Soundbanks and in-memory sounds

Most short sound effects (footsteps, foley, combat, weapons, objects, UI, grunts) are not in the WADs: they are WEMs stored inside Wwise soundbanks, either loose in SFX\*.bnk or embedded in the UE3 packages (.upk). ackit lists them as the catalog archive BANK and writes them (see the end of this page). Survey of the installed game (buildid 3718300), 2026-10-09.

Inventory

where	banks	unique in-memory WEMs
loose `SFX\*.bnk` (Batman/Catwoman footsteps, 32 surfaces each, + `TST_Prep_Media`)	65	1,117
banks embedded in `.upk` packages (in 1,432 of the 2,650 packages)	3,340	14,802

All of them are in the catalog (archive BANK).

The two sets share 119 media IDs: 15,800 unique media IDs in 96,011 places (bank copies). 396 of them are prefetch heads of streamed WAD sounds and 49 are whole copies of WAD recordings (below), so there are 15,355 in-memory sounds. All copies of a media ID are byte-identical except 1C898731 (two variants). The WADs, by comparison, are fully covered: the BKPK tables in the packages reference 2,543 WAD entries, all of them in the catalog.

Embedded WEMs by bank name prefix (a media held by banks of two prefixes counts for both): Speech 7,827, CHR (character foley, combat, bosses) 3,624, PSO 737, WPN 577, NPC 471, OBJ 411, SEQ 253, PSA 203, PX 195, MTN 191, GUI 155, DVC 100, GEN 80, PHY 73, AMB 61, SBJ 50, others < 30. The Speech_ banks (e.g. Speech_EMOTE_Batman, ..._GRUNT) hold speech: efforts, grunts and a few other lines stored once for every language (119 sounds) and localized lines (about 1,450 per language, see Localized banks). All WEMs seen are Vorbis (format tag 0xFFFF), the same codec as the WADs: the loose footsteps are mono (4 stereo); of all 15,355 in-memory sounds 13,982 are mono, 1,196 stereo, 177 have 3-6 channels.

Names

Media IDs have no names of their own: a sound is named after the Wwise event that plays it (event names are in the packages' name and export tables, event ID = FNV-1 of the name), else after its bank.
CookedPCConsole\CookedBanks.txt lists all 3,345 cooked bank names. Bank ID = FNV-1 32 of the lowercased name (the same hash Wwise uses for every name). 3,338 of them are embedded in packages (Music, Music_PDLC also as loose .bnk files), 2 are only loose .bnk files (Global, Init); AMB_OW_A6, AMB_OW_C1, AMB_OW_E1, Speech_EMOTE_Thug_Muffled_Stop and Speech_GFxUI_ArkhamCityStories were found nowhere.
Loose footstep banks are named in their STID chunk (CHR_BatmanFootsteps_Concrete_Media, ...).

Bank layout (version 56, Wwise 2011.1)

Chunks BKHD {u32 version 56, u32 bank id, ...}, DIDX N x {u32 media id, u32 offset, u32 size} (offsets relative to the DATA payload, WEMs 16-byte aligned), DATA, HIRC, STID {u32 type, u32 count, count x {u32 bank id, u8 len, name}}. Init (50C63A23.bnk) has STMG/ENVS instead of media. 701C1363.bnk holds only BKHD.

HIRC Sound object (type 2) payload: u32 object id, u32 plugin id (0x00040001 = Vorbis), u32 stream type (0 = in memory, 1 = streamed, 2 = prefetch), u32 media id, u32 bank id of the media; for in-memory sources then u32 offset, u32 size, where offset = DATA payload position (from the start of the bank) + DIDX offset and size = DIDX size (checked on every in-memory source of the footstep banks and of BmGame.upk). Source kinds over all bank copies: 115,861 in-memory sources of the bank's own media; 2,233 in-memory sources with bank id 0 whose media is not in the same bank (loaded by another bank); 133,075 streamed sources; 2,101 prefetch sources. Every streamed or prefetched media ID is in a BKPK table, i.e. a WAD sound (wad.md). A prefetch source's media is also in the bank's DIDX: that in-memory copy is the head of the streamed WEM (its size = the source's size), which the game plays while the rest is read from the WAD. 396 WAD sounds have such heads (2,101 copies); replacing one of them must rewrite the heads too. 49 more WAD recordings (9-11 per language: game-over taunts, an encryption-card line, a cutscene line, scripted story lines) are also stored whole in banks: an in-memory source with the WAD recording's own media ID, byte-identical to the WAD WEM (84 copies). They are handled like heads: part of the WAD line, written and reverted with it, not sounds of their own (catalog._whole_recordings). Heads and whole copies together: 445 recordings, 2,185 copies (BANK_locations.csv.gz kind p).

