How Mica Levi got Under The Skin of her first film soundtrack

Composing for a film was such new territory for me that I approached Under The Skin like it could suddenly be gone tomorrow. I actually kept it a secret from a lot of people while I was working on it. The first call came from out of the blue, and when I went to meet [director] Jonathan Glazer and [music producer] Peter Raeburn, they showed me some footage and we talked about what the music could be in a pretty abstract way. Jon didn't prescribe anything; he just asked me to follow my own trajectory.

I've heard the word "otherworldly" used a couple of times to describe the music but that wasn't a specific instruction from Jon and Pete. The idea was to follow Scarlett Johansson's character and try to react in real time to what she was experiencing, not to pre-empt or reflect on things that had already happened in the film. Some parts are intended to be quite difficult. If your lifeforce is being distilled by an alien, it's not necessarily going to sound very nice. It's supposed to be physical, alarming, hot.

It was a very immersive experience, and I got obsessed with it. It took about nine months of working pretty constantly. I've made my own instruments in the past but for this I mainly used viola to write and record, although we brought in other players to back up my rusty playing and thicken things up. I used to have a studio in a shipping container so I did some work there initially but after that I was in Pete's studio two or three times a week.

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I previously studied at Guildhall, and the music I wrote back then for string quartet used a lot of harmonics and extended techniques. For Under The Skin, we were looking at the natural sound of an instrument to try and find something identifiably human in it, then slowing things down or changing the pitch of it to make it feel uncomfortable. There was a lot of talk of perverting material. It does sound creepy, but we were going for sexy.

I didn't listen to a lot of other soundtracks while I was writing; I was worried about being porous. A lot of the influences either came from quite visual directions or 20th-century music I'd cut my teeth on at Guildhall: Giacinto Scelsi, Iannis Xenakis and John Cage… these big, music-changing composers. But I also took a lot of inspiration from strip-club music and euphoric dance as well.

It was a totally different experience from making music as Micachu And The Shapes, but I really don't have that many dimensions so there must be some similarities; they both involve collaboration. I first saw the full film at Venice last year, and afterwards there was some cheering and a bit of booing but I think it's good that people have reacted strongly to it. It's hard for me to be objective, but I'm very proud of it.

Under The Skin is in UK cinemas now; the soundtrack is released on 31 Mar