There is provided a digital data transmission system that includes a first unit transmitting a first MLT3 signal, a second unit receiving the first MLT3 signal, and transformers. The second unit includes an equalizer receiving the first MLT3 signal and outputting a second MLT3 signal that is input to a recovery module for the transmitted digital data, and a device placed in feedback to the equalizer. The device receives the second MLT3 signal and outputs a third low frequency signal that is added to the first MLT3 signal. The device has a translation block for the up or down or no translation of the second MLT3 signal according to the low or high or intermediate value of such signal, and a low pass filter receiving the signal output from the translation block and outputting the third signal containing the low frequency component of the second MLT3 signal.