THE South Bank Centre’s annual Ether festival is dedicated to music on the edge, new directions and new fusions; but along the way the London Sinfonietta’s concerts devised with Radiohead’s guitarist-composer Jonny Greenwood also proved the continuing potency of the past. Forget for a moment Greenwood and the band’s vocalist Thom Yorke, greeted with whistles, cheers and a digital-camera blitz. The real wonder, welcomed with relative quiet, was that syrupy French electronic marvel created in the 1930s, the Ondes Martenot. And not the usual one specimen: we had seven of them, grouped at the back like a city skyline.

Crack French executants put six to work on the languorous, ecstatic melody and twiddly accompaniment of Messiaen’s Fête des belles eaux, a showpiece of 1937. Hollywood may have forged a link between the Ondes and science-fiction, but with Messiaen the instrument is used for horticulture. In this Fête you’re in a magic garden, lush and becalmed, unusual blooms and tendrils swaying in the breeze. Wonderful to hear this rare piece.

The wonder of hearing all seven Ondes, with Greenwood added, failed to arrive: during the new arrangements of Radiohead songs, the concert’s climax, the tender creatures became submerged in the sound mix. Still, if you came for fusion, here it was. Arpeggi and Where Bluebirds Fly pulsed and oscillated impressively, with the Sinfonietta supplemented by the Arabic colourings of the Nazareth Orchestra and the sunburnt vocals of Lubna Salame.

These Radiohead numbers were Greenwood’s finest minutes. And we needed more of them, especially after the 12 eaten up earlier by his new concert piece Piano for Children. The motivating idea here was intriguing, with an out-of-tune piano soloist (the unflappable John Constable) clumsily proceeding like a child, cradled by strings. Nothing intriguing, though, about the gauche music. Better results followed from his recent Smear, with smeary sounds dangling in the air from an ensemble and two Ondes (a favourite instrument, obviously).

Elsewhere on this crowded bill the cerebral niceties of Dutilleux’s string quartet Ainsi la Nuit felt out of place, especially with amplification distorting and coarsening. But the sound experiments of Ligeti and mid-1960s Penderecki slotted in neatly. The conductor of this uneven, bitty, but useful carnival was Martyn Brabbins; what a cool dude he is.