bluuebunny/crossref_metadata_2025 huggingface dataset:
Preaspiration in Icelandic: Production and perception
Authors: Pind Jörgen
Published: October 2005

Preaspiration in Icelandic occurs, e.g., when a vowel in a stressed syllable is followed orthographically by ‘‘pp’’, ‘‘tt’’, or ‘‘kk,’’ and is commonly transcribed as [h] before a short stop. Stressed syllables in Icelandic thus present a three way contrast (involving stops) between word forms such as baka [ḅa(lengthening)g̊a], ‘‘to bake,’’ (type V:C), bagga, [ḅag̊(lengthening)a], ‘‘burden’’ (acc.sg.) (type VC:), and bakka, [ḅahg̊a], ‘‘to turn back’’ (type VhC). Durational measurements showed wide variability in segment durations depending on context. However, results also indicate that the ratio of the preaspiration to the vowel duration is reasonably constant and can be viewed as a higher-order invariant, comparable to the vowel/rhyme ratio in the quantity opposition [J. Pind, Phonetica 43, 116–139 (1986)]. Perception experiments showed that preaspiration can be cued by voice offset time, a speech cue analogous to voice onset time. The experiments further showed that durational relationships within the syllable rhyme influenced the perception of preaspiration to a great extent while factors outside the rhyme had a minor influence on the placement of the phoneme boundaries, indicating perceptual constancy.
Let your synthesizer breathe
Authors: Whalen D. H. , Hoequist Charles E.
Published: October 2005

Although synthesizers do not have any air flow, they are representing creatures that do. While it is quite common to have long stretches of speech without audible intake (especially with speakers trained in acting and broadcasting), synthesis might be somewhat less artificial with the intake of breath added. To see whether adding an audible intake would affect the perception of synthetic speech, breath intake (naturally produced) was introduced in a synthesis transcription task. Subjects received the breath-added stimuli on either the first half of the test or the second. The largest effect was a typical one of increased performance in the second half, due to increased experience with the synthesizer. However, those subjects who received the breath second had a much larger improvement than those who had it first, who were essentially the same in the second condition as the first. The results indicate that, as with almost anything that increases naturalness, allowing computers to breathe will improve the perception of synthetic speech. [Work supported by NIH Grant No. HD-01994.]
Physiological correlates of the precedence effect: Implications for neural models
Authors: Yin Tom C. T. , Litovsky Ruth Y.
Published: October 2005

The precedence effect is an illusion whereby two similar sounds, delivered from different locations and in quick succession, are perceived as a single auditory event whose apparent location is dominated by the leading sound. Physiological correlates of the precedence effect have been looked for in the responses of single cells in the inferior colliculus (IC) of anesthetized cats. Studies were conducted in both dichotic and free-field conditions by simulating click pairs with variable interclick delays. Almost all cells show a form of echo suppression, whereby the response to a lagging click is suppressed to half-maximal value for interclick delays of 3–150 ms (mode of 29 ms). This result dictates an important role for inhibition in the binaural circuits of the brainstem. It may also provide a resolution for the paradox in which Colburn’s models of the medial superior olive (MSO) need no inhibition yet there is strong anatomical evidence for the presence of inhibitory synapses in both MSO and IC. [Work supported by NIH DC00116 and NRSA DC00078.]
What determines the sound of a sinusoid?
Authors: Patterson Roy D.
Published: October 2005

‘‘Damped sounds,’’ constructed by repeating a short segment of a sinusoid with an exponential decay, were compared with ‘‘ramped sounds,’’ constructed by reversing each damped sound in time. As the half-life of the decay function decreases through values less than the repetition period, the continuity of the sinusoid is disrupted and its distinctive sound quality fades away. However, these changes occur far sooner for the damped sound. Damped/ramped pairs with the same carrier frequency and repetition rate have identicalpowerspectra, so simple spectral models predict noperceptualdifference for these sounds. Excitation patterns generated with filterbanks and leaky integrators show that damped sounds have sharper spectral peaks than corresponding ramped sounds, so auditory models with simple leaky integrators predict the reverse of what is heard. A new model that employs strobed temporal integration to stabilize neural activity patterns suggests that ramped stimuli sound more sinusoidal because they produce more time intervals near the carrier period, although not in the carrier channel, and the perception is more continuous because the strobe threshold function is asymmetric in time.
In vivo measurement of laryngeal mucosal wave speed in humans
Authors: Wenokur Randall , Berke Gerald S. , Gerratt Bruce R. , Kreiman Jody , Ye Ming
Published: October 2005

