| 摘要 |
To detect an MSK modulation mark from an MSK-modulated wobble signal without fail. A wobble signal of an optical disk is supplied to an address decoding circuit. The address decoding circuit performs exclusive-OR operation of a binarized wobble signal and a reference clock signal generated from the wobble signal by an PLL circuit, to thus compute a proportion of the exclusive-OR result assuming a value of one every half period of a reference clock signal. When there are continuously present a predetermined number of sections or more where a proportion becomes a predetermined threshold proportion or more, the sections are detected as an MSK modulation mark. A system controller changes the threshold proportion in accordance with crosstalk from an adjacent track.
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