On the extraction of early reflection signals for automatic speech recognition

Room reverberation caused by multipath sound wave propagation in acoustic enclosures constitutes an unwanted distortion for automatic speech recognition systems. Multichannel speech enhancement methods often aim to enhance the signal impinging at the microphone array from the source direction while reducing late reverberation. In this paper, we investigate the applicability of spatial filters which constructively combine the direct-path signal with distinct early room reflection signals to increase the direct-to-reverberation ratio and to reduce the word error rate (WER) of automatic speech recognition systems. We present suitable filters and compare them with existing approaches. Results for the simulated acoustic environments indicate that an improvement in WER can indeed be achieved by the spatial filters which account for strong early reflections.