About the Mod: Part One

The following article is an expansion and revision of material found in my book, Linux Music and Sound, published by No Starch Press.

There are many module file types, including the MOD, IT, S3M/STM, XM, MED and 669 formats. The original MOD format was used by ProTracker, one of the first trackers (mod composition software) for the Amiga. Many of the mod filename extensions indicate their origins on a particular tracker: the IT format comes from the Impulse Tracker, S3M/STM is from the ScreamTracker, MED is from the OctaMED tracker and so forth. The various formats differ in the number of tracks allowed, the number of samples supported and the permissible bit resolution of the samples. Fortunately for Linux users, the most popular formats (MOD, XM, and IT) are supported by the available trackers and players.

It should be noted that although trackers load and save modules in only one or two formats, mod players typically support a wide variety of file types. For example, the popular MikMod player, included in almost every mainstream Linux distribution, handles at least fifteen module formats, and the MODPlug plug-in for the excellent XMMS player supports more than twenty mod file types.

What Is a Mod Tracker?

A mod tracker is an application for composing music with only your computer and some sampled sounds. The basic design of a tracker is similar to a MIDI pattern sequencer. A pattern is defined by a number of beats that act as slots in which you place (track) your samples. Each beat includes information about the musical pitch for your sample, its instrument number and volume setting, and optional effects such as vibrato, filters and panning. Patterns are strung together in arbitrary sequences to create a song. The song is then saved in one or more (depending on the tracker) of the various mod formats.

Mod trackers first appeared on Amiga computers. Those machines enjoyed on-board sound support capable of handling up to four channels of 8-bit monaural sampled sound. With the advent of decent affordable PC soundcards, MS-DOS became the next platform of choice for module composers. Today excellent trackers are available for Windows, the Mac and, of course, Linux.

Trackers are especially well suited for making beat-oriented music such as pop/rock, techno and other dance styles, but because any kind of sample can be used the software is certainly not limited to any particular musical style. Check the MOD Archive, MODPlug Central and the United Trackers web sites listed at the end of this article for links to mod collections showing off the wide range of music made with trackers.

Of MIDIs and Mods

A tracker resembles a looping pattern MIDI sequencer. A series of beats or measures defines the loop period, events are placed on beats within the looping pattern, and there is some degree of fine control over the individual event. An event here means any sound file: events can be as simple as a single beat of a kick drum or as complex as an entire drum pattern or violin solo.

A MIDI file is very small compared to a mod, but it contains no sample data and must rely on a soundcard or external synthesizer to process its sounds and effects. A mod file includes sound sample data along with the sequence timing information and is accordingly much larger than a MIDI file.

The General MIDI (GM) patch map provides a specification for a common layout of sounds for all soundcards. However, cards from different manufacturers may fill their GM patch maps with samples of dramatically differing quality. Because a module contains sample data, a mod can be played on any computer with any soundcard, and listeners will hear your music played with exactly the same sounds that you used to compose it.

By now you might be thinking “So why use MIDI at all?” There are some very good reasons: MIDI sequencers are more highly evolved composition tools, with more possible connections to external hardware and auxiliary software utilities; file sizes may be a consideration, particularly if transmitted across low-bandwidth network lines; and the MIDI Manufacturers Association provides an industry-standard specification with a focused set of definitions of MIDI's capabilities.

By contrast the mod scene seems more chaotic. Many trackers have devised their own file types, which has led to a rather bewildering profusion of formats, and there is no governing body to help determine the organized definition and expansion of module capabilities. However, if you want to compose using sampled sounds, if you want listeners to hear your music with exactly the same sounds as you composed it, and if you can live with a rather “middleweight” file format, then module tracking may be just what you're looking for.


Similis sum folio de quo ludunt venti.