a Cepstrum-Based Acoustic Echo Cancellation Technique for Improving Public Address System Performance.

A technique was developed to mitigate the undesirable effects of acoustic feedback in public address systems. The technique is based on echo cancellation, which has been used to compensate for line echo in telephone hybrids and acoustic feedback in teleconference systems. Traditional echo cancellation methods are incapable of solving the problem of acoustic feedback in public address systems, as this problem is more complex than echo cancellation in telecommunications systems. The technique uses adaptive digital filters to compensate for acoustic feedback between public address system loudspeakers and microphones. A filter structure and adaptation algorithm were developed to allow the filters to compensate for the acoustic feedback and to reduce its effects on system performance. The adaptation algorithm uses the complex cepstrum of portions of the digitized microphone output signal. The complex cepstrum provides information regarding the amplitudes and delay times of the primary echoes in the acoustic feedback signals. The technique was simulated using measured acoustical impulse responses and recorded audio signals as microphone inputs. Results of the simulations indicate that the technique is capable of significantly improving the performance of a variety of public address systems.