dw.... you are partially correct, but it's not totally impossible. There is software out that can convert audio to midi, however it only will read so many musical tones. If you record an MP3 or WAV and convert to CDA there are programs that can convert it to midi. You may have to rip the CDA back to WAV or MP3, but that can be done too.
Cd Audio sounds (analog signals) are cuved, midi sounds, however are like a modified square (digital). So, imagine if you tried to take a Music CD, any artist, and tried to convert all the curved signals (each sound, instrument + vocals) to squares, it would sound a mess. However, it can be done if the tones were of just "1" or "2" instruments at different parts, using partial tones of the chords played and rhythms.
try askjeeves.com search CDA TO MIDI
