Patent ID: 8098557

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, wherein the step of calculating the error rate includes: calculating a standard deviation of the difference for each said predetermined group of patterns; detecting the probability of each said predetermined group of patterns; and calculating the error rate based on the standard deviation of the difference, the probability, and the number of errors occurring in each said predetermined group of patterns.