Abstract: An automatic correction circuit is responsive to suitable bit patterns in a bit stream being received from a transmission medium, to generate an error amplitude map of signal distortion being introduced by the transmission medium. The error amplitude map is digitally stored or recorded. After each non zero bit occurrence in the signal stream a synchronized output signal corresponding to the recorded error amplitude map is generated and added to the bit stream being received to reduce signal distortion, whereby information recovery from the received bit stream is improved.

Abstract: A line circuit includes a fixed resistance feed consisting of a pair of resistors connected in series with a d.c. power source and tip and ring leads of a communication line. A variable current feed includes a current sink and a current source also connected in series with the d.c. power source and the TIP and RING leads. Energizing current flow in the communication line results as the combination of currents passed by the two feeds. A control circuit determines the currents conducted by the current source and current sink and introduces variations in these currents in accordance with signals for transmission along the communication line. Differences between current flows in the variable current feed and current imbalance conditions on the communication line are accommodated by the fixed resistance feed which also determines the terminating impedance for the communication line.