Birmingham, the Queen’s birthday weekend. Dudley’s own Lenny Henry is now a sir. Despite Brum being 80-odd miles from the sea, seagulls cry outside the Birmingham Moor St Travelodge, rival to the Henry-approved Premier Inn. A new version of TFI Friday plays out refried bantz on our wall-mounted television – it’s what the culture requires – and during the ad break, puppets sing the virtues of our hotel chain from a room with an identical abstract print to ours hung on the wall behind the bed. One of the puppets has been said to have a passing likeness to David Cameron – I can’t see it myself, but that doesn’t stop it having a certain resonance, about something.

But what? Perhaps I’m reading too much into the surroundings, but in search of a Supersonic 2015, I’ve found England, 2015. The middle of the middle, a market town that swelled into a city flogging leather and jewellery, more recently it's in danger of becoming a destination in itself: a commercial-driven city break with a high speed transport link. That’s not to do Brum down: every walk, every chat, there's friendliness, betraying a city that’s doing all right.

Taxi to Digbeth, site of the 13th Supersonic Festival. Overlooked by grand railway arches and the tatty yet clean-lined modernism of the Custard Factory, there is an elegiac air to the proceedings, a feeling that does not dissipate all weekend.

At warehouse venue Boxxed, The Pop Group are settling into a rendition of the title track from their new album. 'Citizen Zombie' is a reggae-fueled rant against a duped majority, the aforementioned zombies with "factory formed opinions" and "tabloid minds". It’s a fair enough observation in an era in which a new Conservative government is thought to have been elected on a McCarthyite fear ticket, Red Ed under the bed, but as Mark Stewart rants at the lectern in front of his well-drilled – perhaps too well-drilled – band, there’s an inescapable feeling of futility to the performance, as if his on-stage combustibility is somehow sucking the life out the rest of the group.

As political music it doesn’t pack such a punch, and you can’t help getting the feeling that this is because the parameters of control have changed so much since the Pop Group’s best songs were written. Stewart’s slogans – "We are all prostitutes!", "Choose a fucking new television!" – here amount to a kind of loud preaching to the converted in front of a partisan crowd who clap politely after each song but never truly loosen up. There’s still a gnarling kind of fire somewhere, resurfacing in 1979 tracks 'She’s Beyond Good And Evil' and, aptly, 'Thief On Fire'. It’s better when freer but too often the funk is more polite pop than wild punk – "Marxist Jamiroquai", one attendee offers after I try and describe to him the deficiencies of the concert that he had missed.

Later, down the street at the 600-capacity venue the Crossing, a curled wig stutters out of Gazelle Twin’s hoodie as she affects pendulum-like movement. It’s a performance of nuance and threat, of minimal electronics and the techier end of grime. You can't take your eyes off Elizabeth Bernholz, the performer behind the mask. Her movement is lucid, nimble, fierce – but also stunted, engaging in a sort of deferring defiance, like a webpage that’s eternally loading.

The terrain has changed. Today’s outsider music articulates the world of inside: the worlds behind the screen. Plugged-in as standard, under the gaze. The most pertinent cultural interventions are often a tale of the insular. Perhaps the most successful explicitly political aspect of the weekend is Holly Herndon's pretty triumphant turn the next evening in the same venue, starting the set by opening up the Facebook event page for Supersonic and downloading different guests' profile pictures at random and opening them for all to see on the big screens beside the stage. It's a none-too-subtle yet effective comment on the amount we let out into the world through compliance with Facebook-era social media.

The character of Gazelle Twin apparently grew out of the horror of Bernholz's teenage years, PE changing rooms and the horror-making internal anguish over perfection. A study of lack, of not matching up to the might of the spectacle, of pure terror at the self, and in the harm that one can do in reaction to all of the above. A study in the anonymity of despondency, but also in the toughness of the overlooked. 

Friday night’s performance still resonates the next morning as I walk within the capitalist surrealism of the Bullring shopping centre’s studded Selfridges building, which peeks out cheekily from many a Birmingham vista. Traces in the hooded, faceless mannequins that stare ahead, and the legs without torsos that hang from the ceiling. Hundreds upon hundreds of teenagers use these pristine interiors and visual puns as their Saturday backdrop, pinballs in a game of kerching.

A gathering against cuts to local Library services in Victoria Square is dwarfed by the queue for free mini cans of lemony lager at a van near the Bullring. The brightly coloured bottles add to the bright and breeziness of the centre.

Digbeth relates to this effervescent centre the way the desert relates to the Citadel in Mad Max: Fury Road. The thrum of commercial Brum feels far away as you traverse the area between the bus station and where the festival is held. This disparity between commercial centre and postindustrial abandonment feels almost nostalgic. It is a dichotomy that once sustained culture in London, but is coming to an end as the commercial enters the parts of the city it once could not reach –  luxury shops in tube stations, pop-up container boutiques in Shoreditch. I read somewhere that Digbeth was Birmingham’s Shoreditch, but fortunately this isn't the case: there are still working-class pubs here, still a sense of desolation and danger and freedom on the road less travelled. It’s what tied Supersonic to Digbeth in the first place, but like all good, bad and indifferent things, it looks like the more artistic associations might one day come to an end.

