An Echo Canceller Based on the Structure of Dual-auxiliary Filters

The kernel of the echo canceller is the adaptive filter, which is used to estimate the impulse response of the echo path by means of an adaptive algorithm. During double-talk, the near-end input signal contains not only the echo of the far-end input signal, but also the near-end talker’s speech. In this case, the adaptation may be greatly disturbed because the far-end input signal doesn’t correlate with the near-end talker’s speech. The common approach for this is to use a double-talk detector and to enable or disable the adaptation according to the output of the double-talk detector. The double-talk problem hasn’t yet been well solved for acoustic echo cancellation. The conventional method, which compares the receive-in and send-in signal levels, can’t detect the double-talk precisely since the echo pass loss is unknown and variable in the acoustic echo circumstance. In the recent years, correlation method, which assumes that the receive-in signal doesn’t correlate with the near-end talker’s speech absolutely, has been proposed. But the experiments show that sometimes there is some correlation between these two signals. Furthermore, it’s difficult to set an appropriate decision threshold that adapts to all kinds of noise circumstance. It’s difficult to directly detect the double-talk because of the time-variant, delay and non-liner property of the echo path. So the echo canceller with a dual-filter structure was proposed. The main idea of this method is to form a foreground and a background echo models. Only the background model is adapted and its tap weights are transferred to the foreground model when the residual echo produced by the background model is smaller. One problem of the method is that the mistransferring of the tap weights can’t be inhibited especially during double-talk.