Investigations into early and late reflections on distant-talking speech recognition toward suitable reverberation criteria

Reverberation-robust speech recognition has become very important in the recognition of distant-talking speech. However, as no common reverberation criteria for the recognition of reverberantspeech have been proposed, it has been difficult to estimate this. We have thus focused on a reverberation criterion for the recognition of distant-talking speech. The reverberation time is generally currently used as a reverberation criterion for the recognition of distant-talking speech. This is unique and does not depend on the position of the source in a room. However, distant-talking speech recognition greatly depends on the location of the talker relative to that of the microphone and the distance between them. We investigated a suitable reverberation criterion with the ISO3382 acoustic parameters for distant-talking speech recognition to overcome this problem. We first calculated distant-talking speech recognition with early and late reflections based on the impulse response between the talker and microphone. As a result, we found that early reflections within about 12.5 ms from the duration of direct sound contributed slightly to distant-talking speech recognition in non-noisy environments. We then evaluated it based on ISO3382 acoustic parameters. We consequently confirmed that the ISO3382 acoustic parameters are strong candidates for the new reverberation criteria for distant-talking speech recognition.