furnace/papers/format.md

# the Furnace file format (.fur)

while Furnace works directly with the .dmf format, I had to create a new format to handle future additions to the program.

this document has the goal of detailing the format.

**notice:** GitHub's Markdown formatter may break on this file as it doesn't seem to treat tables correctly.

# information

files may be zlib-compressed, but Furnace accepts uncompressed files as well.

all numbers are little-endian.

the following fields may be found in "size":
- `f` indicates a floating point number.
- `STR` is a UTF-8 zero-terminated string.
- `???` is an array of variable size.
- `S??` is an array of `STR`s.
- `1??` is an array of bytes.
- `2??` is an array of shorts.
- `4??` is an array of ints.

the format has changed several times across versions. a `(>=VER)` indicates this field is only present starting from format version `VER`, and `(<VER)` indicates this field is present only before version `VER`.

furthermore, an `or reserved` indicates this field is always present, but is reserved when the version condition is not met.

# format versions

the format versions are:

- 87: Furnace dev87
- 86: Furnace dev86
- 85: Furnace dev85
- 84: Furnace dev84
- 83: Furnace dev83
- 82: Furnace dev82
- 81: Furnace dev81
- 80: Furnace dev80
- 79: Furnace dev79
- 78: Furnace dev78
- 77: Furnace dev77
- 76: Furnace dev76
- 75: Furnace dev75/April Fools' 0.6pre0
- 74: Furnace dev74
- 73: Furnace dev73
- 72: Furnace dev72
- 71: Furnace dev71
- 70: Furnace dev70
- 69: Furnace dev69
- 68: Furnace dev68
- 67: Furnace dev67
- 66: Furnace dev66
- 65: Furnace dev65
- 64: Furnace dev64
- 63: Furnace dev63
- 62: Furnace dev62
- 61: Furnace dev61
- 60: Furnace dev60
- 59: Furnace dev59
- 58: Furnace dev58
- 57: Furnace dev57

- 54: Furnace 0.5.8
- 53: Furnace 0.5.7
- 52: Furnace 0.5.7pre4
- 51: Furnace 0.5.7pre3
- 50: Furnace 0.5.7pre2
- 49: Furnace 0.5.7pre1
- 48: Furnace 0.5.6
- 47: Furnace 0.5.6pre1
- 46: Furnace 0.5.5
- 45: Furnace 0.5.5pre3
- 44: Furnace 0.5.5pre2
- 43: Furnace 0.5.5pre1
- 42: Furnace 0.5.4
- 41: Furnace 0.5.3
- 40: Furnace 0.5.2
- 39: Furnace 0.5.2pre3
- 38: Furnace 0.5.2pre2
- 37: Furnace 0.5.2pre1
- 36: Furnace 0.5.1
- 35: Furnace 0.5
- 27: Furnace 0.4.6
- 26: Furnace 0.4.6pre1
- 25: Furnace 0.4.5
- 24: Furnace 0.4.4
- 23: Furnace 0.4.3
- 22: Furnace 0.4.2
- 21: Furnace 0.4.1
- 20: Furnace 0.4
- 19: Furnace 0.4pre3
- 18: Furnace 0.4pre2
- 17: Furnace 0.4pre1
- 16: Furnace 0.3.1
- 15: Furnace 0.3
- 14: Furnace 0.2.2
- 13: Furnace 0.2.1
- 12: Furnace 0.2

# header

the header is 32 bytes long.

```
size | description
-----|------------------------------------
 16  | "-Furnace module-" format magic
  2  | format version
  2  | reserved
  4  | song info pointer
  8  | reserved
```

