Back in March, Native Instruments -- the company behind the ubiquitous Traktor DJ software -- announced Stems: a music format that lets DJs and remixers to control individual parts of a track. Today Stems launches to the buying public on a number of popular music stores including Beatport and Traxsource have them listed already, Bleep, Juno, whatpeopleplay, and Wasabeat will also be selling them. For years DJs and producers' only chance of finding a cappella versions of songs was to hope a vocal-only recording existed. The advent of the internet made finding these a little easier, but they were still rare. Expensive software can sometimes help you surgically remove parts or a track, or isolate vocals, but the results aren't always very clean. Stems makes all that a thing of the past.