bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of interchannel crosstalk on array performance
Authors: Streit Roy L.
Published: October 2005

It is shown that interchannel crosstalk can always be eliminated before the channel signals enter the beamformer, provided crosstalk levels do not exceed a maximum permissible upper bound and are known exactly. The crosstalk upper bound (in decibels) is shown to be −20 log N, where N is the number of channels in the array. The beam pattern of a general array with arbitrary crosstalk levels, steered in any direction, is derived. Sample beam patterns are presented for arrays of 50 and 100 elements. Expected, or average, beam patterns are derived for interchannel crosstalk coefficients modeled as statistically independent random variables. It is shown that pointing error can occur when crosstalk has nonzero mean. It is also shown how to correct for nonzero mean crosstalk before the signals enter the beamformer, provided these means are known.
Critical angle measurement of elastic constants in composite material
Authors: Rokhlin S. I. , Wang W.
Published: October 2005

Application of critical angle measurement for determination of elastic constants of composite materials is described. For general orientation of the composite material relative to the plane of incidence, three critical angles exist, for quasilongitudinal and fast and slow quasitransverse waves. It is shown that, for any two-dimensional composite material, the critical angles are directly related to the phase velocities of bulk waves in the sample plane. A simple and novel type of goniometer is developed for these measurements which utilize a cylindrical reflector for measurement of the double reflection coefficient. The values of the elastic constants are reconstructed from the measured velocity surfaces by using nonlinear least-squares optimization fitting. Analytical relations between ultrasonic velocity and elastic constants valid for arbitrary anisotropy are implemented in the fitting optimization.
Estimation of average under-ice reflection amplitudes and phases using matched-field processing
Authors: Livingston Ellen , Diachok Orest
Published: October 2005

Average low-frequency under-ice reflection amplitudes and phases in the central Arctic were estimated from long-range (260-km) signals from fixed continuous wave (cw) sources detected on a long (1-km) vertical array (the FRAM IV experiment), using conventional and minimum variance estimators in conjunction with matched-field processing. Theoretical computation of the trial source fields for all assumed ranges and depths was based on a normal-mode code into which were incorporated the under-ice reflection amplitudes and phases by functional dependence on grazing angle. These were varied iteratively to achieve maximum matched-field processor gain with minimum range and depth errors. The resultant best data-fitting amplitudes and phases, which differ significantly from expectations based on existing under-ice scattering models, provide a new benchmark for testing and, it is hoped, a stimulus for the development of refined theories.
The propagation of horizontally polarized shear waves in multilayered anisotropic media
Authors: Nayfeh Adnan H.
Published: October 2005

Exact solutions are presented for the propagation of horizontally polarized shear waves in multilayered anisotropic media. The wave is allowed to propagate along an arbitrary angle θ from the normal to layer interfaces, but restricted to propagate along an axis of symmetry for each layer. The solutions are obtained in two steps. In the first, formal solutions are derived for each layer which relate the field variables at its upper and lower layer surfaces. In the second, the response of the total plate proceeds by satisfying appropriate interfacial conditions across the layers. The results are general and include those pertaining to free waves on a finite-thickness multilayered plate, as well as on periodic media. Several numerical illustrations in the forms of dispersion characteristics are given.
Comments on ‘‘Effects of noise on speech production: Acoustic and perceptual analyses’’ [J. Acoust. Soc. Am. 8
4, 917–928 (1988)]
Authors: Fitch Hollis
Published: October 2005

The effect of background noise on speech production is an important issue, both from the practical standpoint of developing speech recognition algorithms and from the theoretical standpoint of understanding how speech is tuned to the environment in which it is spoken. Summers et al. [J. Acoust. Soc. Am. 84, 917–928 (1988)] address this issue by experimentally manipulating the level of noise delivered through headphones to two talkers and making several kinds of acoustic measurements on the resulting speech. They indicate that they have replicated effects on amplitude, duration, and pitch and have found effects on spectral tilt and first-formant frequency (F1). The authors regard these acoustic changes as effects in themselves rather than as consequences of a change in vocal effort, and thus treat equally the change in spectral tilt and the change in F1. In fact, the change in spectral tilt is a well-documented and understood consequence of the change in the glottal waveform, which is known to occur with increased effort. The situation with F1 is less clear and is made difficult by measurement problems. The bias in linear predictive coding (LPC) techniques related to two of the other changes—fundamental frequency and spectral tilt—is discussed.
Developmental changes in masked thresholds
Authors: Schneider Bruce A. , Trehub Sandra E. , Morrongiello Barbara A. , Thorpe Leigh A.
Published: October 2005

