tsvm/TAUD_NOTE_EFFECTS.md

Taud Tracker Effect Command Reference

Taud is a tracker-style music format derived from ScreamTracker 3's pattern command set, extended to 16-bit effect arguments and a 4096-tone equal-temperament pitch grid. This document defines every effect command a Taud engine must implement. Each command entry has three parts: a plain explanation for composers, compatibility notes for converting patterns from ScreamTracker 3 (ST3), ImpulseTracker (IT) or ProTracker (PT), and implementation details for engine writers.

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1. Sound device

• Bit depth: 8-bit unsigned throughout, including the final mixdown.
• Sample rate: fixed at 32000 Hz.
• Output channels: strictly stereo; the mix bus always produces a two-channel frame even for mono-source samples.

Internal accumulators may widen to 16 or 32 bits during mixing and effect computation, but stored samples and final output are 8-bit.

2. Pitch system — 4096-TET

One octave spans 4096 pitch units ($1000 exactly). A 12-TET semitone therefore equals 4096 ÷ 12 ≈ 341.333 units (≈ $0155.55), which is not an integer; this irrationality is a deliberate consequence of choosing a microtonal native grid. Implementations store channel pitch as a signed integer in Taud units, and convert to playback rate using

playback_rate = reference_rate × 2 ^ (pitch_units / 4096)

Commonly used intervals in Taud units are listed below; all are rounded to the nearest integer.

Interval	Units (exact)	Hex (rounded)
Octave	4096	$1000
Perfect fifth (7 ST)	2389.33	$0955
Tritone (6 ST)	2048	$0800
Major third (4 ST)	1365.33	$0555
Minor third (3 ST)	1024	$0400
1 semitone	341.33	$0155
1/8 semitone (1 finetune)	42.67	$002B
1/16 semitone	21.33	$0015
1/64 semitone	5.33	$0005
1 cent (1/100 semitone)	3.41	$0003

3. Volume system

Per-note and per-channel volume runs from $00 (silent) to $3F (full), a 6-bit range narrower than ST3's 0..$40. Global volume (effect V) runs 0..$FF; this wider range lets the mix bus scale the summed channel output without disturbing individual note volumes. The per-frame mix chain per channel is

mix = sample × note_vol × channel_vol × global_vol >> normalisation_shift

with saturation applied before the 8-bit stereo output.

4. Rows, ticks, patterns, cues

A pattern is a rectangular grid of rows and channels; each cell holds one note event. Playback divides each row into speed ticks (effect A); tempo (effect T) sets the duration of one tick. At 125 BPM and speed 6, one row takes 120 ms and one tick 20 ms. Songs play patterns in a cue sequence; effects B and C navigate this sequence.

5. Default parameters at song start

Parameter	Value
Speed	$06 (6 ticks/row)
Tempo byte	$65 (125 BPM; see effect T for the $18 offset)
Global volume	$80 (mid-scale)
Channel volume	$3F (full)
Pan (all channels)	$80 (centre)
cue index	$0000

6. Effect memory groups

Most effects recall their last non-zero argument when re-issued with $0000. Unlike ST3, which shares one memory slot across most effects, Taud groups memories into four cohorts plus private slots:

• E and F share one slot (pitch slide down and up). Issuing E $0000 recalls the last E-or-F argument and re-applies it as a down-slide; F $0000 does the same as an up-slide.
• G has its own slot (tone portamento).
• H and U share one slot (vibrato speed and depth are jointly recalled; the last-written values persist across both commands).
• R has its own slot (tremolo).

Every other memory-carrying effect (D, I, J, K, L, O, Q, and others) has a private slot.

7. Opcode and argument format

Opcodes are single base-36 digits (0-9, then A-Z); arguments are 16-bit hexadecimal values prefixed with $. A cell is notated OPCODE $HHLL where HH is the high byte and LL is the low byte. Where an effect partitions its argument into sub-fields (for instance, H's speed and depth), the split is spelled out in the command description.

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The effects

A $xx00 — Set tick speed to $xx

Plain. Sets how many ticks each row contains. Lower values make rows shorter and per-tick effects (slides, vibrato) develop faster; higher values stretch the row and give effects more iterations.

Compatibility. ST3 Axx maps one-to-one: Taud A $xx00. ST3 A00 is a no-op; Taud A $0000 is likewise ignored. ProTracker Fxx with xx < $20 maps to Taud A $xx00; Fxx with xx ≥ $20 maps to T instead (see T).

Implementation. If the high byte is non-zero, write it to ticks_per_row; the low byte is reserved and must be zero. The change takes effect from the row on which the A command appears. There is no memory for A.

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B $xxyy — Jump to cue $xxyy

Plain. Finishes the current row, then continues playback at row 0 of the pattern at cue position $xxyy. Use this to create song-level jumps, loops, or branching structures.

Compatibility. ST3 Bxx jumps to an 8-bit cue and maps to Taud B $00xx. The extended 16-bit range means Taud songs may have up to $10000 cue entries.

Implementation. On the last tick of the current row, set the next cue index to the argument and the next row to 0. If the argument exceeds the song length, wrap to the song's defined restart position (cue $0000 by default). Jumps are detected by a visited (cue, row) set so that pathological loops do not prevent song-length computation, though they do not interrupt actual playback. There is no memory for B.

Simultaneous B and C on the same row. If a B command appears in the same row as a C command (on any channel), both fire: B chooses the cue, C chooses the row within that cue. If the two commands appear on different channels, channel priority is ascending channel index — the lowest-numbered channel carrying either effect wins its parameter. If both appear on the same channel row (only possible if one is a volume-column equivalent), the effect column takes precedence.

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C $xxyy — Break pattern to row $xxyy

Plain. Finishes the current row, then skips ahead to row $xxyy of the next pattern in the cue sequence.

Compatibility. ST3 stores Cxx as BCD (so on-disk $10 means decimal row 10); Taud stores the argument as plain binary. When converting from ST3, decode with row = (byte >> 4) × 10 + (byte & $0F). Valid ST3 source bytes are those representing decimal 0..63; out-of-range BCD bytes should clamp to row 0 on import. When exporting back to ST3, encode with byte = ((row / 10) << 4) | (row % 10), clamped at row 63.

Implementation. On the last tick of the current row, advance the cue index by 1 (or honour a co-occurring B), then set the next row to the argument. If the argument exceeds the destination pattern's row count, start the destination pattern at row 0. There is no memory for C.

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D $xy00 — Volume slide (multiple forms)

D's 16-bit argument encodes four mutually exclusive modes using the top nibble and the following byte. All forms operate on the channel's current volume and clip to $00..$3F after each step.

D $0y00 — Volume slide down by $y per non-first tick

Plain. Each tick after tick 0, volume decreases by $y. A D $0400 at speed 8 reduces volume by $1C over the row.

Compatibility. ST3 Dx0 (volume slide down) maps to Taud D $0x00. The ST3 volume cap was $40; Taud's is $3F — a very high-volume sample reaching $40 in ST3 will snap to $3F in Taud.

Implementation. On ticks > 0, subtract the low nibble of the high byte from channel_volume; clamp at $00. Memory is private to D and is keyed on the full original byte (so D $0000 recalls whatever form last ran).

D $x000 — Volume slide up by $x per non-first tick

Plain. Each tick after tick 0, volume increases by $x. Capped at $3F.

Compatibility. ST3 D0y (volume slide up) maps to Taud D $y000.

Implementation. On ticks > 0, add the high nibble of the high byte to channel_volume; clamp at $3F.

D $Fy00 — Fine volume slide down by $y on tick 0

Plain. Applies a one-shot volume reduction of $y on tick 0 only. Independent of speed. A D $FF00 behaves as a fine slide up by $F (so a request for "down by F" is reinterpreted; see below).

Compatibility. ST3 DFy maps directly. The $FF edge case is preserved: ST3 treats DFF as fine slide up by $F rather than fine slide down by $F, and Taud follows suit.

