This entrancing and almost entirely improvised session was one of the creative happenstances the pandemic's restrictions often prompted. In November 2021, the great Norwegian bassist Arild Andersen took this accomplished quartet into Oslo's Rainbow Studio to develop some of his own pieces - but the country's travel restrictions left the musicians to their own devices, with ECM boss and producer Manfred Eicher unable to attend.

On the second day, Andersen - for decades a formidable free-improviser, as 1972's Jan Garbarek/Edward Vesala classic Triptykon confirms - suggested they drift into improv, and the resulting 38 minutes' playing time became the core of this album, with the bassist's composition 'Short Story' completing it.

The improvisations were recorded in two extended parts, which the tracklist splits on the pauses into seven sections. Andersen's bass opens with repeating single notes interspersed with slurred, humming tones shadowed by Helge Lien's softly trickling piano figures, eventually joined by Marius Neset's clipped exhalations on tenor and Håkon Mjåset Johansen's ringing cymbal patterns. Metallically plucked piano strings then contrast with sensuously melodic bass phrasing which Neset joins in breezily gambolling figures, while the saxophonist's long-tone high sounds over soft mallets in the third part recall Jan Garbarek's haunting soliloquys in churches.

A gleeful, skipping folk-dance takes the music out into stretches of increasingly uninhibited ensemble postbop (Lien's and Andersen's impish phrase-swaps and Neset's gathering eloquence over Johansen's hustling drums ignite in the headlong fifth section), part seven withdraws to minimal glistens and murmurs, while Andersen's tenderly soulful 'Short Story' makes a mesmerising gospel-graced finale.

Only improvisers at the top of their game could have made Affirmation as loose yet gracefully melodious as this.