The truth didn't dawn on Austra bandleader Katie Stelmanis until she threw a party at her Toronto apartment a couple of years ago.
"Some guy from my high school came and said, 'Wow, you were such a nerd in school!'" recalls the singer-keyboardist, who has cultivated a Cocteau Twins-cool persona with her group, which plays the Fillmore this weekend backing its new breakup-themed sophomore album, "Olympia."
She adds: "And I was like, 'Huh? What are you talking about? I was not!' But, looking back on it now, I guess I was."
Stelmanis still isn't sure how the apple landed so far from the tree. Her mother was a huge Kate Bush fan, and her father was heavily into Frank Zappa.
But somehow, left to her own childhood devices, she discovered classical music. At 10, she joined the Canadian Children's Opera Chorus, which toured Ontario and also played New York.
"From that point on, I just became obsessed," she says. "I became obsessed with my piano lessons, then I took viola in school and became obsessed with that," she says, sighing. "So, yes, I was just a full-on classical music nerd."
Her high school was so huge, Stelmanis easily blended in with the crowd. "I kept myself slightly separated on purpose, so I wasn't really known as anything. I didn't feel like I had any particular kind of reputation," she says.
When she finally exited the symphonic world, it was cold turkey, with a DIY post-riot grrrl band called Galaxy (whose percussionist, Maya Postepski, now drums for Austra).
"It was the complete opposite of anything I'd ever done before, but it was essential to changing the way my brain perceived and understood music," she says.
The artist implements her regimented training on "Olympia" in the dreamy, elastic synthesizer textures of "Fire," "Sleep" and "Reconcile," trilled in her Florence Welch-acrobatic style, and first heard on Austra's 2011 Polaris Music Prize-nominated debut, "Feel It Break."
"My whole classical background is ingrained in my brain," she says. "But I feel like I'm currently trying to shed a lot of what I learned. In classical, there wasn't any room, or appreciation, for drums or bass. Everything had to be this beautiful melody. And now I can listen to instrumental dance music, or simply beats, and get totally excited."
These days, Stelmanis not only acknowledges her childhood geekiness, she owns it. She and some fellow Toronto indie rockers periodically convene as the orchestral Hot Chocolate Recital.
"We pull out our old classical instruments and play songs for each other," she says. "Although this recital is different from when I was a kid, because it involves a lot of drinking!"Austra
Where: Fillmore, 1805 Geary Blvd., S.F.
When: 9 p.m. Saturday
Contact: (415) 346-6000, www.livenation.com