bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency generalization constrained by pitch processing in the European starling?
Authors: Cynx Jeffrey
Published: January 2006

Earlier work with pitch processing has shown that the European starling (Sturnus vulgaris)—unlike humans—fails to transfer learned pitch discriminations out of the original frequency range (S. Hulse, J. Cynx, and J. Humpal, “Effects of shift in pitch context on serial pitch perception in birds,” in preparation). The present work was undertaken to determine if the failure to generalize is due to the simultaneous active processing of pitch or the inability to make generalizations from simple frequencies. Four wildcaught adult starlings were trained to peck at a lit key only on trials during which a 2000-Hz tone was absent. Once discrimination was achieved, probes were introduced every other session at p = 0.50 to determine generalization from 1000 to 4000 Hz. Findings are in agreement with earlier work, using a Pavlovian procedure, which indicated a range constraint for frequencies [J. E. Trainer, “The auditory acuity of certain birds,” unpublished doctoral dissertation, Cornell Univ. (1946)], but also show that the constraint is interactive with the processing of relative and absolute pitch information.
Time domain methods of investigating acoustic transient phenomena in arrays
Authors: Stepanishen P.
Published: January 2006

A review of linear acoustic transient phenomena in active arrays is presented. Such transients occur as a result of the finite bandwidth of the elements, the time delay caused by the propagation effects in the medium, and acoustic interaction effects among the elements. The characteristics of acoustic radiation from a time dependent monopole and dipole sources are first discussed to address such phenomena. These results are then extended to distributed sources where the importance of edge effects is clearly observed and discussed. Retarded potential methods to account for the effects of boundaries on the transient acoustic field are then presented. Such methods led to the development of impulse response techniques of evaluating acoustic transient phenomena. The impulse response technique is discussed in detail and numerical results are presented to illustrate transient acoustic pressure field and element interaction phenomena in active arrays.
Acoustics of coupled spaces relative to assisted reverberation
Authors: Walker Bruce E. , Sepmeyer Ludwig W.
Published: January 2006

One method of providing variable reverberation in an auditorium is to couple it electroacoustically with an auxiliary reverberation room. Parameters available for control of the composite characteristics include microphone and loudspeaker locations in both spaces, the reverberation time in both spaces, and the gain of the coupling amplifiers. By solving the coupled differential equations representing a simplified model of the arrangement, it was found that a variety of decay “shapes” ranging from concave (rate decreasing with time) to convex could be realized. Reverberation time could be varied over a greater than two to one range, while maintaining a “desirable” straight characteristic. Results of computer simulations for steady-state and transient excitations will be displayed.
A general modification for models of binaural interaction
Authors: Gabriel K. J. , Colburn H. S. , Zurek P. M. , Durlach N. I.
Published: January 2006

Although many studies have demonstrated the relationshio between lateralization and binaural detection, current models of binaural interaction are unable to predict performance in both tasks with the same set of values for the model parameters. By incorporating a mechanism which low-pass filters (averages) interaural time and intensity differences into a simple, narrow-band model of binaural interaction, results from interaural time and intensity discrimination tests can be used to predict correlation discrimination and NoSπ detection results. Evidence for such a low-pass mechanism has most recently been reported by Grantham and Wightman [J. Acoust. Soc. Am. 72, 1178–1184 (1982)]. For both normal listeners and hearing-impaired listeners with a variety of different losses, the predictions of the augmented model suggest that binaural hearing in correlation discrimination and NoSπ detection tasks can be characterized by a listener's sensitivity to interaural time and intensity differences. [Work supported by NIH Grant NS10916.]
Lateralization of clicks based on interaural time: Additivity of information across frequency
Authors: Wenzel Elizabeth M. , Hafter Ervin R.
Published: January 2006

Sensitivity to interaural differences of time was measured for trains of 1 to 32 (n) clicks presented at rates of 400 or 200 per second. The center frequencies of the bandpass clicks were either 4, 5.2, 6, or 7.2 kHz. As in earlier research, plots of log threshold versus log n produced functions whose negative slopes grow more shallow with increasing rate. When sensitivity was measured for composite signals made of clicks whose center frequencies were 4 and 6 kHz, or 4, 5.2, 6, and 7.2 kHz, the slopes of the functions were similar to the single-frequency conditions. However, the intercepts for the two- and four-frequency stimuli were decreased by factors of approximately √ and 2, respectively, relative to the case of single frequencies. These data demonstrate that the rate-dependent saturation of binaural information previously shown to operate within frequency channels [E. R. Hafter and R. H. Dye, J. Acoust. Soc. Am. 73, 644–651 (1983)] does not affect the integration of information across channels. [Supported by NIH.]
A search for central lateral inhibition
Authors: Hartmann W. M.
Published: January 2006

