Photos courtesy of Ultima festival/Henrik Beck

Ultima is a peripatetic festival. A movable feast. With some 15–20 minutes march between venues, I often find myself hoofing it across town to catch some performance or other. During Henrik Hellstenius' piece at the waterfront opera house on Friday night, the walking extends even on to the very stage itself, with the footsteps of singers and musicians, to and from their places, providing a near-perpetual continuo to the scored music.

But it's on the Saturday afternoon, after a wrong turn out of Nordre Gate on the way to the Cikada Ensemble's 1pm performance at the Parktheatret, that I finally came a cropper of all this walking. I rush up to the gate at 13:01. The door is closed. Its keeper will brook no discussion. Oh to be back in France where the stated time will always be considered at least half an hour too soon, whether for concert, dinner party, or suburban train.

2015 marks Ultima's 25th anniversary. A quarter century of new music programming that has seen Harrison Birtwistle, Helmut Lachenmann, and Pierre Henry – to name but a few – rub shoulders with the very best of the contemporary Nordic Wave. Born of the coalition that came together when the ISCM World Music Days was held in Oslo in 1990, the festival is a collaboration between the  Filharmonien, the national opera house, the arts council, the national music school, the cathedral choir, and the society of composers, among many others, all currently shepherded together under the enthusiastic directorship of Lars Petter Hagen.

Hagen was just 15 when he attended the ISCM festival and he had just signed up for the Norwegian Academy of Music. Immediately addicted, he began attending Ultima assiduously, never missing a single instalment. In 2009 he was finally made director.

It's easy to see what got him so hooked. Truly, this is a jewel of a festival. Rarely is new music treated so well, nor presented so engagingly. If it has been no stranger to controversy over its lifespan, with the more conservative elements of the Norwegian press pooh-poohing its excesses and mocking the programme's occasional eccentricities, all the more reason that it must be treasured and preserved.

As I make my way on foot from venue to venue, always a little rushed, trying to cram in as much as possible of the abundant programme, my eyes are opened to a city under transformation, with the arts – for once – seeming to lead the way. Here are a few of the things I learned as I pounded the pavements of Oslo.

Oslo is a musical instrument

It's 12 noon on Saturday and I'm standing in a carpark while a gang of eight young men in black jeans, dark jackets, and white earbuds drum on a large steel gate. The click tracks in their ears are all slightly out of sync, so the sound phases, in waves, like a Steve Reich tape piece.

Then all of a sudden, a few minutes having passed, they're off. Beating their sticks together, or upon railings or paving stones, leading us out of the gate and up the street, eight fashionably dressed pied percussionists. The rhythms are constantly changing in complex polyphony as we march up quiet streets. It's like a dance, spontaneously choreographed; they strike what surfaces come to hand and then, all at once, freeze together with just one player left to keep up a pulse until they all come crashing back in.

Soon we break out of the back streets. Their once almost-private soundworld now encroached upon by the bustle of the city, the whole thing threatens to collapse. Instead it just gets better, making all of us here a party to the liberating sensation of having seized the streets for our own.

At the big crossing where Maridalsveien meets Rosteds Gate, outside the Kiwi Minipris, the drums start to really spread out from what had been a tight circle. At all four points of the crossroads, down streets and round corners, they hammer on road signs and traffic lights. The beeping of the pedestrian crossing adds a delightful pitched pulse to all these clanging percussive sounds now coming from all angles.

Passers-by, about their business or on their way somewhere with friends and family, regard us askance. Still the black-jacketed young men keep tap-tap-tapping, knocking out the rhythms of bouncing balls on every available surface: walls and grates and signal boxes and the a-board of a takeaway pizza place. One guy starts jamming on a drain cover in the middle of the street and a car is nearly forced to swerve to avoid him. They beat out rolls and trills and the revving of automobile engines adds bass and grit.

