A high recording-density and highly reliable optical disc according to the
two-dimensional PRML system is provided in which periodic signal
fluctuations in the readout signal caused by an overall positional
displacement of pits between adjacent tracks can be detected at each
sampling clock timing and can be tracked and compensated. Two-dimensional
inter-symbol interference is compensated during the production and
recording of the pattern of the medium. The readout signal is compensated
by a process of multi-value tracking before symbols are extracted from
the signal.