John Popper of Blues Traveler, Shawna Thompson and Kiefer Thompson of Thompson Square

John Popper of Blues Traveler, Shawna Thompson and Kiefer Thompson of Thompson Square attend the 49th Annual Academy Of Country Music Awards at the MGM Grand Garden Arena on April 6, 2014 in Las Vegas, Nevada.

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"It started out as something small and it's taking on a life of its own," says John Popper of upcoming music.

Reinvention is on Blues Traveler's itinerary and it's bringing along an eclectic slew of collaborators and producers for the ride, including Gavin DeGraw, Plain White T's, 3OH!3 and Thompson Square.

What started out as a companion disc to a possible re-release of "Four," the project — don't call it an album quite yet — is snowballing, says John Popper, Blues Traveler's harmonica-playing frontman.

"We're not sure what to call it yet," says Popper, via a telephone call from a Nashville recording studio. "It started out as something small and it's taking on a life of its own."

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Blues Traveler had just wrapped up recording a song with married country duo Thompson Square, straight off their stop at Country Thunder in Arizona. "They're not only amazing singers, they're amazing songwriters," he says. "We did it very fast."

JC Chasez was recruited for a song with Plain White T's, said guitarist Chan Kinchla in a separate interview. No one should belittle that collaboration, he added. "He (Chasez) is very musical because 'N Sync sang all those harmonies and it's all theory-based," Kinchla explained. "You need to know how music's put together to be able to do that, believe it or not. 'N Sync is such a big pop phenomena that it might be easy to think it was just overproduced. But singing is singing. He really knows the musical side of things. I think his pop sensibility is kind of cool. We're usually a little more rock oriented. It was neat to get that sensibility — especially with us and Plain White T's. He was great in getting the vibe right."

Chasez carried over that "vibe" into the 3OH!3 track, says Popper. "JC Chasez produced the Plain White T's tracks and ended up doing one with 3OH!3. We did two songs with 3OH!3. He sang on the third verse of one and he murdered it," he says.

The song is called "Blowing Up the Moon," which Popper describes as the realization of a dream "everyone" has had.  "The moon's up there and it mocks us all with this light," he says. "I actually wrote something on Facebook about the blood red moon — 'I swear by the blood red moon that is upon the land... that anything is possible and that all you truly desire is yours already for wishing it so!'"

While the list of collaborators may sound stellar, Popper said he's not finished yet. Blues Traveler is only halfway through the project but hopes to have it out by the fall, after it wraps up a summer tour with Sugar Ray, Smash Mouth and Uncle Kracker.

"We have a bunch more people in the works," he says, adding that each writing and producing session has been a learning experience. "We learned there's more to us than ourselves," says Popper. "We push. When you don't think you can do things, you get what you expect. This experience has forced us to discover parts of us we didn't know we had."