming a linear sound-speed gradient, correctly accounts for changes in source–receiver geometry and ground impedance, it consistently underpredicts levels deep within the shadow zone. An empirical method for including the effects of a nonlinear gradient is also considered.
Scattering of acoustic waves by a sphere outside an infinite circular cylinder
Authors: Olsson Sune
Published: October 2005

By employing the null-field approach, the scattering of acoustic waves by an infinite cylinder and a sphere is considered. Sound-hard boundary conditions are assumed and the incident wave is taken as a plane wave. The scattered field is obtained as a complicated mode sum containing the transition matrix of the sphere and the reflection matrix of the cylinder. Also, the transformation functions between the cylindrical and spherical wave functions and the translation functions for the cylindrical wave functions enter into this sum. The farfields are calculated and the implications of energy conservation are explored and used as a numerical check. Numerical results showing the scattering cross section and the farfield amplitude are presented.
Measurement of liner impedance based on the determination of duct eigenvalues by a Fourier–Lommel’s transform
Authors: Auger J. M. , Ville J. M.
Published: October 2005

A new method of measuring the impedance of locally reacting material placed in an acoustic field distributed over higher-order modes is presented. By a Fourier–Lommel’s transform of the acoustic pressure measured in a duct of a cylindrical cross section lined with this material, duct eigenvalues are determined. Impedance is then deduced from the boundary limit relationship taken at the liner face. Experiments have been conducted and show that this method is reliable in determining impedance if care is taken to localize precisely the radial position of the microphone. Also, among previous methods where impedance is deduced from nonlocal measurements, the technique presented has the advantage that it can be experimentally set up in a short-lined duct and not be perturbed by edge effects at boundary cross sections located at the beginning and the end of the liner.
The resolution of modal Doppler shifts in a dispersive oceanic waveguide
Authors: Song Hee Chun , Baggeroer A. B.
Published: October 2005

In this paper, a method for estimating the source velocity from the acoustic signal field propagating in a dispersive oceanic waveguide is presented. The signal is observed at an omnidirectional receiver in the presence of additive white noise. The source transmits a continuous wave (cw) signal, and the source motion is assumed to be uniform (unaccelerated). The ocean is modeled as a waveguide that is horizontally stratified with an arbitrary sound-speed profile in the vertical. The acoustic field generated by a moving point source in terms of normal modes predicts that each mode has a different Doppler shift, which contrasts with a single Doppler shift in a homogeneous unbounded medium. The modes are considered to remain phase locked with each other, i.e., coherent. The source velocity, including the number of modes involved, can be estimated through resolving modal Doppler shifts. The method is a time-domain interpretation of a recently developed eigenstructure technique for a multitarget direction finding with passive antenna arrays, in conjunction with a smoothing preprocessing scheme to deal with coherent modes [Shan et al., IEEE Trans. Acoust. Speech Signal Process. ASSP-33, 806–811 (1985)]. Simulation results that illustrate the performance of the method are presented.
Increased heating by diagnostic ultrasound due to nonlinear propagation
Authors: Bacon David R. , Carstensen Edwin L.
Published: October 2005

The heating of tissues by the absorption of ultrasound is an important safety consideration in the use of diagnostic ultrasound. This paper shows that models of ultrasonic heating for this situation need to take account of nonlinear propagation. Measurements were made of the temperature rise in a sample of tissue-mimicking gel, caused by the application of 3.6-MHz focused ultrasonic beams for 3 min. The propagation path to the focus was in water, to mimic the situation where the fetus is scanned through the full bladder. The effect of nonlinear propagation was seen by changing the pressure amplitude of the pulse, while altering the pulsing regime to preserve a constant spatial-peak temporal-average intensity of 1 W cm−2. When nonlinear distortion was present, an enhancement in the temperature rise was observed, which correlated with the value of the shock parameter. The enhancement ratio was typically up to a factor of 3, and the maximum temperature rise observed was 2 °C. This enhanced heating was seen both at the surface of the tissue-mimicking gel and after propagation through 23 mm of the material. Under conditions of nonlinear propagation, the maximum heating usually occurs in the prefocal region, rather than at the focus.
Low-frequency acoustic propagation loss in shallow water over hard-rock seabeds covered by a thin layer of elastic–solid sediment
Authors: Hughes Steven J. , Ellis Dale D. , Chapman David M. F. , Staal Philip R.
Published: October 2005

