This 1993 recording of Morton Feldman’s cello-and-piano piece Patterns in a Chromatic Field (1981) is a pioneering document, a recording released during a period when Feldman was famous for being little-known and not the all-pervasive presence he is today. At the time Marianne Schroeder had recorded Feldman’s solo piano music for the label (alongside music by John Cage and Anthony Braxton) while Rohan de Saram, whose day job was cellist in the Arditti Quartet, had been playing with the British free improvisation group AMM, an ensemble with an aesthetic that had connections to Feldman’s own and whose pianist, John Tilbury, was also a Feldman specialist. And all those connections implied that Feldman orbited around a new music parallel universe.

Since 1993 other top-notch versions of the score have emerged, mostly noticeably Charles Curtis and Aleck Karis on Tzadik and Deirdre Cooper with John Tilbury on Matchless – labels which, like HatArt, straddle improvised and composed new music (Christian Giger and Steffen Schleiermacher’s coldly professional take is best avoided – MDG, 5/16). But this recording remains the yardstick. Feldman said, issuing one of those enigmatic aphorisms at which he excelled, that this piece ‘is very related to serialism, but also to medieval disciplines of the Kabbalah’, and de Saram and Schroeder play expertly with the freedoms licensed by Feldman’s rigour. The first thing you notice is de Saram sheathing the customary high-register timbre of a cello with a warping falsetto – Feldman’s demands of tessitura (supersonic high harmonics) and his well chosen microtones demand such a response.

Charles Curtis is equally willing to challenge his cello’s comfort zone but de Saram and Schroeder ultimately dive deeper into the work’s mysteries. Abrupt switches of timbre are clearly demarcated, flinging the music back into process, back into the thrilling unknown. And yet you’re never left in doubt about the essentials of the overall structure – gestures that don’t necessarily belong together welded into place, with the joins unseen.