Masked thresholds for octave-band noises with center frequencies of 0.4, 1, 2, 4, and 10 kHz and for a (1)/(3) -octave-band noise centered at 10 kHz were obtained from listeners 6.5 months to 20.5 years of age at two levels of a broadband masker (0 and 10 dB/cycle). Thresholds declined exponentially as a function of age for all stimuli tested. The rate and extent of this decline, but not its asymptote, were independent of the frequency or bandwidth employed. The time course for this change parallels that found for electrophysiological maturation of more central auditory processes.
Analysis of weights in multiple observation tasks
Authors: Berg Bruce G.
Published: October 2005

Multiple observation tasks are often used to investigate observers’ abilities to combine information from different sources or observations. This paper discusses a method for assessing the relative weight given to each observation. First, a theorem that derives the relative weights is stated. A technique for estimating relative weights is then illustrated by analyzing data from a multiple-tone task. In this task, observers listen to a sample of tones drawn from one of two distributions and decide which distribution was sampled. Results show that observers integrate information nonoptimally, attaching greater weight to the first and/or last observations than to observations occurring in the middle of the sequence. The generality of the technique is discussed.
Gap detection as a function of stimulus bandwidth with fixed high-frequency cutoff in normal-hearing and hearing-impaired listeners
Authors: Grose John H. , Eddins David A. , Hall Joseph W.
Published: October 2005

Gap detection was measured as a function of noise bandwidth with constant high-frequency cutoff in both normal-hearing and cochlear-impaired listeners. Band-widening functions were measured in a low-frequency region (0.6-kHz upper cutoff) and a high-frequency region (2.2-kHz upper cutoff). Measures of frequency selectivity were also obtained in the two frequency regions. The results for the normal-hearing listeners indicated that, on a double logarithmic scale, gap thresholds improved more steeply with increasing bandwidth in the higher frequency region than in the lower. However, performance at the narrow bandwidths was independent of frequency region. For the cochlear-impaired listeners, gap thresholds were generally longer than normal in both frequency regions. However, in the higher frequency region, progressively more listeners approached normal values as bandwidth was increased. The elevated gap thresholds were due in part to the higher absolute thresholds and in part to poor ability to process stimulus fluctuation. No correspondence was found between gap detection performance and frequency selectivity.
Lateralization of coherent and incoherent targets added to a diotic background
Authors: Schneider Bruce A. , Zurek Patrick M.
Published: October 2005

Lateralization responses to noise targets were obtained in a diotic noise background. On each trial, a noise target was added to the background noise in one earphone. Subjects were required to identify the earphone containing the target. Noise targets were either coherent or incoherent with the background. The long-term power spectrum of the incoherent target was identical to that of the background noise, and its amplitude was adjusted so that the addition of either the coherent or incoherent target to the background produced the same average increment in power. When 50-ms noise targets were presented in the middle of a 750-ms diotic background, lateralization thresholds were lower for the incoherent targets. The advantage with incoherent targets was shown to depend on the temporal relationships between target and masker. Superior performance with incoherent targets is inconsistent with predictions based on an analysis of interaural phase and amplitude differences. Models based on interaural subtraction, on the other hand, are able to account for the lateralization advantage shown by incoherent targets but are unable to account for the variations in threshold produced by altering the temporal relationships between target and masker.
The design, calibration, and use of a water microjet for stimulating hair cell sensory hair bundles
Authors: Saunders James C. , Szymko Yvonne M.
Published: October 2005

The design, calibration, and use of a noninvasive, noncontact device for stimulating hair cell hair bundles in vitro are described. This device employed a piezoelectric crystal, driven at high frequencies, to generate sinusoidal pressure in a contained fluid volume. The pressure was propagated to the tip of a glass micropipette and the oscillating water jet stimulus produced at the tip was used to stimulate sensory hair bundles. The movements of glass microbeads, caught in the oscillating pressure field of the water jet, provided a means of calibrating this stimulus. The linearity of the jet, its waveform and frequency response, the influence of pipette shape and tip diameter, as well as models to explain the operation of the water jet, are described. The use of this stimulus for measuring hair bundle micromechanics at high frequencies is then demonstrated.
Efficient digital beamforming in the frequency domain
Authors: Maranda Brian
Published: October 2005

The formation of steered beams for a linear array of hydrophones is a necessary task in many sonar systems. In this paper, algorithms for beamforming digital signals in the frequency domain are compared for their computational efficiency and suitability for implementation on an array processor. Methods based on the chirp z transform (CZT) and on interpolation using finite-impulse response (FIR) filters are shown to be the most efficient, although beamforming based on Goertzel’s algorithm is also competitive when the beams are formed in conjugate pairs.
Acoustic wave-field analysis of ultrasonic transducers
Authors: Sung Shung H.
Published: October 2005

