Difference between revisions of "FF9/Sound/AKAO sequence"

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(Add description of custom instrument map)
(Fix AkaoChannelInfo mask bits)
 
(9 intermediate revisions by the same user not shown)
Line 37: Line 37:
 
  AkaoSeqHeader *header;
 
  AkaoSeqHeader *header;
 
  int num_channels = 0;
 
  int num_channels = 0;
  while (int bit = 0; header->mask & (1 << bit)) != 0; bit++)
+
  while (int bit = 0; bit < 32; bit++)
  num_channels++;
+
  if (info.mask & (1 << bit)) != 0)
 +
    num_channels++;
  
 
There is <channels count> offsets to channel opcode data counting from current offset. Each offsets is a relative offset based on the address the offset itself.
 
There is <channels count> offsets to channel opcode data counting from current offset. Each offsets is a relative offset based on the address the offset itself.
Line 100: Line 101:
 
|1
 
|1
 
|
 
|
|The opcode indicates the note key and length. The note will be keyed off 2 ticks before the next note.
+
|The opcode indicates the note key and length.
 
|-
 
|-
 
|0x9A-0x9F
 
|0x9A-0x9F
Line 229: Line 230:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xb4b5|0xB4]]
 
|[[FF9/Sound/Opcodes/0xb4b5|0xB4]]
|Channel Pitch LFO (Vibrato)
+
|Vibrato (Channel Pitch LFO)
 
|4
 
|4
 
|delay: byte, rate: byte, type: byte (0-15)
 
|delay: byte, rate: byte, type: byte (0-15)
Line 235: Line 236:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xb4b5|0xB5]]
 
|[[FF9/Sound/Opcodes/0xb4b5|0xB5]]
|Channel Pitch LFO Depth
+
|Vibrato Depth
 
|2
 
|2
 
|depth: byte
 
|depth: byte
Line 245: Line 246:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xb4b5|0xB6]]
 
|[[FF9/Sound/Opcodes/0xb4b5|0xB6]]
|Turn Off Channel Pitch LFO
+
|Turn Off Vibrato
 
|1
 
|1
 
|
 
|
Line 257: Line 258:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xb8b9|0xB8]]
 
|[[FF9/Sound/Opcodes/0xb8b9|0xB8]]
|Channel Volume LFO (Tremolo)
+
|Tremolo (Channel Volume LFO)
 
|4
 
|4
 
|delay: byte, rate: byte, type: byte (0-15)
 
|delay: byte, rate: byte, type: byte (0-15)
Line 263: Line 264:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xb8b9|0xB9]]
 
|[[FF9/Sound/Opcodes/0xb8b9|0xB9]]
|Channel Volume LFO Depth
+
|Tremolo Depth
 
|2
 
|2
 
|depth: byte
 
|depth: byte
Line 269: Line 270:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xb8b9|0xBA]]
 
|[[FF9/Sound/Opcodes/0xb8b9|0xBA]]
|Turn Off Channel Volume LFO
+
|Turn Off Tremolo
 
|1
 
|1
 
|
 
|
Line 481: Line 482:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xdd|0xDD]]
 
|[[FF9/Sound/Opcodes/0xdd|0xDD]]
|Channel Pitch LFO Depth Slide
+
|Vibrato Depth Slide
 
|3
 
|3
 
|length: byte, depth: byte
 
|length: byte, depth: byte
Line 487: Line 488:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xde|0xDE]]
 
|[[FF9/Sound/Opcodes/0xde|0xDE]]
|Channel Volume LFO Depth Slide
+
|Tremolo Depth Slide
 
|3
 
|3
 
|length: byte, depth: byte
 
|length: byte, depth: byte
Line 523: Line 524:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xe4|0xE4]]
 
|[[FF9/Sound/Opcodes/0xe4|0xE4]]
|Channel Pitch LFO Rate Slide
+
|Vibrato Rate Slide
 
|3
 
|3
 
|length: byte, rate: byte
 
|length: byte, rate: byte
Line 529: Line 530:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xe5|0xE5]]
 
|[[FF9/Sound/Opcodes/0xe5|0xE5]]
|Channel Volume LFO Rate Slide
+
|Tremolo Rate Slide
 
|3
 
|3
 
|length: byte, rate: byte
 
|length: byte, rate: byte
Line 558: Line 559:
 
|bpm = tempo / 218.453333 (approximate)
 
|bpm = tempo / 218.453333 (approximate)
 
More strictly, <code>bpm = 60.0 / (48 * (65536.0 / tempo) * (0x43D1 / (33868800.0 / 8)))</code>
 
More strictly, <code>bpm = 60.0 / (48 * (65536.0 / tempo) * (0x43D1 / (33868800.0 / 8)))</code>
 
Note that this coefficient is different from other games with PlayStation AKAO.
 
