Speech enhancement based on noise adaptive nonlinear microphone array

This paper describes an improved complementary beam-forming microphone array with a new noise adaptation algorithm for efficient speech enhancement. Complementary beamforming is based on two types of beam-formers designed to obtain complementary directivity patterns each other. In this system, two directivity patterns of the beamformers are adapted to the noise directions so that the expectation values of each noise power spectrum are minimized. Using this technique, we can realize the directional nulls for each noise even when the number of sound sources exceeds that of microphones. To evaluate the effectiveness, speech enhancement experiments are performed using both computer simulation and actual devices in real acoustic environments with a two-element array and three sound sources. Compared with the conventional spectral subtraction method cascaded with the adaptive beamformer, it is shown that (1) the proposed array improves the signal-to-noise ratio by more than 6 dB under nonreverberant condition, (2) improvement of 5.5 dB is obtained when the reverberation time is 0.15 sec, and (3) improvement of 4.3 dB is obtained when the reverberation time is 0.30 sec.