Prior to Guitar Hero and Rock Band, Harmonix had already established itself as a company that made game products that focused on music interactivity. Born out of Massachusetts Institute of Technology's Media Lab, the first product made by Harmonix was The Axe: Titans of Classic Rock for DOS-based computers, challenging the player to use four keys on the keyboard to match notes in several songs. Looking to find a place for this type of game, Harmonix' founders Alex Rigopulos and Eran Egozy looked to Japan where music games like PaRappa the Rapper were becoming popular. This led to the creation of Frequency and its sequel Amplitude for the PlayStation 2; both games featured the concept of matching notes for specific instrument tracks along lanes. However, in retrospect, Harmonix found that players had difficulty initially understanding the game, as the presentation was an abstract concept that did not immediately connect the gameplay to the music. The idea of making an easy connection between the game and the music was used as a basis for their Karaoke Revolution games, which including using avatars singing and dancing in time to the music to strengthen the connection; this series was financially successful and helped grow the company.