Identify CHANNEL_FIELD16 as CHANNEL_NOTE_DURATION_MODIFIER

audio/engine.asm

@@ -2205,20 +2205,19 @@ SetNoteDuration:
 	ld e, [hl]
 	inc hl
 	ld d, [hl]
-	; add ??? to the next result
-	ld hl, CHANNEL_FIELD16
+	; add duration modifier to the next result
+	ld hl, CHANNEL_NOTE_DURATION_MODIFIER
 	add hl, bc
 	ld l, [hl]
 	; multiply Tempo by last result (NoteLength * LOW(delay))
 	call .Multiply
 	; copy result to de
 	ld e, l
 	ld d, h
-	; store result in ???
-	ld hl, CHANNEL_FIELD16
+	; store result in NoteDuration and NoteDurationModifier
+	ld hl, CHANNEL_NOTE_DURATION_MODIFIER
 	add hl, bc
 	ld [hl], e
-	; store result in NoteDuration
 	ld hl, CHANNEL_NOTE_DURATION
 	add hl, bc
 	ld [hl], d
@@ -2283,9 +2282,9 @@ Tempo:
 	ld [hl], e
 	inc hl
 	ld [hl], d
-	; clear ???
+	; clear duration modifier
 	xor a
-	ld hl, CHANNEL_FIELD16
+	ld hl, CHANNEL_NOTE_DURATION_MODIFIER
 	add hl, bc
 	ld [hl], a
 	ret

constants/audio_constants.asm

@@ -49,7 +49,7 @@ DEF CHANNEL_PITCH                       rb
 DEF CHANNEL_OCTAVE                      rb
 DEF CHANNEL_TRANSPOSITION               rb
 DEF CHANNEL_NOTE_DURATION               rb
-DEF CHANNEL_FIELD16                     rb
+DEF CHANNEL_NOTE_DURATION_MODIFIER      rb
                                         rb_skip
 DEF CHANNEL_LOOP_COUNT                  rb
 DEF CHANNEL_TEMPO                       rw

macros/ram.asm

@@ -135,47 +135,47 @@ MACRO map_connection_struct
 ENDM
 
 MACRO channel_struct
-\1MusicID::           dw
-\1MusicBank::         db
-\1Flags1::            db ; 0:on/off 1:subroutine 2:looping 3:sfx 4:noise 5:rest
-\1Flags2::            db ; 0:vibrato on/off 1:pitch slide 2:duty cycle pattern 4:pitch offset
-\1Flags3::            db ; 0:vibrato up/down 1:pitch slide direction
-\1MusicAddress::      dw
-\1LastMusicAddress::  dw
-                      dw
-\1NoteFlags::         db ; 5:rest
-\1Condition::         db ; conditional jumps
-\1DutyCycle::         db ; bits 6-7 (0:12.5% 1:25% 2:50% 3:75%)
-\1VolumeEnvelope::    db ; hi:volume lo:fade
-\1Frequency::         dw ; 11 bits
-\1Pitch::             db ; 0:rest 1-c:note
-\1Octave::            db ; 7-0 (0 is highest)
-\1Transposition::     db ; raises existing octaves (to repeat phrases)
-\1NoteDuration::      db ; frames remaining for the current note
-\1Field16::           ds 1
-                      ds 1
-\1LoopCount::         db
-\1Tempo::             dw
-\1Tracks::            db ; hi:left lo:right
-\1DutyCyclePattern::  db
-\1VibratoDelayCount:: db ; initialized by \1VibratoDelay
-\1VibratoDelay::      db ; number of frames a note plays until vibrato starts
-\1VibratoExtent::     db
-\1VibratoRate::       db ; hi:frames for each alt lo:frames to the next alt
-\1PitchSlideTarget::  dw ; frequency endpoint for pitch slide
-\1PitchSlideAmount::  db
+\1MusicID::                  dw
+\1MusicBank::                db
+\1Flags1::                   db ; 0:on/off 1:subroutine 2:looping 3:sfx 4:noise 5:rest
+\1Flags2::                   db ; 0:vibrato on/off 1:pitch slide 2:duty cycle pattern 4:pitch offset
+\1Flags3::                   db ; 0:vibrato up/down 1:pitch slide direction
+\1MusicAddress::             dw
+\1LastMusicAddress::         dw
+                             ds 2
+\1NoteFlags::                db ; 5:rest
+\1Condition::                db ; conditional jumps
+\1DutyCycle::                db ; bits 6-7 (0:12.5% 1:25% 2:50% 3:75%)
+\1VolumeEnvelope::           db ; hi:volume lo:fade
+\1Frequency::                dw ; 11 bits
+\1Pitch::                    db ; 0:rest 1-c:note
+\1Octave::                   db ; 7-0 (0 is highest)
+\1Transposition::            db ; raises existing octaves (to repeat phrases)
+\1NoteDuration::             db ; frames remaining for the current note
+\1NoteDurationModifier::     db
+                             ds 1
+\1LoopCount::                db
+\1Tempo::                    dw
+\1Tracks::                   db ; hi:left lo:right
+\1DutyCyclePattern::         db
+\1VibratoDelayCount::        db ; initialized by \1VibratoDelay
+\1VibratoDelay::             db ; number of frames a note plays until vibrato starts
+\1VibratoExtent::            db
+\1VibratoRate::              db ; hi:frames for each alt lo:frames to the next alt
+\1PitchSlideTarget::         dw ; frequency endpoint for pitch slide
+\1PitchSlideAmount::         db
 \1PitchSlideAmountFraction:: db
-\1Field25::           db
-                      ds 1
-\1PitchOffset::       dw
-\1Field29::           ds 1
-\1Field2a::           ds 2
-\1Field2c::           ds 1
-\1NoteLength::        db ; frames per 16th note
-\1Field2e::           ds 1
-\1Field2f::           ds 1
-\1Field30::           ds 1
-                      ds 1
+\1Field25::                  db
+                             ds 1
+\1PitchOffset::              dw
+\1Field29::                  ds 1
+\1Field2a::                  ds 2
+\1Field2c::                  ds 1
+\1NoteLength::               db ; frames per 16th note
+\1Field2e::                  ds 1
+\1Field2f::                  ds 1
+\1Field30::                  ds 1
+                             ds 1
 ENDM
 
 MACRO battle_tower_struct