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Top 20 Most Read Articles
November 2006
The 20 articles with the most full-text downloads during the month, in descending order.
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Acoustic response from adherent targeted contrast agents J. Acoust. Soc. Am. Volume 120, Issue 6, pp. EL63-EL69 (2006); (7 pages) Online Publication Date: 23 Oct 2006
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In ultrasonic molecular imaging, encapsulated micron-sized gas bubbles are tethered to a blood vessel wall by targeting ligands. A challenging problem is to detect the echoes from adherent microbubbles and distinguish them from echoes from nonadherent agents and tissue. Echoes from adherent contrast agents are observed to include a high amplitude at the fundamental frequency, and significantly different spectral shape compared with free agents (p<0.0003). Mechanisms for the observed acoustical difference and potential techniques to utilize these differences for molecular imaging are proposed.
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A short history of bad acoustics J. Acoust. Soc. Am. Volume 120, Issue 4, pp. 1807-1815 (2006); (9 pages)
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Every branch of science attracts its share of cranks and pseudoscientists, and acoustics has been no exception. A brief survey of those who touched on acoustics is given with quotations from the more interesting or egregious examples. A contrast is drawn between the nineteenth century contrarian’s quarrel with particular theories and the modern new age wholesale rejection of theory. This world-view is traced back to the later scientific writings of Goethe. Examples of pseudoscience applied to biomedical acoustics, architectural acoustics, and audio reproduction are given.
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J. Acoust. Soc. Am. Volume 120, Issue 5, pp. 2908-2925 (2006); (18 pages)
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Speech recognition by normal-hearing listeners improves as a function of the number of spectral channels when tested with a noiseband vocoder simulating cochlear implant signal processing. Speech recognition by the best cochlear implant users, however, saturates around eight channels and does not improve when more electrodes are activated, presumably due to reduced frequency selectivity caused by channel interactions. Listeners with sensorineural hearing loss may also have reduced frequency selectivity due to cochlear damage and the resulting reduction in the nonlinear cochlear mechanisms. The present study investigates whether such a limitation in spectral information transmission would be observed with hearing-impaired listeners, similar to implant users. To test the hypothesis, hearing-impaired subjects were selected from a population of patients with moderate hearing loss of cochlear origin, where the frequency selectivity would be expected to be poorer compared to normal hearing. Hearing-impaired subjects were tested for vowel and consonant recognition in steady-state background noise of varying levels using a noiseband vocoder and as a function of the number of spectral channels. For comparison, normal-hearing subjects were tested with the same stimuli at different presentation levels. In quiet and low background noise, performance by normal-hearing and hearing-impaired subjects was similar. In higher background noise, performance by hearing-impaired subjects saturated around eight channels, while performance by normal-hearing subjects continued to increase up to 12–16 channels with vowels, and 10–12 channels with consonants. A similar trend was observed for most of the presentation levels at which the normal-hearing subjects were tested. Therefore, it is unlikely that the effects observed with hearing-impaired subjects were due to insufficient audibility or high presentation levels. Consequently, the results with hearing-impaired subjects were similar to previous results obtained with implant users, but only for background noise conditions.
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Synthesis of audio spectra using a diffraction model J. Acoust. Soc. Am. Volume 120, Issue 6, pp. EL70-EL77 (2006); (8 pages) Online Publication Date: 03 Nov 2006
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It is shown that the intensity variations of an audio signal in the frequency domain can be obtained by using a mathematical function containing a series of weighted complex Bessel functions. With proper choice of values for two parameters, this function can transform an input spectrum of discrete frequencies of unit intensity into the known spectra of different musical instruments. Specific examples of musical instruments are considered for evaluating the performance of this method. It is found that this function yields musical spectra with a good degree of accuracy.
