bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of measured and predicted sound levels in the space shuttle payload bay
Authors: Wilby John F. , G. Piersol Allan , Wilby Emma G.
Published: January 2006

An analytical model to predict space-average sound levels in the payload bay of the Space Shuttle at lift-off has been developed using power balance methods. The development of the model has been reported earlier [L. D. Pope and J. F. Wilby, J. Acoust. Soc. Am. 62, 906–911 (1977)]; it is now possible to compare the predictions of the model with data from the first three launches. Space-average sound levels in the bay were estimated from measured data and the resulting spectra compared with predictions; discrepancies were observed in the frequency range above 125 Hz. Modifications made to the analytical representation for the payload bay door resulted in much better agreement between measured and predicted sound levels. Payloads present in the bay were modeled analytically, but the predicted effects on space-average sound pressure levels were small because of the small size of the payloads. [Work performed under NASA Contract NAS5-26570.]
Comparative cochlear morphology in echolocating cetaceans
Authors: Ketten D. R. , Starr F. L. , Wartzok D.
Published: January 2006

The anatomy of the cochlea of six species of odontocetes, or toothed whales (Physeter catadon, Grampus griseus, Lagenorhynchus albirostris, Phocoena phocoena, Tursiops truncatus, and Stenella longirostris) was compared using conventional micrography and radiographic techniques including edge enhancement x-ray, CT scan, magnification radiography, and digital subtraction. These species were selected for differences in frequency and patterning of normal and ultrasonic vocalizations in their natural environments. The cochlea were extracted post-mortem and preserved by injection. Whole cochlea were first examined radiographically for species-specific differences in gross morphology and topology, particularly for angular change of the scalae and torsion of membranal and neural components. Specimens were then decalcified and processed for SEM or thin section microscopy. Measurements obtained by both methods are presented and the advantages of the radiographic techniques discussed. The results are compared with the cetacean cochlear models of Wever [Wever et al., Proc. Natl. Acad. Sci. 68, 2381–2385 (1971)] and Fleischer [G. Fleischer, J, Paleon. 50 (1), 133–152 (1976)] and analyzed according to the dimension-frequency correlation techniques of Greenwood [D. D. Greenwood, J. Acoust. Soc. Am. 33, 1344–1356 (1961)] and Hinchcliffe and Pye [R. Hinchcliffe and A. Pye, Int. Audiol. 7, 259–288 (1968)]. [Work supported by NSF.]
Application of SEA in developing a high-frequency vibration test method
Authors: Manning Jerome E.
Published: January 2006

The vibration environment in many aerospace environments extends to very high frequencies (∼100 kHz). However, because of the limitation in test equipment, it is difficult and often impossible to impose a vibration specification on an equipment supplier that extends beyond 4000 Hz. This presentation illustrates the use of SEA to develop the requirements for a new test technique.
Effect of duration on pitch discrimination of complex signals
Authors: Richards Virginia M. , Hafter Ervin R.
Published: January 2006

Discrimination of modulation frequency was measured using trains of n clicks (n = 4 to 52) presented at a rate of 250/s. Each click was the product of a 3500-Hz sinusoid and a Gaussian envelope. Three spectral envelopes were tested, having standard deviations of 350, 560, and 933 Hz. The rate of improvement in performance over duration is reflected in a plot of log-threshold vs log-n. These functions are well defined by two straight lines: for small values of n, the slopes are near −1.0, and for larger n's, the slopes approach −0.5. This suggests a model in which two factors influence the discrimination process. For small n's, the spectral width of individual components in the amplitude spectrum are reduced in proportion to the length of the click train; thus the slope of −1.0. With further increases in n, statistical averaging reduces the effect of neural noise by a factor of the square-root of n; hence the slope of −0.5. The model fit well to all of the data, except those obtained with the widest spectral envelope. This may be due to greater sensitivity to temporal information available in the low-frequency regions of these wideband clicks. [Supported by NIH.]
Temporal microstructural rules for periodicity of random-amplitude sequences
Authors: Pollack Irwin
Published: January 2006

We examine microstructural rules for the emergence of periodicity formed by temporal subpatterns within repeated random-amplitude sequences. The specific subpatterns were weighted either by successive replication, e.g., AAABAAAB … or by differential amplitude weighting, e.g., AAbAAb …, where b is a reduced version of B. For short-duration subpatterns, the dominant periodicity is that of the entire repeated sequence. For long-duration subpatterns, the dominant periodicity is that of the individual subpatterns, depending upon the relative amplitude weighting and the number of replications. [Work supported by NSF.]
Detection of temporal changes in the pitch of complex stimuli
Authors: Yost William A. , Moore Morris
Published: January 2006

