A fully passive echo-canceler using a single microphone

There are many studies on removal or suppression of reverberation. Among them, the approach, in which the impulse-response in a room is measured beforehand, has obtained very satisfactory results. An impulse-response is, however, not invariant, and changes with time depending on the room temperature and humidity, and the relative location between a sound source and a set of microphones. It is troublesome to measure an impulse response exactly each time. So, we have tried to cancel echoes using only one acoustic signal with echoes, obtained through a single microphone. In order to cancel echoes, we have to determine both delay times and amplitude ratios between direct sound and each of reflected sounds. Delay times are obtained as peaks of cepstrum of acoustic signal. Each amplitude ratio is iteratively searched so that resultant recovered sound may have the shortest duration. In the case that there are a few reflected signals, the result of experiment with reverberated signal synthesized using CD sound shows good recovery of an original sound