Birtwistle Games, South Bank Centre, London <br></br> Haitink at 75, Barbican, London

A seismic shift? It sounds like this...

Down on the South Bank, there's a whole lot of Birtwistle going on - a three-week celebration of the UK's most admired musical heavyweight, who turned 70 in July. Musical values may have shifted around him, with minimalism gaining ground and John Tavener's everlasting spirituality winning converts, but Harrison Birtwistle has stuck to his modernist guns for nearly half a century now. His music may have grown richer and technically sharper, but whether rough-hewn or glinting with razor-edged precision, it's all recognisably cut from the same vast blocks from the same seemingly inexhaustible quarry.

Not that everything he does works. Antiphonies (1992), given a determined performance at the Royal Festival Hall last Sunday by the Philharmonia under Christoph von Dohnányi, with pianist Pierre-Laurent Aimard, is a failure. Modernists have rarely been happy with the concerto genre, with its tradition of showy display and matinee-idol opportunities for some glamorised figure constantly seeking attention at the expense of all the other musicians on the platform. Birtwistle describes Antiphonies as concerto-like rather than as a concerto, and therein lies the problem, because the piano's sonorities are too naturally distinctive to adapt successfully to what is essentially a glorified obbligato role.

The vision of Aimard flailing around manfully for a less than generous sonic return while the ground troops of the Philharmonia assaulted him on every side was not a happy one. Even, as here, with amplification, the piano just doesn't cut through. Nor is the material particularly striking in itself - and that's rare in Birtwistle.

Certainly every note from the composer's hand in the London Sinfonietta's Queen Elizabeth Hall programme under David Atherton hit home. There was a sense of nostalgia about this concert, which opened with Ritual Fragment, written in 1990 as a memorial to Michael Vyner, the ensemble's long-term artistic director. But the Sinfonietta seems ever more assured in this difficult music, ever more capable of revealing the quirky, idiosyncratic beauty of its fractured surfaces and mangled lyricism. In Ritual Fragment, they also have to move around the stage, each of them stepping forward in turn to add their own individual melodic shapes to the memorial tribute.

This idea was developed much further in the 1984 Secret Theatre, where the melody is shared between the instrumentalists, who operate like the star players of a 1940s big-band, stepping out of the ensemble to high-profile their contributions directly to the audience. It's characteristic of Birtwistle in its welter of diverse musical imagery, like a sequence of disconnected scenes from an Expressionist film, periods of hyperactivity giving way to uneasy stasis, and ranging from a pawky, Punch and Judy-like humour to manic whistling.

This element of drama, often ritualised, sometimes represented visually, is inherent in much of Birtwistle's instrumental output, but the Sinfonietta's other item, the 1977 Silbury Air, is different. This is a landscape, an exterior one - the inspiration is the enormous, enigmatic 4,500-year-old man-made Silbury Hill in Wiltshire, near where Birtwistle now lives - but presumably an interior one too. With its shifting foreground and background, the material is viewed by Birtwistle from every conceivable angle, including from the inside as he slices his way through it, layer by layer, in a systematic dissection.

Fascinating as these pieces were - Silbury Air's haunted pastoralism places Birtwistle as the heir to, amongst other things, the English visionary tradition of Vaughan Williams and Holst- and superbly delivered by Atherton and the Sinfonietta, the highlight of this grand retrospective thus far has to be Earth Dances, in Dohnányi and the Philharmonia's thrilling performance on Sunday night.

This 40-minute 1986 epic consciously offers a geological comparison. It's like layers of rock, says the composer, fractured by seismic shifts, and the music explores these subterranean fault-lines almost as if an earthquake were still ripping them apart and smashing them back together in new, bizarrely twisted juxtapositions. Birtwistle seems to have absolute control of his material here - though perhaps it's the other way around. At any event its unrelenting power is borderline terrifying. You'd have to go back to The Rite of Spring for something comparable, or perhaps even further back to Beethoven's Seventh.

That too was considered shocking in its day - Weber is supposed to have said after hearing it that his senior colleague was ripe for the madhouse - and if Bernard Haitink's performance with the Dresden Staatskapelle during his 75th-birthday season on Tuesday didn't suggest insanity in the Beethoven family, it certainly pointed to a mind working through the possibilities of non-stop rhythm with obsessive compulsion.

Weber, in fact, began the visiting German orchestra's programme in the shape of a performance of the Freischütz overture that didn't quite gel: its Caspar David Friedrich forest vistas scarcely conjuring up anything very sinister, certainly not the demon-haunted abyss Weber peers into before turning back to the light with sweaty-browed relief. Nor did Hindemith's Symphonic Metamorphoses on Themes of Weber really come off, its edgy elation registering merely as jovial solidity. This showpiece needs a bit of showbiz, something Haitink doesn't really do.

But from the opening bars of the Seventh onwards this looked set to be a vintage performance, and so it proved. Wagner called it "the apotheosis of the dance", and with Haitink and his players responding in full measure to its unstoppable dynamism it was very hard to keep the feet still. There was no actual bopping in the aisles, but I'd be surprised if there wasn't some cavorting in the car-park afterwards.