Bright describes the development of the note track for a given song once it has been licensed for the game as a parallel effort, a process that they have found to be more efficient than their previous work on the "Tony Hawk" games. Once the song was mixed for use by the development team, a "tempo map" was created by one developer; this map denotes the beats in the music which then can be used by the rest of the development team. Once the tempo map was complete, the song was then distributed to the various teams, such as the specific instrument teams or to the animators, to complete the song. Note-for-note tracking from the song was then performed, and in some cases, changes were made to account for sections that cannot be replicated on the game controllers; the final track represented the note track for the Expert difficulty of the song. Note tracks were then reduced and adjusted to create the note tracks for the lower difficulties in the game. A difficulty assessment was made using the final note tracks to determine where the songs were to be placed in the soundtrack progression. The difficulty model is based on that from "", which was adjusted from the "Guitar Hero III" model after the team received negative feedback from players regarding a "brick wall" in the difficulty progression in that game.