Playing a new note in Impulse Tracker need not cut off the note before it. An instrument can specify a new-note action: stop the old sound, let it continue, release it or fade it. A single column of entered notes can therefore leave several voices sounding.
That distinction between an editing channel and a playback voice is one of the useful changes in Jeffrey Lim’s DOS tracker. More columns are not the only way to build a richer arrangement.
Familiar keys, different instruments
Lim’s original manual explains that the program began as an extension to Scream Tracker 3. He wanted to keep its quick keyboard workflow while adding facilities associated with FastTracker II, including more developed instruments and envelopes.
In sample mode, a pattern selects samples more directly. Instrument mode adds a layer that can map notes to samples, shape their sound and decide what happens when another note arrives. An envelope can continue changing a voice after the pattern cursor has moved on. (IT.TXT, sections 1.2 and 2.5.)
Voices still consume resources
The manual distinguishes its 64 directly controlled channels from the limits of particular sound drivers and hardware mixers. It explicitly warns that some channel entries will not sound on hardware with a lower channel limit in sample mode.
Continuing an old note also uses a voice. The result depends on the driver, available resources and the song’s settings. New-note actions give the composer control over that behaviour; they do not supply an unlimited synthesiser.
The IT format carries these decisions with the music. Its technical document separates instrument definitions, sample headers, patterns and envelope information, and records compatibility settings that affect playback. A file extension identifies the family, while those details determine how a player should perform it.
The implementation can be studied
Lim later published the source, including sound and network drivers and supporting documentation. His repository identifies the original 2014 release and explains that it preserves the historical program rather than promising ongoing feature development.
For tracker music, that leaves both sides of the work available to examine: the data describing a performance and the code responsible for turning it into sound.
Sources
- Jeffrey Lim, Impulse Tracker User’s Manual, IT.TXT, especially sections 1.2, 2.5 and the driver qualifications.
- Jeffrey Lim, ITTECH.TXT: original module-format documentation.
- Jeffrey Lim, source repository and README: source-release provenance and included implementation.