Speech waveform recovery from a reverberant speech signal using inverse filtering of the power envelope transfer function

Research on recovering the sound source waveform from signals observed in a room with reverberation is important for diagnosis of mechanical failure a nd improvement of clarity in conference calls. In this paper, the possibili ty is studied for recovery of the original sound waveform from only the rev erberation time information without inverse filtering of the transfer funct ion of the reverberant field. The power envelope of the indoor impulse resp onse is approximated with an exponential function and the envelope of the s peech signal is restored by power envelope inverse filtering of the reverbe rant signal. As a result, the modulation index improvement scale using the difference of the modulation indices of the restored signal and the reverbe rant signal is improved by 60% in the case of a reverberation time of about 1 s and a modulation frequency of 10 Hz in an experiment using the modulat ed noise signal in a reverberant field. In the reverberant speech restorati on experiment, the distortion of the power envelope can be reduced by about 3 dB when the power envelope distortion rates of the restored speech and t he reverberant speech with respect to the original sound are compared. By m eans of bandwidth separation of the reverberant speech signal, the power en velope distortion of each band can be improved. (C) 2000 Scripta Technica.