bluuebunny/crossref_metadata_2025 huggingface dataset:
Speech intelligibility in noise-induced hearing loss: Effects of high-frequency compensation
Authors: Skinner Margaret W.
Published: October 2005

The speech-recognition ability of six listeners with permanent noise-induced hearing losses above 1 kHz was evaluated with the Pascoe High-Frequency Word List spoken by a female talker and presented in the field. In experiment I the words were presented at five intensity levels through five different amplification systems (one with a uniform response and four with increasing amounts of high-frequency emphasis). In experiment II the frequency response of the system associated with the highest scores in experiment I was modified in four ways: elimination of frequencies above 6.3 kHz, addition and deletion of 1/3-octave emphasis at the low-frequency boundary of the hearing loss, and addition of 6-dB high-frequency emphasis. The frequency response that was associated with the highest word-identification score for each listener had between 20 and 33 dB more gain in the frequency region of the hearing loss than did the uniform response. Three major factors were found to affect the word-identification scores: audibility of the speech energy, separation of the third-octave-band levels of the words from the discomfort threshold, and balance between the low- and high-frequency levels of the speech signal.
A physical method for measuring speech-transmission quality
Authors: Steeneken H. J. M. , Houtgast T.
Published: October 2005

A physical method for measuring the quality of speech-transmission channels has been developed. Essentially, the method represents an extension of the Articulation Index (AI) concept, which was developed mainly to account for distortions in the frequency domain (noise, bandpass-limiting). The underlying concept of the present approach, based on the Modulation Transfer Function (MTF) of a transmission channel, has been adapted to account for nonlinear distortions (peak clipping) as well as for distortions in the time domain (reverberation, echoes, AGC). The resulting index, the Speech-Transmission Index (STI), has been correlated with subjective intelligibility scores obtained on 167 different transmission channels with a wide variety of disturbances. The relative predictive power of the STI, expressed in PB-word score, appeared to be 5%. This accuracy is comparable with results obtained from subjective measurements when about four talkers and four listeners are used. Expressed in terms of signal-to-noise ratio, the accuracy is about 1 dB. Pilot studies have been carried out to evaluate the use of the STI for testing digital speech-transmission channels.
General effects of currents and sound-speed variations on short-range acoustic transmission in cyclonic eddies
Authors: Henrick R. F. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

The effects of sound-speed and current variations induced by a mesoscale cyclonic eddy on short-range propagation are considered. A parametric eddy model is used to determine acoustically relevant eddy environmental effects, so that eddy–acoustical effects can be determined for eddies of arbitrary size, strength, and position. Approximations to sound-speed and current structures are used to investigate eddy effects on the three-dimensionality of rays and on ray types. The influence of current and sound-speed variations on travel time is examined, and accurate expressions for per-ray phase variation are obtained. Examples are presented illustrating effects of source–receiver position and orientation on per-ray phase shifts and relative phase spreading of arrivals. Also, general results are presented which illustrate the variations of eddy–acoustical effects as functions of source–receiver range and of eddy size and strength.
Acoustical instruments and measurement: Microphones
Authors: Rasmussen Gunnar
Published: October 2005

The Acoustical Society of America has created the most important forum for advanced discussions and presentations on instrumentation and measurement techniques over the past 50 years. We have all had great benefit from this—not least within the area of transducer development. It is the intention of this paper to give a brief summary of important steps in transducer development and the state of the art in calibration accuracy, where absolute calibration today is reported with standard deviations less than ±0.01 dB. New mircophone development is reported and a history of analog detectors brought up to date.
Cylindrical transducer scatter scanner
Authors: Foster F. Stuart , Arditi Marcel , Hunt John W.
Published: October 2005

A new imaging technique based on scatter at right angles from tissue has been investigated. Separate transmitting and receiving transducers are employed. The transmitting transducer generates a cylindrical wavefront that converges to a line focus in the object. A receiving transducer, aligned coaxially with the line focus, detects the ultrasound waves scattered at 90° from structures in the object. Because of the high degree of cylindrical focusing, the scatter is treated as if it arises from points on or very near the line focus. This allows the use of a ranging approach similar to that employed in conventional pulse–echo imaging. A tomographic image is generated by translating or rotating the two transducers as a unit while appropriately displaying the scatter information. This approach eliminates the depth-of-field problem inherent in pulse–echo imaging without sacrificing the speed or simplicity of the imaging process. The distribution of ultrasound in the field of the cylindrical transducer is treated theoretically for cylinder angles ranging from 30° to 360°. Experimental verification of theory was performed using a 120° cylinder. Here the full width at half maximum of the amplitude of the main lobe was 0.5 λ by 2.3 λ (0.15 mm × 0.7 mm at 5 MHz). An experimental scatter scanner is described, and images of a simple phantom and an in vitro tissue sample are given.
Acoustic flux methods for oceanic guided waves
Authors: Weston D. E.
Published: October 2005