Implementation. On tick 0 only, subtract the low nibble of the high byte from channel_volume. If the low nibble is $0, treat as fine-slide-up by $F. If the high byte is $FF, treat as fine-slide-up by $F.

D $xF00 — Fine volume slide up by $x on tick 0

Plain. One-shot volume increase of $x on tick 0 only.

Compatibility. ST3 DxF maps directly. Volume cap is $3F, lower than ST3's $40.

Implementation. On tick 0 only, add the high nibble to channel_volume; clamp at $3F.

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E $xxxx — Pitch slide down by $xxxx

Plain. Lowers the channel's pitch by the argument per tick. The coarse argument has two distinct interpretations chosen by the song-table f flag (effect 1, bit 1):

• Linear mode (f unset, default): the argument is a value in the 4096-TET pitch grid, subtracted directly from the stored pitch. E $0155 ≈ one semitone per tick.
• Amiga (cycle-based) mode (f set): the argument is a raw ProTracker/ST3 period unit count — the same byte the original tracker stored on disk, unscaled. The engine converts the channel's stored 4096-TET pitch back to an Amiga period, subtracts the argument from that period directly, then converts the result back to 4096-TET. E $0001 therefore corresponds to PT 201 and produces the characteristic non-linear pitch drift of ProTracker-style slides (lower pitches drift more slowly in semitone terms than higher pitches).

Because Amiga period units fit in a single byte (PT/ST3 max value $FF), the coarse range in Amiga mode never approaches the $F000 fine-slide marker, so the same argument-format selector still distinguishes coarse from fine. Fine slides (E $Fxxx) follow the same dual-interpretation rule as coarse: in linear mode the low 12 bits are 4096-TET units; in Amiga mode they are raw tracker period units (the PT E2x / ST3 EFx or EEx digit), applied once per row at tick 0 in period space. A coarse slide uses the full value range; a fine slide applies only once per row.

Coarse and fine modes are distinguished by the high nibble of the argument:

• E $0001..$EFFF — coarse slide: subtracts the full argument from pitch each tick after tick 0. A slide of $0155 drops pitch by one semitone per tick.
• E $F000..$FFFF — fine slide: on tick 0 only, subtracts arg & $0FFF from pitch.
• E $0000 — recalls the last E-or-F argument and applies it as a down-slide, preserving the original form (coarse or fine).

Compatibility. ST3 pitch slides operate on Amiga periods or linear slide units; Taud's storage depends on the song-table mode flag:

• Linear-source ST3 song (linear_slides set in S3M flags → Taud f bit clear):

  • ST3 Exx coarse (where xx < $E0) → Taud E round($00xx × 64/3) (1 ST3 coarse unit = 1/16 semitone = 64/3 ≈ 21.33 Taud units, rounded).
  • ST3 EFx fine → Taud E $F0 round(x × 16/3) (1 ST3 fine unit = 1/64 semitone = 16/3 ≈ 5.33 Taud units, applied once per row).
  • ST3 EEx extra-fine → Taud E $F0 round(x × 16/3) (same unit as fine, applied once per row).

• Amiga-source ST3/PT song (linear_slides clear → Taud f bit set):

  • ST3 Exx coarse / PT 2xx → Taud E $00xx verbatim, with no × 64/3 scaling. The engine reads the stored byte as Amiga period units and applies it in period space, recovering the original tracker's exact period-step count.
  • ST3 EFx fine / EEx extra-fine / PT E2x → Taud E $F00x verbatim (raw period-unit nibble in the low 4 bits), with no × 16/3 scaling. The engine performs the once-per-row fine slide in Amiga period space, mirroring the coarse arithmetic.

The Amiga-mode flag therefore controls two decoder behaviours simultaneously: (a) which numeric scale the converter should have used when emitting coarse arguments, and (b) which arithmetic the engine performs on those arguments per tick. Converters MUST set bit 1 (f) of the song-table flags byte whenever they emit raw period-unit coarse arguments, and MUST NOT mix the two scales within one Taud song.

Because E and F share memory in Taud (narrower than ST3's broad shared memory), an ST3 song that used E00 or F00 to recall a D, G, or Q argument will break on import; the converter must eagerly resolve ST3 recalls into explicit Taud arguments rather than relying on memory.

Implementation. Per-tick processing:

on row start:
    raw = arg
    if raw == 0: raw = memory_EF
    else: memory_EF = raw
    if (raw & $F000) == $F000:          # fine, applied once on tick 0
        mag = raw & $0FFF
        if amiga_mode:
            # mag is a raw tracker period-unit count; subtract pitch ⇒ add period.
            pitch = amiga_slide_down(pitch, mag)
        else:
            pitch -= mag
        mode_this_row = FINE
    else:                                # coarse
        slide_amount_this_row = raw
        mode_this_row = COARSE

on tick > 0:
    if mode_this_row == COARSE:
        if amiga_mode:
            # slide_amount_this_row is a raw tracker period-unit count (no × 64/3 scaling).
            # period = AMIGA_BASE_PERIOD × 2^(−(pitch − C4) / 4096)
            # period_new = period + slide_amount_this_row     # E subtracts pitch ⇒ adds period
            # pitch = C4 + 4096 × log2(AMIGA_BASE_PERIOD / period_new)
            pitch = amiga_slide_down(pitch, slide_amount_this_row)
        else:
            pitch -= slide_amount_this_row

Glissando control (S $1x) snaps the output pitch to the nearest semitone after every slide application; see S $1x.

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F $xxxx — Pitch slide up by $xxxx

Plain. Raises the channel's pitch by the argument per tick, with the same mode-selection scheme as E. Coarse, fine, memory behaviour, and Amiga-mode handling are identical in form but inverted in direction. The same dual-interpretation rule applies to both coarse and fine arguments: 4096-TET units in linear mode, raw tracker period units in Amiga mode.

Compatibility. Same as E. In linear-source songs, ST3 Fxx coarse converts using round(x × 64/3) and FFx/FEx fine/extra-fine use round(x × 16/3). In Amiga-source songs (PT or S3M with linear_slides clear), both forms are stored verbatim: Fxx coarse → F $00xx, and FFx/FEx fine/extra-fine / PT E1x → F $F00x. F and E share one memory slot in Taud. Amiga-mode behaviour is controlled by the same f flag as E; under that flag, both coarse (per-tick) and fine (tick-0 only) F slides are applied in period space.

Implementation. As for E, but add instead of subtract. No upper pitch cap is defined by the effect itself, but the sample-rate conversion at the mixer will saturate well before arithmetic overflow at reasonable playing ranges.

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G $xxxx — Tone portamento with speed $xxxx

Plain. Slides the channel's current pitch toward the note specified in the same row, at $xxxx Taud units per tick (after tick 0), stopping when the target is reached. A row with G and a note does not re-trigger the sample — the note's pitch becomes the portamento target and the already-sounding sample continues at its current pitch.

Compatibility. ST3 Gxx uses an 8-bit value in period-table units; convert to Taud using the same round(× 64/3) scale as E/F coarse (1/16 semitone per ST3 slide unit). ST3 linear mode is the expected import source; Amiga-mode G sources should be treated as linear. G has its own memory slot in both ST3 and Taud, so conversion is straightforward and does not suffer the shared-memory problem of E/F.

Implementation.

on row parse:
    if row has note and G effect:
        target_pitch = period_for(note)
        # do NOT re-trigger sample
    if arg != 0:
        memory_G = arg
    speed_this_row = memory_G

on tick > 0:
    if target_pitch set:
        delta = sign(target_pitch - pitch) × speed_this_row
        pitch += delta
        if sign crossed target: pitch = target_pitch; target_pitch = None

Glissando (S $1x) snaps the output frequency to the nearest semitone ($0155 step approximation) after each advance without changing the internal pitch counter; it affects only what the mixer sees.

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H $xxyy — Vibrato with speed $xx and depth $yy

Plain. Modulates pitch with a low-frequency oscillator (LFO). $xx is the LFO speed (high byte), $yy is the depth (low byte). On H rows the LFO accumulator advances at $xx × 4 per tick through a 256-entry lookup of the selected waveform (see S $3x). The current pitch offset is added to the channel's base pitch for the duration of each tick.