To understand the existence of the binaural edge pitch [Klein and Hartmann. J. Acoust. Soc. Am. 70, 51–61 (1981)] appears to require central lateral inhibition in the human auditory system. We have looked for this effect in central masking experiments. Using the binaural-edge noise, which creates the binaural edge pitch, as a masker, we found pulsation thresholds for sine tones in two frequency ranges where the binaural edge pitch exists. We further found masking level differences using the same pulsation threshold technique. Theoretically the difference between the binaural-edge thresholds and the MLD thresholds should show the peak and valley signature of lateral inhibition. No such structure was found. We suggest that this negative result does not exclude the possibility of central lateral inhibition, but that the time course of central lateral inhibition makes the pulsation threshold technique an inappropriate means for observing the effect. [Work partially supported by the NIH, grant NS 17917.]
Rayleigh wave transmission reciprocity past a step change in elevation
Authors: Chamuel Jacques R.
Published: January 2006

Contradicting experimental, approximate theoretical, and numerical results have been reported in the literature by several authors [L. M. Martel et al., Bull. Seism. Soc. Am. 67, 1277–1290 (1977)] on Rayleigh wave transmission coefficient past a step change in elevation. In this paper, reciprocity for both wave propagation direction across a step is demonstrated experimentally using a new ratio technique eliminating error sources introduced from elastic wave generation, coupling, and detection. Two-dimensional ultrasonic models were used to obtain the data. The experimental transmission coefficient measurements are compared with other published results. The ratio of step height to Rayleigh wavelength tested ranged from 0.159–1.33. The effect of step height on the interference of the transmitted wave components is examined. The conversion between Rayleigh and shear waves at the step plays an important role in the transmission coefficient.
Reflection of narrow ultrasonic beams at fluid/solid interfaces
Authors: Jensen Finn B. , Schmidt Henrik
Published: January 2006

The reflection of ultrasonic beams near the Rayleigh angle for a fluid/solid interface is a well researched subject. Existing theories, however, are all approximate with limitations such as beamwidth large compared to the wavelength, lossless media, parallel beams of particular shape (Gaussian), etc. A new numerical model has been developed to solve the reflection problem without any of the above limitations. This technique is based on the fast-field solution to the wave equation, and solutions can now be obtained for any beamwidth, and for parallel, diverging, and converging beams. Furthermore, due to the numerical efficiency of the computer code, pulsed-beam solutions can be generated in reasonable time using Fourier synthesis of the time signals. Computational results are presented for various beam configurations reflected at water/steel and water/aluminum oxide interfaces, and the results are compared with available experimental data.
Observations of backward leaky Lamb waves in plates
Authors: de Billy Michel , Adler Laszlo , Quentin Gérard
Published: January 2006

We have previously reported [J. Acoust. Soc. Am. 72, 1018–1020 (1982)] that a finite ultrasonic beam produces backward leaky-Rayleigh waves from liquid-solid interface. These backward propagating leaky-Rayleigh waves are of much lower amplitudes than the forward one and observed with a single transducer in pulse-echo mode. The objective of this paper is to report the observation of backward propagating leaky-Lamb waves in plates immersed in water. [Forward propagating leaky-Lamb waves were predicted and observed by Plona, Pitts, and Mayer, J. Acoust. Soc. Am. 59, 1324 (1976).] Several symmetrical and antisymmetrical Lamb modes were identified in brass and stainless-steel plates by measuring the critical angle at which the back reflected signal (to the transmitter) is maximum. Backward propagating leaky-Lamb waves are also observed with a second transducer on the transmitting side of the plate. The measured dispersion curves are in good agreement with theoretical predictions.
Reflection and transmission of obliquely incident Rayleigh waves by a surface-breaking crack
Authors: Angel Y. C. , Achenbach J. D.
Published: January 2006

Reflection, transmission, and scattering of Rayleigh waves that are obliquely incident on a surface-breaking crack are investigated. The formulation of the problem has been reduced to two systems of singular integral equations of the first kind for the dislocation densities across the crack faces. The systems of integral equations are solved numerically. Substitution of the dislocation densities into appropriate representation integrals yields the reflected and transmitted surface waves. Reflection and transmission coefficients are plotted versus the angle of incidence for various values of the wavelength, and versus the wavelength for various values of the angle of incidence. A critical angle of incidence, which depends on the material properties of the solid, has been observed. Beyond this angle no mechanical energy is radiated into the solid by body waves.
Scattering of acoustic waves by a periodic array of elastic strips
Authors: Sezginer A. , Chang S. K.
Published: January 2006

The scattering of a time harmonic plane wave in a fluid incident on an infinite periodic array of thin elastic strips is studied. The strips are coplanar and perpendicular to the plane of incidence. The acoustic displacement potential in the fluid is expressed as a Floquet wave expansion. Mindlin's theory of the bending of thin plates is applied to relate the pressure difference across the elastic strips to the motion of the strips. The shear and bending components of the strip motion are expanded in trigonometric basis functions, such that the shear force and bending moment are zero at the edges of the strips. The expansion coefficients are solved from the linear equations obtained by applying the method of weighted residuals to the boundary conditions on the strips and in the gaps. Anomalous reflection is observed when the incident wave frequency coincides with the transverse resonance frequencies of the strips. Resonance frequencies are observed in close pairs, corresponding to the strip resonant modes with a symmetric and an antisymmetric displacement profile. At normal incidence, the antisymmetric family of modes are not excited. In addition, sharp changes in the Floquet wave coefficients occur, known as the Wood's anomalies, as the frequency of the angle of incidence is swept.
A perceptually based approach to F0 characterization
Authors: Lieberman Philip , Katz Bill , Zimmerman Roger , Jongman Allard , Miller Mark
Published: January 2006

