bluuebunny/crossref_metadata_2025 huggingface dataset:
Extracting the F0’s of two overlapping groups of harmonics
Authors: Carlyon Robert P.
Published: October 2005

Two concurrent harmonic sounds were mixed and passed through a bandpass filter, with cutoffs of either 20–1420 Hz (‘‘low condition;’’ components resolved by auditory system) or 3900–5400 Hz (‘‘high condition;’’ components unresolved). One complex (the ‘‘masker’’) had an F0 of 210 Hz in both intervals of each 2IFC trial. Sensitivity (d’) was measured to F0 differences (‘‘ΔF0’s’’) in the other (‘‘target’’) complex between the two intervals of each trial. In the low condition, listeners could hear two clear pitches in each interval, and performance on the discrimination task was reasonably good (d’ approximately 0.75 for ΔF0=4%) regardless of whether the masker was gated synchronously with the target or started 150 ms before and ended 150 ms after it. In contrast, the mixture in the high condition was perceived as a single, aperiodic sound, similar to a crackle, and discrimination in the presence of an asynchronous masker was close to chance, even for ΔF0=16%. This, together with other findings, suggests that listeners are poor at extracting the F0’s of two groups of overlapping unresolved harmonics. Performance in the high condition was better with a synchronous than with an asynchronous masker, and experiments will be presented which test alternative explanations for this difference.
Trade-off between depth and phase of modulation in the perception of pitch of complex amplitude-modulated tones
Authors: Divenyi Pierre L. , Greenberg Steven , Algazi Alain P.
Published: October 2005

Complex amplitude-modulated (CAM) tones were generated through amplitude modulating a high-frequency carrier fcarH (3–10 kHz) by an AM tone having a modulating frequency and a carrier fcarL about 10% of fcarH modulated at a rate f0 in the 100-Hz range. CAM sounds have been shown to have a low pitch corresponding to f0, whose discriminability decreases as the modulation of fcarL is shifted from AM to QFM phase [S. Greenberg and P. L. Divenyi, Proc. 18th Midwinter Mtg. ARO, p. 55 (1995)]. In the present experiments, pitch discrimination was measured for pairs of CAM tones having fixed f0 differences but either variable depth (1%–200%) or variable phase (1–1.5π) of modulation in the fcarL complex. Results of the experiments show a pattern of modulation depth-phase trade-off over a range is constant above, and much reduced below fcarH=4 kHz. These findings portray time-based pitch extraction as being a process in which phase spectrum plays a role consistent with the one proposed by W. H. Huggins [ 582–589 (1952)] in his theory. [Work supported by NIH and the VA Medical Research.]
A bridge between place and time. II. Its significance for theories of pitch
Authors: Greenberg Steven
Published: October 2005

The opposition between ‘‘place’’ and ‘‘time’’ perspectives in auditory function finds its fullest theoretical expression in the long-standing controversy over the neural basis of pitch. Traditionally, the two perspectives have been viewed as mutually exclusive, with pitch derived from either place or temporal cues, but not both. The controversy persists, in large part, because neither perspective, by itself, can fully account for the full range of perceptual experience associated with the pitch of complex signals [E. F. Evans, Audiology 17, 369–420 (1978)]. It is proposed that pitch stems from the interplay of place and time information, bound together into a coherent representation through the operation of central coincidence-sensitive neural populations. This framework provides a principled basis for understanding the neural mechanisms underlying the major properties of pitch (such as the ‘‘dominance’’ and ‘‘existence’’ regions, the first and second effects of the pitch shift, phase-insensitivity and dichotically mediated pitch) and illustrates the manner in which both frequency selectivity and synchrony are required for computing a signal’s periodicity with precision and reliability.
The effects on comodulation masking release (CMR) of systematic variations in on- and off-frequency masker modulation patterns
Authors: Buss Emily , Richards Virginia M.
Published: October 2005

Detection thresholds were obtained for a 500-Hz tone signal added to a masker comprised of an amplitude modulated tone centered at the signal frequency (on-frequency masker) and an array of amplitude modulated tones centered at 300, 700, 800, 900, 1000, and 1100 Hz (off-frequency maskers). The on-frequency masker was a sinusoidally amplitude modulated tone, and the off-frequency maskers were square-wave modulated tones. On- and off-frequency modulators were either in-phase or of random phase relative to one another, and different conditions used square wave modulators with different duty cycles (0%–100%). The difference between thresholds obtained in the in-phase and random phase conditions (CMRs) were as large as 12 dB, comparable to the CMRs found with perfectly matched modulators. Thresholds in the random phase condition did not depend on duty cycle, but for the in-phase condition the plot of thresholds as a function of duty cycle is ‘‘U’’ shaped. The data are in rough agreement with ‘‘cued-listening’’ models of CMR in which the detection of the added tone is enhanced by the cue provided by the off-frequency masker minima. [Work supported by NIH.]
Mixed modulation masking: AM masking FM and FM masking AM
Authors: Edwards Brent W. , Viemeister Neal F.
Published: October 2005

