Originally Posted by Wikipedia
Dubstep rhythms are usually syncopated, and often shuffled or incorporating tuplets. The tempo is nearly always in the range of 138-142bpm.[9] In its early stages, dubstep was often more percussive, with more influences from 2-step and grime drum patterns. A lot of producers were also experimenting with tribal drum samples, a notable example being Loefah's early release "Truly Dread". Over time, key producers at the time started to experiment with the half-step rhythm which created more of a spacious vibe, and head-nodding rhythm, a feature which started to be used more and more and has become a signature of the genre. Similarly, the half-step rhythm also started to dominate grime, and producers started to lose the more complex and jerky rhythms influenced from 2-step, and started to work with more hip-hop influenced beats.
Dubstep rhythms typically do not follow the four-to-the-floor patterns common in many other styles of electronic dance music such as techno and house but tend to rely on longer percussion loops than the four-bar phrases present in much techno or house. Often, a track's percussion will follow a pattern which when heard alone will appear to be playing at half the tempo of the track; the double-time feel is instead achieved by other elements, usually the bassline. An example of this tension generated by the conflicting tempo can be listened on the right. The song features a very sparse rhythm almost entirely composed of kick drum, snare drum, and a sparse hi-hat, with a distinctly half time implied 71bpm tempo. The track is instead propelled by a sub-bass following a four-to-the-floor 142bpm pattern.
In an Invisible Jukebox interview with The Wire, Kode9 commented on a DJ MRK1 (formerly Mark One) track, observing that listeners "have internalized the double-time rhythm" and the "track is so empty it makes [the listener] nervous, and you almost fill in the double time yourself, physically, to compensate".