While researchers applying quantitative techniques to the characterization of intonation patterns [W. E. Cooper and J. M. Sorensen, Fundamental Frequency in Sentence Production (Springer-Verlag, Berlin, 1981)] have claimed success in relating phenomena such as F0 “resetting” to the presence of syntactic boundaries [J. Breckenridge and M. Y. Liberman, “The declination effect in perception,” unpublished manuscript, Bell Laboratories (1977)], this procedure has been confined to a highly limited corpus of short, simple-declarative read sentences. The degree to which these models can be generalized to spontaneous speech has recently become the subject of controversy [N. Umeda, J. Phonet. 10, 279–290 (1982)]. We therefore examined a corpus of spontaneous and read speech with the intent of finding a quantitative characterization which could be applied across speaking conditions. To this end, we analyzed the data using the “topline” modeling procedure, as well as peak, valley, and all-points rms lines, computed by linear regression. In simple-declarative clauses and sentences, the “topline” model performed adequately. The all-points rms line also performed well and captured the greater degree of variance occuring in spontaneous speech. Given this result, and for reasons of computational simplicity, we felt that an all-points rms line was superior in characterizing the data. This rms model is consistent with auditory processing models.
Measures of phonation types in a natural language
Authors: Kirk Paul L. , Ladefoged Peter , Ladefoged Jenny
Published: January 2006

Using a Kay digital spectrograph, three types of analysis (spectrograms, power spectra, and waveforms) were used to investigate different phonation types in a single natural language (Jalapa Mazatec). In addition to normal voice, this language uses creaky voice and breathy voice to distinguish words. We recorded five speakers producing contrastive vowels that were identical in quality and pitch. The spectrograms showed that in comparison with normal vowels the creaky vowels had glottal pulses at irregular intervals and a greater amplitude in the higher frequencies. The breathy vowels are more clearly distinguished in the onset, and they often lacked discernible pulses. We used power spectra displays to quantify phonation type differences. In creaky vowels the amplitude of the first harmonic in relation to the amplitude of the first formant is less than in normal voice; and in breathy vowels the first formant had less intensity in comparison with that of the first harmonic. Waveforms displayed the irregularities in the glottal pulses and the high degree of first formant damping in creaky vowels. [Work supported by USPHS grant NS 18163-02.]
Perception of height differences in vowels
Authors: Assmann Peter F. , Nearey Terrance M.
Published: January 2006

Vowels contrasting in the phonetic feature of height or openness are differentiated primarily by changes in the frequency of the first formant. Several hypotheses have been proposed to account for the perception of these differences. Mushnikov and Chistovich [Sov. Phys. Acoust. 19, 250–254 (1973)] argue that the frequency of the most prominent harmonic in the F1 region determines the height of a vowel. Carlson et al. [in Auditory Analysis and Perception of Speech, edited by G. Fant and M. A. A. Tatham (Academic, London, (1974)] favor an amplitude-weighted average (center of gravity) of the two most prominent harmonics. Results of matching experiments will be reported in which listeners select the best vowel match along an F1 continuum corresponding to test stimuli with modified amplitude spectra. The effects of F0, number, and frequency of harmonics are investigated. Predicted distances according to several models will be compared with listener's matches. Spectral distance models based on the excitation pattern or loudness density will also be considered. Results are generally consistent with a local center of gravity hypothesis. [Work supported by SSHRC.]
Susceptibility to intense impulses
Authors: Price G. Richard , Lim David J.
Published: January 2006

Price has advanced the view that susceptibility to intense impulses of the type produced by weapons is a function of a spectrally related “critical level” in the ear [J. Acoust Soc. Am. 73, 556–566 (1983); J. Acoust, Soc. Am. Suppl. 1 62, S95(1977)]. This view results in a major disagreement with all damage risk criteria in use in the world by predicting that for equal peak pressures, rifle impulses are more hazardous than cannon impulses. A crucial experiment was run using both ears of 57 cats to test this hypothesis [G. R. Price, J. Acoust. Soc. Am. Suppl. 1 71, S79 (1982)]. Two months post exposure, final electrophysiological measures were made and the ears were perfused for histological processing. Histological measures involving both scanning electron microscopy and serial sectioning and light microscopy (opposite ears of each cat) can now be compared with the earlier electrophysiological measures. The two sets of histological measures show the same picture and they in turn correlate well with the electrophysiological measures.
An acoustic study of Japanese coronal fricative clusters resulting from vowel devoicing
Authors: Kawasaki Haruko
Published: January 2006

