This is Peter Neubäcker from Celemony. You've probably already seen this promo video of his new product, Direct Note Access. It's a new version of the autotune-type pitch correction software which - it appears - can work with polyphonic sound. Record a chord, and it lets you explode that chord and re-tune individual notes. I thought that this was impossible. Peter Neubäcker says "What doesn't work in theory can still work in reality."
Well, maybe. In May 2005, a startup called Zenph Studios claimed to have cracked the problem of polyphonic transcription. They analyse old piano recordings (i.e. Glenn Gould playing Goldberg Variations in 1955) and produce a high-resolution MIDI-type file with exact pedal movements and note/pressure data. They feed that into a Disklavier MIDI grand piano, and record the results. They've had good reviews (at least in audiophile mags) for the recordings.
The potential of this kind of polyphonic transcription is enormous - it would let you sample a performance, not just the recording of a performance. Zenph may be able to do it in a slow, precise, way - presumably with a considerable amount of human help, and they're just pulling out note data, not separating the actual sounds of the notes. Celemony are claiming a lot more. If it works, it's a revolution. It shouldn't be long before you can separate any mixed recording into unmixed tracks. You'll be able to turn any guitar into a guitar synth with no special hardware.
It's very exciting. Does it actually work? I can't imagine how it could, but I know almost nothing about signal processing or the theory of sound. That's where you come in... (More coverage at Create Digital Music)