A numerical method was developed for predicting the radiated acoustic field from arbitrarily shaped ultrasonic transducers. The numerical method was first verified for a spherical transducer, and it was found that the numerical results agreed very well with exact analytical results. The numerical method was then applied to other transducer shapes: toroidal, elliptical, conical, and parabolic transducers. As will be shown in this paper, an ultrasonic transducer’s geometrical shape affects the radiated acoustic field and acoustic beam pattern, and thus characterizes its specific application. For both the focusing- and nonfocusing-type transducers, the ultrasonic characteristics of focal length, depth of field/depth of penetration, beam radius, sidelobe level, and its radial location were calculated and are discussed.
A 5-day long-range sonar record of an extensive concentration of fish
Authors: Weston David E. , Revie Jack
Published: October 2005

The 2-kHz correlation sonar at Perranporth was used to produce a continuous 5-day record in May 1967. The record’s unusual feature is a strong and extended return from a range of the order of 45 km, with apparent extent varying from 5 to 35 km. This echo return must be due to fish, probably sprats. The leading edge of the echo shows a diurnal rather than a tidal variation in range, being about 13 km closer at night. The patterns suggest that at night the sound is attenuated in propagating through the concentration of fish. Other features shown in the record include (a) a storm, (b) phase changes in the interference patterns, (c) the whole dispersion process for some shoals, and (d) some 4-m/s tracks.
Clutter interference and the integration time of echoes in the echolocating bat, E
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Authors: Simmons James A. , Freedman Edward G. , Stevenson Scott B. , Chen Lynda , Wohlgenant Timothy J.
Published: October 2005

The ability of the echolocating bat, Eptesicus fuscus, to detect a sonar target is affected by the presence of other targets along the same axis at slightly different ranges. If echoes from one target arrive at about the same delay as echoes from another target, clutter interference occurs and one set of echoes masks the other. Although the bat’s sonar emissions and the echoes themselves are 2 to 5 ms long, echoes (of approximately equal sensation levels—around 15 dB SL) only interfere with each other if they arrive within 200 to 400 μs of the same arrival time. This figure is an estimate of the integration time of the bat’s sonar receiver for echoes. The fine structure of the clutter-interference data reflects the reinforcement and cancellation of echoes according to their time separation. When clutter interference first occurs, the waveforms of test and cluttering echoes already overlap for much of their duration. The masking effect underlying clutter interference appears specifically due to overlap, not between raw echo waveforms, but between the patterns of mechanical excitation created when echoes pass through bandpass filters equivalent to auditory-nerve tuning curves. While the time scale of clutter interference is substantially shorter than the duration of echo waveforms, it still is much longer than the eventual width of a target’s range-axis image expressed in terms of echo delay.
The acoustic basis for target discrimination by FM echolocating bats
Authors: Simmons James A. , Chen Lynda
Published: October 2005

Past experiments show that echolocating bats of the species Myotis lucifugus and Eptesicus fuscus can discriminate among airborne sonar targets presented in the context of pursuit maneuvers for the interception of prey. These bats distinguish between edible mealworms and inedible spheres of various sizes. Myotis can distinguish between disks and mealworms similar enough in size that the bat’s performance requires the ability to perceive the acoustic equivalent of target shape. Previously observed small differences in the spectrum of echoes from mealworms and disks appear insufficient to distinguish these targets at the performance levels achieved by bats. We measured the acoustic properties of the targets by broadcasting ultrasonic impulses at mealworms, spheres, and disks and recording their echoes, displaying the results in terms of impulse echo waveforms and the frequency response of targets derived from the target transfer function. The echoes from disks and mealworms at various orientations convey the range-axis profile of the target (number and spacing of reflecting points or glints distributed at different ranges) in terms of the impulse structure of their waveforms and in terms of the locations and spacing of notches or nulls in their spectra. For targets that bats can discriminate and that reflect echoes which do not clearly differ in overall amplitude, the targets appear distinguishable from the acoustic representation of their range profile, which is a feature of targets that bats can perceive with great acuity.
Difference limens for phase in normal and hearing-impaired subjects
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

These experiments measure the ability to detect a change in the relative phase of a single component in a harmonic complex tone. Complex tones containing the first 20 harmonics of 50, 100, or 200 Hz, all at equal amplitude, were used. All of the harmonics except one started in cosine phase. The remaining harmonic started in cosine phase, but was shifted in phase half-way through either the first or the second of the two stimuli comprising a trial. The subject had to identify the stimulus containing the phase-shifted component. For normally hearing subjects tested at a level of 70 dB SPL per component, thresholds for detecting the phase shift [i.e., phase difference limens (DLs)] were smallest (2°–4°) for harmonics above the eighth and for the lowest fundamental frequency (F0). Changes in phase were not detectable for harmonic numbers below three or four at the lowest F0 and below 5–13 at the highest F0. The DLs increased slightly for the highest harmonics in the complexes. The DLs increased markedly with decreasing level, except for the highest harmonic, where only a small effect of level was found. Subjects reported that the phase-shifted harmonic appeared to ‘‘pop out’’ and was heard with a pure-tone quality. A pitch-matching experiment demonstrated that the pitch of this tone corresponded to the frequency of the phase-shifted component. For the highest harmonic, the phase shift was associated with a downward shift of the edge pitch heard in the reference (all cosine phase) stimulus. When the phases of the components in the reference stimulus were randomized, phase DLs were much higher (and often impossible to measure), the pop-out phenomenon was not observed, and no edge pitch was heard. Subjects with unilateral cochlear hearing impairment generally showed poorer phase sensitivity in their impaired than in their normal ears, when the two ears were compared at equal sound-pressure levels. However, at comparable sensation levels, the impaired ears sometimes showed lower phase DLs. The results are explained by considering the waveforms that would occur at the outputs of the auditory filters in response to these stimuli.
Normative thresholds in the 8- to 20-kHz range as a function of age
Authors: Stelmachowicz Patricia G. , Beauchaine Kathryn A. , Kalberer Ann , Jesteadt Walt
Published: October 2005