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe00|0xFE 0x01]]
 
|[[FF9/Sound/Opcodes/0xfe00|0xFE 0x01]]
Line 616: Line 615:
 
When <code>times</code> is 0, it will be translated to 256 times.
 
When <code>times</code> is 0, it will be translated to 256 times.
 
|-
 
|-
|[[FF9/Sound/Opcodes/0xa1|0xFE 0x0A]]
+
|[[FF7/PSX/Sound/Opcodes/0xa1|0xFE 0x0A]]
|Load Instrument (With Some Unknown Effect)
+
|Load Instrument (No Attack Sample)
 
|3
 
|3
 
|instrument: byte
 
|instrument: byte
|
+
|Unlike 0xA1, the sample before the loop point is replaced by a short, silence sample.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe0b|0xFE 0x0B]]
 
|[[FF9/Sound/Opcodes/0xfe0b|0xFE 0x0B]]
Line 635: Line 634:
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe0e|0xFE 0x0E]]
 
|[[FF9/Sound/Opcodes/0xfe0e|0xFE 0x0E]]
|Subroutine Jump
+
|Pattern
 
|4
 
|4
 
|destination_offset: signed int16
 
|destination_offset: signed int16
|The subroutine jump cannot be nested. It will overwrite the return address.
+
|Remember the return address and jump to the specified location. It cannot be nested.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe0f|0xFE 0x0F]]
 
|[[FF9/Sound/Opcodes/0xfe0f|0xFE 0x0F]]
|Return from Subroutine
+
|End Pattern
 
|2
 
|2
 
|
 
|
|
+
|Return from opcode 0xFE 0x0E.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe10|0xFE 0x10]]
 
|[[FF9/Sound/Opcodes/0xfe10|0xFE 0x10]]
|Unknown
+
|Allocate Reserved Voices
 
|3
 
|3
|value: byte
+
|count: byte
|
+
|Reserve the specified <code>count</code> of hardware voices. Reserved voices will not be used unless explicitly specified in opcode 0xFE 0x1D.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe10|0xFE 0x11]]
 
|[[FF9/Sound/Opcodes/0xfe10|0xFE 0x11]]
|Unknown
+
|Free Reserved Voices
 
|2
 
|2
 
|
 
|
|Clears the effect of opcode 0xFE 0x10
+
|Set the count of reserved voices to 0.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xa3|0xFE 0x12]]
 
|[[FF9/Sound/Opcodes/0xa3|0xFE 0x12]]
Line 694: Line 693:
 
|Code-referenced to 0xA0. Should not be used.
 
|Code-referenced to 0xA0. Should not be used.
 
|-
 
|-
|[[FF9/Sound/Opcodes/0xfe19|0xFE 0x19]]
+
|[[FF9/Sound/Opcodes/0xa9|0xFE 0x19]]
|Unknown
+
|Channel Volume Slide Per Note On
|?
+
|4
|?
+
|length: byte, volume: byte (0-127)
|
+
|Applies volume slide (opcode 0xA9) for each notes. When <code>length</code> is 0, it will be translated to 256 ticks.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe1a|0xFE 0x1A]]
 
|[[FF9/Sound/Opcodes/0xfe1a|0xFE 0x1A]]
 
|Unknown
 
|Unknown
|?
+
|2
|?
 
 
|
 
|
 +
|Turn something on.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe1b|0xFE 0x1B]]
 
|[[FF9/Sound/Opcodes/0xfe1b|0xFE 0x1B]]
 
|Unknown
 
|Unknown
|?
+
|2
|?
 
