The transfer function is 2T cos(Ï€fT) which is called as cosine filter.

In duobinary coding, the number of output obtained for M-ary transmission is 2M-1.

In duobinary signalling method if one error occurs it repeats everywhere through out the next steps. To avoid this precoding method can be used.

The digital filter incorporates one digit delay and thus it adds the incoming pulse with the value of the previous pulse.

In polybinary signalling method the present binary digit of the sequence is formed from the modulo-2 addition of the j-2 preceding digits of the sequence and the present digit.

If more than three levels are introduced in duobinary signalling technique the bandwidth efficiency increases This method is called as polybinary signalling.

To avoid error propogation precoding method is used. In this each bit is encoded individually without having any effect due to its prior bit or decisions.

The interference at the detector can be cancelled out using these methods in which some controlled amount of ISI is introduced into the data stream.

Each bit can be independently detected in-spite of strong correlation and this provides redistribution of spectral density and also favors low frequencies.

Source encoding includes a sampling of continuous time signals, quantization of continuous valued signals and compression of those sources.