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Analysis, synthesis, and perception of voice quality variations among female and male talkers J. Acoust. Soc. Am. Volume 87, Issue 2, pp. 820-857 (1990); (38 pages)
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Voice quality variations include a set of voicing sound source modifications ranging from laryngealized to normal to breathy phonation. Analysis of reiterant imitations of two sentences by ten female and six male talkers has shown that the potential acoustic cues to this type of voice quality variation include: (1) increases to the relative amplitude of the fundamental frequency component as open quotient increases; (2) increases to the amount of aspiration noise that replaces higher frequency harmonics as the arytenoids become more separated; (3) increases to lower formant bandwidths; and (4) introduction of extra pole zeros in the vocal‐tract transfer function associated with tracheal coupling. Perceptual validation of the relative importance of these cues for signaling a breathy voice quality has been accomplished using a new voicing source model for synthesis of more natural male and female voices. The new formant synthesizer, KLSYN88, is fully documented here. Results of the perception study indicate that, contrary to previous research which emphasizes the importance of increased amplitude of the fundamental component, aspiration noise is perceptually most important. Without its presence, increases to the fundamental component may induce the sensation of nasality in a high‐pitched voice. Further results of the acoustic analysis include the observations that: (1) over the course of a sentence, the acoustic manifestations of breathiness vary considerably—tending to increase for unstressed syllables, in utterance‐final syllables, and at the margins of voiceless consonants; (2) on average, females are more breathy than males, but there are very large differences between subjects within each gender; (3) many utterances appear to end in a ‘‘breathy‐laryngealized’’ type of vibration; and (4) diplophonic irregularities in the timing of glottal periods occur frequently, especially at the end of an utterance. Diplophonia and other deviations from perfect periodicity may be important aspects of naturalness in synthesis. |
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J. Acoust. Soc. Am. Volume 120, Issue 5, pp. 2425-2436 (2006); (12 pages)
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This paper studies the reflection and transmission of plane elastic waves at interfaces in fluid-saturated poroviscoelastic media in which the solid matrix is composed of two weakly coupled solids. The analysis of this problem, not formally performed before, is based on a theory recently developed by some of the authors, which allows us to derive expressions for the reflection and transmission coefficients at a plane interface within this kind of media and their relationship with the energy flux (Umov-Poynting) vector. The results of the present derivation were applied to study the energy splitting that takes place when a plane fast compressional wave strikes obliquely an interface defined by a change in ice content within a sample of water saturated partially frozen sandstone. The numerical results show wave mode conversions from fast to slow compressional and shear waves, with maximum energy conversion on the order of 20% from fast to slow wave modes near the critical angle. This phenomenon was observed at frequencies lying from the seismic to the ultrasonic range, showing that the role of the slow waves must be taken into account when considering wave propagation in this type of media.
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Acoustic characteristics of American English vowels J. Acoust. Soc. Am. Volume 97, Issue 5, pp. 3099-3111 (1995); (13 pages)
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The purpose of this study was to replicate and extend the classic study of vowel acoustics by Peterson and Barney (PB) [J. Acoust. Soc. Am. 24, 175–184 (1952)]. Recordings were made of 45 men, 48 women, and 46 children producing the vowels /i,i,e,ε,æ,a,open‘‘oh’’,o,u,u,Λ,hook backward‘‘eh’’/ in h–V–d syllables. Formant contours for F1–F4 were measured from LPC spectra using a custom interactive editing tool. For comparison with the PB data, formant patterns were sampled at a time that was judged by visual inspection to be maximally steady. Analysis of the formant data shows numerous differences between the present data and those of PB, both in terms of average frequencies of F1 and F2, and the degree of overlap among adjacent vowels. As with the original study, listening tests showed that the signals were nearly always identified as the vowel intended by the talker. Discriminant analysis showed that the vowels were more poorly separated than the PB data based on a static sample of the formant pattern. However, the vowels can be separated with a high degree of accuracy if duration and spectral change information is included. |
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The acoustic signature of bubbles fragmenting in sheared flow J. Acoust. Soc. Am. Volume 120, Issue 6, pp. EL84-EL89 (2006); (6 pages) Online Publication Date: 09 Nov 2006
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Measurements of the sound of bubbles fragmenting in fluid shear are presented and analyzed. The frequency, amplitude, and decay rate of the acoustic emissions from 1.8-mm-radius bubbles fragmenting between opposed fluid jets have been determined. A broad band of frequencies (1.8 to 30 kHz) is observed with peak pressure amplitudes in the range of 0.03 to 2 Pa. While the peak pressure amplitudes show no significant scaling with frequency, the frequency dependence of the decay rates is consistent with the sum of thermal and acoustic radiation losses.