Earlier studies [S. Shattuck-Hufnagel, V. Zue, and J. Bernstein, J. Acoust. Soc. Am. Suppl. 1 64, S92 (1978), V. Zue and S. Shattuck-Hufnagel, Proc. 9th ICPS 2, 215 (1979)] examining English fricative clusters [s∫] and [∫s] across word boundaries (e.g., in “gas shortage” and “tunafish sandwich”) showed that the direction of assimilatory palatalization is predominantly anticipatory: [s∫] often becomes [∫∫], but [∫s] does not. This study investigates the cross-linguistic validity of such a tendency. Four speakers of standard Japanese casually spoke sentences containing fricative clusters [∫s] and [s∫] resulting from devoicing/deletion of an intervening high vowel [i] or [u]. Preliminary observations reveal complex patterns not totally consistent with those for English: anticipatory palatalization in [s∫] in Japanese does not seem as robust a process as in English. Furthermore, perseveratory palatalization, i.e., ∫s→∫∫, and both anticipatory and perseveratory depalatalization, i.e., ∫s→ss, s∫→ss, all of which are relatively rare in English, are found in Japanese data. The results suggest a diffculty in explaining the previous English data in terms of peripheral articulatory control.
Vocalic formant transitions are integrated with noncontiguous fricative noises
Authors: Whalen D. H.
Published: January 2006

Natural-speech fricative noises from fricative-vowel or vowel-fricative syllables were edited so that the noise started out as either [s] or [š] and ended up the other fricative. The overall duration of the noise was held constant, and the proportions of the two parts varied. The vocalic formant transitions supported the phonetic category of one part of the noise or the other. With both initial and final fricatives, the transitions reduced the amount of noise needed to identify a fricative as belonging to the category of the transitions. Thus either the transitions were integrated with noncontiguous acoustic cues, or the transitions had cue value only when contiguous with the appropriate fricative noise. A further experiment placed the same edited noises between two vocalic segments, and subjects identified two fricatives. The perceived ordering of the fricatives was often the reverse of the order of the noises themselves when the transitions were in the opposite order. It thus appears that the transitions are integrated with noncontiguous acoustic cues. [Work supported by NIH.]
Vowel-to-vowel coarticulation in Swahili
Authors: Krakow Rena A. , Manuel Sharon Y.
Published: January 2006

Acoustic data from Swahili (a Bantu language with a five-vowel system) reveal interesting differences in the extent and direction of vowel-to-vowel coarticulation as compared with other languages. Utterances were VpV disyllables, including all combinations of the five vowels with stress on the first vowel, recorded by a native speaker of Swahili. Two major results emerged from the analysis: (i) Previous research on other languages has shown vowel-to-vowel coarticulatory effects across the consonant to be restricted to the vocalic transitions. The present data reveal systematic vowel-to-vowel coarticulatory influence which extends into the steady-state portion of the transconsonantal vowel. (ii) A second important cross-linguistic difference is found in examining the relationship between the magnitude and direction of these effects. The first vowel, which is stressed, is found to be more affected by the quality of the second vowel than vice versa. In Swahili, then, anticipatory effects of coarticulation exceed carryover effects. This is in contrast to Fowler (1981) in which she shows stronger carryover than anticipatory effects for VCVs in English. [Work supported by NICHD.]
Theoretical prediction of sound attenuation in a liquid-filled rectangular flow duct using a viscoelastic-fluid composite liner
Authors: Ko Sung H. , Ho Louis T.
Published: January 2006

A theoretical investigation was made of the sound attenuation in a two-dimensional, liquid-filled duct treated with a composite liner consisting of a viscoelastic slab and a fluid layer, which is backed by a perfectly rigid plate. The viscoelastic material is a rubber-like material that has a loss factor associated with the shear modulus, and is characterized by Lame constants and the material density. The fluid layer of the composite liner is assumed to be lossless and nondispersive medium, and is characterized by the fluid density and the speed of sound. The fluid contained in the lined duct is assumed to be inviscid and characterized by the fluid density and the speed of the sound. The eigenvalue equation was derived based on the theory of elasticity, the acoustic wave equation in the presence of the flow in the duct, the acoustic wave equation in the absence of the flow for the fluid layer of the composite liner, and pertinent boundary conditions. The eigenvalue equation was solved numerically for a given duct geometry, the liner configuration, the composite liner material properties, and the flow velocity. Then, the sound attenuation was obtained using the calculated eigenvalues.
A novel concept for vibration isolation
Authors: Graham Thomas S.
Published: January 2006

This paper describes a novel concept for combining linear springs to synthesize various force-deflection curves as might be useful for particular problems of machinery isolation. (A force-deflection curve with a plateau is easily synthesized, for example.) The concept involves combining a negative spring, produced by a standard spring acting against lever arms, in series and parallel with standard springs. It is suggested that such devices may be useful where the use of rubber for machinery isolation is inappropriate.
Hearing conservation: Regulatory status and issues
Authors: Suter Alice H.
Published: January 2006