The repetition pitch of ripple noise was temporally varied to determine the relationship between the rate of pitch variation and the perception of pitch change. Listeners were asked to discriminate between flat spectral noise and ripple noise whose ripple density was temporally varied in a sinusoidal manner. The spectrum of the temporally varying ripple noise stimulus was 1 + m cos{2f[g(T)]}; where f is frequency, m is the modulation depth of the spectral ripple, and g(T) = T + T sin 2ft, where T is the delay used to generate ripple noise, T is the range of pitch change, f is the rate (Hz) of pitch change, and t is time. The repetition pitch of ripple noise is directly related to the delay, T. At each rate of pitch variation the depth of modulation (m) was varied in the adaptive, forced-choice task until the listener was at 71% correct in his or her ability to discriminate ripple noise from flat noise. For a variety of conditions the results indicate that listeners are unable to detect the change in the pitch of ripple noise at rates of pitch change that exceed 2–5 Hz. This in turns implies that the auditory system is slow (200–500 ms estimated integration time) in its ability to process the complex stimulus of ripple noise. [Work was supported by the National Science Foundation.]
Temporal tuning curves and their relation to frequency tuning curves
Authors: Schroder Anna C. , Cudahy Edward
Published: January 2006

Temporal tuning curves for a 1000-Hz, 10-ms, 10-dB SL sinusoidal signal with a 500-, 1000-, or 1500-Hz, 10-ms sinusoidal masker were measured using a 2IFC adaptive procedure. Frequency tuning curves for the 10 dB SL, 1000-Hz signal were also measured for 10- and 500-ms simultaneous maskers. Five normal hearing listeners were employed. The frequency tuning curves for the brief masker were broader than those for the long masker, especially on the high-frequency side of the signal. Marked differences were not found between the temporal tuning curves for the three masker conditions. The implications of these results for relations between auditory frequency and temporal analysis will be discussed.
Generalization of learning in auditory pattern discrimination
Authors: Leek M. R.
Published: January 2006

Frequency discrimination for tones embedded in a varying sequence of ten brief tones can be extremely poor. Yet after repeated exposure to a constant tonal sequence, listeners demonstrate discrimination of changes in a target component almost as fine as for the target tone presented alone [e.g., C. S. Watson et al., J. Acoust. Soc. Am. 60, 1176–1186 (1976)]. It is clear, however, which aspects of the constant pattern are learned, thereby allowing the listener to overcome the effects of the surrounding tonal context on discrimination of the target. This experiment investigated generalization to new patterns of the learned target and learned context to assess their contributions to pattern discrimination. Four listeners were trained in a same-different task to discriminate small frequency changes in a 920-Hz target tone, which was the second element in a ten-tone pattern. Frequency difference limens were subsequently determined for the learned target tone embedded in a different tonal context, and for different targets when the context was held constant. Listeners were unable to maintain small difference limens for the target tone when the surrounding elements of the pattern were changed. Varying the target in the learned context, however, proved much less disruptive. Variations in the frequencies and the frequency contour of the learned context served to illustrate the relative importance of these characteristics. Results indicated that direct experience with a target tone contributes little to discrimination performance as long as the frequency contour of the pattern remains stable within certain limits.
Development of auditory thresholds in young chickens
Authors: Gray Lincoln , Rubel Edwin W.
Published: January 2006

Absolute auditory thresholds were estimated in chickens within 12 h of birth and at 4 days after hatching. A two-interval, forced-choice staircase procedure was modified to use momentary suppressions in chick's peeping as indications of correct and incorrect responses. The estimated thresholds of both ages were the same at low frequencies (250–500 Hz). At higher frequencies (1–2 kHz), however, 4-day-old chicks had thresholds about 20 dB lower than the 0-day-old chicks. Thus absolute thresholds are a function of both frequency and age. These thresholds are likely to reflect perceptual development for two reasons: (a) Similar thresholds from both ages at low frequencies show that developmental differences are not due to differences in the sensitivity of the testing procedure; and (b) thresholds obtained from the 4-day-old birds are similar to other estimates from mature birds. In conclusion, responsiveness to low frequencies develops before responsiveness to higher frequencies. [Work supported by NIH.]
Phase effects and profile analysis
Authors: Green David M. , Mason Christine R.
Published: January 2006

Randomizing the phase of the components of a tonal complex on each presentation has little effect on detection of an intensity increment of the central component. The complex consisted of eleven equal amplitude tones ranging from 200 to 5000 Hz. The spacing between adjacent components was equal on a logarithmic frequency scale. The signal was a sinusoid added in-phase to the central, 1000-Hz component. The overall sound pressure level of the sound was varied on each presentation according to a rectangular distribution with a range of 40 dB and a median sound pressure level per component of 45 dB. Over 50 complexes with different waveforms were generated by randomly selecting different starting phases for each component. Eight of these waveforms were selected, and each was presented as the complex for more than 500 trials in a 2AFC experiment. Thresholds for a signal added to each of these different complexes had a total range of only 2.4 dB. In a final test, we selected a different waveform on each presentation. Signal threshold was elevated by only 3 dB. [Work supported by NIH.]
Apparent echolocation by a sixty-day-old bottlenosed dolphin, Tursiops truncatus
Authors: Carder Donald A. , Ridgway Sam H.
Published: January 2006