# song info

```
size | description
-----|------------------------------------
  4  | "INFO" block ID
  4  | reserved
  1  | time base
  1  | speed 1
  1  | speed 2
  1  | initial arpeggio time
  4f | ticks per second
     | - 60 is NTSC
     | - 50 is PAL
  2  | pattern length
     | - the limit is 256.
  2  | orders length
     | - the limit is 256 (>=80) or 127 (<80).
  1  | highlight A
  1  | highlight B
  2  | instrument count
     | - the limit is 256.
  2  | wavetable count
     | - the limit is 256.
  2  | sample count
     | - the limit is 256.
  4  | pattern count
 32  | list of sound chips
     | - possible soundchips:
     |   - 0x00: end of list
     |   - 0x01: YMU759 - 17 channels
     |   - 0x02: Genesis - 10 channels (compound!)
     |   - 0x03: SMS (SN76489) - 4 channels
     |   - 0x04: Game Boy - 4 channels
     |   - 0x05: PC Engine - 6 channels
     |   - 0x06: NES - 5 channels
     |   - 0x07: C64 (8580) - 3 channels
     |   - 0x08: Arcade (YM2151+SegaPCM) - 13 channels (compound!)
     |   - 0x09: Neo Geo CD (YM2610) - 13 channels
     |   - 0x42: Genesis extended - 13 channels
     |   - 0x43: SMS (SN76489) + OPLL (YM2413) - 13 channels (compound!)
     |   - 0x46: NES + VRC7 - 11 channels (compound!)
     |   - 0x47: C64 (6581) - 3 channels
     |   - 0x49: Neo Geo CD extended - 16 channels
     |   - 0x80: AY-3-8910 - 3 channels
     |   - 0x81: Amiga - 4 channels
     |   - 0x82: YM2151 alone - 8 channels
     |   - 0x83: YM2612 alone - 6 channels
     |   - 0x84: TIA - 2 channels
     |   - 0x85: VIC-20 - 4 channels
     |   - 0x86: PET - 1 channel
     |   - 0x87: SNES - 8 channels
     |   - 0x88: VRC6 - 3 channels
     |   - 0x89: OPLL (YM2413) - 9 channels
     |   - 0x8a: FDS - 1 channel
     |   - 0x8b: MMC5 - 3 channels
     |   - 0x8c: Namco 163 - 8 channels
     |   - 0x8d: OPN (YM2203) - 6 channels
     |   - 0x8e: PC-98 (YM2608) - 16 channels
     |   - 0x8f: OPL (YM3526) - 9 channels
     |   - 0x90: OPL2 (YM3812) - 9 channels
     |   - 0x91: OPL3 (YMF262) - 18 channels
     |   - 0x92: MultiPCM - 28 channels
     |   - 0x93: Intel 8253 (beeper) - 1 channel
     |   - 0x94: POKEY - 4 channels
     |   - 0x95: RF5C68 - 8 channels
     |   - 0x96: WonderSwan - 4 channels
     |   - 0x97: Philips SAA1099 - 6 channels
     |   - 0x98: OPZ (YM2414) - 8 channels
     |   - 0x99: Pokémon Mini - 1 channel
     |   - 0x9a: AY8930 - 3 channels
     |   - 0x9b: SegaPCM - 16 channels
     |   - 0x9c: Virtual Boy - 6 channels
     |   - 0x9d: VRC7 - 6 channels
     |   - 0x9e: YM2610B - 16 channels
     |   - 0x9f: ZX Spectrum (beeper) - 6 channels
     |   - 0xa0: YM2612 extended - 9 channels
     |   - 0xa1: Konami SCC - 5 channels
     |   - 0xa2: OPL drums (YM3526) - 11 channels
     |   - 0xa3: OPL2 drums (YM3812) - 11 channels
     |   - 0xa4: OPL3 drums (YMF262) - 20 channels
     |   - 0xa5: Neo Geo (YM2610) - 14 channels
     |   - 0xa6: Neo Geo extended (YM2610) - 17 channels
     |   - 0xa7: OPLL drums (YM2413) - 11 channels
     |   - 0xa8: Atari Lynx - 4 channels
     |   - 0xa9: SegaPCM (for DefleMask compatibility) - 5 channels
     |   - 0xaa: MSM6295 - 4 channels
     |   - 0xab: MSM6258 - 1 channel
     |   - 0xac: Commander X16 (VERA) - 17 channels
     |   - 0xad: Bubble System WSG - 2 channels
