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Top 20 Most Read Articles
June 2010
The 20 articles with the most full-text downloads during the month, in descending order.
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Exploring the benefit of auditory spatial continuity J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL258-EL264 (2010); (7 pages) Online Publication Date: 28 May 2010
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Continuity of spatial location was recently shown to improve the ability to identify and recall a sequence of target digits presented in a mixture of confusable maskers [
Best et al. (2008). Proc. Natl. Acad. Sci. U.S.A. 105, 13174–13178
]. Three follow-up experiments were conducted to explore the basis of this improvement. The results suggest that the benefits of spatial continuity cannot be attributed to (a) the ability to plan where to direct attention in advance; (b) freedom from having to redirect attention across large distances; or (c) the challenge of filtering out signals that are confusable with the target.
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Internal waves as a proposed mechanism for increasing ambient noise in an increasingly acidic ocean J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL235-EL239 (2010); (5 pages) Online Publication Date: 20 May 2010
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The effect on the ambient noise level in shallow water of the ocean growing more acidic is modeled. Because most noise sources are near the surface, high-order acoustic modes are preferentially excited. Linear internal waves, however, can scatter the noise into the low-order, low-loss modes most affected by the changes in acidity. The model uses transport theory to couple the modes and assumes an isotropic distribution for the noise sources. For a scenario typical of the East China Sea, the noise at 3 kHz is predicted to increase by 30%, about one decibel, as the pH decreases from 8.0 to 7.4.
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New Fellows of the Acoustical Society of America J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3858-3858 (2010); (1 page) Online Publication Date: 09 Jun 2010
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J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL240-EL245 (2010); (6 pages) Online Publication Date: 20 May 2010
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In this study, the properties of the scattered acoustic vector fields generated by simple rigid motionless spheres are investigated. Analytical solutions are derived from general acoustic pressure scattering models, and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented. The ability to extract scattered field features is illustrated with measurements obtained from a recent in-air experiment using an anechoic chamber and acoustic intensity probes to measure the scattered acoustic vector field from motionless rigid spheres.
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Measurement of thickness or plate velocity using ambient vibrations J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL252-EL257 (2010); (6 pages) Online Publication Date: 28 May 2010
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Assuming the Green’s function is linear with respect to the boundary conditions, it is demonstrated that flexural waves detected by a point receiver and a circular array of point receivers centered on the previous receiver are proportional regardless location of the source and geometry of the plate. Therefore determination of plate velocity or thickness is done from the measurement of ambient vibrations without using any emitter. Experimental results obtained with a plate of non regular geometry excited with a single transducer or a remote loudspeaker are shown to verify the theoretical approach.
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Sound-field reproduction systems using fixed-directivity loudspeakers J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3590-3601 (2010); (12 pages) Online Publication Date: 09 Jun 2010
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Sound reproduction systems using open arrays of loudspeakers in rooms suffer from degradations due to room reflections. These reflections can be reduced using pre-compensation of the loudspeaker signals, but this requires calibration of the array in the room, and is processor-intensive. This paper examines 3D sound reproduction systems using spherical arrays of fixed-directivity loudspeakers which reduce the sound field radiated outside the array. A generalized form of the simple source formulation and a mode-matching solution are derived for the required loudspeaker weights. The exterior field is derived and expressions for the exterior power and direct to reverberant ratio are derived. The theoretical results and simulations confirm that minimum interference occurs for loudspeakers which have hyper-cardioid polar responses.
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Perception of articulatory dynamics from acoustic signatures J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3717-3728 (2010); (12 pages) Online Publication Date: 09 Jun 2010
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This study investigated the degree to which the articulatory trajectory of the tongue dorsum in the production of a vowel-vowel sequence is perceptually relevant. Previous research has shown that the tongue dorsum takes a path that leads to a pattern of area function change, termed the pivot pattern. In this study, articulatory synthesis was used to generate paths of tongue motion for the production of the vowel sequence /ai/. These paths differed in their curvature, leading to stimuli that conform to the pivot pattern and stimuli that violate it. Participants gave naturalness ratings and discriminated the stimuli. The acoustic properties were also compared to acoustic measurements made on productions of /ai/ by 34 speakers. The curvature of the tongue path and the curvature of the F1-F2 trajectory correlate highly with the naturalness-rating task results, but not the discrimination results. However, the particular way in which constriction location changes, particularly whether the change is discrete or continuous, and the maximal velocity of F2 through the transition, explain the perceptual patterns evident in both perception tasks, as well as the patterns in the observed acoustic data. Consequences of these results for the links between production and perception and the segmentation problem are discussed.