Little is known about the ontogeny of echolocation in dolphins. A bottlenosed dolphin calf born at our facility in San Diego Bay was observed continuously for two hours each day and randomly at other times. Squeals were heard about ten seconds after birth and whistlelike calls soon thereafter but we did not notice head scanning movements concurrent with high-frequency pulses until the dolphin's sixtieth day of life. On this day we noticed that the calf would examine items such as a human foot inserted in the water by approaching, head scanning, and pulsing. A hydrophone placed in the water elicited the same behavior. Seven pulse trains were recorded at distances of 1–3 m. Peak frequencies ranged from 33 to 120 kHz with 3-dB bandwidths of 28–81 kHz.
Comparative observations on odontocete sonar signals from captive animals
Authors: Kamminga Cees
Published: January 2006

In this paper a comparative analysis of typical sonar signals of several species of littoral and riverine dolphins in captivity is presented. The sonar wave shapes compared include those recently obtained from two species, whose acoustic behavior has not been described previously in literature, i.e., the off-shore Lagenorhynchus albirostris and the fresh water population of Irrawadi; Orcaella brevirostris. The latter fit very well in the picture established thus far from a large collection of echolocation data. A study of these sonar signals reveals the noteworthy fact that—apart from the Commerson's signal—they all share a rather simple, basic wave shape. This can best be understood and classified in terms of the well-known uncertainty relation in communication theory and enables us therefore to link bioacoustics with mathematical physics. The signals approach the theoretical lower bound for the product of the time duration and frequency bandwidth and could therefore be designated as “small time-duration bandwidth” signals. They are thus well suited as a class of elementary optimal time-frequency signals. The frequency range of interest in the first described class of cetacean sonar is situated at a dominant frequency below 100 kHz, while in the Phocaena and Commerson group this dominant value goes up to around 120 kHz. The latter thus enabling those small animals to resolve spatial differences in their habitat up to an order of magnitude of nearly a centimeter.
Broadband signal selection and generation for channel sounding
Authors: Birdsall T. G.
Published: January 2006

Two classes of signals and applications are considered. The T class, for deep water work where ray paths are an appropriate model, requires a processed output waveform that is a short pulse with zero amplitude beyond a small neighborhood of the peak. The F class, for shallow water work where mode theory is an appropriate model, or for multioctave work where propagation varies significantly across frequency, requires a definite power spectrum. Although related, the two types of requirement are different in practice. Appropriate signal processing that balances signal-to-noise ratio and resolution will be discussed; it is called “factor-inverse matched-filtering.” A specific measure of spectral flatness, together with in-band fractional power, are combined to yield a signal efficiency measure. Emphasis is placed on continuous periodic signals. The T-class signals to be discussed are binary, digital, phase-modulated by m sequences; variations are augmented m sequences and frequency modulation. The F-class signals to be discussed are linear FM and a particular digital discrete FM signal called PDFM.
The importance of correlators
Authors: Carter G. Clifford
Published: January 2006

A tutorial review of generalized cross correlators and their importance to passive sonar signal processing will be presented. A discussion of the effects bandwidth, and integration time as well as multipath and multitarget interferences will be included. The presentation will emphasize broadband aspect of correlation processing including degradations experienced by narrow-band components. Fundamental limits on performance will be discussed.
Broadband signal processing in communication systems
Authors: Adams Stanley L. , Brill Michael H.
Published: January 2006

The broadband characteristics of the underwater acoustic propagation channel determine both the approach to communicating and the performance which can be achieved. This paper presents a detailed broadband characterization of the channel and uses this characterization to describe approaches to communication. Performance bounds are calculated and compared to channel capacity results.
Wideband, frequency-domain beamforming for coherent signal processing
Authors: Weber Mark E. , Heisler Rodney
Published: January 2006

Coherent detection processors for sonar (e.g., matched filters for active systems) require continuous time series as input and have conventionally been associated with delay-and-sum time-domain beamformers. As an alternative, we have extended frequency-domain beamforming techniques to retain the coherence of wideband signals and have demonstrated efficient software for computing continuous time-series beams for flexible postprocessing. Using computer-generated “acoustic-array” data, the beamformer was shown to preserve the envelope, spectrum, and correlation properties of signals while yielding near theoretical performance in reducing beam side-lobe levels. Advantages over a conventional delay-and-sum beamformer are: (1) elimination of the need for high input sampling rates to achieve acceptable beam patterns—the frequency-domain approach is insensitive to the sampling rate provided it exceeds the (band-pass) Nyquist rate; (2) reduction of high-beam side-lobe levels caused by malfunctioning array elements—the response of missing array elements is readily estimated in the frequency domain by interpolating from the spectra of neighboring sensors; (3) minimization of hardware requirements—all stages of signal processing (bandpass filtering, holefixing, beamforming, time-line reconstruction, and matched filtering) can be efficiently performed in a general purpose array processor.
Frequency spreads of broadband signals reflecting from a random surface
Authors: Brill Michael H. , Zabal Xavier , Adams Stanley L.
Published: January 2006

