“You won’t believe all that sound is coming from two people!” People always say that about rock duos — and there are a lot of rock duos these days. But the truth is, you usually can believe it. What those people mean is, “That guitar player sure is loud!”

It’s different with Tartufi. The San Francisco Bay Area band released three records as a power trio, starting a decade ago, but their sound actually got bigger when it switched to a duo of Lynne Angel and Brian Gorman. More than a lineup change, Angel and Gorman sought a new musical direction. Beginning with 2006’s Us Upon Buildings Upon Us, they dropped their old material from their sets and started playing a moody, highly complicated style of indie rock that often starts out sparse and quiet and builds up to something very loud and dense with harmony and then abruptly switches to quiet again. To pull this off live, they play multiple instruments and looping effects pedals.

Artists such as Tune-Yards’ Merrill Garbus have made looping pedals a big part of their acts, but few do it as seamlessly as Tartufi. The duo’s music is based around shifts in dynamics and tempo, not in the kind of repetition you find in dance music or hip-hop, so you often may not realize you’re hearing a loop at all. It’s hard enough to imagine how they remember to play the basic parts to something like the 26-minute-long “The Butterless Man,” but it’s astounding that they can play multiple parts.

Maybe it won’t always seem so unusual. Angel and Gorman have started a music school for kids. The future is going to blow our minds.

TARTUFI: Tin Can Alehouse, Monday, August 20, 9 p.m. 619-955-8525. $5.