Want to mix and scratch like a professional DJ? To be a good DJ you need to understand the concepts of mixing tracks, adding cool effects, and of course you need a good sense of rhythm to line up the beats. This how to video explains how to use the roll feature on the DJM-400 mixer. This video samples some music from channel 1 and takes it to channel 2. Then the instructor messes around with the buttons that can lengthen or reduce the original roll. Watch this DJ tutorial so you can learn how to use the roll feature on the DJM-400 mixer.