Volume 132, Issue 2, August 2012
- jasa express letters
- letters to the editor
- general linear acoustics 
- nonlinear acoustics 
- aeroacoustics, atmospheric sound 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- transduction 
- structural acoustics and vibration 
- noise: its effects and control 
- architectural acoustics 
- acoustic signal processing 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- music and musical instruments 
- bioacoustics 
- acoustical news
- book reviews
- reviews of acoustical patents
Index of content:
- JASA EXPRESS LETTERS
132(2012); http://dx.doi.org/10.1121/1.4730328View Description Hide Description
A three-dimensional Cartesian parabolic-equation model with a higher-order approximation to the square-root Helmholtz operator is presented for simulating underwater sound propagation in oceanwaveguides. The higher-order approximation includes cross terms with the free-space square-root Helmholtz operator and the medium phase speed anomaly. It can be implemented with a split-step Fourier algorithm to solve for sound pressure in the model. Two idealized oceanwaveguide examples are presented to demonstrate the performance of this numerical technique.
132(2012); http://dx.doi.org/10.1121/1.4731639View Description Hide Description
A recent experiment showed that coherent long-range acoustic communication is feasible in deep water over a ∼550 km range between a source towed slowly at ∼75 m depth and a horizontal line array towed at 3.5 knots at ∼200 m depth. This letter further demonstrates that diversity combining mitigates channel fading and increases the output signal-to-noise ratio. Using sparse channel-estimate-based equalization, three transmissions are combined successfully to decode a 40 Hz bandwidth (230–270 Hz) 8 phase-shift-keying communication signal, achieving an effective data rate of 17 bits/s at ∼550 km range.
Effects of word frequency, contextual diversity, and semantic distinctiveness on spoken word recognition132(2012); http://dx.doi.org/10.1121/1.4731641View Description Hide Description
The relative abilities of word frequency, contextual diversity, and semantic distinctiveness to predict accuracy of spoken word recognition in noise were compared using two data sets. Word frequency is the number of times a word appears in a corpus of text. Contextual diversity is the number of different documents in which the word appears in that corpus. Semantic distinctiveness takes into account the number of different semantic contexts in which the word appears. Semantic distinctiveness and contextual diversity were both able to explain variance above and beyond that explained by word frequency, which by itself explained little unique variance.
132(2012); http://dx.doi.org/10.1121/1.4734242View Description Hide Description
A recent experiment showed that coherent long-range acoustic communication (200–300 Hz) is feasible in deep water over a ∼550-km range between a source and a horizontal towed array (∼100 m aperture). The low input signal-to-noise ratio (SNR) (e.g., −10 dB) at an element level required conventional beamforming to enhance the SNR of the communication signals for subsequent channel equalization and decoding. This paper demonstrates that with a larger aperture (∼200 m), multiple adjacent beams can be exploited to further improve the communication performance, achieving an almost error-free data rate of 100 bits/s for QPSK modulation at ∼550 km range.
132(2012); http://dx.doi.org/10.1121/1.4734387View Description Hide Description
Underwater and in-air noise evaluations were completed in performance pool systems at Georgia Aquarium under normal operating conditions and with performance sound tracks playing. Ambient sound pressure levels at in-pool locations, with corresponding vibration measures from life support system (LSS) pumps, were measured in operating configurations, from shut down to full operation. Results indicate noise levels in the low frequency ranges below 100 Hz were the highest produced by the LSS relative to species hearing thresholds. The LSS had an acoustic impact of about 10 dB at frequencies up to 700 Hz, with a 20 dB re 1 μPa impact above 1000 Hz.
132(2012); http://dx.doi.org/10.1121/1.4736711View Description Hide Description
This study examines English speakers’ relative weighting of two voicing cues in production and perception. Participants repeated words differing in initial consonant voicing ([b] or [p]) and labeled synthesized tokens ranging between [ba] and [pa] orthogonally according to voice onset time (VOT) and onset f0. Discriminant function analysis and logistic regression were used to calculate individuals’ relative weighting of each cue. Production results showed a significant negative correlation of VOT and onset f0, while perception results showed a trend toward a positive correlation. No significant correlations were found across perception and production, suggesting a complex relationship between the two domains.
