| 摘要 |
An optical disc for recording an information signal having a plurality of states has a portion on which a groove is formed in a predetermined direction, and the groove has a nominal position in the direction perpendicular to the predetermined direction over a predetermined length that represents a first state the information signal. The disc also has a portion on which the groove is not formed that represents a second state of the information signal. The groove can also be displaced from its nominal position in the direction perpendicular to the predetermined direction over a predetermined length, the amount of the displacement representing at least one further state of the information signal. An apparatus for reproducing such a disc has a light source illuminating the optical disc, at least two detectors that each generate an electrical signal in response to light by the optical disc, a first and a second calculating circuit each for calculating at least one result signal in response to the electrical signals from the detectors, and a multiple-value signal generator that generates an output signal having a plurality of states in response to a first result signal from the first calculating circuit and a third signal. The third signal is derived from the first result signal and a second result signal from the second calculating circuit.
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