The Occupational Safety and Health Administration published the final decisions on its hearing conservation amendment on 8 March 1983. Certain changes are likely to cause confusion when OSHA personnel enforce the standard. Employers now must use personal monitoring in cirumstances where area monitoring is “generally inappropriate” unless they can show that “area sampling produces equivalent results.” Also, OSHA has changed the term “significant threshold shift” to “standard threshold shift,” which some individuals interpret to mean an ordinary or expected shift in hearing level. Most changes from the January 1981 version are towards a performance rather than a specification approach, which may result in less rigorous hearing conservation practices, increasing the likelihood that employees will suffer noise-induced hearing loss before intervention can occur. Consequently, three critical issues have emerged. First, employers and consultants need a standard, practical method of testing hearing protector attenuation as it occurs in the field. Second, OSHA needs to derate the Noise Reduction Rating to reflect real world use, and third, employers need an objective method by which to evaluate the effectiveness of their hearing conservation programs.
Measurement of employee noise exposure—Sound level meter procedures
Authors: Flynn Daniel R.
Published: January 2006

Even in this era of sophisticated digital instrumentation, the simple hand-held sound level meter continues to hold its place as a workhorse in the measurement of employee noise exposure. The history of the sound level meter for such measurements is briefly reviewed and a summary is given of the major advantages and disadvantages of using a sound level meter for occupational noise exposure measurements. Some of the problems, perils, and pitfalls of conducting such measurements are highlighted. A brief review is given of accuracy requirements and calibration procedures. Spatial sampling problems are briefly discussed. The remainder of the talk concentrates on temporal sampling procedures for determination of employee noise exposure associated with time-varying noise; a simple procedure is described for accurate measurement of noise dose using a hand-held sound level meter.
Do dosimeters overestimate contributions from impulsive noise?
Authors: Earshen John J.
Published: January 2006

The Occupational Safety and Health Administration published the final version of its hearing conservation amendment on 8 March 1983. It states explicitly that contributions from all noise, impulsive, intermittent, and continuous must be included in determining worker noise dose. In addition it is stated that measurements must be made with instruments possessing A-weighting and slow response. Many claims have been made that dosimeters overestimate contributions from impulsive noise (e.g., defense submissions and testimony in the Collier-Keyworth case and Friend of the Court submission by Chocolate Manufacturers Association). The CMA document presents results comparing theoretical computation for waveforms having short pulse components to results obtained with a variety of dosimeters currently in use. The instrument readings are high compared to the theoretical computations; thus it is concluded that dosimeters overestimate. This paper demonstrates that dosimeters complying with the OSHA stipulation to include A-weighting and slow response do not overestimate. Conclusions reached in the CMA brief are critically affected by ignoring the dynamic properties of Slow Response when performing theoretical determination of predicted dose for specified pulsed waveforms. It has been suggested, and in several instances demonstrated, that the discrepancy between computed and measured values disappear if fast response is substituted. Mathematical analysis of the idealized dosimeter transfer function verifies this conclusion. It should be noted that the discrepancy reappears for pulse duration of less than 0.125 s. The issue to be resolved is not one of instrument performance; rather it is whether the stipulation of A-weighted slow response is justifiable.
Risk assessment for populations wearing hearing protectors
Authors: Sachs Felix Z.
Published: January 2006

The considerations and parameters underlying the assessment of risk of hearing loss for a population wearing personal hearing protective devices (HPD's) are examined. A damage risk function for a protected population is developed, and measures of hearing protector effectiveness are defined. It is noted that the Noise Reduction Rating (NRR) formulation of protector effectiveness cannot be validly used as a population-oriented measure of hearing protector effectiveness. In the population-oriented context, real-ear attenuation values for hearing protectors obtained under user-fit conditions must be used, but the mean value should only be reduced by 1/4 to 1/2 of a standard deviation in order to provide the required statistical confidence. Finally, some numerical examples of hearing protector effectiveness are developed using computer simulation akin to the Monte Carlo method.
Comparison of hearing protector single-number rating methods
Authors: Marraccini Leonard C.
Published: January 2006

During the last ten years, various organizations have developed single-number rating methods for hearing protectors. These values have been used to approximate the amount of noise reduction obtained by using these devices. From the hearing protector attenuation data obtained from the American National Standards Institute test procedures, the organizations have mathematically arrived at single numbers such as the “R factor”, the “NRR”, and “D factor”, and so on. These are based on various items such as actual noise spectrums, pink noise spectrums, standard deviation of the attenuation data, etc. This paper compares the various single number ratings which have been calculated for six different hearing protectors, and the methods used. As can be seen, the single number rating varies considerably. Advantages and disadvantages of each method is also discussed. Finally, application of the values to on-the-job situations will be discussed.
Impulse contribution of total worker noise dose
Authors: Erdreich John
Published: January 2006

