Patent ID: 8085641

Claim:
A reproduced signal evaluation method for an optical disc on which information is written by using code with a minimum run length of 2T and from which the information is reproduced by using an adaptive equalization technique and a PR(1,2,2,2,1)ML technique, the method comprising the steps of: using, as the adaptive equalization technique, a FIR filter with tap coefficients restricted to be centrosymmetric; obtaining a maximum likelihood bit array in such a way that a reproduced signal obtained from the optical disc is binarized in the PR(1,2,2,2,1)ML technique; generating at least one of a left shift bit array in which an edge of a focused recording mark in the maximum likelihood bit array is shifted to the left by 1T while limitation on a minimum run length of 2T or longer is satisfied, and a right shift bit array in which the edge of the focused recording mark in the maximum likelihood bit array is shifted to the right by 1T while the limitation on the minimum run length of 2T or longer is satisfied; generating a target signal corresponding to at least any one of the maximum likelihood bit array, the left shift bit array and the right shift bit array; and calculating, as an evaluation index of the focused recording mark, an edge shift, a length or a position of the focused recording mark on the basis of a Euclidean distance difference between the target signal and the reproduced signal, and evaluating quality of the reproduced signal based on the evaluation index thus calculated, wherein the left shift bit array and the right shift bit array each are obtained by an exclusive OR operation of the maximum likelihood bit array and a mask bit array, and the step of generating at least one of the left shift bit array and the right shift bit array includes the steps of: when the maximum likelihood bit array includes “000111” or “111000,” generating both the left shift bit array by using a mask bit array “001000” and the right shift bit array by using a mask bit array “000100”; when the maximum likelihood bit array includes “000110” or “111001,” generating the left shift bit array by using a mask bit array “001000”; when the maximum likelihood bit array includes “100111” or “011000,” generating the right shift bit array by using a mask bit array “000100”; and when the maximum likelihood bit array includes “1110011000” or “0001100111,” generating both the left shift bit array by using a mask bit array “0010100000” and the right shift bit array by using a mask bit array “0000010100.”