You can do this manually but with the same result as most of the plugins out there. The bottom line is, unless you have access to the multitrack session, you're SOL. The best way to get vocal free tracks is to redo them yourself. Otherwise, go buy the Karaoke disc at your local chinatown for $10.

You could buy the rights to use the backing tracks from the publishing co. but that will cost you some decent money.

Yep, most of those work on the idea of shifting, say, the right channel 180 degrees out of phase and playing that with the left. What that does is (sort of) removes, or lowers, anything that is similar in both tracks, (which would be in the middle pan) but leaves right and left channels, although they are now out of phase.

Since most lead vocals these days are panned center, it theoretically wipes out the vocal. And the bass. And the kick drum...and anything else that is in, or close to, the center panned.

You won't notice a whole lot of difference in widely-panned, dissimilar instruments unless you know. But, if you have, say, a guitar left, and a different guitar right, some elements of both guitars' tonalities may meet and cancel out those elements, while leaving the rest.

All this is why you hear a phasey or flangey sound. And, I'll bet the bottom kinda dropped out, too.

Of course, if you try this with an early stereo Beatles tune, not much will drop out at all, because they were pretty much discrete stereo.

I always wondered if there was a way to turn it BACK around, after the center was removed, but it hurts my brain to think about it. :-?

Kapt.Krunch

If you want to eliminate vocals from commercial recordings here is something else to make the technique works better.

Just like with an analog console or with software, the trick here is one of goofball spectral processing. What I mean by this is that the same technique of combining the left Channel with the right Channel who's phase has been inverted. Combined to Mono (this can actually also be done in stereo) will cancel everything in the center image. Well, you don't want to cancel the bass drum, cancel the bass guitar at least. In the way you can preserve those is to simply rolloff everything below 100 hertz. Simply lowering the bass control on the right Channel so to speak. Now this will give you the vocal cancellation but it will preserve much of the bass and bass drum since most of their energy is below the vocal frequencies. Yes, you will still hear a lot of the reverb since the reverb is not common to either Channel. This will also include the lead vocalist who you will hear reverberate in the background. It's actually quite difficult to get people to precisely mimic the original vocalist's phrasing. But if you can't manage that, the original background vocalist reverb will now appear to be more of your singers reverb if their phrasing matches the original recording precisely. I accomplished that with a great opera singer who wanted to sing along with a Barbra Streisand album called Broadway. This was a very experienced singer who never tried this before. In the end, we had a spectacular recording without Barbara.

This vocal suppression technique can also be accomplished in stereo which is what I did. Basically it's the same as above times two. Left channel is combined with an out of phase right channel. And the right channel is combined with an out of phase left channel. You utilize a high pass filter on a primary left & right channel and you have stereo vocal cancellation with low frequencies intact.

Could I get some uni with my karaoke? Arigato!
Ms. Remy Ann David

Right, this is not gonna work, I know it...

If we do what remy suggested, and successfully remove the vocals, while having the backing track, is it possible to flip the phase of both channels and use the vocalless, inverted stereo to phase out everything but the vocals in the original mix?

Edit:
Tried it. Sort of works. Basically sums to mono, creates an unbelievable flange, and if you invert the phase of one of the copies of the track, you get perfect, beautiful, unadulterated silence.
Was a bit unclear on this though, you can all probably ignore me and I can stick with my phased out mono image.