     |   - 0xae: OPL4 (YMF278B) - 42 channels
     |   - 0xaf: OPL4 drums (YMF278B) - 44 channels
     |   - 0xb0: Seta/Allumer X1-010 - 16 channels
     |   - 0xb1: Ensoniq ES5506 - 32 channels
     |   - 0xb2: Yamaha Y8950 - 10 channels
     |   - 0xb3: Yamaha Y8950 drums - 12 channels
     |   - 0xb4: Konami SCC+ - 5 channels
     |   - 0xb5: tildearrow Sound Unit - 8 channels
     |   - 0xde: YM2610B extended - 19 channels
     |   - 0xe0: QSound - 19 channels
     |   - 0xfd: Dummy System - 8 channels
     |   - 0xfe: reserved for development
     |   - 0xff: reserved for development
     | - (compound!) means that the system is composed of two or more chips,
     |   and has to be flattened.
 32  | sound chip volumes
     | - signed char, 64=1.0, 127=~2.0
 32  | sound chip panning
     | - signed char, -128=left, 127=right
 128 | sound chip parameters
 STR | song name
 STR | song author
  4f | A-4 tuning
  1  | limit slides (>=36) or reserved
  1  | linear pitch (>=36) or reserved
  1  | loop modality (>=36) or reserved
  1  | proper noise layout (>=42) or reserved
  1  | wave duty is volume (>=42) or reserved
  1  | reset macro on porta (>=45) or reserved
  1  | legacy volume slides (>=45) or reserved
  1  | compatible arpeggio (>=45) or reserved
  1  | note off resets slides (>=45) or reserved
  1  | target resets slides (>=45) or reserved
  1  | arpeggio inhibits portamento (>=47) or reserved
  1  | wack algorithm macro (>=47) or reserved
  1  | broken shortcut slides (>=49) or reserved
  1  | ignore duplicate slides (>=50) or reserved
  1  | stop portamento on note off (>=62) or reserved
  1  | continuous vibrato (>=62) or reserved
  1  | broken DAC mode (>=64) or reserved
  1  | one tick cut (>=65) or reserved
  1  | instrument change allowed during porta (>=66) or reserved
  1  | reset note base on arpeggio effect stop (0000) (>=69) or reserved
 4?? | pointers to instruments
 4?? | pointers to wavetables
 4?? | pointers to samples
 4?? | pointers to patterns
 ??? | orders
     | - a table of bytes
     | - size=channels*ordLen
     | - read orders then channels
     | - the maximum value of a cell is FF (>=80) or 7F (<80).
 ??? | effect columns
     | - size=channels
 1?? | channel hide status
     | - size=channels
 1?? | channel collapse status
     | - size=channels
 S?? | channel names
     | - a list of channelCount C strings
 S?? | channel short names
     | - same as above
 STR | song comment
  4f | master volume, 1.0f=100% (>=59)
     | this is 2.0f for modules before 59
 --- | **extended compatibility flags** (>=70)
  1  | broken speed selection
  1  | no slides on first tick (>=71) or reserved
  1  | next row reset arp pos (>=71) or reserved
  1  | ignore jump at end (>=71) or reserved
  1  | buggy portamento after slide (>=72) or reserved
  1  | new ins affects envelope (Game Boy) (>=72) or reserved
  1  | ExtCh channel state is shared (>=78) or reserved
  1  | ignore DAC mode change outside of intended channel (>=83) or reserved
  1  | E1xx and E2xx also take priority over Slide00 (>=83) or reserved
  1  | new Sega PCM (with macros and proper vol/pan) (>=84) or reserved
  1  | weird f-num/block-based chip pitch slides (>=85) or reserved
  1  | SN duty macro always resets phase (>=86) or reserved
 20  | reserved
```

