The gorgeous, avant-folk pop of Portland, Oregon's AU (pronounced a-you) reflects an aural appreciation of the beauty of the natural world. The airy, highly percussive tunes of the duo — multi-instrumentalist and singer Luke Wyland and drummer Dana Valatka — should fill up the big, open loft of the Pistol quite nicely. Though often compared with Animal Collective, AU is distinguished by its use of space, transitioning from sparse, slow-building instrumental soundscapes to more raucous numbers that use a wide array of bells, horns and hand claps layered over minimalistic marching-band rhythms. After the show Tuesday, AU returns to the area in November, opening for Why? at the Jackpot. But catching this group at a more intimate venue might be a golden opportunity.