Modules are digital music files, made up of a set of samples (the instruments) and sequencing information, telling a mod player when to play which sample on which track at what pitch, optionally performing an effect like vibrato, for example. Thus mods are different from pure sample files such as WAV or AU, which contain no sequencing information, and MIDI files, which do not include any custom samples/instruments. Mods are extremely popular in the demo world and offer a way of making music of an acceptable level of quality rather cheaply. With the advent of high-quality sound hardware, new generations of mods may even rise to a sound quality nearing that of professional equipment.