Extending previous time-spread work by the present authors [J. Acoust. Soc. Am. Suppl. I 73, S11 (1983)], the frequency spreading of an acoustic signal reflecting from an ocean bottom (in the presence of source and receiver motion) is computed using a simple geometric-acoustic model. In that model, a ray reflects specularly from each bottom facet, and arrives at the receiver if and only if the position and slope of the facet provide the requisite specular path. The model provides a connection between the expected power flux into the receiver aperture from a particular facet and the slope distribution of the bottom (assumed constant in depth). For a cw signal, the frequency spread can be computed by histogramming in Q = (f − f0)/f0 the expected relative energy from a grid of bottom facets. (Here, f0 is the frequency emitted at the source, and f is the frequency of the received signal.) The quantity Q depends only on the position of the facet, range, depth, and source and receiver velocities: it does not depend on f0, so long as the ray paths are independent of frequency, as in the present model. In fact, the expression for Q is the time derivative of delay time for a broadband signal, as well as having a narrow-band interpretation. Computed frequency-spread curves are presented for several source/receiver geometries. Because relative energy vs Q is a function of the channel and not of the sent signal, it may help to connect the broadband scattering function with the expected distribution of power in time and frequency from an input power impulse.
A study of the statistical properties of broadband signals
Authors: Machell Fred W. , Penrod Clark S.
Published: January 2006

A common assumption in the processing of broadband acoustic signals is that the underlying processes are Gaussian. Although Gaussian processes arise naturally in the ocean acoustic environment, another motivation for the Gaussian assumption is the desire for analytically tractable results and simple algorithms. In this paper, a broadband propagation model is used to analyze the statistical properties of random signals propagated in a deep ocean environment. In particular, measurements of the first-order probability density functions associated with the source and received signals will be presented for several source-receiver configurations. These measurements provide insight into the appropriateness of a Gaussian assumption in broadband processing. They also illustrate the effects of acoustic propagation mechanisms on the statistical structure of a signal. Measurements of correlation functions are presented to show the effects of multipath propagation. [Work supported by the Office of Naval Research.]
Spectral high-pass filtering effects of broadband spatial normalization
Authors: Perl Robert
Published: January 2006

Broadband energy detection is dependent upon a reliable estimate of the noise background. The energy at the output of a beam of an acoustic array is usually compared to the mean energy of its neighboring beams, and a detection is declared if a large discrepancy exists. This process of spatial normalization is equivalent to a high-pass filter which attenuates those spectral components which are substantially smaller than the design frequency of the array. This effect arises because of the substantial beam overlap at lower frequencies which precludes a totally independent estimate of the background. The spatial normalization high-pass filtering effect has been calculated for a variety of normalization schemes for linear and circular arrays. In general, the attenuation of the filter is 6 dB/oct at frequencies much smaller than the design frequency of the array. Specific frequency response curves are presented, and the ramifications to broadband energy detection are discussed. These include modifications to the design of the Eckart filter, and the reduced noise bias effects from anisotropic remote shipping.
Techniques for isolating resonances in experimentally obtained broadband acoustic echoes
Authors: Numrich S. K. , Dale N. H. , Dragonette L. R.
Published: January 2006

Theoretical descriptions of the scattering behavior of solid and hollow elastic bodies submerged in water have been given in terms of the form function of the body. These computations, usually carried out for a wide range of ka or frequencies, constitute a broadband analysis of the target's response. When performed in spherical or cylindrical geometries, the results of the computation can be separated into the rigid and purely elastic (or resonance) terms. Techniques have been developed for performing similar separations in experimentally obtained echoes for elastic targets. Of particular interest are the responses from bounded finite bodies for which no analytical model exists. Illustrations will include backscattered returns from solid and hollow targets not amenable to analytical solution. In the case of the hollow targets, plate waves generated by the incident sound will be identified using these broadband methods of target interrogation and analysis.
Pattern recognition by means of a hybrid adaptive autoregressive processing system
Authors: Schnitta-Israel Bonnie
Published: January 2006

An automatic pattern recognition algorithm, consisting of event detection, feature extraction, and a decision process, was developed. The complete processing system was labeled SIGNET. The feature extraction aspect of SIGNET formulated the autoregressive (AR) coefficients from a hybrid adaptive AR algorithm in combination with a weighted linear threshold element into a linear prediction residual (LPR). The structure of the data sequence was then identified by extracting those LPR segments, which established event type boundary phenomena. SIGNET was evaluated on two sets of data. The first set was comprised of nine independent underwater transient sources. The percent of correct recognition of SIGNET in that evaluation ranged from 93 to 98. The second data set was from a strong impulsive seismic source. The percent of correct recognition was 97. The mathematical foundation of SIGNET was also used successfully as a basis for a multiple source identification technique. [Work supported by ONR/Environmental Sciences.]
Linear gain and phase in seismic neurons
Authors: Lewis Edwin R.
Published: January 2006