In a series of experiments, the masking of AM by FM and the masking of FM by AM was investigated. All modulation was sinusoidal, and the carrier was a 1 kHz tone. The masking of 16-Hz AM by FM as a function of the modulation frequency of the FM showed the same broad tuning seen with AM modulation masking [Bacon and Grantham, 2575–2580 (1989)]. This is consistent with FM being primarily encoded as AM for small modulation depths. Masking of 16-Hz FM by AM showed broader tuning; this can be attributed to the ‘‘second cue’’ for FM hypothesized by Edwards and Viemeister [ 733–740 (1994)]. AM detection thresholds also were obtained as a function of the modulation index, β, of the FM masker. Thresholds approached 100% modulation depth for large β, indicating an inability to process energy fluctuations that occur in both time and frequency. Finally, thresholds were obtained as a function of the relative phase between the masker and signal modulations. These phase results are discussed with respect to current modulation encoding theories. [Work supported by DC00683.]
Gap detection thresholds measured for symmetric and asymmetric marker frequency combinations surrounding a silent temporal gap
Authors: Formby Craig , Li Sheldon , Sherlock LaGuinn
Published: October 2005

Temporal gap detection (TGD) thresholds were measured between sinusoids that varied in frequency from 2000 to 3100 Hz for combinations of 2, 3, or 4 markers (e.g., combinations of one or two pre-gap markers with one or two post-gap markers). Sinusoidal frequencies F1 and F4 were used as pre-gap markers, while F2 and F3 served as post-gap markers. TGD thresholds were measured from three normal-hearing adults who tracked 70.7% correct detection thresholds adaptively across blocks of 50 2AFC trials. For symmetric marker conditions, where a pair or pairs of pre- and post-gap markers are equivalent in frequency on both sides of the silent gap (e.g., F1=F2 or F1=F2 and F3=F4), TGD thresholds are small (i.e., <10 ms). However, for asymmetric marker conditions, where only three markers are presented on a trial (e.g., F1=F2, F2≠F3, no F4), performance is highly variable. TGD thresholds for asymmetric marker conditions may be very large (e.g., 20–80 ms), and tend to increase as the frequency separation is increased between markers F3 or F4 and markers F1=F2. These patterns of TGD results are inconsistent with a masking process and probably reflect mechanisms that are important in grouping of auditory images. [Research supported by NIH and The Center for Language and Present address: AT&T Bell Laboratories, 200 Laurel Ave., Middletown, NJ 07748.
Peak detection for auditory sound discrimination
Authors: Goldstein Julius L. , Hall Joseph L.
Published: October 2005

Auditory detection of envelope maxima in temporal responses of cochlear frequency-analyzing filters has been hypothesized to account for phase effects in psychophysical discrimination [J. L. Goldstein, 458–479 (1967)]. Re-examination of this hypothesis in the context of asymmetry of masking [R. Hellman, Percept. Psychophys. 11, 241–246 (1972)] reveals that it also provides an adequate explanation for this phenomenon. Peak discrimination between a tone and tone masker plus narrow-band-noise probe is more sensitive to probe energy than is the inverse discrimination between noise and noise masker plus tone probe, in agreement with psychophysics. Simulations of this model indicate that asymmetry of masking is a function of the product of noise bandwidth and temporal duration. Psychophysical experiments on masking asymmetry were performed with both masker and probe bandwidth ranging from pure tone to supracritical band. The experimental design included both fixed and roving levels, with random phases fixed throughout each experiment. A standard detection-theory model was fit to the data, assuming that ratios of peaks or of normalized peaks are measured by an optimal noisy discriminator. Predictions based upon stimulus envelopes are in good agreement with the data.
Noise environments and their effects. Recreational exposures
Authors: Axelsson Alf
Published: October 2005

Many efforts have been made lately to combat occupational noise exposure, and the situation in many industries concerning noise preventive measures seems promising. Conversely, with regard to recreational activities the situation seems less promising. There are reasons to raise concerns about noisy activities such as personal cassette players (PCPs), pop/rock concerts, car stereos, motor sport, shooting activities, etc. For most of the musically oriented activities the situation is probably generally satisfactory; even if the sound levels frequently are very high, the exposure time and number of exposures/year is limited. For impulsive noisy activities the situation is more serious. As is well known, the impulsive noise in connection with the use of weapons, fire-crackers, and toy-cap guns without hearing protection may lead to a permanent noise induced hearing loss under accidental conditions. The general attitude concerning recreational noisy activities should obviously be to strive for lower sound levels, limited exposure, and better use of hearing protection.
Aircraft noise control
Authors: Stephens David G.
Published: October 2005

