1. In an echo cancellation system of the type which is interposed between a signal receiving path on which an input signal travels and a signal sending path on which an unwanted echo signal travels, and which includes means for generating an echo replica signal which is subtracted from the echo signal to produce an echo residual signal; the combination which comprises: first adaptive signal processing means connected to receive the input signal from said receiving path and to receive a fed-back echo residual signal, and operable for performing convolution of the input signal with a signal based upon the fed-back echo residual signal to produce a first intermediate result which defines the system zeros of the signal path; second adaptive signal processing means connected to receive the echo signal from said sending path and to receive the fed-back echo residual signal, and operable for performing convolution of the echo signal with a signal based upon the fed-back echo residual signal to produce a second intermediate result which defines the system poles of the signal path; and means for combining said first and second intermediate results and said echo signal to yield the echo residual signal.