In nearly quiescent seismic environments, many bullfrog (Rana catesbeiana) saccular afferent axons exhibit ongoing activity, typically ranging from 10 to 80 spikes/s. Low-level vibration of the whole animal [see H. Koyama et al., Brain Res. 250, 168–172 (1982) for methods] produces linear modulation of this activity, allowing one to define small-signal linear transfer ratios and to observe tuning curves for such axons. Each tuning curve to date reflects multiple resonances, sometimes coalescing with no intervening antiresonances, sometimes separated by simple antiresonances. The latter typically are much sharper than the resonances on either side, indicating that they are not simply concomitants of additive parallel resonances. Phase lag typically increases by two cycles or more with increasing frequency through the tuning range (roughly 10 to 200 Hz), with abrupt half-cycle declines through the antiresonances. Resonant and antiresonant frequencies vary from axon to axon, usually lying between 20 and 120 Hz. The amplitudes of peak transfer ratios vary approximately from 50 to 200 spikes/s per cm/s2. At 100 Hz, where it occasionally is found, the latter corresponds to approximately one spike/s response for whole-animal displacement of 10 pm. [Supported by NSF Grant BNS-8005834.]
Neuropsychology of music: A critical review of past work and future perspectives
Authors: Marin Oscar S. M.
Published: January 2006

Localized brain lesions may result in disorders of music perception, recognition, reading, or may alter vocal or instrumental performance. Amusias appear in this way to be disorders in the field of music equivalent to those encountered in aphasias, agnosias, or apraxias in the areas of language and speech, visual perception, and general motor skills. Thus, amusias pose the same problems with respect to hemispheric specialization, and localization of function. The relationship between nervous structure and function, brain localization or specialized brain processors to a particular behavior depends largely on the cognitive structure and characteristics of the system on which such behavior is based. Thus it depends, for instance, on how constant, stable, or universal the cognitive system is; it depends on the sensory modalities on which it is based, on its requirements for sensory perceptual analysis, on its higher cognitive codes or categories, on its use of information storage systems, syntactic algorithms, and linkages to other systems. In light of these factors, a review of the clinical literature of the various types of amusias will be presented. Parallelisms or contrasts with equivalent disorders of speech and language, and visual perceptual disorders will be discussed.
Relative and absolute pitch perception by birds
Authors: Hulse Stewart H.
Published: January 2006

European starlings (Sturnus vulgaris) were trained to discriminate a class of rule-based, four tone ascending pitch patterns from a comparable class of descending pitch patterns. Then a series of transfer tests examined the birds' ability to maintain the discrimination under various transformations of the original pitch stimuli. The birds performed well when shifts in tone height occurred to novel exemplars within the original pitch training range, but not when shifts occurred to novel exemplars outside that range. When information about the direction of pitch change was reduced by shortening the patterns, the birds could solve the discrimination on the basis of the first two tones in a pattern, although performance improved as pattern length and, therefore, amount of information increased. The same series of transfers showed that in producing accurate discrimination the birds were using pitch cues based on both an absolute and relative perception of pitch. The data have implications for a comparative study of information processing in pitch perception.
Perception of rhythmic structures
Authors: Hirsh I. J.
Published: January 2006

The concern of auditory research with pitch and spectrum has led to an emphasis on individual phonemes in speech and on notes in music. Even the sequential properties of transitions in speech or of melody in music have emphasized changes in spectrum. While rhythmic structures often are aspects of such patterns, they may be studied in a “pure” form. The rhythmic grouping reported since the late 19th century was an interesting observation, but did not lead much further. Also, early studies on listeners' hearing of rhythmic patterns may have been much affected by an imitative, tapping response, accompanied by characteristics of a motor system. Seashore, in his test of musical aptitudes, studied rhythmic perception through a same-different procedure but did not exploit the technique toward notions of stimulus complexity, or good or easy structures. Whether such pattern properties will accord with Martin's syllabic structures, or Garner's groups of runs and gaps, remains to be worked out by studies on recognition and discrimination. Data from a study along these lines will be discussed. [Work supported by NINCDS.]
The role of auralization in pitch or tonality recognition
Authors: Ward W. Dixon
Published: January 2006

Previous research [E. Terhardt and W. D. Ward, J. Acoust. Soc. Am. 72, 26–33 (1982)] has shown that most trained pianists can tell when a particular selection from Bach's “;Well-Tempered Clavichord” has been shifted upward or downward in key from the original signature, performing at a level significantly better than chance even when this transposition is only one semit. This result implies that these persons posses some form of absolute pitch, or absolute tonality, even though they claim little or no ability to name isolated pitches. The degree to which this recognition process depends on auralization (anticipation of how the excerpt should sound) arising either from the oral announcement of the correct key that precedes each excerpt or from the (untransposed) visible score on the answer sheet was examined by removing these cues. Performance declined slightly but remained above chance, indicating that auralization, while helpful, is not essential. So unless there isa “best” key for any given piano composition, and Bach unerringly chose it, these pianists' recognition of transposition was based at least partly on long-term memory of the excerpts as heard in the original key. [Research supported by the Bryng Bryngelson Communication Disorders Research Fund.]
The physics of acoustics transients
Authors: Junger Miguel C.
Published: January 2006

