What are echo suppressors and echo cancellers?
[top] These are active devices used by the phone company to suppress the reflection of an analog signal or positive feedback (singing) on the phone network. The effect of the echo on a voice connection is undesirable. Imagine that as you spoke into the phone’s microphone, there was a short delay and you hear your own voice back over the earpiece. A soft echo that comes back fast enough is not bothersome to the average person. A more delayed echo is annoying. A echo suppressor works by allowing only one direction to transmit at a time so as to entirely eliminate the effect of an echo. An echo suppressor is able to switch between each end very rapidly, typically within 5msec. Network echo suppressors make full-duplex communication impossible. However, modems can deactivate these devices by sending the 2100Hz answer tone at the beginning of the connection. An echo canceller subtracts a locally generated replica of the predicted echo based on the signal propagating in the forward direction
