Reproduced signal processing method, reproduced signal processing

Abstract

A reproduced signal processing circuit includes a variable gain amplifier to which a signal read from a medium by a reproducing head is inputted; an analog-to-digital converter for converting a signal outputted from the variable gain amplifier into a digital signal; and a variable frequency oscillator for supplying an operation clock signal to the analog-to-digital converter. A reproduced signal processing method includes the steps of operating a first control loop for controlling the variable gain amplifier; operating at least either one of a second control loop and a third control loop, the second control loop controlling the variable frequency oscillator, the third control loop controlling the variable frequency oscillator; filtering by analog filter means the read signal inputted to the variable gain amplifier; operating at least one of first, second, and third noise detecting operations, the first noise detecting operation detecting presence or absence of a noise by comparing an amplitude of the output signal from the variable gain amplifier with a predetermined threshold value, the second noise detecting operation detecting a noise during an operation period of the second control loop, the third noise detecting operation detecting a noise during an operation period of the third control loop; and changing the range of cutoff frequency of the analog filter means in accordance with a result from at least one of the first, second, and third noise detecting operations, thereby controlling at least one of the first, second, and third control loops.