An echo canceling system receives and transmits audio signals between a
far end and a near end. During single talk, which is when only one end is
originating audio, the path back to the originator is impeded by echo
cancellation and attenuation. When there is double talk, which is when
both ends are originating audio, the attenuation is removed, or at least
significantly reduced. This is achieved by using ERLE, which itself is a
known signal used for other purposes in an echo cancellation system, to
provide information as to when double talking is occurring. This allows
for stopping the attenuation for the double talk situation, which is the
desired result.