ASA 124th Meeting New Orleans 1992 October

1pPAb4. Reverberant transfer functions and cepstrum dereverberation.

Mikio Tohyama

NTT Human Interface Labs., Tokyo, 180 Japan

Richard H. Lyon

Dept. of Mech. Eng., MIT, Cambridge, MA 02139

Tsunehiko Koike

NTT Advanced Tech., Tokyo, 167 Japan

Inverse filtering for transfer functions (TFs) in a reverberant space is an important issue in sound and vibration control. ``Robust'' inverse filtering procedures are needed for the TF variations. The TF can be thought of as a stochastic process on the frequency axis due to random occurrences of poles and zeros. This paper describes the pole-zero statistics of the TFs, and shows that the trend of TF phase is predictable. However, inverse filtering for source waveform recovery is still a problem because of the nonminimum-phase property of the TF and the local variability of the TF phase. Blind dereverberation is proposed without the TFs by ``minimum-phase cepstrum windowing'' for pulselike source waveform recovery. A reverberant response to the source signal is composed of the minimum-phase and all-pass components. The minimum-phase components of the source waveform can be recovered from the minimum-phase cepstrum of the response. This recovery process is less sensitive to the observation location and the changes of the TFs.