In the MSN encoded form, the symbols of each block of the present invention define a running digital sum (RDS) value, defined as RDS([a.sub.0a.sub.1 . . . a.sub.N-1])=-.SIGMA..sub.i(-1).sup.a.sub.i where the symbols a.sub.i belong to the set {0, 1} and the sum extends for values of i from 0 to N-1. An encoder is configured to satisfy at least one of the following characteristics: a) blocks of symbols with a given length (L) are used for encoding, wherein RDS=RDS.sub.0+4.K, where K is an integer, RDS is the said running digital sum, RDS.sub.0 is defined as zero for even values of the said length (L), and one for odd values of said length (L), and b) blocks of symbols with a given length (L) are used for MSN coding and encoding is effected by selecting encoded blocks such that the set of running digital sum (RDS) values is the set with the minimum number of elements that satisfy the required rate value, defined as the ratio between the length of the input blocks and the length of the output blocks. A decoder with a simplified trellis structure is used for decoding (as in decoding a digital signal read from media on which the signal in question has been recorded via a vertical or perpendicular magnetic recording technique, for example).