Measurement of laryngeal mucosal wave speed is potentially important for understanding laryngeal vibration and for guiding phonosurgery. However, measurement of wave speed requires knowledge of distance or phase angle on the vocal folds, and has not been possible in awake patients. A new method permitting such measurements in an office setting is described. This method can be applied using either a calibrated fiberoptic nasopharyngoscope or a calibrated laryngoscope to measure absolute distances in the larynx accurately, reliably, and noninvasively. Wave speeds were measured in one normal male speaker at varying levels of F0 and intensity. Across conditions, measured mucosal wave speed ranged from 0.29 to 1.18 m/s. Wave speeds varied significantly with vocal intensity (r=0.72), but not with F0 (r=0.14). Theoretical implications of these findings will be discussed, along with clinical applications of the new techniques.
Syllable internal timing: Effects on vowel and consonant duration
Authors: Behne Dawn M. , Nygaard Lynne C.
Published: October 2005

The present study investigates the effects of vowel quality, postvocalic voicing, sentence position, focal stress, and speaking rate on the internal timing of syllable components. Previous findings [D. M. Behne and L. C. Nygaard, J. Acoust. Soc. Am. 90, 2254 (A) (1991); D. M. Behne and L. C. Nygaard, J. Acoust. Soc. Am. 91, 2340 (A) (1992)] have confirmed the combined effects of these factors on vowel duration and have shown that consonants can also be independently affected by sentence position, focal stress, and speaking rate. The goal of this paper is to characterize the internal timing of both component vowels and consonants when these factors affect syllable timing. Using the vowels /i,o,a,æ/, conversations were developed with /kVt/ and /kVd/ as target words. In each conversation a target word occurred in initial and final sentence position and was either focused or nonfocused by the discourse. Twelve subjects produced each conversation at three speaking rates. The results indicate that (1) speaking rate and focal stress have a global effect on syllable-internal timing, influencing both vowel and consonant durations, (2) phrase-final lengthening affects the nucleus and postvocalic consonant, and (3) postvocalic voicing and inherent vowel duration locally affect vowel duration, but have little effect on neighboring consonants. These findings verify that the factors being investigated can concurrently influence the syllable-internal timing, and suggest a hierarchy of effects on the internal-timing of a syllable, from speaking rate to inherent vowel duration.
Rhythm and compression in Caribbean Spanish
Authors: Cedergren Henrietta J. , Toledo Guillermo
Published: October 2005

The goal of this research was the observation of temporal relations and degrees of compression in spontaneous speech. Recorded materials of casual speech from one female and one male speaker of a dialect of Panamanian Spanish were studied. Acoustic measurements were made by examining phonetic segments, syllables, and rhythmic groups embedded in intonational phrases through the use of digital spectrograms and oscillographic traces. Results indicate low degrees of temporal compression; rhythmic group duration shows significant linear correlation with rhythmic group size. In addition, rhythmic groups in intonational phrase preboundary position are subject to local deceleration, which affects both the penultimate stressed syllable and the following unstressed final syllable. Both speakers reveal a positive relation between the duration of the stressed and unstressed syllables. These findings suggest that casual speech style in this dialect has both syllable-timing and a locally bound deceleration. [Work supported by SSHRCC.]
Effects of rib complexity on plane wave localization phenomena
Authors: Photiadis Douglas M.
Published: October 2005

Spatial irregularity of an array of line masses has been previously predicted to give rise to Anderson localization of plane waves on a fluid-loaded plate. Here, the effects of additional rib complexity: nonvanishing moment of inertia, the ability to support vibrational waves along the rib, and the influence of some simple models of internal structure, are considered. It is shown that this system is nearly equivalent to a nearest-neighbor coupled line array where each site is now represented by two degrees of freedom, the effective force and moment exerted by each scatterer. In the absence of fluid-loading this immediately implies that any degree of irregularity produces Anderson localization. Simulation results illustrating typical localization effects in the presence of fluid-loading will be presented. Generally, more accurate modeling of the rib impedance is found to increase the rib scattering strength and hence increase localization phenomena.
Determination of electrical drives for a cylindrical wave-number calibration array
Authors: Luker L. D.
Published: October 2005

The ‘‘flow noise’’ produced by a turbulent boundary layer is generally characterized by pressure distributions that are transported along the surface at speeds much less than the sound speed in water and therefore have spatial wave numbers that are larger than the acoustic wave number. This paper describes several methods for computing the electrical drives for a prototype cylindrical wave-number calibrator (CWC) designed to generate a pressure field consisting of essentially a single nonacoustic wave number inside the free-flooded calibrator. This geometry is suitable for the evaluation of line acoustic sensors such as in towed sonar arrays. The prototype CWC consists of a cylindrical tube of PVDF with an electrode pattern along the tube length that allows the PVDF to be operated as 40 independent bands each of which can be driven at a specified amplitude and phase. The required drive voltages are calculated using the electroacoustic transfer matrix of the CWC at the desired drive frequency. This transfer matrix can be determined by actual measurements or by using a computer model of the CWC. Drives were computed using transfer matrices that were determined with several modeling methods including the acoustic-radiation program CHIEF and the finite-element program ATILA. Measured pressure fields inside the CWC are compared with desired and predicted fields at selected spatial wave numbers for drive frequencies of 800 and 1600 Hz. These results are also compared with previous results produced using measured transfer matrices. [Work jointly supported by ONR and ONT.]
Concerning the ‘‘displacement thickness theory’’ of boundary layer noise
Authors: Powell Alan
Published: October 2005

