Echo canceller and echo suppressor for frequency divisional attenuation of acoustic echoes

摘要

An echo cancelling circuit is composed of digital circuits. An echo canceller is supplied with lower send-in and receive-in components derived from a send-in and a receive-in digital signal, respectively, in a lower frequency band below a predetermined frequency. The echo canceller produces a lower digital signal component which is free from a lower echo signal component. The echo canceller furthermore produces a control signal indicative of presence and absence of a lower voice signal component in the lower send-in component. Controlled by the control signal and supplied with a higher send-in component of a frequency band higher than the predetermined frequency, an adjustable attenuator produces a higher digital signal component in which a higher echo signal component is suppressed with no attenuation and either a constant or an adjustable positive attenuation given to the higher send-in component when the control signal indicates presence and absence of the lower voice signal component, respectively. The lower and the higher digital signal components are combined into a send-out signal exempted from the echo signal, which may or may not comprise a reverberation signal introduced into the send-in digital signal by audible sound reproduced from a voice signal carried by the receive-in digital signal.