Abstract: A linear prediction analysis is performed for each frame of a speech signal to determine the coefficients of a short-term synthesis filter and an open-loop analysis is performed to determine a degree of frame voicing. At least one closed-loop analysis is performed for each sub-frame to determine an excitation sequence which, when applied to the short-term synthesis filter, generates a synthetic signal representative of the speech signal. Each closed-loop analysis uses the impulse response of a filter consisting of the short-term synthesis filter and a perceptual weighting filter, by truncating the impulse response to a truncation length that is no greater than the number of samples per sub-frame and is dependent on the energy distribution of the response and the degree of voicing of the frame.

Abstract: The echo canceller comprises an adaptive filter receiving the coefficients of a direct discrete transform into the frequency domain, computed on successive blocks of an input signal and fed via an inverse transform circuit to the subtractive input of an adder for forming an output signal going to the network, and an adaptor circuit for adapting the coefficients of the filter. The adaptor circuit receives the coefficients of successive transforms of blocks of output signal samples via a noise reducer.