The streamlines just outside a boundary layer are pushed away from the wall by the displacement thickness δ* as the flow slows down. Hydrodynamic fluctuations in δ* have been considered to act as a compact monopole source distribution at the edge of the boundary layer, see Laufer etal. (1964), Lauchle (1981, 1989), Sornette and Lagier (1984, 1986). However, Rayleigh’s (normal velocity) formula applied to a plane just outside the layer reduces to the δ* theory only if the acoustic (sound-speed-dependent) contribution of the fluctuations there, due to the sound sources that must be within the layer, can be safely ignored. For a monopole source the δ* theory yields the correct result, although the net strength must be zero (because of continuity), except for viscous dissipation effects. It also yields the correct results for tangential dipoles, pertinent to net wall shear stresses, and for tangential longitudinal quadrupoles. But the δ* theory cannot represent normal longitudinal quadrupoles, an essential complementary component of plane boundary layer noise, Powell (1991): the extensive (noncompact) acoustic field contribution to the plane source distribution is then essential.
Acoustical applications of wavelets: Audio coding and sonar
Authors: Tewfik Ahmed H.
Published: October 2005

Wavelets are a family of basis functions for the space of finite energy signals. In a wavelet decomposition, a signal is expanded in terms of translates and dilates of a single function. Wavelets provide a flexible decomposition of signals. This flexibility is the foundation of a new generation of advanced low-bit-rate, high-quality audio coding procedures. By adaptively choosing the wavelet representations of consecutive segments of the audio signal one can optimally exploit the masking effect in human hearing. The performance of the resulting coding techniques surpasses that of known nonwavelet-based approaches. Another important property of wavelet decompositions is the fact that one can relate the structure of the wavelet coefficients of a given signal to the local time and frequency domain characteristics of the signal. In sonar processing, this fact has been exploited by a new class of robust direction of arrival estimation algorithms that can deal with background correlated noise of an unknown correlation structure. These algorithms separate signal from noise by analyzing the structure of the wavelet coefficients of the array outputs.
Dynamic finite-element calculation of excitation modes in periodic and disordered Lucite–steel composite systems
Authors: Sheng Ping , Zhou Minyao
Published: October 2005

Recent experiment by L. Ye etal. on Lucite–steel composite system [Phys. Rev. Lett. 69, 3080 (1992)] has demonstrated the localization of bending waves. This is particularly surprising on first sight because the huge acoustic impedance mismatch between Lucite and steel would seem to imply that Lucite should have very little effect on the steel. A dynamic finite-element approach was used to calculate the excitation modes in a 2-D periodic structure consisting of a steel plate decorated by a checkerboard pattern of Lucite blocks. The results show that the coupling between the steel plate bending wave and the flexural resonances of the Lucite blocks can drastically alter the dispersion relation of the bending wave, whereas the effect of periodicity is minimal. Since the Lucite flexural resonance frequencies depend on the Lucite block height, its effect on the bending wave can be tuned in terms of the frequency as demonstrated experimentally by Ye etal. This talk will also report the results of calculations on a random 1-D Lucite–steel system. In particular, the localization characteristics will be emphasized.
Ultrasonic monitoring of tensile, fatigue, or creep specimens in situ
Authors: Hazony D. , Welsch G. , Halford G.
Published: October 2005

A method is proposed for monitoring tensile, fatigue, or creep specimens while the testing is in progress. Two transducers, one transmits—one receives, are imbedded in both ends of the specimen. Sharp time-limited ultrasonic pulses permeate through the specimen from either end along the principle axis. Axial and radial strains may be monitored simultaneously by selectively tracking two of the received echoes. [see D. Hazony, ‘‘Edge effects in short pulse piezoelectric transducers,’’ J. Acoust. Soc. Am. 86, 1230–1233 (1989), Sec. IV]. The method is especially useful at elevated temperatures, aggressive environments, relatively high fatigue-cycling frequencies, and a wide range of strains. Generation and growth of cracks may also be tracked and monitored. Data may be gathered from the beginning to the last few microseconds in the life of the specimen. Salient features of the tests will be discussed. Actual data, slides, and a video tape will be presented. [Work supported by TecSonics, Inc. of Twinsburg, Ohio.]
Meshing noise from timing chain drives
Authors: Liu S. P. , Hayek Sabih I. , Wang K. W. , Trethewey M. W.
Published: October 2005

