ADAPTIVE ECHO CANCELLING CIRCUIT FOR USE IN A LONG- DISTANCE TELEPHONE NETWORK

摘要

Abstract of the Disclosure:For use in combination with a loudspeaker and at leastone microphone, for example, by attendants in an auditorium, anecho cancelling circuit comprises a self-adaptive echo cancellerresponsive to a lower frequency component, such as below 1.7 kHz,of a receive-in signal for self-adaptively cancelling a correspondingcomponent of a reverberation signal included in a send-in signalduring each interval during which an audio signal reaches thecircuit from a remote party. For a higher frequency reverberationsignal component, an echo suppressor or a voice switch may reducea weaker one of two signals which are either the higher frequencysend-in and receive-in signal components or a combination of areverberation component cancelled signal with the higher frequencysend-in signal component and the whole receive-in signal. Alternatively,a less expensive echo canceller non-adaptively cancels a partof the reverberation signal in response to the receive-in signal.The lower frequency component of the partially reverberation cancelledsignal is used by the self-adaptive echo canceller as the lowerfrequency send-in signal component. An acoustic output may oncebe reproduced by the loudspeaker in response to the receive-insignal and then converted to an electric signal for supply tothe echo cancelling circuit.