Copy-proof recording medium and device for adding copy-proof interference signal

摘要

A copy-proof interference signal or signals is/are added to the composite color video signal to be recorded on a recording medium in the vicinity of the horizontal synchronous signal. The interference signal comprises a pulse having a narrow width compared to the width of the horizontal synchronous signal pulse. A negative going pulse may also be added to the front porch of the horizontal synchronous signal so as to compensate for area-decrease of the horizontal synchronous signal due to the addition of an interference signal. The interference signal may be added to the videl signal region which is close to the leading edge of the horizontal synchronous signal so that the interference signal does not cause the occurrence of noises or distortion in a reproduced picture. When the interference signal-added composite color video signal is directly applied to a monitor TV, satisfactory color pictures can be obtained as usual. However, when the signal reproduced from the recording medium is once recorded by a video tape recorder (VTR), only nonpractical color pictures can be obtained with the signal from the VTR because the phase-restoring operation of chromatic signal on reproduction is disturbed by the interference signal.