Reproduced signal evaluating method, information recording medium, reproducing device, and recording device

An information recording medium on which a data sequence including marks and spaces in combination is recordable, wherein:

• the information recording medium has a track on which the data sequence is recordable;
• a reproduction signal from the information recording medium is evaluated using a prescribed method;
• the prescribed method includes:
• a step of generating a binary signal using a PRML signal processing method from a signal obtained by reproducing the data sequence from the information recording medium;
• and
• a differential calculation step of calculating a differential metric using a first state transition path having a maximum likelihood and a second state transition path having a second maximum likelihood, and a reproduction signal, the first state transition path and the second state transition path being obtained based on the binary signal;
• and
• in a pattern including a shortest mark and a shortest space adjacent before or after the shortest mark, a shift amount of an edge adjacent to the shortest space of the shortest mark is obtained from a differential metric calculated regarding one of:
• a first pattern in which a space adjacent to the shortest mark and not adjacent to the shortest space is longer than the shortest space;
• and
• a second pattern in which a mark adjacent to the shortest space and not adjacent to the shortest mark is longer than the shortest mark,
• wherein where a reference cycle of the data sequence is T, the shortest mark and the shortest space each have a length of 2T;
• and
• where binary data of a pattern including the shortest mark and the shortest space adjacent to each other is represented by “0” and “1”, the shift amount of the edge of the shortest mark is obtained from a differential metric calculated regarding a pattern, the binary data of which is “x110011000x” or “x111001100x” (“x” is “0” or “1”).