Compatibility. ST3 Hxy uses 4-bit nibbles for speed and depth; convert by nibble-repeating each into Taud's bytes: ST3 H27 → Taud H $2277. This preserves the effective LFO rate and peak depth. H and U share memory in Taud (they did in ST3 too).

Unlike ProTracker, ST3 vibrato fires on tick 0 as well; Taud follows ST3.

Implementation. The reference sine table is OpenMPT's 64-entry 8-bit table, indexed pos >> 2 through a 256-entry logical LFO (equivalently, a 256-sample 4×-oversampled sine peaking at ±$7F):

ModSinusTable[64] =
    00 0C 19 25 31 3C 47 51 5A 62 6A 70 75 7A 7D 7E
    7F 7E 7D 7A 75 70 6A 62 5A 51 47 3C 31 25 19 0C
    00 F4 E7 DB CF C4 B9 AF A6 9E 96 90 8B 86 83 82
    81 82 83 86 8B 90 96 9E A6 AF B9 C4 CF DB E7 F4

Per row/tick:

on row parse (H):
    if (arg >> 8)  != 0: memory_HU.speed = arg >> 8
    if (arg & $FF) != 0: memory_HU.depth = arg & $FF

on every tick (including tick 0):
    sine = ModSinusTable[(lfo_pos >> 2) & $3F]    # signed -$80..+$7F
    pitch_delta = (sine × memory_HU.depth) >> 6
    applied_pitch = base_pitch + pitch_delta
    lfo_pos = (lfo_pos + memory_HU.speed × 4) & $FF

At maximum speed and depth ($FFFF), peak pitch_delta is $7F × $FF >> 6 ≈ $1FA — about 1.5 semitones. On a fresh note, if the current LFO waveform retrigger bit is clear (S $3x with $x < $4), lfo_pos resets to 0. When the waveform is "random", a fresh random value is drawn every tick rather than read from the table.

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U $xxyy — Fine vibrato with speed $xx and depth $yy

Plain. Same LFO as H but four times finer in pitch — useful for subtle microtonal warbles.

Compatibility. ST3 Uxy uses nibbles; nibble-repeat each to convert. U shares memory with H.

Implementation. Identical to H except the shift is 8 instead of 6:

pitch_delta = (sine × memory_HU.depth) >> 8

Peak at maximum settings: $7F × $FF >> 8 ≈ $7E, about 0.4 semitone — exactly a quarter of H's peak.

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I $xxyy — Tremor with on-time $xx and off-time $yy

Plain. Rapidly gates the channel on and off. Volume plays normally for $xx + 1 ticks, then mutes for $yy + 1 ticks, repeating. Counters persist across rows and only reset on a fresh I row with a new argument.

Compatibility. ST3 Ixy uses nibbles ($xy) with the same semantics; convert by nibble-repeating each into Taud bytes: ST3 I47 → Taud I $4477. The +1 behaviour on both counters comes from ProTracker and is preserved throughout. Memory is private.

Implementation.

on row parse (I):
    if arg != 0: memory_I = arg
    on_time  = ((memory_I >> 8)  & $FF) + 1
    off_time = ( memory_I        & $FF) + 1

on every tick:
    if phase == ON:
        play at full channel volume
        tick_in_phase += 1
        if tick_in_phase >= on_time: phase = OFF; tick_in_phase = 0
    else:
        force output volume to 0 (base volume preserved for later effects)
        tick_in_phase += 1
        if tick_in_phase >= off_time: phase = ON; tick_in_phase = 0

A zero $xx or $yy input becomes 1 tick after the +1, never zero.

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J $xxyy — Microtonal arpeggio with offsets $xx00 and $yy00

Plain. Cycles the playing pitch through three values across consecutive ticks: the note, the note plus $xx00 Taud units, and the note plus $yy00 Taud units, repeating. At the default 50 Hz tick rate (speed 6, 125 BPM), this produces a classic chord-arpeggio effect; because Taud's grid is 4096-TET, the intervals can be microtonal.

The encoding places each 8-bit offset byte into the high byte of a 16-bit pitch delta, giving 256 discrete intervals per arp voice with a resolution of $0100 ≈ 0.75 semitone per step. This is coarser than E/F's 16-bit slides, but adequate for arpeggios and well-suited to non-12-TET intervals.

Compatibility. ST3 Jxy uses nibbles as 12-TET semitones; Taud uses bytes as $0100-scaled 4096-TET offsets. The conversion is therefore lossy — 12-TET intervals that are not multiples of 3 semitones incur ±25 cent rounding error. The table below gives the best Taud byte for each 12-TET semitone offset:

Semitones	Taud byte	Taud units	Error (cents)
0	$00	0	0
1	$01	256	−25
2	$03	768	+25
3	$04	1024	0
4	$05	1280	−25
5	$07	1792	+25
6	$08	2048	0
7	$09	2304	−25
8	$0B	2816	+25
9	$0C	3072	0
10	$0D	3328	−25
11	$0F	3840	+25
12	$10	4096	0

For example, ST3 J37 (minor chord) imports as Taud J $0409; ST3 J47 (major chord) as Taud J $0509. Memory is private and stores the full 16-bit argument.

Implementation.

on row parse (J):
    if arg != 0: memory_J = arg
    off1 = (memory_J >> 8) & $FF    # high byte
    off2 =  memory_J       & $FF    # low byte

on every tick:
    selector = tick_within_row mod 3
    if selector == 0:   voice_pitch = base_pitch
    elif selector == 1: voice_pitch = base_pitch + (off1 << 8)
    elif selector == 2: voice_pitch = base_pitch + (off2 << 8)

The tick_within_row mod 3 counter resets every row start (so every row begins at base_pitch). A subsequent E/F slide after a J row resumes from the last arpeggiated voice's pitch, not from base_pitch — this mirrors ST3's kST3PortaAfterArpeggio quirk and is deliberately preserved.

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K $xy00 — Dual: vibrato continuation and volume slide $xy

Plain. Unimplemented. On ST3, continues a previously started vibrato (H or U) without retriggering it, while applying a volume slide of $xy per non-first tick. Fine volume slides are not available in this form.

Compatibility. ST3 Kxy maps directly. Implementations must convert K to an explicit pair of commands: H $0000 (continue with stored speed/depth) combined with volume-column command 1.$xy (volume slide), and emit both.

Implementation. Execute the per-tick vibrato update as if an H command were active with argument $0000 (recall), then execute a D $0y00 or $x000 slide using the bytes of the K argument: high nibble as up-slide, low nibble as down-slide. If both nibbles are non-zero, down-slide takes precedence (matching ST3). K has no memory of its own; it uses H/U's stored speed and depth.

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L $xy00 — Dual: tone portamento continuation and volume slide $xy

Plain. Unimplemented. On ST3, continues a previously started tone portamento (G) without retriggering, while applying a volume slide of $xy per non-first tick. Fine volume slides are not available here.

Compatibility. ST3 Lxy maps directly. Like K, L must be equivalently implemented as G $0000 plus a volume-column slide.

Implementation. Execute the per-tick G update (recalling G's stored speed), then the D slide as in K. L has no memory of its own.

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O $xxyy — Set sample offset to $xxyy

Plain. On the row where it appears, jumps the sample playhead to byte $xxyy of the sample data. If the sample is looped and the requested offset exceeds the loop end, the offset wraps around through the loop as if playback had reached that point naturally.

Compatibility. ST3 Oxx is 8-bit, addressing offset xx × $100. On import, copy the ST3 byte into Taud's high byte and zero the low byte: Taud O $xx00. ProTracker 9xx maps identically. The Taud 16-bit form allows byte-precise seeking within samples larger than $100 bytes. Memory is private.

Implementation. On the row start, set the sample playhead to arg (in bytes, relative to the sample's start). Apply the loop-wrap calculation if the sample has loop points and arg > loop_end: arg = loop_start + ((arg - loop_start) mod loop_length). The O command does not retrigger the sample; it only relocates the playhead for an already-triggered note.

