Index of content:
Volume 5, Issue 3, July 2004
5(2004); http://dx.doi.org/10.1121/1.1675811View Description Hide Description
A generalized model combining experimental normal mode radiation efficiency and total damping trendlines and structural acoustics systematics was developed to examine violin quality-related trends in radiation damping and fraction-of-vibrational-energy-radiated up to 8 kHz. was similar for “good” and “bad” violins. and exhibit a “knee” at the critical frequency, where reached its maximum value of The critical frequency falls significantly lower for “good” than “bad” violins (3-violin samples for each), which imparts a relative enhancement to acoustic output near 3 kHz for “good” violins, independent of any bridge contribution or excitation method.
Monitoring formation of high intensity focused ultrasound (HIFU) induced lesions using backscattered ultrasound5(2004); http://dx.doi.org/10.1121/1.1652131View Description Hide Description
Backscattered radio frequency (RF) data collected in a series of in vitro experiments, in which HIFU lesions were created in bovine liver tissue, were analyzed using two signal processing approaches to visualize temporal evolution of lesion formation. Change in round-trip travel time provides information related to temperature change during and after therapy. Changes in the RF spectrum related to changes in scattering properties of the heated region were observed before visible changes appeared on B-mode images. Effect of increased attenuation in the necrosed tissue region was also observed. Results demonstrate potential for these two techniques in image-guided HIFU therapy.
5(2004); http://dx.doi.org/10.1121/1.1689691View Description Hide Description
Four listeners were asked to identify the direction of frequency change, up versus down, for frequency-modulated (FM) and virtual-frequency (VF) glides. VF glides are generated by co-modulating a pair of fixed-frequency tones so that the spectral center-of-gravity moves. Performance in direction identification (D-ID) decreased as glide duration decreased for both types of glides. Further, performance was better when the glide increased in frequency than when it decreased. Finally, the VF D-ID task was more difficult than the FM task, but the patterns of performance were similar. These results suggest similar processing mechanisms for the two types of glides.
Speech perception in noise with a two-sensor frequency-domain minimum-variance (FMV) beamforming algorithm5(2004); http://dx.doi.org/10.1121/1.1740797View Description Hide Description
The performance of a two-sensor based, frequency-domain minimum-variance beamforming algorithm (FMV) to extract a signal in the presence of multiple interferers was evaluated. Speech reception thresholds(SRT) and speech intelligibilitymeasures were obtained from listeners with normal hearing or with mild-to-moderate sensorineural hearing loss. Word and sentence length stimuli were processed through the FMV algorithm, directional microphones alone, or with a simple delay-and-sum beamformer. Listener’s ratings of speech intelligibility, percent of words repeated correctly, and threshold for words and sentences in the presence of four competing signals showed the FMV to provide significant performance benefits across different listening environments.
5(2004); http://dx.doi.org/10.1121/1.1756031View Description Hide Description
A new analytical technique for deriving transducer equivalent circuit parameters from complex electrical admittance data is presented. The new method handles low figure of merit transducers (those having weak coupling and/or low but does not require phasor subtraction or similar geometrical manipulations of the admittance loop. Four parameters of the unloaded, single degree-of-freedom equivalent circuit are extracted from a simple analysis of the capacitance curve, B(ω)/ω, and one additional parameter is obtained from the dissipation curve, G(ω)/B(ω). This technique simplifies the evaluation of developmental transducers, particularly those using marginal or weakly polarized materials.
5(2004); http://dx.doi.org/10.1121/1.1755731View Description Hide Description
The increasing demand for the retrieval and classification of audio utterances from multimedia databases, gives rise to the need for the implementation of effective feature extraction techniques. Most recent techniques employ temporal-related features and magnitude spectral features. In the proposed method, we use both the magnitude and phase spectrum of the signals to derive the features. By overcoming the discontinuity problems of phase, phase may be used as an additional feature stream. The experimental results derived from ten classes of gunshots show that, for certain classes, there is an improvement of 14% when both magnitude and phase information is employed, compared to the case when only the magnitude feature vector is used. Also, the results reported here show that the reliability of the method is increased, demonstrating the complementary nature of magnitude and phase.
5(2004); http://dx.doi.org/10.1121/1.1759731View Description Hide Description
A study is presented of the acoustic signals produced by raindrops impacting on the surface of water contained in a sensor assembly. The impact generates low frequency damped pressure waves in water. The low frequency spectrum of this signal is seen to be fairly consistent and is used for measuring the kinetic energy of the raindrops from which the drop-size distribution and the rain intensity are estimated. The proposed method is computationally efficient and can be implemented with simple DSP hardware.