Abstract: An adaptive echo canceller for digital data transmission systems permits full duplex, i.e., simultaneous bidirectional transmission, operation at full bandwidth over two-wire transmission facilities. A transversal filter arrangement digitally synthesizes a cancellation signal for unwanted leakage, i.e., echoes, through hybrid junctions directly from the digital data input symbols, rather than from the analog transmitter output. An error control signal for correlation with tap signals on the transversal filter is derived from the output of the receiver, instead of its input.