Since their arrival twenty years ago, the post-folk duo Quasi have consistently been alt pioneers. From the bedroom-ish bop of early albums like R&B Transmogrification and Featuring “Birds” to the deeper sonic explorations of more recent work, the Portland, OR team has, at least peripherally, informed much of indie music over the last two decades. It's their ability to reconcile dark themes with light pop sensibilities, usually with just some guitar or keyboards and sparse drumming - along with bountiful boy-girl harmonies - that make them a ton of fun to listen to, even when they are saying bleak things about the world. The twenty year anniversary aspect is all the more auspicious, given that the group hasn't really paused, and have also split time working with other groups like Sleater-Kinney, Wild Flag, and Elliott Smith in between writing and touring. Catch them tonight at the Tralf (622 Main St.,7PM, $15), where they'll perform with the proto-punk-influenced anti-folk underground-hero Jeffrey Lewis.