The Custard Factory is no longer able to accommodate Supersonic's needs; events are apparently harder to plan because much of the site is now sub-let, which means you need to negotiate with numerous parties to put on events there. Founder Lisa Meyer is looking to branch out around Birmingham, and not for entirely reactive reasons, but to make use of the city as a whole. "Empty spaces are really hard to get your hands on in Digbeth – many have been taken on by developers," says Meyer. "Digbeth is still important to us as a hub because so many of our peer arts organisations are based here and we want to be able to show off Birmingham’s artist-led spaces. But it’s important for us to be able to re-imagine the festival both in terms of spaces, partners and the programme and so having activity based around the city was important this year and I think will continue to evolve. For example the opening night was located at Town Hall in the city centre, the Mooglab was at Birmingham City University in Eastside, the All Ears exhibition was at Millennium Point."

Part of Meyer and Supersonic’s bid to move away from the reliance on Digbeth is the accommodation of projects like Circumstance’s A Folded Path, a kind of walking opera, with hand-held box speakers triggered by GPS technology at different points in the city. Circumstance was set up by Duncan Speakman, Tom Abba and Chrome Hoof’s Sarah Anderson. Beginning at an edge of Digbeth that is earmarked for redevelopment when HS2 arrives, the eight-strong group I'm in is led by Speakman, who hurries us on our way. He’s like a moving conductor, guiding us along past traffic and into the nooks and corners of Birmingham city centre. He's constantly aware of the areas we should be aiming for and the next destination on the map to give the section a different acoustic potential, all the while teasing out chance collisions between the ambience of Birmingham on a Saturday and our the sound collected ensemble.

Written originally for the city of Porto, Speakman tells me that he feared it wouldn’t transfer well to Birmingham, but the work, featuring violin, guitar and gamelan orchestra, has adapted well. The power of the piece is the tension found in being a participant – you’re both audience and performer, imposing this eerie, charged music on the city around you. There are exchanges with passersby going about their days, their private wistful stares or shared jokes becoming part of your internally concocted narrative. At one point I hear a woman cry "I’ve got a headache!" when a particularly abrasive section is playing as we near New Street end of Birmingham city centre.

Circumstance intervenes into spaces you don’t feel you are allowed to be without a purpose. The phrase Speakman uses is "uncontrolled" – not public – space, perhaps because of the difficulty surrounding just what is and isn’t public space today. We bomb into the ground floor of a multi-storey car park, filling it with noise. We don’t pass unnoticed. On the way out into daylight, a man jams his hand on the wheel of his 4 x 4, hooting aggressively as he swoops passed, showing his disgust and perhaps attempting to somehow police the situation.

Back at the Crossing, drum and synth duo Tomaga follow their rhythmic impulses in a set that evokes Drums Not Dead-era Liars, before Danish free-form jazz-drone quartet Selvhenter revel in the layers and layers of driving sax-trombone-violin-drum noise that they will into being. At Boxxed, Eternal Tapestry affect a psych jam like a grown-up No Age, feedback and reverb cascades building a hallucinatory bridge between early Pink Floyd and trigger-happy neo-psych, before Ben Chasny smashes it down with his riff-happy Six Organs of Admittance.

The Bug and Earth – AKA Kevin Martin and Dylan Carlson – fill the room with slow-moving, maximalist drone and gut-gurgling bass. But what’s really needed at this point of the weekend is the introduction of Flowdan after Carlson vacates the stage. Lurking in front of a shadow-shielded Martin, barking his flow of chill menace, he finally brings the party to Supersonic. An intense, tightly packed throng forms in front of the stage; we lap up everything the duo throw at us. A Saturday night treat of a scratchy, boomy grime set based around The Bug's latest, Angels & Devils, but with added surprises such as Dizzee's 'I Luv U' and a blink and you'll miss it rendition of 'Skeng' (that admittedly doesn't get to the high-point of the song when Flowdan starts chatting about the 'earse).  The highlight might be 'Function', originally voiced by Manga, all waspish synthetic melody line and the on-point refrain: "I'm just trying to function."

In a cafe by a canal in Digbeth the next morning, political illustrator and collagist Gee Vaucher of Crass, Napalm Death's Nick Bullen and Oscar Kasperek, a Polish artist politicised after being imprisoned for refusing conscription in the 1980s, sit discussing art and politics with punk's perennial anchor-man, John Robb. It's an interesting event, if slightly stunted at first partly due to Kasperek speaking through an interpreter. What comes out most strongly is that artists who turn to political work do so for reasons largely unknown. Vaucher was excluded from a competition when she was a child for her work's political nature; Bullen in turn was led to making zines after being turned on to punk through Crass. For Kasperek, the State dictated that his art was political after his stint in the clink, but he thought it just art, and a useful bartering tool in exchange for tea and cigarettes back when he was still inside.  

After a weekend in which some of the most penetrating performances came from behind masks, through GPS triggers or from the darkest recesses of a barely-lit stage, for Newcastle's Richard Dawson, the personable is political. Daylight shines through the skylights at Boxxed. Dawson has a voice that could probably fill any space he wished, with or without a microphone. At the end of a set that included a crunching instrumental variation on 'Judas Iscariot', the opener to his last album Nothing Important, and an anecdote about his cat who only ate DVDs before crumbling into dust, he ends with a rendition of old north-east folk song 'Joe The Quilt-maker'.  "Few people can cheer a winter's day like garrulous Joe the quilt-maker," bellows Dawson, but it's a story on a downward trajectory: poor Joe dies in a pool of blood outside his own front door. On the train out of Birmingham, as I watch cranes stood frozen before they begin tickling the horizon again tomorrow, the melody still lingers in the memory. It has been lodged there ever since.