The annual musical binge that is Southbank's Meltdown Festival has taken on a decidedly chi-chi quality in recent years, with the likes of David Bowie, Patti Smith and Jarvis Cocker acting as both star headliners and savvy directors.

This year the venue has selected a very different eminence as frontman and curator, American jazz legend Ornette Coleman. It's a brave choice; Coleman is hardly a household name. No one is yet sure who will be brought in by the Pulitzer Prize winner, who at 78 can still shine and startle as a performer, as he showed at the Royal Festival Hall two years ago. He will perform two shows as part of the Meltdown programme.

From the outset he has attracted acolytes and detractors in equal measure. His landmark albums, The Shape of Jazz to Come (1959) and Free Jazz (1960) were revolutionary, dispensing with chord structures in favour of improvisation, with Ornette starring on quirky plastic alto sax. Subsequently he explored world music, classical composition - 1972's Skies of America was recorded with the London Symphony Orchestra - and electric jazz. Along the way he also took up trumpet and violin, and inducted his son, Denardo, as his drummer.

Since then Ornette and Denardo have become a family firm, and the drummer will doubtless leave his imprint on Meltdown 2009. Coleman himself is clearly just getting attuned to his role as musical director, proving as keen to talk metaphysics as music, though his passion for creation is undiminished. "I write every day," he says. "I prefer the title of composer to jazz musician, and composing ideas, not just musical ones, that can serve humanity."

His outlook, he says, and the musical system he terms "harmolodics", has always been shaped by his early life in Fort Worth, Texas. His first love was the blues, and despite a reputation as a champion of dissonance, his playing has retained a bluesy feel. "I was born in the South, where there wasn't much opportunity, and I have never wanted to feed that class system, a monarchy system in sound. I have never liked categories. Whoever is playing the notes, they're still the same notes."

On Skies of America, I say, he has a track called "The Men Who Live in the White House" - what about the new guy in residence there? "That number was asking what do those people want to achieve - is it to help us become better human beings and to make existence more valuable? Human beings are the most valuable asset on earth."

Denardo is more direct. "I don't care for all the dire talk going on," he says. "Maybe this is a good time for people committed to freedom in music, in art."

That's an ethos that fits Meltdown, which seems likely to include a strong New York contingent - sax player John Zorn, perhaps, who cut a Coleman tribute album, bassist Charlie Haden, whom Ornette cites as his closest ally in pursuit of "what we call The Idea", or light-hearted Lou Reed, who has also worked with him. "It's early days," says Denardo of any line-up. Watch this space