Using a prototype high-frequency audiometer, auditory thresholds in the 8- to 20-kHz range were obtained from 240 subjects ranging in age from 10–60 years. These measurements were obtained in interest of developing a normative database for frequencies above 8 kHz, and to evaluate intersubject variability as a function of age. An analysis of variance (ANOVA) revealed significant effects of frequency, age, and sex, and a significant frequency-by-age interaction. The largest changes in sensitivity with age occurred between 40 to 59 years. Below approximately 15 kHz, the intersubject variability of threshold estimates increased as a function of both age and frequency. Further analysis revealed that the age-related changes in variability were related to absolute thresholds rather than to age per se. When data are converted to dB HL (relative to the youngest group tested), the region of maximum hearing loss shifts to lower frequencies with increasing age, and threshold shifts with age are greatest in the 13- to 17-kHz range.
Comparison of the noise attenuation of three audiometric earphones, with additional data on masking near threshold
Authors: Berger E. H. , Killion Mead C.
Published: October 2005

The noise-excluding properties of a standard supra-aural audiometric earphone, a widely used circumaural-supra-aural combination, and an insert earphone sealed to the ear with a vinyl foam eartip were measured in a diffuse-field room complying with ANSI S12.6-1984. Data on attenuation were obtained monaurally with the nontest ear plugged and muffed. Results for the supra-aural earphones generally agreed well with previously reported measurements. A broadband masking noise was used to directly test the ANSI S3.1-1977 permissible background noise levels for measuring to audiometric zero using standard audiometric earphones. This ‘‘ANSI noise’’ raised the average thresholds of 15 normal-hearing test subjects by 3 to 5 dB at the octave frequencies from 500 to 4000 Hz. With a noise conforming to the less stringent OSHA-1983 regulation, average thresholds were elevated 9 to 17 dB. An ‘‘ENT office noise’’ with an overall sound level of 54 dBA raised average thresholds even further, by as much as 29 dB at 500 Hz. Use of the circumaural system in the office noise limited the threshold elevation to 11, 5, 2, and 0 dB at the four octave frequencies tested. With the fully (‘‘deeply’’) inserted foam eartips, the threshold elevation in the simulated office noise was 2 dB or less at all test frequencies. Actual threshold elevations agreed closely with predictions based on a critical ratio calculation utilizing measured sound field noise levels and measured earphone attenuation values.
Parametric generalized Gaussian density estimation
Authors: Varanasi Mahesh K. , Aazhang Behnaam
Published: October 2005

The primary objective of this paper is to compare the large-sample as well as the small-sample properties of different methods for estimating the parameters of a three-parameter generalized Gaussian distribution. Three estimators, namely, the moment method (MM), the maximum-likelihood (ML), and the moment/Newton-step (MNS) estimators, are considered. The applicability of general asymptotic optimality results of the efficient ML and MNS estimation techniques is studied in the generalized Gaussian context. The asymptotic normal distributions of the estimators are obtained. The asymptotic relative superiority of the ML estimator or its variant, the MNS estimator, over the moment method is studied in terms of asymptotic relative efficiency. Based on this study, it is concluded that deviations from normality in the underlying distribution of the data necessitate the use of the efficient ML or MNS methods. In the small-sample case, a detailed comparative study of the estimators is made possible by extensive Monte Carlo simulations. From this study, it is concluded that the maximum-likelihood method is found to be significantly superior for heavy-tailed distributions. In a region of the parameter space corresponding to the vicinity of the Gaussian distribution, the moment method compares well with the other methods. Further, the MNS estimator is shown to perform best for light-tailed distributions. The simulation results are shown to lend support to analytically derived asymptotic results for each of the methods.
Line mobilities of infinite plates
Authors: Ljunggren Sten
Published: October 2005