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Q $xy00 — Retrigger note every $y ticks with volume modifier $x

Plain. Retriggers the currently playing sample at an interval of $y ticks, optionally modifying its volume on each retrigger according to $x. The retrigger interval runs across rows until a new Q with a different $y or no Q at all.

Compatibility. ST3 Qxy maps directly. The $y == 0 behaviour is preserved from ST3: the entire effect is ignored (no retrigger, and memory is not updated). Memory is private.

ProTracker E9x is equivalent to Taud Q $0x00 (retrigger only, no volume change).

Implementation. A per-channel tick counter advances every tick, including tick 0. When it reaches $y, the sample retriggers (keeping current pitch), the counter resets to 0, and the volume modifier $x applies. The counter resets only when a row has no Q command; successive Q rows share and advance the counter.

The volume modifier table, computed with arithmetic (no LUT), is:

$x	Action	$x	Action
0	no change	8	no change
1	vol − $01	9	vol + $01
2	vol − $02	A	vol + $02
3	vol − $04	B	vol + $04
4	vol − $08	C	vol + $08
5	vol − $10	D	vol + $10
6	vol × 2 / 3	E	vol × 3 / 2
7	vol × 1 / 2	F	vol × 2

Multiplicative cases use integer arithmetic: vol × 2 / 3 is (vol × 2) / 3 (truncated); vol × 3 / 2 is (vol × 3) / 2; vol × 1 / 2 is vol >> 1; vol × 2 is vol << 1. All results clip to $00..$3F after.

A note previously silenced by a cut (^^^ or SCx earlier in the row) is not retriggered, matching ST3's kST3RetrigAfterNoteCut rule.

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R $xxyy — Tremolo with speed $xx and depth $yy

Plain. Modulates volume with an LFO, symmetrically with H's pitch modulation. $xx is LFO speed, $yy depth; the waveform is selected by S $4x.

Compatibility. ST3 Rxy uses nibbles; convert by nibble-repeat. ST3's volume cap is $40; Taud's is $3F — very deep tremolo that would have briefly clipped at $40 in ST3 may clip slightly earlier in Taud. R has its own memory slot (not shared with H/U).

Implementation. Identical machinery to H with a larger shift to fit the narrower volume range:

on row parse (R):
    if (arg >> 8)  != 0: memory_R.speed = arg >> 8
    if (arg & $FF) != 0: memory_R.depth = arg & $FF

on every tick (including tick 0):
    sine = ModSinusTable[(lfo_pos >> 2) & $3F]
    vol_delta = (sine × memory_R.depth) >> 9
    applied_vol = clamp(base_vol + vol_delta, 0, $3F)
    lfo_pos = (lfo_pos + memory_R.speed × 4) & $FF

Peak at maximum settings: $7F × $FF >> 9 = $3F — the full volume range. Retrigger behaviour tracks the S $4x waveform nibble bit 2: cleared means retrigger on new note, set means preserve LFO position.

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T $xxyy — Tempo set or tempo slide

Taud splits T by which byte carries the value:

T $xx00 (high byte non-zero) — Set tempo

Plain. Sets the Taud tempo byte to $xx. The resulting BPM is $xx + $18: Taud byte $00 → 24 BPM, $65 → 125 BPM (default), $FF → 279 BPM.

Compatibility. ST3 Txx (where xx ∈ $20..$FF) stores BPM directly; convert with taud_byte = xx − $18. Taud byte $08 corresponds to ST3's minimum BPM of 32; Taud bytes below $08 are inexpressible in ST3 and should round up to $08 (BPM 32) when exporting. OpenMPT's extended tempo slides (T $0x down, T $1x up) in S3M files map to Taud T $00xx — see below.

ProTracker Fxx with xx ≥ $20 maps to Taud T $(xx − $18)00; Fxx with xx < $20 maps to A (speed) instead.

Implementation. If the high byte is non-zero, set tempo_byte = arg >> 8; derive BPM = tempo_byte + $18; compute tick duration as samples_per_tick = 32000 × 5 / (BPM × 2) = 80000 / BPM (integer truncated) at the fixed 32000 Hz output rate. Example: BPM 125 → 640 samples per tick; BPM 24 → 3333 samples per tick; BPM 279 → 286 samples per tick. There is no memory for set-tempo.

T $00xy (high byte zero) — Tempo slide

Plain. Adjusts the tempo continuously during the row. $00_0y (low nibble under a zero high nibble within the low byte) slides BPM down by $y per non-first tick; $00_1y slides up. Out-of-range encodings ($00_20 through $00_FF) are reserved and behave as no-ops.

Compatibility. ST3 itself has only the set form; the slide forms originate in the OpenMPT/Schism extension of S3M. On export to strict ST3, slide forms are unrepresentable and should be approximated as an equivalent set-tempo on a later row.

Implementation.

on row parse (T with high byte == 0):
    low = arg & $FF
    if (low & $F0) == $00:
        slide_dir = DOWN
        slide_amount = low & $0F
    elif (low & $F0) == $10:
        slide_dir = UP
        slide_amount = low & $0F
    else:
        ignore row

on tick > 0 (if slide armed):
    if slide_dir == DOWN: tempo_byte = max($00, tempo_byte - slide_amount)
    else:                 tempo_byte = min($FF, tempo_byte + slide_amount)
    recompute samples_per_tick for next tick

A tempo slide's memory slot is separate from the set-tempo path and is private to T-slide.

---

V $xx00 — Set global volume to $xx

Plain. Sets the global mix bus volume (0..$FF). $00 is silence; $FF is full. The default is $80.

Compatibility. ST3's global volume is 0..$40; convert with taud_v = st3_v × 4, clamped at $FF. On export, st3_v = taud_v >> 2, clamped at $40. IT's global volume is 0..$80; convert with taud_v = it_v × 2, clamped at $FF. On IT, the very first V 00 command must be resolved as the song's initial global volume.

Implementation. Write the high byte to global_volume on the row the command appears. The low byte is reserved. ST3's kST3NoMutedChannels rule applies: V on a muted channel is ignored by ST3; for strict-compatible playback Taud follows suit, but new Taud compositions should avoid muting channels that carry global effects.

---

W $xy00 — Global volume slide

Plain. Similar to D $xy00, but applies to the global volume.

Compatibility. IT Wxy maps directly.

Implementation. See effect D, apply to the global volume instead.

---

X $xx00 — Fine Set Panning

Plain. Unimplemented. On IT, sets the panning position of the current channel, $00 being full-left and $FF being full-right.

Compatibility. Convert to S $80xx.

Implementation. Not applicable.

---

Y $xxyy — Panbrello (panning vibrato) with speed $xx and depth $yy

Plain. Modulates panning with an LFO, symmetrically with H's pitch modulation. $xx is LFO speed, $yy depth; the waveform is selected by S $5x.

Compatibility. IT Yxy uses nibbles; convert by nibble-repeat. IT's panning cap is $40; Taud's is $3F — very deep vibrato that would have briefly clipped at $40 in IT may clip slightly earlier in Taud. Y has its own memory slot.

Implementation. Identical machinery to H with a larger shift to fit the narrower volume range:

on row parse (Y):
    if (arg >> 8)  != 0: memory_Y.speed = arg >> 8
    if (arg & $FF) != 0: memory_Y.depth = arg & $FF

on every tick (including tick 0):
    sine = ModSinusTable[(lfo_pos >> 2) & $3F]
    vol_delta = (sine × memory_Y.depth) >> 9
    applied_vol = clamp(base_vol + vol_delta, 0, $3F)
    lfo_pos = (lfo_pos + memory_Y.speed × 4) & $FF

Peak at maximum settings: $7F × $FF >> 9 = $3F — the full panning range. Retrigger behaviour tracks the S $5x waveform nibble bit 2: cleared means retrigger on new note, set means preserve LFO position.