Controlled experiments on a specially constructed timing chain drive test stand have shown that the most significant noise source in roller chain drives is from impacts between the chain links and the sprocket teeth during their meshing process. Despite its importance, a study that can analytically predict and experimentally verify the characteristics of meshing noise has yet to be performed. A method is presented that can quantify the meshing noise as a function of the critical system parameters, such as chain speed, tension, mass and shape of chain links, and sprocket geometry. A comprehensive model that integrates the chain transverse and longitudinal vibrations with the sprocket motion is developed. The approach also couples the local meshing impulse with the global system dynamic response of the vibrating chain. Parametric tests were carried out on a test stand in which a roller chain and up to three sprockets could be tested. Besides the chain speed and tension, the local vibration and the sound pressure levels are recorded. This fundamental investigation provides new insight into roller chain noise problems. [Work supported by General Motors Corp.]
Pilot study of simulated spaciousness
Authors: Bradley John S. , Soulodre G. A. , Popplewell N.
Published: October 2005

Spaciousness is said to include the sense that the sound in a concert hall is enveloping, that the apparent source width is increased, and the general feeling of being in a room or space. Strong early lateral reflections are generally accepted as essential for adequate spaciousness. The influence of other factors such as the level and the spectrum of the sound is not so well understood. This paper reports the results of initial subjective evaluations of simulated sound fields with varied early lateral reflections. Using paired comparison tests, judgments of the apparent source width were found to be well correlated with two types of objective measures (LF and IACC). As reported in earlier studies, louder sounds were judged to be more spacious and lower frequencies also led to greater apparent source width. [Work partially supported by the Natural Sciences and Engineering Research Council of Canada.]
Spaciousness judgments of binaurally reproduced sound fields
Authors: Soulodre G. A. , Bradley John S. , Stammen Dale
Published: October 2005

Spaciousness is known to be a key subjective parameter in determining the acoustical quality of a concert hall. Spaciousness is described as the sense of being enveloped by the sound, or as an increase in the apparent width of the soundstage. Inter-aural cross correlations (IACC) and lateral energy fractions (LF) are two objective measures used to describe the relative spaciousness of concert halls. However, the two measures often do not correlate well with each other. In this study binaurally simulated sound fields were presented to listeners in paired comparison tests. Listeners were asked to identify the more spacious of the two sound fields. Binaural simulations of various North American concert halls were produced by convolving source material with impulse responses measured using a dummy head. The measured LF and IACC values are compared with the judged spaciousness. [Binaural impulse response data were obtained from a measurement tour partially supported by the Concert Hall Research Group.]
The split-step Padé solution
Authors: Collins Michael D.
Published: October 2005

The parabolic equation (PE) method has been the most efficient range-dependent propagation model in ocean acoustics ever since the split-step Fourier solution was developed [F. D. Tappert, ‘‘Numerical solutions of a canonical nonlinear dispersive wave equation,’’ SIAM Rev. 16, 140 (1974)]. Since the asymptotic accuracy of the split-step Fourier solution is restricted to leading order (a serious limitation for some problems), the PE method was extended to higher-order asymptotic accuracy using Padé approximations. Until recently, the higher-order PE has been solved using relatively inefficient finite-difference solutions, and the split-step Fourier solution has remained in widespread use despite the accuracy improvements. To improve efficiency without sacrificing accuracy, we apply Padé approximations to achieve higher-order accuracy in both the numerics and the asymptotics. The split-step Padé solution, which has been implemented for both fluid and elastic media, achieves both higher-order asymptotic accuracy and the efficiency of the split-step Fourier solution. This finite-difference solution is one to three orders of magnitude faster than other finite-difference solutions.
Source localization based on coherent scattering from a rough seafloor in an uncertain underwater environment
Authors: Haralabus George , Alexandrou Dimitri , Nolte Loren W.
Published: October 2005

In the present localization scenario, direct propagation from the source to the receiver is not permitted. The received field is comprised only by acoustic waves scattered from an infinitely hard seafloor and it is calculated using the Kirchhoff approximation. The performance of the optimum uncertain field processor is successfully tested in two mismatch situations, where either the location of the receiver array or the dimensions of bottom features are imperfectly known. The degradation of the localization performance due to discrepancies between the actual and the assumed scattering surface is demonstrated. This surface difference is expressed as a nondeterministic microroughness layer characterized by its root-mean-square height and its correlation length. Sensitivity study results are presented as a function of these two parameters. [Work supported by the Office of Naval Research, Code 1125GG, through contract No. ONR-N00014-93-I-0049 and Code 11250A, through contract No. ONR-N00014-91-J-1448.]
The variable domain transform and detection and the simultaneous measurement of velocity and position of a target
Authors: Roosnek N.
Published: October 2005

It is known that for the detection of targets the cw pulse gives the best velocity resolution. The FM pulse gives a superior result for the position of the target. The latter, depending upon the form of the FM pulse, is biased by the velocity of the target. In the case of a large bandwidth pulse length product, the output of the pulse compression, the ambiguity function, depends upon the velocity and the form. The ambiguity function of the linear periodic FM pulse is invariant for the velocity. The other forms are sensitive for the velocity of the target. In this paper it will be shown that this property can be used nicely for the detection and measurement of the velocity and position of the target by means of the variable domain transform, which was presented in an earlier publication [N. Roosnek, J. Acoust. Soc. Am. 92, 3207–3212 (1992)]. The results of the application of this technique to classical FM and other FM pulse forms will be presented.
Determination of texture coefficients in hexagonal polycrystalline aggregates with orthorhombic symmetry using ultrasonic waves propagating on one to three principal planes
Authors: Kielczynski P. J. , Moreau A. , Bussière J. F.
Published: October 2005

