It was foolish, in retrospect, to expect anything resembling a linear conversation with Cedric Bixler-Zavala, lead singer and lyricist of exuberantly coiffured musical test-pilots The Mars Volta, whose style has always veered between rigorously disciplined arrangements and the freest kind of improvisatory noodling. While other musicians would be vigorously plugging their latest album - in The Mars Volta's case, Octahedron, greeted thus far with the kind of mixed reviews that reveal more about the critics than the band - Bixler wants to talk about what's on his turntable.

"I'd been listening to a lot of Scott Walker lead singer of the Walker Brothers, as a lot of that stuff just got re-released. Also, I'm a really big fan of Roky Erickson - he's got a lot of loud rock, but he does these beautiful ballads. Plus, I love the fact that a lot of his lyrics border on the absurd - because he's a little cuckoo, you know? So that, and Vic Chestnut, and The Wicker Man soundtrack ... most of the stuff I've gotten into recently is off that Finders Keepers label. They do these great B-Music compilations, which have everything from Turkish psych rock to Bollywood soundtracks."

The list goes on, yet avoids those names one would expect when considering the "prog" label that has dogged The Mars Volta since Bixler and fellow bandmate Omar Rodriguez-Lopez put all-conquering post-hardcore outfit At The Drive-In on permanent hiatus and went off to record a jazz-punk concept album (a move regarded by many at the time as emptying a shotgun into the cash-cow's skull). Their debut, De-Loused In The Comatorium, was a surrealistic, genre-mashing broadside against minimalism, which intimidated the critics as much as it impressed them. Since then, chronic accusations of self-indulgence have made "prog" a permanent facet of The Mars Volta's image, despite the fact they couldn't be further from the horrors of King Crimson and Yes.

Bixler, to his credit, has said repeatedly they take the word "progressive" literally, and don't see anything progressive in singing about hobbits and spaceships. For Octahedron, the Californian-born band instead looked to their roots.

"We come from a Latin culture where the subject of the Devil is often predominate and usually feared, because that's just the way Catholicism is. So I definitely wanted to go down that road and explore that kind of subject matter, as well as what a family must feel like when their loved ones are kidnapped, especially in South America where kidnapping's an industry. The feeling of putting the ransom note down instead of actually reading it ... the bleak feeling of the desert ... stuff like that."

And in that, they are successful - Octahedron's greatest strength is its evocative nature, indicative of the way The Mars Volta carry with them not only a sound and a mood but an imaginary landscape - a place of dry heat, red light, old ghosts and narcotic hangovers. It will be interesting to see how such an illusory vista will translate to T in the Park, with its 50/50 chance of rain and pale blue audiences.

The Mars Volta's live shows are notoriously lively affairs - the crowds are often largely made up of At The Drive-In fans who have stuck by their heroes throughout their experimentation, and thus retain a mosh-pit sensibility. On stage, Bixler's distinctive falsetto vocals are punctuated by stunning feats of acrobatic prowess, from backflips to apparent epileptic fits. Given the exhaustion that's inevitable at the end of such touring, what does the band do on its off-time?

"I just try and watch movies and listen to music that's the exact opposite of us. Get away from the loud people, y'know? But that's kinda hard cause we're all loud people," he laughs. "Between tours, we sometimes scatter, but our drummer's been trying to instil this family vibe in us, which is really great since he's still kind of the new guy - he's like 24, I'm 34 - and he takes it really seriously. He's never been part of a rock band' before, he was more of a session musician for all these great artists ... I mean, he introduced us to Booker T the other day. I was always saying, You played with Booker T, man!' and he's like, Nah, that's hella-boring.' Gah! He doesn't really understand the significance of it."

Before we end our encounter with a brief discussion about Doctor Who - Bixler and Rodriguez are unashamed geeks - I ask, given the ever-changing line-up of the band, is there anyone Bixler would like to work with? "It'd be fun to work with Brian Eno, but I doubt he'd be interested in going backwards and doing stuff that he's done already, which unfortunately is what I'd want to do. But then I can appreciate wanting to move forward."

The Mars Volta's fans can do the same.

The Mars Volta will be playing the Radio 1/NME Stage at T In The Park on Friday, 10th of July.