Method of providing adaptive echo cancellation

Abstract

A method of adaptive echo cancellation finds application for example in the hands-free facilities of telecommunications terminals, to compensate for disturbing echoes from the acoustic feedback between loudspeaker (1) and microphone (2). It is known to simulate these echoes (h(k)) with digital filters, and to subtract them from the echo-affected microphone signal (z(k)). The realization usually requires a signal processor with a high operating speed, a floating point logic and a large memory space. The task is to present a cost-effective method, which can be used under different acoustic conditions. The invention fulfills this task by using a known FIR filter (5), whose filter coefficients (c.sub.1 to c.sub.N) are determined according to the NLMS algorithm. The step width (.alpha.), which determines the changing speed of the filter coefficients (c.sub.1 to c.sub.N), can be made a function of one or more of various factors, including the current loudspeaker-microphone coupling (dlm), a quality criterion (Q) of the excitation, the existence of local speech signals (lokspk), the existence of briefly fluctuating local noises (lnoise), and the efficiency of the echo canceller. A special scaling of the coefficient values in conjunction with the adaptive step width control, advantageously permits the use of short FIR filters and cost-effective fixed-point computers.