IN THEORY John Wallace is talking me through De Profundis, his new work for the East Neuk Festival. In practice it's more like he's performing it.

"… And then the bass drums will be rhum, rhum, rhum and there's this dominant 13th chord …"

He suddenly ramps up the volume: "RHUM, RHUM, RHUM, BOOM, RAAH …"

Wallace, former principal trumpet with the Philharmonia Orchestra and for most of this century Principal of the Royal Conservatoire of Scotland, is sitting in his eyrie in Glasgow's South Side doing what comes naturally to him. When it comes to music, he could enthuse for Scotland.

In his time Wallace, 68, has played at royal weddings (Charles and Di's to be precise), and had pieces written for him by James Macmillan and Sir Peter Maxwell Davies. Now, when others of a similar age are enjoying their retirement, he's still beavering away, most notably on this year's "big project" for the East Neuk Festival.

De Profundis draws on both traditional plainchant and Henry Walford Davies's chorale setting of the penitential Psalm. It draws, too, on Wallace's own background and history.

A few days before we meet in Glasgow I watch Wallace conduct a rehearsal in Glenrothes with the Tullis Russell Mills brass band. It is the band in which Wallace himself cut his teeth as a musician (as did his father Kiff before him) and now Wallace and the band are working on an improvisation that draws on the plainchant and Hebridean psalms to create an installation that speaks to the mining traditions of Fife.

For the festival the band – all amateurs – will join Wallace's own ensemble, The Wallace Collection, to play in a darkened barn while the audience – wearing lamps on their heads – wander between them.

"We're used to sitting in band formation playing to an audience from the stage," points out David Chesney who plays trombone for Tullis Russell, "So, yeah, challenges …"

"We've played at big festivals before," adds tenor horn Steven Craig, "but what we're doing with De Profundis is a completely different to anything we've ever done or probably will ever do again. That's exciting."

For Tullis Russell it's a new chapter in a long-running story. The band was formed in 1919 so it is closing in on its centenary. It has outlasted the paper mill that it grew up around, which closed a couple of years ago.

The band itself has long attracted members outwith the mill setting anyway. Chesney, originally from Northern Ireland and now based in Saint Andrews is an orthopaedic surgeon by day. He has been with the band for the last six or seven years, playing community and Christmas concerts. "Playing in the band has to be fun. People have to enjoy it. It's a hobby."

A hobby and yet also a tradition. "It represents a musical organisation that has been here longer than the town," points out Craig. A health and safety manager when he's not playing with the band, Craig, 58, has been a member of Tullis Russell since the 1960s when Wallace's father was the band's conductor. "We've always operated with strict morals and principles," he adds. "If we say we are going to do something we do it."

But yes, he says, it's fun too. He's had the chance to play in the Albert Hall and the Sydney Opera House with the band.

De Profundis, however, represents something new and different. There's a real sense of anticipation about Wallace's renewed relationship with the band. "It's an exciting time because he's a big name," says Craig.

The band's involvement with the East Neuk Festival also suggests a new future for the very brass band tradition itself. Because, make no doubt about it, it is under pressure. "I grew up in Yorkshire," points out percussionist and youth band manager Mark Koziel, "and by the time I left to come up here in 2006, bands were closing down. They were dying. It's more fun to sit at a computer and a Playstation than go out and play a brass instrument.

"I am passionate about the youth band set-up. That needs to be at the forefront of the organisation's mind because it's the future of the band. And John's fantastic at getting involved with the kids."

For Wallace, De Profundis is a way to tap into his own memories of his miner grandfather and the brass band tradition that has been so much part of his family's life. But more than that, he says back in Glasgow, it's about tomorrow as much as it is about all our yesterdays.

"The great pleasure for me is working with people who love it. They really love the playing and the challenge for me is convincing them that they are good enough to do this, that they can move with the times and still be relevant. This isn't all about the past. This is really about the future of brass bands as well."

John Wallace, the Wallace Collection and the Tullis Russell Mills brass band will play De Profundis at The Bowhouse by St Monans, Fife on Saturday, at 6pm. www.eastneukfestival.com