This is probably a dumb question, but a while ago, in another thread I asked about the cost of preparing DLC. The unanimous answer was that the biggest cost was splitting the original master into the various parts, ie, guitar, bass, drums & vocals. This seemed fair enough at the time but I've been thinking about it some more.
My new question is this... Why is it necessary to do this? The sound we hear when playing is the complete band, as originally recorded, with the note highways telling us which colours should be played.
Why would it not be possible to hire very competent session musicians, or even a Beatles tribute band, have them play the instruments as accurately as possible, and then use their notes on the display, still with the "real" Beatles music playing?
I'm pretty sure that the best of session musos would be able to replicate the playing of the individual Beatles instruments and voices with incredible fidelity, those guys are GOOD. For the vocals only accurate pitch would be required, they wouldn't have to actually sound like the Beatles.
It seems to me actual separation of the original recording would only be necessary if the volumes of the original instruments needed to be varied during gameplay but this never seems to happen. (Hitting a wrong note for your instrument or not hitting at all would still be signalled by a sound effect, as is currently done.)
Forgive me if the answer to this question is obvious, but I'm just not sure what function the apparently costly separation process achieves? Can somebody fill me in?