Defect detecting apparatus

Claim 1

In a system for reproducing from a recording medium a video signal having a predetermined frequency band recorded as a frequency-modulated video signal having a predetermined frequency shift, an apparatus for detecting a signal defective portion in the reproduced video signal which comprises: a frequency demodulator comprising zero-crossing detector means for frequency-demodulating the reproduced frequency-modulated video signal to produce a frequency-demodulated output signal and a low-pass filter for deriving a video signal of said predetermined frequency band from said demodulated output signal; filtering means for receiving the demodulated video signal from said zero-crossing detector to produce a filtered output signal, said filtering means having a low cut-off frequency substantially above the highest frequency of said predetermined frequency band of said video signal and having a high cut-off frequency below twice the lower limit frequency of the frequency shift of said frequency-modulated video signal; a first level comparator for receiving said filtered output to generate a first output signal when said filtered output becomes larger than a first predetermined level; second level comparator for receiving said filtered output to generate a second output signal when said filtered output becomes smaller than a second predetermined level which is predetermined to be smaller than said first predetermined level; and adder means for adding said first and second output signals of said first and second level comparators to produce an output signal representing the signal defective portion in said reproduced video signal.