MAGNETIC DISC CHECK APPARATUS

PROBLEM TO BE SOLVED: To check even a large capacity magnetic disc with high accuracy. SOLUTION: A magnetic head 10 writes the predetermined signal to a magnetic disc and also reads the signal stored n the magnetic disc. An envelope generating circuit 14 generates an envelope signal of the readout signal. A low-pass filter 16 cuts a high frequency element of this envelope signal. A slice level circuit 18 amplifies an output signal of the low-pass filter with the predetermined amplification factor to generate a slice level signal. This amplification factor may be changed depending on the measuring condition of a magnetic disc. A comparator 20 compares a slice level signal and envelope signal. The comparator 20 can provide a response with relatively higher accuracy because the signal is not a readout signal but its envelope signal and it is lower than the readout signal in the frequency. An error processing circuit 22 specifys an error part of the readout signal from an output signal of the comparator 20.