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."