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New speech harmonic structure measure and its applications to speech processing J. Acoust. Soc. Am. Volume 120, Issue 5, pp. 2938-2949 (2006); (12 pages)
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The harmonic structure can be easily recognized in time-frequency representation of speech signals in adverse environment. The harmonicity is a measure of the completeness of a harmonic structure. This paper presents a new harmonic structure measure that extends the conventional harmonicity to a set of harmonicities. They are expressed in terms of the grid harmonicity, the temporal harmonicity, the segment-spectral harmonicity, and the segmental harmonicity. The grid harmonicity measures the completeness of individual harmonics in each frame. The grid harmonicities in a frame are summed up to form a temporal harmonicity for representing the strength of harmonicity. The segment-spectral harmonicity, computed by summing specific grid harmonicity over a segment, evaluates the integrity of individual harmonics across a segment. The segmental harmonicity evaluates the total strength of harmonic structure within a segment. This set of harmonicities is available for a systematic analysis of the harmonic structure and effective to several speech processing tasks. The applications to speech distortion analysis, robust fundamental frequency estimation, robust voicing detection, and speech enhancement are demonstrated.
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Scattering of antiplane shear waves by layered circular elastic cylinder J. Acoust. Soc. Am. Volume 115, Issue 2, pp. 515-522 (2004); (8 pages) Online Publication Date: 30 Jan 2004
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An exact analytical solution for the scattering of antiplane elastic waves by a layered elastic circular cylinder is obtained. The solution and its degenerate cases are compared with other simpler models of circular cylindrical scatterers. The effects of the geometrical and physical properties of the interphase are studied. Numerical results confirm the existence of a resonance mode in which the scatterer’s core undergoes a rigid-body motion when the outer layer of the scatterer is very compliant. This resonance mode has been attributed [Liu et al., Science 289, 1734 (2000)] to a new mechanism for the band gap formed in the extremely low frequency range for phononic crystals made of layered spherical scatterers. Numerical results also show the existence of a similar resonance mode when the outer layer of the scatterer has very high mass density. © 2004 Acoustical Society of America. |
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New Fellows of the Acoustical Society of America J. Acoust. Soc. Am. Volume 120, Issue 5, pp. 2387-2388 (2006); (2 pages)
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Advantages of the Hilbert Huang transform for marine mammals signals analysis J. Acoust. Soc. Am. Volume 120, Issue 5, pp. 2965-2973 (2006); (9 pages)
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While marine mammals emit variant signals (in time and frequency), the Fourier spectrogram appears to be the most widely used spectral estimator. In certain cases, this approach is suboptimal, particularly for odontocete click analysis and when the signal-to-noise ratio varies during the continuous recordings. We introduce the Hilbert Huang transform (HHT) as an efficient means for analysis of bioacoustical signals. To evaluate this method, we compare results obtained from three time-frequency representations: the Fourier spectrogram, the wavelet transform, and the Hilbert Huang transform. The results show that HHT is a viable alternative to the wavelet transform. The chosen examples illustrate certain advantages. (1) This method requires the calculation of the Hilbert transform; the time-frequency resolution is not restricted by the uncertainty principle; the frequency resolution is finer than with the Fourier spectrogram. (2) The original signal decomposition into successive modes is complete. If we were to multiply some of these modes, this would contribute to attenuate the presence of noise in the original signal and to being able to select pertinent information. (3) Frequency evolution for each mode can be analyzed as one-dimensional (1D) signal. We not need a complex 2D post-treatment as is usually required for feature extraction.
