Music: Pumping up the volume: Nick Kimberley reviews Glenn Branca at the Queen Elizabeth Hall and Michael Nyman at the Barbican Hall

The words 'technology' and 'music' sometimes seem antithetical, the one inhuman, the other redemptively human. Yet it is technology that, historically, has made music possible, whether supplanting the fortepiano with the extended sonorities of the pianoforte, for example; or offering up the awesome possibilities of the full-blown symphony orchestra. One of technology's happiest gifts has been extra volume, yet in our own time, few composers have exploited the most obvious means of cranking up the volume: amplification.

Last week, two composers who embrace amplification - Michael Nyman, Glenn Branca - demonstrated their different ways of adapting it. For Nyman, amplification is not about volume per se, but about presence, not quite the same thing. The idea is to make the separate textures apparent. For Branca, volume itself is an instrument, perhaps his main device. Not everyone appreciates it. Although his Queen Elizabeth Hall audience presumably knew what to expect, many left at the first opportunity - but their places were quickly taken by those sitting further back, eager to get nearer to Branca's almost tangible wall of sound.

Branca's amplification fuses rather than separates the musical elements in his ensemble (nine guitars, two of them bass, and a drummer). When one of the bassists took up an electric keyboard, it was at first impossible to discern the different sound, buried deep in the mix. Only gradually did the ear locate the tiny difference. In Branca's music, apparently contradictory aesthetic impulses merge: Futurism's espousal of industrial noise; the lo-tech thrash of 1960s guitar combos like the Spotnicks; anarcho-punk outrage. The melange generates a mighty aural onslaught. As guitars hammer out single chords, or fast and hard tremolandoes, and the dummer beats out rudimentary rock rhythms, the ears seem to hear a ghost in the machine - sonic overtones which, I imagine, are happy accidents that Branca invites rather than controls. The experience is simultaneously exhilarating and numbing.

Branca conducts like a ragdoll attempting every dance Chubby Checker ever invented. Michael Nyman is cool and distant, directing his band with the merest twitch. At last week's Barbican concert (celebrating the composer's 50th birthday), the thrust of the amplification was comparatively gentle, allowing different instrumental lines to mingle so that it was sometimes momentarily, and beguilingly, unclear which instrument is the source of which sound.

Nyman's familiar propulsive sounds dominated the first half in two pieces celebrating balletic motion: The Final Score pays tribute to Nyman's footballing heroes; while The Fall of Icarus, conceived as part of a dance installation, seems an aural pre-echo of dancers in motion. What should have been the showpiece - the UK concert premiere of Nyman's score for The Piano - was less successful. What had been marvellously suggestive on screen seemed thin, as if the music required an extra element to replace the vanished images. The solo piano pieces skirted dangerously close to cocktail lounge tinkling. Perhaps, in evoking 19th-century idioms, Nyman sacrificed some of his uniquely quirky humour, which makes so many of his film scores perfectly viable outside the cinema.