The purpose of this paper is to describe the research program in aircraft acoustics being conducted by the NASA–Langley Research Center. The program includes research to understand, predict, and reduce the sources of aircraft noise; to quantify the transmission of noise through the atmosphere and/or aircraft structures; and to define the effects of noise on people and structures. The research is focused on a broad range of aircraft with emphasis on advanced subsonic transports including conventional and tiltrotor rotorcraft, supersonic transports, high-performance military vehicles and hypersonic configurations. Specialty areas of research include computational aeroacoustics, jet noise, rotating blade acoustics, and structural and subjective acoustics. The resulting technology is used to design and operate aircraft to reduce community noise impact and/or to minimize the effects of noise on structural integrity and interior noise.
Twenty-five years of progress in noise standardization
Authors: Schomer Paul D.
Published: October 2005

This paper documents the more than ten-fold growth in the number of Standards and the program of work carried out by the ASA Standards directorate for the American National Standards Institute (ANSI) and for related international work with the International Organization for Standardization (ISO) and the International Electro-technical Commission (IEC). Not only has there been a huge increase in the work effort, but the emphasis has changed greatly. Now we work to ensure that ISO Standards are fair to all players and to ensure that ANSI Standards are compatible with ISO. While major U.S. industries are participating in this effort, more participation is needed by industry and government. Case histories are used to show how our efforts in the standards process are currently helping some U.S. manufacturers to market their products worldwide. Major industries with some significant involvement include automotive, construction and agricultural equipment, computer and business machines, hearing conservation equipment, and audiological testing, and sirens and alarms. Many other industries such as aircraft, mining, rotating electrical machinery, and manufacturers of acoustical materials, attenuators, mufflers, and soundproof enclosures currently lack significant involvement in the ISO process. Thus greater involvement is required by significant sectors of U.S. industry.
Acoustic radiation pressure in an infinite lossy medium
Authors: Jiang Zhong-Yue , Greenleaf James F.
Published: October 2005

Theories on acoustic radiation pressure associated with plane acoustic waves and lossless media have been examined extensively. The radiation pressure produced by a non-plane wave in a lossy unbounded medium was analyzed. The distinction between Lagrangian and Eulerian pressure was used to clarify the understanding of radiation pressure. The radiation pressure exerted on a perfectly absorbing pointwise target by an arbitrary acoustic wave in an unbounded lossy medium was then considered. By using an indirect approach developed in Chu and Apfel [B.-T. Chu and R. E. Apfel, 1673–1687 (1982)], the radiation pressure was analyzed without appealing to the detailed solutions of the governing fluid dynamic equations. It was shown that even in lossy media with arbitrary waves, the radiation pressure experienced by a pointwise target is equal to the Langevin pressure which is the time average energy density at that point. The radiation pressure exerted on a specific target by an arbitrary acoustic wave in an infinite lossy medium was studied and a concise theoretical result was obtained. [The work was supported by grants CA 43920 and HL 41046 from the National Institutes of Health.]
Measurements of finite-amplitude acoustic pulses radiated from focused piston sources in water
Authors: Averkiou Michalakis A. , Crum Lawrence A. , Hamilton Mark F.
Published: October 2005

Measurements of finite-amplitude acoustic pulses radiated by a focused piston source in water are reported. Pulses with center frequency of 2.25 MHz, durations ranging from two to ten cycles, and peak sound pressures up to 3 MPa were measured with a wideband (1–20 MHz) membrane hydrophone. The combined effects of focusing, diffraction, and finite-amplitude distortion on short pulses are demonstrated. Propagation curves for the peak positive and peak negative pressure along the axis of the source are shown. The peak negative pressure, which is an important factor in cavitation dynamics, is maximized in the prefocal region and shifts closer to the source with increasing source amplitude, as predicted earlier [Averkiou etal., 3306(A) (1993)]. Tissue images during treatment with a therapeutic ultrasound device that show increased cavitation activity in the prefocal region are presented. The measurements are compared with theoretical predictions based on the KZK equation and good agreement is found. [Work supported by the National Institutes of Health.]
The relationship between rays and modes in a waveguide with large-scale inhomogeneities
Authors: Virovlyansky Anatoly L.
Published: October 2005

The well-known results of Tindle and Guthrie, Felsen, and other authors on studying the relationship between rays and normal modes in a range-independent waveguide are generalized for a waveguide with large-scale inhomogeneities of refractive index. It is shown that in complete analogy with the range-independent case, the raylike behavior of a cluster of normal modes takes place. The notion of Fresnel zones for normal modes is introduced, which is analogous to the usual Fresnel zones introduced for rays. Using Fresnel zones for modes one can simplify the analysis of mode scattering at large-scale inhomogeneities (such as an opaque screen or an inhomogeneity of refractive index) in a waveguide. Simple and statistical averaging-suited formulas are deduced to calculate mode amplitude variations under scattering at inhomogeneities of refractive index, which are ‘‘mode analogues’’ of the formulas of geometrical optics and those of the Rytov method.
Some general properties of ray arrival sequences in an underwater sound channel
Authors: Virovlyansky Anatoly L.
Published: October 2005

