FF7/PSX/Sound/AKAO sequence

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Introduction

AKAO sequence is the most complicated part of the FF7 sound system. ("AKAO" is the signature string, which implies that the sound format has developed by Square Enix sound programmer Minoru Akao.)

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

The sequence data can be found in all FF7 game modules: Field, Battle, Worldmap and in minigames.

All files with exension *.SND are AKAO.

  • MINI/ASERI2.SND - Battle Arena theme
  • MINI/SENSUI.SND - used in Submarine minigame
  • ENEMY6/OVER2.SND - game over sequence
  • ENEMY6/FAN2.SND - battle win "fanfare" sequence
  • MOVIE/OVER2.SND - same game over sequence, don't know, why to duplicate data

Other AKAO sequences are hard-wired in other files.


File Structure

Header (size: 16 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 - sizeof(header)
  uint16_t reverb_type;           // reverb type (range from 0 to 9)
  struct AkaoTimeStamp timestamp; // creation time
};

struct AkaoTimeStamp
{
  uint8_t year_bcd;               // year (in binary coded decimal)
  uint8_t month_bcd;              // month (in binary coded decimal, between 0x01 - 0x12)
  uint8_t day_bcd;                // day (in binary coded decimal, between 0x01 - 0x31)
  uint8_t hours_bcd;              // hours (in binary coded decimal, between 0x00 - 0x23)
  uint8_t minutes_bcd;            // minutes (in binary coded decimal, between 0x00 - 0x59)
  uint8_t seconds_bcd;            // seconds (in binary coded decimal, between 0x00 - 0x59)
};

Channel Info (size: 4 bytes + 2 bytes * <channels count>)

struct AkaoChannelInfo
{
  uint32_t mask;                         // represents bitmask of used channels in this song
  uint32_t start_offsets[num_channels];  // offsets to channel opcode data
};
int num_channels = 0;
while (int bit = 0; ((info.mask & 0xFFFFFF) & (1 << bit)) != 0; bit++)
  num_channels++;

First there is 32-bit number (offset 0x10), which represents bitmask of used channels in this song.

After this bitmask, there is <channels count> offsets to channel opcode data counting from current offset. Each offsets is a relative offset based on the address *next to* the offset itself. (This is a general rule for early versions of AKAO to interpret relative offsets.)


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 (from no-arguments, to 3 arguments).

Drum Instrument Map Table

When a song uses a drum kit with opcode 0xEC, 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 5-byte items.

struct AkaoDrumKeyAttr
{
  uint8_t instrument;   // corresponding to opcode 0xA1
  uint8_t key;          // note number when playing the drum note
  uint16_t volume;      // corresponding to opcode 0xA8 (lower 8bit is a fractional part of the volume)
  uint8_t pan;          // corresponding to opcode 0xAA
}

Example (Home-Created AKAO Sequence):

Header

41 4b 41 4f - AKAO string

34 12 - song ID: 0x1234

16 00 - data length 0x16 in hex or 22 in decimal

04 00 - reverb type: 4 (large studio)

96 12 18 22 46 28 - created at 1996-12-18 22:46:28


Channel Info

01 00 00 00 - this indicates, that used only one channel

00 00 - offset to first channel opcodes: in our example 0x00 means that next to this offset is opcodes for first channel


Channel Commands

e8 a8 66 - sets tempo, parameter 0x66a8

ea 00 50 - sets reverb depth

a8 55 - load sample 0x55 from INSTR.ALL to channel

aa 40 - sets channel volume

c2 - turns on reverb effect

a1 0c - sets volume pan

c8 - sets loop point

66 - 0x66 % 11 = 3 (3 means to take 3rd number from play length table), 0x66 / 11 = 9 (9 means to take pitch[9] from loaded instrument record index)

ca - returns to saved loop point with opcode c8


This example plays Chocobo "Whoo-Hoo" (instrument number 0x55) repeatedly.


Sound Opcode List

Opcode Summary Length Operands Note
0x00-0x99 Note, Tie, Rest 1 The opcode indicates the note key and length. The note will be keyed off 2 ticks before the next note.
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.
0xE0-0xE7 Unimplemented 1 Code-referenced to 0xA0. Should not be used.
0xE8 Tempo 3 tempo: uint16 bpm = tempo / 214.998204 (approximate)

More strictly, bpm = 60.0 / (48 * (65536.0 / tempo) * (0x44E8 / (33868800.0 / 8)))

Note that this coefficient is different from other games with PlayStation AKAO.

0xE9 Tempo Slide 4 length: byte, tempo: uint16 When length is 0, it will be translated to 256 ticks.
0xEA Reverb Depth 3 depth: uint16
0xEB Reverb Depth Slide 4 length: byte, depth: uint16 When length is 0, it will be translated to 256 ticks.
0xEC Turn On Drum Mode 3 drum_map_offset: signed int16 The drum_map_offset is a relative offset pointing to the drum instrument map table, which determines the instrument for each keys.
0xED Turn Off Drum Mode 1
0xEE Unconditional Jump 3 destination_offset: signed int16 This instruction can be used to make an infinite loop.
0xEF CPU-Conditional Jump 4 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.
0xF0 Jump on the Nth Repeat 4 times: byte, destination_offset: signed int16 When times is 0, it will be translated to 256 times.
0xF1 Break the Loop on the Nth Repeat 4 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.

0xF2 Load Instrument (No Attack Sample) 2 instrument: byte Unlike 0xA1, the sample before the loop point is replaced by a short, silence sample.
0xF3 Unknown 1 There is no actual use in music.
0xF4 Turn On Overlay Voice 3 instrument: byte, instrument2: byte Play the same melody by different instruments on two voice channels. A free voice channel is required to work. Note that the two channels share the playback rate, and the pitch is not calculated for each instruments.

Used in the song "Anxious Heart".

0xF5 Turn Off Overlay Voice 1
0xF6 Overlay Volume Balance 2 balance: byte (0-127) When the balance is 0, the volume of the primary voice will be 100% (127/128) of original and that of the secondary voice will be 0%. 127 is the opposite.
0xF7 Overlay Volume Balance Slide 3 length: byte, balance: byte (0-127) When length is 0, it will be translated to 256 ticks.
0xF8 Turn On Alternate Voice 2 release_rate: byte (0x00-0x1f) This instruction allows subsequent notes to be played on two alternating channels. At the same time, the ADSR release rate will be set to the specified value. A free voice channel is required to work.

Check "Opening - Bombing Mission", "Tifa's Theme" and "Fortress of the Condor" for actual usage.

0xF9 Turn Off Alternate Voice 1
0xFA-0xFC Unimplemented 1 Code-referenced to 0xA0. Should not be used.
0xFD Time Signature 3 ticks_per_beat: byte, beats_per_measure: byte Note that two parameters can be 0. This pattern is used for initialization.
0xFE Measure Number 2 measure: byte
0xFF Unimplemented 1 Code-referenced to 0xA0. Should not be used.