[citation][nom]Collie147[/nom]Very tough to do! I toyed with the idea in college when I was studying electronics and sound engineering. I took the idea from noise cancelling earphones, as I was driven demented by screaming teenagers, deafening repetitive trance/lady gaga on repeat and obnoxious phonecalls from gossips who told their life story every day on the bus. Principal was simple, sound was captured by a mic and played back out of phase by a speaker at the same volume - cancelling out all the background or ambient sound. My problem was that it always ended up that the mic picked up on what the speaker produced and inevitably ended up feeding back (tested in a room the size of a bus it never worked, large open spaces work best!) How they tackled this I have no idea, but its a doozey![/citation]
I think you got the message wrong. It is designed to repeat what you said, not re-send it as an out-of-phase wave to 'cancel' the sound. As it said, it's like toddlers mocking you by repeating what you said. Yeah, studies have shown that DAF can induce mental stress so it'll definitely shut up almost anyone when applied to them