Analytical solutions are presented for the input mobilities of an isotropic infinite plate with no fluid load. An infinitely long, massless beam is assumed to excite one of the faces of the plate at a fairly low frequency. The plate is described by means of the general equations of motion for three-dimensional elastic bodies, which leads to solutions for the plate that beside bending, longitudinal, and shear waves also incorporate low-frequency Lamb and Love modes. It is shown that the expression for the mobility due to a shear wave excited by an in-line force is similar to that of the mobility due to the longitudinal wave excited by a horizontal force; the only difference is that the shear wave speed is inserted instead of the longitudinal wave speed. It is also shown that, in the case of excitation with a vertical or a horizontal force, the mobilities with respect to the longitudinal waves are much smaller than those connected with the bending waves. An interesting conclusion is that the influence of the Lamb and Love modes is, in general, less important than in the case of point excitation.
A higher-order parabolic equation for wave propagation in an ocean overlying an elastic bottom
Authors: Collins Michael D.
Published: October 2005

A higher-order elastic parabolic equation (HEPE) is derived for wave propagation in depth-dependent and weakly range-dependent fluid/solid media. Galerkin’s method is used to discretize the depth operators in the HEPE within layers in which depth variations in the Lamé constants and density are continuous. Discontinuities in material properties are handled with centered differences for the interface conditions between layers. The numerical solution of the HEPE also involves the method of alternating directions and Crank–Nicolson integration. The HEPE is applied to underwater wave propagation problems involving a water column over an elastic bottom including a weakly range-dependent problem. The accuracy of the HEPE is demonstrated with benchmark calculations.
Simple approximate formulas for backscattering of sound by spherical and elongated objects
Authors: Stanton Timothy K.
Published: October 2005

The scattering of sound by objects is a complex process and is dealt with both analytically and numerically. Regardless of method, calculation of the exact scattered field is quite laborious and may require much computer time as well as human time to program the computer. In order to simplify calculations of the backscattering by a fluid sphere, Johnson combined low- and high-frequency limits in a heuristic manner to obtain a simple closed-form solution (named the ‘‘high-pass’’ solution) [J. Acoust. Soc. Am. 61, 375–377 (1977)]. In this present article, his approach is refined and generalized so that the backscattering by bodies of other shapes can be described. The general model is evaluated for the sphere, prolate spheroid, straight finite cylinder, and bent finite cylinder. The scattering geometries for these specific examples are limited to normal and near-normal incidence for the elongated objects, although the general model can accommodate other geometries provided the exact solutions exist. Comparisons are made of the scattering of these objects using both modal series solutions and the high-pass solutions for fluid, elastic, rigid and fixed, and gaseous materials over a wide range of frequencies. The high-pass solutions are formulated in a general way so as to describe scattering by idealized objects where their shape is simple (i.e., sphere, spheroid, etc.) and their material is lossless, and by nonideal more realistic objects where their shape may be irregular and their material lossy. Calculations of both ‘‘ideal’’ models and ‘‘nonideal’’ models are compared with the modal solutions by using converged modal series for the ideal cases and truncated (keeping just the first two terms) as approximations for (irregular only) nonideal cases. In addition to the numerical simulations, some of the high-pass solutions and corresponding modal series solutions are compared with data involving ideal objects (machined Dural) and nonideal objects (marine organisms: shrimp, euphausiids, and fish). The numerical and experimental results show promise for use of the high-pass models for quick estimates of backscattered sound of many types of objects.
On the losses due to storm bubbles in oceanic sound transmission
Authors: Weston David E.
Published: October 2005

The attenuation due to shallow wind-generated bubbles is reviewed for oceanic sound propagation at low-kHz frequencies. One contribution comes from the near-resonant bubbles, where the effect of the damping is discussed. Another contribution comes from the thermal losses in the mass of small bubbles near the peak in the bubble size spectrum. Both are greatly affected by the surface decoupling or Lloyds mirror phenomenon. Second-order effects such as refraction and saturation can be important, but tend to be controlled by the surface decoupling. Mutual interference effects should also be considered more generally and should really be combined in a theory incorporating surface roughness. Experimentally, the bubble attenuation is difficult to disentangle from surface-wave scattering and also from fish attenuation; in fact, it is suggested that the bubble effect is the least certain of the three.
Laser Doppler anemometry detection of hydroacoustic particle velocity
Authors: Dubbelday Pieter S. , Schau H. C.
Published: October 2005

The method of laser Doppler anemometry is applied to the measurement of particle velocity in a hydroacoustic field. The field is created in an Underwater Sound Reference Detachment-type G19 calibrator. The anemometer is operated in the forward-scattering mode. Seeding particles of varying material and size are dispersed in the acoustic medium (water). The laser Doppler anemometry results are compared with the values for the velocity obtained from the pressure gradient measured by a hydrophone.
Peak-picking fundamental period estimation for hearing prostheses
Authors: Howard David M.
Published: October 2005

