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It was my understanding (from long ago...) that the macrovision signal in the vertical interval went significantly over 100% in order to provoke the automatic gain control and get their desired effect. There are several 'normal' signals that exist in the vertical interval -- closed-captioning, vertical-interval timecode, vertical-interval test signals, and Neilsen data among them. They all are "allowed" up to 100%, so a macrovision signal limited by clipping to 100% shouldn't cause gain control problems. Have I actually tried this to defeat macrovision? Nope, never had the cause, or time, to do so. So if others actually have tried it, with a tweakable tbc monitored by a scope, I'll of course defer to their direct experience. But I do know that VITS, the vertical-interval test signal, often uses a one line of full 100% colorbars to do its business. So if a auto-level control can handle one line of full level in the VBI, I would think it could handle five (or whatever) if clipped to 100%.
I recall hearing at the time that RF out from the playback deck, routed to RF in of the record deck, was a way to evade the issue. Quality would be not-so-great, though.
I do know many small broadcast switchers totally rebuilt the VBI, as well as pro TBCs or frame synchs, because they would be the first place to look when closed-caption data was being mistakenly stripped from a known-good captioned source. A switcher or effects box that will do a simple wipe will also take care of the matter.
Looking at the macrovision wiki reveals folks that have been sued or absorbed due to their success in defeating macrovision. That would be the beginning of my search for a solution on the used gear market.
Good luck!
Chip
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