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Journal of the Acoustical Society of America

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Aug 2005

Volume 118, Issue 2, pp. 555-1220

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Correcting the use of ensemble averages in the calculation of harmonics to noise ratios in voice signals

Carlos A. Ferrer, Eduardo González, and María E. Hernández-Díaz

J. Acoust. Soc. Am. Volume 118, Issue 2, pp. 605-607 (2005); (3 pages) | Cited 1 time

Online Publication Date: 04 Aug 2005

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A correcting formula for the estimation of harmonics-to-noise ratios (HNR) based on ensemble-averaging techniques is derived. The original method yields a biased approximation which is more accurate as the number of averaged pulses (N) increases. However, the method treats gradual waveform changes incorrectly as noise, which is worsened for large values of N. The obtained formula allows the use of as few averaged pulses as desired, while allowing the complete removal of the bias from the estimate of HNR.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech

Supplementary notes on the Gaussian beam expansion

Desheng Ding, Xiangjie Tong, and Peizhong He

J. Acoust. Soc. Am. Volume 118, Issue 2, pp. 608-611 (2005); (4 pages) | Cited 4 times

Online Publication Date: 04 Aug 2005

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The letter provides alternatively a simple way of computing the Fresnel field integral, a further extension to the Gaussian-beam expansion. The zeroth-order Bessel function of the first kind is expanded into an approximate sum of Gaussian functions. The field integral is then expressible in terms of these simple functions. The approach is useful in treatment of the field radiation problem for a large and important group of piston sources in acoustics. As examples, the calculation results for the uniform and the simply-supported piston sources are presented, in a good agreement with those evaluated by numerical integration.
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43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.20.Bi Mathematical theory of wave propagation
43.20.El Reflection, refraction, diffraction of acoustic waves

Application of the phase gradient method to the study of the resonances of a water-loaded anisotropic plate

L. Guénégou and O. Lenoir

J. Acoust. Soc. Am. Volume 118, Issue 2, pp. 612-615 (2005); (4 pages)

Online Publication Date: 04 Aug 2005

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The phase gradient method is applied to cubic and orthotropic plates. It consists in simply obtaining the positions and the widths of their frequency and angular resonances from the plots of the frequency and angular derivatives of the phase of the reflection coefficient of the immersed plate. There is a good match with the results obtained from the calculation of the modes of the immersed plate in the corresponding complex planes. Moreover, these two derivatives allow us to obtain frequency and angular quality factors.
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43.20.Ks Standing waves, resonance, normal modes
43.20.Fn Scattering of acoustic waves

Time reversal processing for source location in an urban environment

Donald G. Albert, Lanbo Liu, and Mark L. Moran

J. Acoust. Soc. Am. Volume 118, Issue 2, pp. 616-619 (2005); (4 pages) | Cited 7 times

Online Publication Date: 04 Aug 2005

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A simulation study is conducted to demonstrate in principle that time reversal processing can be used to locate sound sources in an outdoor urban area with many buildings. Acoustic pulse propagation in this environment is simulated using a two-dimensional finite difference time domain (FDTD) computation. Using the simulated time traces from only a few sensors and back propagating them with the FDTD model, the sound energy refocuses in the vicinity of the true source location. This time reversal numerical experiment confirms that using information acquired only at non-line-of-sight locations is sufficient to obtain accurate source locations in a complex urban terrain.
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43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.28.Js Numerical models for outdoor propagation
43.20.El Reflection, refraction, diffraction of acoustic waves
43.50.Vt Topographical and meteorological factors in noise propagation

Transducer hysteresis contributes to “stimulus artifact” in the measurement of click-evoked otoacoustic emissions

Sarosh Kapadia, Mark E. Lutman, and Alan R. Palmer

J. Acoust. Soc. Am. Volume 118, Issue 2, pp. 620-622 (2005); (3 pages) | Cited 2 times

Online Publication Date: 04 Aug 2005

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Click-evoked otoacoustic emissions from the human ear are typically several orders of magnitude smaller than the stimuli that elicit them—a measurement technique that attempts to cancel the stimulus signal from the recorded waveform is therefore typically employed. In practice, an imperfect cancellation of the stimulus is achieved, leaving a “stimulus artifact” that obscures the early part of the emission. Input-output nonlinearities of the transducers used in recording emissions are acknowledged as one source of the stimulus artifact. Here an additional source of this artifact, related to hysteresis in the magnetic “receivers” (loudspeakers) used in such recordings, is identified and discussed.
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43.64.Jb Otoacoustic emissions
43.64.Yp Instruments and methods

Place-pitch discrimination of single- versus dual-electrode stimuli by cochlear implant users

Gail S. Donaldson, Heather A. Kreft, and Leonid Litvak

J. Acoust. Soc. Am. Volume 118, Issue 2, pp. 623-626 (2005); (4 pages) | Cited 49 times

Online Publication Date: 04 Aug 2005

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Simultaneous or near-simultaneous activation of adjacent cochlear implant electrodes can produce pitch percepts intermediate to those produced by each electrode separately, thereby increasing the number of place-pitch steps available to cochlear implant listeners. To estimate how many distinct pitches could be generated with simultaneous dual-electrode stimulation, the present study measured place-pitch discrimination thresholds for single- versus dual-electrode stimuli in users of the Clarion CII device. Discrimination thresholds were expressed as the proportion of current directed to the secondary electrode of the dual-electrode pair. For 16 of 17 electrode pairs tested in six subjects, thresholds ranged from 0.11 to 0.64, suggesting that dual-electrode stimuli can produce 2–9 discriminable pitches between the pitches of single electrodes. Some subjects demonstrated a level effect, with better place-pitch discrimination at higher stimulus levels. Equal loudness was achieved with dual-electrode stimuli at net current levels that were similar to or slightly higher than those for single-electrode stimuli.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Fe Discrimination: intensity and frequency
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