Author: HobbitDur

  1. Sound sample bank
    1. AKAO bank header
    2. Section length
    3. How the PC engine handles this section
    4. Presence statistics (199 eleven-section c0m files)
    5. Modding implications
    6. Reference (names & addresses)

Sound sample bank

This section is a single AKAO ADPCM sample / instrument bank — the waveform data referenced by the Sounds sequences. It can be empty.

Unlike the sounds section (which holds several small sequence blocks), this section is exactly one large AKAO block, typically 8–18 KB. It begins directly with the "AKAO" magic — there is no per-section position table.

AKAO bank header

Offset Length Description
0x00 4 bytes Magic "AKAO"
0x04 2 bytes Bank id (301, 302, 303… — increments per monster file; matches the bank id field of the file’s category-1 Sounds blocks)
0x06 2 bytes 0
0x08 4 bytes 0
0x0C 4 bytes 0
0x10 4 bytes 0x0006B000 — constant in every file. SPU-RAM destination address for the sample upload (≈ 428 KB into SPU RAM, above the reserved music/stream area)
0x14 4 bytes Size of the ADPCM sample body to transfer
0x18 4 bytes 0xD0 (208) — constant. Size of the header / instrument-table region that precedes the sample body
0x1C 4 bytes 0x10 (16) — constant. Instrument / region count in the header block
0x20 … Instrument headers, then ADPCM sample data

The field values 0x10, 0x18, 0x1C are constant across all monster files. Their meanings follow the AKAO sample-bank transfer-header layout: the header describes a DMA of the ADPCM body to SPU RAM at address 0x6B000. They are marked “inferred” because the PC executable never dereferences them (its consumer is a stub — see below).

Section length

There is no length field inside the section for the reader to trust; the engine computes it from the section table:

len(this section) = offset[10] - offset[9]

If offset[9] == offset[10] the section is empty (no bank).

How the PC engine handles this section

At battle-load time, battle_monster_dat_loader processes this section in its load phase:

sec10 = &file[ offset[9] ];                 // this section start
sec11 = &file[ offset[10] ];                // textures section start
if (sec11 == sec10)                          // empty bank -> skip
    goto next_phase;

// find a free sound-bank slot (0..2) in the 3-bit allocation mask
slot = first_clear_bit(SoundBankSlotAllocMask);   // max 3 concurrent banks
if (slot >= 3) goto next_phase;
entity->command_queue.sound_bank_slot = slot;
SoundBankSlotAllocMask |= (1 << slot);

BankUpload_Stub();                           // no-op on PC

The final call — the sample-bank-to-SPU DMA slot — is return_0, a 2-instruction null stub (xor eax, eax / retn). Its effects on the PC release:

  • This section is not copied into battle work RAM (the model-blob copy stops at offset[9]) and its bytes are not uploaded to the (software) SPU.
  • Only bookkeeping happens: a slot bit in SoundBankSlotAllocMask is reserved on load and cleared on entity unload; the mask is reset when a battle location is set up. Nothing reads a slot back to fetch sample data.
  • The header fields at 0x10/0x14/0x18/0x1C are consequently never read by the PC executable — their interpretation above comes from the AKAO bank-header layout.

The section is therefore inert on the PC release: retained in the files and slot-allocated, but its sample upload is a no-op. Monster SFX on PC are played through the global DirectSound engine keyed by a hardcoded executable table — see Sounds → The SFX path.

Presence statistics (199 eleven-section c0m files)

Combination Count
Both section 9 and 10 present 113
Section 9 only (no embedded bank) 24
Section 10 only 0
Neither (silent / non-combat entry) 62

A bank (section 10) never appears without sequences (section 9). The 24 “section 9 only” monsters reference a shared/global sample bank rather than an embedded one. c0m127.dat is the special case with only 2 sections (7 and 8) and therefore no sound sections.

Modding implications

  • Editing or replacing this section has no audible effect on the PC release (its upload is stubbed).
  • Keep the section structurally consistent with the header table: the loader relies on offset[10] - offset[9] to detect an empty bank and to place offset[10] (the textures section) correctly.
  • The bank id at 0x04 is informational on the PC release.

Reference (names & addresses)

FF8_EN.exe:

Name Address Role
battle_monster_dat_loader 0x507120 Parses the monster .dat; reserves the bank slot
return_0 0x46C040 Null stub (xor eax,eax; retn) at the bank upload site
BS_SetLocation1 0x508260 Resets the sound-bank slot mask at battle-location setup
SoundBankSlotAllocMask 0x1D98B38 3-bit allocation mask (≤ 3 concurrent monster banks)
Bank SPU dest addr 0x0006B000 Constant 0x10 header field value (SPU-RAM upload address)