Alva Noto
According to Sakamoto, his musical interests were moving towards "sound and music" rather than just "music" while producing the album, and thus he incorporated field recordings to capture "lots of strange sounds." Sakamoto did the field recordings by walking through streets in New York City, Tokyo, Kyoto, and Paris with a cell phone microphone in his hand, activity that made up for four months of the album's production. The sounds he captured were those all people unavoidably encounter in everyday life, such as street noise, animal sounds, leaves, water, and rain. Composing the score for "The Revenant" (2015), a film very heavy on themes about nature in both its story and music, influenced how Sakamoto produced "async". For "Walker," Sakamoto spent around ten to fifteen minutes recording his footsteps while walking in a forest filled with leaves, which makes up most of the track. It was a forest that surrounded Philip Johnson's Glass House, which Sakamoto later used to record the improvisational piece "Glass" with Alva Noto.