The formal energy-flux solution for range-averaged level in a varying duct depends on the definition of transmission loss, on the local impedances, and in a complicated way on the vertical angles and cross-track variations. But for most purposes a very simple low angle version is sufficiently accurate and well established to be virtually independent of the detailed profile. Surprisingly, the convergence factor with circular symmetry is also independent of the detailed profile; this is true for unbounded media as well. Depth transforms are presented for the angular distributions of intensity, initially without specific reference to sources. Angular distributions for discrete sources show some characteristic zeros and infinities. It is shown that only the Gaussian distribution is self-reproducing with changes in depth. The law of conjugate depths states that intensities will be equal at such depths, and it is expected that this law will be very robust. Work on these and allied energy-flux methods is reviewed.
Optimum range and bearing estimation with randomly perturbed arrays
Authors: Schultheiss Peter M. , Ianniello John P.
Published: October 2005

The absolute minimum attainable values of incremental mean-square error in bearing and range estimation caused by random perturbations of sensor locations are determined and compared with the performance of conventional processors. At low signal-to-noise ratios the optimum estimator realizes no improvement over the conventional systems; at high signal-to-noise ratios it realizes only slight improvement.
Measurements of the growth of air bubbles by rectified diffusion
Authors: Crum Lawrence A.
Published: October 2005

Measurements are reported of the growth of air bubbles in water by rectified diffusion at 22.1 kHz. Values of the threshold acoustic pressure amplitude were obtained as a function of bubble radius, liquid surface tension, and gas concentration. Measurements of the rate of growth of bubbles by rectified diffusion were also obtained as a function of acoustic pressure amplitude for a range of different values of the liquid–vapor surface tension. It was determined that although both the threshold and the growth rate were in agreement with theory for normal values of the surface tension of water, the addition of a surfactant caused the observed thresholds and growth rates to deviate from the predicted values. Surface wave activity that could increase the diffusion rate by acoustic streaming was not detected at low radii and is not thought to be the principal mechanism for the increased diffusion. Some possible explanations are given for the effect.
Temperature variation of the acoustical properties of laboratory sediments
Authors: Bell David W. , Shirley Donald J.
Published: October 2005

The compressional wave speed and attenuation and the shear wave speed and attenuation of unconsolidated artificial laboratory sediments have been measured as a function of temperature. No overburden or pore pressure in excess of that found at a few centimeters depth was applied. The compressional wave speed of the sediment was found to vary approximately as would water. Shear wave speed appears to be independent of temperature within the accuracy of the measurement. Attenuation of both types of acoustic waves was also found to be independent of temperature.
Investigation of chemical sound absorption in seawater by the resonator method: Part I
Authors: Mellen R. H. , Browning D. G. , Simmons V. P.
Published: October 2005

Resonator measurements in synthetic media show that sound absorption in seawater is caused by chemical relaxations involving B(OH)3 and MgCO3 in addition to MgSO4. The MgCO3 relaxation can be modeled as a two-step MgCO03 ion-pair association in which a monomolecular step controls the absorption process. The B(OH)3 relaxation involves a similar two-step association of the B(OH)−4 ion in which interactions with the pH buffer system play a crucial role. A number of other relaxations are observed, but their contributions are negligible under seawater conditions.
Acoustic flux formulas for range-dependent ocean ducts
Authors: Weston D. E.
Published: October 2005

A concise energy-flux formulation is used to investigate the range- averaged acoustic propagation in ocean ducts. Examples treated have isovelocity, linear, and parabolic sound speed profiles. The results are expressed as the product of a scale factor and, for the latter two examples, a depth factor. The scale factor has a similar form in each case, and remains simple and easy to use even when the profile is asymmetrical and the parameters vary with range. The appropriate solution for transmission from an isovelocity duct to a duct of arbitrary profile is also given. Surprisingly, the depth factor generally has a nominal infinity when receiver depth equals source depth in an unchanging but stratified duct, or when velocity at the receiver equals that at the source, or for scaled depths in a range-dependent duct. These infinites are discussed from the flux, ray, and mode viewpoints and a ray-tracing demonstration is provided. For the special case of axial source and receiver, the character of the infinite is different, and an important point is that it occurs only for velocity minima sharper than that of the parabolic profile. The latter profile has in several respects a critical nature.
Localization of noise bands by Old World monkeys
Authors: Brown C. H. , Beecher M. D. , Moody D. B. , Stebbins W. C.
Published: October 2005

