ABSTRACT
Echo controllers were first developed for use in long-distance telecommunications in order to control line echo. Modem digital mobile networks have a significant time delay because of the need for speech compression and coding for transmission, and so the requirement for acoustic echo cancellation is at least as great as for network or line echo cancellation. Other possible applications of acoustic echo cancellation include a voice-controlled audio system: in this case, the microphone will pick up sound from the audio loudspeakers which will tend to interfere with the recognition of voice commands. The design of any adaptive echo canceling algorithm implicitly assumes that the impulse response changes, if at all, much slower than the rate of adaption. In practice, rapid changes of echo path will occur: the microphone may get moved, the loudspeaker volume may be turned up, or the near-end talker may move.
