Music: Singer Richard Thompson is final act at Philadelphia Folk Festival, which he first played at 40 years ago with Fairport Convention

HARD TO BELIEVE it was 40 summers ago that Richard Thompson first played the Philadelphia Folk Festival.

Still one of the most vibrant and prolific of folk-rock composers and performers - and widely regarded as one of the world's greatest guitar players - he returns to the festival this weekend with a new album ("Dream Attic") to tout and the mission of closing the event, all by his lonesome.

"Whoa, that's great, fantastic," Thompson murmured in a recent chat when told of his honor as Sunday night's concert capper, on a bill that includes his friend and former bandmate Iain Matthews, the Great Groove Band, Joe Pug, Susan Werner (in a new configuration with Natalia Zukerman and Trina Hamlin), Scottish exports Malinky, Rockin' Acoustic Circus and the balmy, Bayou bluesy Subdudes.

"I'd better be good, that's all I can say."

Thompson talked of Philadelphia as being "one of the greatest towns for folk, thanks also to WXPN and, um, the caliber of the print journalism."

And the wag remembers his debut at the festival like it was only, oh, a couple decades ago. 'Twas with Fairport Convention, the legendary English band that charged up traditional folk ballad motifs with pounding beats, fiery fiddle, smokey singing by the much-emulated Sandy Denny and young Thompson's already amazing, Celtic snake charmer electric guitar solos and ruthless-to-the-core vocalizing.

"The festival people put us on in the afternoon because of concerns we'd play too loud and annoy the neighbors at night. And they still told us to 'try and keep the noise down, chaps,' " he recalled. "What a waste of time. We just played as loud as we possibly could. Everyone was dancing at the end. That may have been another no-no. But we all survived."

Well, most of us. One tune on his new album, "A Brother Slips Away," bemoans the loss of "three old friends who recently died within a few months - a musician friend, a filmmaker and an old woman. It was a brutal time. But as a songwriter, you use a song in a cathartic way. It's a lot cheaper than therapy and does seem to help."

Ever one to challenge himself, Thompson's "Dream Attic" set (out Aug. 31 on Shout! Factory) is a unique project, cut live in concert with a bristling electric band yet featuring all new material. Other highlights include: a surreal portrait of the "Burning Man" festival that was "true, all true," he swore; a rousing sing-along, "Big Sun Falling in the River," that you wish would never end; a winsome suggestion to do things differently the next time "If Love Whispers Your Name," and a typically (for Thompson) perverse character sketch of serial killer "Sidney Wells."

That one kinda connects to the artist's upbringing as the offspring of a Scotland Yard inspector, as does another entry, "Crimescene," though he suggested "it's really a metaphor for the aging process, the assault on your body."

"What can I say? There were a lot of criminology books in the house and I read them all," Thompson declared. "And if you write fiction, you need to consider all aspects of the human condition. People are sometimes revealing in extreme situations. And there's the potential for monstrous behavior in all of us."

Getting his band to learn a complete album's worth of material, then go out and perform it live with a recorder running "is the opposite of how music is usually learned, perfected and recorded, one song at a time," shared the artist. "We did a bit of research and couldn't come up with another album that's ever been made this way. And at times, the process almost drove us mad."

His initial impetus was a fan telling Thompson that "I play differently, better in concert than I do in the studio. So I thought, let's pursue this a little further. We have a fantastic band that can really cut it, so let's just go for it."

Was there also a notion of saving money, making an album on the cheap?

"That's another concept. In this disturbing time of record companies not having support funds, you do look for ways to save money. In the studio you can always do another take or fly someone in to overdub a sax solo. In the concert situation, things are out of your control, but in a funny way that can work to your advantage. We actually recorded shows eight nights, but the first five were really rehearsals and the last three were all done in the same club. And our audiences rarely made noises during the performances. They were so respectful, it's sickening."

While he comes off as one of the most commanding musical figures on stage and disc, in interview Thompson seems a rather modest, self-effacing sort, an impression enhanced by his sometime stammer.

He's quick to downplay his recent honors as curator for the Meltdown Festival in London, a distinction previously bestowed on the likes of David Bowie and Elvis Costello, and his Mojo Les Paul Award from Gibson Guitars and Mojo, Britain's top music magazine.

But when you've been on as many "world's greatest guitar player" lists as Richard Thompson has . . .

"It's a funny thing. People are very partisan about their guitar heroes. I think it's very difficult to compare them. Everyone has their voice and individuality. And I kind of hate the polls, because they've got Keith Richard at number 3 and Andre Segovia at 57. They're both fine players in their own right, but to put them on the same list . . .

"You know Eric Clapton had a hard time when they started calling him God," added our fave. "It made him very self-conscious about his playing. So I basically try to ignore that. I think of myself as a songwriter who gets up and plays. I'm an accompanist. But sometimes I do get carried away."