ProTracker module effects

Every cell has an effect: a number from 0 to F in the low half of its third byte, and an 8-bit parameter in its fourth. Trackers write it as three hexadecimal digits, such as C20 or A0F. The effects below are ProTracker 2.3D’s, as the ProTracker 2 clone reproduces them; earlier programs had fewer of them, and a few behaved differently.

Ticks

Each row lasts a number of ticks, the speed, 6 unless the song sets another. Tick 0 is when the row’s notes are played. Some effects act once, on tick 0; the others act on every tick after it, ticks 1 to speed − 1, so their strength depends on the speed. At the default tempo a tick lasts 20 ms. x and y below are the parameter’s two hexadecimal digits, xx the whole byte.

The effects

Effect	Name	What it does
`0xy`	arpeggio	On every tick, cycles between the note, the note + `x` semitones and the note + `y` semitones (tick number mod 3 gives 0, 1, 2). `000` is no effect.
`1xx`	slide up	On ticks 1 onwards, takes `xx` from the period, raising the pitch; not below 113 (B-3).
`2xx`	slide down	On ticks 1 onwards, adds `xx` to the period; not above 856 (C-1).
`3xx`	tone portamento	Slides from the current pitch towards the row’s note by `xx` a tick, without restarting the sample. `300` keeps the last speed.
`4xy`	vibrato	Wobbles the pitch: `x` is the speed, `y` the depth. 0 in either keeps the last value.
`5xy`	tone portamento and volume slide	Goes on with the last `3xx`, and slides the volume as `Axy`.
`6xy`	vibrato and volume slide	Goes on with the last `4xy`, and slides the volume as `Axy`.
`7xy`	tremolo	Like vibrato, on the volume.
`8xx`	(not used)	Does nothing in ProTracker. Many PC players use it for panning.
`9xx`	sample offset	Starts the sample `xx` × 256 bytes in. `900` uses the last value.
`Axy`	volume slide	On ticks 1 onwards, raises the volume by `x`, or if `x` is 0 lowers it by `y`; kept within 0 to 64.
`Bxx`	position jump	After this row, goes on at position `xx` of the order table.
`Cxx`	set volume	Sets the volume to `xx`, 0 to 64; above 64 is taken as 64.
`Dxy`	pattern break	After this row, goes on at the next position, at row `x` × 10 + `y` (the digits are read as decimal). A row above 63 means row 0.
`Exy`	extended	One of the 16 extended effects, chosen by `x`.
`Fxx`	set speed or tempo	`01` to `1F`: the speed, in ticks a row. `20` to `FF`: the tempo, in beats a minute. `F00` stops the song.

Extended effects

Effect	Name	What it does
`E0x`	filter	Switches the Amiga’s low-pass filter (the power LED filter): `x` = 0 on, 1 off.
`E1x`	fine slide up	Takes `x` from the period once, on tick 0.
`E2x`	fine slide down	Adds `x` to the period once.
`E3x`	glissando	`x` = 1: tone portamento moves in whole semitone steps; 0: smoothly.
`E4x`	vibrato waveform	0 sine, 1 ramp down, 2 square (3 is also square); add 4 to keep the waveform’s position when a new note starts.
`E5x`	set finetune	Uses finetune `x` (as in the header) for this row’s note.
`E6x`	pattern loop	`E60` marks the start of a loop; `E6x` goes back to it `x` times.
`E7x`	tremolo waveform	As `E4x`, for tremolo.
`E8x`	(not used)	Karplus-Strong in ProTracker 1; switched off in 2.3D’s replay routine.
`E9x`	retrigger	Restarts the sample every `x` ticks.
`EAx`	fine volume up	Raises the volume by `x` once.
`EBx`	fine volume down	Lowers the volume by `x` once.
`ECx`	note cut	Sets the volume to 0 on tick `x`.
`EDx`	note delay	Plays the row’s note on tick `x` instead of tick 0.
`EEx`	pattern delay	Holds this row for `x` more rows’ time. Effects go on; the notes are not played again.
`EFx`	invert loop	From ProTracker 1.1: inverts the bytes of the sample’s loop one at a time, at a rate set by `x`; it changes the sample data as it plays. In NoiseTracker this number was funk repeat.

ProTracker’s own behaviour

Songs were written by ear against ProTracker, so a player that wants them to sound right copies its replay routine, quirks included. From the ProTracker 2 clone’s replayer:

A sample number without a note sets that sample’s volume at once and loads its loop. The sample already playing is not restarted; the new loop takes over when it reaches its end.
On tick 0 with a note: E5x sets the finetune before the note is looked up; 3xx and 5xy set the target of the slide without restarting the sample; EDx holds the note back.
9xx is applied twice on a row with a note, once before the note is played and once after, so the stored start moves on twice; a later retrigger then starts further in. An offset at or past the end of the sample cuts it to one word.
Vibrato moves the period by (wave × depth) / 128, and tremolo the volume by (wave × depth) / 64. The sine is a table of half a wave in 32 steps, rising from 0 to 255 and back.
The ramp waveform of tremolo looks at the vibrato’s position, not the tremolo’s: a bug in ProTracker that players keep.
A tempo set with F20 or above takes effect one tick late.
The fine effects (E1x, E2x, EAx, EBx) and E6x and EEx act on tick 0, and act again on each repeat of a row held by EEx.
On the ticks after the first, the period is put back to the stored one for every effect except 0 to 6 and E, so a vibrato ends as soon as a row has no vibrato.
F00 stops the song. Several of the files examined for this site end that way.

Which program added which effect

A module from an older program uses only the effects it knew, and later programs play them the same way, with one exception, EFx:

Program	Effects
D.O.C. Soundtracker 2.0 (1988) and the Soundtrackers after it	`0`, `1`, `2`, `B`, `C`, `D`, `E` (filter), `F` (speed)
NoiseTracker 1.0 (1989)	`3` tone portamento and `4` vibrato, with speeds up to 31
ProTracker 1.0 (1990)	the E commands, and tempo with `F20` and above
ProTracker 1.0b and 1.0c (1990)	pattern loop, glissando and finetune
ProTracker 1.1a (1990)	`EFx` becomes invert loop, replacing NoiseTracker’s funk repeat

Songs that use F with values of 32 or more were written for ProTracker’s tempo; in a player from before it they are speeds.

StarTrekker’s modules

Modules marked FLT4 or EXO4 come from StarTrekker, whose E commands start its own synthesised sounds and macros rather than ProTracker’s extended effects. As OpenMPT does, the explorer leaves the E commands out of these files and plays an Fxx above 31 as speed 31.