Many if not most sound fields, whether natural or man-generated, desirable or objectionable, are too transitory to be approximated with steady-state solutions. Furthermore, transient pulses are used increasingly to explore the frequency dependent characteristics of waveguides, geological formations, and echo-ranging targets. This shifts the burden from effectively steady-state measurements at various frequencies to signal processing of transient signals, an evolution facilitated by today's computer capability. In spite of their importance, transients are effectively ignored in standard text books with the exception of application-oriented fields such as room acoustics and loudspeaker theory. This review paper deals with basic phenomena associated with impulsively accelerated and decelerated boundaries. Transient radiation loading and farfields are described for planar and convex pulse generators. Energy partition between incompressible nearfield and acoustic farfield is illustrated. Finally, requirements are formulated for the equivalence of transient and cw scattering measurements.
Transient acoustic sources
Authors: Bouyoucos John V. , Nelson David E. , Selsam Roger L.
Published: January 2006

The characteristics of several different classes of transient, underwater acoustic sources are set forth and compared. Two relatively new sources—the water gun and imploding piston source—are compared with more well-established explosive devices and air guns. Characteristics examined include spectral features, efficiency of energy conversion, peak source levels, size, weight, and depth dependence. In addition, the performance advantages and limitations of the various source types in multi-source arrays is discussed.
The Rayleigh distance and geometric nearfield size of nonplane sound radiators
Authors: Kuntz Herbert L. , Hixson Elmer L. , Ryan William W.
Published: January 2006

The geometric nearfield of a finite acoustic radiator is the area around the radiator where the sound pressure level does not follow spherical or cylindrical spreading. The geometric nearfield has been studied extensively for circular and rectangular piston radiators. The Rayleigh distance D = ka2/2, where k = 2πf/c, f is the frequency, c is the sound speed, and a is half the largest dimension, has been used to approximate the size of the geometric nearfield of plane radiators. We found that, for variously shaped radiators, the Rayleigh distance is useful in approximating the geometric nearfield size. As with plane radiators, we found large SPL changes with radial distance in the geometric nearfield. One implication is that in noisy environments, where the SPL aroung a large machine may, necessarily, be measured in the nearfield, the sound power contribution to the sound field can be grossly underestimated. Knowledge of the nearfield size may be useful in industrial situations for determining the validity of sound power estimates. [Work supported by the U.S. Coast Guard.]
Cliff Temple Baptist Church: Acoustics for worship and recording
Authors: Campbell Russell C. , Lysiak Richard J.
Published: January 2006

Cliff Temple Baptist Church, located in Dallas, Texas, prides itself on its excellent music facilities which are not only used for worship, but also for recording RCA's Dallas Symphony series of digital Red Seal albums. Reviewers such as David Hall [Stereo Rev. 46, 76 (1981)] have highly praised the acoustics of Cliff Temple, as well deserved according to this study. Four types of objective data consisting of noise measurements, echograms, reverberation plots, and characteristic spectra, are used to determine sound field characteristics present in the hall. Using wide dynamic range analysis techniques [R. Campbell and R. Lysiak, Bull. Am. Phys. Soc. 28, 200 (1983)] greatly enhanced the measurement of acoustical parameters, giving insight into the subjectively perceived superb acoustical qualities. The objective data is then applied to subjective categories which are used for comparison of Cliff Temple Baptist Church with other facilities. [R. Campbell, M. S. thesis, Texas Christian University (1983).]
The decay of sound in rooms with amplification systems
Authors: Patronis Eugene T. , Uzzle Ted
Published: January 2006

The regenerative behavior of sound reinforcement systems affects the sound level and interacts with the reverberative decay of souns in enclosures in which they operate, in ways not previously described. For a system of loop gain A(s)B(s), the sound levels will be −20 log[1 − A(s)B(s)](dB) above those predicted by classical feedforward methods. After the source of sound to be amplified is shut off, the regenerative loop will continue producing sound, and will take P/ − 57.6 log[A(s)B(s)](s) to decay 60 dB, where P is the regenerative path length (m). Methods for calculating and measuring the decaying loop, by itself and in combination with the room's reverberation time, are given.
Envelope-based lateralization of low-frequency waveforms
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: January 2006

