FF7/PSX/Sound/AKAO sequence

Introduction

AKAO frames are most complicated frames in FF7 sound system. ("AKAO" is frame magic, probably developed by Minoru Akao, Square Enix sound programmer :) )

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

This frames are 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 frames are hard-wired in other files.

AKAO frame structure

Header (size: 16 bytes)

struct AkaoHeader
{
  static const uint8_t magic[4]; // "AKAO" C-string aka frame *MAGIC*
  uint16_t id;                   // frame ID, used for playing sequence
  uint16_t length;               // frame length - sizeof(header)
  uint16_t reverb_type;          // reverb type (range from 0 to 9)
  uint8_t unknown[6];            // some numbers, can't find their usage
};

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

First there is 32-bit number (offset 0x10), which represents bitmask of used channels in this frame, after this frame there is <channels count> offsets to channel opcode data counting from current offset.

Channel Commands [AKAO Opcodes]

Most complicated part.

For every channel in AKAO frame there is set of commands to perform. This is similar to Field opcodes. Here I'll call this sound commands "opcodes". Every opcode has it's own number of arguments (from no-arguments, to 3 arguments).

Example (home-created AKAO frame):

Header

41 4b 41 4f - AKAO string

34 12 - frame ID: 0x1234

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

04 00 96 12 18 22 46 28 - unknown data

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

0xA0 (Finish Channel)

0xA1 (Load Instrument)

0xA3 (Volume Modifier)

0xA5 (Pitch Divider)

0xA8 (Channel Volume)

0xAA (Channel Pan)

0xC8 (Loop Point)

0xCA (Return to Loop Point)

0xE8 (Tempo)

0xEA (Reverb Depth)

0xC2 (Turn On Reverb)

0xFD (Unknown)

0xFE (Unknown)

0xB4 (Unknown)

0xE0 (Unimplemented, code-referenced to 0xA0)

0xE1 (Unimplemented, code-referenced to 0xA0)

0xE2 (Unimplemented, code-referenced to 0xA0)

0xE3 (Unimplemented, code-referenced to 0xA0)

0xE4 (Unimplemented, code-referenced to 0xA0)

0xE5 (Unimplemented, code-referenced to 0xA0)

0xE6 (Unimplemented, code-referenced to 0xA0)

0xE7 (Unimplemented, code-referenced to 0xA0)

0xFA (Unimplemented, code-referenced to 0xA0)

0xFB (Unimplemented, code-referenced to 0xA0)

0xFC (Unimplemented, code-referenced to 0xA0)

0xFF (Unimplemented, code-referenced to 0xA0)

0xCD (Unimplemented)

0xD1 (Unimplemented)