# instrument

notes:

- the entire instrument is stored, regardless of instrument type.
- the macro range varies depending on the instrument type.
- "macro open" indicates whether the macro is collapsed or not in the instrument editor.
- FM operator order is:
  - 1/3/2/4 (internal order) for OPN, OPM, OPZ and OPL 4-op
  - 1/2/?/? (? = unused) for OPL 2-op and OPLL
- meaning of extended macros varies depending on instrument type.
- meaning of panning macros varies depending on instrument type:
  - for hard-panned chips (e.g. FM and Game Boy): left panning is 2-bit panning macro (left/right)
  - otherwise both left and right panning macros are used

```
size | description
-----|------------------------------------
  4  | "INST" block ID
  4  | reserved
  2  | format version (see header)
  1  | instrument type
     | - 0: standard
     | - 1: FM (OPM/OPN)
     | - 2: Game Boy
     | - 3: C64
     | - 4: Amiga/sample
     | - 5: PC Engine
     | - 6: AY-3-8910
     | - 7: AY8930
     | - 8: TIA
     | - 9: SAA1099
     | - 10: VIC
     | - 11: PET
     | - 12: VRC6
     | - 13: OPLL
     | - 14: OPL
     | - 15: FDS
     | - 16: Virtual Boy
     | - 17: Namco 163
     | - 18: SCC
     | - 19: OPZ
     | - 20: POKEY
     | - 21: PC Speaker
     | - 22: WonderSwan
     | - 23: Lynx
     | - 24: VERA
     | - 25: X1-010
     | - 26: VRC6 (saw)
     | - 27: ES5506
     | - 28: MultiPCM
     | - 29: SNES
     | - 30: Sound Unit
  1  | reserved
 STR | instrument name
 --- | **FM instrument data**
  1  | alg (SUS on OPLL)
  1  | feedback
  1  | fms (DC on OPLL)
  1  | ams (DM on OPLL)
  1  | operator count
     | - this is either 2 or 4, and is ignored on non-OPL systems.
     | - always read 4 ops regardless of this value.
  1  | OPLL preset (>=60) or reserved
     | - 0: custom
     | - 1-15: pre-defined patches
     | - 16: drums (compatibility only!)
  2  | reserved
 --- | **FM operator data** × 4
  1  | am
  1  | ar
  1  | dr
  1  | mult
  1  | rr
  1  | sl
  1  | tl
  1  | dt2
  1  | rs
  1  | dt
  1  | d2r
  1  | ssgEnv
     | - bit 4: on (EG-S on OPLL)
     | - bit 0-3: envelope type
  1  | dam (for YMU759 compat; REV on OPZ)
  1  | dvb (for YMU759 compat; FINE on OPZ)
  1  | egt (for YMU759 compat; FixedFreq on OPZ)
  1  | ksl (EGShift on OPZ)
  1  | sus
  1  | vib
  1  | ws
  1  | ksr
 12  | reserved
 --- | **Game Boy instrument data**
  1  | volume
  1  | direction
  1  | length
  1  | sound length
 --- | **C64 instrument data**
  1  | triangle
  1  | saw
  1  | pulse
  1  | noise
  1  | attack
  1  | decay
  1  | sustain
  1  | release
  2  | duty
  1  | ring mod
  1  | osc sync
  1  | to filter
  1  | init filter
  1  | vol macro is cutoff
  1  | resonance
  1  | low pass
  1  | band pass
  1  | high pass
  1  | channel 3 off
  2  | cutoff
  1  | duty macro is absolute
  1  | filter macro is absolute
 --- | **Amiga instrument data**
  2  | initial sample
  1  | mode (>=82) or reserved
     | - 0: sample
     | - 1: wavetable
  1  | wavetable length (-1) (>=82) or reserved
 12  | reserved
 --- | **standard instrument data**
  4  | volume macro length
  4  | arp macro length
  4  | duty macro length
  4  | wave macro length
  4  | pitch macro length (>=17)
  4  | extra 1 macro length (>=17)
  4  | extra 2 macro length (>=17)
  4  | extra 3 macro length (>=17)
  4  | volume macro loop
  4  | arp macro loop
  4  | duty macro loop
  4  | wave macro loop
  4  | pitch macro loop (>=17)
  4  | extra 1 macro loop (>=17)
  4  | extra 2 macro loop (>=17)
  4  | extra 3 macro loop (>=17)
  1  | arp macro mode
  1  | reserved (>=17) or volume macro height (>=15) or reserved
  1  | reserved (>=17) or duty macro height (>=15) or reserved
  1  | reserved (>=17) or wave macro height (>=15) or reserved
 4?? | volume macro
     | - before version 87, if this is the C64 relative cutoff macro, its values were stored offset by 18.
 4?? | arp macro
     | - before version 31, this macro's values were stored offset by 12.
 4?? | duty macro
     | - before version 87, if this is the C64 relative duty macro, its values were stored offset by 12.
 4?? | wave macro
 4?? | pitch macro (>=17)
 4?? | extra 1 macro (>=17)
 4?? | extra 2 macro (>=17)
 4?? | extra 3 macro (>=17)
  4  | alg macro length (>=29)
  4  | fb macro length (>=29)
  4  | fms macro length (>=29)
  4  | ams macro length (>=29)
  4  | alg macro loop (>=29)
  4  | fb macro loop (>=29)
  4  | fms macro loop (>=29)
  4  | ams macro loop (>=29)
  1  | volume macro open (>=29)
  1  | arp macro open (>=29)
  1  | duty macro open (>=29)
  1  | wave macro open (>=29)
  1  | pitch macro open (>=29)
  1  | extra 1 macro open (>=29)
  1  | extra 2 macro open (>=29)
  1  | extra 3 macro open (>=29)
  1  | alg macro open (>=29)
  1  | fb macro open (>=29)
  1  | fms macro open (>=29)
  1  | ams macro open (>=29)
 4?? | alg macro (>=29)
 4?? | fb macro (>=29)
 4?? | fms macro (>=29)
 4?? | ams macro (>=29)
 --- | **operator macro headers** × 4 (>=29)