Shallow-water seabeds are often varied and complex, and are known to have a strong effect on acoustic propagation. Some of these seabeds can be modeled successfully as fluid or solid half-spaces. However, unexpectedly high propagation loss with respect to these models has been measured in several regions with rough, partially exposed, hard-rock seabeds. It is shown that the high propagation loss in these areas can be modeled successfully by introducing a thin layer of elastic–solid sediment over the hard-rock substrate. Propagation loss predictions using the safari fast-field program exhibit bands of high loss at regularly spaced frequencies. Normal-mode calculations show resonance phenomena, with large peaks in the modal attenuation coefficients at these same frequencies, and with rapid changes in the mode wavenumbers. Bottom reflection loss calculations indicate that the high propagation loss is due to absorption of shear waves in the sediment layer.
Hydroacoustic characteristics of scattering layers in the Northeastern Atlantic Ocean
Authors: Orl/owski Andrzej
Published: October 2005

The hydroacoustic characteristics of scattering layers measured during a cruise of the R/V Professor Siedlecki in 1984 during the months July and September, are presented in the form of vertical and horizontal distributions of column scattering strength and volume backscattering strength. These distributions are compared with the results of physical and biological sampling. Acoustical measurements were carried out using a 38-kHz echo sounder and an analog integration system connected with a computer. Biological sampling was conducted by using a Bongo net and a large pelagic trawl with a small mesh inset, of the type used for commercial krill catches. This paper presents parameters of diel migrations of scattering layers, investigated between latitudes 37°–46° N and longitudes 12°–30° W for a 24-h period. The relative stability of the value of column scattering strength during the 24-h period and its relationship to catch results indicate that acoustical measurements are a promising tool for a quick, large-scale description of scattering layers. The results presented are also useful as a guide for future surveys having the same objective.
Theoretical model of acoustic backscatter from a smooth seabed
Authors: Hines Paul C.
Published: October 2005

Currently available mathematical models of acoustic scattering from the ocean bottom generally fail to predict backscatter levels of sufficient magnitude for two limiting cases: as the bottom becomes increasingly smooth and as the grazing angle becomes small. In this paper a mathematical model of acoustic backscattering that attempts to address these shortcomings for the case of a sediment bottom is derived. In the model, scattering is caused by fluctuations in sediment porosity. The model allows for penetration of the incident wave into the bottom at subcritical grazing, and retransmission of scattered spherical waves through the (planar) interface. The frequency and grazing angle dependence of the acoustic backscatter are determined primarily by the correlation function of the porosity fluctuations, while the magnitude of the backscatter is controlled by the mean-square value of these fluctuations. Numerical results obtained from the model are tested against backscatter data available in the literature for several sediment bottoms over a wide range of frequencies (30–500 kHz). Agreement between the model and literature data is good.
Articulation rate and the duration of syllables and stress groups in connected speech
Authors: Crystal Thomas H. , House Arthur S.
Published: October 2005

Further analyses have been made on readings of two scripts by six talkers [T. H. Crystal and A. S. House, J. Acoust. Soc. Am. 72, 705–716 (1982); 84, 1932–1935 (1988); 83, 1553–1573 (1988)]. Durations of syllables and stress groups are compared to earlier data and various pertinent published reports, and are used to evaluate reports of articulation rate variability. The average durations of syllables of different complexity have a quasilinear dependency on the number of phones in the syllable, where the linear factor and the vowel durations are functions of stress. The duration of stress groups has a quasilinear dependency on the number of syllables and the number of phones. It was found that variability of articulation rate, measured as the average syllable duration for interpause intervals (runs), is not random, but is the natural consequence of the content of the run. Durations of comparable runs of different talkers are highly correlated. Major determinants of average syllable duration are the average number of phones per syllable and the proportion of either +stress phones or +stress syllables in the run.
Comodulation masking release as a function of bandwidth and test frequency
Authors: Haggard M. P. , Hall J. W. , Grose J. H.
Published: October 2005

