Terry Riley’s proto-minimalist classic In C is ordinarily launched via a punched out high-C pulse on a keyboard, a rallying cry around which instrumentalists begin the serious business of feeling, and indeed thinking, their way through Riley’s mosaic of 53 melodic fragments. But this performance by the combined forces of the Ragazze String Quartet and percussion group Slagwerk Den Haag offers a radical alternative – the pulse is discreetly shunted towards the background, utterly charming the senses with an often delicate mechanism of light pizzicato strings and mallet percussion.

Clearly, this vision of In C is a world away from Riley’s own 1968 recording, where multitracked woodwind, brass and percussion (with Riley himself especially prominent on saxophone) generated a rough-diamond heterophony not too far removed from the free-jazz energies of John Coltrane’s landmark large ensemble album Ascension. Everything in this new version is entirely within Riley’s rules (musicians move through the sequence at will, judging how the next module might shape and/or transform the enveloping mass of sound), but it’s a performance that also raises some pertinent philosophical questions.

My senses sniff a degree of pre-performance planning. When, around 22'20", the pulse melts into a wash of string and bowed vibraphone harmonics, before it is picked up again as a treading-water bass-line by pizzicato cello, the intentionality is obvious. There’s nothing to indicate that musicians can’t pre-plan. But In C’s USP was always Riley’s invitation to escape the strict narrative of a score, allowing players to determine forward impetus through careful listening – reading the moment rather than the notes.

But I mustn’t be overly ideological. This performance deals up moments of sheer magic; for example at 10'50" where the initial ensemble chatter narrows into a chirpy violin riff around which flinty string pizzicatos and clanging metal percussion spin; or the increasingly insistent groove that steers the music towards its end point. Sunrise of the Planetary Dream Collector, written originally for the Kronos Quartet, is reimagined here for the Ragazze Quartet and jazz trio Kapok as a minimalist lollipop – with grooves reminiscent of 1970s jazz/rock fusion group Weather Report, and a corker of a climactic drum solo.