> "No, I'm not playing someone else's CDs, we have a choir singing these live -- can't you hear the imperfections and that the soprano missed that eighth?"

That's precisely the issue. It is technologically impossible to solve the problem by analyzing the audio.

1. Two different performances could be audibly indistinguishable.

2. An infringing copy isn't necessarily indistinguishable. Often they have their own imperfections.