Fever Ray stated she uses Steinberg Voice Machine Software Plugin in the studio, posted on PitchFork.com during an interview.
"Pitchfork: While we're talking about the sound and the recording, I'm sure you've been asked this question way too many times, but how do you achieve that effect on your vocals? KDA: There are so many software programs that you can use. But I actually bought a physical machine, a TC-Helicon Live, which is very fun to use. But I also use the Steinberg VoiceMachine software plugin, which I think is also good. But with the Helicron machine, you can do like four harmonies at the same time, so I use it in "Concrete Walls"."