1. Field of the Invention
The present invention generally relates to acoustic echo cancellers and, more particularly, to a background training method for conferencing or telephony acoustic echo cancellers.
2. Background of the Invention
An acoustic echo is an undesirable condition that results from sound that emanates from a speaker being fed back into a microphone. To reduce or eliminate such echo, an acoustic echo canceller is employed. However, for the acoustic echo canceller to be effective, it has to be trained.
Unfortunately, a key problem with acoustic echo cancellers is that during the training period itself, an acoustic echo is present. To minimize this echo, one can use a training signal, but this subjects the user to an annoying sound (e.g., high energy, full bandwidth). Alternately, one can start with the set of coefficients from the last operation of the echo canceller, but if the acoustic environment changed, the stored coefficients will be invalid or possibly worse than starting from a zero coefficient point. The coefficients correspond to an adaptive filter included in the acoustic echo canceller. The adaptive filter functions to adapt the acoustic echo canceller to the environment in which it is employed.
A more complicated approach to minimizing the echo period involves temporarily muting a return channel when a remote user at a remote station is speaking, and allowing the echo canceller to train during this time. However, this approach disadvantageously reduces the system to half-duplex communication during training. Another approach involves reducing the local speaker volume when a local user is speaking into the microphone so as to reduce the canceling requirements of the adaptive filter.
Accordingly, it would be desirable and highly advantageous to have a background training method for an echo canceller that overcomes the above-described problems of the prior art.