The acuity of auditory localization in Old World monkeys (Macaca) was determined psychophysically for 44 noise bands graded in bandwidth and center frequency. The acuity of localization was assessed through the method of constant stimuli under free-field conditions in an anechoic chamber. Monkeys were trained through positive-reinforcement operant-conditioning procedures to report a change in azimuth of the signal by releasing a response disk. The results show that localization thresholds are dependent upon the bandwidth of the signal over much of the macaque’s range of audibility. Thresholds for the detection of a change in location varied from 18° (for a signal 250 Hz in bandwidth centered at 11 200 Hz) to 4° (for a signal 8000 Hz in bandwidth centered at 8000 Hz). The results suggest that the localization of spectrally complex signals is determined by a mechanism sensitive to periodicity (time-domain) information across the monkey’s range of audibility.
An improved WKB calculation for a two-dimensional cochlear model
Authors: Steele Charles R. , Miller Christine E.
Published: October 2005

The finite difference calculations of Neely [E.D. thesis, California Institute of Technology, Pasadena, CA (1977)] and the WKB solution of Steele and Taber [J. Acoust. Soc. Am. 65, 1001–1006 (1979)] generally agree, except in the ’’phase plateau’’ region, where both are irregular. In the present work, an improvement in the accuracy of the WKB procedure is gained by using a closed-form integral which gives the phase and damping functions in the short wavelength region. The present results agree qualitatively with the preceding but show a smooth variation with frequency and distance along the cochlea.
The theoretical gain limitations of a passive vertical line array in shallow water
Authors: Hamson Rachel M.
Published: October 2005

A theoretical study is presented on the response of a vertical array of hydrophones to shallow-water signal and noise fields. A normal-mode propagation model was used to provide the incident signal field. The field due to wind-generated noise was obtained from a recently developed model based on wave theory. Two methods of combining hydrophone outputs are investigated: broadside beamforming and a mode-matching approach. In the first case, limitations to signal gain are found due to the propagation properties of the shallow water environment. The highest gains are achieved with an array of length 15λ to 30λ. The second method involves applying amplitude and phase weightings in accordance with the shape of the largest signal mode. This enhances the signal gain for arrays longer than 8λ. The values of signal gain are primarily dependent on range and bottom type. The noise gain is found to be very dependent on sound speed profile; noise is rejected by a broadside array to a greater extent in summer conditions than in winter. Overall results for shallow-water array gains show degradation from deep-water gains of between 8 and 20 dB for a 20λ array for the cases studied.
Ray path analysis of sediment shear wave effects on bottom reflection loss
Authors: Vidmar Paul J.
Published: October 2005

The effect of sediment shear wave propagation on bottom reflection loss (RL) from a typical deep sea sediment layer is analyzed by means of a ray path decomposition of the acoustic field. The amplitude of each shear (S) and the compressional (P) ray is obtained from the interface reflection and transmission coefficients. These coefficients are analyzed by means of an expansion in the parameter ε which is proportional to the relatively small S-wave velocity of marine sediments. Ray paths with amplitudes up to order ε2 are identified and used to develop a qualitative ray path model of RL. P-wave conversion at the sediment–substrate interface is the dominant mechanism for sediment S-wave excitation. To order ε2, RL is the result of the interference of three waves in the water whose amplitudes are proportional to ε0, ε1, and ε2. Comparison with RL obtained from a computational model shows that the ray path model correctly predicts the dependence of RL on frequency, S-wave speed, S-wave attenuation, and P-wave attenuation.
Horizontal acoustic refraction through ocean mesoscale eddies and fronts
Authors: Weinberg N. L. , Clark J. G.
Published: October 2005

Computer simulations are used to investigate horizontal acoustic refraction through strong ocean fronts and solitary mesoscale eddies (e.g., Gulf Stream rings). Using purely horizontal refraction ignoring other effects, horizontal deflections in excess of 1° are computed. Observed deflections will be critically dependent on the experimental configuration. This study is designed to be most relevant to observations in a fixed system experiment.
Measuring phoneme boundaries four ways
Authors: Ganong William F. , Zatorre Robert J.
Published: October 2005

In order to determine whether the concept ’’phoneme boundary’’ has validity independent of the particular experimental paradigm used to measure it, four procedures were used to locate phoneme boundaries on two acoustic continua: a VOT continuum, and a formant transition continuum. The procedures were a standard identification test, a version of the method of adjustment, an adaptive psychophysical procedure (PEST), and a version of the method of limits. The procedures differed in reliability, and there were substantial individual differences in the locations of the phoneme boundaries, but the correlations between boundary locations for each subject found by the different methods were quite high. Thus the ’’locus of the phoneme boundary’’ represents an internal variable which can be measured in a number of different ways. We also examined a subsidiary question. A hardware synthesizer does not produce identical waveforms given the same stimulus parameters twice. Do these different tokens produce the same perceptual responses? In the identification tests, different tokens of the various stimuli elicited different average rating responses. Thus, there are reliable (but quite small) token effects for synthetic speech stimuli which can affect phonetic perception.
Modern analysis procedures for multiple input/output problems
Authors: Bendat J. S.
Published: October 2005

