Aidan O'Rourke is agonising over his job description.

Can he call himself a composer when his output is still relatively modest compared to, say, James MacMillan or Eddie Maguire?

Then there's the question of whether he can be a composer in residence when he's away on tour so much, working with an increasing array of bands including the hugely popular Blazin' Fiddles, the brilliantly adventurous fiddle- accordion-guitar trio Lau, and world/jazz/trad crossover group Cascade.

The fiddler from Seil Island, near Oban, is being a bit hard on himself. His 2003 Celtic Connections New Voices commission, Sirius, continues to stir interest - and as well as writing for Cascade he has extended works on the stocks for Tobermory arts centre, An Tobar's tenth anniversary in June and Ceol Mor, the junior version of folk orchestra The Unusual Suspects.

As for his residency at the Tolbooth in Stirling, despite periods of absence which have caused his original 12 months in the role to be extended to two and a half years, he has made a definite impression on the schools and communities in the Stirling area. He's now instantly recognised as "the music man" by previously sceptical pupils. His musicianship, knowledge and enthusiasm have inspired young musicians to apply for further education courses in traditional music. And he's about to deliver 92.4 Degrees, the second of his new works for the Tolbooth, as part of the venue's roots music festival, The Blend, which also features guitar legend Davey Graham and Cajun music star CJ Chenier.

"It's been a great experience for me as a musician," he says. "There have been frustrations, such as working with kids from a halfway house for the homeless and losing a great wee drummer because he made up with his parents. Though I could hardly say, Gonnae keep no' speakin' to them for a while longer, the band's just gettin' good,' I suppose. But the whole thing has given me a great insight into how a venue operates, which is good for a musician to see.

"Being involved in programme meetings and budgets and seeing the details that can go into running a concert - people don't appreciate how much goes into putting music on - means that I now understand what's involved and can work with promoters to make things run more smoothly for them and us."

The actual composing part of his residency has, he says, been a dream. Where other commissions he has worked on might offer guidelines and suggestions that influence the shape of the music, his "piper payers" at the Tolbooth, Alasdair Campbell and Carolyn Paterson, have given O'Rourke a completely free hand.

"It's like being a kid in a sweetie shop," he says. "But then you start to write for the Danish fiddler Harald Haugaard and the pianist David Milligan, who are both fantastic musicians, and it becomes quite a scary sweetie shop. I'd never written for the piano before so that was quite a challenge. But once I started I got really interested in the harmonic possibilities and when I sent David his part he came back to me and said it was fine, thank goodness."

The music was all written with the specific players and their instruments' capabilities in mind. For instance, Ross Ainslie, who'll be playing Scottish smallpipes, has extended their range through his exceptional technique, so O'Rourke knew he'd be able to cope with certain note patterns. The addition of Jarlath Henderson's uilleann pipes and Simon Thoumire's concertina alongside Donald Hay's percussion offered further tonal options and inspiration at the writing stage.

"I think composing does get a bit easier the more you do it, although where you are physically can have some bearing on how well the writing flows," says O'Rourke. "When I wrote the previous piece for the Tolbooth, I remember I did a lot of the writing on buses because I wasn't happy where I was living in Edinburgh. This time, I went back home to Seil and melodies just came to me. I had about 30 ideas, some of them complete tunes, some just motifs, and I brought them back here to Linlithgow to work on them. I've also moved up in the world. I passed my driving test and have a car now, so I'd go out and drive around, singing to myself, and then park and play the tunes on the fiddle."

With a tour for Lau imminent, beginning with their first album's launch at the Bongo Club in Edinburgh on Monday, O'Rourke won't have long beyond The Blend to play the composer in residence before he's off on his travels again. But it's never a case, he says, of out of sight, out of mind.

"I think I'll always have a connection with the Tolbooth after this residency is up, and when I'm away I often have ideas that I can work on with the schools and community projects when I come back," he says. "It's important to leave something behind and if I can get more people involved in playing music, maybe in a community ceilidh band - get people dancing, too - then I'll feel I've achieved something worthwhile." Aidan O'Rourke's 92.4 Degrees plays at the Tolbooth, Stirling, tonight. For full details of The Blend 2007, visit www.theblendfestival.com or call 01786 274000.