Akustisk Delbands Eko-släckare med LMS och RLS

The increasing use of modern hands free communication systems such as video conferencing, computer communications, and vehicle mounted cellular telephones brings the demand for high-quality acoustic echo cancellation up to focus. In these applications the echo path which has to be identified typically has long time duration, the order of 100 ms. For this identification the length of the filter will be long. This report evaluates the Normalized Least Mean Square (NLMS) and the Weighted Recursive Least Square (WRLS) algorithms for acoustic echo cancelling using a delayless subband scheme. Subband signal processing has shown to be efficient both when it comes to convergence rate and level of echo suppression. The evaluation is performed for real speech signals sampled from a conversation using a hands free set mounted in an automobile, and a conversation using conference telephony equipment in a conference room. A comparison of subband and fullband algorithms is made both with respect to the computational cost and level of echo suppression. Results show that when the impulse response is very long, i.e. in such environments as conference rooms, the subband approach is beneficial. In a car environment the size of enclosure and damping means that the response is quite short and a conventional echo canceller could perform as well as a subband echo canceller. In the study, finite word length effects have not been considered.Rapporten utvärderar Akustisk Eko-släckning under verkliga rumsförhållanden för bl.a. konferens telefoni. Vi visar att i stora lokaler uppstår problem med konventionella metoder och föreslår därför att använda delbands-metoder. Resultat med verkliga data simuleringar presenteras