Index of content:
Volume 119, Issue 2, February 2006
- ACOUSTIC SIGNAL PROCESSING 
A cross-spectrum weighting algorithm for speech enhancement and array processing: Combining phase-shift information and stationary signal properties119(2006); http://dx.doi.org/10.1121/1.2149767View Description Hide Description
In this paper, a gain function for noise cancellation with a two-channel microphone array is presented. This gain function combines ideas from one- and multichannel algorithms. It is developed using a minimum mean square error estimator for the amplitude of the speech signal from the cross spectrum between two microphone signals. To consider speech pauses and the absence of spectral components of the speech, an extension of this gain function is presented. The performance of the overall gain function is shown in terms of the cancellation of (diffuse) driving noise as well as the cancellation of an interfering speech signal, both recorded in a car.
119(2006); http://dx.doi.org/10.1121/1.2151791View Description Hide Description
In recent years, research into object classification based on ultrasonic sensing has shown that sonar is a rich source of data suitable for robust classification for specific classes of objects. However, these systems lack generality, precision, and are often slow as they need to collect and integrate multiple scans. The objective was the development of more efficient techniques for ultrasonic based object recognition through an inversion of the extended form of Freedman’s “image pulse” model. Earlier work extended this model, originally developed for a fluid medium with coincident transmitter/receiver configurations, to noncoincident configurations in air. This extended model was inverted, producing one that would calculate the geometry of a scattering body from an analysis of echoes received after insonification of the body with ultrasonic pulses. Quantitative verification of this model with various scattering bodies proved elusive, with low correlation between experiment and theory due to matrix instability and difficulties in obtaining data of sufficient accuracy. However, qualitative trends in the data indicate the model is essentially correct, though very sensitive to measurement precision and media characteristics, and there is reason to believe that further work under more controlled laboratory conditions and/or a different medium would verify the model’s validity quantitatively.
119(2006); http://dx.doi.org/10.1121/1.2150152View Description Hide Description
This paper presents a derivation of the time reversal operator decomposition (DORT) using the sonar equation. DORT is inherently a frequency-domain technique, but the derivation is shown in the time-frequency domain to preserve range resolution. The magnitude of the singular values is related to sonar equation parameters. The time spreading of the time-domain back-propagation image is also related to the sonar equation. Noise-free, noise-only, and signal-plus-noise data are considered theoretically. Contamination of the echo singular component by noise is shown quantitatively to be very small at a signal-to-noise ratio of . Results are shown from the TREX-04 experiment during April 22 to May 4, 2004 in deep, shallow water southwest of the Hudson Canyon. Rapid transmission of short, wide linear frequency modulated beams with center frequencies of 750, 1250, 1750, 2250, 2750, and are used. Degradation caused by a lack of time invariance is found to be small at and nearly complete at . A back-propagation image at shows focusing on the echo repeater. These results are discussed with comments about further research.