Patent ID: 8068399

Claim:
A signal evaluation method for evaluating a read signal, retrieved from an information recording medium, based on a binarized signal that has been generated from the read signal by a PRML method, the method comprising the steps of: detecting the patterns of multiple paths that are associated with the binarized signal and that merge into the same state; getting the ideal value of a correct pattern that is associated with the binarized signal and the ideal value of an erroneous pattern that is associated with the correct pattern; calculating the difference between a distance from the ideal value of the correct pattern to the read signal and a distance from the ideal value of the erroneous pattern to the read signal; calculating, based on the difference, an expected error rate for each predetermined group of patterns by the PRML method; and calculating a standard deviation that is associated with a total error rate, which is obtained by adding together the error rates of the predetermined groups of patterns, and that is used for evaluating the read signal.