Waveform Inversion (Cancel Vocals)

rogerroll · Post by **rogerroll** » Sat Jul 14, 2007 12:24 am

I have an idea for an "hidden track in plain sight" type of thing.

I know that if you invert the waveform of, let's say the right channel, and paste it over the left channel, it'll cancel out everything dead center in the mix and leave everything on the fringes in the resulting mono waveform. In ideal conditions, people try this to cancel vocals from pop songs, and just get the instrumental.

My idea is to do it backwards. Have a wall of static dead center. With a song hidden on the left or right channel at a fairly low volume so it's not audible over/under the static unless you're really paying attention. That way, when someone cancels the center as described above, they'll end up with the song clearly audible and absolutely no static.

Will this work? How about if, instead of static, it's another song mixed mono and dead center? Do you know of an easy way to try/test this?

Any help would be appreciated.

Adam! · Post by **Adam!** » Sat Jul 14, 2007 3:23 am

It can be done. On the most recent NIN album, there is a song where, for about 2 seconds, there's a wall-of-noise that's 180 degrees out-of-phase, with the vocal very quiet panned center. Mix the two tracks together and the noise disappears, and the vocals (which say "Red Horse Vector") are all that's left. That message directed you to a webpage that had more content/videos related to the album. Very well hidden, but in plain sight.

The only problem I could think of would be if it would work with mp3's, as static is very hard to encode, and the compression codec will tend to "duck" quieter sounds (aka your hidden message).

fluffy · Post by **fluffy** » Sat Jul 14, 2007 11:29 am

Yeah, even if mp3 encoding doesn't kill the vocal, it will certainly mess up the static such that the two things no longer quite cancel out (since mp3 compression is lossy and psychoacoustic).

Adam! · Post by **Adam!** » Sat Jul 14, 2007 12:51 pm

Mmm, what if you used joint-stereo mode when encoding? Seeing as roger's Static and his Hidden Track would be separated completely by the encoder's Mid-Side processor, I think after decoding it might still cancel nicely.

Not sure though, maybe I'll try it.

rogerroll · Post by **rogerroll** » Sat Jul 14, 2007 3:56 pm

I'm not planning on having this in any form as an mp3. And the instructions (themselves hidden) will probably specify that they not be ripped as mp3. It's also quite possible that it will be extremely difficult to rip in the first place. It's a CD-only release, for reasons that will become apparent to the listener when he or she receives the album.

Mostess · Post by **Mostess** » Wed Jul 18, 2007 6:03 am

rogerroll wrote:And the instructions (themselves hidden) will probably specify that they not be ripped as mp3.

Somehow this seems self-defeating. Although I doubt a CD of noise is begging to be ripped.

signboy · Post by **signboy** » Sat Jul 21, 2007 10:19 am

What about phase inverting the left and right channels, then burying your hidden bit in the center, so that when the song is listened to in stereo, which it most likely will be, your stuff will be hidden, but when it's listened to in mono, the hidden part will pop right out.

Adam! · Post by **Adam!** » Sat Jul 21, 2007 11:14 am

signboy wrote:What about phase inverting the left and right channels, then burying your hidden bit in the center, so that when the song is listened to in stereo, which it most likely will be, your stuff will be hidden, but when it's listened to in mono, the hidden part will pop right out.

That's what happens in the Nine Inch Nails song I mentioned. Trouble is, the inversion is extremely obvious when you hear it, so "hidden" is probably the wrong word.

rogerroll · Post by **rogerroll** » Sun Jul 22, 2007 12:20 am

I ended up finishing this project, by the way. Instead of static, I aimed my mic[rocassette used as a mic]rophone out the window and recorded crickets. It worked out quite well.