Several recent investigations suggest that listeners either cannot or do not use interaural temporal disparities (ITDs) in the envelope of low-frequency waveforms in lateralization tasks [G. B. Henning, J. Acoust. Soc. Am. 68, 446–453 (1980); G. B. Henning and J. Ashton, Hearing Res. 4, 185–194 (1981); G. B. Henning, Hearing Res. 9, 153–172 (1983)]. Listeners in those studies may have been unable to process these ITDs principally because of the types of stimuli presented. We employed an acoustic pointing task in which listeners varied the interaural intensitive difference of a 500-Hz narrow-band noise (the pointer) so that it matched the intracranial position of a second, experimenter-controlled stimulus (the target). Target stimuli were sinusoidally amplitude-modulated tones centered on 500 Hz or 1 kHz, and modulated at 25, 50, or 100 Hz. Targets were presented with either the entire waveform delayed or with only the envelope delayed. Our results suggest that delays of the envelope do affect the lateral position of our low-frequency targets. However, the envelope-based cues appear to interact with those provided by the fine-structure which appear to be dominant.
Quantitative analysis of pulsed pseudo-Rayleigh waves
Authors: van der Hijden J. H. M. T.
Published: January 2006

Acoustic pseudowaves (leaky waves) along a plane interface are studied in the space-time domain. Analysis of the Green's function as derived by the Cagniard-de Hoop method allows a quantitative description of the propagation of a pseudo-Rayleigh pulse along a fluid/solid interface. After applying the Cagniard-de Hoop method the answer has the form of a convolution of the input signal of the source with the explicitly obtained space-time Green's function (“system's response”), which clearly shows each feature of the time behavior of the acoustic quantities at different locations and their dependence on the material parameters involved. From an analytic study of the space-time Green's function for the reflected pressure a quantitative description of the pseudo-Rayleigh phenomenon has been derived. This includes a condition which limits the range of existence and an equation for the travel speed. A pseudo-Rayleigh factor which determines the relative strength of the phenomenon is defined and the decay of pulsed wave motion along the interface is studied. Using this factor it becomes clear why the pseudo-Rayleigh wave is very strong at a water/steel interface, while it does not exist on, e.g., a water/ice interface. Numerical results will be shown.
Numerical simulation of acoustic propagation at a fluid-solid interface
Authors: Randall Curt
Published: January 2006

Propagation of acoustic pulses in the neighborhood of the interface between fluid and solid half-spaces is investigated numerically using the finite difference technique. The solid half-space may be homogeneous, or it may comprise several distinct solids of differing acoustical properties. The solid-solid interface may have arbitrary orientation with respect to the fluid-solid interface. Plots of the displacement fields clearly illustrate the wavefronts, headwaves, and surface modes near the fluid-solid interface. In the case of the inhomogeneous solid, reflection, transmission, and mode conversions at the solid-solid interface, and subsequent interactions with the fluid-solid interface give rise to a multiplicity of decay pulses. The origin and physical significance of each of these decay pulses is made evident by the displacement field pilots.
Acoustic waves along a fluid-filled borehole with a concentric solid layer
Authors: Chang S. K. , Everhart A. H.
Published: January 2006

Transient acoustic waves in a fluid-filled cylindrical borehole with a concentric elastic solid layer are complicated by acoustic modes that result from the presence of the solid layer. A real axis integration technique [Tsang and Radar, Geophys. 44, 1706–1720 (1979)] is used to compute waveforms excited by an isotropic point source placed on the axis of the hole. It is evident that dispersive acoustic modes are an important feature of the elastic wave propagation for this configuration. There are at least four classes of modes caused by the solid layer: the Stoneley mode, which is sometimes referred to as a tube wave; the compressional modes, caused by compressional wave reflections in the solid layer; the shear modes, caused by shear wave reflections; and the hybrid modes, due to mode conversions at the interfaces. A study of the dispersion, attenuation, and residue of the modes provides an explanation for most of the features in the waveforms.
Perceived critical distances between F1−F0, F2−F1, F3−F2
Authors: Syrdal Ann K. , Gopal H. S.
Published: January 2006

A critical spectral distance of 3 to 3.5 critical bands (bark) between first and second formant frequencies in simplified two-formant synthetic Russian vowels has been reported by Chistovich and her colleagues. Syrdal [J. Acoust. Soc. Am. Suppl. 1 71, S105 (1982)] transformed fundamental frequency and formant frequency values from naturally produced American English vowels into Bark values from which three distance measures were calculated: F1−F0, F2−F1, and F3−F2. Her proposed auditory-model of vowel perception reduced between-speaker variability and provided a perceptually based quantitatively defined link between some acoustic and phonetic features. In the present series of experiments, several synthetic two-vowel continua were constructed, each with a varying frequency parameter which crossed a critical distance in either of the 3-bark difference dimensions. Critical distances over the 3-bark difference dimensions, estimated by phoneme boundaries calculated from vowel identification tests, will be compared with each other and with previous estimates. Some effects of duration on the phoneme boundary estimates of critical distance will also be discussed. [Work supported by NIH].
Atypical VOT categories in Hebrew and Spanish
Authors: Raphael Lawrence J. , Tobin Yishai , Most Tovah
Published: January 2006