Some properties of ray arrival sequences valid in a waveguide with an arbitrary sound-speed profile are ascertained using the simple approximate formula connecting differences in ray travel times and adiabatic invariants of their trajectories. It is noted that the following conservation law takes place: The mean difference in travel times of rays having their launch angles inside the fixed narrow angular interval does not depend upon the distance between the source and the receiver. This law holds true not only in the range-independent waveguide but in the adiabatically varying waveguide as well. Some general conclusions concerning the relationship between travel times and launch angles of rays reaching the receiver are made.
Computer model versus reality in a nonshoebox orchestra hall. Part II
Authors: Griesinger David
Published: October 2005

The Portland (Maine) City Hall Auditorium was the venue for acquisition of occupied and unoccupied acoustical data on 4 October 1994, using the MLSSA system. An ODEON (c) computer model of this hall, created by Kirkegaard and Associates, is used to estimate acoustical parameters from the same source and receiver locations as used in the live audience acquisition. The data collected in the hall are analyzed for musical intelligibility and reverberance using new and modified standard measures. Comparisons are made to the informal impressions of the listeners at the concert. The relevant usefulness of the data estimated from the computer model is discussed. The role of computer model surface definitions with respect to coefficients of absorption and diffusion is investigated. [Work supported by the Concert Hall Research Group.]
A room acoustics measurement system round robin
Authors: Bradley J. S.
Published: October 2005

This paper reports preliminary results of a room acoustics measurement system round robin. The round robin uses a commercial digital reverberator to represent three standard rooms that can be sent from one measurement group to another. Thus the tests compare basic calculation procedures and do not include the effects of variations due to types and placement of transducers. Each participant measures octave band values of monaural measures such as decay times, early/late ratios, and RASTI values on three different reverberator settings. Where possible, participants can also measure interaural cross correlations. Initial comparisons include both commercially available measurement systems and the measurement systems of individual research groups. The initial results will compare measurements from groups in North America, Japan, and Europe. Subsequent work will seek to explain the cause of the observed differences.
Technical matters relating to the measurement of interaural cross-correlation (IACC) coefficients in concert halls and opera houses
Authors: Hidaka Takayuki , Okano Toshiyuki
Published: October 2005

The interaural cross-correlation coefficient (IACC) has been shown to be an important measure, along with others, of the quality of acoustics in concert halls and opera houses [Schroeder etal., 1199 (1974); Ando, ConcertHallAcoustics (Springer-Verlag, Berlin, 1985)]. When measured in auditoriums with binaural heads (real or dummy) using an impulse source, means must be adopted to achieve accuracy and precision, and to select the type of impulse and processing methods to make IACC most useful in the prediction of acoustical quality. Subjects covered include: (1) type of impulse, (2) convolution signal, (3) integration limits, (4) directivity and positions of source in the hall, (5) parameters of head, (6) comparisons of measurements made with real and dummy heads, (7) value of torso, (8) measuring positions in hall, (9) comparison of measurements of IACC in halls with upholstered and nonupholstered seats, (10) comparison with IACC measurements made by other laboratories, and (11) some preliminary data on differences among IACCs measured in occupied and unoccupied halls.
Interaural cross-correlation (IACC), lateral fraction (LF), and low- and high-frequency sound levels (G) as measures of acoustical quality in concert halls
Authors: Hidaka Takayuki , Beranek Leo L. , Okano Toshiyuki
Published: October 2005

Interaural cross-correlation coefficient (IACC) and lateral efficiency (LF) as correlates with subjective ratings [see companion paper, L. Beranek, ‘‘Determination of categories of acoustical quality in concert halls’’ (this session)] were analyzed. To make IACC sensitive to quality ratings, a multi-octave-band average was developed, based on Blauert etal. [Acustica 59, 292] and on a subjectively derived set of equal ASW contours that showed the 0.5, 1.0, and 2.0 octave bands to be of equal importance. This IACC3 was divided into IACCE3 integrated over first 0.08 s after arrival of the direct sound, and IACCL,3 same, 0.08 to 1 s. Subjective judgments were also made to determine the effects of increased sound levels of symphonic music at frequencies above and below 355 Hz on apparent source width ASW. IACCE3 and GL both appear important for determining ASW. The measured quantity [1−IACCE3] alone was found to separate the 17 concert halls of this study for which IACC data were available into the same three category groups as those determined from the interviews. Lateral fraction (LF) was found to extend over a very small range and there were so many overlaps among halls when separation into three rating groups was attempted that LF was judged not to be suitable for rating acoustical quality.
Correlations between categories of acoustical quality for forty concert halls and measured physical parameters for them: RT, EDT, IACC, LF, G, ITDG, BR, C(80) and diffusion
Authors: Beranek Leo L.
Published: October 2005

