Circadian is the sixth full-length album under name Thuoom. The starting point was an hour-long live improvisation played in a cave (Ambient Evening 6, Parainen, Finland). During this event, Tuomo did an a cappella piece while Barque Sound Experiment (aka BSE) played synthesizers. While for most of the tracks there are no hints of synths, two tracks feature BSE sounds extensively. Nevertheless, Tuomo considers this his first a cappella full-length. The end result features more relaxed ambient sounds than the previous release, Fokus.

Instruments used on this record: Human voice alongside Arturia Microbrute Analog Synthesizer & Korg MS-2000, all echoing in a cave.