 
|
 
|
 +
|Clears the effect of opcode 0xFE 0x1A.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe1c|0xFE 0x1C]]
 
|[[FF9/Sound/Opcodes/0xfe1c|0xFE 0x1C]]
 
|Unknown
 
|Unknown
|?
+
|3
|?
+
|value: byte
|
+
|Obsoleted opcode? As far as I learned from the assembly code, it probably does nothing.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe1d|0xFE 0x1D]]
 
|[[FF9/Sound/Opcodes/0xfe1d|0xFE 0x1D]]
|Unknown
+
|Use Reserved Voices
|?
+
|2
|?
 
 
|
 
|
 +
|Allow using the reserved voices to play the sound of the current track. If they are all used, the remaining voices will instead be used normally.
 +
 +
Use opcode [[FF9/Sound/Opcodes/0xfe10|0xFE 0x10]] to allocate reserved voices.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xfe1e|0xFE 0x1E]]
 
|[[FF9/Sound/Opcodes/0xfe1e|0xFE 0x1E]]
|Unknown
+
|Use No Reserved Voices
|?
+
|2
|?
 
 
|
 
|
 +
|Disable the effect of opcode 0xFE 0x1D.
 
|-
 
|-
 
|[[FF9/Sound/Opcodes/0xa0|0xFE 0x1F]]
 
|[[FF9/Sound/Opcodes/0xa0|0xFE 0x1F]]

Latest revision as of 12:38, 30 July 2020

Introduction

AKAO sequence is similar to MIDI sequence - it's custom tracker format for playing sequence sound, well tuned specially for PSX.


File Structure

Header (size: 64 bytes)

struct AkaoSeqHeader
{
  static const uint8_t magic[4];  // "AKAO" C-string
  uint16_t id;                    // song ID, used for playing sequence
  uint16_t length;                // data length (including this header)
  uint16_t reverb_type;           // reverb type (range from 0 to 9)
  uint8_t field_0A[6];
  uint32_t field_10;
  uint16_t sample_set_id;         // associated sample set ID
  uint16_t field_12;
  uint32_t field_14;
  uint32_t field_18;
  uint32_t field_1C;
  uint32_t mask;                  // represents bitmask of used channels in this song
  uint32_t field_24;
  uint32_t field_28;
  uint32_t field_2C;
  uint32_t instrument_map_offset; // relative offset to custom instrument map (0 if unused)
  uint32_t drum_map_offset;       // relative offset to custom drum map (0 if unused)
  uint32_t field_38;
  uint32_t field_3C;
};

Channel Offsets (size: 2 bytes * <channels count>)

struct AkaoChannelInfo
{
  uint32_t start_offsets[num_channels];  // offsets to channel opcode data
};
AkaoSeqHeader *header;
int num_channels = 0;
while (int bit = 0; bit < 32; bit++)
  if (info.mask & (1 << bit)) != 0)
    num_channels++;

There is <channels count> offsets to channel opcode data counting from current offset. Each offsets is a relative offset based on the address the offset itself.


Channel Commands [AKAO Opcodes]

For every channels in an AKAO sequence, there is a set of commands to perform. This is similar to Field opcodes. Here I will call this sound commands "opcodes". Every opcode has its own number of arguments.

Custom Instrument Map Table

When a song uses custom instruments with opcode 0xFE 0x14, a custom instrument map table will be placed after the end of AKAO opcode sequence.

This table consists of a collection of zones representing performance settings for a particular key range. A zone is an 8-byte item, and an instrument can have one or more regions.

struct AkaoInstrumentZoneAttr
{
  uint8_t instrument;   // corresponding to opcode 0xA1
  uint8_t low_key;      // lowest key (in note number)
  uint8_t high_key;     // highest key (in note number)
  uint8_t ar;           // ADSR: attack rate (0-127)
  uint8_t sr;           // ADSR: sustain rate (0-127)
  uint8_t s_mode;       // ADSR: sustain mode (1: linear increase, 3: linear decrease, 5: exponential increase, 7: exponential decrease)
  uint8_t rr;           // ADSR: release rate (0-31)
  uint8_t volume;       // adjust the note volume to n/128 of the original volume (0 will keep the original volume)
}

- Zones must be ordered from low key to high key - The final zone of the instrument must be a terminator filled with 0s (more precisely, a zone with ADSR sustain mode of 0 is considered a terminator)

Drum Instrument Map Table

When a song uses a drum kit with opcode 0xFE 0x04, a drum instrument map table will be placed at the end of the sequence. The table determines the instrument, channel volume and pan for each keys.