A follow-up investigation into the mechanisms that underlie improved recognition of dysarthric speech132(2012); http://dx.doi.org/10.1121/1.4736952View Description Hide Description
Differences in perceptual strategies for lexical segmentation of moderate hypokinetic dysarthric speech, apparently related to the conditions of the familiarization procedure, have been previously reported [Borrie et al., Language and Cognitive Processes (2012)]. The current follow-up investigation examined whether this difference was also observed when familiarization stimuli highlighted syllabic strength contrast cues. Forty listeners completed an identical transcription task following familiarization with dysarthric phrases presented under either passive or explicit learning conditions. Lexical boundary error patterns revealed that syllabic strength cues were exploited in both familiarization conditions. Comparisons with data previously reported afford further insight into perceptual learning of dysarthric speech.
132(2012); http://dx.doi.org/10.1121/1.4734575View Description Hide Description
There has been growing interest in recent years in masking that appears to have its origin at a central level of the auditory nervous system—so-called informational masking (IM). Masker uncertainty and target-masker similarity have been identified as the two major factors affecting IM; however, no theoretical framework currently exists that would give precise meaning to these terms necessary to evaluate their relative importance or model their effects. The present paper offers a first attempt at such a framework constructed within the doctrines of the theory of signal detection.
Sensitivity to a break in interaural correlation is co-modulated by intensity level and interaural delay132(2012); http://dx.doi.org/10.1121/1.4734241View Description Hide Description
This study investigated whether sound intensity affects listeners’ sensitivity to a break in interaural correlation (BIC) embedded in wideband noise at different interaural delays. The results show that the detection duration threshold remained stable at the intensity between 60 and 70 dB SPL, but increased in accelerating fashion as the intensity decreased toward 40 dB SPL. Moreover, the threshold elevated linearly as the interaural delay increased from 0 to 4 ms, and the elevation slope became larger as the intensity decreased from 50 to 40 dB SPL. Thus, detecting the BIC is co-modulated by both intensity and interaural delay.
Frequency dependent directivity of guided waves excited by circular transducers in anisotropic composite plates132(2012); http://dx.doi.org/10.1121/1.4734392View Description Hide Description
Lamb wave propagation in fiber-reinforced composite plates is featured by a pronounced directivity of wave energy transfer along the fibers from a point surface source. In the case of non-point (sized) source, the main lobe of radiation diagram may turn with frequency up to the orthogonal to the fibers direction. This effect has been theoretically studied and physically explained in the context of semi-analytical integral-equation based mathematical model. The present paper gives its experimental verification.
132(2012); http://dx.doi.org/10.1121/1.4734555View Description Hide Description
Two approaches to the automated detection of alarm sounds are compared, one based on a change in overall sound level (RMS), the other a change in periodicity, as given by the power of the normalized autocorrelation function (PNA). Receiver operating characteristics in each case were obtained for different exemplars of four classes of alarm sounds (bells/chimes, buzzers/beepers, horns/whistles, and sirens) embedded in four noise backgrounds (cafeteria, park, traffic, and music). The results suggest that PNA combined with RMS may be used to improve current alarm-sound alerting technologies for the hard-of-hearing.
Accounting for delay of energy transfer between coupled rooms in statistical-acoustics models of reverberant-energy decaya)132(2012); http://dx.doi.org/10.1121/1.4734591View Description Hide Description
A statistical-acoustics model for energy decay in systems of two or more coupled rooms is introduced, which accounts for the distribution of delay in the transfer of energy between subrooms that results from the finite speed of sound. The method extends previous models based on systems of coupled ordinary differential equations by using functional differential equations to explicitly model dependence on prior values of energy in adjacent subrooms. Predictions of the model are illustrated for a two-room coupled system and compared with the predictions of a benchmark computational geometrical-acoustics model.
Voice gender differences and separation of simultaneous talkers in cochlear implant users with residual hearing132(2012); http://dx.doi.org/10.1121/1.4737137View Description Hide Description
Perception of a target voice in the presence of a competing talker, of same or different gender as the target, was investigated in cochlear implant users, in implant-alone and bimodal (acoustic hearing in the non-implanted ear) conditions. Recordings of two male and two female talkers acted as targets and maskers, to investigate whether bimodal benefit increased for different compared to same gender target/maskers due to increased ability to perceive and utilize fundamental frequency and spectral-shape differences. In both listening conditions participants showed benefit of target/masker gender difference. There was an overall bimodal benefit, which was independent of target/masker gender difference.
The effects of binaural spectral resolution mismatch on Mandarin speech perception in simulated electric hearing132(2012); http://dx.doi.org/10.1121/1.4737595View Description Hide Description
This study assessed the effects of binaural spectral resolution mismatch on the intelligibility of Mandarin speech in noise using bilateral cochlear implant simulations. Noise-vocoded Mandarin speech, corrupted by speech-shaped noise at 0 and 5 dB signal-to-noise ratios, were presented unilaterally or bilaterally to normal-hearing listeners with mismatched spectral resolution between ears. Significant binaural benefits for Mandarin speech recognition were observed only with matched spectral resolution between ears. In addition, the performance of tone identification was more robust to noise than that of sentence recognition, suggesting factors other than tone identification might account more for the degraded sentence recognition in noise.
