Speech enhancement using nonlinear microphone array based on noise adaptive complementary beamforming

This paper describes an improved complementary beamforming microphone array based on the new noise adaptation algorithm. Complementary beamforming is based on two types of beamformers designed to obtain complementary directiv ity patterns with respect to each other. In this system, during a pause in the target speech, two directivity patterns of the beamformers are adapted to the noise directions of arrival so that the expectation values of each n oise power spectrum are minimized in the array output. 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 and speech recognition experiments are per formed based on computer simulations with a two-element array and three sou nd sources under various noise conditions. In comparison with the conventio nal adaptive beamformer and the conventional spectral subtraction method ca scaded with the adaptive beamformer, it is shown that (1) the proposed arra y improves the signal-to-noise ratio (SNR) of degraded speech by more than 6 dB when the interfering noise is two speakers with the input SNR of below 0 dB, (2) the proposed array improves the SNR by about 2 dB when the inter fering noise is bubble noise, and (3) an improvement in the recognition rat e of more than 18% is obtained when the interfering noise is two speakers o r two overlapped signals of some speakers under the condition that the inpu t SNR is 10 dB.