Broadband beamforming with adaptive postfiltering for speech acquisition in noisy environments

In this paper the implementation of a broadband beamformer which is built up by several harmonically nested subarrays for each octave band combined with optimal postfiltering is described. This method has the advantage of providing large sensor distances for the postfilter estimation by simultaneously controlling the directivity of the array. The selection of an optimal postfilter is discussed in detail and its estimation based on a Nuttall/Carter method for spectrum estimation is described. The resulting noise reduction system yields improved performance in diffuse noise fields and no distortions in the case of coherent direct path noise. Furthermore, the system is robust to steering misadjustment