Comodulation masking release (CMR) was investigated as a function of signal frequency (0.5–4.0 kHz) and the total bandwidth of noise centered on the signal frequency. Taking noncomodulated noise of the same bandwidth as the reference condition, CMR for modulated noise increased with increasing bandwidth of the flanking noise outside the critical band centered on the signal tone; however, this growth asymptoted for broad total bandwidths. These bandwidth effects were expressed by scaling the width of the flanking bands beyond the critical band centered on the signal frequency, approximately according to a critical bandwidth scale. After this scaling, signal frequency had negligible effect on CMR magnitude. For the low modulation frequencies involved, a beneficial effect on CMR at high carrier frequencies would not be expected, and none was observed. Some further trends in the masked thresholds in comodulated and noncomodulated conditions, and the choice of appropriate reference condition are discussed.
Pure-tone increment detection in harmonic and inharmonic backgrounds
Authors: Henn Carol C. , Turner Christopher W.
Published: October 2005

The present study investigated the effect of increasing the number and frequency range of background components upon the detection of an increment to the intensity of the center component. Previous studies [e.g., Green et al., J. Acoust. Soc. Am. 75, 1163–1167 (1984)] have demonstrated that, for background stimuli consisting of logarithmically spaced pure-tone components, as the number of background components is increased, the threshold for detection of an increment to the center component is decreased. The present study investigated this effect using harmonically spaced, as well as logarithmically spaced, backgrounds, because many natural sounds, including voiced speech sounds, consist of harmonically spaced components. Two conditions were employed for both types of backgrounds, fixed-level and roving-level within a trial. Group results revealed a small decrease in threshold with increasing number of components only for the fixed-level, logarithmically spaced backgrounds. No decrease in threshold was observed for the other three conditions, including the roving-level, logarithmically spaced backgrounds which were the same as those used by Green et al. (1984). The present results suggest that the decrease in signal threshold with increasing number of background components exists only under limited conditions and that it is a highly individual phenomenon. The present results also suggest that the effect does not occur for harmonically spaced complexes such as most natural sounds including voiced speech.
Acoustical impedance measurements by the two-microphone-three-calibration (TMTC) method
Authors: Gibiat V. , Laloë F.
Published: October 2005

A method is discussed for measuring the acoustical impedance of woodwind instruments that is relatively fast and insensitive to the ambient acoustical noise. The apparatus is essentially made of a measurement head, which is an approximately cylindrical cavity fitted with two microphones (in practice often three or more for technical reasons) and, at one of its ends, a loudspeaker; the other end is connected to the acoustical cavity under study (the instrument). The loudspeaker emits acoustical chirps and the signals provided by the microphones are Fourier transformed with the help of a microcomputer, which also extracts from the results the acoustical impedance as a function of frequency. A relatively high dynamic range is needed in order to match the high quality factor of the resonances of musical instruments, especially at low frequencies. To meet this requirement, it was found necessary to take into account the acoustical losses inside the head as well as the mutual perturbation of the microphones or various perturbations arising from geometrical imperfections of the cavity. This can be done automatically and without long calculations by using a calibration method, based on the successive use of three reference cavities, which are described and discussed in detail in this article. The method has been tested with cylindrical cavities and gives satisfactory results in terms of peak positions and heights. Impedance curves of clarinets have also been measured. The three-calibration technique eliminates several sources of systematics and corrects automatically for various perturbations, such as perturbations of the acoustical field by the microphones, and allows the study of instruments of various diameters.
Auditive and cognitive factors in speech perception by elderly listeners. II: Multivariate analyses
Authors: van Rooij J. C. G. M. , Plomp R.
Published: October 2005

