“Class of ’88 reunion,” announces Sonic Boom. He has just played “Transparent Radiation” and is about to launch – launch may not be the right word, exactly; slope, perhaps? – into an excellent “When Tomorrow Hits”. In front of me, someone is wearing a “Goo” t-shirt. On the way to the Roundhouse, someone randomly proffered an open bottle of amyl. Only Sonic Boom’s haircut appears to have changed, slightly, in the intervening 20 years.

I’m pathologically wary of nostalgia, but there is something in the air tonight which gets to me. Perhaps it’s the most coherent set I’ve seen involving Sonic Boom for the best part of 20 years. More likely, it’s the prospect of My Bloody Valentine, chipped out of aspic (along with their merchandise), for a poignant and unbelievably powerful reunion, bringing back not just memories, but, at the height of the “You Made Me Realise” holocaust especially, physical experiences that I’ve rarely had since, well, 1992.

But we’ll get to that later. First, they look uncannily as they left us. Kevin Shields, as the one member of the band I’ve spotted this century, seems to have grown younger in preparation for these shows. And here they are, beginning with “Only Shallow”, entirely diffident to the extraordinary noise they’re making.

A few things cross my mind. First, and critically, it’s an accepted fact that My Bloody Valentine are one of the most influential bands of their generation. But how much do their myriad followers actually sound like them? On this evidence, it’s clear: not that much. It’s not just the unparsable sounds coming out of Shields and Bilinda Butcher’s guitars, or the way they interact with the flutter of sequencers.

No, it’s the sheer intense forcefulness of the music. I’m reminded, belatedly, that the most crucial influence on them in the late ‘80s wasn’t, as is usually claimed, the Jesus & Mary Chain, but was in fact Dinosaur Jr. The pace here, especially in “Feed Me With Your Kiss” and “Nothing Much To Lose”, is obliteratingly close to hardcore. And even on the legendarily vague “To Here Knows When”, Colm O’Ciosoig’s drumming is vigorous and constant, a firm anchor to all the nebulous instability spinning around it.

Was it always quite like this? It’s hard to remember precisely, but of the half-dozen or so Valentines shows I saw between ’87 and ’92, one of my most resilient memories is of their unpredictability. There was one particular show at Oxford Poly, as it was then, which may have been the first night of the “Isn’t Anything” tour, and which was remarkable for their complete inability to get through an entire track without screwing up. If memory serves, “Lose My Breath” was the only song that emerged more or less intact. Bilinda Butcher spent the best part of an hour looking unfathomably sheepish, and promised to come back for another gig. As far as I remember, they never did.

There’s a brief false start to “When You Sleep” tonight, but otherwise, the reinvigorated MBV now seem to have an unusual kind of slickness to them. Other bands might not have quite caught up with them, but perhaps technology has. Or perhaps, for all their talk, other bands don’t want to catch up with MBV, are not confident enough that their audiences will withstand such extreme volumes and frequencies.

This, clearly, is not a problem for Kevin Shields. There are free earplugs available at the Roundhouse, and signs on the walls which actually advise you to wear them, which I do. My wife is being tougher, until the sixth tune, when she asks me what they’re playing. I tell her to put her plugs in; she sticks her fingers in her ears and immediately locates the piercing banshee riff of “I Only Said”, hitherto obscured by the thunderstorm of noise.

Weirdly, then, wearing earplugs – not something I usually do – actually enhances the gig. That way, you can hear Shields’ strafing, Rother-esque riffs in “Slow”, identify that, yes, the implacable Butcher is just about singing throughout. And, most importantly you can withstand the holocaust. The standard comparison for the 25-minute whiteout section of “You Made Me Realise” is to a plane taking off: on the Drowned In Sound messageboard, someone discovered they were playing close to 130 decibels – “the equivalent of “Military jet aircraft take-off from aircraft carrier with afterburner at 50 feet,” apparently.

I am, embarrassingly, in the lavatories when this begins, and the way the cubicle shakes makes me understand, indeed, why you’re not allowed to use toilets on planes during take-off. When I get back into the venue, a good proportion of the audience already have their fingers in their ears. The music, generally, seems to be hitting me in the knees, and my trouserlegs are palpably flapping.

I’m generally sceptical of the usefulness of extreme volume: I wrote a long and moderately grumpy live review of Techno Animal for The Wire some years back, suggesting that loudness was a macho stunt, more or less. What strikes me now, facile though it may sound, is that loudness works if you like what is being played loud (I didn’t much, when it came to Techno Animal). My Bloody Valentine’s strategy seems predicated on making music hit your entire body: it’s up to you, the listener, to decide whether you want the assault to be as total on your ears, or whether you choose to mediate it with earplugs.

I’m glad I did. My ears were still buzzing when I came out, but I don’t think the long-term disintegration of my hearing was palpably accelerated by Saturday’s gig. What was enhanced was a renewed sense of the value of My Bloody Valentine. How strange, how remarkable, that one of the most important bands of my formative years should turn out even better than I remembered them to be.

No new songs, of course.

But how was it for you? Let me know. . .