Through the cooperation of many acoustical laboratories, architects, and hall managers, physical measurements of reverberation time (RT), early decay time (EDT), early interaural cross-correlation coefficient [IACC(E)], lateral fraction (LF), sound-pressure level (G), initial-time-delay gap (ITDG), bass ratio (BR), early/reverberant energy ratio [C(80)], and diffusion [IACC(L)] have been collected in whole or in part for 66 concert halls and 10 opera houses. RTs are for both occupied and unoccupied conditions; others are for unoccupied states. The parameters IACC or LF, or both, are available for only 40 of the concert halls. The above acoustical parameters for these halls are individually correlated with the rating categories given in the companion paper [Beranek, ‘‘Determination of Categories of Acoustical Quality in Concert Halls’’]. It is shown that six of these quantities seem necessary to correlate physical data with the subjective ratings, namely, RT (or EDT), IACC(E), G, ITDG, BR, and some measure of diffusion not yet developed.
The use of the Sabine and Eyring reverberation time equations to churches
Authors: Carvalho António Pedro O.
Published: October 2005

Reverberation time (RT) measurements were taken at several source/receiver locations in 41 Catholic churches in Portugal built in the last 14 centuries, using the impulse–response method. The use of the Sabine and Eyring reverberation time equations was tested to estimate the measured RTs in this sample of churches. The effect of coupled spaces was analyzed, and a new algorithm for the application of the Sabine equation in churches was developed producing an average of 16% in the differences between the predicted and measured RTs compared to 71% using the standard Sabine equation. Coupled spaces were found to act as windows with a characteristic absorption coefficient depending on their dimensions. The recesses in churches were grouped in three types: main altar area, chapels, and lateral aisles, each having a particular acoustical behavior. It was found that those recesses only acted as coupled spaces if their length/opening–width≳0.6 or if the aisle–width/opening–height≳0.4 in lateral aisles. The remaining differences found between the RTs measured and predicted with this new algorithm were hypothesized to be related to what was called a reverberantceilingeffect, which is presumed to be due to a two-dimensional reverberant sound field that builds up near a very tall ceiling. [Work supported by JNICT/Ministry of Planning and Univ. of Porto, Portugal.]
Electromagnetic interference (EMI) concerns and electromagnetic compatibility (EMC) modeling for acoustic instrumentation
Authors: Dixon David S.
Published: October 2005

Traditionally, the electromagnetic interference (EMI) concerns of submarines have been dominated by the susceptibility of low-frequency subsystems associated with acoustic, control, and electromagnetic systems. The uniqueness of the efforts to ensure the nondegraded operation of these systems is the fact that the frequency range of the susceptible systems and the typical EMI sources overlap. Therefore, many low-frequency, low-amplitude signals can be degraded by low-frequency conducted and radiated EMI created by the power generation and distribution system. Power line rectification and switching harmonics are radiated magnetically as well as conducted along cables, shields, and ground plane components. In addition, the use of modern wideband digital systems coupled with the use of lightweight, low-cost, nonmetallic enclosures has produced an additional concern caused by the rapidly increasing radiated electric field environment. In summary, the electromagnetic environmental (E3) concerns associated with acoustic instrumentation in very similar to the E3 concerns that are required for shipboard systems. This paper will discuss the typical EMI coupling mechanisms that will degrade the expected performance of low-frequency systems, such as audiometers, acoustic instrumentation, telephones, cabling, etc. In addition, it will discuss the EMI models that have been developed for components as well as the latest analysis and predictive EMC design techniques that have been developed to achieve cabinet and compartmental (room) compatibility.
OIML standards on performance requirements for acoustical instruments
Authors: Chappell Samuel E.
Published: October 2005

The International Organization of Legal Metrology (OIML) is a treaty organization, having currently 53 (voting) member and 40 (non-voting) member nations, most of the latter nations being characterized as developing. OIML’s objective is to harmonize national regulations for the performance requirements of legal measuring instruments among member nations in order to facilitate international commerce of measuring instruments and affected products, to ensure public health and safety, and to protect the environment. This effort intends to avoid or minimize technical barriers to international trade. An OIML technical committee or subcommittee develops OIML recommendations (standards or model performance regulations) to address particular types or classes of instruments. If approved, member nations have a moral obligation to implement a recommendation in their national regulations for the instrument addressed. The obligation applies both to new regulation and to harmonizing any existing regulations. This presentation addresses OIML work projects for acoustical instruments and the potential impact of relevant OIML recommendations on instrument manufacturers. The basis for requirements including electromagnetic compatibility and the means by which the United States participates in the work are covered.
Complicated cases and shielded rooms: Audiometric booths shielded to attenuate electromagnetic interference (EMI)
Authors: Nedzelnitsky Victor
Published: October 2005