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J. Acoust. Soc. Am. Volume 120, Issue 4, pp. 2366-2379 (2006); (14 pages)
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The widespread use of powerful, low-frequency air-gun pulses for seismic seabed exploration has raised concern about their potential negative effects on marine wildlife. Here, we quantify the sound exposure levels recorded on acoustic tags attached to eight sperm whales at ranges between 1.4 and 12.6 km from controlled air-gun array sources operated in the Gulf of Mexico. Due to multipath propagation, the animals were exposed to multiple sound pulses during each firing of the array with received levels of analyzed pulses falling between 131–167 dB re. 1 μPa (pp) [111–147 dB re. 1 μPa (rms) and 100–135 dB re. 1 μPa2 s] after compensation for hearing sensitivity using the M-weighting. Received levels varied widely with range and depth of the exposed animal precluding reliable estimation of exposure zones based on simple geometric spreading laws. When whales were close to the surface, the first arrivals of air-gun pulses contained most energy between 0.3 and 3 kHz, a frequency range well beyond the normal frequencies of interest in seismic exploration. Therefore air-gun arrays can generate significant sound energy at frequencies many octaves higher than the frequencies of interest for seismic exploration, which increases concern of the potential impact on odontocetes with poor low frequency hearing.
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On the sound field of a circular membrane in free space and an infinite baffle J. Acoust. Soc. Am. Volume 120, Issue 5, pp. 2460-2477 (2006); (18 pages)
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An enhanced method for calculating the radiation characteristics of a tensioned circular membrane in free space is presented using an analytical solution to the infinite integral in the free-space Green’s function in cylindrical coordinates. This enables direct calculation of the surface pressure series coefficients by equating the coefficients of the resulting Bessel series in a set of simultaneous equations. Eliminating both numerical integration and least-squares minimization improves calculation speed and accuracy. An infinite baffle is introduced to provide an indication of what the theoretical limit of the bass performance would be using a very large enclosure. Furthermore, analytical solutions to the pressure field integrals are presented. A force transmission coefficient is introduced, which is the ratio of the total radiation impedance to the motional impedance. The motional, radiation, and diaphragm impedances of the damped membrane are calculated, together with the near- and far-field pressure responses and efficiency. A comparison is made between the on-axis response (without damping) calculated using this method and using a finite element model. It is demonstrated that good correlation between the two calculation methods can be achieved provided the elements are small enough and a sufficiently large model is used at the frequency extremes.
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The partial-wave expansion for scattering in waveguides J. Acoust. Soc. Am. Volume 120, Issue 5, pp. 2518-2525 (2006); (8 pages)
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The scattering of acoustic waves by objects located inside a waveguide is discussed, assuming that the scattering amplitude for the object in an extended uniform medium is known. The scattering process is described by using an expansion of the scattering amplitude in terms of spherical harmonics. An appropriate multipole decomposition of the waveguide Green’s function is developed and the effective scattering amplitude in the waveguide is obtained. An important property of the effective scattering amplitude, the generalized optical theorem, is obtained and its implications for scattering in a waveguide are discussed. The scattering problem is formulated entirely and explicitly in terms of the waveguide Green’s functions, which makes this approach very flexible in regard to the choice of the incident field. It also establishes the connection between propagation and scattering and allows for the independent computation of the propagation and scattering aspects of the problem. This is the main advantage of using the scattering amplitude in an extended uniform medium as an input. The connection of this work with previous work in scattering in waveguides is discussed.
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Properties of an electrostatic transducer J. Acoust. Soc. Am. Volume 120, Issue 5, pp. 2658-2667 (2006); (10 pages)
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A thin and flexible transducer design for use in air is described. It is fabricated from three or more layers of material to form an electrostatic device with many interesting properties. The new acoustic source has an excellent high-frequency response and can be used as an acoustic radiator over a wide range of frequencies, in both the audible and ultrasonic frequency ranges. The frequency response and directivity are both modeled and compared to theory, where it is demonstrated that the device operates in a manner consistent with a plane piston source.
