The concept of improvisation in music is, while not completely wedded to jazz, at least bound to it quite tightly. Obviously this doesn't have to be so tightly bound with all the traditional and conventional instrumentation and form, as the all-star group Æthenor go a long way to demonstrating. Comprised of Stephen O'Malley from Sunn O))), Daniel O'Sullivan and Christopher Rygg of Ulver and renowned drummer Steve Noble, album En Form for Blå was entirely improvised – or 'automatically composed', according to functionalist turn of phrase on the sleeve – at three shows in Oslo last year. The title itself is telling, being remarkably close to Miles Davis's 52-year-old classic Kind of Blue, and thus the scene is set for 54 minutes or so of whatever can be thrown our way and conjured up in the group's minds, fingers and mouths.

Sometimes it's a struggle to work out what setting, mood and general atmosphere any music is best consumed in, but in En Form for Blå that's part of the discovery and listening process. Each track - or movement, if you will - has its own distinct theme, but a Rhodes organ – set in motion early in 'Jocasta' – is a mainstay in every piece, offering consistency if not exactly sense to the mutterings, ramblings and motifs concocted from an array of percussive and droning implements. Despite the calibre of the group's past works, both outside of Æthenor and within it, wiping expectations away is advisable. It's definitely a different beast to the band's previous full-length, Faking Gold and Murder, with the tangible tension build-ups – used to great effect – a lot less obvious, if not entirely unused, as the opening 'Jocasta' and following 'One Number of Destiny in Ninety Nine' show, totalling 27 minutes between them, with peaks and troughs aplenty.

'Vivarium' is the arguably beefiest of the seven tracks, emerging like a HEALTH soundcheck with battered skins and all, before a semblance of coherence and structure forms around a warped, resonant guitar line not far off the timbre of a ringing glass. 'Vyonmagami Plume' is the record's most captivating and darkest tract (which is going some way) as explosions in the background are punctuated by seemingly unrelated darting synth-stabs and wails on the higher end, leaving you unsure of just where to place your ears, which sound to focus on.

En Form For Blå is a record where it's tempting and possible to zone out of and forget that you're even listening, let alone any specifics of sound. Still, there aren't really any specifics, given the nature of its recording, in so much that there was no planning, no pre-meditation, no end goal. Maybe that in itself is part of the project's failings, but moving deeper in and out of the individual tracks and the entire piece is still rewarding. There should be enough cracks and cymbal whacks to keep even those with the most wandering of brains listening intently for the majority of the way.