The great irony of the Nitty Gritty Dirt Band's landmark 1972 release Will the Circle Be Unbroken is that nobody realized how truly groundbreaking it was at the time.

A generation-straddling collaboration between "West Coast longhairs" the Nitty Gritty Dirt Band and bluegrass, folk and country legends like Doc Watson, Maybelle Carter and Earl Scruggs, it was considered something of a vanity project at the time.

"We had just had a major pop hit with 'Mr. Bojangles,' so our band was all over the charts and on pop radio, especially," recalls band member Jeff Hanna. "So we had the leverage to make Will the Circle Be Unbroken. If we had not had that hit, our record company wouldn't have given us the freedom and budget to make a record. But we were so passionate in wanting to do the Circle record, and they said, 'Well, go ahead. You're not totally crazy. You just had this hit song.'"

The album put the Dirt Band on the country charts for the first time with "I Saw the Light," performed with Roy Acuff. But the bulk of the project's recognition came much later, as other artists and fans sang its praises.

"Bruce Hornsby did one of those 'desert island disc' Q&As where he was talking about the three or four albums he would take on a desert island, and Will the Circle Be Unbroken was one of them," Hanna recalls. "It really surprised me, and we were all really flattered by that. And then I met Bruce Springsteen years ago, and the first thing out of his mouth when I told him what band I played in was Will the Circle Be Unbroken and what an impact it had on him."

It's hard to imagine now, when everyone from B.B. King to the late Notorious B.I.G. to Kenny G have duet releases on their resumes, but back in the early '70s, such collaborative efforts were rare. Rarer still was the uniting of what audiences then saw as a West Coast folk-pop band and their musical heroes from the hills of Tennessee -- traditional country and bluegrass artists who garnered skepticism even inside Nashville.

"In Nashville, somebody wrote an article that said, 'Why are these guys recording an album with these quote-unquote dinosaurs?'" Hanna recalls, adding, "which was really offensive to us! But I think we proved them wrong."

All of which helps explain why the original three-disc set, with its elaborate gatefold packaging, disappeared from record store bins decades ago. Of course, the original Circle went on to become one of the most iconic albums of all time, certified platinum and sparking two follow-ups (Volume Two released in 1989, Volume III in 2002). CDs and downloads have kept the music available to fans, but the original experience has been long gone.

Until now. In honor of Circle's 40th anniversary, the three-disc set has been remastered from the original analog tapes and rereleased on vinyl for the first time ever. A high-definition digital HDTracks edition is also now available.

Hanna describes the remastered project as "returned to its glory."

"This record was recorded all live," he says. "And so a lot of the sound quality loss that you would get in analog recording by mixing multi-track tapes down to quarter-inch stereo for your masters wasn't an issue. There was no middle in the process. It went directly to first generation tape, which gave it a really amazing, immediate, beautiful quality in the sound. We're really proud of the way the record sounded."

The reissue is yet another sign of vinyl's comeback, a trend spurred not just by audiophiles but a generation raised on their parents' and grandparents' LP collections.

"There's something about the ritual of listening to a vinyl disc," Hanna observes. "I think the process of putting the needle down, listening to side one, flipping it over, listening to side two ... there's a whole generation of us that came up with that. It was a tactile experience. And also," he laughs, "the artwork on CDs requires magnifying glasses!"

Another irony of Circle is that the music it introduced to mainstream audiences has indeed come full circle, living on today in such artists as Mumford & Sons, the Lumineers and the Civil Wars.

Back in '72, nobody quite knew how to label the original Circle album. Hanna recalls that Roy Acuff, who wouldn't commit to the project until he'd heard what the longhaired boys had been up to, listened to the track "Nine Pound Hammer" and responded, "Aw, well, that's just country!" Later when Circle celebrated its 30th anniversary, music journalists called it a "roots music" collection.

Today the popular label is Americana. Which begs the question: With the current marketability of Americana artists, could there be a Circle IV in the future?

"That's something we haven't taken off the table," Hanna says. "We never thought we'd do a Circle II, and we ended up doing a Circle II and a Circle III."

Today what Hanna appreciates most about the making of the album was the chance to perform with so many legends, most of whom have long since passed away.

"People like Doc Watson, Earl Scruggs, Jimmy Martin, Mother Maybelle Carter and Roy Acuff -- getting to play music with them was incredible," he says. "It was extremely fun and extremely scary, having that tape rolling with people that just played with such jaw-dropping, amazing musicianship. And they were all so gracious! It was generation spanning, and it also bridged a cultural gap. A high water mark for our band, for sure."