Tracker is the generic term for a class of music sequencer software which, in its purest form, allow the user to arrange sound samples stepwise on a timeline across several channels. A tracker’s interface is primarily numeric; notes are entered via the alphanumeric keys of the computer keyboard, while parameters, effects and so forth are entered in hexadecimal. A complete song consists of several small multi-channel patterns chained together via a master list.

There are several elements common to any tracker program: samples, notes, effects, tracks (or channels), patterns, and orders.

A sample is a small digital sound file of an instrument, voice, or other sound effect. Most trackers allow a part of the sample to be looped, simulating a sustain of a note.

A note designates the frequency at which the sample is played back. By increasing or decreasing the playback speed of a digital sample, the pitch is raised or lowered, simulating instrumental notes (e.g. C, C#, D, etc.).

An effect is a special function applied to a particular note. These effects are then applied during playback through either hardware or software. Common tracker effects include volume, portamento, vibrato, retrigger, and arpeggio.

A track (or channel) is a space where one sample is played back at a time. Whereas the original Amiga trackers only provided four tracks, the hardware limit, modern trackers can mix a virtually unlimited number of channels into one sound stream through software mixing. Tracks have a fixed number of “rows” on which notes and effects can be placed (most trackers lay out tracks in a vertical fashion). Tracks typically contain 64 rows and 16 beats, although the beats and tempo can be increased or decreased to the composer’s taste.

A basic drum set could thus be arranged by putting a bass drum at rows 0, 4, 8, 12 etc. of one track and putting some hihat at rows 2, 6, 10, 14 etc. of a second track. Of course bass and hats could be interleaved on the same track, if the samples are short enough. If not, the previous sample is usually stopped when the next one begins. Some modern trackers simulate polyphony in a single track by setting the “new note action” of each instrument to cut, continue, fade out, or release, opening new mixing channels as necessary.

A pattern is a group of simultaneously played tracks that represents a full section of the song. A pattern usually represents an even number of measures of music composition.

An order is part of a sequence of patterns which defines the layout of a song. Patterns can be repeated across multiple orders to save tracking time and file space.

There are also some tracker-like programs that utilize tracker-style sequencing schemes, while using real-time sound synthesis instead of samples. Many of these programs are designed for creating music for a particular synthesizer chip such as the OPL chips of the Adlib and SoundBlaster sound cards, or the sound chips of classic home computers. These programs are also often called “trackers” and are listed in this article.

Tracker music is typically stored in module files where the song data and samples are encapsulated in a single file. Several module file formats are supported by popular music player programs such as Winamp or XMMS. Well-known formats include MOD, MED, S3M, XM and IT.

Tracker music lives on today. It can be found in modern computer games such as the Unreal series, Deus Ex and Hitman: Codename 47 as well as a considerable number of indie games, like Need For Madness by Radical Play. However, the easy availability of software samplers/synthesizers and sequencers has caused some professional musicians to adopt other music software. Nonetheless, tracker software continues to develop. Some of the early Amiga trackers such as ProTracker and OctaMED have received various updates, mostly for porting to other platforms. ProTracker having resumed development in 2004, with plans for releasing version 5 to Windows and AmigaOS, but only version 4.0 beta 2 for AmigaOS has been released. Other cross-platform trackers include Renoise, MilkyTracker, Schism Tracker, GoatTracker, and Skale.

Buzz, ModPlug Tracker, Renoise, Psycle, and others offer features undreamed-of back in the day (improved signal-to-noise ratios, automation, VST support, internal DSPs and multi-effects, multi I/O cards support etc.).

During 2007, Schism Tracker, Renoise, and Modplug Tracker (OpenMPT) were the most active in development. Development is resuming on Skale and reViSiT, which is technically a Tracker VST plugin in the spirit of Impulse Tracker, not a stand alone program.

Trackers are also becoming increasingly popular with professional musicians, particularly in genres such as IDM, where fine control over sample playback is needed. Venetian Snares, for instance, has released a video on Youtube of his track Vache playing in Renoise.