  4  | AM macro length
  4  | AR macro length
  4  | DR macro length
  4  | MULT macro length
  4  | RR macro length
  4  | SL macro length
  4  | TL macro length
  4  | DT2 macro length
  4  | RS macro length
  4  | DT macro length
  4  | D2R macro length
  4  | SSG-EG macro length
  4  | AM macro loop
  4  | AR macro loop
  4  | DR macro loop
  4  | MULT macro loop
  4  | RR macro loop
  4  | SL macro loop
  4  | TL macro loop
  4  | DT2 macro loop
  4  | RS macro loop
  4  | DT macro loop
  4  | D2R macro loop
  4  | SSG-EG macro loop
  1  | AM macro open
  1  | AR macro open
  1  | DR macro open
  1  | MULT macro open
  1  | RR macro open
  1  | SL macro open
  1  | TL macro open
  1  | DT2 macro open
  1  | RS macro open
  1  | DT macro open
  1  | D2R macro open
  1  | SSG-EG macro open
 --- | **operator macros** × 4 (>=29)
 1?? | AM macro
 1?? | AR macro
 1?? | DR macro
 1?? | MULT macro
 1?? | RR macro
 1?? | SL macro
 1?? | TL macro
 1?? | DT2 macro
 1?? | RS macro
 1?? | DT macro
 1?? | D2R macro
 1?? | SSG-EG macro
 --- | **release points** (>=44)
  4  | volume macro release
  4  | arp macro release
  4  | duty macro release
  4  | wave macro release
  4  | pitch macro release
  4  | extra 1 macro release
  4  | extra 2 macro release
  4  | extra 3 macro release
  4  | alg macro release
  4  | fb macro release
  4  | fms macro release
  4  | ams macro release
 --- | **operator release points** × 4 (>=44)
  4  | AM macro release
  4  | AR macro release
  4  | DR macro release
  4  | MULT macro release
  4  | RR macro release
  4  | SL macro release
  4  | TL macro release
  4  | DT2 macro release
  4  | RS macro release
  4  | DT macro release
  4  | D2R macro release
  4  | SSG-EG macro release
 --- | **extended op macro headers** × 4 (>=61)
  4  | DAM macro length
  4  | DVB macro length
  4  | EGT macro length
  4  | KSL macro length
  4  | SUS macro length
  4  | VIB macro length
  4  | WS macro length
  4  | KSR macro length
  4  | DAM macro loop
  4  | DVB macro loop
  4  | EGT macro loop
  4  | KSL macro loop
  4  | SUS macro loop
  4  | VIB macro loop
  4  | WS macro loop
  4  | KSR macro loop
  4  | DAM macro release
  4  | DVB macro release
  4  | EGT macro release
  4  | KSL macro release
  4  | SUS macro release
  4  | VIB macro release
  4  | WS macro release
  4  | KSR macro release
  1  | DAM macro open
  1  | DVB macro open
  1  | EGT macro open
  1  | KSL macro open
  1  | SUS macro open
  1  | VIB macro open
  1  | WS macro open
  1  | KSR macro open
 --- | **extended op macros** × 4 (>=61)
 1?? | DAM macro
 1?? | DVB macro
 1?? | EGT macro
 1?? | KSL macro
 1?? | SUS macro
 1?? | VIB macro
 1?? | WS macro
 1?? | KSR macro
 --- | **OPL drums mode data** (>=63)
  1  | fixed frequency mode
  1  | reserved
  2  | kick frequency
  2  | snare/hi-hat frequency
  2  | tom/top frequency
 --- | **Sample instrument extra data** (>=67)
  1  | use note map
     | - only read the following two data structures if this is true!
 4?? | note frequency × 120
     | - 480 bytes
 2?? | note sample × 120
     | - 240 bytes
 --- | **Namco 163 data** (>=73)
  4  | initial waveform
  1  | wave position
  1  | wave length
  1  | wave mode:
     | - bit 1: update on change
     | - bit 0: load on playback
  1  | reserved
 --- | **even more macros** (>=76)
  4  | left panning macro length
  4  | right panning macro length
  4  | phase reset macro length
  4  | extra 4 macro length
  4  | extra 5 macro length
  4  | extra 6 macro length
  4  | extra 7 macro length
  4  | extra 8 macro length
  4  | left panning macro loop
  4  | right panning macro loop
  4  | phase reset macro loop
  4  | extra 4 macro loop
  4  | extra 5 macro loop
  4  | extra 6 macro loop
  4  | extra 7 macro loop
  4  | extra 8 macro loop
  4  | left panning macro release
  4  | right panning macro release
  4  | phase reset macro release
  4  | extra 4 macro release
  4  | extra 5 macro release
  4  | extra 6 macro release
  4  | extra 7 macro release
  4  | extra 8 macro release
  1  | left panning macro open
  1  | right panning macro open
  1  | phase reset macro open
  1  | extra 4 macro open
  1  | extra 5 macro open
  1  | extra 6 macro open
  1  | extra 7 macro open
  1  | extra 8 macro open
 --- | **even more macro data** (>=76)
 4?? | left panning macro
 4?? | right panning macro
 4?? | phase reset macro
 4?? | extra 4 macro
 4?? | extra 5 macro
 4?? | extra 6 macro
 4?? | extra 7 macro
 4?? | extra 8 macro
 --- | **FDS instrument data** (>=76)
  4  | modulation speed
  4  | modulation depth
  1  | init modulation table with first wave
  3  | reserved
 32  | modulation table
 --- | **OPZ instrument extra data** (>=77)
  1  | fms2
  1  | ams2
 --- | **wavetable synth data** (>=79)
  4  | first wave
  4  | second wave
  1  | rate divider
  1  | effect
     | - bit 7: single or dual effect
  1  | enabled
  1  | global
  1  | speed (+1)
  1  | parameter 1
  1  | parameter 2
  1  | parameter 3
  1  | parameter 4
```

