finally, a question right up my alley...
there are fcc regulations regarding audio and video levels for broadcast. there is a maximum allowable level, but most shows record within the legal limits, often a bit below the max to be sure.
commercial producers, however, record and transfer their shows to the broadcasters at the maximum level, often pushing or slightly topping the limits, for obvious reasons.
so when broadcast back to back, the commercials sound louder.
it's all just a matter of tweaking a few dB's, but no one actively rides the audio levels from commercial to program, and vice versa, so long as they're within or close to specs.
video levels are more closely watched because of their nature. go to high on your white level, and your speakers will buzz. go too hot on your chroma, and the picture will bleed or wash out. there's not as much leighway with video as there is with audio.
the digital world including high definition should eventually change all of that.
forget subliminal messages. that's too easy.
did you know that a provider can imperceptibly speed up a show, and be able to slip in an extra commercial or two? it's illegal, but it's done.
something i was working on tonight was encoding a signal into the vertical interval preventing tivo like devices from recording "the masters" highlights on other-than-cbs broadcasts.
sit back and relax, we are in control...
in nomine patri, et fili, et spiritus sancti.
Meh nom eh noh...doot dooooo do do do.