Matheos and Portnoy initially considered having a different vocalist perform on each track; this idea was scrapped as they decided the constant change in vocalist would disrupt the flow of the album. Vocalists considered included Steve Walsh, Steve Hogarth, Steven Wilson and John Arch. Portnoy particularly pushed for Daniel Gildenlöw to sing on the album. Early on in the album's production, Gildenlöw wrote some vocal melodies and lyrics for two songs and completely wrote another song. Matheos liked Gildenlöw's ideas, but did not want to take the music in the same direction Gildenlöw did. Moore ended up performing most of the vocals on the album. In order to keep the album from becoming too similar to Chroma Key, Matheos and Portnoy decided to feature a guest vocalist on one track. Steven Wilson (of Porcupine Tree) wrote lyrics and performed vocals on the track "ShutDOWN". He was chosen because his music in Porcupine Tree was similar in style to the music on the album. Portnoy also credited Wilson as "a pioneer of his genre".