# wavetable

```
size | description
-----|------------------------------------
  4  | "WAVE" block ID
  4  | reserved
 STR | wavetable name
  4  | wavetable size
  4  | wavetable min
  4  | wavetable max
 4?? | wavetable data
```

# sample

```
size | description
-----|------------------------------------
  4  | "SMPL" block ID
  4  | reserved
 STR | sample name
  4  | length
  4  | rate
  2  | volume (<58) or reserved
  2  | pitch (<58) or reserved
  1  | depth
     | - 0: ZX Spectrum overlay drum (1-bit)
     | - 1: 1-bit NES DPCM (1-bit)
     | - 4: QSound ADPCM
     | - 5: ADPCM-A
     | - 6: ADPCM-B
     | - 7: X68000 ADPCM
     | - 8: 8-bit PCM
     | - 9: BRR (SNES)
     | - 10: VOX
     | - 16: 16-bit PCM
  1  | reserved
  2  | C-4 rate (>=32) or reserved
  4  | loop point (>=19) or reserved
     | - -1 means no loop
 ??? | sample data
     | - version<58 size is length*2
     | - version>=58 size is length
```

# pattern

```
size | description
-----|------------------------------------
  4  | "PATR" block ID
  4  | reserved
  2  | channel
  2  | pattern index
  4  | reserved
 ??? | pattern data
     | - size: rows*(4+effectColumns*2)*2
     | - read shorts in this order:
     |   - note
     |     - 0: empty/invalid
     |     - 1: C#
     |     - 2: D
     |     - 3: D#
     |     - 4: E
     |     - 5: F
     |     - 6: F#
     |     - 7: G
     |     - 8: G#
     |     - 9: A
     |     - 10: A#
     |     - 11: B
     |     - 12: C (of next octave)
     |       - this is actually a leftover of the .dmf format.
     |     - 100: note off
     |     - 100: note release
     |     - 100: macro release
     |   - octave
     |     - this is an signed char stored in a short.
     |     - therefore octave value 255 is actually octave -1.
     |     - yep, another leftover of the .dmf format...
     |   - instrument
     |   - volume
     |   - effect and effect data (× effect columns)
     | - for note/octave, if both values are 0 then it means empty.
     | - for instrument, volume, effect and effect data, a value of -1 means empty.
 STR | pattern name (>=51)
```

# the Furnace instrument format (.fui)

the instrument format is pretty similar to the file format, but it also stores wavetables and samples used by the instrument.

```
size | description
-----|------------------------------------
 16  | "-Furnace instr.-" format magic
  2  | format version
  2  | reserved
  4  | pointer to instrument data
  2  | wavetable count
  2  | sample count
  4  | reserved
 4?? | pointers to wavetables
 4?? | pointers to samples
```

instrument data follows.

# the Furnace wavetable format (.fuw)

similar to the instrument format...

```
size | description
-----|------------------------------------
 16  | "-Furnace waveta-" format magic
  2  | format version
  2  | reserved
```

wavetable data follows.