Extracting FMOD Bank Audio (FSB5) & Custom Vehicle Sounds

How to pull WAVs out of an FMOD Studio .bank (e.g. an Assetto Corsa car soundset) and wire them up as a 7DTD vehicle's engine/horn sounds. Verified July 2026 building the Supra mod's 2JZ soundset from paris_toyota_supra_a90_s1.bank.

.bank anatomy

An FMOD Studio bank is a RIFF/FEV container (event/mixer metadata) with a single embedded FSB5 sample blob — find it with data.find(b'FSB5'). FSB5 header (60 bytes, version 1): 4s magic, u32 version, numSamples, sampleHeadersSize, nameTableSize, dataSize, codec. Codec 2 = raw PCM16 — Assetto Corsa banks use it, so extraction is pure Python (no Vorbis). Codec 15 = Vorbis → use vgmstream-cli instead (see the Wwise note for the download).

Per-sample header is a u64 (layout per vgmstream fsb5.c — several Python libs get this wrong): bit 0 = has-extra-chunks, bits 1–4 = rate index (8=44100, 9=48000), bits 5–6 = channel mode (0=1ch, 1=2ch), bits 7–33 = data offset in 32-byte units, bits 34–63 = sample count. Extra chunks follow while bit 0 of a u32 is set: size = (c>>1)&0x7FFFFF, type = (c>>25)&0x7F (1=channels override, 2=freq override, others skippable). Name table: numSamples u32 offsets, then NUL-terminated strings. Sample byte-length = next sample's offset − own offset (offsets are sorted & 32-byte aligned), capped to count*2*channels.

Working extractor: Supra/tools/extract_bank.py (bank → named WAVs).

AC soundset naming (French!)

• ral = ralenti = idle loop — the key find.
• pot/pot2 = exhaust RPM loops, adm = intake loops, rev = top-end layer, each as Insert 1..18 RPM slices (~6.2 s seamless loops, low→high).
• *acc01..08 = on-throttle rev loops low→high; *bas* = off-throttle.
• pet* = pétarade (backfire pops), valv* = blow-off (decaying — good shutoff), rupt = limiter, plus horn, gear_up/dn, skid, wind, etc.
• Audio-blind sanity checks that worked: RMS envelope in fifths (steady = loop, decaying = shutoff-shaped) and zero-crossing rate to rank RPM slices.
• Third naming convention: rpm-numbered takes (bksy Mazda ND, 2026-07-18): samples named by their centre rpm plus a take letter — 3068a, 5531a, idle_1332, mic variants like 6419b_inside, and off-throttle takes suffixed _off (3917b_off). The _off takes are overrun recordings and must be excluded from the on-throttle crossfade ladder (an even-spread rung pick once chose 5531a_off OVER 5531a — the engine went limp mid-pull). The idle's true rpm comes from the FMOD event graph (1318 for the ND) or the name digits; AC cars do not all idle at ~850.
• Names lie — always duration-gate transient roles (2026-07-17): the ASW McLaren 765LT's growlshiftpop02 is a 45 s on-throttle growl LOOP, not a shift pop. Name-matched as the "gear click" and layered onto the shift one-shots it played as a constant unreal whine over the whole pull. A real click is ≤ ~2.5 s, blow-off ≤ ~3 s, accel/decel one-shots ≤ ~8 s (AssettoCar sounds.rs::classify now enforces these). Related: when mixing multi-layer rungs, trim to the SHORTEST layer — padding to the longest leaves a tail where one quiet layer plays alone, which becomes a periodic dropout in a loop; and an overlay must never extend its base clip.

Wiring into a 7DTD vehicle (XML only)

1. Ship clips as WAVs inside the mod's asset bundle (an AssetBundleBuild.assetNames list can mix a prefab + AudioClips; asset name for lookup = file name without extension).
2. Config/sounds.xml: <append xpath="/Sounds"> with SoundDataNodes cloned from the vanilla SUV nodes (Data/Config/sounds.xml ~line 13100), ClipName="#@modfolder:Resources/<bundle>.unity3d?<clip>" — clips load via DataLoader.LoadAsset<AudioClip>, so the modfolder syntax works. Reuse vanilla AudioSource name="@:Sounds/Prefabs/AudioSource_Vehicle.prefab" (AudioSource_SmallHorn.prefab for horns). Loop="true" on loop clips. Keep the <Noise> lines or the vehicle becomes silent to zombies.
3. vehicles.xml engine part: gear1..4 strings embed accelSound, decelSound, then any number of 8-float sound-range groups ((tokens-10)/8), each ending in a loop name; plus sound_start, sound_shut_off, and vehicle-scope hornSound.

