HE comes on stage in his wheelchair, his arms held out like a plane. By his own admission, John Martyn is often flying. At first, it's hard to make much of those eccentric, slurred vocals - suggesting acute inebriation or perhaps a speech impediment. Until you remember how to listen to John Martyn, and then he really sings.

Martyn possesses the remains of one of the most influential singing voices in popular music, having inspired everyone from Joni Mitchell to Paul Weller. He launches into a reprise of his 1973 album Solid Air - only the second time he has ever performed it live in its entirety. At least, it's supposed to be in its entirety. He rearranges the tracks to keep you on your toes, and you have to play spot the lyric.

"Don' wanna knowww 'boud eevil, ah onaly wanna knowww 'boud luv "

Hearing John Martyn is a bit like listening to an old valve radio and searching for Radio Luxembourg. Every so often it tunes in and you get lifted by a warm wave of recognition, before the music disintegrates into random noise and cold static.

"Maay-ah you uh neahvvirr lay you hed down "

Of course, all those years of hard-living have taken their toll. Martyn has lost most of his upper range, but the basso is more profundo than ever.

"An ahm livin' onnah zzzzzzolidaire."

He didn't like Solid Air when he first recorded it, didn't think his singing was good enough. He worried that his innovative phrasing had more to do with his altered state than jazz. Martyn couldn't believe his own virtuosity - and sometimes, it seems he still can't.

He admits to having spent most of his waking life chemically enhanced, and it shows. He lost a leg a couple of years ago. "I'm a living leg-end," he quips, reaching for another guitar."Aye well. Best foot forward. Heh-heh."

Sitting mountainous on the Royal Concert Hall stage, seeming to take up as much space as his band, he mutters in an exaggerated Glasgow accent and shouts at the occasional heckler, but you don't come to John Martyn for onstage banter. You come to witness living history. And he deserves such recognition, even if he doesn't feel worthy. His chat suggests he's not sure whether he is a charlatan or a genius, but what the hell? Most folk rock icons in their 50s would be relaxed in their celebrity, comfortable in their veneration, but you get the impression that John Martyn is still an uncomfortable Scot at heart who feels he still has to prove himself.

Why else surround himself with such a bloodless band? The electric piano, fretless bass and ranting sax sound very together and professional (everything Martyn isn't) But it's too smooth, too dinner jazz. It's like listening to Leadbelly in a chill-out remix.

Really, to hear Martyn properly, he has to be solo, as he was meant to be. Playing his acoustic guitar on full echo, gibbering into the microphone. His solos are extraordinary, voice and instrument merging into one sound.

"Mahh jeeelly rowl oan the banks o' therivvah fowgetabtomrw."

Martyn is 58 but looks older, and you wonder how much longer he'll be around to perform. "I'm just very difficult to kill," he says mordantly. True, but it gets you in the end.

Celtic Connections has always prided itself on being a broad musical church, adds Sue Wilson, but hearing a Slayer cover epitomises just how far it's won the trust of artists and audiences to keep stretching its wings. Glasgow rockers Aereogramme paid tribute to the heavy metal band when closing Tuesday's Ballads Of The Book gig, a live preview of the eponymous Chemikal Underground album, due out next month.

The project saw 18 Scottish writers providing lyrics for a cross-genre selection of their musical compatriots. Six acts brought the album to the stage, each performing their track from the record as well as some of their own material. As well as Aereogramme, other standouts included Alasdair Roberts, whose quavery croon and vibrant guitar work adorned poet Robin Robertson's composition, The Leaving, alongside songs from his new CD The Amber Gatherers, and Karine Polwart, with a sublime setting of Edwin Morgan's The Good Years.

Later that night, L'Occidentale de Fanfare made their Celtic Connections debut. An 11-piece French extravaganza with - literally - no strings attached, they feature two percussionists and five brass players, plus accordion, piccolo, bombarde and bagpipes.

Mixing traditional rhythms and melodies from their native Languedoc with jazz and wider world music influences, their brightly patterned, groove-driven sound united echoes of La Bottine Souriante, the Peatbog Faeries and classic big-band music, while lively stagecraft set the seal on a splendidly entertaining show.

One way and another, there was a lot riding on Wednesday's Real World concert. Featuring artists from as far afield as Africa and central Asia, it was the most conspicuous example of the festival's expanded horizons under new artistic consultant Donald Shaw, and also the first time Peter Gabriel's celebrated record label had produced such an event in Scotland.

A near-capacity crowd was treated to a succession of outstanding performances, starting with the young Mauritanian singer-songwriter Daby Touré, whose supple, soaring vocals were framed by bracingly taut, reggae-infused guitar, bass and percussion backing.

Next up were Cuillin Music, the band who continue to promote the rich creative legacy of visionary composer and performer Martyn Bennett, who died two years ago. With Kirsten Bennett on synth/percussion, fiddlers Adam Sutherland, Greg Lawson and Martin Swan, and Ross Ainslie and Fraser Fifield on pipes and whistles, they delivered a thrilling handful of tracks from Bennett's Bothy Culture and Hardland albums, keeping the flame alive by reworking the material rather than seeking simply to replicate the originals. Then came Uzbekistani singer Sevara Nazarkhan, a pixie-like figure with a ferocious voice, matched by a dub, dance and electronica backdrop from her four-piece band.

Finally the Fruitmarket resounded to the mighty guitar virtuosity of Skip "Little Axe" McDonald, flanked by the heavy-duty rhythm team of Doug Wimbish and Keith LeBlanc (of the Sugarhill Gang) with live mixing by DJ/producer Adrian Sherwood. Drawing largely on the recent Little Axe album Stone Cold Ohio, they stirred together a dark, delicious stew of blues, gospel and soul.

The 14th Celtic Connections draws to a close tonight, with Shaw's careful balance between continuity and innovation endorsed by a walloping 30% increase in ticket sales over last year, putting the festival easily on course to outstrip its previous attendance total of 100,000. Even in the least publicised areas of the programme, there were successes. The free morning schools concerts have seen a dozen or so headline acts from around the world performing to over 15,000 local children, while contenders on the Danny Kyle Open Stage were chosen from a record 200-plus applicants, some flying in especially from Sweden and Norway to perform.

Next year will pose fresh challenges, notably finding another new home for the Festival Club - the Holiday Inn West being due for demolition - but after this year's showing they can be met with justly restored confidence.