Method and apparatus for transmitting a digital signal

Abstract

A PCM digital signal is provided with double-interleaving and error-correction encoding to protect against errors occurring during transmission, which can be carried out by magnetic recording and reproducing. The PCM signal is processed as error correcting blocks of several data word sequences and an associated error correction word sequence, and the double-interleaved sequences are then transmitted as transmission blocks. Up to one erroneous word in each error correction block can be corrected by using the error correction word sequence. Any uncorrectable word can be compensated by substituting a synthetic word interpolated from immediately preceding and following data words known to be correct. The distance between successive data words is made as great as possible so that a long burst error is unlikely to affect the ability to compensate uncorrectable errors. To achieve this, alternate words of the PCM signal are distributed to odd and even groups of sequences, and the interleaving is carried out by imparting different delay times to the respective sequences such that the greatest delay time imparted to the odd sequences is less than the shortest delay time imparted to the even sequences. The error correction word sequence is provided with a delay time intermediate the greatest delay time of the odd sequences and the shortest delay time of the even sequences.