Despite a name that sounds like a mainstream guitar-rock summit, the Power 
of the Riff festival spotlights a bevy of 
beyond-underground metal bands who wouldn’t know a radio-friendly hook if 
it bit them. Following up Saturday’s 
performances by doom rockers Pentagram, New York hardcore lifers Agnostic Front, and others, today’s selection of groups is arguably more extreme. Headliners Sunn 0))) have cultivated their trademark belly-rumbling distorted drone over the past decade, and Southern Lord, the record label that one of their members owns, helped curate the other bands on the bill. Those groups include doom metallers Winter, grindcore group Repulsion, hardcore rippers Double 
Negative, black-metal sludge dredgers Coffinworm, hardcore howlers Salvation, and vegan grindcore growlers Dead in the Dirt. No Nickelback fans allowed.

Sun., Sept. 2, 5 p.m., 2012