[commieneko]

No, it actually was "legal" as in FCC regulations; and you could get fines for broadcasting signal out of spec. (Though I've never known of it happening.)

I'm not sure what the situation is now with digital TV. My last years in the industry were before the mandatory switch, and the places I was working were simulcasting. So we were creating stuff that was NTSC safe. By then most of the software we were using took care of keeping things in spec, but some of the older equipment we were using, mostly character generators and few really cranky old switchers and effects boxes, still required that we be careful about our input levels.

[robomartin]

OK, you are probably right. It's been a while. I played in broadcast some time ago.

I think you jogged my memory further. I think the way it worked is that the transmitter over-modulation due to illegal levels would/could interfere with adjacent channels and that's why the FCC made the rules.