This paper reviews the basis for new efficient data analysis procedures to solve multiple input/output problems. Practical iterative computational techniques are explained for obtaining conditioned spectral density functions, partial and multiple coherence functions, and other desired quantitites. Examples are given on how to identify different multiple correlated noise sources and how to determine their separate frequency response functions to any desired response point.
Harmonic generation in organ pipes, recorders, and flutes
Authors: Fletcher N. H. , Douglas Lorna M.
Published: October 2005

A simplified treatment is given of the mechanism of sound production in musical instruments driven by air jets, which is sufficiently explicit that semiquantitative predictions can be made about the effects of certain variables upon the harmonic structure of the sound produced. In particular it is found that the amplitude of the even harmonics, generally, and of the second harmonic, particularly, is quite critically dependent upon the offset of the pipe lip from the symmetry plane of the jet. A completely symmetrical relationship (zero offset) reduces the generated amplitude of the second harmonic by a large factor. Experimental results with an adjustable organ pipe are found to confirm these predictions. The implications of these results for the voicing of organ pipes and recorders and for subtle tonal variation in flute playing are briefly discussed.
Signal models for low bit-rate coding of speech
Authors: Flanagan J. L. , Ishizaka K. , Shipley K. L.
Published: October 2005

A traditional model of the speech signal has provided the underpinning of vocoder technology since the inception of analysis/synthesis telephony. The model is a first-order approximation to human speech generation in which the source of vocal sound and the resonant acoustic system are treated as linear, separable elements. This source-system model cannot properly account for a number of acoustic factors now known to exist in speech generation. We propose and implement here a signal model based more directly upon the phsyics of of speech generation. We also implement parametric control of the synthesis model by an adaptive procedure that minimizes the spectral difference between a human speech input and the synthetic output of the model.The adapted parameters constitute a low bit-rate representation of the input human speech. We test a preliminary form of the system by computer simulation and demonstrate that in simple inital trials the signal model is able to adapt in a realistic manner.
Acoustic correlates of some phonetic categories
Authors: Stevens Kenneth N.
Published: October 2005

Some of the acoustic properties that distinguish one speech sound from another are reviewed. The point of view is that the auditory system responds to sounds with different acoustic properties in distinctive ways, and that these special responses play an important role in selection and classification of the inventory of sounds that are used in language. Examples of several of these acoustic properties are discussed and illustrated, including the presence or absence of rapid spectrum change, abruptness of amplitude change, voicing and aspiration, and gross spectral properties relating to place of articulation for consonant and vowels.
Representation of speech-like sounds in the discharge patterns of auditory-nerve fibers
Authors: Delgutte Bertrand
Published: October 2005

It is now possible to study how acoustic characteristics important for speech discrimination are represented in the discharge patterns of auditory-nerve fibers. The electrical activity of single auditory-nerve fibers in response to speech-like sounds (single and two formant synthetic stimuli and ’’fricative’’ noise bursts) was recorded with microelectrodes in anesthetized cats. Results demonstrate that a conceptualization of some basic properties of responses to simple acoustic stimuli is useful in interpreting qualitatively how certain characteristics of speech-like sounds can be coded. Specific examples are given for (1) the rapid changes in amplitude and spectrum that occur for each syllable, (2) the fundamental frequency of voiced sounds, and (3) the spectral envelope of fricative consonants. It is also shown that the presence of background noise can have qualitatively different effects on how various characteristics of speech-like sounds are represented.
Applicability of white-noise nonlinear system analysis to the peripheral auditory system
Authors: Johnson Don H.
Published: October 2005

A functional series is capable of describing the input–output relationship of a general class of systems, linear or nonlinear. Wiener and his associates demonstrated methods by which these functionals could be measured from the response of the system to white noise. This paper is a critique of the application of this functional series approach to the measurement of the input–output relationship of the peripheral auditory system. The Wiener functionals are shown to be dependent on the parameters of the white noise used to measure them. The approximation of the output of a system by a truncated Wiener series is shown to have unpredictable error properties when inputs other than white Gaussian noise are used. Estimates of the Wiener functionals using the white-noise approach do not converge when the system has a point process output (e.g., spike train output).
Speech discrimination in deaf subjects with cochlear implants
Authors: Eddington Donald K.
Published: October 2005

Electrical stimulation of the auditory nerve is being investigated as a way to provide information useful for speech communication in the profoundly deaf. Single-channel systems that tend to stimulate all fibers alike have had little success in achieving this goal. Multichannel systems that allow excitation of more complex temporal–spatial patterns of activity are now being introduced. Psychoacoustical experiments providing evidence that electrodes of a multichannel implant are able to separately excite distinct groups of neural elements are reviewed. New results using multiple electrodes and speech-like stimuli are presented. The synthetic stimuli were vowels (/a/, /i/, /u/) and consonant–vowel (CV) syllables (/ba/, /da/, /ga/, /ta/). Vowels and CV syllables were presented in an AXB discrimination task with different signal processing schemes and electrode configurations. A four-channel, frequency-selective system produced faultless discrimination scores for all stimuli and spontaneous recognition of the vowels while the scores for the single-channel system were generally much lower. Although understanding free running speech by the profoundly deaf does not seem imminent, the results presented indicate that the multichannel system tested shows more promise of approaching this goal than the single-channel scheme.
Acoustic-reflex thresholds for noise stimuli
Authors: Margolis Robert H. , Dubno Judy R. , Wilson Richard H.
Published: October 2005

