| 摘要 |
PROBLEM TO BE SOLVED: To facilitate the setting of parameters of a read channel when an offset is measured and make correctly measurable an optimum offset even when there is a medium defect or the like. SOLUTION: The magnetic disk apparatus has a measurement pattern write part 60 and an optimum offset measurement part 62. The measurement pattern write part 60 writes a random pattern to adjacent tracks of both sides of a measurement track, and then writes a preamble pattern whereby a PR4 equalization characteristic is normally obtained even with a simple low pass filter characteristic in an initial setting. The optimum offset measurement part 62 while changing on offset amount obtains a mean square error MSE per one sample by dividing, by the number N of samples, the sumΣof squares of a difference (y-W)2 between PR4-equalized sample value (y) and a preliminarily set sample ideal value (e) in the case without noises, and sets an offset which minimizes the MSE as an optimum offset.
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