---

8 $xyzz — Bitcrusher

Plain. Applies a bitcrusher to the current voice. The crusher has two independent stages — a sample-rate reducer (zz, sample-and-hold) and a bit-depth quantiser (y) — and shares its clipping mode (x) with effect 9 (Overdrive). The two stages are orthogonal: enabling either is sufficient to engage the effect, and either can be active alone.

• x — clipping mode (shared with effect 9): 0 clamp (hard limit at ±1.0), 1 fold (ping-pong around ±1.0; values outside the range mirror back symmetrically), 2 wrap (saw-tooth wrap mod 2; ±1 are fixed points so no DC step at the boundary). Values 3..F are reserved and treated as clamp.
• y — bit depth, range $1..$F. 0 disables the quantiser stage. 1 reduces the voice to a 1-bit (sign-only) signal. 8..F are accepted but produce no audible quantisation, since TSVM's mix bus is already 8-bit; they are reserved for future hardware revisions.
• zz — sample skip, range $00..$FF. 0 disables skip; non-zero N holds the post-quantiser output for N additional output samples (i.e. emit one fresh sample every N+1). The held value is the bitcrusher's output, so the sample-and-hold is downstream of the quantiser and the shared clipper.
• 8 $0000 disables both stages and resets the shared clipping mode to clamp.
• 8 $x000 updates only the shared clipping mode and leaves the active depth/skip undisturbed — useful for switching between clamp/fold/wrap mid-pattern without retyping the whole argument. The same form on effect 9 has identical semantics.

Compatibility. Unique to Taud — no ST3/IT/PT equivalent. The effect has no memory: every cell that names effect 8 must spell out its full argument (apart from the $x000 shorthand described above). 8 $1100 ⇒ 1-bit, no skip, fold-clipped — a useful sanity check pattern.

Implementation. Per-voice state: bitcrusherDepth (0..15; 0 = quantiser off), bitcrusherSkip (0..255), bitcrusherCounter (mod skip+1), bitcrusherHeld (last emitted sample), and clipMode (0..2, shared with effect 9). On row parse:

on row parse (8 $xyzz):
    voice.clipMode = x & 3
    if arg == $0000:
        voice.bitcrusherDepth = 0
        voice.bitcrusherSkip = 0
        voice.bitcrusherCounter = 0
    else if y == 0 and zz == 0:
        # x000 — clip-mode-only update; preserve depth/skip/counter
        pass
    else:
        voice.bitcrusherDepth = y
        voice.bitcrusherSkip   = zz
        voice.bitcrusherCounter = 0

On every output sample, after applyVoiceFilter and after the overdrive stage of effect 9:

on output sample (per voice):
    if voice.bitcrusherCounter == 0:
        s' = sample          # post-overdrive input
        if 1 ≤ voice.bitcrusherDepth ≤ 7:
            s' = clip(s', voice.clipMode)         # ensure in-range before quantising
            levels = (1 << voice.bitcrusherDepth) - 1
            q = round((s' + 1) × 0.5 × levels)    # nearest integer; clamp to [0, levels]
            s' = (q / levels) × 2 - 1
        voice.bitcrusherHeld = s'
        out = s'
    else:
        out = voice.bitcrusherHeld
    if voice.bitcrusherSkip > 0:
        voice.bitcrusherCounter = (voice.bitcrusherCounter + 1) mod (voice.bitcrusherSkip + 1)

The clipper is shared between effects 8 and 9 and is implemented as a single helper:

clip(x, mode):
    if mode == 1:                        # fold (triangle)
        while x > +1: x = 2 - x
        while x < -1: x = -2 - x
        return x
    if mode == 2:                        # wrap (saw, period 2)
        v = ((x + 1) mod 2 + 2) mod 2
        return v - 1
    return clamp(x, -1, +1)              # mode 0 (and reserved values)

The voice-FX state is preserved verbatim by the NNA-ghost copier, so the post-NNA tail of a note keeps the same timbre as the foreground voice that spawned it.

---

9 $x0zz — Overdrive

Plain. Amplifies the voice's post-filter signal and routes it through the shared clipper. With x = 0 (clamp) the effect is a hard-knee soft-clipping distortion; with x = 1 (fold) it becomes a wave-folder; with x = 2 (wrap) it produces aggressive aliased fuzz with sawtooth-style discontinuities at the rails. Volume is not re-normalised after clipping — 9 $00FF clamp-clipped plays at roughly the same loudness as the dry voice once everything saturates. The middle nibble is reserved and must be zero.

• x — clipping mode (shared with effect 8): 0 clamp, 1 fold, 2 wrap (see effect 8 for the precise transfer functions). Values 3..F are reserved and treated as clamp.
• zz — amplification index, range $00..$FF. The applied gain is (16 + zz) / 16, so $00 is 1.0× (effect inactive), $10 is 2.0× (+6 dBFS), $F0 is 16.0× (+24 dBFS), and $FF is 16.9375× (≈ +24.55 dBFS).
• 9 $0000 resets the overdrive (gain returns to unity, the stage stops processing) and resets the shared clipping mode to clamp.
• 9 $x000 updates only the shared clipping mode and leaves the active amplification undisturbed — symmetric with 8 $x000.

Compatibility. Unique to Taud — no ST3/IT/PT equivalent. The effect has no memory.

Implementation. Per-voice state: overdriveAmp (0..255; 0 = effect off) and clipMode (shared with effect 8). On row parse:

on row parse (9 $x0zz):
    voice.clipMode = x & 3
    if arg == $0000:
        voice.overdriveAmp = 0
    else if zz == 0:
        # x000 — clip-mode-only update; preserve amp
        pass
    else:
        voice.overdriveAmp = zz

On every output sample, after applyVoiceFilter and before the bitcrusher stage of effect 8:

on output sample (per voice):
    if voice.overdriveAmp > 0:
        sample = sample × (16 + voice.overdriveAmp) / 16
        sample = clip(sample, voice.clipMode)

When both effects 8 and 9 are active on the same voice the chain is filter → overdrive (×gain → clip) → bitcrusher (bit-depth quantise → sample-skip hold). Because the clipper is shared, changing clipMode from either effect propagates to the other on the next sample — there is one mode per voice, not one per stage.

---

The S subcommand family

S is a multiplexing opcode; the high nibble of the high byte selects the sub-effect, and the remainder is the sub-argument.

S $1x00 — PT/ST3/IT Glissando control

Plain. $1000 turns glissando off; $1100 turns it on. When on, tone portamento (G) output is quantised to the nearest semitone ($0155 approximation) before being sent to the mixer. The internal G pitch counter still advances smoothly; only the audible pitch steps. This command is implemented sorely for ST3/IT compatibility and therefore only works in 12-TET context.

Compatibility. ST3/IT S10/S11 and PT E30/E31 maps directly. In Taud, "nearest semitone" uses the best integer approximation: round pitch / $155 to the nearest integer, multiply by $155; equivalently, snapped = (pitch + $AB) / $155 × $155. Because $155 is an approximation of 4096/12, accumulated rounding across many octaves will drift by up to a few cents; this is documented behaviour and intentional given the microtonal grid.

Implementation. Maintain a per-channel boolean glissando_on. When G updates pitch, if glissando_on is set, compute display_pitch = round(pitch × 12 / 4096) × 4096 / 12 (using integer division with rounding) and send display_pitch to the mixer; otherwise send pitch directly.

---

S $2x00 — Set fine-tune

Plain. Overrides the current note's fine-tune by applying a fixed 4096-TET offset. The index $x selects one of sixteen predefined pitch offsets, following ScreamTracker 3's Hz-based fine-tune table but expressed directly in Taud units. This command is implemented for ST3 compatibility.

Compatibility. The index scheme matches ST3 exactly: $8 is the baseline (no change), $0..$7 are progressively flatter, $9..$F are progressively sharper. The Hz reference values come from the ST3 User's Manual and are reproduced here for auditability; the Taud offset is log2(Hz / 8363) × 4096, rounded to the nearest integer. Format converters are advised to apply offset to the note value directly.

