FF9/Sound/AKAO sequence

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; header->mask & (1 << bit)) != 0; bit++)
  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. 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	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	Subroutine Jump	4	destination_offset: signed int16	The subroutine jump cannot be nested. It will overwrite the return address.
0xFE 0x0F	Return from Subroutine	2
0xFE 0x10	Unknown	3	value: byte
0xFE 0x11	Unknown	2		Clears the effect of opcode 0xFE 0x10
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? It probably does nothing.
0xFE 0x1D	Unknown	2		Turn something on.
0xFE 0x1E	Unknown	2		Clears 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.