An insertion loss control method for supplementing cancellation effect deteriorated by echo path change in hands free telecommunication system

In this paper, we propose a method preventing howling from occurring by inserting a large loss into the talking circuit. Hands free telecommunication systems are generally formed by applying an acoustic echo canceler to reducing the acoustic coupling between a loudspeaker and a microphone. However, the system possibly causes the howling when the echo path change deteriorated the reduction effect of the acoustic coupling. The occurrence of the howling can be prevented by inserting a large loss into the talking circuit. Oppositely, this insertion loses the advantage of the two-way communication that is fulfilled in telecommunication system. We propose a method distinguishing between the echo path change and the double-talk and thereby restricting the insertion of the large loss only after the echo path change. Finally, we verify, using computer simulation, that the proposed method operates the hands free telecommunication system stably.