In part I of this study [van Rooij et al., J. Acoust. Soc. Am. 86, 1294–1309 (1989)], the validity and manageability of a test battery comprising auditive (sensitivity, frequency resolution, and temporal resolution), cognitive (memory performance, processing speed, and intellectual abilities), and speech perception tests (at the phoneme, spondee, and sentence level) were investigated. In the present article, the results of a selection of these tests for 72 elderly subjects (aged 60–93 years) are analyzed by multivariate statistical techniques. The results show that the deterioration of speech perception in the elderly consists of two statistically independent components: (a) a large component mainly representing the progressive high-frequency hearing loss with age that accounts for approximately two-thirds of the systematic variance of the tests of speech perception and (b) a smaller component (accounting for one-third of the systematic variance of the speech perception tests) mainly representing a general performance decrement due to reduced mental efficiency, which is indicated by a general slowing of performance and a reduced memory capacity. Although both components are correlated with age, it was found that the balance between auditive and cognitive contributions to speech perception performance did not change with age.
Summation bandwidths at threshold in normal and hearing-impaired listeners
Authors: Higgins Maureen B. , Turner Christopher W.
Published: October 2005

The bandwidths for summation at threshold were measured for subjects with normal hearing and subjects with sensorineural hearing loss. Thresholds in quiet and in the presence of a masking noise were measured for complex stimuli consisting of 1 to 40 pure-tone components spaced 20 Hz apart. The single component condition consisted of a single pure tone at 1100 Hz; additional components were added below this frequency, in a replication of the Gässler [Acustica 4, 408–414 (1954)] procedure. For the normal subjects, thresholds increased approximately 3 dB per doubling of bandwidth for signal bandwidths exceeding the critical bandwidth. This slope was less for the hearing-impaired subjects. Summation bandwidths, as estimated from two-line fits, were wider for the hearing-impaired than for the normal subjects. These findings provide evidence that hearing-impaired subjects integrate sound energy over a wider-than-normal frequency range for the detection of complex signals. A second experiment used stimuli similar to those of Spiegel [J. Acoust. Soc. Am. 66, 1356–1363 (1979)], and added components both above and below the frequency of the initial component. Using these stimuli, the slope of the threshold increase beyond the critical bandwidth was approximately 1.5 dB per doubling of bandwidth, thus replicating the Spiegel (1979) experiment. It is concluded that the differences between the Gässler (1954) and Spiegel (1979) studies were due to the different frequency content of the stimuli used in each study. Based upon the present results, it would appear that the slope of threshold increase is dependent upon the direction of signal expansion, and the size of the critical bands into which the signal is expanded.
Minimum audible movement angles as a function of sound source trajectory
Authors: Saberi Kourosh , Perrott David R.
Published: October 2005

Auditory resolution of moving sound sources was determined in a simulated motion paradigm for sources traveling along horizontal, vertical, or oblique orientations in the subjects’s frontal plane. With motion restricted to the horizontal orientation, minimum audible movement angles (MAMA) ranged from about 1.7° at the lowest velocity (1.8°/s) to roughly 10° at the highest velocity (320°/s). With the sound moving along an oblique orientation (rotated 45° relative to the horizontal) MAMAs generally matched those of the horizontal condition. When motion was restricted to the vertical, MAMAs were substantially larger at all velocities (often exceeding 8°). Subsequent tests indicated that MAMAs are a U-shaped function of velocity, with optimum resolution obtained at about 2°/s for the horizontal (and oblique) and 7–11°/s for the vertical orientation. Additional tests conducted at a fixed velocity of 1.8°/s along oblique orientations of 80° and 87° indicated that even a small deviation from the vertical had a significant impact on MAMAs. A displacement of 10° from the vertical orientation (a slope of 80°) was sufficient to reduce thresholds (obtained at a velocity of 1.8°/s) from about 11° to approximately 2° (a fivefold increase in acuity). These results are in good agreement with our previous study of minimum audible angles long oblique planes [Perrott and Saberi, J. Acoust. Soc. Am. 87, 1728–1731 (1990)]. In summary, the results suggest that: (1) the ability to detect motion is essentially independent of the path traveled by the source, with one noted exception, sources moving within a few degrees of the vertical plane and (2) auditory resolution of sound sources in motion is a U-shaped function of velocity with resolution degrading as velocities increase or decrease beyond an optical velocity range.
A single-interval adjustment-matrix (SIAM) procedure for unbiased adaptive testing
Authors: Kaernbach Christian
Published: October 2005