A method to characterize the texture of hexagonal polycrystalline aggregates with orthorhombic macroscopic symmetry is presented. Previous methods are extended to the analysis of waves propagating on three principal planes of the material. Five coefficients of the crystallographic orientation distribution function, W200, W220, W400, W420, and W440, are determined from angular variations of the phase velocity of the four ultrasonic modes considered: the bulk longitudinal waves, Rayleigh surface waves, the fundamental symmetric plate mode (in the long-wavelength limit), and shear-horizontal mode. Analytical expressions for the texture coefficients are found for an arbitrary number of principal planes. Measurements are reported for a Zr–2.5wt%Nb pressure tube, an alloy used in CANDU nuclear reactors. The angular variations of the phase velocity of leaky Rayleigh waves and leaky surface skimming compressional waves are measured with a line-focus acoustic microscope. The results agreed with neutron scattering measurements.
Causal time domain parabolic wave equations for power law absorption
Authors: Szabo Thomas L.
Published: October 2005

The classic parabolic time domain wave equation describes acoustic propagation in a medium in which absorption is a quadratic function of frequency. For the general case of power law absorption, α(ω)=α0‖ω‖y, where α0 and y are arbitrary real positive constants and ω is angular frequency, generalized time domain parabolic wave equations are presented. The differential loss operator in the original classic parabolic equation is replaced by a single propagation convolution operator that accounts for both absorption and dispersion. These operators, based on new time causal relations, have different forms for y as an even or odd integer or noninteger. The new equations are compared to those in the literature corresponding to the cases y=0.5 (acoustic duct), y=1.0 (medical and underwater applications), and y=0 or 2 (classic forms).
Acoustic pressure peak created at the impact of a missile on a gas–liquid interface: ‘‘The problem of the splash of the diver’’
Authors: Fromont Bernard , Lagier Michel , Sornette Didier
Published: October 2005

A physical mechanism for the amplitude of the pressure peak created by the impact of a missile at a gas–liquid interface is proposed. The different factors affecting this acoustic pressure peak are discussed. They include the inclination of the missile trajectory, the existence of wavelets roughening the surface of the gas–liquid interface, and the finite compliance of the missile. The difference between the impact and a true shock is stressed: the missile impact indeed creates a true acoustic shock that however plays no role in the generation of the high-pressure peak.
Oscillations of a deformed drop in an acoustic field
Authors: Shi T. , Apfel Robert E.
Published: October 2005

Because of the importance of acoustic levitation technology and no existing theory of oscillations of deformed drops in acoustic fields, a boundary integral technique, developed by Baker etal. [J. Fluid Med. 123, 477–501 (1982)], has been modified to study oscillations of axisymmetric liquid drops in air. The method consists of determining evolution equations for the position and velocity potential on the surface of the drop. The motion of the surface is determined from the potential by solving an integral equation. The potential is updated every time step by using the Bernoulli equation that depends on gravity, interfacial tension force, and acoustic radiation pressure. The acoustic field is determined for every time step by the Fourier transformation method developed by us. Given initial position and potential along the drop surface, the drop will oscillate around its equilibrium positions where it is statically deformed, which can be computed by introducing numerical damping. Some results on oscillations and frequencies of acoustically deformed drops will be presented. [Work supported by NASA through JPL Contract No. 958722.]
Underwater PVDF acoustic intensity probe
Authors: Van Tol David , Hughes W. Jack
Published: October 2005

The desired characteristics and properties of an underwater intensity probe are best achieved by constructing the sensor out of the polymer polyvinylidene fluoride (PVDF), which has the properties of high sensitivity, small thickness, and an impedance close to that of water. An array is being designed to measure the acoustic intensity in two dimensions and at several collinear points. Since the characteristic impedance of PVDF is close to that of water, the PVDF sensors are almost acoustically transparent. This helps to minimize the scattering and interference caused by the probe. The probe array is designed for use over a frequency range of 500 Hz to 5 kHz. Design data will be presented, and calibration measurements of magnitude and phase will show how well the probe performed. Some of the advantages, disadvantages, and construction problems with PVDF sensors will also be addressed.
Phase space engineering for mid- and high-frequency submerged structural acoustics: A wave is a wave is a wave, but what is a wavelet?
Authors: Felsen L. B.
Published: October 2005