The table consists of a repetition of 8-byte items.

struct AkaoDrumKeyAttr
{
  uint8_t instrument;   // corresponding to opcode 0xA1
  uint8_t key;          // note number when playing the drum note
  uint8_t ar;           // ADSR: attack rate (0-127)
  uint8_t sr;           // ADSR: sustain rate (0-127)
  uint8_t s_mode;       // ADSR: sustain mode (1: linear increase, 3: linear decrease, 5: exponential increase, 7: exponential decrease)
  uint8_t rr;           // ADSR: release rate (0-31)
  uint8_t volume;       // adjust the percussion volume to n/128 of the original volume (0 will keep the original volume)
  uint8_t pan : 7;      // corresponding to opcode 0xAA
  uint8_t reverb : 1;   // reverb on/off (0: off, 1: on)
}


Sound Opcode List

Opcode Summary Length Operands Note
0x00-0x99 Note, Tie, Rest 1 The opcode indicates the note key and length.
0x9A-0x9F Unimplemented 1 Should not be used.
0xA0 Finish Channel 1
0xA1 Load Instrument 2 instrument: byte (0-127)
0xA2 Overwrite Next Note Length 2 length: byte Ignores the regular length (delta-time) of the next note and overwrites it with the specified length.
0xA3 Channel Master Volume 2 volume: byte (0-127)
0xA4 Pitch Bend Slide 3 length: byte, semitones: signed byte When length is 0, it will be translated to 256 ticks.
0xA5 Set Octave 2 octave: byte (0-15)
0xA6 Increase Octave 1
0xA7 Decrease Octave 1
0xA8 Channel Volume 2 volume: byte (0-127)
0xA9 Channel Volume Slide 3 length: byte, volume: byte (0-127) When length is 0, it will be translated to 256 ticks.
0xAA Channel Pan 2 pan: byte (0-127) 64 is the center.
0xAB Channel Pan Slide 3 length: byte, pan: byte (0-127) When length is 0, it will be translated to 256 ticks.
0xAC Noise Clock Frequency 2 clock: byte (0x00-0x3f)
0xAD ADSR: Attack Rate 2 attack_rate: byte (0x00-0x7f)
0xAE ADSR: Decay Rate 2 decay_rate: byte (0x00-0x0f)
0xAF ADSR: Sustain Level 2 sustain_level: byte (0x00-0x0f)
0xB0 ADSR: Decay Rate & Sustain Level 3 decay_rate: byte (0x00-0x0f), sustain_level: byte (0x00-0x0f)
0xB1 ADSR: Sustain Rate 2 sustain_rate: byte (0x00-0x7f)
0xB2 ADSR: Release Rate 2 release_rate: byte (0x00-0x1f)
0xB3 ADSR: Reset ADSR 1
0xB4 Vibrato (Channel Pitch LFO) 4 delay: byte, rate: byte, type: byte (0-15) When rate is 0, it will be translated to 256 ticks.
0xB5 Vibrato Depth 2 depth: byte The most significant bit of the depth determines the amplitude range.

When it is 0, the range is up to about ± 50 cents (amplitude is 15/256 compared with range type 1).

When it is 1, the range is up to about ± 700 cents.

0xB6 Turn Off Vibrato 1
0xB7 ADSR: Attack Mode 2 attack_mode: byte (1 or 5)
0xB8 Tremolo (Channel Volume LFO) 4 delay: byte, rate: byte, type: byte (0-15) When rate is 0, it will be translated to 256 ticks.
0xB9 Tremolo Depth 2 depth: byte
0xBA Turn Off Tremolo 1
0xBB ADSR: Sustain Mode 2 sustain_mode: byte (1, 3, 5 or 7)
0xBC Channel Pan LFO 3 rate: byte, type: byte (0-15) When rate is 0, it will be translated to 256 ticks.
0xBD Channel Pan LFO Depth 2 depth: byte
0xBE Turn Off Channel Pan LFO 1
0xBF ADSR: Release Mode 2 release_mode: byte (3 or 7)
0xC0 Channel Transpose (Absolute) 2 semitones: signed byte
0xC1 Channel Transpose (Relative) 2 semitones: signed byte
0xC2 Turn On Reverb 1
0xC3 Turn Off Reverb 1
0xC4 Turn On Noise 1
0xC5 Turn Off Noise 1
0xC6 Turn On Frequency Modulation 1
0xC7 Turn Off Frequency Modulation 1
0xC8 Loop Point 1 Remember the current offset as a loop point and increase the nesting level of the loop.
0xC9 Return to Loop Point Up to N Times 2 times: byte On the Nth repeat, this instruction will end the current loop by decrementing the nesting level of the loop. Otherwise, it will increment the loop counter and return to the loop point.

