The story of how composers Morton Feldman and John Cage met is now famous: in 1950, feeling dismayed by an audience’s discourteous reaction to Anton Webern’s Symphony, Op. 21 at a New York Philharmonic performance, Feldman decided to leave the concert. In the lobby he encountered Cage, who was there for the same reason. They quickly established a rapport and embarked on a friendship that was to influence their respective creative outputs.

This year, the Ether festival at the Southbank Centre featured a concert solely dedicated to Feldman’s For John Cage (1982). It is a 70-minute work for violin and piano that invites the performers to traverse a myriad of inflections, intonations and asymmetric patterning. Notes are rendered repetitively in variable constellations of duration and shading, making for a measured musical construction that is deceptively static. This gradually evolving world of sounds is the hallmark by which Feldman has come to be known. His pursuit of stillness and sagacious exploration of colour shun strident atonal fireworks, inaugurating instead a series of unanswered musical propositions. Such investigations were originally provoked by Cage, who encouraged Feldman to relinquish his fidelity to serial technique and devise compositional tools that were not shackled to past models.

It was also through Cage that Feldman met some of the most celebrated figures of the New York art scene. For Feldman this prompted a life-long fascination with the relationship between music and painting, most notably played out in his music for the Rothko Chapel. It was no surprise that Monday’s concert attracted, amongst other musicians, several exotically-dressed artistic personages (one sporting an unforgettable sequined bow tie). For the conservative concert-goer, the lack of programme notes may have been challenging. I hope this was a decision made to privilege abstract musical experience over reductive explanation, rather than simply a result of technical difficulties. Possibly as a tonic to the lack of light reading, an ice cream kiosk was entrenched by the entrance.

When John Tilbury (piano) and Darragh Morgan (violin) began their performance it was clear that we would be offered a highly intuitive interpretation of this work. Morgan proceeded to drag a Baroque bow across his violin strings with swan-like poise, teasing out a variety of mannerisms from minimal note combinations. In turn, Tilbury sustained a range of piano sonorities, controlling their harmonic orbit with a careful application of varying pressure to the keys.

In 1966 Cage and Feldman were recorded in conversation at the radio station WBAI in New York. Among the topics they discussed was the effect of modern-day intrusions on their compositional creativity. Feldman cited the blaring of radios in pubic places as interference to the deep thought necessary to produce art, while Cage sought to absorb such phenomena as a part of his music. It was a small irony that Feldman’s For John Cage had a great many intrusions to contend with at this concert. The Purcell Room was teeming with rustling clothes, catastrophic coughing and provocatively-timed nose-blowing. One audience member provided an intermittent accompaniment of heavy breathing (whether this was the product of divine inspiration or somnolent unwinding, we shall never know). Then followed several exits: a young man wielding his rucksack defiantly en route to the double doors, a second objector who took a moment to regard the audience with disgust before leaving the hall, and a final trio that included one young woman desperately trying to creep in high heels.

While the deserters marched onwards to the ice cream kiosk, the musicians continued with stoic concentration. Indeed, such exits came to be missed thereafter as they had almost become part of the performance (a contribution that Cage would no doubt have appreciated). Why might music composed 30 years ago initiate this response? It is tempting to reduce Feldman’s ideas to basic explorations of tone colour, but there is more at stake in this late work than we might suspect. The composer’s unorthodox notation of accidentals suggests something beyond expressive inflection: it seems instead to call for the actual variation of intonation whereby the pitch ceases to be “in tune”. While Morgan’s handling of intonation was sometimes disorientating, there were magnificent moments where he found openings to elucidate untempered harmonics in the piano resonances with a related pitch on the violin. The work hints at the possibility of modulating into untempered systems of tuning – an exercise that, if taken up by contemporary composers, could radically alter the parameters of art music.

The composition came to a close that was punctuated by a cynical nose-blow (presumably an attempt to underscore Feldman’s expulsion from canonical paradise). However, it was heartening to see several members of the audience stand to applaud this fine performance, and even more delightful to hear a young enthusiast shout out from the shadows, “Again!”