Sometimes I think, in the end, only the voice truly matters. Dress it however you wish, zhuzh it up with textural condiments: cool electronics, warm strings, harsh noise, romantic rhythm, ambient atmospherics. It’s all decoration. The human voice is what we respond to most fervently and instinctively in popular music.

This – far from infallible – notion occurred to me while attending a concert celebrating 50 years of the Scottish Chamber Orchestra as part of Celtic Connections, Glasgow’s annual (and always inventive) festival of roots music. Led by American conductor Eric Jacobsen, the SCO opened with a lively rendition of Mendelssohn’s Hebrides Overture before providing supple, sympathetic support for four voices. Each was unique and evocative. One was truly transportive.

When Buchanan sings, Glasgow is reborn as a widescreen cinematic landscape

Though there was no headline act, the ovation which greeted Paul Buchanan when he sauntered on stage after the interval – looking like an elegantly ageing arts tutor in some underfunded Russell Group uni – gave the game away. Waiting for the audience to settle, Buchanan read my mind: ‘What if it’s not any good?’ he said.

Stage appearances from the former Blue Nile singer and songwriter are rare. In his home city, they come stacked with contextual significance. Across just five albums – four with the Blue Nile, one solo – Buchanan has rendered Glasgow as a city worthy of romantic re-imagining. It sometimes seems that his entire creative raison d’être is to provide an aural response to the question posed in Alasdair Gray’s Lanark: ‘Glasgow is a magnificent city. Why do we hardly ever notice that?’ The answer: ‘Because nobody imagines living here… If a city hasn’t been used by an artist, not even the inhabitants live there imaginatively.’

Well, Buchanan has used it, in the same way Frank Sinatra used New York. When he sings, Glasgow is reborn as a widescreen cinematic landscape, every citizen walking the streets knee deep in their own arthouse movie. In his voice there is black rain and red sandstone; reflected car headlights and blurred neon; wide avenues, cobbled lanes; melancholic dusk and gleaming dawn.

We hear these stirrings in his short set, featuring four songs arranged for orchestra by Kate St John. ‘Let’s Go Out Tonight’, in particular, from the 1989 Blue Nile album Hats, was ravishingly romantic. The jewel-like miniature ‘Mid Air’ was impossibly fragile, while a new song, ‘Snow’, suggested an imminent solo album will not stray far from these streets.

Buchanan returned for an encore, but before that there had been other fine voices to reckon with. As the singer in Lau, the expansive and innovative folk trio, Orcadian Kris Drever has a voice you would follow into battle – or perhaps strike to warn your village of an impending attack. Not to suggest that it’s loud or showy, but boy, it’s clear and strong, brimming with truth and authority. On an epic, spell-like rendition of the traditional folk tune ‘The Cruel Brother’, with Aoife O’Donovan and Inge Thomson on backing vocals, Drever sang as though the centuries-old tale of fratricide and bloody vengeance had happened just that morning.

Later, US singer-songwriter O’Donovan performed pieces from a new work ‘America, Come’, which explores the women’s suffrage movement. It was more fun than it sounds. O’Donovan sang with a warm, assured resonance and her set featured the most full-blooded arrangements of the evening, which made fine use of the local CREATE chamber choir, drums and electric bass. Even then, only some of her melodically interesting songs cut through.

First on the bill was Celtic harpist Maeve Gilchrist, originally from Edinburgh, now Brooklyn-based. She didn’t sing, but her playing did. Gilchrist has many voices – rippling, dreamy, complex, surging, rhythmic – and had barely revved up into full expression when her short set was over.

For an encore, everyone returned to perform ‘Happiness’, the opening track on the Blue Nile’s third album, Peace at Last. Drever sang a verse and played the simple refrain on his guitar. Buchanan chimed in. The choir joined him. So did some of us. The results were practically hymnal.

Then the ensemble trundled off, the house lights flickered on, and the audience booed (this was booing as praise; love expressed as disappointment). Buchanan duly strolled back into view, sheepishly confessing that they had no other songs to perform. This seemed an avoidable oversight. He sang ‘Mid Air’ again, even more pin-drop perfect this time, before the whole bunch came back to play ‘Happiness’ for the second time in ten minutes.

It was a strangely ragged conclusion to a stellar night. Pianist and Celtic Connections artistic director Donald Shaw shrugged: ‘I told Paul people would want to hear more than four songs…’ We’d have stayed for 40. The power of the voice, you see.