When times is 0, it will be translated to 256 times.

0xCA Return to Loop Point 1 This instruction will increment the loop counter.
0xCB Reset Sound Effects 1 Reset sound effects such as noise, frequency modulation, reverb, overlay voice and alternate voice.
0xCC Turn On Legato 1 This instruction will stop the regular key on and key off performance of the subsequent notes and update the pitch only.
0xCD Turn Off Legato 1
0xCE Turn On Noise and Toggle Noise On/Off after a Period of Time 2 delay: byte When delay is 0, it will be translated to 257 ticks.
0xCF Toggle Noise On/Off after a Period of Time 2 delay: byte When delay is 0, it will be translated to 257 ticks.
0xD0 Turn On Full-Length Note Mode 1 This instruction will stop the regular key off performance of the subsequent notes.
0xD1 Turn Off Full-Length Note Mode 1
0xD2 Turn On Frequency Modulation and Toggle Frequency Modulation On/Off after a Period of Time 2 delay: byte When delay is 0, it will be translated to 257 ticks.
0xD3 Toggle Frequency Modulation On/Off after a Period of Time 2 delay: byte When delay is 0, it will be translated to 257 ticks.
0xD4 Turn On Playback Rate Side Chain 1 Duplicate and use the playback frequency of the previous voice channel.
0xD5 Turn Off Playback Rate Side Chain 1
0xD6 Turn On Pitch-Volume Side Chain 1 Multiply the playback frequency of the previous voice channel to the output volume. Lower pitch will make the volume smaller.
0xD7 Turn Off Pitch-Volume Side Chain 1
0xD8 Channel Fine Tuning (Absolute) 2 amount: signed byte The pitch can be changed in the range of one octave above and below.

The amount is the multiplicand for the playback frequency, not a log-based parameter like cents. For example, when the amount is 127, the pitch will be multiplied by 127/128 (about +1 octave). Negative value ​​will lower the pitch.

0xD9 Channel Fine Tuning (Relative) 2 amount: signed byte The amount will be added to the current tuning amount.
0xDA Turn On Portamento 2 speed: byte When speed is 0, it will be translated to 256 ticks.
0xDB Turn Off Portamento 1
0xDC Fix Note Length 2 length_to_add: signed byte Ignore the regular length (delta-time) of subsequent notes and set to the fixed length. The length_to_add parameter will be added to the current length value. (the initial value is 0)
0xDD Vibrato Depth Slide 3 length: byte, depth: byte When length is 0, it will be translated to 256 ticks.
0xDE Tremolo Depth Slide 3 length: byte, depth: byte When length is 0, it will be translated to 256 ticks.
0xDF Channel Pan LFO Depth Slide 3 length: byte, depth: byte When length is 0, it will be translated to 256 ticks.
0xE0 Unknown 1
0xE1 Unknown 2 value: byte
0xE2 Unknown 1 Clears the effect of opcode 0xE1
0xE3 Unimplemented 1 Code-referenced to 0xA0. Should not be used.
0xE4 Vibrato Rate Slide 3 length: byte, rate: byte When length is 0, it will be translated to 256 ticks.
0xE5 Tremolo Rate Slide 3 length: byte, rate: byte When length is 0, it will be translated to 256 ticks.
0xE6 Channel Pan LFO Rate Slide 3 length: byte, rate: byte When length is 0, it will be translated to 256 ticks.
0xE7-0xEF Unimplemented 1 Code-referenced to 0xA0. Should not be used.
0xF0-0xFD Note, Tie, Rest with Length 2 length: byte
0xFE 0x00 Tempo 4 tempo: uint16 bpm = tempo / 218.453333 (approximate)

