Dubstep is 21st-century head music adapted for the body, cross-wiring the sub-bass psychedelia of dub reggae with the restlessness of jungle and garage. The Hyperdub label reps the genre's experimental side, and this two-CD anthology, split between signature and unreleased material, is a perfect primer. Melancholic visionary Burial and the eclectic label chief Kode9 are the "stars," but acts like Darkstar, whose sad-robot bounce "Need You" sounds like Daft Punk outside an ex's window at 4 a.m., wait in the wings. Tracks like Joker's "Digidesign" posit a novel experience: the meditative party jam.