James Murphy of LCD Soundsystem is not, by most standards, a typical frontman. His band are second on the bill to Daft Punk in front of the Hyde Park thousands. But Murphy spends a good part of the set scratching his head, picking his ears and tinkering, obsessive-compulsively, with the tightness of his drummer’s kit. Occasionally, he dances, pounding up and down on the spot like a post-punk Ozzy Osbourne. He does, though, manage to pull off one of the most curiously moving moments I’ve experienced at a gig in a long time.

I’ve written plenty about Murphy and LCD here and here; in fact, I think I’ve probably played “Sound Of Silver” more than any other album this year. Today at this festival, though, the poignancy of Murphy’s music rises to the surface.

Mostly, the live LCD is a prickly thicket of bass and drums, a sort of linear and relentless extrapolation of Talking Heads, a sinews-and-sweat physical manifestation of techno. The apposite “Daft Punk Is Playing At My House” is closer to hardcore than filtered house here, Murphy bawling, manic, still distracted by the drumkit.

But when they play “All My Friends”, I have a mild epiphany of sorts. It’s a great song on record, of course, but in the midst of Wireless the words – about being on tour away from those you love, about getting too old to party as much as you used to, that sort of thing – seem unusually profound. There’s Murphy onstage, awkward but crooning beautifully, and there’s thousands of people going fairly crazy in front of him. The effect is at once celebratory and reflective, and remarkable.

Before LCD, I caught a bit of the London rapper Plan B, who now seems to be presenting himself ostensibly as Rage Against The Machine Unplugged. “Sick 2 Def” remains a terrific and inventive song, but much here – notably covers of Blur and Roots Manuva – is pretty cack-handed. And the rapper is a grim, charmless figure – has someone shouting, “Are you happy?” ever sounded so joyless? – who takes himself far too seriously.

Which is not something you could ever say about CSS. The six Brazilians remind me a bit of a disco Sugarcubes at times this afternoon, not least in the way they are vaguely arty in such a daft, uninhibited way. Central to this is frontwoman Lovefoxxx, whose performance involves stripping off one sequinned catsuit to reveal another one underneath, drinking a bright red cocktail and a glass of champagne simultaneously, and sucking helium out of the onstage balloons directly before songs. She’s also a compelling bad dancer, which oddly makes the show more rather than less enjoyable.

The tunes help, of course. And while the Tom Tom Club-aping “Let’s Make Love And Listen To Death From Above” is still outstanding, one or two others – notably “The Beautiful Song” – are very nearly as good. And who’d have thought that L7‘s “Pretend We’re Dead” would be so improved by a Brazilian synthpop treatment?