This has been asked before, though not precisely.
I'm hoping everyone understands why "blacker than black" is a problem...
It's because it looks like a sync pulse-- The pulse that tells the electron beam to go back to the left side of the screen or to the top-left of the screen.
Successful CRT televisions in general had to be very tolerant of noisy, out of spec signals because of those dastardly battery powered VHS camcorders that were pervasive during the 1980's-90's. There's so much that needs to go on and not enough room to do it exactly right based on the technology of the time. Plus we're talking a mechanical tape feed that is subject to wobble and actual stretching of the recording material. So the played back signal is going into unsafe ranges constantly. The family that bought their shiny new top-of-the-line (ultimately piece of crap, heavy NiCad battery powered, belt driven, DC brush motor, power sucking, overheating) camcorder is not going to blame the brand-new camcorder, but complain to the TV manufacturer that it doesn't display correctly. The picture is stable in the viewfinder, it must be the TV, they'd (correctly) say.
I've seen the many different responses from TVs and capture devices I've tested with an $0D colour signal:
1. Wobbly areas of the screen in horizontal strips. (loss of horizontal blank integrity?)
2. Wobbly/rolling screen in general. (loss of vertical blank integrity?)
3. Drops the signal entirely. (probably same as 2 but for a TV that's converting to digital)
4. $0D rendered at same colour as regular black.
5. $0D rendered slightly darker than regular black.
6. Introduction of $0D causes the black level to renormalize after several seconds, causing a slow transition from 4 to 5 as it becomes the "new" black.
NTSC, but not PAL, has something called
setup. This is a difference between the blanking level (not the sync level) and the black level. Sync is -40 IRE, blanking is 0 IRE, and black is 7.5 IRE.
Someone should convert the voltage levels on
NTSC video to IRE units so that analog video geeks can make better sense of it.
I feel like there's a better explanation somewhere whose indexing terms I'm missing.