Determining and interpreting the near and far zone mid-frequency acoustic scattering characteristics of submerged elastic structures in both the frequency and time domains requires wave-orientedspatiallydependentpre- andpost-signalprocessing. The most general framework for data analysis and synthesis is the eight-dimensional (space-time)—(wave-number-frequency) phase space that grants access by transforms and projections to various lower-dimensional subdomains that highlight distinct phenomenologies. In phase space engineering, ‘‘wavelets’’ are important basis elements for phenomenological and numerical parametrization, but there are two kinds: those usually proposed in favor of the wave aspect are smooth (analytic) compactpropagators like beams or wavepackets, whereas those usually proposed in favor of the numericalprocessing aspect have boundedsupport and are generally nonsmooth. Thus, neither wavelet basis meets the demands of the other. Because scattering signatures from submerged structures have strong features driven by wave phenomenology, the processing must utilize space-wave-number portions of the phase space in addition to the conventional time frequency. Examples are shown to illustrate various wave-based parametrizations. The challenge is to construct a self-consistent hybrid scheme for phase space engineering that exploits the best of both types of wavelets. Then one can say: awaveletisawaveletisawavelet. [Work supported by ONR.]
Application of wavelet analysis to machinery diagnosis
Authors: Wilson Gary R. , Ladd Mark D. , Priebe Russell D. , Baugh Kevin W.
Published: October 2005

Conventional time-frequency spectral analysis, typically conducted with discrete Fourier transforms (DFTs), represents a signal as the sum of complex harmonic exponentials, and results in an analysis that has the same time and frequency resolution at all frequencies represented in the DFT. However, some processes are better represented as the sum of functions at different time scales rather than at different frequencies. Wavelet analysis provides such a representation, and under certain conditions can be interpreted as an analysis whose time and frequency resolutions change with frequency, as opposed to the constant time and frequency resolution of the DFT. Two different types of processes associated with rotating machinery, bearing vibrations, and periodic mechanical transients, are shown from physical considerations to have time scale properties that are appropriate for wavelet analysis. Measurements of bearing vibrations and mechanical transients were made and both Fourier and wavelet analyses were applied to each of the measurements to demonstrate their associated time-scale properties and the potential benefits of wavelet analysis for machinery diagnostics. [Work supported by ONR.]
Predictability of the acoustic field in a shallow water waveguide
Authors: Frisk George V. , Rajan Subramaniam D.
Published: October 2005

The ability to predict the sound field magnitude and phase in a shallow water waveguide is critically dependent upon accurate knowledge of the acoustic properties of the environment. In this paper, attention is focused on the influence of the geoacoustic properties of the seabed on the predictability of the field. Emphasis is placed on the use of geoacoustic parameter estimates obtained from modal inversion techniques. Some of the research questions to be addressed include: (1) What is the measure of predictability? (2) What are the errors associated with various inversion methods and how do they affect predictability? (3) What is the effect of noise in the data? (4) How useful are geoacoustic parameter estimates obtained over a band of frequencies in predicting the sound field outside that band? Examples using both real and synthetic data will be discussed. [Work supported by ONR.]
Issues in numerical modeling of shallow water seismoacoustics
Authors: Schmidt Henrik
Published: October 2005

Over the last couple of decades significant progress has been made in modeling seismoacoustic propagation in shallow water. Thus, for example, environmental features such as a stratified, elastic bottom is a standard feature in several propagation models, even range-dependent ones with the development of the elastic PE. The past emphasis on deterministic propagation modeling has been driven by the primary interest in passive sonar systems for shallow water. However, with the increased importance of active sonar scenarios in shallow water, as well as the significance of acoustics for underwater communication, a wide range of new issues face the acoustic modelers. Thus, at the higher frequencies involved, the traditional wave theory models are not particularly efficient, and classical approaches such as ray tracing should be re-visited and modified to properly account for bottom interaction in particular. In addition, the spatial and temporal coherence becomes an important issue, in particular in relation to the oceanographic and geophysical variability, raising a need for stochastic seismoacoustic models. Another important issue is reverberation from the rough and inhomogeneous, elastic bottom. The various issues are illustrated using simulated and real data, and the associated needs for new mathematical and numerical models are discussed.
How well do physical oceanographic (P.O.) models and routine P.O. measurements help predict acoustic propagation in shallow water?
Authors: Lynch James F. , Duda Timothy F.
Published: October 2005

In trying to answer the question posed in this title, the following outline is followed. First, the dominant oceanographic processes that effect shallow water (coastal) acoustic propagation in the 50-Hz to 2-kHz band is identified. Next, how well these ocean processes are understood and modeled, and how the models are constrained by standard input data is investigated. The limits of predictability of the ocean field (spatially and temporally) are then examined. The issue of the sensitivity of the acoustic field to the particular ocean processes is investigated, followed by the predictability of the acoustic field propagating through the ocean processes. The various measures of the acoustic field (proploss, coherence, etc.) one uses to quantify the ocean/acoustic interaction are considered, reflecting the needs of various acoustics applications. Which acoustics models are appropriate for describing propagation through particular oceanographic fields is also addressed. Finally, the impact of this forward modeling study on possible inverse problem studies for the oceanography is discussed.
Some recent developments in phase match of microphones
Authors: Wong George S. K.
Published: October 2005