A real-time peak-picking fundamental period estimation device is described which is used in advanced hearing prostheses for the totally and profoundly deafened. The operation of the peak picker is compared with three well-established fundamental frequency estimation techniques: the electrolaryngograph, which is used as a ‘‘standard,’’ hardware implementations of the cepstral technique, and the Gold/Rabiner parallel processing algorithm. These comparisons illustrate and highlight some of the important advantages and disadvantages that characterize the operation of these techniques. The special requirements of the hearing prostheses are discussed with respect to the operation of each device, and the choice of the peak picker is found to be felicitous in this application.
Respiratory response to a decrease in velopharyngeal resistance
Authors: Warren Donald W. , Morr Kathleen E. , Putnam Rochet Anne , Dalston Rodger M.
Published: October 2005

Individuals with congenital velopharyngeal impairment generally maintain adequate levels of intraoral pressures during consonant production by increasing respiratory effort. The purpose of the present study was to determine if normal individuals respond to a decrease in velopharyngeal resistance in a similar way. The velar mechanism was perturbed by having subjects voluntarily lower the soft palate during a series of words involving plosive consonants. The pressure-flow technique was used to measure oral pressures, calculate velopharyngeal orifice resistance, and estimate velopharyngeal orifice area. Inductive plethysmography was used to measure breathing volumes associated with the words. The data indicate that, in most instances, intraoral pressure remained at appropriate levels (>3.0 cm H2O) after velar lowering. Speech breathing volume did not change during inspiration, but increased during speech expiration when the velopharyngeal port was open. The difference was statistically significant (p<0.01). Duration of the utterance did not change across conditions. A mechanical model was then used to determine how intraoral pressure would be affected by simulating the same conditions in a passive system. The modeling data revealed that pressure would drop threefold. It was concluded that increased respiratory volumes tend to stabilize intraoral pressure when vocal tract resistance is experimentally reduced.
Temporal gaps in noise and sinusoids
Authors: Green David M. , Forrest Timothy G.
Published: October 2005

The ability of human observers to detect partially filled or completely silent intervals (gaps) was measured using a variety of different waveforms. The slopes of the psychometric functions for gap detection using broadband noise are dependent upon the amount of noise remaining during the gap. For completely silent intervals, the psychometric function covers a range of only 2 ms, but the psychometric functions for partially filled intervals are less steep. The detection of gaps in narrow-band noise (surrounded by complementary band-reject maskers) is strongly influenced by the signal-to-noise ratio. The signal bandwidth and center frequency also influence detectability. Gap detection improved as signal bandwidth increased, and detection improved when signal bands containing gaps were centered at higher frequencies. Detection of gaps in single components of a 21-component, equal-amplitude complex also showed lower thresholds as the frequency of the component containing the gap increased. Increasing the number of components in the complex that contained the gap improved the detectability of the gap, more so when the gaps were all presented at the same time (synchronous condition). Uncertainty about the temporal position of the gap within the observation interval made the gap more difficult to detect. This temporal uncertainty effect occurred for gaps in broadband noise, in narrow-band noise, and in sinusoidal waveforms.
Analysis of a synthetic Tadoma system as a multidimensional tactile display
Authors: Tan Hong Z. , Rabinowitz William M. , Durlach Nathaniel I.
Published: October 2005

The Tadoma method is a means of speech reception based on tactile monitoring of the articulatory process. A ‘‘synthetic’’ Tadoma system, involving an artificial face with six facial actions, has been developed as a first-order approximation to the natural Tadoma system. Experiments were conducted to explore the information-transmission characteristics of the synthetic Tadoma system in terms of the four facial movements it incorporates: upper lip in–out, lower lip in–out, lower lip up–down, and jaw up–down movements. Discrimination experiments showed that the just-noticeable difference associated with each movement is about 9% of the reference displacement. One-dimensional (1-D) absolute identification experiments produced, on the average, 1.6 bits of information transfer. Four-dimensional (4-D) identification experiments produced information transfers in the range of 3–4 bits. Of the four dimensions considered, performance on the lower lip up–down movement was most affected, and performance on the jaw up–down movement was least affected, by simultaneous roving movements on the other dimensions. As a result of the interaction among the movement channels, the sum of the 1-D information transfers exceeds the 4-D information transfer. However, the sum of the 1-D information transfers obtained from tests with roving parameters is approximately equal to the 4-D information transfer (possibly exemplifying a ‘‘generalized information-transfer additivity law’’). In general, both the discrimination and identification results appear unexceptional and, hence, the reception of facial movement information by itself does not appear to account for the extraordinary success of the Tadoma method.
Stereausis: Binaural processing without neural delays
Authors: Shamma Shihab A. , Shen Naiming , Gopalaswamy Preetham
Published: October 2005

