Eyegor is right. Vocal removal is achieved by inverting the phase of either the L or R track, then mixing to it mono. The out of phase signals cancel, and the vocals remain because they are always mixed in the "center" of the mix. The other instruments are not, they are panned left and right. That's why vocal isolation is so hard, because you can't just do the opposite technique of vocal removal, because there isn't one! Good luck.