XM, standing for "extended module", is an audio file type introduced by Triton's FastTracker 2.
[2] XM introduced multisampling-capable[3] instruments with volume and panning envelopes,[4] sample looping[5] and basic pattern compression.
It also expanded the available effect commands and channels, added 16-bit sample support, and offered an alternative frequency table for portamentos.
This documentation is however said to be incomplete and insufficient to properly recreate the behaviour of the original program.
The MilkyTracker project has expanded the documentation of the XM file format, in an attempt to replicate not only the behaviour of the original software but also its quirks.