A neural network model is proposed for the binaural processing of interaural-time and level cues. The two-dimensional network measures interaural differences by detecting the spatial disparities between the instantaneous outputs of the two ears. The network requires no neural delay lines to generate such attributes of binaural hearing as the lateralization of all frequencies, and the detection and enhancement of noisy signals. It achieves this by comparing systematically, at various horizontal shifts, the spatiotemporal responses of the tonotopically ordered array of auditory-nerve fibers. An alternative view of the network operation is that it computes approximately the cross correlation between the responses of the two cochleas by combining an ipsilateral input at a given characteristic frequency (CF) with contralateral inputs from locally off-CF locations. Thus the network utilizes the delays already present in the traveling waves of the basilar membrane to extract the correlation function. Simulations of the network operation with various signals are presented as are comparisons to computational schemes suggested for stereopsis in vision. Physiological arguments in support of this scheme are also discussed.
Shadowed and simple reaction times in stutterers and nonstutterers
Authors: Harbison Dan C. , Porter Robert J. , Tobey Emily A.
Published: October 2005

Stutterers may experience difficulties in preparing and executing responses. This study investigated these possibilities as well as the possibility that stutterers may experience difficulty in the selection of responses. Two reaction-time tasks were investigated: a shadowing response in which speakers exactly repeated vowel sequences they heard, and a simple response in which speakers said [u] regardless of the identity of the vowel stimulus. Two groups of six adult male subjects, stutterers and nonstutterers, participated. Stimuli consisted of vowel–vowel ‘‘syllables’’ whose initial duration (response foreperiod) was randomly varied from 500 to 1500 ms. Electromyographic (EMG) and acoustic measures were obtained for each response condition. The EMG response latencies, acoustic response latencies, and execution times (EMG latency less the acoustic response latency) were examined for the fluent responses. Results indicated stutterers were, on average, 34 ms slower on acoustic responses than nonstutterers regardless of the task or foreperiod. However, stutterers’ and nonstutterers’ EMG latencies were not significantly different. Further analysis indicated that the overall slower acoustic responses of stutterers were accounted for almost entirely by longer execution times. Stutterers’ difficulties thus appear to lie after response initiation suggesting they have problems in coordination of gestures during execution of fluent responses.
Auditive and cognitive factors in speech perception by elderly listeners. I: Development of test battery
Authors: van Rooij J. C. G. M. , Plomp R. , Orlebeke J. F.
Published: October 2005

This study compares performance of 24 young normal-hearing (aged 18–28 years) and 24 elderly (aged 61–85 years) listeners on auditive (sensitivity, frequency selectivity, and temporal resolution), cognitive (memory performance, processing speed, and divided attention ability), and speech perception tests (at the phoneme, spondee, and sentence level). Its principal aim is to assess whether the tests selected yield meaningful results. The results obtained will be used to reduce the test battery in order to be manageable in a second study on a much larger number of elderly listeners. The relationships between the tests are explored by multivariate statistical methods. The results show that: (a) in young listeners, individual differences in speech perception performance are remarkably small resulting in low correlations between the tests, while in the elderly tests of phoneme, spondee, and sentence perception overlap considerably; (b) speech perception in the elderly seems to be largely determined by hearing loss at the higher frequencies, whereas the effects of other auditive and cognitive factors seem to be relatively small or absent; and (c) performance in the elderly is only partly correlated with age.
Active noise control in ducts: Some physical insights
Authors: Snyder Scott D. , Hansen Colin H.
Published: October 2005

The mechanisms of active noise control in a duct are examined. Acoustical measurements are used to determine directly the acoustic power flow associated with both primary and secondary sources as a function of secondary to primary source strength ratio and volume velocity relative phase angles. A complete analytical model is also developed which allows calculation of individual source power flows and total downstream power flow as a function of source strengths and relative phase angles for finite size sources. It is evaluated for monopole and dual secondary source arrangements, but can be extended easily to any number of secondary sources. The model considers a finite size primary source in the plane of the duct cross section and evaluates the effect that the secondary sources have on the primary source power output. Measurements of individual source output powers and total downstream acoustic powers agree well with theoretical predictions. It is demonstrated that, for the monopole system, sound attenuation is achieved primarily by suppression of the primary source acoustic power output, with a little remaining power being absorbed by the secondary source. For the dual secondary source system, it is shown that the power is primarily absorbed by the secondary sources, but that, at phase and amplitude values slightly different to optimum, noise reduction is achieved by a combination of energy absorption and primary source power suppression. The analysis also demonstrates the dependence of the achievable noise reduction on secondary source size and location with respect to the primary source.
Transfer function phase and truncated impulse response
Authors: Tohyama Mikio , Lyon Richard H.
Published: October 2005

Transfer function (TF) phase can be analyzed from the impulse response in a vibrating system. This letter analyzes the truncated impulse response of such a system and its phase characteristic by using a simple two-pole model. The estimated phase turns out to be highly sensitive to the window length of the truncated impulse response used for phase analysis. The minimum-phase behavior of a TF for example, is changed into a nonminimum-phase characteristic due to the truncation. An exponential window is recommended for the data analysis of vibrating systems in order to reduce the effect of truncation on the phase.
Sound propagation in vibrationally excited N2/CO and H2/He/CO gas mixtures
Authors: Ruppel Timothy H. , Shields F. Douglas
Published: October 2005

