techniques are provided for applying modulation constraints to data streams using a short block encoder . a short block encoder encodes a subset of the bits in a data stream . then , the even and odd interleaves in a data stream are separated into two data paths . a first modulation encoder encodes the even interleave according to a first modulation constraint . a second modulation encoder encodes the odd interleave according to a second modulation constraint , which in general coincides with the modulation constraint for even interleave .