Electromagnetic compatibility (EMC) issues involving acoustical instruments, especially their susceptibility and immunity to electromagnetic interference (EMI), are increasing in importance. This increase is driving domestic and international standards development. Of particular significance is the impact on commercial practice and international trade of two Councils of the European Communities directives regarding generic apparatus (Council Directive 89/336/EEC, 3 May 1989) and medical devices (Council Directive 93/42/EEC, 14 June 1993). Directive 93/42/EEC is being interpreted to include hearing aids and audiometric instruments. Numerous voluntary International Electrotechnical Commission (IEC) electroacoustical performance standards are available for some of these instruments. However, extension of these complicated standards to include all pertinent EMC issues is difficult. Development of standards for other instruments, such as those for measuring auditory brain-stem response, would be even more difficult. In some circumstances, the use of shielded rooms to attenuate radiated EMI is practical and cost-effective. In the U.S.A., at least, existing standards for measuring such shielded-room performance were not specifically developed for audiometric booths. Methods in some of these standards have been adapted and applied to that purpose. Selected standards, methods, and some considerations regarding their application to measuring the shielding performance of audiometric booths in hospital/clinical environments are discussed.
Effect of electromagnetic interference on a continuous wave ultrasonic field
Authors: Cosnowski David L. , Hastings Mardi C.
Published: October 2005

Continuous-wave ultrasound for imaging and other measurement applications requires the use of a separate source and receiver transducer. When this system is used in air or water, the receiver transducer often detects a signal at the ultrasonic frequency even in the absence of a target. At ultrasonic frequencies, significant electromagnetic coupling between the transducers can occur due to their own and extraneous electromagnetic fields. This study examines the effect of this interference on the 3-dB sample volume defined by the crossed beams. The sample volume is determined mathematically by modeling the source and receiver transducers as plane piston radiators [J. Zemanek, 181–191 (1971)]. The effect of interference is obtained by adding a constant term to the sample volume matrix, which, in general, is complex. Experimental measurements using an ultrasonic source and receiver in air at several frequencies from 40 to 100 kHz correlate well with model predictions. The electromagnetic interference was found to have a significant effect on the observed field. [Work supported by NSF Grant No. MSS 9058607.]
Occupational noise exposures: Where do we stand today?
Authors: Suter Alice H. , Johnson Daniel L.
Published: October 2005

There have been several major improvements in the field of occupational noise exposure over the last 25 years. ISO 1999 has been revised and now provides an accepted method of relating hearing loss to noise exposure. Hearing protection devices have been improved considerably, impulse noise is being assessed more effectively, and there has been a shift among U.S. agencies toward using the equal-energy rule in noise exposure standards. Perhaps the most important advancement has occurred with the promulgation of OSHA’s hearing conservation amendment to its noise standard. The future, however, poses many challenges: OSHA’s noise standard needs revision, more emphasis on enforcement is needed, engineering controls should be re-emphasized after many years of inattention, and total reliance on hearing protection devices should be de-emphasized. In addition, the benefits of the hearing conservation amendment need to be extended to currently underserved workers, such as miners and workers in construction, agriculture, and the oil and gas industries. Perhaps the greatest challenge is the need to investigate the effectiveness of hearing conservation programs on a national scale to determine the extent to which they are actually preventing hearing loss.
Three-dimensional acoustic/geoacoustic propagation modeling of the New Jersey Atlantic generating station site
Authors: Badiey Mohsen , Botseas George , Lee Ding , Siegmann William L.
Published: October 2005

Propagation effects of 3-D geological features in shallow water sediment layers at the Atlantic generating station (AGS) continental shelf site are investigated. Profiles of compressional and shear sound speed, attenuation, and density have been generated from 23 available geological cores at the AGS site and discussed in connection with a recent acoustic experiment conducted there [Badiey etal., 3593–3604 (1994)]. A 3-D geoacoustic data set is constructed from these profiles using interpolation schemes based on Akima splines and on krieging. Correlation properties of the sound speeds and density fields clearly show the existence of sublayer geological features. The geoacoustic fields, along with detailed bathymetry and water sound speed, are used for input a 3-D frequency domain PE propagation model. Both 3-D and N×2-D simulations are performed over a circular region corresponding to the experimental configuration. Relative influences of sediment sound-speed structure and water–sediment interface topography on transmission loss are determined for frequencies up to 1 kHz. Simulation results are compared with spectra obtained from the broadband experimental transmission loss.
Use of empirical orthogonal functions to estimate wave number variance in a stochastic shallow-water channel
Authors: Longfritz Michael J. , Siegmann William L. , Jacobson Melvin J. , Badiey Mohsen
Published: October 2005

The variances of horizontal acoustic wave numbers in stochastic shallow-water environments are estimated using empirical orthogonal functions (EOFs). Using perturbation methods and an adiabatic normal-mode propagation model, the wave number fluctuations are related to range variations in the ocean and/or sediment sound-speed profiles, which can be conveniently and efficiently represented by EOFs. This relationship can be used to estimate both the wave number deviations arising from selected realizations of the stochastic ensemble and the overall wave number variance. The procedure is illustrated by application to a shallow-water waveguide with a multilayered sediment bottom. Both the layer depths and the intralayer sound speeds are modeled as random variables. The accuracy of the estimation procedure is investigated for various choices of the layer depth and sound-speed statistics by comparing with results from computational simulations. A particular environment examined is the New Jersey Shelf Atlantic Generating Site, where relatively extensive geoacoustic profiles are available [M. Badiey etal., 3593–3604 (1994)]. Comparisons are made between results from the estimation procedure and from the KRAKEN and FEPE propagation codes.
Analysis of spatial-time characteristics of broadband pulse propagation through ocean sound channels by using shallow water acoustical mode propagation model
Authors: Sidorovskaia Nataly A. , Werby Michael F.
Published: October 2005

