Day two, and i’m here ridiculously early (well, by artist/writer/layabout standards – actually it’s just after midday) for the weekend’s other unmissable act besides Company Flow, that being Canadian heavy metal trio Godspeed You! Black Emperor. Wait – heavy metal trio? That’s what the programme says, anyway.

Godspeed You! Black Emperor is a Canadian power trio, often compared to fellow Canadians Rush. The band’s musical style is hard rock and heavy metal although the band itself is reluctant to embrace this label. The band once described themselves as a cross between Emerson, Lake and Palmer and The Who.

It’d seem too weird – somewhat disrespectful – for the festival organisers to have written this, so the only conclusion I can come to is that, hilariously, the band have themselves written their own fake bio, an unexpected move for a band with GY!BE’s reputation for seriousness. (I tried to draw a quick comparison in my head between Godspeed and Rush, but the closest I can come is a shared taste for huge sonics, long songs and non-mainstream politics, tho thankfully GY!BE aren’t awful libertarians.)

Anyway, luckily the band’s approach hasn’t changed that drastically in the years since I’ve last seen them (pre-smoking ban – most of the nine members chain-smoked throughout). Theirs is still an enormous, cinematic sweep, shot through with equal parts dread and beautiful optimism. Playing in the venue’s smaller West Hall, where presumably the ability to close all the doors for the right atmosphere, they begin with a drone of ambience, strings and guitar squall that keeps building and building to what seems like an impossible volume, before breaking into what sounds like – thrillingly – long-rumoured new material, melodies that sound middle Eastern-influenced played with skyscraping dynamics. The first piece lasts for half an hour of the two-hour set, but it stays compelling throughout. It’s weird to think of a group like GY!BE having “hits”, but the rest of the set comprises plenty of their formidable back catalogue, from “Moya” to the part of “East Hastings” that won them a wider audience soundtracking deserted London on the 28 Days Later soundtrack. The West Hall this afternoon is anything but deserted, and as the band members start to depart the stage one by one, it seems like Sunday just peaked very early.

A number of Portishead side-projects and associates dot the weekend’s schedule, but the most interesting-looking one is the live soundtracking of the 1928 silent film The Passion of Joan of Arc by ‘head multi-instrumentalist Adrian Utley and Goldfrapp man Will Gregory. Commissioned by Bristol’s Colston Hall venue, it’s played here by an ensemble of Monteverdi choristers, a horn section, various guitarists (including Utley himself), weird disorienting what-can-only-be synthesizers, and a variety of harps, with the film projected onto the large screen behind them.

The playing throughout is top-notch, and while there are a few moments where the soundtrack doesn’t seem to address Carl Theodor Dreyer’s classic directly, these are overwhelmingly outnumbered by the times when the music, by turns lush and harrowing, perfectly sync up with the film’s emotional nuances. A lot of The Passion‘s pioneering technique involved the use close-ups of the actors’ faces to convey emotional intensity (in particular, Renée Jeanne Falconetti as Joan is extraordinary), and the score’s steady building in the last half-hour (reminiscent of Godspeed’s intro earlier) ensures a devastatingly effective climax. Although the film’s English subtitles, placed conventionally at the bottom of the screen, are sometimes blocked by the players (especially when the choir stand for their sections), it’s pretty easy to get the gist of what’s going on. Full credit to the composers, and especially the musicians, who go for 90 minutes without missing a beat. This is the kind of unusual, exciting work ATP fests present best.

I can’t lie, it is pretty intense, though. Perhaps some sort of frenetic, amazing jazz quartet would lighten the mood? Well, fortunately, Acoustic Ladyland are playing in the Panorama Room (sort of a big conservatory). Frustratingly, this is the first time I’ve heard of the group, and also their last gig (although they’re apparently reforming this year under a different name and with a complete new set of songs). The group, including members of Polar Bear and Trio VD, take a Naked City/Brötzmann-esque approach but add a bizarre sense of groove – I don’t think I’ve heard any other free jazz this danceable. The size of the crowd makes it hard to see the band, but about halfway through someone manages to dislodge one of the giant balloons from the ceiling, which promptly gets batted around like a giant beach ball and used to knock down other balloons. At one point, the balloons start to land very close to the band, if not actually on top of them, and for an amazing moment it seems as if the group might be improvising around them landing and being batted back up again. It’s frustrating to have discovered such a joyful, energising band just as they split, but I’ll be paying keen attention to whatever they decide to do next.

Next, a pretty unexpected collaboration: neo-pagan graphic novelist Alan Moore performing a live reading of a self-created new myth, fusing symbolism with real events from the life of American experimental filmmaker Harry Everett Smith, accompanied by SunnO)))/Khanate man Stephen O’Malley on droning ambient guitar, and with a 1957/1964 animated film by Smith projected behind the duo. If you think that sounds pretty odd, you’d be right; it also turns out to be one of the most extraordinary things I have ever seen. Seemingly dressed as a sparkly wizard, Moore reads four extended segments (with short breaks in between each) in his rich East Midlands burr, concerning – and this is very hard to translate to paper – themes of creation and destruction, antiquated medical equipment, Harry Smith’s quest to make himself an artificial woman, a stolen valuable watermelon, and as the programme has it, “a transportation to heaven, and the subsequent return to Earth on the day Edward VII dedicated the Great Sewer of London”.

The closest thing I can compare the film to, meanwhile, is like the stuff Terry Gilliam used to do for Monty Python, but with the comic/satirical intent replaced with creepy lysergic headfuckery. For a full forty minutes. After it’s over, the group I’m with have to retire open-mouthed outside to sit down for a while, just to try and process what we’ve just seen. This is only the third performance Moore and O’Malley have done together, but if you get an opportunity to see them, drop everything. Seriously. These words do not do this performance justice.

After missing Portishead last night, I’m obviously keen to see them today; my slight fear that all that’s gone before them today might make them seem a little anti-climactic is unfounded, though they’re solid rather than awe-inspiring. Expanded to six for the live performance, their set draws liberally on all three albums, mixing the expected classics from their days of being pigeonholed as trip-hop’s poster children (“Sour Times”, “Glory Box”) to a pummelling rendition of “Machine Gun”. Beth Gibbons‘ emotion-soaked vocals are the focal point, somehow both fragile and hugely powerful.

Apart from a bizarre misfire with one song (which they make four or five attempts to start before abandoning altogether - either the drummer couldn’t nail his cue, or it was a weird piece of in-joke performance art), the band are muscular and well-drilled, and the atmosphere is completed by a distinctly British take on the kind of claustrophobic big-screen visuals the likes of Godspeed have made their own.

It’s a set that cranks up anticipation for any potential fourth album the group might be making, at the end of a day that will maintain ATP fans’ high expectations of whatever the festival itself will do next.