Approximation of a nonlinear distortion function for combined linear and nonlinear residual echo suppression

This work shows a novel method to suppress linear and nonlinear residual echo components after application of a linear echo canceler. The main idea is to separately treat linear and nonlinear residual echo components, as linear echo is reduced by AEC, while nonlinear echo passes the AEC unchanged. In particular, it is shown that a very simple model, such as a hard clipping function, is sufficient to approximate the nonlinear residual echo power; and that the clipping threshold can be estimated by comparing the broad-band predicted nonlinear residual echo power (produced with the current clipping threshold estimate) to the broad-band observed nonlinear residual echo power (obtained through linear AEC and subtraction of the linear residual echo power, as determined with linear coupling factors). Experimental evaluations show ERLE improvements by up to 14.9 dB compared to linear echo cancellation and suppression at a negligible decrease in speech quality during double talk.