A long-time institution at Celtic Connections, the Transatlantic Sessions concerts are always one of the fastest sell-outs.

Revisiting the kinship between Celtic music and Americana, the concerts originated after the festival launched in the same year as the first TV series of that name.

As winning concepts go, it's a bit of a no-brainer: hand-pick from the myriad A-list Scottish, Irish and US artists in town for their own headline gigs, add a few more special guests, closet them together for a couple of days' rehearsal and then pile them all on stage, in accordance with the project's founding goal of "the ultimate back-porch session".

Its similarly long-time musical directors, Shetland fiddler Aly Bain and Dobro godhead Jerry Douglas, remain at the helm of each year's happy crew, which this time featured fellow Nashville heavyweights Nanci Griffith and Kathy Mattea, plus Scottish singers Eddi Reader and Julie Fowlis. On both vocal and instrumental duties were rootsier stateside stars like recent Grammy winner Tim O'Brien, Alison Krauss sideman Dan Tyminski and old-timey maestro Bruce Molsky, while guitarists Russ Barenberg and John Doyle extended the list of legendary pickers. The home team of accompanists included Bain's regular sparring partner Phil Cunningham, fiddler John McCusker, drummer James Mackintosh and even festival director Donald Shaw on accordion and piano, among a total cast of 16.

Besides the obvious virtues inherent in assembling such a cornucopia of musical class, the bonus of these gigs is the artists' palpable pleasure at sharing the stage with each other, by way of old acquaintance or new. The big names get a buzz from doing something down-home and informal, while the harder-core folkies enjoy the extra glitter of limelight. The show's balance between preparation and spontaneity seemed well struck on this occasion, with sufficient of the former to enable plenty of opulent full-ensemble arrangements, while retaining an aura of suitably laid-back conviviality.

Mattea offered the first of several tributes to John Martyn, who died last Thursday and who, like her, took part in that very first Transatlantic Sessions TV series back in 1994. In remembrance she sang a lovely version of May You Never, with Reader on backing harmonies, while a good many of those present subsequently had their own tall tales of Martyn's exploits to recount.

Griffith's song contributions included the 20-year-old It's a Hard Life Wherever You Go, in celebration that its first two verses, addressing Irish sectarianism and US racism, had since been rendered largely irrelevant, and a new one, The Loving Kind, about the couple who overturned America's ban on interracial marriage. Her voice isn't the limpid instrument it once was, but what it's lost in sweetness it's more than gained in depth and grit.

With Celtic Connections incorporating the launch of Homecoming Scotland, this year's Transatlantic Sessions was subtitled Bringing It All Back Home, and billed as reflecting a more specific focus on songs and tunes that began their journey on Scottish or Irish soil before crossing and re-crossing the pond.

There actually wasn't much of that in evidence, but the concert's pre-existing conceptual framework, together with the live reunion of traditions unfolding right there among the musicians, in age-old yet freshly-minted music, broadly fulfilled the brief nonetheless. And when the highlights ranged from Douglas's extraordinary soloing in his all-acoustic arrangement of Hey Joe - "by that great bluegrass icon Jimi Hendrix" - to a sublimely mellow ditty from O'Brien based on a Caribbean street-trader's chant, few were minded to quibble. "It's like singing along to all your favourite records," exulted Reader, before delivering a lush, luxuriant rendition of Willie Nelson's I Guess My Heart Just Settled Back To Earth, and it certainly felt like a privilege to be listening in.