Patent ID: 8121226

Claim:
A computer-implemented method for evaluating a quality of a read signal obtained by using a head of an optical disc apparatus, and adapted to the Partial Response Maximum Likelihood (PRML) method by evaluating a binary code decoded from the read signal, comprising the steps of: obtaining a read signal, by using a head of an optical disc apparatus; decoding a binary code from the read signal obtained by the head of the optical disc apparatus; generating an error bit sequence having one bit edge shift from the binary code decoded from the read signal obtained by a head of an optical disc apparatus; calculating, using a Euclidian distance calculator, an Euclidian distance on the error bit sequence with respect to a predetermined target signal level, and calculating an Euclidian distance on the binary code under the assumption that the binary code has a correct bit sequence; calculating, using a Euclidian distance difference calculator, a Euclidian distance difference defined as a difference between the Euclidian distance on the binary code assumed to have a correct bit sequence and the Euclidian distance on the error bit sequence; calculating, using an average Euclidian distance calculator, an average Euclidian distance from the target signal level, the average Euclidian distance corresponding to a 1-bit shift pattern of the target signal level; calculating, using a normalized sequence error calculator, a normalized sequence error by subtracting the average Euclidean distance from the Euclidean distance difference and then dividing the result of subtraction by the average Euclidean distance; and evaluating, using a computer, a signal quality of the binary code assumed to have a correct bit sequence, by using the normalized sequence error.