A new unbiased adaptive procedure is described that requires only half as many presentations in achieving the same precision as the well-known two-interval forced-choice (2IFC) 2-step procedure. The procedure is based on a yes–no task which avoids redundant presentation time. Furthermore, certain psychophysical studies can only be realized with yes–no tasks. Every trial contains randomly presented signals or noises and the answer is either yes or no. The outcome (hit, miss, false alarm, correct rejection) is taken into account by adjusting the signal level in a staircase manner. The adjustment matrix is set up to induce a neutral response criterion. Its convergence point can be adjusted at will. The single-interval adjustment-matrix (SIAM) procedure is compared to von Békésy and 2IFC transformed up–down methods using a Monte-Carlo simulation. The SIAM procedure proves to be the fastest of the unbiased procedures. A test on four subjects verified these results. Implications for optimum track length and the number of reversals to discard are discussed.
Coding of spectral fine structure in the auditory nerve. II: Level-dependent nonlinear responses
Authors: Horst J. Wiebe , Javel Eric , Farley Glenn R.
Published: October 2005

Phase-locked discharge patterns of single cat auditory-nerve fibers were analyzed in response to complex tones centered at fiber characteristic frequency (CF). Signals were octave-bandwidth harmonic complexes defined by a center frequency F and an intercomponent spacing factor N, such that F/N was the fundamental frequency. Parameters that were manipulated included the phase spectrum, the number of components, and the intensity of the center component. Analyses employed Fourier transforms of period histograms to assess the degree to which responses were synchronized to the frequencies present in the acoustic stimulus. Several nonlinearities were observed in the response as intensity was varied between threshold and 80–90 dB SPL. Response nonlinearities were strong for all signals except those with random phase spectra. The most commonly observed nonlinearity was an emphasis of one or more stimulus components in the response. The degree of nonlinearity usually increased with intensity and signal complexity and decreased with fiber frequency selectivity. Half-wave rectification introduced synchronization to the missing fundamental. The strength of the response at the fundamental was related to stimulus crest factor. Signals with low center frequencies and high crest factors often elicited instantaneous discharge rates at the theoretical maximum of πCF. This suggests that the probability of spike generation approaches one during high-amplitude waveform segments. Response nonlinearity was interpreted as arising from three sources, namely, cochlear mechanics, compression of instantaneous discharge rate, and saturation of average discharge rate. At near-threshold intensities, fibers with high spontaneous rates exhibited responses that were linear functions of stimulus waveshape, whereas fibers with low spontaneous spike rates produced responses that were best described in terms of an expansive nonlinearity.
Neural correlates of psychophysical release from masking
Authors: Mott John B. , McDonald Lynn P. , Sinex Donal G.
Published: October 2005

Responses of chinchilla auditory-nerve fibers were measured for stimulus conditions analogous to those in which psychophysical release from masking has been observed in humans. The maskers were two equal power, narrow-band noise stimuli with different amplitude envelopes. The neurons in the sample fell into three groups that resolved the maskers’ envelopes with varying degrees of accuracy. The boundaries of these groups were not sharply delineated by characteristic frequency (CF) but were dependent on the relationship between the masker level and the neurons’ thresholds at the masker frequency. For the neurons that best preserved the maskers’ envelope fluctuations, a neural release from masking was observed; rate-based neural masked thresholds were higher for the masker with the least fluctuating envelope. The results suggest that neural and psychophysical release from masking arises because the probe evokes larger rate changes, relative to the background response to the masker, during periods of low masker energy. Between two otherwise equivalent maskers, the one with the periods of lowest energy will produce the lower masked thresholds because rate changes are larger and more detectable.
Spatial Fourier transform method of measuring reflection coefficients at oblique incidence. I: Theory and numerical examples
Authors: Tamura Masayuki
Published: October 2005