The effect of noise bandwidth on the acoustic-reflex threshold was studied in 12 normal-hearing adult subjects by independently varying the cutoff frequencies of low-pass (fL=100 Hz) and high-pass (fH=6000 Hz) computer-generated noises. Adjusting the cutoff frequency of the low-pass or high-pass activating stimuli over the 700–6000 Hz range resulted in a change in the reflex threshold of 4 dB/octave. As the cutoff frequency of the low-pass noise was reduced below 700 Hz, more rapid increases in reflex thresholds occurred. For high-pass stimuli, very small changes in reflex thresholds were noted as the lower cutoff frequency was increased from 100 to 700 Hz. The data suggest that between 700 and 6000 Hz equal spectral regions of a noise stimulus contribute equally to the reflex threshold, and that energy below 700 Hz contributes little to the sensitivity of the reflex.
Tuning curves of cochlear and brainstem responses in the guinea pig
Authors: Mitchell Curt , Fowler Cynthia
Published: October 2005

A tone-on-tone masking paradigm was used to determine tuning curves of cochlear and brainstem responses in the guinea pig. The tuning curves are considered to be a measure of the frequency specificity of these potentials. Calculated Q10 values are used as an indicator of the sharpness of tuning of these potentials. The tuning curves of cochlear and brainstem responses were found to be similar with both showing considerable frequency specificity.
Vibrational relaxation rates in N2/CO2 mixtures as determined from low-frequency sound absorption measurements
Authors: Shields F. Douglas , Bass H. E.
Published: October 2005

Zuckerwar and Griffin [J. Acoust. Soc. Am. 68, 218–226 (1980)] have recently used a resonance tube to extend measurements of sound absorption in N2/CO2 mixtures to much lower frequency to pressure ratios (f/p) than previously obtained. Their results, when compared with previous measurements at higher CO2 concentrations, confirm that the nitrogen relaxes by a series process involving two v–v and one v–t exchange. A value of 7.5×10+4±10% s−1 atm−1 for the rate of the reaction CO2(00 °1)+N2?CO2(0310)+N2+416 cm−1 is obtained.
A comparison of the theory of sound transmission through a fluctuating ocean with temporal measurements by Jobst
Authors: DeFerrari H. A. , Leung R.
Published: October 2005

Statistics of acoustic fluctuations are predicted from Λ–φ values computed for an experimental geometry used by Jobst. Experimental results are then compared with the theory of sound transmission through a fluctuating ocean [Flatté et al., Sound Transmission Through a Fluctuating Ocean (Cambridge, New York, 1979)]. The stable transmission measured over a range of 450 km is consistent with theoretical prediction but there are still many uncertainties owing to lack of detailed environmental data at the time of the experiment.
Present status in flextensional transducer technology
Authors: Brigham G. , Glass B.
Published: October 2005

Use of flextensional transducers has been limited historically by an inability to design them accurately and by their apparent unsuitability for phased or conformal arrays. Reliable design requires development of cost-effective, relatively accurate, and preferably algebraic mathematical models. However, most early analytical research centered around large computer models; these were generally accurate, but too complex and expensive to provide important physical insight. Recent work on an equivalent circuit for Class IV flextensional transducers produced unrestrained equations of the required accuracy for peak radiated power, resonant halfpower bandwidth, resonant frequency, and the optimum power-bandwidth product design that represents the smallest, lightest, Class IV transducer for any acoustic requirements. This paper briefly summarizes the analytical background of the model; recent experimental work; application to several sonars, including both expendable and ship systems; and the ultimate capabilities of Class IV devices.
Some unusual sounds of apparent biological origin responsible for sustained background noise in the Timor Sea
Authors: Cato Douglas H.
Published: October 2005

Observations of ambient noise in the shallow, tropical Timor Sea north of Australia have shown a predominance of noise of apparent biological origin over much of the audio frequency band. Four of the most commonly occurring sounds which were responsible for the prevailing noise from 100 Hz–2 kHz and which do not appear to have been observed elsewhere, are described. These sounds are quite distinctive in character. Three of the sounds show several harmonics with fundamental frequencies in the range 70–220 Hz, and have durations of 2–4 s. In two of these sounds, the harmonics show a regular modulation of their amplitude, and in one of the sounds, the harmonics rise in frequency by about one octave over the duration of the sound. The fourth sound is nonharmonic and consists of a train of pulses containing four shorter pulses. The mean source levels of the sounds are estimated to lie between 127 and 150 dB re 1 μPa at 1 m.
Technique for frequency division/multiplication of speech signals
Authors: Flanagan J. L. , Christensen S. W.
Published: October 2005

