It has taken a long time for Evan Johnson to get his due. A composer whose work is marked with mysterious intent and ambiguous direction, he has made it hard for himself – largely because he has made it hard for everyone else. In a discussion with Tim-Rutherford Johnson back in 2010, he admitted that his work was going to take time finding the right people: ‘my music tends to exist at boundaries of difficulty, endurance and notational complexity, and its appeal is limited as a result’. In fact, those traits are perhaps the most exciting thing about his music. His uncompromising vision and rarefied approach to writing scores has rewarded performers with completely new experiences, affecting them in uniquely strange ways. It’s kind of self-sabotage, doing an Evan Johnson piece – but who could possibly resist?

Johnson’s music begins with notation. It is, in his words, the ‘medium’ in which he works; sound might be the concern of the musicians who pick up his music sheets, but the writing is what matters to him. Johnson’s work lies at the edge of the format, like a Matrix structure with limits he’s trying to escape the confinements of. For most, notation is a language that indicates sound; its purpose is to give us something that directly communicates what music should be played. For Johnson, there’s more; notation is what forms sound, yes, but it can do more. Talking to the Riot Ensemble, he described his notes as a ‘semi-opaque code, generating situations for performers’. His sheets are networks of ambiguity and obtrusiveness, made not for musicians to understand and resolve, but to live in.

Something interesting happens when these pieces meet the listener. With the notation hidden, and Johnson’s elusive instructions concealed, the listener hears only a ‘shadow’ of what Johnson has written. A new version emerges, one with dark spaces and lost history. The listener experiences an echo of the real, Johnson’s sparse crawl of acoustic sounds passed down like whispers of what was once a whole truth. In many pieces, Johnson presents performers with physically and mentally demanding material that can barely be heard anyway. They burn stamina; it resounds to the audience as near-silence. The music is not shared, but scattered, Johnson describing his audiences as ‘less hearing and more overhearing’.

So: difficult music with mysterious definitions. Who’s up for it? It is, of course, the Riot Ensemble. The group are already familiar with Johnson’s music of shadows: in 2016, they performed Lart de toucher le clavecin 3, a work inspired by French baroque composer François Couperin. Like that work, they’re now taking on a piece written around the harpsichord: Linke Hand eines Apostels, commissioned by hcmf// and BBC Radio 3, focuses on ‘tensed strings, frail resonances, and hammered attack’, utilising harpsichord player Goska Isphording as a ‘soloist’ – in as much as she’s the most audible part. The piece’s intensity comes from its fragility – as if Johnson was trying to write imbalance and uncertainty into the notes.

With Linke Hand eines Apostels, The Riot Ensemble have opted into an evil spell. The piece bursts into existence, sparked up by a collective bang of instrumentation. It’s instantaneous, a moment of ecstasy – and for the rest of the piece’s duration, it’s dying off, the music fading ever outward. With these disquieting arrangements, Johnson creates new, uncomfortable relationships for the ensemble’s members. They find themselves trapped in a volatile environment – one of their own making. Johnson calls it ‘an extremely quiet, disappearing unstable fantasia’; he talks of passages being ‘silence-filled’, of groups of players as being ‘mostly inactive’. The piece moves like ‘unreliable thread’. It becomes one of those musical shadows Johnson makes: are the musicians the ones pulling the strings, making the malevolence, or is this piece a lifeline for them, something they’re desperately trying to grab a hold of?

Johnson’s chief inspiration for Linke Hand eines Apostels was a sketch by Albrecht Dürer, made in preparation for one the renaissance painter’s vast oil paintings. It literally means ‘left hand of an apostle’, and that’s what the drawing is: a very finely detailed image of a hand. The precision and beauty of this sketch would have been completely lost in the painting that resulted, the hand only a tiny fragment of the full image. But it makes sense that Johnson would zoom in on this sketch. He found the intensity; he found the moment in the process when Dürer really strained himself. The sketch is like something out of a Johnson piece: a transformation, one that the listener might never know happened.