Phase match data for condenser microphones obtained with a new coupler are discussed. The protective grids of the microphones have some influence on the phase match at frequencies above 1 kHz. The phase match theory is based on the exchange microphone method [J. Acoust. Soc. Am. 90, 1253–1255 (1991)], which is also capable of discerning the phase match between the amplifiers of the two measuring channels. The performance of the coupler is verified with direct electrical measurement of the phase difference between the two channels and by comparison with the corresponding measurements provided by the coupler. A comparison is made between the data obtained with the coupler and those acquired with the electrostatic actuator method. Since the electrostatic actuator method does not expose the microphone back cavity pressure equalizing vent to the same excitation, the phase match readings provided by the electrostatic actuator method are confirmed to be not valid, particularly at low frequencies.
Source level discrimination by the lateral line system of the mottled sculpin, Cottus bairdi
Authors: Coombs Sheryl , Fay Richard R.
Published: October 2005

A conditioned feeding response of the mottled sculpin was used to measure level discrimination by the lateral line system as a function of source level, frequency, and distance. Level discrimination limens (LDLs) were determined with a 6-mm-diam, sinusoidally vibrating sphere placed in front of the trunk lateral line system at varying distances from the trunk of the fish. LDLs were relatively independent of frequency over most of the detection bandwidth, with mean values ranging from 5–6 dB from 10 to 50 Hz at a fish-to-source distance of 15 mm. The mean LDL at 100 Hz, near the upper end of the frequency range of the lateral line system was 8–9 dB at the same source distance. Mean LDLs at 10 and 20 dB above detection threshold were not significantly different, nor were mean LDLs at distances ranging from 7.5 to 30 mm for a 50-Hz, 10-dB SL source. The level-encoding features of posterior lateral line fibers innervating the trunk were also determined from data previously collected under stimulus conditions nearly identical to those used for behavioral studies. Afferent fibers responded to level increments with increases in both spike rate and phase-locking over most of the conditions used in behavioral experiments. Although it was impossible to eliminate spike rate as a level-encoding mechanism at any stimulus condition, phase-locking appeared to be a strong candidate at low source levels and vibration frequencies. These results show that level discrimination abilities by the sculpin lateral line system are within the range of capabilities of vertebrate auditory systems and that phase-locking in peripheral fibers may be important for encoding stimulus level by the lateral line.
Passive acoustic localization of the Atlantic bottlenose dolphin using whistles and echolocation clicks
Authors: Freitag Lee E. , Tyack Peter L.
Published: October 2005

A method for localization and tracking of calling marine mammals was tested under realistic field conditions that include noise, multipath, and arbitrarily located sensors. Experiments were performed in two locations using four and six hydrophones with captive Atlantic bottlenose dolphins (Tursiops truncatus). Acoustic signals from the animals were collected in the field using a digital acoustic data acquisition system. The data were then processed off-line to determine relative hydrophone positions and the animal locations. Accurate hydrophone position estimates are achieved by pinging sequentially from each hydrophone to all the others. A two-step least-squares algorithm is then used to determine sensor locations from the calibration data. Animal locations are determined by estimating the time differences of arrival of the dolphin signals at the different sensors. The peak of a matched filter output or the first cycle of the observed waveform is used to determine arrival time of an echolocation click. Cross correlation between hydrophones is used to determine inter-sensor time delays of whistles. Calculation of source location using the time difference of arrival measurements is done using a least-squares solution to minimize error. These preliminary experimental results based on a small set of data show that realistic trajectories for moving animals may be generated from consecutive location estimates.
Intermodulation distortion (F2−F1) in inner hair cell and basilar membrane responses
Authors: Nuttall A. L. , Dolan D. F.
Published: October 2005

Round window (RW) recordings in guinea pigs show a large response at the frequency of the quadratic difference tone (QDT) at F2−F1 for high-frequency (≳8 kHz) tone pairs. The magnitude of the RW response is dependent on frequency and level of the primaries. The QDT cochlear microphonic produced is largest for primaries with a frequency separation of approximately 900 Hz. Its source is probably the local activity of hair cells in basal cochlear locations where the high-frequency tones interact. QDT measurements from locations inside the organ of Corti show that the magnitude of the QDT is largest in the inner hair cell (IHC) region and monotonically increases as the difference in the frequency of the primaries decreases. Measured as IHC intracellular ac receptor potential, the QDT appears to be the result of a mechanical stimulus to the cell rather than as an inherent property of the nonlinear transduction in the IHC. However, QDT of the same form is not evident in the velocity responses of the basilar membrane. These results suggest that the outer hair cells (OHC) produce a strong quadratic distortion product mechanical force to stimulate inner hair cells. This mechanical drive may not be present, or is a weak component, in basilar membrane motion.
A comparison of N1 of the whole nerve action potential and wave i of the brain-stem auditory evoked response in Mongolian gerbil
Authors: Burkard Robert , Voigt Herbert F. , Smith Robert L.
Published: October 2005