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Environment-specific noise suppression for improved speech intelligibility by cochlear implant users J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3689-3695 (2010); (7 pages) Online Publication Date: 09 Jun 2010
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Attempts to develop noise-suppression algorithms that can significantly improve speech intelligibility in noise by cochlear implant (CI) users have met with limited success. This is partly because algorithms were sought that would work equally well in all listening situations. Accomplishing this has been quite challenging given the variability in the temporal/spectral characteristics of real-world maskers. A different approach is taken in the present study focused on the development of environment-specific noise suppression algorithms. The proposed algorithm selects a subset of the envelope amplitudes for stimulation based on the signal-to-noise ratio (SNR) of each channel. Binary classifiers, trained using data collected from a particular noisy environment, are first used to classify the mixture envelopes of each channel as either target-dominated (SNR ≥ 0 dB) or masker-dominated (SNR<0 dB). Only target-dominated channels are subsequently selected for stimulation. Results with CI listeners indicated substantial improvements (by nearly 44 percentage points at 5 dB SNR) in intelligibility with the proposed algorithm when tested with sentences embedded in three real-world maskers. The present study demonstrated that the environment-specific approach to noise reduction has the potential to restore speech intelligibility in noise to a level near to that attained in quiet.
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Vocal tract adjustments in the high soprano range J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3771-3780 (2010); (10 pages) Online Publication Date: 09 Jun 2010
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Twelve sopranos with different levels of expertise (4 nonexperts, 4 advanced, 4 professionals) sustained pitches from A4 ( ∼ 440 Hz) to their highest pitch (ranging from C6 to D7, i.e., from ∼ 1000 to 2300 Hz). The frequencies of their first two vocal tract resonances (R1 and R2) were measured by broadband excitation at the mouth and compared with the voice harmonics (f0, 2f0, etc). Lip articulation was measured from simultaneous video recordings. Adjustment of R1 near to f0 (R1:f0 tuning) was observed below C6 to D6 ( ∼ 1000–1200 Hz) for both expert and non-expert singers. Experts began this tuning at lower pitches. Some singers combine R2:2f0 adjustment with R1:f0 tuning. Some singers increased mouth area with increasing pitch over the whole R1:f0 tuning range. Other singers showed this strategy on the higher part of the R1:f0 range only, and used another, as yet unidentified, articulatory strategy on the lower part. To achieve very high pitches, some singers extended the range of R1:f0 tuning as far as E6 to F#6 ( ∼ 1300–1500 Hz) while others adjusted R2 near f0 over the highest pitch range.
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A deterministic (non-stochastic) low frequency method for geoacoustic inversion J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3422-3429 (2010); (8 pages) Online Publication Date: 09 Jun 2010
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It is well known that multiple frequency sources are necessary for accurate geoacoustic inversion. This paper presents an inversion method which uses the low frequency (LF) spectrum only to estimate bottom properties even in the presence of expected errors in source location, phone depths, and ocean sound-speed profiles. Matched field processing (MFP) along a vertical array is used. The LF method first conducts an exhaustive search of the (five) parameter search space (sediment thickness, sound-speed at the top of the sediment layer, the sediment layer sound-speed gradient, the half-space sound-speed, and water depth) at 25 Hz and continues by retaining only the high MFP value parameter combinations. Next, frequency is slowly increased while again retaining only the high value combinations. At each stage of the process, only those parameter combinations which give high MFP values at all previous LF predictions are considered (an ever shrinking set). It is important to note that a complete search of each relevant parameter space seems to be necessary not only at multiple (sequential) frequencies but also at multiple ranges in order to eliminate sidelobes, i.e., false solutions. Even so, there are no mathematical guarantees that one final, unique “solution” will be found.
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J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3577-3589 (2010); (13 pages) Online Publication Date: 09 Jun 2010
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It has been demonstrated theoretically and experimentally that an estimate of the Green’s function between two receivers can be obtained by cross-correlating acoustic (or elastic) ambient noise recorded at these two receivers. Coherent wavefronts emerge from the noise cross-correlation time function due to the accumulated contributions over time from noise sources whose propagation path pass through both receivers. Previous theoretical studies of the performance of this passive imaging technique have assumed that no relative motion between noise sources and receivers occurs. In this article, the influence of noise sources motion (e.g., aircraft or ship) on this passive imaging technique was investigated theoretically in free space, using a stationary phase approximation, for stationary receivers. The theoretical results were extended to more complex environments, in the high-frequency regime, using first-order expansions of the Green’s function. Although sources motion typically degrades the performance of wideband coherent processing schemes, such as time-delay beamforming, it was found that the Green’s function estimated from ambient noise cross-correlations are not expected to be significantly affected by the Doppler effect, even for supersonic sources. Numerical Monte-Carlo simulations were conducted to confirm these theoretical predictions for both cases of subsonic and supersonic moving sources.
