Adaptive Microphone Array Employing Spatial Quadratic Soft Constraints and Spectral Shaping

The convenience and the ease of use provided by hands-free operation of speech communication devices mean that speech enhancement schemes are becoming indispensable. In this chapter, two subband adaptive microphone array schemes are presented, which aim to provide good speech enhancement capability in poor signal to noise ratio situations. The basic commonality of the adaptive microphone array schemes is that they approximate the Wiener solution in an adaptive manner as new data comes in. Furthermore, both schemes include a quadratic constraint to prevent the trivial zero solution of the weights and to avoid suppression of the source of interest. The constraint is included to provide robustness against model mismatch and good spatial capture of the target signal. Furthermore, by using a subband structure the processing allows a time-frequency operation for each channel. As such, both schemes utilize the spatial, spectral, and temporal domains in an efficient and concise manner allowing a computational effective processing while maintaining high performance speech enhancement. Evaluations on the same data set, gathered from a car, show that the proposed schemes achieve good noise suppression up to 20 dB while experiencing very low levels of speech distortion.