As a follow-up to two previous studies, we examine the feasibility of dividing the bandwidth of a speech signal while keeping the time dimension intact. We utilize the real and imaginary parts of the short-time Fourier transform to describe contiguous bandpass segments of the signal spectrum. We implement a frequency division that maintains unchanged the Hilbert envelope of the waveform for each bandpass segment. We show that the resulting signal can be usefully confined to one-half the original bandwidth. Transmission can be effected either by an analog channel of one-half bandwidth, or by digitally encoding at one-half the conventional Nyquist rate. Reanalysis at the receiver and complementary multiplication of the spectrum parameters reconstruct the signal to the original bandwidth. Analysis, transmission, reanalysis, and reconstruction processes are not transparent. They provide an output of less than typical toll quality, but of reasonably good communications quality. A potential use for the method might be the simultaneous transmission of voice and data over a single voice circuit. We also show that the division and multiplication technique can be used to modify the time dimension of the speech signal (i.e., compress or expand the time scale) while keeping the frequency dimension intact.
Linear prediction on a warped frequency scale
Authors: Strube Hans Werner
Published: October 2005

Linear prediction is considered with respect to a nonlinear frequency scale obtained by a first-order all-pass transformation. The predictor can be computed from a frequency-warped autocorrelation function obtained from the power spectrum or by a direct linear transformation of the original acf. Three numerical procedures are compared. Alternatively, the predictor can be determined from a covariance matrix or (adaptively) from continuously formed correlations, suitably defined according to the all-pass transformation. Prediction-error minimization and spectral flattening are no longer equivalent criteria. In the synthesis part of a vocoder or APC system, no inverse transformation is required, since the direct form of the analysis and synthesis filters can be modified so as to immediately realize the warped transfer function. Single-word intelligibility is compared for a predictive vocoder on a ’’Bark’’ scale and a linear frequency scale. The Bark scale yields results around 90% even at predictor orders of 5 to 7. More possible applications have been given previously by other authors.
Signal-to-noise ratio gain of sparse array processors
Authors: Earwicker Martin J.
Published: October 2005

In this paper general expressions are derived for the signal-to-noise gain of sparse array processors which take account of both broadband signal and noise fields and the finite averaging times of real processors. This is achieved by considering the covariance between the fluctuations in pairs of estimates of cross-correlation functions between hydrophone outputs. In the case of sparse arrays comprising many hydrophones and for low input signal-to-noise ratios, it is shown that the signal-to-noise gain of such a processor is 4.3 dB less than that of a filled array ’’sum square’’ processor using the same number of hydrophones.
Theoretical design of optimum planar sound diffusers
Authors: de Jong B. A. , van den Berg P. M.
Published: October 2005

In room acoustics one often is confronted with sound fields that have an insufficient degree of diffusion. We present a theoretical design of artificial diffusers that can be used to improve this situation. For the two-dimensional case, the diffuser consists of a pattern of slots with different depths. The key problem is to determine the depth distribution for optimum diffusion. The properties of the boundary of the diffuser are represented by a position-dependent surface admittance. Then, the boundary-value problem can in principle be treated rigorously. We show that the inverse problem of calculating the depth profile of the diffuser from a prescribed reflectivity distribution can be solved as well. With the aid of the latter procedure we are able to design an optimum planar diffuser, when design frequency and angle of incidence of the incident sound wave are given. Some designed diffusers are present.
Comparison of variational and finite element solutions of Helmholtz’s equation
Authors: Laura P. A. A. , Gutiérrez R. H. , Sánchez Sarmiento G.
Published: October 2005

This paper deals with some numerical experiments on the determination of natural frequencies of vibration of doubly connected membranes of complicated boundary shape. Finite element results are compared with values obtained using an approximate method which consists of constructing appropriate coordinate functions which identically satisfy the boundary conditions and use of a variational approach to generate a simple frequency equation. The results are in good agreement with values previously published in the open literature which have been calculated using a conformal mapping-variational approach.
Pulse propagation in a randomly perturbed ocean: Single pulse statistics
Authors: Kohler Werner E.
Published: October 2005

A statistical theory of broadband single pulse propagation in a random ocean is presented. The mutual coherence function of the received signal is derived using an analysis based upon coupled mode theory. As propagation range increases, the combined effects of modal dispersion and random fluctuations spread the pulse and decompose it into a series of multiple arrivals.
Diffraction of sound by an impedance paraboloid
Authors: Cole John E. , Garrelick Joel M.
Published: October 2005