Broadband pulse propagation through an oceanic sound channel is investigated to characterize some important oceanic properties, namely, the vertical sound profile, bottom structure, and also source localization. Examples of waveguides with surface and bottom ducting are considered. The new fast normal mode method (SWAMP) based on a new expansion method allows one to study the high frequency range in which large numbers of modes can be excited. In this situation the complicated structure of the wavefront that is the result of the interference of the low-order trapped refractive modes and the high-order reflected modes is observed in the waveguides. To understand the structure of this informatively rich wavefront, two techniques are presented: The static spatial-time maps of the sound field intensity distribution in a waveguide and video movies permitting one to observe the time evolution of a pulse through the fixed spatial region. The later technique gives much additional information on the process and can offer additional insight into the nature of pulse evolution along a waveguide. [Work sponsored by the Office of Naval Research.]
Exploratory wavelet transform analysis of seismoacoustic data
Authors: Smith Randall W. , Stotts Steven A. , Koch Robert A.
Published: October 2005

The one-dimensional continuous wavelet transform is applied to the analysis of seismoacoustic data. The data consist of received signals, due to an impulsive source, measured by a triaxial seismometer. The wavelet transform provides a time-frequency decomposition of the signal, which in turn yields information about dispersion and arrival times of the various propagation modes. The primary goal of the analysis is to explore methods for extracting information from the time-frequency representation. The use of the wavelet transform will be complemented by modeling efforts. In particular, the different modes of propagation, estimating geoacoustic parameters, and localizing the source will be identified and analyzed.
Signal denoising using matching pursuits
Authors: Trappe Wade
Published: October 2005

This paper will examine in brevity the matching pursuit algorithm proposed by Mallat and Zhang which yields an adaptive signal decomposition that may be used to derive a phase plane representation of a signal. Matching pursuits is closely related to wavelet analysis and may be considered a superset of wavelet multiresolution analysis. A methodology for coherent feature extraction, or denoising, using matching pursuits will be developed and explained. Acoustic signals derived from speech and music will be examined. Synthetic white noise and acoustic noise will be injected and matching pursuits will be used to attempt to remove noise from these signals.
Design of M-sequences for a shallow water transmission experiment
Authors: Forsythe S. E. , Badiey Mohsen
Published: October 2005

Narrow-band signals centered at frequencies from 600 Hz to 7 kHz were transmitted from a fixed projector to a fixed hydrophone array located 200 m away as part of the shallow water acoustic/geologic experiments at the New Jersey Atlantic Generating Station Site. Both the projector and hydrophone array were fixed 2 m off the ocean floor in roughly 15 m of water. The signals were Gaussian pulses 1 m in width modulated by weighted binary maximal length sequences (M-sequences). These M-sequences were designed to increase effective signal-to-noise ratio while retaining the time/space discrimination of the original Gaussian pulse. The pulse width was narrow enough to allow separation of component arrivals (e.g., direct and bottom reflection). A design method is presented that allows simultaneous control of frequency- and time-domain content of the transmitted signal. Examples of recovery of the transmitted signals and their multipath information are presented.
Effect of ergodicity failure on detection performance prediction
Authors: Ioup George E. , Pflug Lisa A. , Ioup Juliette W.
Published: October 2005

Formulas based on the noise variance and the first four signal moments to predict the performance at the minimum detectable level of ordinary and higher order correlation central ordinate threshold detectors have been derived. The passive prediction formulas have been reported and will be published. The active prediction results have also been presented. These prediction formulas agree remarkably well with computer-based Monte Carlo simulations. A breakdown in the agreement has been observed for simulations containing a small number of sample points—in the observation window for the passive case and in the signal for the active case. This breakdown can be traced to the inapplicability of the ergodicity assumption for various time averages over a small number of sample points, since key steps in the derivations contain the interchange of expectations and summations for nonlinear terms. Small sample number time averages lead to correlation central ordinate value probability density functions which are non-Gaussian. Prediction errors in the formulas as great as 2 dB are observed for simulations with 32 sample points. These errors decrease as the number of sample points is increased. Both passive and active examples are given. [Research supported by ONR/NRL-SSC.]
A study of the effective properties of complex scatterers using multiresolution decomposition
Authors: Steinberg B. Z. , McCoy J. J.
Published: October 2005

