Acoustic echo cancellation for stereophonic teleconferencing

In long-distance telephony, echoes arise due to impedance mismatches at various points in the telephone circuit. Adaptive line echo cancelers have been used successfully for over a decade to combat this problem. Echoes also arise in teleconferencing, due to acoustic coupling between microphone and loudspeaker in each conference room. This problem is similar to the line echo problem; however, the echo paths are much longer and much more variable in this case. In this paper a further complication that arises if stereophonic transmission is used for teleconferencing is discussed: There is an inherent nonuniqueness in estimating the echo paths. It appears that the only way to resolve this nonuniqueness is by somehow decorrelating the signals in the two stereo channels. Several methods of decorrelation are discussed and how they affect adaptive echo canceller performance as well as stereophonic perception is shown.