The diffracted field of a paraboloid of revolution with a locally reacting surface is derived and computed results for both rigid and mass-like impedance are presented. A shadow region in which the pressure decreases rapidly is found for those positions far in wavelengths from the vertex. Results at positions in the shadow zone are shown to approach those of an impedance cylinder of equivalent radius.
The collapse of bubbles in compressible hydraulic oils
Authors: Shima Akira , Fujiwara Tokuichi
Published: October 2005

In the present paper, an equation of the state of compressible hydraulic oils was derived by using the relation between pressure and bulk modulus obtained by Klaus–O’brien. As a result, it was shown that in the case where the bulk modulus was shown by a linear function of pressure, Tait’s equation as an empirical formula was obtained and the constants in the equation were derived theoretically. Further, using the derived equation, the equation of bubble motion was derived by means of an approximate solution using the Poincaré–Lighthill–Kuo coordinate perturbation method. The effects of liquid compressibility on the bubble behavior and impulse pressure were numerically clarified.
Elastic wave behavior across linear slip interfaces
Authors: Schoenberg Michael
Published: October 2005

A model for an imperfectly bonded interface between two elastic media is proposed. Displacement across this surface is not required to be continuous. The displacement discontinuity, or slip, is taken to be linearly related to the stress traction which is continuous across the interface. For isotropic interface behavior, there are two complex frequency dependent interface compliances, ηN and ηT, where the component of the slip normal to the interface is given by ηN times the normal stress and the component tangential to the interface is given by ηT times the shear stress and is in the same direction. Reflection and transmission coefficients for harmonic plane waves incident at arbitrary angles upon a plane linear slip interface are computed in terms of the interface compliances. These coefficients are frequency dependent even when the compliances are real and frequency independent. Examples of the effects of buried slip interfaces on reflection coefficient spectra and on Love-wave dispersion relations are presented.
Interpretative modeling of deep-ocean sediments and their physical properties—A foreword
Authors: Gorsline D. S. , Holcombe T. L.
Published: October 2005

An introduction to the papers of the participants in the US Naval Ocean Research and Development Activity (NORDA) workshops.
Theoretical aspects of sound transmission in sediments
Authors: Stoll Robert D.
Published: October 2005

The structure of a general theory for acoustic wave propagation in ocean sediments is reviewed with emphasis on the determination of meaningful parameters from data in the literature. It is shown that acoustic properties are nonlinear functions of cyclic strain amplitude and static stress level so that only a limited amount of the available data is useful for studies of acoustic propagation. An example of geoacoustic modeling is presented based on the theory and some new data for Stoneley wave velocities measured in situ are evaluated with the aid of the model.
Geoacoustic modeling of deep-sea carbonate sediments
Authors: Milholland Phillip , Manghnani Murli H. , Schlanger Seymour O. , Sutton George H.
Published: October 2005

A systematic study has been made of physical and acoustic properties of 269 DSDP core samples representing a complete ooze-chalk-limestone sequence on the Ontong–Java Plateau (sites 288 and 289) and a sequence of clay-rich carbonate sediments in the Coral Sea Basin (site 210). Gradational increases in density (ρ), compressional velocity (Vp), shear velocity (Vs), compressional and shear velocity anisotropies (Ap, As: horizontal velocities faster than vertical velocities), and shear velocity orientation anisotropy (Aso: horizontally propagated shear velocities are faster when the particle motion is horizontal rather than vertical) are directly related to increasing depth (subbottom) and diagenetic stage. Silica enrichment increases ρ, Vp, and Vs but does not significantly affect Ap and As. Clay enrichment, on the other hand, decreases ρ, Vp, and Vs and increases Ap and, to a greater degree, As. It is found that Ap≳As in carbonate sediments, whereas As≳Ap in clay-rich sediments. Viable models are discussed to explain observed velocity anisotropy. Laboratory measurements agree with two previously published velocity-depth functions determined by seismic wide-angle measurements. A derived geoacoustic model accounts for the observed property-depth-diagenesis relationship for the first 1000 m of the ooze-chalk-limestone sequence, and predicts values of ρ, Vp, Vs, porosity (φ), Poisson’s ratio (σ), shear modulus (μ), Ap, As, and As0.
Heuristic physical property model for marine sediments
Authors: Matthews J. E.
Published: October 2005

On the basis of compressional wave velocity, the deep-sea sediment layer can often be divided into two zones: an upper zone where velocity appears to increase monotonically with depth, although secondary effects resulting from stratigraphic variability are usually present; and a lower zone where large velocity variations occur rapidly and unpredictably with depth. In the upper zone, physical properties were parameterized in terms of the single variable porosity, which is assumed to decrease exponentially with depth. This model incorporates mutually independent data sets, e.g., corrected core porosities from consolidation measurements, thermal measurements from bore holes, and compressional wave velocities from seismic measurements. These data are few and highly variable, but demonstrate general trends consistent with the simple compaction model. Only in the presence of biogenic material does the lower zone exist. Lithification in this zone appears to be dominated by chemical processes, and the term, ’’zone of induration,’’ is suggested. This simplistic model is based upon considerable speculation and imprecise data, and is thus proposed only as a working hypothesis for future investigations.
Laboratory measurements of shear wave attenuation in saturated sand
Authors: Brunson Burlie A. , Johnson Richard K.
Published: October 2005

