Development of a compact two-sensor directional audio-capturing device

摘要

A directional audio-capturing device is highly desirable for normal communication in a noisy environment, and to enhance the quality of speech signal for the hearing impaired. In this paper, we propose a compact directional audio-capturing device which reduces the background noise in relation to speech signal which originates from a desired direction. This device contains three functional units: (1) a differential microphone formed by two omni-directional microphones connected in an endfire orientation, (2) adaptive beamforming and (3) echo shaping of the residual output signals to further improve the signal-to-noise ratio. The adaptation is based on a control scheme using the differences in the spatial responses between the omni-directional and the differential microphone signals. A post-processing scheme using echo-shaping filter is used to further suppress any residual interferences. A real-time implementation of our proposed scheme has been constructed and its performance measured. The experiments indicate a polar pattern with good interference cancellation, with an average interference suppression of as much as 22dB. Our experiments also indicate lower speech distortion using our proposed system. In term of speech quality, the improvement is indicated by the mean-opinion-score (MOS) scale. The MOS has been obtained from both subjective tests conducted using ten listeners, as well as using the perceptual evaluation of speech quality tool indicated in ITU-T standards document. (c) 2005 Elsevier B.V. All rights reserved.