$x	Reference Hz	Taud offset
$0	7895	−$0154
$1	7941	−$0132
$2	7985	−$0111
$3	8046	−$00E4
$4	8107	−$00B8
$5	8169	−$008B
$6	8232	−$005D
$7	8280	−$003B
$8	8363	$0000
$9	8413	+$0023
$A	8463	+$0046
$B	8529	+$0074
$C	8581	+$0098
$D	8651	+$00C8
$E	8723	+$00F9
$F	8757	+$0110

ProTracker E5x maps to Taud S $2x00 with the same index meaning.

Implementation. On the row, look up the offset from the table and add it to the channel's base pitch before any other per-tick effect processes. The offset persists until another S $2x command or a note-reset event.

---

S $3x00 — Vibrato LFO waveform

Plain. Selects the shape of the vibrato (H and U) oscillator.

$x	Waveform	Retrigger on new note?
$0	Sine	Yes
$1	Ramp down (sawtooth)	Yes
$2	Square	Yes
$3	Random	Yes
$4	Sine	No
$5	Ramp down	No
$6	Square	No
$7	Random	No

Compatibility. ST3 S3x and ProTracker E4x maps directly.

Implementation. Store vibrato_waveform = $x & $3 and vibrato_retrigger = (($x & $4) == 0) for the channel. The ramp-down shape is $7F − ((pos & $3F) << 2) across one logical cycle; the square shape is sign(sine(pos)) × $7F; random draws a fresh rand() & $FF − $80 every tick. On a new note, if vibrato_retrigger is true, reset lfo_pos = 0.

---

S $4x00 — Tremolo LFO waveform

Plain. Selects the shape of the tremolo (R) oscillator; value encoding is identical to S $3x.

Compatibility. ST3 S4x and ProTracker E7x maps directly.

Implementation. As for S $3x, but applied to R's separate state (tremolo_waveform, tremolo_retrigger, and tremolo lfo_pos).

---

S $5x00 — Panbrello LFO waveform

Plain. Selects the shape of the panbrello (Y) oscillator; value encoding is identical to S $3x.

Compatibility. IT S5x maps directly.

Implementation. As for S $3x, but applied to Y's separate state (panbrello_waveform, panbrello_retrigger, and panbrello lfo_pos).

---

S $6x00 — Fine pattern delay

Plain. Extends the current row by $x ticks. If multiple S6x commands are on the same row, the sum of their parameters is used.

Compatibility. IT S6x maps directly.

Implementation. Maintain a per-row accumulator fine_delay_extra on the tracker state, initialised to 0 at the start of every row parse (including pattern-delay repetitions caused by S $Ex). Each S $6x command encountered during the row scan adds $x to fine_delay_extra. The row then runs for speed + fine_delay_extra ticks instead of the usual speed ticks before advancing to the next row.

on row parse (S $6x):
    fine_delay_extra += x       # sum across all channels

row ends when:
    tick_in_row >= ticks_per_row + fine_delay_extra

S $6x and S $Ex are orthogonal: when S $Ex is active the current row repeats $x additional times, and each repetition is itself extended by fine_delay_extra (re-accumulated from the same row's S $6x commands). There is no memory for S $6x; $x == 0 is a no-op.

---

S $7x00 — Note/Instrument actions

Plain. Performs following action to the note.

$x	Operation	Description
$0	Past Note Cut	Cuts all notes playing as a result of New Note Actions on the current channel
$1	Past Note Off	Sends a Note Off to all notes playing as a result of New Note Actions on the current channel
$2	Past Note Fade	Fades out all notes playing as a result of New Note Actions on the current channel
$3	NNA Note Cut	Sets the currently active note's New Note Action to Note Cut
$4	NNA Note Continue	Sets the currently active note's New Note Action to Continue
$5	NNA Note Off	Sets the currently active note's New Note Action to Note Off
$6	NNA Note Fade	Sets the currently active note's New Note Action to Note Fade
$7	Volume Envelope Off	Disables the currently active note's volume envelope
$8	Volume Envelope On	Enables the currently active note's volume envelope
$9	Panning Envelope Off	Disables the currently active note's panning envelope
$A	Panning Envelope On	Enables the currently active note's panning envelope
$B	Pitch Envelope Off	Disables the currently active note's pitch or filter envelope
$C	Pitch Envelope On	Enables the currently active note's pitch envelope

Compatibility. IT S7x maps directly.

Implementation. Engines maintain a mixer-private background-voice pool per playhead, separate from the addressable foreground voices. When a fresh note retriggers a still-active foreground voice, the engine reads the effective NNA — the per-voice override set by S $73..$76 if present, otherwise the instrument's default NNA (instrument record byte 186, low two bits) — and acts on the displaced voice as follows:

• Note Cut (1): discard the foreground state in place; no ghost is created.
• Note Off (0): clone the foreground voice into the background pool and set its key-off flag, releasing any sustain loop. The clone's volume envelope plays out and fadeout decays from full.
• Continue (2): clone the foreground voice into the background pool unchanged; envelopes and sample position continue from where they were.
• Note Fade (3): clone the foreground voice into the background pool and immediately begin fadeout decay without releasing sustain. The volume envelope keeps looping its sustain region while fadeoutVolume drains to zero.

Note Fade and Note Off are distinct: Note Fade does not set key-off, so the volume envelope's sustain loop continues to cycle; Note Off does set key-off, breaking sustain. Both share the same fadeout slope (volumeFadeoutLow + (fadeoutHigh & 0x0F << 8) units per tick out of 1024).

The background pool is reaped when a ghost's fadeoutVolume drops to zero or its sample finishes (non-looping). Pool size is implementation-defined; the reference engine caps it at 64 ghosts per playhead and evicts the oldest on overflow. Background voices receive only passive per-tick maintenance (envelope advance, fadeout decay, auto-vibrato, filter coefficient refresh) — no row-driven effects (vibrato/tremolo/arpeggio/Q-retrigger/cut/delay) ever target them, since they are not addressable from the pattern.

S $70..$72 (Past Note Cut/Off/Fade) operate on every ghost whose sourceChannel matches the issuing channel: $70 drops them outright, $71 sets key-off on each, $72 begins fadeout on each.

S $73..$76 write the per-voice NNA override on the currently active foreground voice so that its next NNA event uses the overridden action. The override is cleared on every fresh trigger.

S $77..$7C toggle the volume / panning / pitch-or-filter envelope on the currently active voice. While disabled, the envelope is frozen (no advancement) and the mixer treats its contribution as unity (envVolume / envPan / envPfValue all replaced by the neutral 1.0 / 0.5 / 0.5).

---

S $80xx — Set channel pan position

Plain. Sets the channel pan to $xx, with $00 being full left and $FF being full right. $80 is centre. When this command and panning column's Set Pan are both present, this command takes precedence.

Compatibility. IT Xxx maps directly. ST3 S8x uses a 4-bit value.

1. convert by nibble-repeat: ST3 S83 → Taud S $8033. Panning column command 0.$xx has the same semantics and is the preferred form when a pan column is available in the pattern. ProTracker 8xx (fine pan) and E8x (coarse pan) both map into Taud's 8-bit pan — the ProTracker 8-bit form maps directly; the 4-bit form nibble-repeats.
2. convert to PanEff: ST3 S8x → PanEff 0.yy, where yy = round(4.2 * x)

Implementation. Write channel_pan = arg & $FF. The pan value is applied at the mixer: left_gain = (($FF − pan) × $100) >> 8, right_gain = (pan × $100) >> 8, with both applied before the global volume stage.

---

S $Bx00 — Pattern loop

Plain. Sets a loop point and loops within a pattern. S $B000 marks the current row as the loop start (per channel, not per song); S $Bx00 with $x > 0 returns playback to the saved row and plays the intervening range $x more times (so $B200 plays the loop twice total beyond the initial pass).

Compatibility. ST3 SBx maps directly. ProTracker E6x maps to Taud S $Bx00.

