Frequency domain acoustic echo canceller that handles asynchronous A/D and D/A clocks

An implicit premise in using an acoustic echo canceller (AEC) is that the clock for A/D conversion for a microphone and the clock for D/A conversion for a loudspeaker work synchronously. Even a slight difference in sampling rate between the clocks critically degrades the echo cancelling performance. This paper describes a method of making an AEC in the frequency domain that can handle a mismatch in sampling rate between A/D and D/A conversion. The method recursively estimates the sampling-rate offset by a simple extension of the well-known LMS algorithm, and corrects it through two mechanisms, frame-step control and phase rotation, which obviate the need for any explicit resampling operation. Experimental results show that this method provides an echo suppression level comparable to a standard AEC without mismatch for an offset of up to 1000 ppm.