Laboratory measurements of shear wave attenuation as a function of frequency were made using recently developed ceramic bimorph bender transducers to excite transverse particle motion in a medium grain water-saturated sand. The measurements were made at 13 frequencies from 450 to 7000 Hz. Multicycle sine-wave pulses were used to insure steady-state vibration at the measurement frequency. Attenuation was determined from the slope of a linear least-squares fit to the maximum received level versus transducer separation data. This not only affords an estimate of the attenuation but allows confidence intervals to be placed around that estimate. The attenuation values’ which increased with frequency from 5 dB/m at 450 Hz to 120 dB/m at 7000 Hz’ did not exhibit a simple first-power frequency dependence. The results were compared with predictions based on a two-component model developed by Stoll and were consistent in both amplitude and frequency dependence.
Comparison of velocity–depth characteristics in western North Atlantic and Norwegian Sea sediments
Authors: Houtz R. E.
Published: October 2005

The western North Atlantic was divided into 17 sediment provinces, and sonobuoy sound velocities were compiled from each region. The regions were analyzed statistically to develop least-squares regressions of the form V=V0+Kt, where t is one-way vertical travel time. Eight regions provided velocity functions, four were inadequately sampled, and five provided mean values from single-layer solutions in sediment bodies less than 1 km thick. The eight values of K are grouped very closely about a mean of 1.14±0.17 km/s2. By contrast, 12 regions from the Norwegian Sea yield 10 values of K that range from 0.6 to 2.5 km/s2. The three highest values (≳2.1 km/s2) are clearly separable from the rest and were measured on data from the Voring plateau, Jan Mayen ridge, and eastern Greenland margin. These three regions are uniquely floored by thick Mesozoic epicontinental sediments that predate the breakup of the Norwegian Sea. These older sediment bodies account for most of the regional heterogeneity in the velocity functions of the Norwegian Sea. Approximately one fifth the surface area of the North Atlantic is floored by sediments thinner than 200 m. Within these vast areas, principally near the midocean ridges, the sound velocity of acoustic basement is a crucial factor in developing low-frequency propagation models. A contour map of basement refraction velocities in the North Atlantic shows a rough increase from 3.5 km/s near the mid-Atlantic ridge to 5.0 km/s at variable distance from the ridge. The region in which geoacoustic models are most sensitive to basement velocity is between 15 ° and 30 °N, where sediment cover thinner than 200 m account for about half the surface area. A significant portion of this area is topographically rough and does not yield reliable basement refraction data. Interval velocities from the thinner deposits of pelagic sediment seaward of the abyssal plains, are greater by about 200 m/s than those from the continental rise and abyssal plains at comparable depths of overburden. The difference suggests that sound velocities in the predominantly pelagic sediments increase more rapidly with depth than they do in the silty hemipelagic clays and turbidites nearer the continents.
Interval velocity and attenuation measurements in sediments from marine seismic reflection data
Authors: Wrolstad Keith
Published: October 2005

Deterministic source signature deconvolution has been applied to the processing of marine airgun wide angle and vertical profiler data. The resulting improvement in reflection event timing accuracy allowed the computation of more reliable interval velocities for upper sedimentary layers by the T2−X2 method, provided that the layer thickness limitation of the method was not exceeded. Computations of frequency dependent attenuation were also made from the data by a procedure using frequency domain univariate least-squares regression. Estimates of maximum attenuation were made for an abyssal plain and a turbidite sedimentary environment off the coast of Oregon. The interval velocity and attenuation in the upper layers of the turbidite environment correlate well with the average material type found in the core of nearby DSDP site 174 (sandy silt with greater than 60% sand). The maximum estimated attenuation at about 100 Hz in the abyssal plain environment (silts and clays) was found to be greater than that for the sea fan environment.
Quantum mechanical theory of nonlinear interaction of ultrasonic waves
Authors: Bajak Ivan L. , Breazeale M. A.
Published: October 2005

Nonlinear interaction of ultrasonic waves is discussed from the very general quantum mechanical viewpoint. By using the concept of three-phonon interactions one is able to derive formulae for power and intensity of ultrasonic waves generated through nonlinear mixing of two ultrasonic waves, as well as the formula for parametric amplification of an ultrasonic wave through its nonlinear interaction with another ultrasonic wave. The effect of attenuation on nonlinear ultrasonic wave interactions also is discussed, and it is shown that in some situations attenuation strongly affects the generation of the second harmonic of an initially sinusoidal ultrasonic wave. It is shown that in the correspondence limit, the quantum mechanical viewpoint gives results which are in very good agreement with results obtained from classical physics.