"Gem tracks", the pattern of notes for a song, were developed by a team in Harmonix, taking usually a day to develop the tracks for one song. Tracks were designed to include key notes to "make [the player] feel as if [he is] a brilliant musician". Software algorithms were used to assess the difficulty of the tracks, and the quality assurance team helped to rebalance the tracks for accuracy and difficulty. The software also allowed Harmonix to quickly make changes to the set list or to recreate the tracks for a song to make sure the overall difficulty of the game was appropriate. Harmonix' past games "Frequency" and "Amplitude" aided in designing the visual interface for these gem tracks, such as how big to make the gems and how fast they should move on screen.