This is a new version of a music analysis program (like Amazing Slow Downer or Transcribe). It's primarily intended for guitar players, so some of the nifty transcribing features don't work for melodeon. But what you do get is far better than anything else I've tried. A bit spendy ($49 or $89 for a family pack).
Key features:
-- drag your tune from iTunes into Capo
-- slow down & pitch adjustment -- everyone does this, but the slow down is on a nice microadjusting slider
-- chord detection which works much much better than in Transcribe. As it plays the tune, you click on the beat and it puts chords in -- a test with a John Spiers track caught nearly every chord correctly.
-- (the killer feature) a very very pretty spectrographic analysis of the track. You can click on individual bumps in the spectrograph to see which notes are being played. I tested this with a Tony Hall track and spotted a very neat passage where he plays the tune, and then at the same time (presumably with his other right hand) a neat counterpoint melody. You can see both clearly in the spectrograph.
-- gorgeous and maclike.
Mac users should download and have a play -- in the demo mode you can play with any given track for five minutes before it degrades the sound quality. It's Leopard only because it uses some of the new APIs there -- the earlier version works on older versions of the OS but probably doesn't have the core things that excite me as a melodeon player.