De acordo com este artigo, de Post Magazine , não havia instrumentos, mas havia vocalizações de guitarra, baixo e bateria, além de um beatbox. Com a técnica de vocalização, aparentemente você está cantando através de um instrumento, então ainda é sua voz, e não o instrumento que está causando o som (pense em Peter Frampton e em sua caixa de conversa).
Kevin O’Connell, re-recording mixer at Universal Sound Studios, handled the music and dialog mix on the film. For each of the 80 songs delivered for the final mix, there were up to 120 tracks of a cappella singing and vocalizations. O’Connell said, “I would have the main characters on the first 10 to 12 tracks, and the secondary characters on the next 10 to 12 tracks. Then I’d have scads of background vocals, beatbox, guitar vocalizations, bass vocalizations, and drum vocalizations.”
O’Connell took the principle tracks and panned them around the stage to match where the characters were dancing while they were singing. Next he filled in the background characters vocals. Then he filled the track in with the different instrument vocalizations of guitars, drums, bass, beatbox, and any other vocalized samples that came with the song. He said, “When you see it, you’ll find it hard to believe that there were actually no instruments during any of those songs.”
O artigo fala sobre os processos de gravação e mixagem do filme - muito interessante!