Discussing Spector's Wall of Sound technique, Wilson identified the tack piano and organ mix in "I Know There's an Answer" as one example of himself applying the method. Compared to Spector, Brian produced tracks that were of greater technical complexity by using state-of-the-art four-track and eight-track recorders. Most backing tracks were recorded onto a Scully four-track 288 tape recorder before being later dubbed down (in mono) onto one track of an eight-track machine. Wilson typically divided instruments by three tracks: drums–percussion–keyboard, horns, and bass–additional percussion–guitar. The fourth track usually contained a rough reference mix used during playback at the session, later to be erased for overdubs such as a string section. "Once he had what he wanted," Britz said, "I would give Brian a 7-1/2 IPS copy of the track, and he would take it home."