When Arnold Schoenberg issued his now famous decree – that John Cage was an inventor of genius, not a composer, because he had no feel for harmony – he failed to realise that Cage, along with about seven-eighths of the world’s population, might conceive of music without reference to ideas birthed by Papa Bach or earlier. Cage’s late-period “number pieces” espoused his concept of “anarchic harmony”: the whole raison d’être behind conventional harmony of course is that it isn’t anarchic but, by handing musicians free-floating pitch material (to be played within a duration indicated in brackets above the stave) and encouraging the unprompted overlap of evolving parts, Cage liberated sound from any obligation to find its way home.

Naysayers moan that an ageing Cage exploited this set-up to crank out new works with ruthless, conveyor belt-like efficiency. But Four4 , performed here by four British free improvisers, and One, played by a pianist famous for her New York School sympathies, tell us that the number pieces are what you make them. The score in this context isn’t “the music”: it’s merely an instruction for how to embed sonic events inside silence, a rethink of notational principles that makes the Another Timbre disc so striking. Here are four musicians who live or die by what they find during improvisation, and the counterpoint of their chiselled sounds growing as they slide against the constraints of Cage’s time brackets, which often plunges them into enforced silence, is a trip.

Sabine Liebner’s textbook performance of One is one thing but her disc comes properly alive during One2 , where she walks between four pianos, loading each instrument with site-specific sounds – like that electronic trilling hum at 21'03" which subsequently reappears against the shifting sands of other emerging sounds – a process that “fakes” the essential number piece experience of a resonating chamber packed with intersecting echoes and shadows. ASLSP, meaning ‘As SLow aS Possible’, was written in 1985, just before the number pieces, and is a further meditation on time which unlocks basic principles that fed the number pieces and governed everything Cage wrote. He stood in opposition to Western harmony because harmonic function imposed a contrived, artificial time-flow against the harmony of silence. We all know about Flight of the Bumble Bee-type virtuosity; but what exactly does playing chords and notes “as slowly as possible” mean? How slow is slow? Here Liebner is virtuosically sensitive to lending every sound dignity, space and significance, testing the grain, like seeing how slowly she can ride a bike before it stops and she falls off.