Decoding method and decoding device

A decoding device for decoding digital information based on a detection signal obtained from a medium having a predetermined frequency characteristic, comprising:

• a first frequency spectrum calculation unit that calculates a first frequency spectrum in a predetermined frequency range from the detection signal in a predetermined segment;
• a second frequency spectrum calculation unit that calculates 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 unit that calculates a difference between the first frequency spectrum and the second frequency spectrum;
• and
• a decoding unit that decodes 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 unit is a frequency range that is lower than a normalized frequency (2·NA·T)/λ when 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.