ST3 has a long-documented bug where pattern delay (SEx) inside a pattern-loop range causes the loop counter to decrement multiple times per visit, producing unintended behaviour. Taud fixes this bug. On import, ST3 songs that relied on the bug will loop fewer times in Taud. Converters that want bit-exact ST3 playback should emit a warning when SBx and SEx appear in the same channel within a loop range, or optionally flatten loops by duplicating rows.

Implementation. State per channel: loop_start_row (defaulting to 0 at each pattern entry) and loop_count (defaulting to 0).

on row event (S $Bx00):
    x = (arg >> 8) & $0F
    if x == 0:
        loop_start_row = current_row
    else:
        if loop_count == 0:
            loop_count = x
            jump next_row -> loop_start_row
        else:
            loop_count -= 1
            if loop_count > 0:
                jump next_row -> loop_start_row
            # else loop_count hits 0 on its own; fall through to next row

on pattern change: loop_start_row = 0; loop_count = 0

The crucial bug fix relative to ST3: the loop-counter decrement happens once per actual row playback, not once per tick-0 invocation. When SBx shares a row with SEx (pattern delay), the pattern-delay machinery replays the row as a unit, but the SBx state machine treats the whole delay group as a single visit. Implement this by gating the SBx decrement on pattern_delay_repetition == 0.

---

S $Cx00 — Note cut in $x ticks

Plain. Silences the note on tick $x of the current row by forcing the channel's output volume to 0. The sample continues running internally, so a later volume-change or retrigger event can resume audio.

Compatibility. ST3 SCx maps directly. ProTracker ECx also maps directly. ST3 ignores SC0 (treats it as no cut at all); Taud preserves this.

Implementation. On tick $x, set output_volume = 0 but leave base_volume unchanged. If $x ≥ speed, the cut never fires. If $x == 0, the command is ignored. Set the note_was_cut flag so a later Q retrigger on the same row is suppressed.

---

S $Dx00 — Note delay for $x ticks

Plain. Delays the triggering of the note (and any co-row instrument, offset, and volume event) until tick $x. Until then, any currently playing note continues.

Compatibility. ST3 SDx maps directly. ProTracker EDx also maps directly. SD0 plays the note normally on tick 0. If $x ≥ speed, the note never plays on this row and does not carry over to the next row. Some trackers allow playback of "malformed" note delays ($x greater than current tick speed). Taud discards those notes. If such note events have been encountered during conversion, they must be corrected on the converter.

Implementation. On row parse, defer the note-trigger event (including sample selection, volume, offset, and any volume-column effect) until tick $x. On tick $x, execute the deferred trigger. When combined with pattern delay (S $Ex00), the deferred trigger re-fires at the start of each row repetition — matching ST3's kRowDelayWithNoteDelay behaviour. If $x is greater than current tick speed, the note must be discarded (see compatibility notes above)

---

S $Ex00 — Pattern delay for $x row-repeats

Plain. Repeats the current row $x additional times (so $x = 0 means no repeat and the row plays once; $x = 3 means the row plays four times total). Notes do not retrigger across repetitions, but per-tick effects re-run and tick-0 events (fine slides, delayed notes) re-fire on each repetition.

Compatibility. ST3 SEx maps directly. ProTracker EEx also maps directly. Simultaneous SEx on multiple channels: ST3 uses the first SEx in pan order (L1..L8 then R1..R8); Taud uses the first SEx in ascending channel-index order for predictability. Converters that encounter ST3 songs relying on the pan-order rule should emit a warning.

Q retrigger counters do not reset between SEx repetitions.

Implementation. Row duration becomes speed × (1 + arg_x) ticks. Treat each repetition as a fresh row for tick-0 purposes (so fine slides, delayed notes, and the like re-trigger), but do not reset arpeggio, vibrato, or tremolo LFO positions, and do not decrement SBx's loop counter more than once across the whole delay block.

---

S $Fxxx — Funk repeat with speed $xxx (non-destructive)

Plain. Produces a hiss-like progressive inversion of the sample loop, toggling individual bytes over time for a gritty textural effect. Setting $x = 0 turns the effect off; higher $x advances the inversion faster.

Compatibility. ProTracker EFx is destructive — it XORs bytes directly in the sample data, permanently corrupting the sample. Taud's implementation is non-destructive: the XOR is applied at playback time through a per-instrument bit-mask, leaving source samples pristine. ST3 does not implement SFx at all and will parse Taud's S $Fx00 as a no-op; converters targeting ST3 should drop the effect. ProTracker EFx imports as Taud S $Fyyy, where yyy = funk_table[x].

Implementation. Each instrument carries a funk_mask bit array, one bit per byte of the loop region, all zero at song start. A per-channel counter funk_accumulator and a per-channel funk_write_pos track progress.

funk_table[16] = { 0, 5, 6, 7, 8, $A, $B, $D, $10, $13, $16, $1A, $20, $2B, $40, $80 }

on every tick (when S $Fxxxx is active with x != 0):
    funk_accumulator += funk_length
    while funk_accumulator >= $80:
        funk_accumulator -= $80
        bit = funk_mask[funk_write_pos]
        funk_mask[funk_write_pos] = bit XOR 1
        funk_write_pos = (funk_write_pos + 1) mod loop_length

on sample byte read during loop playback:
    raw_byte = sample_data[offset_in_loop]
    if funk_mask[offset_in_loop] == 1:
        output_byte = raw_byte XOR $FF
    else:
        output_byte = raw_byte

S $F000 clears funk_accumulator but leaves funk_mask intact (so the accumulated inversion pattern persists until the instrument is reset). On a fresh note or instrument-change event, Taud optionally resets funk_mask to all zero; this is a per-implementation choice, but the recommended default is reset on instrument-change, preserve on pure note retrigger.

---

Volume column effects

Each cell carries a 6-bit value field plus a 2-bit selector field for the volume column. The four selectors are:

• 0.$xx — Set volume to $xx (6-bit, $00..$3F). Equivalent to a note's default volume.
• 1.$xx — Volume slide up by $xx per non-first tick (4-bit). Volume clamps at $3F.
• 2.$xx — Volume slide down by $xx per non-first tick (4-bit). Volume clamps at $00.
• 3.$Sx — Fine volume slide on tick 0 only. The high bit $S of the value selects direction (0 = down, 1 = up); the low 4 bits $x ($0..$F) are the magnitude. Equivalent in scale to D $xF00 / D $Fy00 but with a 5-bit cap. Fires once per row regardless of speed.

Volume-column effects do not consume the main effect slot; a cell can carry both (for instance, a tone portamento in the effect slot and a volume slide in the volume column).

When the converter folds an ST3 K, L, M, or N effect into the volume column, the slide-up / slide-down nibbles map to selectors 1 / 2 (clamped to 6 bits — values above $3F clip).

NOTE: 3.00 — is No-op

---

Panning column effects

The panning column uses the same 6-bit value + 2-bit selector layout:

• 0.$xx — Set pan (6-bit, $00..$3F mapped onto the channel's 8-bit pan space; $01 = full left, $1F = centre-left, $20 = centre-right, $3F = full right). For 8-bit precision use S $80xx instead.
• 1.$xx — Pan slide right by $xx per non-first tick (4-bit).
• 2.$xx — Pan slide left by $xx per non-first tick (4-bit).
• 3.$Sx — Fine pan slide on tick 0 only, same direction-bit encoding as the volume column's selector 3.

NOTE: 3.00 — is No-op. When Set Pan and S $80xx are both present, S-command takes precedence.

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Effects That Modifies Global Behaviour

Effects in this section modifies the behaviour of the mixer. Primary intention of the commands is to provide switches for legacy tracker and modern DAW behaviours.

1 $xx00 — Global behaviour flags

Plain. Sets mixer-wide behaviour flags. Available flags are:

0b 0000 0mfp

• p unset: Linear panning mode (tracker-accurate). Centre panning gets 3 dB boost. Default setting.

• p set: Equal-power panning mode. L/R amplitude is at 0.707 when centre-panned.