For several years there has been controversy concerning whether impulsive noise should be included in determining the noise dose to which a worker is exposed. Clearly, the impulsive noise components reach the ear and should be considered in determining hazard. However, recent court rulings held that, since appropriate instrumentation is not available to the industrial hygienist for impulse measurement, the calculations and tables in the OSHA Hearing Conservation Amendment should not include this noise. How much of a difference does not including impulse noise make in the total dose? Measurements in 14 plants made with a 40-kHz bandwidth and either a 40-dB or a 72-dB dynamic range were analyzed and the total OSHA dose and the OSHA dose for the impulses alone were calculated. The impulses account for as much as 20% of the exposure time. In this short period, however, the impulse noise accounts for up to 50% of the total dose. Eliminating impulses from dose calculation may result in worker exposure estimates half of the actual dose.
Theoretical method for a range-dependent fast field program
Authors: Gilbert K. E. , Kuperman W. A. , Grimm R. E.
Published: January 2006

A fast field program (i.e., a Green's function method) is an accurate and flexible means for treating wave propagation in a range-independent environment. Until now, however, there apparently has been no theory for applying the method to a range-dependent environment. This paper derives and applies a fast field method for one-way wave propagation in a range-dependent environment. The method is based on the solution of the elliptic wave equation for an arbitrary vertical source distribution. On a given range step, the vertical source distribution is taken to be the field at the end of the previous step. It is shown analytically and numerically that this approach does, in fact, give the correct solution for one-way propagation in a range-dependent environment.
A new fast-field solution to propagation in multilayered solid environments
Authors: Schmidt Henrik
Published: January 2006

During the last decade the fast field program (FFP) has been an important tool for modeling wave propagation in stratified media. The earlier models of this type were based on a solution of the depth-separated wave equation by means of the Thomson-Haskell method. In this new FFP model a more direct and faster solution technique is employed. The field is expressed in terms of unknown scalar potentials. At each interface the boundary conditions yield a linear system of equations in the Hankel transforms of the potentials. Using a technique similar to the one used in finite-element programs, these equations are mapped into a global system which is solved with an efficient band-solver. Contrary to the Thomson-Haskell method, the new technique can treat several sources and receivers with one single solution. Hence, the field produced by vertical source arrays can be determined. Even with one source and receiver the computational speed has been improved by an order of magnitude, and pulse calculations by means of Fourier synthesis have become feasible. The features of the model are illustrated through a few computational examples.
Modeling of sound propagation over Dickins Seamount
Authors: Jensen Finn B.
Published: January 2006

Experimental data for sound propagation across a steep seamount (14° mean slope) was recently reported [G. R. Ebbeson and R. G. Turner, J. Acoust. Soc. Am. 73, 143–152 (1983)]. The broadband data exhibit a frequency-dependent shadowing effect with a drop in sound level just behind the mount of more than 20 dB at 12.5 Hz. An earlier attempt to explain these propagation features using the parabolic-equation technique gave promising results [F. B. Jensen, W. A. Kuperman, and H. Medwin, J. Acoust. Soc. Am. Suppl. I 68, S52 (1980)]. The data have now been subjected to a detailed modeling using both range-dependent ray theory and the recently developed wide-angled parabolic equation theory [D. Lee, G. Botseas, and J. S. Papadakis, J. Acoust. Soc. Am. 70, 795–800 (1981)]. It is found that the full complexity of the propagation situation is well handled by both the acoustic models, and that the shadowing is due to the cutoff of steep propagation paths (bottom-bounce paths) by the seamount, leaving mainly waterborne paths to propagate beyond the mount. For these latter paths the surface-decoupling loss essentially determines the frequency dependence of the measured loss.
A range reflection parabolic equation
Authors: Tappert Frederick D. , Lee Ding
Published: January 2006

Application of the standard parabolic wave equation to solve real problems requires a clever selection of the reference wavenumber k0. An extended parabolic equation, earlier developed [F. D. Tappert, The Parabolic Approximation Method (Springer-Verlag, Berlin, 1977), Lecture Notes in Physics, Vol. 70, pp. 224–287], is re-introduced. This parabolic wave equation has range refraction capability and is totally k0-independent. The existing Implicit Finite-Difference (IFD) model was applied to test the range refraction parabolic equation. Results compare favorably with known solutions for weakly range dependent environments, but yield significant corrections for propagation through strong oceanic fronts. [Work supported by NUSC.]
The uniform WKB normal mode code: Applications to cw and broadband propagation
Authors: Henrick R. F. , Brannan J. R. , Warner D. B. , Forney G. P.
Published: January 2006