Available data indicate that most languages employ three categories of Voice Onset Time (VOT) to distinguish homorganic stop consonants. The three categories, voicing lead/short lag/long lag, are temporally discrete and, in the opinion of some researchers, may coincide with psychoacoustically predetermined regions of auditory sensitivity. Moreover, speakers of languages which display a two-way opposition (i.e., /ptk/ vs /bdg/) seem to employ adjacent VOT categories (e.g., short lag and long lag) and not the extreme categories (i.e., voicing lead and long lag) to differentiate stops having the same place of articulation. Data gathered from native (but bilingual) speakers of Hebrew and Puerto Rican Spanish reveal that they commonly use either the extreme categories of VOT or voicing lead and a category intermediate to short and long lag. These data, together with those previously reported for Canadian French, Danish, and Korean, raise questions about the specific relationship between auditory sensitivity and the determination of VOT categories in natural languages. [Research supported by NINCDS.]
Implications of ear canal geometry for various acoustical measurements
Authors: Stinson Michael R.
Published: January 2006

Recent work has demonstrated that the geometry (size, shape) of the human ear canal leads to a sound field, at high frequencies, that varies within the canal in a complicated fashion. In particular, the eardrum terminates the ear canal at a rather sharp angle, and significant variations of sound pressure (over 15 dB) arise over the eardrum surface above 10 kHz. The implications of these observations, as they apply to several aspects of hearing research, will be discussed, utilizing a three-dimensional horn equation approach that has been developed. Knowledge of the sound pressure distribution within the ear canal is important in the extension of audiometry to high frequencies, and for guiding the development of hearing aids. Studies of auditory processes that use a reference microphone in the ear canal become increasingly sensitive to microphone location as higher frequencies are used; estimates of the errors of reproducibility are given. Present acoustic network models of the middle ear assume a uniform sound pressure at the eardrum; possible ways of handling a non-uniform pressure distribution are discussed.
Portuguese nasalized vowels and nasal consonants: Their relation to following consonants
Authors: Maxwell Edith M.
Published: January 2006

Pilot spectrographic results indicate that Brazilian Portuguese demonstrates a relationship similar to that found in English between syllabic nucleus duration and the voicing characteristic of a following obstruent: vowels lengthen before voiced obstruents and shorten before voiceless obstruents. Also, a nasal consonant in Portuguese acts in conjunction with a preceding vowel as a syllabic nucleus; for example, if in a syllabic nucleus a vowel does not show the duration expected before a given obstruent, the nasal duration compensates, and vice versa. New data from six speakers of Brazilian Portuguese derived from computer analysis will be presented which confirm the preliminary results. The acoustic characteristics of nasalized vowels and nasal consonants in Portuguese will also be described, as well as the extent to which a prenasal vowel is nasalized. The difference between phonemically nasal vowels and vowels nasalized because they are adjacent to a nasal consonant (e.g., [1χ] lã, “wool” vs [pʌ̃nᴜ] pano, “cloth”) will also be discussed.
Comparative measurements on viscoelastic materials used for vibration damping
Authors: Pillot Christian , Wilson Geoffrey L.
Published: January 2006

In a previous paper at the 99th meeting of the Acoustical Society of America in Atlanta in 1980 a new viscoelastometer was described. This instrument enables the Young's modulus and loss factor to be easily obtained over a wide range of frequencies and temperatures. The prototype of this instrument is being used in a continuing project for the systematic evaluation of the properties of a wide variety of commercially available materials. The method will be. described and some examples given.
Measurement of the damping characteristics of metal matrix composites using a resonant dwell technique
Authors: Timmerman Nancy S.
Published: January 2006

The resonant dwell technique, first developed by Heine, was used to measure loss factors at the fundamental frequency of several cantilever beam samples. Nine different metal matrix composites and three unfilled base metals were tested to study stress and temperature dependence. Three temperatures and four stress levels were used in the study, and the fundamental frequency of all samples was between 100 and 200 Hz. The results indicate increasing loss factor with increasing stress level. Loss factors of the composite materials were lower at elevated temperature when compared with room temperature, while the loss factors of the unfilled base metals were higher. [Work supported by AMMRC.]
HYPER: A hybrid parabolic equation-ray model for high-frequency underwater sound propagation
Authors: Tappert Frederick
Published: January 2006

The parabolic equation (PE) propagation model contains all diffraction effects, PE applies to fully range-dependent environments, and PE has no upper limit of validity in frequency. However, simple operation count estimates show that PE execution times increase proportional to at least the square of frequency, and thus PE becomes impractical to run on minicomputers at high frequencies (above about 500 Hz). The equations of geometrical acoustics can be solved in fully range dependent environments with execution times independent of frequency, but amplitudes and phases are not reliable because these equations do not contain diffraction effects. The HYPER (Hybrid PE-Ray) model uses only the ray trace portion of geometrical acoustics to locate the important propagation paths. Then HYPER solves a modified parabolic equation in a small region (decreasing with increasing frequency) near the ray paths and computes amplitudes and phases. Theoretical calcuations show that HYPER provides uniformly valid diffractive solutions in fully range dependent environments with execution times nearly independent of frequency. Thus HYPER should be practical to run on minicomputers at very high frequencies.