This week Harrison, who teaches piano on the Royal Conservatoire of Scotland's jazz course, has been premiering his first work for the adventurous chamber music group Mr McFall's Chamber. Part of a programme that features arrangements of music by friends and rivals Frank Zappa and Captain Beefheart, their contemporary George Crumb and a new piece by saxophonist Martin Kershaw, Harrison's composition is based on Beefheart's monologue The Dust Blows Forward and marks the pianist's first foray into working with voice samples.
He's worked with singers - Carol Kidd and the late Tam White are among those who have called on Harrison's considerable accompaniment skills - and creating electronic sounds has been a feature of his adventures with free-spirited jazz trios Trianglehead and Breach. Beefheart, however, represented a particular challenge.
"I'd heard some of his more straight-ahead stuff through Tam White, who was a big fan," says Harrison down the line from Lyth, near Wick, where he's recording a new solo piano album. "But when I got the commission from the McFalls I thought I'd follow the theme of the programme, which is Freak Out, and delve into some of his denser work and went straight to Trout Mask Replica, which is still quite a heavy musical experience - there's so much going on in there."
The sound of Beefheart's unaccompanied and uncompromising vocal on The Dust Blows Forward was the first thing that caught his attention.
"What I liked about it was, he's kind of singing it, although it's not in pitch, and it's a really interesting way of vocalising," he says. "But the challenge I faced was stretching this piece that's two minutes long on the album into a work that lasts 12 minutes. I didn't want to just pad it out. I wanted to stay close to the spirit of the original."
He was helped by the possibilities offered by another new experience: writing for French horn. The McFalls line-up for Freak Out, which takes its name from a classic Zappa album, pitches Alec Frank-Gemmill, principal horn with the Scottish Chamber Orchestra, alongside McFalls regulars, cellist Su-a Lee, violist Brian Schiele, violinist Robert McFall and Rick Standley (playing bass guitar here) as well as jazz drummer Stuart Brown and percussionists Iain Sandilands and Tom Hunter.
"Alec's a pretty monstrous player and he's been really helpful," says Harrison. "I'd never written for a line-up like this before at all but it turned out to be a treat because the French horn, for me, has a rustic quality that fits in really well with the words of The Dust Blows Forwards. I became really immersed in the poem and could recite it from memory fairly quickly, and it suggests a lot of images of Americana, such as the smokestacks, and the desperation of Beefheart's youth living in the desert."
Harrison has, he concedes, taken some liberties in constructing a piece in four sections from the 25 lines of speech on the original recording, and will be bringing the good Captain back from the dead so that the ensemble can play with and around him as he delivers The Dust Blows Forward over the sound system.
"There are one or two moments where I've twisted the timbre of his voice but otherwise the original track is intact," he says. "I hope Beefheart himself would approve of what I've done because there's a lot of room for improvisation, as well as a healthy dose of electronics, and although it has been a challenge for me, the piece itself is, I think, a lot of fun."
It's also some distance musically from the album Harrison is concerned with as we speak. On retreat in Caithness, he's got his head stuck into the Great American Songbook and is finally laying down the solo piano album that he's been procrastinating over for the past three or four years. With the luxury of a full week in a studio, as opposed to the jazz musician's usual lot of a day or two, he's been able to spend time examining each song.
"It has a practical side in that I really need something I can sell at gigs, a kind of calling card, if you like," he says. "But I've been able to find some lesser known standards and different ways of approaching ones I already knew, so it will be familiar and yet not so familiar."
McFall's Chamber Freak Out is at Brunton Theatre, Musselburgh, tonight, and reviewed on page 16.