Auditory brainstem responses to chirps delivered by an insert earphone with equalized frequency response132(2012); http://dx.doi.org/10.1121/1.4737915View Description Hide Description
Recently it has been demonstrated that auditory brainstem responses, ABRs, to chirps are larger with the ER-2 than with the ER-3A insert earphone due to differences between the corresponding amplitude-frequency responses. Therefore a modified chirp, which equalizes the amplitude-frequency response of the ER-3A, is constructed and subsequently compared to the unmodified chirp. ABRs are recorded from 20 normal-hearing subjects in response to the two chirps delivered by the ER-3A earphone at a wide range of levels. The results confirm that the modified chirp generates significantly larger ABRs than the unmodified chirp at levels below 60 dB nHL.
132(2012); http://dx.doi.org/10.1121/1.4737596View Description Hide Description
Studies of spoken-word recognition have revealed that competition from embedded words differs in strength as a function of where in the carrier word the embedded word is found and have further shown embedding patterns to be skewed such that embeddings in initial position in carriers outnumber embeddings in final position. Lexico-statistical analyses show that this skew is highly attenuated in Japanese, a noninflectional language. Comparison of the extent of the asymmetry in the three Germanic languages English, Dutch, and German allows the source to be traced to a combination of suffixal morphology and vowel reduction in unstressed syllables.
132(2012); http://dx.doi.org/10.1121/1.4737592View Description Hide Description
Although single-microphone noise reduction methods perform well in stationary noise environments, their performance in non-stationary conditions remains unsatisfactory. Use of prior knowledge about speech and noise power spectral densities in the form of trained codebooks has been previously shown to address this limitation. While it is possible to use trained speech codebooks in a practical system, the variety of noise types encountered in practice makes the use of trained noise codebooks less practical. This letter presents a method that uses a generic noise codebook for speech enhancement that can be generated on-the-fly and provides good performance.
- LETTERS TO THE EDITOR
132(2012); http://dx.doi.org/10.1121/1.4733552View Description Hide Description
The distance at which harbor porpoises can hear underwater detonation sounds is unknown, but depends, among other factors, on the hearing threshold of the species for impulsive sounds. Therefore, the underwater hearing threshold of a young harbor porpoise for an impulsive sound, designed to mimic a detonation pulse, was quantified by using a psychophysical technique. The synthetic exponential pulse with a 5 ms time constant was produced and transmitted by an underwater projector in a pool. The resulting underwater sound, though modified by the response of the projection system and by the pool, exhibited the characteristic features of detonation sounds: A zero to peak sound pressure level of at least 30 dB (re 1 s−1) higher than the sound exposure level, and a short duration (34 ms). The animal’s 50% detection threshold for this impulsive sound occurred at a received unweighted broadband sound exposure level of 60 dB re 1 μPa2s. It is shown that the porpoise’s audiogram for short-duration tonal signals [Kastelein et al., J. Acoust. Soc. Am. 128, 3211–3222 (2010)] can be used to estimate its hearing threshold for impulsive sounds.
132(2012); http://dx.doi.org/10.1121/1.4733557View Description Hide Description
Users of bilateral cochlear implants and a cochlear implant combined with a contralateral hearing aid are sensitive to interaural time differences(ITDs). The way cochlear implant speech processors work and differences between modalities may result in interaural differences in shape of the temporal envelope presented to the binaural system. The effect of interaural differences in envelope shape on ITD sensitivity was investigated with normal-hearing listeners using a 4 kHz pure tone modulated with a periodic envelope with a trapezoid shape in each cycle. In one ear the onset segment of the trapezoid was transformed by a power function. No effect on the just noticeable difference in ITD was found with an interaural difference in envelope shape, but the ITD for a centered percept was significantly different across envelope shape conditions.
- GENERAL LINEAR ACOUSTICS 
132(2012); http://dx.doi.org/10.1121/1.4730974View Description Hide Description
The dynamic effective mass density and bulk modulus of an inhomogeneous medium at low frequency limit are discussed. Random configurations in a variety of two-dimensional physical contexts are considered. In each case, effective dynamic mass density and bulk modulus are calculated based on eigenmode matching theory. The results agree with those provided by Martin et al. [J. Acoust. Soc. Am. 128, 571–577 (2010)] obtained from effective wavenumber method.