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J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3356-3371 (2010); (16 pages) Online Publication Date: 09 Jun 2010
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Understanding acoustic scattering from objects placed on the interface between two media requires incorporation of scattering off the interface. Here, this class of problems is studied in the particular context of a 61 cm long, 30.5 cm diameter solid aluminum cylinder placed on a flattened sand interface. Experimental results are presented for the monostatic scattering from this cylinder for azimuthal scattering angles from 0° to 90° and frequencies from 1 to 30 kHz. In addition, synthetic aperture sonar (SAS) processing is carried out. Next, details seen within these experimental results are explained using insight derived from physical acoustics. Subsequently, target strength results are compared to finite-element (FE) calculations. The simplest calculation assumes that the source and receiver are at infinity and uses the FE result for the cylinder in free space along with image cylinders for approximating the target/interface interaction. Then the effect of finite geometries and inclusion of a more complete Green’s function for the target/interface interaction is examined. These first two calculations use the axial symmetry of the cylinder in carrying out the analysis. Finally, the results from a three dimensional FE analysis are presented and compared to both the experiment and the axially symmetric calculations.
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Finite-element modeling of depth and range dependent acoustic propagation in oceanic waveguides J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3319-3326 (2010); (8 pages) Online Publication Date: 09 Jun 2010
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Finite-element models (FEMs) of ocean acoustic waveguides are capable of predicting the full wave solution including the effect of inhomogeneities and interfaces. However the method appears computationally feasible at present only for low to intermediate frequencies. The FEM discussed in this paper treats the radiation boundary condition involving multiple propagating modes using a penalty function approach. The effect of a point source has been represented as a pressure boundary condition on a small boundary surrounding the source. The FEM has been validated with a few examples of ideal waveguides. The FE results for a range and depth dependent parallel waveguide—an ASA benchmark problem [
F. B. Jensen and C. M. Ferla, J. Acoust. Soc. Am. 87, 1499–1520 (1990)
]—compare well with published results.
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Detection of damage in concrete using diffuse ultrasound J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3315-3318 (2010); (4 pages) Online Publication Date: 09 Jun 2010
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This letter demonstrates the potential for using diffuse ultrasound measurements to detect damage in concrete. Two different solutions to the diffusion equation, an infinite three-dimensional (3D) volume model that neglects geometric boundaries and a finite 3D cuboid model, are used for the required curve fitting procedure to determine the influence of geometric boundaries on the solution. The measurements consider two types of microcrack damage in concrete, alkali-silica reaction and thermal damage, and show that the measured diffusivity parameter is related to the amount of damage in each specimen.
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Using cross-correlations of elastic diffuse fields for attenuation tomography of structural damage J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3311-3314 (2010); (4 pages) Online Publication Date: 09 Jun 2010
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A scanning laser Doppler vibrometer is used to measure, at multiple grid points, the diffuse vibrations (50–150 kHz) propagating over a thin aluminum plate with complex geometry. These diffuse vibrations were generated by a few pulsed laser impacts randomly distributed outside of the measurement grid. The pairwise cross-correlations of the diffuse field recorded at all grid points provided an estimate of the first antisymmetric Lamb mode direct arrival between these grid points. Attenuation tomography imaging of a simulated structural damage is performed based on the relative amplitude variations of these direct arrivals between the damaged and undamaged conditions.
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The role of off-frequency masking in binaural hearing J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3666-3677 (2010); (12 pages) Online Publication Date: 09 Jun 2010
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The present studies examined the binaural masking level difference (MLD) for off-frequency masking. It has been shown previously that the MLD decreases steeply with increasing spectral separation between a pure tone signal and a 10-Hz wide band of masking noise. Data collected here show that this reduction in the off-frequency MLD as a function of signal/masker separation is comparable at 250 and 2500 Hz, indicating that neither interaural phase cues nor frequency resolution are critical to this finding. The MLD decreases more gradually with spectral separation when the masker is a 250-Hz-wide band of noise, a result that implicates the rate of inherent amplitude modulation of the masker. Thresholds were also measured for a brief signal presented coincident with a local masker modulation minimum or maximum. Sensitivity was better in the minima for all NoSπ and off-frequency NoSo conditions, with little or no effect of signal position for on-frequency NoSo conditions. Taken together, the present results indicate that the steep reduction in the off-frequency MLD for a narrowband noise masker is due at least in part to envelope cues in the NoSo conditions. There was no evidence of a reduction in binaural cue quality for off-frequency masking.
