Patent ID: 8130617

Claim:
A method of controlling a playback condition, comprising: irradiating a track of an optical disk where no data is recorded with a laser beam having a power level lower than a mark formation level and higher than a playback laser power level; detecting a state of an initial signal as a first state of a signal representing a reflectivity level caused by a return light reflected from the track of the optical disk where no data is recorded; continuously irradiating the track of the optical disk where no data is recorded with a laser beam having a power level lower than the mark formation level and higher than a playback laser power level; detecting a state of a second signal as a second state of a signal representing a reflectivity level caused by a return light reflected from the track where no data is recorded of the optical disk during the continuous irradiating; calculating a variation or a rate of change of a state of a signal representing a reflectivity level based on the first state of the initial signal and the second state of the second signal; specifying a compensation amount of a playback condition corresponding to a time between detecting the first state and detecting the second state or corresponding to a laser irradiation frequency when the variation or the rate of change of the state of the signal exceeds a threshold; and setting a playback condition in which the specified compensation amount of the playback condition is reflected.