System for locking a clock onto the frequency of data recorded on a storage medium

A method of locking onto a frequency of data encoded on a medium, taking frequency variations in the physical travel of the medium into account, comprising:

• producing a servo reference clock and a read reference clock that, based on a feedback signal, track frequency variations in the physical travel of the medium;
• producing a recovered clock signal based on the servo reference clock and the read reference clock;
• and
• making a fine resolution error measurement, with a digital phase locked loop, between the recovered clock signal frequency and the servo reference clock frequency, the fine error measurement being used to create the feedback signal.

A method of producing an offset write clock for writing data on a medium, comprising:

• producing a read clock locked onto a frequency of data encoded on the medium;
• providing a time domain offset signal representing a desired time domain write offset;
• and
• adjusting the read clock with the time domain write offset signal to produce the offset write clock.