Instrument envelopes (volume, panning, pitch)

What it is#

In impulse-tracker (and FT2) an instrument wraps a sample with envelopes — volume, panning and, in IT, pitch — drawn as nodes over ticks, optionally with a sustain loop that holds while the note is on and a normal loop. They are the sample tracker's version of the C64's instrument-tables: per-note shaping without pattern commands.

How to do it (Impulse Tracker)#

• Volume envelope as reverb: loop the reverb tail of a sample (ping-pong loops work best), trim the excess (ALT-L), then a decaying volume envelope shapes the loop into a natural tail; NNA continue keeps it from being clipped by the next note; a sustain loop instead of a loop lets === release it (source: s-tw081-it-tip-of-the-week).
• The reverb tail itself is made offline — parameters and a gated-reverb recipe on reverb-and-compression (source: s-tw118-reverb-and-compression).
• Pitch-envelope siren: a sine sample with a pitch envelope whose sustain loop oscillates up and down; the loop length in ticks is the rate; because it is an envelope, bending the note's pitch does not change the siren's rate or depth (source: s-tw081-it-tip-of-the-week).
• Pitch envelope + Jxx on noise: a long falling pitch envelope over a looped noise/timbre sample with a column of arpeggio commands gives analog-style sweeps (Skaven's trick); fade with the volume column (source: s-tw081-it-tip-of-the-week).
• Panning envelopes for beat loops: tune the loop to C-5 at the song's BPM, make the envelope exactly the loop's length, pan it back and forth in step with kicks and snares; never draw beyond 00/64; two slightly different loops crossing each other's path is a stereo effect to use sparingly (source: s-tw075-it-percussion-tips).
• Pitch envelopes are rarely useful for percussion; volume envelopes not much either — there volume swing wins (source: s-tw075-it-percussion-tips).

FastTracker 2 invented the model (source: s-ft2-manual): an instrument holds a volume envelope, a panning envelope, one auto-vibrato, up to 16 samples and a key split; one envelope pixel is one tick (50 per second at 125 BPM, about six seconds across the window); the sustain point holds until key-off (Caps Lock), then the fadeout rate takes over; predefine 1 is applied to every loaded sample; Lxx sets the envelope position from the pattern; turning the volume envelope off leaves the vibrato on. A note keeps ringing after release with an envelope at full volume and fadeout 0. Envelopes were the feature that sold the format in 1995: jase's Music Contest 3 winner was an XM made partly to "display its benefits (eg in envelopes) over s3m" (source: s-tw022-interview-jase), balrog left X-Tracker for FT2 because of them (source: s-tw042-interview-balrog), and u4ia found FT2's volume envelopes and panning "so close to CD quality" (source: s-tw067-interview-u4ia). OpenMPT (source: s-openmpt-manual-instruments): volume 0–100 %, panning ±32 around the current pan, pitch in quarter-tone steps (±16 semitones) or the same envelope acting as a filter cutoff; envelope loop, sustain loop (IT considers it first, XM whichever comes first), Envelope Carry (do not restart on the next note — use an NNA other than Note Cut), a release node from which the envelope resumes on note-off with the following nodes relative to the release volume; the fade lasts 32768 ÷ fadeout ticks; envelopes are tick-based, so they speed up with the tempo but not with pitch.

Mechanics (from the IT manual and format doc)#

Each of the three envelopes has up to 25 nodes at tick positions, an on/off flag, a loop and a sustain loop given as node numbers (the sustain loop holds until note off ===). Fadeout starts when an NNA fade triggers, when the volume envelope ends, on note off without a volume envelope, or on note off with the envelope's normal loop on; S77/S78 switch the volume envelope off/on per note. Pitch-envelope values are half semitones, interpolated 64 times per unit for smooth slides; in later versions the pitch envelope can be flagged as a filter envelope, and instruments carry an initial filter cutoff and resonance. A channel is freed when the volume envelope ends at 0 or the fadeout reaches silence (sources: s-it-manual, s-ittech).

LSDj: the wave channel has no envelope — you draw one#

The wave channel has no ADSR and no usable release: "the E command is mostly useless for the wave channel, giving you only the range E00-E03". The community answer since at least 2013 is a frame envelope — draw the same waveform at falling volumes across a synth's 16 waves, set PLAY to MANUAL, and step through them with F01 per table row, with Gxx setting the table speed. One synth gives 16 volume steps; F10 steps into the next synth, so two chained synths give a 32-frame envelope (source: s-chipmusic-lsdj-wav-channel-release).

Two hazards from the same thread: F is relative and accumulates (F05 F05 lands on frame 0A — prefer repeated F01), and touching the synth screen afterwards silently overwrites every hand-drawn wave in that synth (later versions ask first). Frame changes click on most hardware; align their rate to the beat so the clicks land with the percussion.

Since LSDj 8 the same shape is easier to get from the synth itself — a LIMIT ramp across the waves, which is also how you sidechain the channel (sidechain-pump; source: s-defensemech-wave-channel-ramble).

Related#

new-note-actions · adsr-envelope · stereo-panning · randomization-and-probability · instrument-tables · reverb-and-compression · fasttracker-2 · xm-format

Sources#

s-tw081-it-tip-of-the-week · s-tw075-it-percussion-tips · s-ft2-manual · s-openmpt-manual-instruments · s-it-manual · s-ittech · s-tw118-reverb-and-compression · s-tw022-interview-jase · s-tw042-interview-balrog · s-tw067-interview-u4ia · s-chipmusic-lsdj-wav-channel-release · s-defensemech-wave-channel-ramble