When the carrier frequency superimposed on the high frequency is kept constant and the regeneration double speed is increased, the upper end of the regenerated signal bandwidth is close to the carrier frequency. As a result, it is difficult to separate the two by the bandwidth limitation of the analog system. In addition, when the carrier frequency is increased to facilitate separation of the two, there is a problem that the control of the recording waveform becomes difficult. By using the aliasing phenomenon during AD conversion, the carrier frequency is transformed into the attenuation domain of the adaptive equalizer, and the carrier amplitude is suppressed while preventing leakage to the bandwidth of the regenerated signal.

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