More strictly, bpm = 60.0 / (48 * (65536.0 / tempo) * (0x43D1 / (33868800.0 / 8)))

0xFE 0x01 Tempo Slide 5 length: byte, tempo: uint16 When length is 0, it will be translated to 256 ticks.
0xFE 0x02 Reverb Depth 4 depth: uint16
0xFE 0x03 Reverb Depth Slide 5 length: byte, depth: uint16 When length is 0, it will be translated to 256 ticks.
0xFE 0x04 Turn On Drum Mode 2 The drum map offset is recorded in the file header.
0xFE 0x05 Turn Off Drum Mode 2
0xFE 0x06 Unconditional Jump 4 destination_offset: signed int16 This instruction can be used to make an infinite loop.
0xFE 0x07 CPU-Conditional Jump 5 condition: byte, destination_offset: signed int16 Jump if the condition variable matches condition. The value of the condition variable can be set from the game program.
0xFE 0x08 Jump on the Nth Repeat 5 times: byte, destination_offset: signed int16 When times is 0, it will be translated to 256 times.
0xFE 0x09 Break the Loop on the Nth Repeat 5 times: byte, destination_offset: signed int16 Unlike 0xF0, this instruction will end the current loop by decrementing the nesting level of the loop.

When times is 0, it will be translated to 256 times.

0xFE 0x0A Load Instrument (No Attack Sample) 3 instrument: byte Unlike 0xA1, the sample before the loop point is replaced by a short, silence sample.
0xFE 0x0B Unknown 6 offset: signed int16, offset2: signed int16
0xFE 0x0C-0x0D Unimplemented 2 Code-referenced to 0xA0. Should not be used.
0xFE 0x0E Pattern 4 destination_offset: signed int16 Remember the return address and jump to the specified location. It cannot be nested.
0xFE 0x0F End Pattern 2 Return from opcode 0xFE 0x0E.
0xFE 0x10 Allocate Reserved Voices 3 count: byte Reserve the specified count of hardware voices. Reserved voices will not be used unless explicitly specified in opcode 0xFE 0x1D.
0xFE 0x11 Free Reserved Voices 2 Set the count of reserved voices to 0.
0xFE 0x12 Channel Master Volume Slide 3 length: byte, volume: byte (0-127) When length is 0, it will be translated to 256 ticks.
0xFE 0x13 Unimplemented 2 Code-referenced to 0xA0. Should not be used.
0xFE 0x14 Load Custom Instrument (Key-Split Instrument) 3 instrument: byte The custom instrument number corresponds to the custom instrument map pointed from the file header. Note that the number is different from the regular sample number used in opcode 0xA1.
0xFE 0x15 Time Signature 4 ticks_per_beat: byte, beats_per_measure: byte Note that two parameters can be 0. This pattern is used for initialization.
0xFE 0x16 Measure Number 3 measure: byte
0xFE 0x17-0x18 Unimplemented 2 Code-referenced to 0xA0. Should not be used.
0xFE 0x19 Channel Volume Slide Per Note On 4 length: byte, volume: byte (0-127) Applies volume slide (opcode 0xA9) for each notes. When length is 0, it will be translated to 256 ticks.
0xFE 0x1A Unknown 2 Turn something on.
0xFE 0x1B Unknown 2 Clears the effect of opcode 0xFE 0x1A.
0xFE 0x1C Unknown 3 value: byte Obsoleted opcode? As far as I learned from the assembly code, it probably does nothing.
0xFE 0x1D Use Reserved Voices 2 Allow using the reserved voices to play the sound of the current track. If they are all used, the remaining voices will instead be used normally.

Use opcode 0xFE 0x10 to allocate reserved voices.

0xFE 0x1E Use No Reserved Voices 2 Disable the effect of opcode 0xFE 0x1D.
0xFE 0x1F Unimplemented 2 Code-referenced to 0xA0. Should not be used.
0xFE 0x20-0xFF Unimplemented (Out of Range) n/a Do not use.
0xFF Unimplemented 1 Code-referenced to 0xA0. Should not be used.