In a recent interview with Tiny Desk, Ólafur Arnalds explains the latest addition to his musical ensemble: two haunted pianos behind him, that seem to be playing by themselves. He presses a chord on his electronic keyboard and a waterfall of delicate notes run off the keys of the pianos, their hammers visibly moving, like a self-playing pianola but seemingly with their own minds. “What I can say, is that I’ve spent two years and all of my money on this — to make my pianos go bleep-bloop.”

Arnlads ‘bleep-bloops’ – a somewhat mysterious concoction caused by musical software that conjures patterns in tune with the notes he plays – is just one of the experiences at Arnalds’ sold-out performance in London. And it’s a fine example of an artist who composes music that stretches well beyond the recording, that strives to be best served live.

Olafur RAH 3 - credit Dominic Nicholls

Olafur Arnalds – credit Dominic Nicholls

Accompanying Arnalds and his string quartet is an understated light show. Much like Arnalds’ music, it’s based on minimalist techniques. A glowing sunrise of pink light at the back of the stage; a heartbeat of warm light pulsing over the stage; the crisscrossing of white lights to create a moving film of shadows on the backdrop. It isn’t over-complicated, but it works.

A simple piano line from Arnalds opens the set; in the darkness, a quartet of strings twinkle in and out around him, and the shadows of large mountainous pianos flanking them. Then steadily, the cyclonic power of the strings kicks in. Two bright lights whirl around and around in a dizzying tornado. Crackles of percussion thunder through the theatre.

This is what takes his show beyond music and into the elemental, and it’s certainly a fundamental facet to his latest album ‘re:member’. The senses are confused and stimulated by tremelos of light and flickerings of piano notes, and it’s this that earns such a warm response from the audience. A dawn, a night sky, a storm – all are captured in the symphony of music and visual.

But the best comes in his encore, where he plays ‘Lag Fyrir Ömmu’. It’s a nice enough recording, but something you wouldn’t expect to be a show stopper – until now. Returning to the crowd alone, he sits at the piano, explaining, in his affable and warm way, how the song is a tribute to his late grandmother – ‘we sat in the hospital together, and listened to Chopin in silence, and then I came home and wrote this song’. It starts simply enough, a sad melody, muffled by the physicality so distinct to a real piano, like a cry into the dark. Then softly, the strings come in, calling back, from indistinct places on the stage of the wings. Tiny lights glow like fireflies in the dark. He slows down and plays his final note and the strings continue on, echoing, eternal – a sonorous choir of ghosts in the shadows. As they die away, the silence from the audience is absolute, ten seconds, maybe more. For a moment, we are joined in our shared belief, our combined mourning – as though Arnalds has lifted the curtain to the afterlife, and we are sat there together in the dark, listening to the people we love and miss breathing on the other side.