Localized banks

Speech banks are localized inside the (language-neutral) packages: one AkBank export starts with a language list (FStrings INT FRA ITA DEU ESN) and then holds one block per language, in that order: the BKPK table(s) of the speech WAD entry for that language (wad.md) and a complete bank, with the same bank ID in every language. ackit gives each bank and each BKPK table the language of its position in that list (an export whose block count differs from its language count would be reported; none does). Each in-memory media gets the languages of the banks that hold it (BANK.csv column language): 8,092 sounds are language-neutral, 1,450-1,456 belong to one voice language, 6 to several (5 shared by INT/FRA/ITA/ESN while DEU has its own, 1 by INT/FRA/ITA); a media stored in the banks of every language is listed as '' (the same recording everywhere; 167 of these are voice lines, e.g. efforts and radio chatter). A catalog shows the neutral sounds plus the loaded language's lines; names are unique per language.

Lines: one recording per language

Implemented in ackit/lines.py, checked by ackit verify --catalog. A voice line exists once per language, and the game ties the recordings together itself:

Every WEM of a speech WAD has exactly one row in its own language's BKPK table (media ID, offset, size): 10,816 of 10,816 in each of the 5 languages, no row without a WEM. 657 media IDs are used by several languages (cinematics, emotes, Clayface), each at another position in each language's WAD, so the tables are kept per language and never merged.
Every recording, streamed, prefetched or in memory, is the source of a Wwise Sound object; Sound objects, events, actions and containers have the same IDs in every language, only the media differ. A line = the recordings that are sources of the same Sound objects: 12,434 lines (WAD and in-memory), each with exactly one recording in each of the 5 voice languages (61,485 recordings), no Sound object with two recordings in one language. Line identity (line column) = the smallest Sound object ID.
Prefetched sources count too: the 81 lines with a prefetch head (396 recordings over the 5 languages; mostly the game-over taunts) are linked only through them. A WAD recording that a bank also stores whole (49) is the same recording (same media ID), so its line is unchanged and the bank copies are written with it.
5 recordings per language are stored twice in that language's WAD (same media ID in two entries, byte- identical, e.g. Speech_STEEL_A1_CH2_Thug_behinddoormuffled and DIA_SteelA1Muffled): the second place is a copy of the line (same line, keeps its position name) and is written and reverted with it, because the game plays whichever place the loaded package's table names.
Independent checks (no BKPK involved): every WAD recording is named as a source by a Sound object of a bank of its own language (54,055 of 54,055); every stored head or whole copy equals the start of the recording its line gives it (2,185 of 2,185); a line's recordings have similar lengths across languages (11,761 of 12,434 within a factor 1.5; the others are different edits, e.g. a 0.55 s ESN line vs 5.46 s elsewhere).

Banks inside packages

The packages are LZO-compressed UE3 packages (upk.md); ackit decompresses them itself and searches the uncompressed data for BKHD (banks) and BKPK (WAD indexes). (The first survey used Gildor's decompress.exe; ackit/upk.py gives identical data.)
Bank blobs in packages: 41,798 for 3,340 bank IDs. Many banks are copied into several packages (e.g. CHR_CatwomanFoleySuit 31 times, CHR_BatmanFoleyBelt 26). 302 bank IDs occur as several blobs with different media subsets (often one WEM each, several per package), so a bank's media set is the union of all its blobs.
Largest: CHR_RobinFoleyCape 300 WEMs, CHR_BatmanFoleyCape 282, CHR_Clayface 263, CHR_NightwingFoley 242, CHR_CatwomanFoleySuit 225, CHR_MrFreeze 176, CHR_Combat 166.

How ackit edits them

Catalog archive BANK (one row per media ID) + data/catalog/BANK_locations.csv.gz (every copy, and the heads and whole copies of WAD speech recordings); built by tools/build_catalog.py, checked by ackit verify --catalog.
A replacement is written in place into every copy (no larger than the smallest copy), so DIDX/HIRC offsets and sizes and the package layout never change. Loose banks are patched directly; in packages only the touched blocks are re-encoded (upk.md). A sound left in one package only would let the game load the original from another one.
Each copy is filled exactly, never zero-padded: every in-memory WEM the game ships ends exactly at its slot's end, and the game plays a replacement followed by zero padding there as silence (findings 24: footsteps replaced that way were silent in game; filled, they play). A smaller replacement is grown to the slot size with a label list chunk before data (LIST{adtl, labl}, the form the game's own WEMs use for markers; ackit/wem.py: fill), so the encoder leaves at least 26 spare bytes, an even number.
Replacing a speech line that has prefetch heads or whole copies rewrites them: a head gets the first bytes of the new, zero-padded line (the start of the streamed WEM as the WAD stores it); a whole copy is filled like an in-memory sound.
Design and revert rules: docs/decisions.md (4b). The same WEM rules apply (wem.md).

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