Most of (but not all) chip sounds are synthesised by simply dividing a clock square wave to get a square wave of desired frequency, and sometimes using a sawtooth/triangle wave from volume LFO or an (ADSR) envelope to get some kind of ring modulation. LFOs are used to control or influence a sound parameter such as pitch or filters in a repeating cycle.
Common file formats used to compose and play chiptunes are the SID, YM, SNDH, MOD, XM, several Adlib based file formats and numerous exotic Amiga file formats.
