Source coding vs channel coding

Source coding removes redundancy from the source data to represent it with the fewest bits (data compression), e.g. Huffman, Shannon-Fano, run-length coding. It improves efficiency and reduces bandwidth or storage.

Channel coding deliberately adds controlled redundancy (parity bits) to the data so that the receiver can detect and correct errors caused by noise, e.g. Hamming, CRC, convolutional codes. It improves reliability but increases the number of bits sent.

Source coding comes first at the transmitter, and channel coding is applied afterwards; the receiver reverses them in the opposite order.