If you've heard of the demoscene, especially in the era of the Amiga and the ZX Spectrum, you've likely heard tracker files, and the MOD file format. These files store music in a way similar to MIDI nowadays, in the way that data for what note to play is stored rather than the sound of the instrument playing that note.
Unlike MIDI, the sound of each instrument a single note is stored as well, which is then frequency-shifted higher or lower to sound like the instrument is playing different notes by playing it at specific sampling rates higher or lower than the one it was recorded at.
Please note that this MOD Player is still in progress and does not work yet. If you're looking for a program to play tracker music you have, don't use this one just yet. Instead, I recommend using the open-source and much loved VLC player. In addition to MOD files, it will also play all other tracker music file formats that I've seen.
- PulseAudio