Complexity in the context of radiation and scattering of waves can be intuitively perceived as the analytical and computational difficulties encountered when a radiating system interacts with a medium or a scatterer that are described on a wide range of length scales. The wavelength λ constitutes a physically motivated discriminator of the various length scales pertaining to a time harmonic scattering problem. It is convenient to refer to the length scales of the order of λ and above as the macroscales, and to the length scales much smaller than λ as the microscales. A complexity frequently encountered in scattering problems is the one characterized by a microscale heterogeneity that occupies domains in space measured on the macroscale. A new formulation, tuned to govern the macroscaleresponsecomponent, has been presented in several recent papers. This formulation is sufficient for estimating the radiation of a sound field into the far-field of a surrounding fluid. In this presentation we concentrate on the formulation’s implications. The questions addressed are: What type of microscale heterogeneity has no footprint in macroscale response measures? What classes of microscale heterogeneity have an identical footprint in macroscale response measures?
Investigation of three-dimensional bathymetric refraction using laboratory scale modeling
Authors: Glegg Stewart A. L. , LaVigne Anthony , Riley Joseph M.
Published: October 2005

Experimental measurements have been carried out to identify the effect of bathymetry on three-dimensional underwater sound propagation. The measurements have been conducted over a 1/10 000th scale model of the Santa Lucia Escarpment off the coast of California. Experiments measured the bearing error obtained in locating a source with a horizontal line array using a phase-wave beamformer. The results of this experiment demonstrated significant variations in the measured bearing error. Differences in the detected bearing of the variations beamformer and the actual source location were as large as 18 deg, with the magnitude of these errors being a function of bearing line and source frequency. An analytical solution of the acoustic field in a shear supporting wedge using the method of images has been used to approximate the results of the bearing error experiment. Comparison of experiment and theory shows the same effects with bearing errors of the same magnitude. [Work supported by ONR.]
Acoustic interaction with a propagating internal soliton wave packet in shallow water
Authors: Broadhead Michael K.
Published: October 2005

One-way ocean acoustic propagation through shallow water internal waves was numerically simulated, where the oceanographic model consisted of a two-layer density/temperature stratified fluid overlying flat bathymetry. For sufficiently small amplitudes in a lossless medium, shallow water internal waves are governed by the Korteweg–de Vries (KdV) equation, which possesses soliton solutions. A finite difference scheme was used to numerically time evolve initial conditions, the details of which determine the number and properties of the soliton events that emerge. The internal waves (in a center-of-mass frame) were introduced through the index of refraction in the acoustic wave equation. Range-dependent normal mode and PE models were used to compute transaction-loss for various frequencies (100 Hz–10 kHz), for different times during the soliton wave packet evolution, and for different initial conditions. For lower frequencies, refraction effects caused an increase in the mean TL level due to increased bottom interaction, while for higher frequencies, the predominant effect was spatial/temporal fluctuations and the enhancement of surface duct propagation. Dispersive terms exist for all but special initial conditions, but their amplitudes were generally too low to be significant. [Supported by Office of Naval Research and Naval Research Laboratory.]
Jovian acoustics: Short-range observation and long-range prediction
Authors: Collins Michael D. , McDonald B. Edward , Kuperman W. A. , Siegmann William L.
Published: October 2005

Waves were observed propagating in the stratosphere of Jupiter near the impact sites of several of the fragments of Comet Shoemaker-Levy 9. Concentric rings appearing in Hubble Space Telescope images have tentatively been identified as gravity and acoustic waves based on their horizontal group speeds of 450 and 900 m/s. Interpreting the images is complicated by the fact that the outer ring is located amidst the debris of the collapsed fireball. Since the fireball rose back through the obliquely oriented path of the incoming fragment, the debris field is asymmetric and offset from the impact site. It is therefore unlikely that the outer ring is part of the debris. If waves are observed far from the impact sites, they might provide new information about the Jovian atmosphere. A three-dimensional adiabatic mode solution predicts that the Jovian zonal winds cause horizontal caustics to form to the east and west of the impact sites about 10 h after impact. An adiabatic mode solution has also been derived for gravity waves, which exhibit similar horizontal caustics. Although the acoustic and gravity wave equations are drastically different, the horizontal wave equations for the mode coefficients are identical.
Global-scale acoustic modeling in an ocean overlying elastic bathymetry
Authors: Orris Gregory J. , Collins Michael D. , Deane Grant , Porter Michael B.
Published: October 2005

A three-dimensional propagation model is presented that takes into account the elastic properties of the ocean bottom and is applicable to problems of long range and low frequencies. This method allows global-scale calculations appropriate for ocean monitoring programs to be performed with environments for which solution techniques have been heretofore unavailable. The model is an extension of the adiabatic parabolic-equation method, which uses the normal-mode solutions in the waveguide for the depth dependence of the acoustic field. A modified two-dimensional parabolic equation model is used to determine the range and azimuth dependence of the acoustic field, thus providing a three-dimensional solution. It is shown that the inclusion of elastic material, with both compressional and shear waves, in bathymetric features causes larger loss and larger shadow zones behind sea mounts and islands due to the effective softening of the material. The method is compared with exact solutions and experimental results and is found to be in excellent agreement for regimes for which the adiabatic approximation is valid (i.e., for regions of slowly varying bathymetry and sound-speed profiles).