Measurements of the resonant reverberation of sound in a tube containing N2/H2, N2/He, N2/CH4, and N2/H2O mixtures have shown an amplification of the sound following a rapid excitation of the gas by an electric discharge [F. D. Shields and L. D. Lafleur, J. Acoust. Soc. Am. 83, 2186–2189 (1988)]. This effect has been named SACER (sound amplification from controlled excitation reactions). This paper reports similar measurements in N2/CO and H2/He/CO mixtures. It has been possible in the past to determine vibrational relaxation times and relaxation times for conduction of translational and vibrational energy to the tube walls from the changes in the observed translational temperature of the gas following the electric discharge. In the work reported here, these rates have been confirmed by direct measurement of the decay times of the CO infrared emission.
Structural power-flow analysis using a mobility approach of an L-shaped plate
Authors: Cuschieri J. M.
Published: October 2005

In the analysis of the vibration response and structure-borne vibration transmission between elements of a complex structure, statistical-energy analysis (SEA) or finite-element analysis (FEA) are generally used. However, an alternative method is to use vibrational power-flow techniques that can be especially useful in the midfrequencies between the optimum frequency regimes for FEA and SEA. Mobility power-flow analysis has, in general, been used for one-dimensional beamlike coupled structures or for point-coupled structures. In this paper, the power-flow technique is extended to two-dimensional platelike coupled structures joined along a common edge. Because of the inherent advantages in using this power-flow approach, frequency or spatial averaging is not required, and thus the resonant modal response of the coupled structure is determined. The mobility power-flow results are compared to results obtained using FEA and SEA. The agreement with FEA results is good at low frequencies. However, the power-flow technique has an improved computational efficiency as the frequency increases. Compared to the SEA results, the power-flow results show a closer representation of the actual modal response of the coupled structure.
A Poynting vector formulation for thin shells and plates, and its application to structural intensity analysis and source localization. Part I: Theory
Authors: Romano Anthony J. , Abraham Phillip B. , Williams Earl G.
Published: October 2005

This paper deals with a formulation of the Poynting vector (structural intensity) for thin shells and plates, and its application to structural intensity analysis and source localization. The procedure begins with the insertion of a Taylor series expansion of the displacement components (about the middle surface of the shell) directly into the three-dimensional representation of the Poynting vector. From this representation, an average power flow per unit length, or equivalently an intensity resultant, is derived, whose form permits expressibility in terms of force and moment resultants. The corresponding equations of continuity for energy are derived for both body and surface forces, and the time integral of the net outflow is developed, yielding a technique for source localization. This technique offers a method for the determination of the structural intensity of thin, elastic shells and plates, and is successful for source localization.
Application of the articulation index to the speech recognition of normal and impaired listeners wearing hearing protection
Authors: Wilde Graham , Humes Larry E.
Published: October 2005

The present study examined the application of the articulation index (AI) as a predictor of the speech-recognition performance of normal and hearing-impaired listeners with and without hearing protection. The speech-recognition scores of 12 normal and 12 hearing-impaired subjects were measured for a wide range of conditions designed to be representative of those in the workplace. Conditions included testing in quiet, in two types of background noise (white versus speech spectrum), at three signal-to-noise ratios (+5, 0, −5 dB), and in three conditions of protection (unprotected, earplugs, earmuffs). The mean results for all 21 listening conditions and both groups of subjects were accurately described by the AI. Moreover, a single transfer-function relating performance to the AI could describe all the data from both groups.
Intensity discrimination as the driving force for loudness. Application to pure tones in quiet
Authors: Hellman William S. , Hellman Rhona P.
Published: October 2005

Loudness functions and their associated neural-count functions are derived for steady-state tones at 250 and 1000 Hz from measurements of intensity discrimination obtained under gated and continuous conditions. The calculations are based on a multichannel generalization of the McGill–Goldberg counting model [J. Acoust. Soc. Am. 44, 576–581 (1968)]. Using the data for just noticeable differences (jnd) in intensity as input, the generalized version gives an integral relation between the neural-count function N(x) and the intensity-jnd function, where x=I/I0 and I0 is the reference intensity. Loudness functions are generated through the prescription L(x)=AN(x)−B. To determine how the detailed shapes of the intensity-jnd functions affect the form of the loudness function within the model, integration was performed over the intensity-jnd functions with and without a power-function approximation. Over a range of intensity levels from 20–95 dB, the best agreement between the calculated and measured loudness functions is obtained from the unaltered intensity-jnd functions. Consistent with psychophysical evidence and several models of intensity coding, the results predict that the output of the whole auditory nerve is unnecessary to maintain the large dynamic range observed for loudness and intensity discrimination.