Verdict: four stars

Various venues, Glasgow

Counterflows is no timid affair: here is a festival that trusts its audience to handle what it dishes out by way of bold, borderline mystifying experiments in sound art and, judging by sizeable and attentive Friday and Saturday crowds at this fourth edition, the trust goes both ways.

On Saturday round about teatime I had my eyes cast heavenwards along with the rest of the congregation at Glasgow University Chapel, trying to make sense of unworldly sounds being unleashed by Sten Sandell's organ improvising.

He made the beast throb, palpitate and squeal; he was clearly drawn to its extreme ends, with notes so high and piercing it hurt, and so low you didn't so much hear as feel them at the back of the skull.

Down on our level, saxophonist Evan Parker kept things grounded with softer-edged lines and the occasional frenetic Parkerian blast, so irrepressibly exuberant he had to circular breath for long minutes to uphold the flow.

I'm not sure how much of a duo this performance really was, or whether each musician was simply doing his thing in the congenial company of the other.

Either way, that the playing ended just as the chapel bells chimed time was a nice touch of straight-up synchronicity after the fray.

Friday opened with a Counterflows commission by Richard Youngs, a musician ever game for a new challenge.

Experiment for Demolished Structures involved four vocalists positioned in four corners of the CCA theatre, each sombre-faced and clearly concentrating hard.

They wove their voices into a chilly, awkward tableau - occasionally the polyphony produced a chord or overlapped in palpable ways; mostly the space between the voices was all-too wide.

A more resonant acoustic might have helped meld things, but even here the text was tricky to decipher. The lines 'you make my eyes sore' and 'safe from the town planners' stood out.

A highlight was violinist Angharad Davies's duo with Sebastian Lexer. Barefoot in the middle of Garnethill Multi-Cultural Centre, she played while rotating slowly under a faded disco ball, several Chinese dragon masks looming behind her on the back wall.

She scraped her bow across the strings to produce grunts and splutters; looped and distorted by Lexer, these sounds set the imagination flying.

Grunts became growls or purrs or engines or scraping chairs. Davies then introduced clear, fragile long notes high above, but things fell apart as she loosened the strings right out of the violin.

It was like witnessing an act of self-destruction, the infliction of discomfiting chaos out of which came a new calm. The deep frequencies were still there in the backdrop - a heartbeat, or the shelling of a faraway city, or the bass lines of a party to which you're not invited - but the piece ended in serenity, content in the imperfect but beautiful here and now.

I was less enthralled by Hisato Higuchi, a fedora-toting Japanese balladeer whose breathy, extravagantly mellow crooning made for a long 45 minutes.

An ebullient set from veteran free jazzer Daniel Carter and electronicist Owen Green solved the soporifics: they treated us to joyously raucous, blink-and-you-miss-it improv, with Carter producing furious catches of melody and borderline riffs while Green's electronics chattered, shadowed, pestered and mimicked, spinning off into lovably daft sonic realms.