Ben Johnston’s got to be some kind of genius. Anyone who can simultaneously make a string quartet sound like a hyper-sophisticated electronic gizmo which IRCAM, if it’s lucky, might hope to acquire by the year 3010, and like four boiled-as-an-owl cowboys busking their way through outback folk tunes, more than satisfies Schopenhauer’s criteria about men of genius hitting targets that no one else can see – while the talented merely hit targets others find a bit tricky.

Now 84, Johnston has largely sat on the margins as composers with broadly comparable interests, such as Harry Partch, Lou Harrison and Gloria Coates, have each enjoyed their renaissance. “Johnston explored European classical music and pondered the path it might have taken if not limited by equal temperament,” the booklet-notes explain, which is as good a précis of his approach as anything I can think of.

His mature works are written entirely in just intonation – extracting melodic intervals direct from the harmonic series, thus bypassing equal temperament’s harmonic gerrymandering – and this concentration on tuning is Johnston’s portal into reimagined pasts and dizzying futures. His String Quartet No 10 (1995) hallucinates about the past lives of the archetypal Classical string quartet. Structural scaffolding, which ought to be supporting the sonata-form opening movement, wobbles like a Roobarb and Custard animation because just intonation trashes the required harmonic hierarchies; the last movement culminates with “Danny Boy” reclaimed from over-ripe pub balladry by Johnston’s even riper tuning.

String Quartet No 5 (1979) dives ever deeper into the eddy, transforming and redistributing folk material, disguising familiar melodic hooks with camouflaged just-intonation harmonics which reveal galaxies of texture no one knew existed. Johnston’s First Quartet (1959) is resourceful enough academic serialism; and, apropos the Kepler Quartet’s genius playing, they hit notes few other groups could even hear.