Abstract: A signal processing device used for an apparatus capable of optically reproducing information from a recording medium is disclosed. In the signal processing device, a signal including information recorded at positions adjacent to a prescribed position is multiplied by k. The multiplied signal is subtracted from a signal mainly including information recorded at the prescribed position. In the signal processing device, the coefficient k is adjusted as follows. In one case, the coefficient k is varied depending on the signal strength. In another case, the processed signals are held at appropriate timings and a signal used as an index is obtained from two or more such signals. The coefficient k is optimized based on the index. In yet another case, the coefficient k is periodically varied in a synchronous manner with the fundamental period of the information recorded on the recording medium.

Abstract: An optical disc apparatus for recording, reproducing or erasing an information signal by converging a light flux onto a recording layer through a transparent substrate. The apparatus includes one or a plurality of optical heads having a plurality of objective lenses whose aberrations have respectively been corrected for a plurality of disc substrates of different thicknesses, a cartridge for enclosing the optical disc, a discrimination hole which is formed on the cartridge, and a sensor for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal. In accordance with the result of the discrimination as to the thickness of the loaded optical disc, the objective lens, in which the occurrence of the aberration is smallest, is used, so that the information signal can preferably be recorded, reproduced or erased onto/from the optical discs having different substrate thicknesses.