If not for Bob Crawford, we might never know of Scott and Seth Avett.

And if not for Scott and Seth Avett, we might not know of the hookiest string band in America.

Crawford plays bass in The Avett Brothers, the crazy-good roots band from North Carolina that blows into Portland tonight for a sold-out show at the State Theatre.

With banjo, guitar, cello, standup bass and piano, the band fuses bluegrass influences with rock, gospel and pop.

Crawford joined up with the brothers in 2001. He auditioned in a parking lot on a Sunday night. They plowed through some traditional country songs, then Seth and Scott showed him an original or two they had written.

He remembers being impressed enough that he wanted to meet up again later and try different things. They hit it off, and together built the foundation of what would become The Avett Brothers. When playing live, the band also includes Joe Kwon and Jacob Edwards.

The Avetts have grown into one of the more popular acoustic bands in the country, appearing on all the late-night TV shows, in major music festivals and, earlier this year on the Grammys, with Bob Dylan singing a wailing, ragged version of “Maggie’s Farm.”

Crawford was the one who made it happen.

“Scott and I were about to go to grad school. It was the summer before that final push to get in, and it was the last opportunity to go on the road with the band, to go travel and play music and see what it was like,” Crawford said by phone from the road.

“We had an upright bass, banjo and guitar. We didn’t even need electricity, really. We just needed some places to play. I suggested it. I said, ‘If I book a tour, will you guys go?’ They expressed their lack of confidence in me, which made me probably work harder.”

Crawford cobbled together a press kit and sent it to clubs up and down the East Coast and into the Midwest. He booked about 25 shows in clubs and small rooms from Charlotte up through New Jersey and west to Wisconsin.

“It taught us that we could do it, that being a touring band was something we could do,” he said.

Rolling back into North Carolina still high from the people they met in their travels, Crawford told the other two, “I guess there are places we need to get back to.”

They’ve been on the road since. Their success has been a slow build, with one tour growing into another. Even with their recent explosion in popularity, the experience never felt out of control. They’ve managed their expectations and balanced their appeal with the realization that it could end anytime.

“We never sat around and talked about when we make it. But we’ve never talked about not doing it, either,” Crawford said. “As long as you had the next couple of weeks booked and were making money to pay rent, that’s all we had to worry about. As long as it kept progressing.”

The Brothers released several albums, and broke into the mainstream with the 2007 CD “Emotionalism.” A year later, they hooked up with producer Rick Rubin to record “I and Love and You.”

They write smart, lyrical songs with soaring harmonies and driving tempos. They are sweet and delicate and uncommonly energetic.

The brothers do most of the writing, although Crawford calls it a collaborative process.

“It’s very much where one person may have an idea or a thought about how something should go, and another person has an idea about how that part could be slightly turned,” he said.

“Everything becomes something beyond the individual ideas. It becomes a collaborative piece of work. Scott and Seth write the bulk of the lyrics, but it’s not hard for me to feel a part of every song.”

Since “I and Love and You,” the Avetts have released one live album. They are about halfway through the next studio album; Crawford expects it will be released early in 2012.

Crawford called the Grammy Awards “a surreal experience. We went into it not knowing what to expect, but promising it would be a great time and that we would enjoy it as much as we could.”

He still has not watched a tape of the show, and has no intention of doing so. He recalls the curtain opening, the mike stand crashing and the band plowing forward unbowed, just as it has done for a decade. Always forward, enjoying the moment for what it is.

“I remember staring straight ahead and seeing Neil Young in the front row and looking over at Joe Kwon and just smiling,” he said. “We were on top of the world.”

Staff Writer Bob Keyes can be contacted at 791-6457 or at:

bkeyes@pressherald.com

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twitter.com/pphbkeyes