Speech enhancement by multiple beamforming with reflection signal equalization

In real environments, the presence of room reverberations seriously degrades the quality in sound capture. To solve this problem, multiple beamforming, which forms directivity not only in the direction of the desired sound source but also in the direction of reflection images, was proposed by Flanagan et al. (1993). However, it is difficult to apply this method practically in real environments, since this application requires that the distortion of reflection sound signals by wall impedances be equalized. The paper proposes a multiple beamforming algorithm that equalizes the amplitude-spectrum and phase-spectrum of reflection signals by a cross-spectrum method. Evaluation experiments are conducted in real environment. In a SDR (signal to distortion ratio) evaluation, the proposed multiple beamformer achieves signal distortion reduction more effectively than the conventional single beamformer and the conventional multiple beamformer without equalization. In addition, in an automatic speech recognition evaluation, the equalized multiple beamformer achieves a higher recognition performance than those of the above conventional beamformers.