An Adaptive Acoustic Echo Canceler for Hands-Free Teleconferencing

On the use of cepstral analysis in acoustic feedback cancellation

“…The condition G(e jω , n)D(e jw )F (e jω , n) < 1 is the gain condition of the Nyquist's stability criterion and therefore is hereafter called Nyquist's gain condition (NGC) of the PA system. The NGC of the PA system is sufficient to ensure the system stability because it considers all the frequency components while the Nyquist's stability criterion considers only those that satisfy the phase condition defined in (4). As a consequence, the broadband gain K (n) of the forward path must be lower than the MSG of the PA system to fulfill it.…”

“…(4) This means that if a frequency component is amplified with a phase shift equal to an integer multiple of 2π after going through the open-loop transfer function of the PA system, G(q, n)D(q)F (q, n), then this frequency component will never disappear from the system. After each loop through the system, its amplitude will increase resulting in a howling at that frequency, a phenomenon known as Larsen effect [1,2].…”

“…Such a scheme is shown in Fig. 2 and is very similar to acoustic echo cancellation (AEC) commonly used in teleconference systems [4,5].…”