A Music tracker (short version tracker) is a type of music sequencer software for creating music. The music is represented as discrete musical notes positioned in several channels at discrete chronological positions on a vertical timeline. The file format used for saving songs is called a module file. Later trackers departed from solely using module files, adding other options both to the sound synthesis (hosting generic synthesizers and effects or MIDI output) and to the sequencing (MIDI input and recording), effectively becoming general purpose sequencers with a different user interface.