Then you just cancel it out without affecting your audio!

Ummm... how would you generate the anti-phase audio? If you are using your stereo to generate it, I suspect there would be considerable impact on the sound quality when the stereo was trying to do "double duty". Or would you have a separate amplifier and speaker set for the anti-phase sound?

Getting the anti-phase sound pickup to differentiate between extraneous noise generated from outside the vehicle, and the in-cabin noise generated by the stereo system might prove difficult. (No problem with my Mozart, but with something like Nine Inch Nails I'm not sure I could tell the difference myself, much less have it done with a microphone and a computer algorithm.)

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"