That's a pretty interesting question here. To my understanding, it is allowed to use a few bars of otherwise copyrighted tunes and songs. Cutting up such a song into bits and pieces and recycle its bits somehow differently was never a question in the past - imagine some tune sort of scambled via some grinder - who would have wanted to listed to such a jam.

With bits and pieces recycled via Band-in-a-Box, though, it appears feasible now to jam along in some reasonable sense. First time in history.

Plus it's all about backing tracks and harmonies, which usually cannot be copyrighted. Copyrighting usually is all about melodies and songs.

Martin