It's hard to imagine a better setting (all right, Bulgarian hilltop barn aside) for this extraordinary choir.

Founded in the early 1950s, discovered by the record industry in the mid-70s, touring world-music circuits since the late 80s, these 22 women and two plucky men produce a resonance every bit as awesome as Kelvingrove's great echoey vaults. Under the fierce precision of conductor Dora Hristova the singers have their routine down pat, reconfiguring between numbers like a team of elaborately costumed synchronised swimmers.

They've performed their greatest hits hundreds of times, of course, and the edges are by now glossy-smooth. The indelible magic comes down to a few key factors: the strange beauty of Bulgaria's folk songs; the off-kilter rhythms that set your feet tapping to time signatures you could never count; the brazen harmonic arrangements – barbershop to stabbing dissonance, meandering incantations to meshes of microtonal white noise; the range of vocal colour in everything from nasal duos to earthy 22-part ensemble. And all of it is delivered with airtight precision.

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There was no explanation of what the lyrics are about or (my particular beef) who wrote the stunning harmonisations, so the choir keeps its mysteries fresh. But who really cares; to hear them sing is utterly transporting.