Sound-range semantics (decompiled VPEngine.updateEngineSounds)

Per range: pitchMin,pitchMax, volMin,volMax, fadeMin,fadeMax,fadeRange, name. rpmPercent = (rpm - gear.rpmMin)/(gear.rpmMax - gear.rpmMin) (0 at idle); pitch and volume lerp by it. Pitch values are OFFSETS from the AudioSource prefab's base pitch 1.0 (Handle.SetPitch does pitch + basePitch) — that's why vanilla max ranges are negative (-.4 = 0.6× playback). The fade pair is a window in pitch-offset units: the loop fades to 0 over fadeRange when its current pitch falls below fadeMin or rises above fadeMax; volume < 0.01 stops the handle. Design consequences (Supra 2026-07):

• Vanilla's 2-range gears leave a mid-rpm hole: idle (pitch window .12+.1) is gone by rpm ≈ .3 while the max loop (fade-in below -.2) isn't full until rpm ≈ .5 — and each upshift resets the virtual rpm to ~15% of the band. Reads as "engine goes away while driving".
• A single AC layer as a loop sounds thin — mix the loop-aligned RPM-slice layers offline (pot + pot2 + adm (+ rev near redline); same slice number = same length, loops stay seamless) into each shipping loop.
• The endgame fix: emulate FMOD's RPM-slice crossfade directly in the range system (this is what finally sounded right). AC records the engine at ~18 fixed RPMs and crossfades neighboring slices, bending each only a few % in pitch — never stretching one loop across the band. 7DTD's ranges express this exactly:
  1. Measure each slice's fundamental f0 (numpy FFT + harmonic product spectrum; repair octave-glitched cells against the other layer families — e.g. intake often reads an octave low). The slices form a ladder (Supra bank: 37→457 Hz over 18 slices; ral idle = 57.2 Hz).
  2. Ship K anchors (idle + every other slice), map the gear band linearly onto f_lo..f_hi Hz, then per anchor: pitchMin = f_lo/f0 − 1, pitchMax = f_hi/f0 − 1 (pitch offsets are linear in rpm, so each anchor crosses native 1.0× exactly at its recorded rpm), fadeMax = (√r_next − 1)/2, fadeMin = (1/√r_prev − 1)/2 (handoff at the log-midpoint between anchors), fadeRange = the smaller of the distances to the neighbors' native pitches (so each loop is silent by the time its neighbor is native).
  3. Simulate before shipping: replay updateEngineSounds math over p = 0..1 and check the summed volume has no holes (target ≈ 0.85–1.25) and per-loop playback stays within ~0.85–1.2×. Inactive ranges cost nothing (vol < .01 stops the handle); ~2 loops play at any instant. Same 8-range stack in every gear — each gear sweeps the full ladder, which fits the arcade rev model.
• Blow-off valve on throttle lift: decel one-shots fire when rpm decays to rpmDownShiftPoint, so overlay the BOV whoosh on the decel clips' heads — NOT on sound_shut_off (that plays when the engine turns off / on exit). With no engine-off recording in the bank, render shutoff as an idle spin-down (resample with falling rate + fade — see make_vehicle_sounds.py).

Name resolution gotcha: Audio.Manager.ConvertName ends with StripOffDirectories (Path.GetFileName(name).ToLower()) on both registration and lookup — vanilla's Vehicles/Suv/suv_accel1 references resolve to the node named suv_accel1. So directory prefixes in vehicles.xml are cosmetic, and custom node names must be flat and globally unique (supra_idle_lp, not Vehicles/Supra/idle_lp).

Other facts learned decompiling VPEngine (the engine part class — there is no VehiclePartEngine):

• Accel/decel are one-shots via entity.PlayOneShot; loops via Manager.Play(entity, name, wantHandle: true) with pitch/volume driven per-frame from the sound-range floats.
• The turbo sound is a hardcoded global node name vehicle_turbo — overriding it affects every vehicle; there's no per-vehicle slot.
• 7DTD has no gearshift sound slot; accel one-shots fire on gear change, so bake a shift click into the head of accel2/3 WAVs if you want audible shifts (Supra/tools/make_vehicle_sounds.py overlays gear_up at 70%).
• Loudness: match clips to a common RMS (~-16 dBFS, peak-limited) and let the XML range volumes do the balance — AC raw samples vary wildly.

Related

• Extracting WEM Audio (Wwise) — same job for Wwise containers (vgmstream)
• Vehicles — the rest of the vehicles.xml schema
• Asset Bundles — building/loading #@modfolder bundles