Christopher Mercer is a Leeds producer convinced dubstep can be ecstatic as well as stoned-somber. "Woo Boost" was one hot example. This joint with Dirty Projectors main diva Amber Coffman — a pro-forma r&b come-on set to an awesome, gut-rumbling bass pulse — is another. And here's betting his work on M.I.A.'s new set will keep the beat engorged.