Patent ID: 8797832

Claim:
A decoding method for decoding digital information based on a detection signal obtained from a medium having a predetermined frequency characteristic, comprising: a first frequency spectrum calculation step of calculating a first frequency spectrum in a predetermined frequency range from the detection signal in a predetermined segment; a second frequency spectrum calculation step of calculating a second frequency spectrum corresponding to an expectation signal of a pattern of the digital information that is present in the predetermined segment and obtained via the medium; a frequency spectrum difference calculation step of calculating a difference between the first frequency spectrum and the second frequency spectrum; and a decoding step of decoding the digital information by selecting a pattern in which the difference between the first frequency spectrum and the second frequency spectrum is minimized as a decoding result; wherein: the medium includes an optical disc, and the predetermined frequency range used in the frequency spectrum difference calculation step is a frequency range that is lower than a normalized frequency (2·NA·T)/λ wherein the length of one channel bit where the digital information is recorded on the optical disc is denoted as T, the wavelength of light irradiated to the optical disc is denoted as λ, and a numerical aperture of an objective lens that condenses the light onto the optical disc is denoted as NA.