The present study seeks to provide empirical support for the assumption that wave i of the gerbil brain-stem auditory evoked response (BAER) corresponds to N1 of the whole nerve action potential (WNAP) by comparing the latency and amplitude of BAER wave i and WNAP N1. Fourteen 3-month old gerbils were anesthetized with Nembutal and Urethane-Dial. Normothermia was maintained by a homeothermic blanket system. BAERs were recorded with Grass needle electrodes placed subdermally. The WNAP was recorded with a silver wire placed in the round window niche. WNAP and BAER were simultaneously recorded with a passband of 100–10 000 Hz. Responses consisted of 500 sweeps, and two responses were obtained for each condition. Clicks were 25-μs electrical pulses. Tonebursts were shaped with a Hanning window, with 1-ms rise and fall times. Toneburst frequencies included 1, 2, 4, 8, and 16 kHz. For each stimulus, responses were obtained at levels of 30, 50, 70, and 90 dB pSPL. SPL was measured near the entrance to the ear canal with an Etymotic ER-7C probe microphone. Dependent variables were the latency and amplitude of N1 of the WNAP and wave i of the BAER. The latencies of wave i and N1 were very similar. Mean (across animal) latencies of N1 and wave i were within 70 μs for all six stimuli (clicks, tonebursts) and all four levels. Latency/intensity function slopes for N1 and wave i were also very similar, with both dependent variables showing an increasing latency/intensity function slope with decreasing toneburst frequency. The N1/wave i amplitude ratio was computed. Interestingly, this amplitude ratio appears to increase with increasing stimulus level. In addition, stimulus spectrum influenced the N1/wave i amplitude ratio, but this pattern was dependent on whether peak amplitudes were measured from peak-to-following-trough, or from baseline to peak. This suggests that cochlear regions may be differentially weighted for the far-field and near-field recordings. The similarity of N1 and wave i peak latencies supports the assumption that wave i of the BAER is a far-field reflection of N1 of the WNAP.
Binaural maximum length sequence auditory-evoked brain-stem responses in human adults
Authors: Lasky Robert E. , Shi Ying , Hecox Kurt E.
Published: October 2005

This study compared monaural and binaural maximum length sequence auditory-evoked brain-stem responses (MLS ABRs) in normal hearing adults. The first experiment demonstrated that reliable binaural MLS ABRs could be recorded which were essentially the same as those recorded monaurally. The second experiment generalized this finding by assessing a range of intensities including threshold stimuli. ABR thresholds, wave V latency × intensity and amplitude × intensity functions, wave V latency and amplitude reproducibility, and waveform reproducibility were comparable for the monaural and binaural MLS ABRs with some minor qualifications. In the third experiment, comparability of monaural and binaural MLS ABRs was generalized to a range of rates from those used conventionally to rates far faster than possible with signal averaging. Again, there was little difference between the binaural and monaural MLS ABRs over the range of rates assessed.
A maximum-likelihood method for estimating thresholds in a yes–no task
Authors: Green David M.
Published: October 2005

A maximum-likelihood procedure for estimating threshold values in a yes–no task is presented. In computer simulations of this procedure, it is demonstrated that the variability of the threshold estimates is little affected by the density of the hypotheses tested for a fixed range, or by serious misestimates of the slope of the psychometric functions. The threshold value is also largely independent of the starting value of the signal. The standard deviation of the threshold estimates appears to decrease with the square root of the number of trials, with a 2- to 3-dB standard deviation possible if only 12 trials are used in the threshold estimates. Data are presented using human listeners tested on 5 days. Two threshold estimates, based on 12 trials, were made at each of the six audiometric frequencies on each day. The mean data appear sensible, and the standard deviation of the measured thresholds is about 3 dB. Using this procedure, it takes less than 3 min to measure the audiogram for a single ear.
Wave solutions in three-dimensional ocean environments
Authors: Harrison C. H.
Published: October 2005

A three-dimensional wave solution is developed for variable depth but isovelocity environments by transforming the wave equation into a suitable coordinate system. These solutions can be compared with existing known solutions derived from a ray point of view where the vertical modes propagate like horizontal rays. A general approach for arbitrary profiles is used to give explicit analytical solutions for various particular topographies including troughs and ridges. The behavior of these solutions is well known since they all have analogs in ordinary two-dimensional refracting media. Because this approach does not invoke the adiabatic approximation or ray invariants but evidently has similar limitations it throws some light on the limits of validity of these alternative approaches. In passing, some interesting problems in normalization are encountered, and investigations into slope and curvature restrictions reveal some general relations between average slope, curvature or higher derivatives for realistic surfaces. Numerical modelers, who currently only have the ocean wedge as a 3-D benchmark solution, now have an extended repertoire of benchmarks.