Delay-free low-cost step-gain estimation for adaptive filters in acoustic echo cancellation

Abstract Step-gain control for acoustic echo cancellation filters is extremely important for the speech quality enhancement achieved by the adaptive algorithm. A very useful step-gain control method was proposed as early as 1982 in Yamamoto and Kitayama (Trans. IECE Japan 65 (1) (January 1982) 1–8), but it introduces additional delay in the signal path. To avoid this in time-critical transmission systems like wired telephony, a second parallel filter was suggested so that the delay could be eliminated form the signal transmission path. Unfortunately, this structure obviously requires double filtering effort. As another principle disadvantage of both realizations, the adaptation tends to freeze, i.e. the filter cannot track the time-variant room impulse response. In this contribution, we present a modified step-gain estimation method. Although it only requires one filter, it neither introduces a delay, nor does it exhibit the freezing behavior. This method therefore provides a complete step-gain control system which can efficiently be implemented in low-cost real-time applications.