Speech enhancement using nonlinear microphone array with complementary beamforming

This paper describes an improved spectral subtraction method by using the complementary beamforming microphone array to enhance noisy speech signals for speech recognition. The complementary beamforming is based on two types of beamformers designed to obtain complementary directivity patterns with respect to each other. In this paper, it is shown that the nonlinear subtraction processing with complementary beamforming can result in a kind of the spectral subtraction without the need for speech pause detection. In addition, the design of the optimization algorithm for the directivity pattern is also described. To evaluate the effectiveness, speech enhancement experiments and speech recognition experiments are performed based on computer simulations. In comparison with the optimized conventional delay-and-sum array, it is shown that the proposed array improves the signal-to-noise ratio of degraded speech by about 2 dB and performs about 10% better in word recognition rates under heavy noisy conditions.