Alternative modulation codes for the compact disc

Examples are given to show how modulation coding for magnetic recording channels can be used to generate various codes for compact disc recording. The particular (2,10) code now used in compact discs is known as eight-to-fourteen modulation (EFM). The overall rate is 8/17, however, since three code symbols are inserted between each block of 14 code symbols to ensure that the entire sequence satisfies the (2,10) constraint (and to limit the low-frequency content of the input waveform). A brief review is given of the theory of run-length limited codes, the (2,7) code currently used in magnetic recording, sliding block (2,10) codes, and more general codes for optical recording that have higher density ratios than the currently used EFM code, while still satisfying the (2,10) constraint