• f unset: Linear tone mode. Pitch shift will behave like MIDI/ImpulseTracker/ScreamTracker linear mode. Coarse and fine E/F arguments are stored as 4096-TET pitch units and subtracted/added directly from the stored pitch.

• f set: Amiga (cycle-based) tone mode. Pitch shift will behave like ProTracker/ScreamTracker default mode. Coarse and fine E/F arguments are stored as raw tracker period units (the unscaled byte/nibble from the source PT/S3M/IT file) and applied in Amiga period space. Tone portamento (G) remains linear regardless of mode.

• m unset: IT fadeout-zero policy. An instrument with stored volume fadeout = 0 does not fade out on key-off; the voice plays through until the volume envelope ends it (or never, if there is no envelope).

• m set: FT2 fadeout-zero policy. An instrument with stored volume fadeout = 0 is cut on the first tick after key-off (or NNA Note-Fade). Nonzero fadeouts behave identically in both modes — the per-tick decrement is always fadeout / 65536 in unity-volume units.

Implementation.

• Panning-linear:
  • L_gain = if (pan < 0x80) 1.0 else 1.0 - (pan - 128.0) / 128.0
  • R_gain = if (pan < 0x80) pan / 128.0 else 1.0
• Panning-equal-power:
  • L_gain = cos(pi*x / 512.0)
  • R_gain = sin(pi*x / 512.0)
• Amiga tone (both coarse and fine E/F pitch slides). The slideArg is a raw tracker period-unit count (no scaling), with sign matching linear mode (negative for E, positive for F). Coarse slides apply on every non-first tick; fine slides apply once on tick 0 — the per-step arithmetic is identical:
  • AMIGA_BASE_PERIOD = 428.0 (period at the Taud reference pitch C4 for a standard 8363 Hz instrument, NTSC clock — identical to PT "C-2" period 428)
  • period = AMIGA_BASE_PERIOD × 2^(−(noteVal − C4) / 4096)
  • period_new = period − slideArg (E subtracts pitch ⇒ adds period; F adds pitch ⇒ subtracts period)
  • noteVal_new = C4 + 4096 × log2(AMIGA_BASE_PERIOD / period_new)

Initialisation from the song table. The same flags byte is stored in the song-table entry (see file format §Song Table). A Taud player should write this byte to MMIO playhead register 7 before starting playback; the mixer then applies it as the initial state on every reset, and subsequent in-pattern 1 effects may override it.

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ProTracker to Taud conversion table

This table maps each PT effect to its Taud equivalent. Arguments follow PT's two-nibble form and expand to Taud's 16-bit form as shown.

PT effect	Taud effect	Notes
0 $xy	J $xxyy	Arpeggio; nibble-repeat each byte. See the 12-TET → Taud table above for conversion losses
1 $xx	F $00xx (Amiga mode, f set)	Portamento up; raw PT period units, applied in period space
2 $xx	E $00xx (Amiga mode, f set)	Portamento down; raw PT period units, applied in period space
3 $xx	G round($0xxx × 64/3)	Portamento to note; G is always linear (4096-TET units) regardless of mode
4 $xy	H $xxyy	Vibrato; nibble-repeat each byte.
5 $xy	L $xy00	Combined portamento + volume slide (see compatibility note)
6 $xy	K $xy00	Combined vibrato + volume slide (see compatibility note)
7 $xy	R $xxyy	Tremolo; nibble-repeat
8 $xx	S $80xx or panning column 0.$xx	Fine pan
9 $xx	O $xx00	Sample offset
A $xy	Volume column 1.$xy	Volume slide
B $xx	B $00xx	Position jump
C $xx	Volume column 0.$xx	Set volume
D $xx	C $00xx (after BCD decode)	Pattern break
E $0x	S $000x	(UNIMPLEMENTED) Set filter
E $1x	F $F00x (Amiga mode, f set)	Fine pitch slide up; raw PT period units, applied in period space at tick 0
E $2x	E $F00x (Amiga mode, f set)	Fine pitch slide down; raw PT period units, applied in period space at tick 0
E $3x	S $1x00	Glissando control
E $4x	S $3x00	Vibrato waveform
E $5x	S $2x00	Set fine-tune
E $6x	S $Bx00	Pattern loop
E $7x	S $4x00	Tremolo waveform
E $8x	S $80xx or panning column 0.$xx	Coarse pan (nibble-repeat)
E $9x	Q $0x00	Retrigger
E $Ax	Volume column 3.$1x	Fine volume slide up
E $Bx	Volume column 3.$0x	Fine volume slide down
E $Cx	S $Cx00	Note cut
E $Dx	S $Dx00	Note delay
E $Ex	S $Ex00	Pattern delay
E $Fx	S $Fx00	Funk repeat
F $xx (xx < $20)	A $xx00	Set speed
F $xx (xx ≥ $20)	T $(xx−$18)00	Set tempo

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ScreamTracker 3 conversion notes

These quirks of ST3 are worth preserving or flagging when importing S3M files into Taud:

Shared memory across effects. In ST3, a single memory slot backs D, E, F, I, J, K, L, Q, R, and S. A $00 argument on any of these recalls whichever effect last wrote a non-zero argument. Taud narrows this to four cohorts (EF / G / HU / R) plus private slots. The converter must eagerly resolve ST3 recalls — walking the pattern in playback order, tracking the shared memory value, and emitting explicit Taud arguments wherever an ST3 recall crosses a cohort boundary. Otherwise a Taud player will either recall the wrong value or recall $0000.

Cxx BCD encoding. ST3 stores pattern-break row numbers as BCD on disk ($10 means decimal 10). Taud uses binary. Decode on import; encode on export. Out-of-range BCD bytes (decimal 64 or higher) clamp to row 0.

Tempo range. ST3 accepts tempos $20..$FF (BPM 32..255); Taud accepts bytes $00..$FF (BPM 24..279). Imported ST3 tempos must be shifted down by $18; Taud tempos below $08 and above $E7 cannot be represented in ST3 and should clamp on export.

SBx + SEx interaction. ST3 miscounts loop iterations when pattern delay is active inside a pattern loop; Taud fixes this. Songs that depended on the bug for their intended playback will loop fewer times in Taud. Flag such songs on import.

Simultaneous SEx priority. ST3 uses pan order (L1..L8, R1..R8); Taud uses ascending channel-index order. Rare; flag on import if multiple channels carry SEx in the same row.

Muted channels. ST3 skips all effect processing on muted channels (no volume change, no tempo change, no jumps); Taud follows this rule for strict compatibility but recommends that new compositions avoid muting channels that carry global effects.

Volume cap. ST3's volume caps at $40; Taud's at $3F. Notes that reached $40 in ST3 (a rare edge) will play marginally quieter in Taud.

Global volume scale. ST3's 0..$40 maps to Taud's 0..$FF with a ×4 scale on import, truncated ÷4 on export.

Linear pitch slides. ST3's slide arithmetic is period-based (Amiga) or linear-table-indexed; Taud carries both interpretations and selects between them via the song-table f flag. Conversion rules:

• ST3 linear mode (linear_slides set in S3M flags): coarse forms (Exx/Fxx) use round(× 64/3) (1/16 semitone per ST3 unit); fine/extra-fine (EFx/EEx/FFx/FEx) use round(× 16/3) (1/64 semitone per ST3 unit). Taud f flag is clear; the engine subtracts the stored 4096-TET argument directly from the channel pitch.
• ST3 Amiga mode (linear_slides clear): both coarse (Exx/Fxx) and fine/extra-fine (EFx/EEx/FFx/FEx) are stored verbatim as raw ST3 period units — coarse as E/F $00xx, fine as E/F $F00x — with no scaling. Taud f flag is set; the engine applies both forms in Amiga period space at playback, exactly recovering the source's period-step count and the non-linear pitch character.
• G (tone portamento) is always converted with round(× 64/3) and treated as linear, regardless of mode.

Default tempo byte. Taud's default $65 equals 125 BPM under the $18 offset; this is not the same as ST3's $7D default, which maps to Taud $65 after subtracting $18. Converters must remap on both import and export.

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End of reference.