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Echolocation signals of a beaked whale at Palmyra Atoll J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3790-3799 (2010); (10 pages) Online Publication Date: 09 Jun 2010
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Acoustic recordings from Palmyra Atoll, northern Line Islands, central Pacific, showed upsweep frequency modulated pulses reminiscent of those produced by beaked whales. These signals had higher frequencies, broader bandwidths, longer pulse durations and shorter inter-pulse intervals than previously described pulses of Blainville’s, Cuvier’s and Gervais’ beaked whales [
Zimmer et al. (2005). J. Acoust. Soc. Am. 117, 3919–3927
;
Johnson et al. (2006). J. Exp. Biol. 209, 5038–5050
;
Gillespie et al. (2009). J. Acoust. Soc. Am. 125, 3428–3433
]. They were distinctly different temporally and spectrally from the unknown beaked whale at Cross Seamount, HI [
McDonald et al. (2009). J. Acoust. Soc. Am. 125, 624–627
]. Genetics on beaked whale specimens found at Palmyra Atoll suggest the presence of a poorly known beaked whale species. Mesoplodon sp. might be the source of the FM pulses described in this paper. The Palmyra Atoll FM pulse peak frequency was at 44 kHz with a −10 dB bandwidth of 26 kHz. Mean pulse duration was 355 μs and inter-pulse interval was 225 ms, with a bimodal distribution. Buzz sequences were detected with inter-pulse intervals below 20 ms and unmodulated spectra, with about 20 dB lower amplitude than prior FM pulses. These clicks had a 39 kHz bandwidth (−10 dB), peak frequency at 37 kHz, click duration 155 μs, and inter-click interval between 4 and 10 ms.
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J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3430-3439 (2010); (10 pages) Online Publication Date: 09 Jun 2010
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Detecting a target by measuring its forward scattered field is of interest for harbor surveillance because target strength levels are generally higher in the forward direction than in the backward direction for simple geometries. An acoustic barrier based on forward scattering was demonstrated in a nearly range-independent shallow water environment. The experimental location was characterized by high reverberation, low temporal signal coherence, and, as a result, few stable multipath arrivals due to the fluctuating sea surface. This high-frequency experiment utilized a vertical source array, broadcasting broadside pulses, and a vertical receiver array spanning the water column. The signal of interest was the aberration (in space and time) caused by the acoustic forward scattering field of crossing targets (2-m-long aluminum cylinder, 1-m-diameter steel sphere and pair of scuba tanks). Hence, the spatial and temporal coherence of the recorded acoustic signals was first investigated to assess the stability of the early acoustic arrivals in this rapidly fluctuating coastal environment. A principal component analysis of the stable portion of the recorded acoustic signals was then used to determine the crossing time of the target and to isolate some of its scattered wavefield components.
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J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3385-3393 (2010); (9 pages) Online Publication Date: 09 Jun 2010
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Underwater ambient noise measurements were carried out in a shallow (15–20 m) brackish water in the archipelago of the Gulf of Finland for period of 1 year. The absence of traffic noise made it possible to study wind driven effects in ambient noise at lower frequencies. The ambient noise comes mostly from local sources and the propagation effects are shown to be negligible. The ambient noise develops bubble type spectral features above 100 Hz as wind speed increases. Sharp spectral declines are observed below 500 Hz, which are most likely due to resonances from oscillating bubble clouds created by breaking waves. The low frequency range of the observed declines may partly be attributed to the larger bubble size in fresh and brackish waters. In the present study the wind speed dependence factor was ∼ 2.4 at 200 Hz, which is significantly higher than the typical factor of ∼ 1.5 for the ocean environment. The average high-frequency spectral slope was −4.9 dB/octave which is ∼ 1 dB/octave less than for typical deep water slopes. No significant seasonal effects were found in any parameter calculated from the ambient noise spectra.
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J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3560-3568 (2010); (9 pages) Online Publication Date: 09 Jun 2010
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Measured absorption coefficients in reverberation chambers often differ from theoretical random incidence absorption coefficients, because ideal assumptions for the theoretical random incidence absorption coefficient are not fulfilled during measurements in actual reverberation chambers. Therefore sound intensity distributions on absorber under measurement conditions have been simulated using a phased beam tracing, and used as correction functions for reducing discrepancies between the measured and theoretical absorption coefficients. Two reverberation rooms were investigated by assuming that a test specimen was attached to a vertical surface and the floor. The frequency-dependent sound intensity distributions on absorbers were found to be affected by the reverberation chamber geometry and dimensions, the absorption capability of the specimen, and the placement of the specimen. High frequency intensity distributions above 1 kHz were similar for all studied cases, but some variations in low frequency intensity distributions were observed. If the non-uniform intensity distribution and a finite size effect are taken into account for correcting the theoretical absorption coefficients, a good agreement is found between corrected and measured statistical absorption coefficients. The non-uniform sound intensity can account for the discrepancy at high frequencies.
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