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When I was in grade school, my music teacher used to emphasize the importance of the human voice as an instrument: Once, she said, she showed up to jam with some musicians, and was chastised for coming to the session empty-handed. “But my instrument is here!” she said, pointing to her throat.

With Brooklyn musician Julianna Barwick, sometimes it’s hard to tell her processed voice apart from the sparse guitar lines or piano phrases she occasionally throws in the mix. Much of what she does could be considered a cappella; in the end, it doesn’t really matter.

Of course, the Italianate term a cappella literally means “in chapel style” or “from the chapel.” Barwick’s musical history traces back to actual chapels. Her father was a youth minister, and Barwick sang in church choirs as a child.

She had other stints singing, and even gave opera a try in Tulsa, Okla.  Barwick eventually relocated to New York, where she studied photography. For a time, she and her friends met up for Wednesday dinner parties that always transformed into musical happenings. Sometimes Barwick found herself playing an electric guitar with tons of reverb and delay. Then, a friend introduced her to a loop pedal. Barwick loved harmonizing but had no desire to play in a band, so using the loop pedal and some proper effects, she began singing with herself.

Soon enough, Barwick made Sanguine, and followed up with Florine, an album named after her grandmother. On Florine, every song is made of about three loops that fade in and out and obtain more embellishments through computer and effect alterations. Through looping, Barwick has found a way to create ethereal and evoking vocal melodies. Writers like describing her as a one-woman choir.

Barwick performs tonight and tomorrow with Andrew Bird at 6th & I Synagogue at 8 p.m.