Automatic accompaniment

Here's a great video demonstrating how much fun automatic accompaniment systems can be:



The video demonstrates Andrew Robertson's (C4DM) live drumming controlled automatic accompaniment system: "James Sedwards (guitar) and Jeremy Doulton (drums) improvise a rock track by recording loops of bass and guitar. This is done in Ableton Live with B-Keeper controlling the tempo so they stay in time even when speeding up."

Here's a link to one of the publications describing the system (PDF).