A method and apparatus of converting a series of data words into modulated signals generates for each data word, a number of intermediate sequences by combining mutually different digital words with that data word, scrambles the intermediate sequences to form alternative sequences, translates each alternative sequence into a (d,k) constrained sequence, measures for each (d,k) constrained sequence, not only an inclusion rate of undesired sub-sequence but also a running DSV (Digital Sum Value), and selects one (d,k) constrained sequence having small inclusion rate for recording on an optical or magneto-optical recording medium among the (d,k) constrained sequences having maximum value of running DSV. smaller than a preset limit. Accordingly, efficient DSV control can be achieved for even relatively-long sequences.