Question for the audio experts (and I promise this is relevant to the thread). If you have an instrumental version of a song, how hard is it to use that to extract the vocals from the full mix? I know it's theoretically possible if the mixes are otherwise exactly the same, but that wouldn't be the case here.
The reason I ask is the original single release of "Wicked Game" included an instrumental mix with all vocals, lead and background, taken out, but everything else kept the same. The best kind of karaoke track, in other words. I have this single, though only on cassette, which is why it wouldn't be an exact match.
Answering because I have some information on this, not because I consider myself an audio expert
In short, it's not very helpful. Record companies purposefully mix the instrumentals slightly different, usually at different speed. Not something you would notice as a listener, but enough so that waveforms no longer match. The way DIY karaoke/multitracks work is substraction, but that requires exact matches. People like OrangeHarrison, and to a lesser extent myself, could maybe make something with audio that doesn't quite line up, but it's not going to be the smoking gun you're hoping it would be.
For example, at one point I thought of doing the entire Rocky Horror Picture Show soundtrack. I got the 35-year (?) anniversary blu-ray since it had 7.1 Master Audio! I bought a freaking blu-ray drive. I learned how to extract the 7.1 stems out of the blu-ray. Only to find out the 7.1 mix conveniently did not remove the vocals from any one channel, so you couldn't turn that into karaoke. Oh well, this special edition blu-ray ALSO had karaoke stems in it, so you could have the lyrics on screen and just have the (clean) backing track playing. So I'll rip the vocal-less karaoke track, then substract from the 7.1 master audio (after converting to stereo) and I will have foiled the company ... nope. Slightly different audio speed, so it was useless. So to this day I have the 7.1 stems, I have the backing tracks, and I have the high quality stereo audio files all from the blu-ray, and I have had no success in getting vocals separated into anything usable