Post-filtering for Stereo Acoustic Echo Cancellation

The transmission of a spatial acoustical impression is one aim of high-quality video conferencing systems. Therefore, the transmission of stereo speech signals is a major task of such a device. Compared to the mono-case, specific problems arise, if an acoustic echo canceller (AEC) is one component of the transmission device. Its echo attenuation in the receiving room degrades, if spatial statistics in the sending room vary. Simulation results indicate that short echo cancellers are less sensitive regarding this “stereo problem”. However, to achieve sufficient echo attenuation a post-filter should be applied. In this paper, we introduce a new method to design a post-filter for stereo acoustic echo cancellation. A vital task during the design procedure is the estimation of the residual echo’s power spectral density (PSD) at the output of the stereo acoustic echo canceller (Stereo AEC). This estimate is sensitive regarding the “stereo problem”, too. Therefore, we show up an effective way to increase its robustness and give a theoretical foundation. The result is a combination of a short Stereo AEC and a post-filter, which reveals less and shorter degradation of echo attenuation after spatial modifications in the sending room than a long Stereo AEC, which shows the same steady-state performance.