Patent ID: 8018810

Claim:
A method for decoding a reproduced signal using maximum likelihood decoding and detecting a recording shift of a recording mark recorded on a recording medium, comprising: a first step of detecting m number of patterns corresponding to an edge portion of the recording mark among n number of state transition paths selected using the maximum likelihood decoding, where n is an integer greater than or equal to 2, m is integer smaller than or equal to n; a second step of performing a predetermined process using Pa, Pb and Pstd, where Pa is an index indicating a probability of the state transition in a pattern of the detected m number of patterns, Pb is an index indicating a probability of the state transition in another pattern of the detected m number of patterns, and -Pstd is defined as a value of Pa−Pb when Pa=0 or Pstd is defined as a value of Pa−Pb when Pb=0; and a third step of detecting an amount of the recording shift of the edge portion of the recording mark or a direction of the recording shift of the edge portion of the recording mark, based on information obtained from the predetermined process in the second step.