instrument volume fadeout

terranmon.txt

@@ -2008,13 +2008,12 @@ Instrument bin: Registry for 256 instruments, formatted as:
             - IT: look for sample's SusLoop flag
     Bit16   Volume envelope sustain/loops and flags
         * Sustain is implemented by enabling 't' flag. FastTracker has no 'Sus Loop' but only 'Sus Point'; use same value for start and end index
-        0b 0ut sssss pcb eeeee
+        0b 0ut sssss 0cb eeeee
             s: sustain/loop start index
             e: sustain/loop end index
 
             b: use envelope
             c: envelope carry
-            p: (IT) fadeout is zero; (XM) fadeout is cut
 
             t: the loop must sustain (key-off escapes the loop)
             u: set to enable the sustain/loop
@@ -2055,10 +2054,18 @@ Instrument bin: Registry for 256 instruments, formatted as:
         * ImpulseTracker has range of 0..128; multiply by (255/128) then round to int
             - ImpulseTracker also has samplewise default volume (0..64) and samplewise global volume (0..64), and they must be taken into account because Taud has no samplewise config, following the ImpulseTracker spec
         * FastTracker2 has range of 0..64; multiply by (255/64) then round to int
-    Uint8  Volume Fadeout low bits (IT: 1..256; XM: 0..255)
+    Uint8  Volume Fadeout low bits
     Bit8   Fadeout and vibrato
         0b 0000 ffff
             f: Volume Fadeout high bits
+        * Combined 12-bit fadeout value is the engine's per-tick decrement, in 1/65536 units
+          (a unity-volume voice silenced over (65536 / fadeout) ticks after key-off).
+        * Stored 0: behaviour depends on Global Behaviour bit 'm' (see Song Table) —
+          IT mode (m=0) leaves the voice unfaded; FT2 mode (m=1) cuts on key-off.
+        * Source-format mapping:
+            - IT: stored fadeout (0..1024) MUST be doubled on import (taud = it × 2);
+              Taud's per-tick scale matches FT2 natively, so IT values are scaled to match.
+            - FT2: stored fadeout (0..0xFFF) is passed through unchanged.
     Uint8  Volume swing (0..255 full range)
     Uint8  Vibrato speed
         * ImpulseTracker has samplewise vibrato speed (0..64), and they must be taken into account because Taud has no samplewise config
@@ -2073,7 +2080,7 @@ Instrument bin: Registry for 256 instruments, formatted as:
     Uint8  Pan swing (0..255 full range)
     Uint8  Default cutoff (0..254 full range, 255 to off (-1 on IT). Effect range equals to that of ImpulseTracker -- 127 in IT is equal to 254 in Taud)
     Uint8  Default resonance (0..254 full range, 255 to off (-1 on IT). Effect range equals to that of ImpulseTracker -- 127 in IT is equal to 254 in Taud)
-    Uint16 Sample detune (in 4096-TET unit) (XM finetune scale need to be rescaled accordingly)
+    Uint16 Sample detune (in 4096-TET unit) (FT2 finetune scale need to be rescaled accordingly)
     Bit8   Instrument Flag
         0b 000 www nn
             n: New note action. 00: note off, 01: note cut, 10: continue, 11: note fade (arranged differently to IT)
@@ -2098,7 +2105,7 @@ TODO:
     [x] implement sample loop sustain
         "Caveat: on a foreground voice, key-off (row.note == 0x0000) currently sets voice.active = false at AudioAdapter.kt:1713, which silences the channel immediately. Sustain-loop escape therefore only takes effect on background voices spawned by NNA "Note Off" — which matches the IT idiom of layering a new note over a sustained one. Let me know if you also want the foreground key-off to keep the voice playing through fadeout."
     [x] cue and pattern compression of the Taud format (taud_common.py, taud.mjs)
-    [ ] figure out how IT (8 bits) and FT2 (12 bits) handles volume fadeout numbers, and come up with a compatible Taud spec, then implement
+    [x] figure out how IT (0..256) and FT2 (0..FFF + cut) handles volume fadeout numbers, and come up with a compatible Taud spec, then implement
     [ ] implement bitcrusher (eff sym '8')
 
 
@@ -2314,6 +2321,11 @@ Endianness: Little
     Uint16  Current Tuning base note (1..65533). A4 (western default) is 0x5C00. C9 (tracker default) is 0xA000. If zero, assume the tracker default value
     Float32 Frequency at the base note. Tracker default is 8363.0. If zero, assume the tracker default
     Uint8   Flags for Global Behaviour (effect symbol '1')
+        0b 0000 0mfp
+            p: panning law         (0=linear, 1=equal-power)
+            f: tone mode           (0=linear pitch slides, 1=Amiga period slides)
+            m: fadeout-zero policy (0=IT — stored fadeout 0 means no fadeout;
+                                    1=FT2 — stored fadeout 0 means cut on key-off)
     Uint8   Song global volume
         * ImpulseTracker has range of 0..128; multiply by (255/128) then round to int
     Uint8   Song mixing volume