Echo canceller for coded signals

An echo canceller, for use in a digital transmission system employing coded signals, comprises a memory (2O; 22) for storing a plurality of digital words, each comprising an estimate of the echo corresponding to a unique address word. Each address word comprises a sequence of the input binary signal plus at least one state bit, the state of which represents the coding applied to the sequence. The echo canceller also comprises a digital-to-analogue converter (68) for converting the outputs of the memory (2O; 22) into echo signal estimates, subtractor means (7O) for subtracting each echo signal estimate from the input binary signal, and updating means (78; 8O), responsive to the output of the subtractor means (7O), for increasing or decreasing the value of the corresponding digital word in the memory.