A device that restores the d.c. component or low-frequency component to a signal that has had its low-frequency components removed by a circuit element with high impedance to direct current. The device may also be used to add d.c. or low frequency to a signal lacking these components.

Direct-current restoration is used in television receivers to reconstruct the original video signal. It is required either to restore the d.c. component to the received signal as in alternating-current transmission or to correct for the presence of an unwanted spurious d.c. component.