HRESULT EchoSet(BOOL fEchoOn);
Sets the state of echo canceling on the incoming audio stream.
· Returns NOERROR if successful, or one of these error values:
E_INVALIDARG
E_OUTOFMEMORY
SRERR_NOTSUPPORTED
SRERR_VALUEOUTOFRANGE
fEchoOn
[in] State of echo canceling. TRUE turns on echo canceling, FALSE turns it off.