If Mozart is the ancestor of most of the duets here, as Paul Griffiths observes in his booklet-notes, the genetic print lies not only in the complementary relationship between violin and viola explored in the Sinfonia concertante, K364 (and echoed in an ingenious palindrome by the young Bartók), but in the two marvellous Duets of 1783, where he takes pains to offset the apparent austerity of the instrumentation by hinting that there are more than two voices in discourse, or that they have more than one topic of discussion. Skalkottas and Martinu do this with formidable bunches of multiple-stopping, the one in vigorous disputation, the other in playful and garrulous good humour.

Heinz Holliger and Giacinto Scelsi introduce the voices of the performers to twine with tingling sensitivity around their instruments. Microtonal fluttering will be like nails down a blackboard to some, no doubt, but I have to admit that I found the effect more like that of a good massage; Holliger especially knows just where to press and where to caress the points of tension. He wrote these “sketches” for this husband-and-wife partnership and celebrates that distinctive quality Zehetmair’s playing has of dancing round the head of a volcano; so do Rainer Killius’s Icelandic song to a bottle and a rebarbative sort of anti-encore by Johannes Nied, forming the bookends of this entirely original recital, which demands and repays more attention each time I return to it.