MUSIC / The generation game: Robert Maycock on the London Sinfonietta and Capricorn playing old new music and new new music

The trouble with 25th anniversaries is that the next generation has usually taken over. For the London Sinfonietta there's an unfortunate extra twist: it reaches its quarter-century just when, in the eyes of the world, the music it grew up with - never widely appreciated at the best of times - is passing into the realm of the deeply unloved. Can we still believe that in another few decades, listeners will 'catch up'? Hardly: the world of steady progress and advance that this assumes has been gone for years.

You don't have to applaud the changes, but too many in the new-music scene turn a blind eye. If times are worse, it isn't the London Sinfonietta's fault; but it has to react. Will it become a sort of museum for the music by Carter and Henze and Boulez that, pretty soon, few others will have the skill or the patience to play? Or will it plunge into a future for which its trusty chamber-orchestra format might not be the best-adapted means of survival? A bit of both, seems to be the answer from the last of its 'Happy Returns' series at the Queen Elizabeth Hall on Tuesday - an answer which dropped it neatly between two stools. Conducted energetically by Lothar Zagrosek, it played early-Eighties pieces by Witold Lutoslawski and Brian Ferneyhough with the glaring, almost surreal intensity and virtuosity that has long characterised its performances (and to be fair, Lutoslawski is a composer who inspires fondness more widely than most). Then came Michael Torke's Monday and Tuesday.

Here is one of the most formidably equipped and aggressively engaging composers of the generation that could be called post-minimal, or even post-rock. And post-Sinfonietta: the rasping, rotating bits of tune, punchy syncopations and added beats, relentless pace and abrasive harmonies, sit uneasily on so traditional a body of players. This commissioned piece is full of vigour and diversity, pulsing with rhythmic life; but the experience was like a genteel hybrid of Copland and Reich, the wind solos too cosy and the strings too sweet. The oddest idea was to write it in two movements that go through much the same processes at the same speed, using similar material and taking nearly the same time. Is this a built-in way of achieving that elusive second performance?

At the ICA, Adrian Jack's latest 'New MusICA' series ended on Sunday when the ensemble Capricorn, with its usual flair, played a mix of the fresh, the stale, and the incomprehensible from two generations formed in the musical scene of Cologne. Mauricio Kagel was the senior figure - still not much taken up in Britain, a fact which may explain the enthusiastic response to five recent pieces from an incomplete cycle called Die Stucke der Windrose. They are typical character pieces, full of whimsies and non sequiturs, elegantly wrought and sensitively scored. Imagine, say, a tango composed by Beethoven, taken through the looking-glass, deconstructed and then crushed, leaving a joke cadence as the players stare vacantly outwards: that, roughly, was the effect of the first.

But they give diminishing returns. Kagel operates on a not very subtle level of irony, lavishing his skill on side-effects; the jokes and fancies all merge. The best moment came in the second piece, working itself up to something like a scream, which at least sounded wholehearted. The concert's best moments, on the other hand, came with one of its two new commissions for piano quartet. Gerald Barry's music has long been a cause taken up by Jack: here too there is a layer of ironic detachment, but it is overwhelmed by a manic intensity of expression, often in gleeful dance rhythms driven by some raging demon.

This quartet was both frantic and extrovert, at least to start, with Irish melodic inflections pressed through close counterpoint and coming out like a warped variation on the scherzo in Beethoven's Archduke. Sections alternate rapidly and mechanically; there's a Stravinskian edge about the writing, recalling music by Kevin Volans. Later, quiet ideas filter through, softening (weakening?) the impact. Here, though, is a piece that captivates on many levels - unlike the dismal quartet by Walter Zimmermann, which went through all the motions, but off on some wavelength of its own I was not equipped to receive, quiet, continuous, dissonant, and ingrown.