A new method using spatial Fourier transform has been developed to measure reflection coefficients at oblique incidence. The method involves the measurement of complex pressure distributions on two parallel planes lying close to the surface of a test material and decomposing each of the complex pressure distributions into plane-wave components by using two-dimensional spatial Fourier transform. The incident and reflected plane-wave components on the surface of the test material can be mathematically separated by the use of plane-wave propagation theory. This separation leads to the determination of reflection coefficients at arbitrary angles of incidence. Investigation has been made into the error due to the finite size of the measurement area to show that the magnitude of the error can be reduced by using a dipole source instead of a monopole source. Numerical examples are given to illustrate the validity of the method.
Outer acoustic streaming
Authors: Lee Chun P. , Wang Taylor G.
Published: October 2005

There is a general formulation by Nyborg that accounts for the streaming inside the viscous boundary layer on a solid surface in the presence of a sound wave [W. L. Nyborg, J. Acoust. Soc. Am. 30, 329 (1958)]. Using the streaming velocity at the edge of the viscous layer from Nyborg’s theory as a slip boundary condition, the streaming pattern at large outside the layer for various geometries is calculated. Compressibility of the first-order wave motion is retained, such that its effect is reflected in the boundary condition for the secondary flow, although the latter is considered as incompressible. For the case of a cylinder or a sphere situated at a velocity antinode of a plane standing wave, it is found that the streamlines are closed loops as a consequence of compressibility. If the solid body is displaced from the antinode, the vortex pattern becomes asymmetric. A weak viscous drag acts on the object in the direction opposing the displacement. As a reaction, a weak net flow arises in the direction of the displacement. These findings are consistent with observations, and are absent in previous theoretical treatments of the problem, in which the oscillating flow is assumed to be uniform and incompressible.
Acoustic radiation from an impulsive point source in a continuously layered fluid—An analysis based on the Cagniard method
Authors: de Hoop Adrianus T.
Published: October 2005

The acoustic radiation generated by an impulsive point source in a continuously layered fluid with depth-varying parameters is investigated theoretically with the aid of the modified Cagniard method. Using a one-sided time Laplace transformation with a real positive transform parameter, a Fourier transformation with respect to the horizontal space coordinates and appropriate one-sided Green’s functions, the system of transform-domain differential equations in the depth coordinate is rewritten as a system of integral equations that can be solved by a Neumann iteration. The modified Cagniard method leads to space-time expressions for the relevant iterates that physically are representative for the successively reflected waves. This iterative method is shown to be convergent in the time domain for any continuous and piecewise continuously differentiable depth profile in the inertia and compressibility properties of the fluid. To show the generality of the method, the fluid is assumed to show anisotropy in its volume density of mass, which is the kind of anisotropy that shows up in the equivalent medium theory of a finely layered fluid. The continuously refracted waves emitted by the source and the singly, continuously, reflected waves are discussed in detail. With this technique, no difficulties arise with ‘‘turning rays,’’ as is the case in the asymptotic ray theory of the (real) frequency-domain analysis of the problem.
Wave equation solution by step marching in space
Authors: Pai D. M.
Published: October 2005

This paper presents a step-marching method for a wave equation solution in inhomogeneous media. The solution obtained is the transmission signal. The method expands the solution in terms of plane waves, which during propagation, are mixed by the medium inhomogeneity. Like the parabolic equation (PE) method, the present method is step marching in space and thus allows for efficient solutions. From comparison to analytic solutions, the present method is more accurate than the parabolic equation method away from the major propagation direction.
Solution of fluid–structure interaction problems using a coupled finite element and variational boundary element technique
Authors: Jeans Richard A. , Mathews Ian C.
Published: October 2005

