Removing the vocals from a recording is a bit like trying to remove the eggs from a cake after it is baked. All of the frequencies in the recording are mixed together with the vocals sharing frequencies with other instruments and it is very difficult to achieve. If the vocals are panned dead center in a mix, you can subtract the left channel from the right channel thus removing the center channel but it will remove everything from the center channel, not just the vocals. This is best done with Sound Forge Channel Converter which already has a Vocal Cut preset. For more control and to isolate vocals, you might want to try a Freeware VST plug-in called Voice Trap.
There is another solution called Sony Spectral Layers Pro that will allow you to “take the eggs back out of the cake”. It is an amazing piece of software that lets you isolate sounds and remove them or keep them and remove everything else. You should definitely check it out.
