BoC and Vocal Isolation

[Aerial Boundaries]

Audacity isn't the best suited tool for this tbh. You're better off with a dedicated vst or something.

[Peacock Tail]

You're right. You get much better results with Izotrope for example but at least everyone can have a bash at it with Audacity.

[Jonse]

"Close to impossible" is hyperbole. Isolation of sounds - vocals or otherwise - from existing audio tracks are always relative to the source and can take time. Generally speaking, I'd say about 50% of these sort of things can be done pretty smoothly. As was mentioned (and is not mentioned enough), if the source audio is mixed in a particular way then simply inverting two mono tracks derived from the stereo recording will occasionally remove or greatly silence 90% of something by cancelling it out. What that applies to is relative to the stereo width most of the time. Sometimes you get lucky and you get exactly what it was you were looking for. If this doesn't work, EQ and noise gates along with re-recording (from an external source) and what I would refer to as audio sharpening via foley are the tools of the trade. MrMessiah said it well. There's a certain amount of inherent possibility and trying to extract a voice within a mono recording layered under a bunch of sounds is like trying to put bricks together with school glue. Point however is that if someone knows what they're doing, they can generally do this sort of thing well enough to provide a sample that will sound effectively isolated within the final mix of tracks like that of Boards.

All that said, you'll never totally get it 99% of the time. I could believe that the "there's a mad me, when I get angry" bit in Sixtyten could have been cleaned up enough from a source like that clip. When it gets played with not a single bit of noise underneath before the song live though? Not a chance it came from that source.