Now ducking down another residential side street, beating on lamp posts and door jambs. People poke their heads out of their homes like what the fuck is this? and there's a delicious sense of being in on some secret, being part of a conspiracy to subvert the city, to pervert its very bones and make them rattle with some occult music. Even the birds in the park seem to be in on it, tweeting their approval as if pre-composed.

Every lamp post in the park has a different pitch and standing in the middle as the eight drummers roll their sticks upon the poles, the whole place shimmers as if the park itself were about to come.

Koka Nikoladze's roving composition, Sound Stencil 0.1, finally ends, some 45 minutes after it began, with all 8 of the drummers, pounding together upon the support strut for the floodlights in front of the taco stand in the square at Youngs Gate. I don't know how it all must have seemed to people going about their Saturday who just caught some brief moment, here or there. But following the journey from start to finish made every surface in the city come alive. In my head these streets still thrum with secret harmonies.

Harry Partch designed all sorts of extraordinary musical instruments – but nobody else seems to know quite what to do with them

Harry Partch, that most maverick of American maverick composers, first began redesigning the orchestra to suit his own peculiar purposes in the early 1930s. By the end of the '60s, he had built at least 27 different, wildly diverse-sounding instruments, from the earth-shaking bass tones of the Marimba Eroica to the Hammond-like Chromelodeon with its 43 pitches per octave.

A few years ago the Cologne-based Ensemble MusikFabrik set about reconstructing these instruments from Partch's original designs. For some odd reason they built them in a pale wood, like pine, instead of Partch's original dark spruce, so they have this sort of flatpack Scandinavian look. Nonetheless they remain absolutely extraordinary implements.

Here in Oslo's Kanonhallen, lit through shifting coloured gels, the scene recalls some Hollywood vision of a mad scientist's lab, with wild looking Cloud Chamber Bowls and curiously neo-classical Kitharas poking through a fog of dry ice and blue light as if about to produce an invisibility serum or give life to some Frankenstein's monster.

Watching the ensemble perform Partch's own And on the Seventh Day Petals Fell in Petaluma is an utterly beguiling experience, like hearing a series of baroque dance suites composed for alien lifeforms far more sophisticated than any here on earth. Following the multicoloured scores of the Californian composer-theorist, the players' hands weave fluidly about the various re-imagined zithers, xylophones, and just-intoned guitars producing flurries of notes unique in pitch and timbre, each perfectly adapted to the task assigned to it.

But an odd thing happens when they turn the same tools to new, specially-commissioned works by Simon Steen-Andersen and Helge Sten. It's immediately clear that no-one else has the faintest idea what to do with these things.

Steen-Andersen seems to have tried to use as few of the instruments as possible – and as few notes as possible on those he did use. Korpus, essentially, is a drone piece. And one that you can quite easily imagine being re-scored for practically any contemporary ensemble. It's not bad. It just seems like a bit of a missed opportunity.

Sow Your Gold In The White Foliated Earth, on the other hand, by Helge 'Deathprod' Sten sounds rather like a particularly spooky episode of The X-Files: big on atmosphere, but not much real meat. It evinces little sense of anyone really engaging with Partch's theories of otonality and utonality. He seems rather to regard this odd group of objects just as splendid generators of sound effects. But, yeah, sure, it works.

Lasers! Lasers! Lasers!

Up until a few years ago, I'm sure laser light shows were one of those things generally considered to have been consigned to the dustbin of pop music history, alongside other prog rock excesses like guitar solos the length of American sitcoms, Roger Dean-designed gatefold sleeves, and Arthurian concept albums. But a few years ago I found myself sitting in a room at the Centre d'Art Contemporain in Geneva, listening to Robert Henke of Monolake talk about his new project: lasers.

Fast forward to 2014: I finally got to see Henke's Lumière in action at a festival in Riga and I must admit to being pretty impressed by it. Here was something that seemed to go beyond anything Pink Floyd could have even dreamed of: spiralling 3D geometric shapes, constantly shifting in a fog of dry ice, hovering somewhere above the stage, synced perfectly with a sinuous electronic soundtrack. It was arresting, hypnotic, and it felt new – like, something that technology had only recently made possible. Lasers!