The increased interest in the modeling of underwater acoustic signals which are time limited or possess significant frequency bandwidth has resulted in a variety of broadband propagation codes. However, these codes are typically limited in utility by extremely long run times or in accuracy by simplifying assumptions. The approach taken here it to use uniform asymptotic approximations to the normal modes of the sound channel to obtain both accuracy and numerical efficiency. These approximations are based on the WKB approach but include corrections for modes that turn near boundaries and near mode turning points. This uniform WKB model approach leads to further efficiencies in multiple frequency broadband or pulsed propagation. The accuracy of this approach and the importance of these corrections is first illustrated for a cw signal. Subsequent examples show accurate results for both broadband and time pulsed signals. Run time comparisons show reductions of two orders of magnitude in comparison to conventional broadband codes.
Impulsive wave propagation and the cuspoid caustics
Authors: Brown Michael G.
Published: January 2006

The caustics of short wavelength wave propagation may be classified according to catastrophe theory. After establishing this connection the behavior of the time-dependent wave field due to an impulsive wave in the vicinity of the general cuspoid catastrophe is examined. Numerical results are presented for the fold, cusp, and swallowtail catastrophes which show the smooth variation of the time-dependent acoustic field as the control parameters are varied. These results vividly demonstrate the phenomenon of ray focusing, showing the number of rays which converge at each catastrophe, the resulting phase shifts they undergo as well as their decay in shadow regions. Analytical results are given which describe the most important properties of the time-dependent acoustic field on and at large distances away from each of the cuspoid catastrophes.
Impulsive wave propagation and the elliptic, hyperbolic, and parabolic umbilic caustics
Authors: Brown Michael G.
Published: January 2006

The time-dependent wave field due to an impulsive wave in the vicinity of the elliptic, hyperbolic, and parabolic umbilic caustics is examined. Numerical results are presented which show the smooth variation of the time-dependent acoustic field in the vicinity of all three caustics. Analytical results are given which describe the most important properties of these wave fields. The time-dependent structures of these wave fields are qualitatively different than those associated with the cuspoid caustics. The reason for the difference stems from the difference in phase shifts which individual ray arrivals undergo as a result of touching one of the two types of caustic (cuspoid versus umbilic).
Estimation of mesoscale sound speed perturbations via underwater acoustic tomography
Authors: Chiu Ching-Sang , Desaubies Yves
Published: January 2006

The inverse problem in ocean acoustic tomography corresponds to the estimation of the parameters characterizing the sound speed fluctuations due to mesoscale eddies from the acoustic travel time data. A deterministic model of the sound speed perturbation field δc is presented. In the model δc is assumed to be generated by a small number of Rossby waves and accounts for most of the data variance. Thus, δc is determined by only a few wave parameters, that is the amplitudes, wavenumbers and phases of the waves. The forward problem of travel time and ray path fluctuations due to δc and currents is studied by computer simulations and results are presented. An iterative method to estimate the wave parameters of the nonlinear system of the inverse problem is discussed and preliminary results in applying it to the data of the 1981 experiment are presented.
Reciprocity calibration of transducers in a plane-wave resonator
Authors: Burmaster Charles L. , Garrett S. L.
Published: January 2006

In an article by Rudnick [J. Acoust. Soc. Am. 63, 1923 (1978)] a procedure for the “reciprocity calibration of transducers in unconventional geometries” was described. The theory presented by Rudnick has been tested experimentally and extended to include the effects of the compliance of nonideal transducers on the quality factor of the plane-wave resonances. A computer controlled system with automated switching was designed and built to acquire and process the resonance data required for the reciprocity calculations. Two reversible transducers and one microphone were mounted in the cylindrical resonant cavity to allow a six-way round robin self-consistency check of the experimental precision. The absolute accuracy of the sensitivity thus obtained is then compared with the results of a conventional reciprocity technique [ANSI S1.10-1966 (R1976)] and/or manufacturers specifications. [Work supported by ONR.]
An improved fiber optic lever transducer
Authors: Cuomo Frank W.
Published: January 2006

The concept of a bifurcated fiber optic transducer has been described and applied to the measurement of pressure and temperature. This approach has been used to design low-frequency hydrophones [F. W. Cuomo, J. Acoust. Soc. Am. 73, 1848–1857 (1983)]. The sensitivity of this device is proportional to the total number of adjacent transmit/receive fiber pairs used in the bundle. For good sensitivity the transmit/receive fiber distribution must be maximized while the total number of fibers must be large. This paper discusses an improved bifurcated fiber optic transducer comprising one transmit fiber and two receive fibers, each receive fiber having a different core diameter. The three fibers are separated at one end and combined at the distal end in the vicinity of a miniature reflective surface sensitive to axial motion caused by minute pressure changes such that any displacement of the reflector from equilibrium will increase or decrease the illuminated areas of the two receive fibers and will generate a processed output signal proportional to this motion. The major relevant improvements over prior designs include a probe of minimal dimensions, a greatly improved sensitivity, and an output independent of variations at the input.
Computation of a piezoelectric deep-submergence transducer by three-dimensional finite element method
Authors: Tocquet B. , Boucher D. , Debus J. C. , Tierce P.
Published: January 2006