This work is concerned with the numerical modeling of elasto-acoustic problems applied to thin shells and specifically curved plates. A finite element formulation of the elastic problem is coupled to a variational boundary element solution of the acoustic problem. This solution to the acoustic problem, proposed by Mariem and Hamdi [J. B. Mariem and M. A. Hamdi, Int. J. Num. Methods. Eng. 24, 1251–1267 (1987)], is implemented using high-order isoparametric elements, and attention is given to techniques of accelerating the numerical implementation for solutions at multiple frequencies. These techniques include a reduction in the problem size through the use of symmetry and, more importantly, the interpolation of the fluid impedance matrix within the frequency regime. The advantages in using this variational formulation are, first, the manner in which a highly singular integral operator is made amenable to numerical approximation, second, its application to nonclosed thin shells, and, third, its numerical implementation leads to the formulation of a symmetrical fluid matrix.
Effect of a concentric ring baffle on the electrical driving-point impedance of a sonar transducer at an air–water surface
Authors: Yuan C. , Stumpf Folden B.
Published: October 2005

Measurements of the electrical driving-point impedance loop of a small sonar transducer mounted at an air–water surface were made in the presence of a single concentric ring. A soft (styrofoam) and then a hard (brass) ring was placed around the transducer with the top surface of the ring coincident with the air–water surface. A significant unloading of the transducer was seen for the styrofoam ring. The effect for the brass ring was to increase the loading on the transducer. This experiment might be used in an instructional acoustics laboratory.
Transient wave response of the violin body
Authors: Molin Nils-Erik , Wåhlin Anders O. , Jansson Erik V.
Published: October 2005

In this investigation, the dispersive, transient wave propagation field of a complete violin excited by a mechanically induced impulse at the top of the bridge is presented. By means of double pulsed holographic interferometry with a ruby laser as light source the propagating wave field is recorded. From presented interferograms, it is seen that initially the top plate acts mainly as a nonsymmetric dipole with centers at the two bridge feet. The back plate is strongly coupled to the motion of the top plate by the sound post and acts more like a monopole. Thus the position of the sound post is crucial to the performance of the instrument. The free edges at the f-holes are very early reached by the dispersive bending waves of high amplitude probably giving a significant contribution to the sound of the violin family instruments.
Alternate focusing fluids for passive acoustic targets
Authors: Boehme H. , Stockton James E.
Published: October 2005

Fluid-filled, focusing spheres are often used as passive acoustic targets because of their relatively high target strength and aspect-independent characteristics. A fluid mixture consisting of equal parts by weight of trichlorotrifluoroethane and carbon tetrachloride provides a near-optimum index of refraction. The incentive to investigate alternate filling fluids arises because of the potentially hazardous nature of carbon tetrachloride. Target strength measurements were made on stainless steel spherical floats filled with pure inert fluorochemicals as well as other fluid mixtures. Results indicate that passive acoustic targets can be successfully designed using focusing fluids less hazardous than carbon tetrachloride.
Vowel amplitude variation associated with the heart cycle
Authors: Orlikoff Robert F.
Published: October 2005

Modulation of the acoustic amplitude of a sustained vowel across the cardiac (ECG) cycle was examined by signal-averaging techniques. Ten normal men prolonged [a] at a comfortable F0 maintained within three SPL ranges: 60–68, 70–78, and 80–88 dB. Peak-to-peak amplitude variation associated with the heart cycle averaged 8.5% (s.d.=5.4) re: mean, varying from about 14% at low SPLs to approximately 3% at high SPLs. The amplitude modulation was estimated to account for 11.8% of the measured short-term amplitude perturbation (shimmer), ranging from about 5% to almost 22% for individual samples. The mean deterministic shimmer (Sd ) was 0.036 dB (s.d.=0.019), with a trend toward decreasing Sd with increasing SPL. Additionally, fundamental frequency variation across the heart cycle within these phonations was comparable to that observed by Orlikoff and Baken [J. Acoust. Soc. Am. 85, 888–893 (1989)], and was shown to be uninfluenced by vocal SPL, although deterministic jitter (Jd) did decrease with vocal intensity. The results are discussed in terms of how the phonovascular relationship may affect the reliability and interpretation of acoustic shimmer measures.