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Anomalous negative dispersion in bone can result from the interference of fast and slow waves J. Acoust. Soc. Am. Volume 120, Issue 5, pp. EL55-EL61 (2006); (7 pages) Online Publication Date: 09 Oct 2006
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The goal of this work was to show that the apparent negative dispersion of ultrasonic waves propagating in bone can arise from interference between fast and slow longitudinal modes, each exhibiting positive dispersion. Simulations were carried out using two approaches: one based on the Biot-Johnson model and one independent of that model. Results of the simulations are mutually consistent and appear to account for measurements from many laboratories that report that the phase velocity of ultrasonic waves propagating in cancellous bone decreases with increasing frequency (negative dispersion) in about 90% of specimens but increases with frequency in about 10%.
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J. Acoust. Soc. Am. Volume 120, Issue 4, pp. 2328-2339 (2006); (12 pages)
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A finite element model is formulated to study the steady-state vibration response of the anatomy of a whale (Cetacea) submerged in seawater. The anatomy was reconstructed from a combination of two-dimensional (2D) computed tomography (CT) scan images, identification of Hounsfield units with tissue types, and mapping of mechanical properties. A partial differential equation model describes the motion of the tissues within a Lagrangean framework. The computational model was applied to the study of the response of the tissues within the head of a neonate Cuvier’s beaked whale Ziphius cavirostris. The characteristics of the sound stimulus was a continuous wave excitation at 3500 Hz and 180 dB re: 1 μPa received level, incident as a plane wave. We model the beaked whale tissues embedded within a volume of seawater. To account for the finite dimensions of the computational volume, we increased the damping for viscous shear stresses within the water volume, in an attempt to reduce the contribution of waves reflected from the boundaries of the computational box. The mechanical response of the tissues was simulated including: strain amplitude; dissipated power; and pressure. The tissues are not likely to suffer direct mechanical or thermal damage, within the range of parameters tested.
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Control Methods Used in a Study of the Vowels J. Acoust. Soc. Am. Volume 24, Issue 2, pp. 175-184 (1952); (10 pages) Online Publication Date: 29 Jun 2005
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Relationships between a listener's identification of a spoken vowel and its properties as revealed from acoustic measurement of its sound wave have been a subject of study by many investigators. Both the utterance and the identification of a vowel depend upon the language and dialectal backgrounds and the vocal and auditory characteristics of the individuals concerned. The purpose of this paper is to discuss some of the control methods that have been used in the evaluation of these effects in a vowel study program at Bell Telephone Laboratories. The plan of the study, calibration of recording and measuring equipment, and methods for checking the performance of both speakers and listeners are described. The methods are illustrated from results of tests involving some 76 speakers and 70 listeners. |
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Theory of Propagation of Elastic Waves in a Fluid‐Saturated Porous Solid. I. Low‐Frequency Range J. Acoust. Soc. Am. Volume 28, Issue 2, pp. 168-178 (1956); (11 pages) Online Publication Date: 29 Jun 2005
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A theory is developed for the propagation of stress waves in a porous elastic solid containing compressible viscous fluid. The emphasis of the present treatment is on materials where fluid and solid are of comparable densities as for instance in the case of water‐saturated rock. The paper denoted here as Part I is restricted to the lower frequency range where the assumption of Poiseuille flow is valid. The extension to the higher frequencies will be treated in Part II. It is found that the material may be described by four nondimensional parameters and a characteristic frequency. There are two dilatational waves and one rotational wave. The physical interpretation of the result is clarified by treating first the case where the fluid is frictionless. The case of a material containing viscous fluid is then developed and discussed numerically. Phase velocity dispersion curves and attenuation coefficients for the three types of waves are plotted as a function of the frequency for various combinations of the characteristic parameters. |
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