AUSTIN, Texas - Angel Olsen wrote the songs on Burn Your Fire for No Witness, her startlingly good, emotionally searing new album, in a fever.

"I got back from tour and I didn't want to talk to anyone," said Olsen. She's an alt-folk singer of 27, with an arresting voice, and she plugs in and plays loud on Burn, her third and most riveting album. She plays a sold-out show at Johnny Brenda's on Wednesday.

As she spoke, Olsen was sitting on a park bench on a bright, cool Texas morning during the South by Southwest Music Festival in March. The night before, a drunken driver had plowed his car into a crowd outside the Mohawk, the Austin club where Olsen had played earlier in the day. The crash killed four people and injured more than 20 others.

"It opens your mind that it could have happened anywhere," Olsen said. "It could have been me. It could have been my bandmates."

About her feverish burst of songwriting, she said: "That's a really interesting writing process to go through. You spend so much time living, and not really writing. And then you wake up one day and you read something, or you hear a song, and you're like, 'Wow!'

"And you can't stop. You can't sleep, and you can't see anybody. You're just writing. That happened a lot in Chicago" - where Olsen, who grew up in St. Louis, used to live before moving to Asheville, N.C., last fall - "and it happened for this record. It was not a healthy time for me physically, because I was not sleeping.

"I just had this realization that someday I'm going to get really old," Olsen said, "and I'm going to pass away, and I don't feel like sleeping right now. I feel like writing. I feel like making a bunch of [ stuff ]. It's sort of like fasting in a way. It's probably not good to do it in the long term."

The Mohawk show was Olsen's first-ever SXSW gig. Bathed in blue light, she performed before a crowd squeezed too tightly into a tiny room. As always, she looked outwardly calm and placid as she sang songs that roiled with inner tumult, like "Forgiven/Forgotten" and "Hi-Five," which nods to Hank Williams with its opening line, "I feel so lonesome I could cry."

"You don't really get a sound check, and you're under a lot of pressure to be awesome. No sound check, and here are all the advertising companies: Be awesome. If you can still have fun under that amount of pressure, it was fun. Did I do it right? I think I did it right."

Olsen sang some songs accompanying herself on guitar, as she did almost exclusively on her startlingly intimate first two albums, Strange Cacti (2011) and Half Way Home (2012). And she sang backed by a trio, letting her crystalline voice, which can recall Joan Baez in its upper range, soar above the maelstrom.

The transition to a more aggressive style - Angel Olsen goes electric! - is dramatic on Burn Your Fire. But her ability to communicate a depth of emotion, in simple, direct language isn't compromised one "Iota," to cite one title. "I can hear you crying, and I am crying too," Olsen sings on "Dance Slow Decades." "The world might be lying, but so are you."

Olsen is the adopted child of parents who had already raised families of their own. Her father is in his 80s, her mother in her 70s, and she has siblings a generation or more older than her. "It was," she said, "kind of a luxury to have a bunch of parental units to observe. 'I don't want to be like you, I'll be a little like you.' "

She learned how to sing after her mother gave her a Panasonic tape recorder.

"I remember going into my bathroom and recording stuff, and figuring out how to do harmonies on tapes. I became obsessed with training myself to feel the notes, and memorizing the way I felt when I sang the notes. That was an obsessive thing I did as a kid, and it was important to me. I love listening to Don Covay, or people who sing like that. Who sing the way a Baptist preacher yells."

After moving to Chicago, Olsen sang in the band of songwriter Will Oldham, who performs as Bonnie Prince Billy, among other sobriquets, before embarking on her solo career. When she wrote Burn Your Fire, she drew on her experience with Oldham, particularly with the band the Babblers, in which they covered songs from Kevin Coyne and Dagmar Crouse's 1979 album Babble.

"In that band, I was using my voice in this yelly, screechy, punk-rock way almost," Olsen said. "That's what I was trying to do for this record. . . . It's an obvious change, I'm not going to deny it."

Olsen's songs seem intensely personal, and "everything you create is inspired by something real," she said. But she described her songwriting process as "theatrical."

"I'm trying to go into character as if a person is having a conversation with another person," Olsen said. "I don't want to write a song where it's like, 'I kinda sort of feel like this is real.' I want each song to be like cutting out a different scene from a film. Almost if I could encapsulate an extreme moment in song. That's what I want to do for each one."

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