The atmosphere of Belvedere’s, a dive bar on Butler Street in Pittsburgh’s Lawrenceville neighborhood — with its stage and pool tables and little in the way of ambiance — was completely transformed by the bass. It reminded me of a water jet cutter. Taking water and streaming it at such a high rate that it could slice into steel and marble? Genius. In the same way, the sound system was taking these records that, all together might not add up to much — a drum pattern and a bassline, some sound effects — and pushing them out at such a volume as to consume all the empty space in the room. I imagined that it might be transforming the molecules in the very air that surrounded me.

Under the right conditions, this is dubstep. The product of a handful of DJs and producers driven to forge a new sound, it is comprised of elements familiar to the London underground — drum and bass, two-step garage, hip-hop, for starters — yet it is still somehow very exciting, very different. Initially the sole province of tiny clubs and pirate radio stations, the last few years have seen a radical evolution of this mutant dance music genre, spurred on every bit as much by the internet as by the devotion of its fans.