"Always show your workings" they impressed upon us in Maths and Science classes at school, and that's just what Black Tempest - AKA Surrey musician Stephen Bradbury - has done on this sprawling 3CD release on his own Tempest Towers label. While the first disc documents a rare live performance, headlining the second stage on Friday night at last year's Supernormal Festival, the second two discs showcase the home studio works-in-progress and rehearsals that built towards the final set. That many of these are even more engrossing for the home listener than the actual live tracks is one justification for such a seemingly self-indulgent compendium; another is the notion of documenting a journey, or rather two journeys - the narrative contained within the live performance itself, and the series of experiments that led to its realisation.

Supernormal is a three-day experimental arts and music festival that began in 2010, evolving out of the long-running Braziers International Artist's Workshop. These annual residential sessions at Braziers Park in Oxfordshire - a 17th century country house and grounds - facilitate and encourage creative collaborations between artists in different disciplines and from different backgrounds, and the same spirit informs the intimate (500 capacity), idealistic open-air event, intended to be "part festival, part village fete, part living gallery and part critical forum." Alongside exhibitions, installations, debates and film screenings, last year Black Tempest joined a music bill that included veteran mavericks Cindytalk, Skullflower and the Cravats, and younger malcontents like Gnod, the A Band, Hamilton Yarns and Teeth of the Sea.

Using a combination of digital and analogue electronic instruments - his stage set-up is also helpfully documented in the CD booklet, and includes a couple of moogs, a Doepfer Dark Energy synthesiser and a Mellotron Emulator - Black Tempest's lengthy instrumental compositions seem to draw equally on experimental techno, New Age/Ambient, psychedelic-prog-krautrock and the classical avant-garde. But it's the German Kosmiche music influences that are most apparent, even if Black Tempest does give a peculiarly English twist to themes originally developed by the likes of Kraftwerk, Klaus Schulze, Popul Vuh and, especially, Tangerine Dream. It's appropriate that his next release is to be a cover of Schulze's 'Bayreuth Return' on an album paying tribute to the German Brain label, to be released on cult label Fruits de Mer. But the Englishness comes over in the dry, unpretentious sense of humour, the image of Bradbury as an eccentric scientist, onstage in his white lab coat, and particularly in the way his electronic music somehow evokes the rolling rural landscape of southern England. Supernormal encourages a spontaneous artistic response to the immediate environment, and Black Tempest seems to be doing just that.

Opening with the twitter of birdsong over ominous, low-lying plains of drone, 'Astral Pastoral Part 3' adds a spindly, constantly shifting electronic refrain that repeatedly sinks and then re-surfaces as the sonic scenery shifts gently around you, like hills and fields viewed from the window of a car or a slow-moving commuter train. An anchoring bass pulse appears almost subliminally around the seven-minute mark, creating an unsettlingly hypnotic effect that's jarringly - but endearingly - broken by Bradbury's blokeish tones as the track ends, responding to the audience's whoops and applause. Relatively brief at just over four minutes, 'Proxima' evokes the nightmarish ambience of Tangerine Dream's Zeit album, before 'Tanks but no Tanks' ("a song about an imaginary invasion") begins with the wail of distant air raid sirens, the rattle of anti-aircraft guns and the menacing grind of massed bombers overhead. The centrepiece of the first disc, this track mixes library footage of the Second World War with layers of ominous electronic sound- the unrelieved circular tension of the sequencer parts edgy and nervous, the swelling synth drones all humanity and sorrowful grandeur, near-classical in their yearning, tone-poem simplicity. And lent perhaps unintended significance by juxtaposition, the flute-like cries of encore track 'Proxima X' suggest rebirth, the land gradually recovering from the rape of war, and the steady, sub-bass heartbeat and rising sequencer notes conveying struggle, growth and stubborn life. Intentionally or not, the four tracks together conjure a narrative of an idyllic natural landscape gradually encroached upon by darkening skies and metaphorical stormclouds, ravaged by war before a tentative but undeniable recovery.

This idea of the live set as a site-specific musical installation is given credence by the much longer, earlier version of 'Proxima X' that opens the second disc. This has a very different feel, the emphasis on the rhythmic elements moving it aggressively forward into hard-edged krautrock territory. Though the eventual live version was undoubtedly right for the occasion, I personally prefer this overloaded studio take, which already justifies the decision to include 'rehearsal tapes' alongside the core of a live album. The propulsive darkness of 'Proxima Y' follows a curve from early Tangs to John Carpenter to Richie Hawtin, Berlin atmospherics ripped with nasty acid squelches; the Moroder-meets-Suicide 'Proxima Beta' is another heavy, throbbing beast; and 'Proxima Delta', while slightly less oppressive, confirms that Supernormal could easily have got a far fiercer and indeed blacker Tempest than the relatively benign manifestation they in fact encountered.

'Astral Pastoral part 2' is also darker and edgier than its successor- far less pastoral, much more astral, in the sense of evoking the Lovecraftian awfulness of deep space- while a near twenty-two minute run-through of 'Part 3' on the third disc sits somewhere between the two. 'Proxima V' is bristling, cold and metallic, a rusting hulk of a space cruiser drifting through the void. One could argue that three work-in-progress versions of 'Tanks but no Tanks,' totalling over half an hour of music, and a third, twenty-minute reprise of 'Proxima X' are crying out for a dictatorial A&R man to say "no more!" and illustrate the flaws in the artist-as-label-boss business model. But the quality of the release isn't diluted by such largesse, and this is, after all, total immersion music- you could be listening for one hour, three, twenty-four or seventy-two and it wouldn't matter. You would only travel further into the eye of the Tempest.