The advantages of deep-submergence transducer are well known although practical solutions to solve high-pressure problems are very few. In this paper, such a system is studied. The radiating area of the transducer is a ring, on the inner face of which several length expander motors are fixed in a star shape. Every motor is composed of a ceramic stack and a tail mass. No mechanical connection is able to transmit exterior static or dynamic forces to the motors. This transducer has mainly two resonance frequencies which can be used: one is lower than the resonance frequency of the ring alone, the other is slightly higher than the motor resonance. To analyze this transducer, a finite element computer code (ATILA) has been developed. In water, the vicinity of the transducer is modelized with 3D fluid elements up to an exterior surface, the boundary reflection being damped through use of a suitable radiation impedance. So, in air eigenmodes, transmitting voltage response, directivity patterns, and electrical impedance can be computed. In this paper, the experimental results obtained with a deep-submergence transducer are compared with the theoretical ones.
Sidedness and perception for single echo of some ordinary sounds
Authors: Zaccone Terry S. , Schubert Earl D.
Published: January 2006

Nine different sound-sample sequences ranging in temporal predictability from white noise to English speech were recorded with a single echo delayed from zero to 100 ms. The sounds were recorded in the presentation modes of monaural, dichotic, and mixed (original to both cars, delayed in one). The single repetition intensity was equal to, and 3 and 6 dB greater than, that of the original sound. Subjects were asked to indicate when the echo was perceived and, in separate tests, on which side they perceived the sound. In general, the ability of the subjects to choose the side of the leading signal diminished as the repetition delay increased past 20 ms. They were expected to perceive temporal order rather than sidedness as the delay became longer than 20 ms. Even for sounds with pronounced envelope, the subjects were not able to regain identification of sidednesS out to 100-ms delay. Presentation of different sound types resulted in significant differences in performance. White noise presented the most difficult task, as shown by the low percentage of identification of the leading car. The female singer and violin yielded the highest percentages for leading-car identification.
Pitch and spectral estimation of speech based on auditory synchrony model
Authors: Seneff Stephanie
Published: January 2006

This paper describes a system for processing sonorant regions of speech, motivated by knowledge of the human auditory system. The spectral representation is intended to reflect a proposed model for human auditory processing of speech, which takes advantage of synchrony in the nerve firing patterns to enhance formant peaks. The auditory model is also applied to pitch extraction, and thus a temporal pitch processor is envisioned. The spectrum is derived from the outputs of a set of linear filters with critical bandwidths. Saturation and adaptation are incorporated for each filter independently. Each “spectral” coefficient is determined by weighting the amplitude response at that frequency (corresponding to mean firing rate) by a measure of synchrony to the center frequency of the filter. Pitch is derived from a waveform generated by adding the (weighted) rectified filter outputs across the frequency dimension. The system performance is evaluated by processing of a variety of signals, including natural and synthetic speech, and results are compared with other processing methods and with known psychoacoustical data from these types of stimuli. [Work supported in part by NINCDS and the System Development Foundation.]
Factors affecting the use of noise-band vocoders as acoustic models for pitch perception in cochlear implants
Authors: Laneau Johan , Moonen Marc , Wouters Jan
Published: January 2006

Although in a number of experiments noise-band vocoders have been shown to provide acoustic models for speech perception in cochlear implants (CI), the present study assesses in four experiments whether and under what limitations noise-band vocoders can be used as an acoustic model for pitch perception in CI. The first two experiments examine the effect of spectral smearing on simulated electrode discrimination and fundamental frequency (F0) discrimination. The third experiment assesses the effect of spectral mismatch in an F0-discrimination task with two different vocoders. The fourth experiment investigates the effect of amplitude compression on modulation rate discrimination. For each experiment, the results obtained from normal-hearing subjects presented with vocoded stimuli are compared to results obtained directly from CI recipients. The results show that place pitch sensitivity drops with increased spectral smearing and that place pitch cues for multi-channel stimuli can adequately be mimicked when the discriminability of adjacent channels is adjusted by varying the spectral slopes to match that of CI subjects. The results also indicate that temporal pitch sensitivity is limited for noise-band carriers with low center frequencies and that the absence of a compression function in the vocoder might alter the saliency of the temporal pitch cues.
Transducer sensitivity compensation using diagonal preconditioning for time reversal and Tikhonov inverse filtering in acoustic systems
Authors: Dumuid Pierre M. , Cazzolato Ben S. , Zander Anthony C.
Published: January 2006

Filters are commonly used in sound reproduction and communication systems as a means of compensating for the response of the electro-acoustic plant. Two commonly used filter designs in the field of acoustics are the time reversal filter and the Tikhonov inverse filter. In this paper the influence of transducer sensitivities on the performance of these filters is examined. It is shown that the sensitivity of the transducers can negatively affect the performance of the resulting filter. To compensate for the decrease in performance, diagonal preconditioning can be implemented in the system. It is shown that by using diagonal matrices, which minimize the condition number of the system, the loss in performance arising from unbalanced sensitivities is minimized. This paper proposes an algorithm to find such a set of diagonal matrices and results are presented showing the improvements in performance arising from the modified filter design.