Impulse Tracker is a multi-track digital sound sequencer proliferated on the MS-DOS platform. It was authored by Jeffrey Lim and discontinued after version 2.15. It was available as freeware, though the author supplied extra features (like saving stereo WAV files, possibility to use an IPX network mode) in exchange for some cash. It reigned among the popular trackers of its time including ScreamTracker 3 and FastTracker.
One of the features which set this MOD editor apart was NNAs, New Note Actions. If a new key-on command is received in the same channel as another instrument which is still being played, NNAs allow the user to customize the action that next occurs:
- Cut: New instrument sound replaces current playing instrument.
- Continue: Old instrument continues to play following its defined ADSR curve.
- Off: Old instrument instructed to begin release section of its ADSR curve.
- Fade: Old instrument fades out to 0 volume at a designated rate overriding any ADSR information.