All Friday at Ultima there is a palpable buzz about the evening's laser show from Atom TM and Robin Fox. People whispered that these were, like, military grade lasers and potentially very dangerous. All of which just seemed to add to the allure of the thing. Lasers, inevitably, seem to conjure up visions of zap guns and deep space battles. Like electronic music itself, they have somehow succeeded in connoting "hi-tech" for more than half a century. Lasers!

When it finally begins, even the concert itself seems to spend most of its time hyping its own wonders. Like some cheap sideshow magician, it carries on promising marvels soon-to-come right up to its end, leaving the impression that the whole show is just an elaborate build-up to some spectacular display that never quite arrive.

Mr. Fox, a vocoderised voice declared, will combine red, green, and blue light to make white. Gosh, I thought, that will undoubtedly be hugely impressive to anyone who skipped secondary school physics. Only it never even happens. This fantastic Mr. Fox does not at any point succeed in combining his lasers into a single sheet of dazzling white.

So, what do we actually get? Some music that sounds like something not-particularly noteworthy off a late 90s Rephlex compilation and some red, green, and blue lights wiggling about, seemingly at random. Well, colour me amazed. Good work, boys.

M.C. Schmidt from Matmos does a mean Robert Ashley

Robert Ashley first began developing the music for his "television opera" Perfect Lives in sessions at the Kitchen in New York, and elsewhere, from 1978, aided and abetted by pianist 'Blue' Gene Tyranny. First broadcast in the UK on Channel 4 in 1983, it has been called – and by no less a critic than Kyle Gann – America's "great epic poem … our own personal Iliad.”

Ashley died in March 2014. Matmos first performed their own interpretation of Perfect Lives nine months later at Issue Project Room in Brooklyn. For Ultima, they have revived their version of the first and last chapters (of the original seven) backed by a string quintet (following Peter Gordon's original orchestrations) and two additional vocalists (more or less following the choral parts originally taken by David van Tieghem and Jill Kroesen). Drew Daniel stoands hunched over his Macbook at the side while Schmidt, centre stage looking debonair as fuck, owns the narrator's part originally delivered by Ashley himself.

To be sure, Schmidt is not quite doing Robert Ashley. He does not ape Bob's distinctively airy – almost seraphic – midwest tones. But one can think of few performers involved in the contemporary avant-garde who could carry off the part with such panache, such charm, such confidence. Truly, this is a performance that seems to unite the entire audience with a warm, fuzzy glow. Curiously, however, as composed as he sounded, from my vantage point in the second row from the front, I can't help notice that when he plays guitar (in 'The Backyard'), Schmidt's leg wobbles rapidly in a manner that I can only presume implies a touch of nerves.

You simply can't imagine something like this happening here

As I mentioned at the start, Ultima festival involves the collaboration of the Oslo Filharmonien, the national opera house, the arts council, the national music school, the cathedral choir, and the society of composers. So the whole thing kicks off with Olivier Messiaen's Turangalila symphony at the Sinfonia, later the brilliant Plus-Minus Ensemble performed at the national opera house, and elsewhere some of the most prestigious ensembles and venues in the country were marshalled for the sake of contemporary music.

Just think about that for a moment. Can you imagine, even for a moment, a festival dedicated entirely to new and experimental music taking place in London with the collaboration of our closest equivalent institutions? With concerts of new music taking place at the Royal Opera House, the Royal Albert Hall, and the Coliseum? And with the kind of lavish funding that has here been so generously bestowed?

On my last night in Oslo, I find myself at dinner sat next to Igor Toronyi-Lalic of the London Contemporary Music Festival. In most major European cities, you simply couldn't call something The contemporary music festival. People would say, which one? What astonished both Toronyi-Lalic and myself is that up until they started three years ago, there simply was no regular annual festival of contemporary music in London. For all the consistent brilliance of the LCMF's programme, there remains still nothing with anything like the scale and institutional support that Ultima receives. The question is, why not?