SFX pack anatomy: how a SONICHAOS pack actually gets built

A SONICHAOS SFX pack is not a folder of sounds; it is a folder of sounds that pass nine specific checks before the pack ID gets minted. This post walks every step from the location scout to the signed metadata file that ships next to the WAVs.

The recording session

Every pack starts with a location brief. A "city ambience, summer evening, no traffic" pack is recorded across three or four districts on two or three different evenings, never one long session. The contributor logs the address, the wind speed, the temperature, and the nearest source of unwanted noise (a generator, a building site, a crowded patio). That log lands in the pack metadata as a line per take.

Microphone choice is per-pack, not per-contributor. Close work uses a Sennheiser MKH 416 for shotgun pickup of a single subject, an MKH 8050 for tighter directional capture in noisy rooms, and a Schoeps CMIT for quieter interiors where the 416 self-noise becomes audible. Stereo ambience runs an ORTF pair of MKH 8040s on a stereo bar at 17 cm spacing, 110 degrees apart. Hydrophone work, when a pack calls for it, runs an Aquarian H2a with a Sound Devices MixPre-6 II.

Levels track to -18 dBFS on the loudest expected hit, with the pre-amp gain set once at the start of the session and not touched. Re-gaining mid-session creates a level mismatch the edit pass cannot fully recover.

The edit pass

Every take lands in Reaper for triage and iZotope RX 11 for repair. The chain is fixed:

1. Spectral De-noise on the room tone, learned from a 2-second silent region at the head of each take. Reduction is set at 6 dB, never higher; the goal is to lift the noise floor, not erase it.
2. De-reverb on takes recorded in reflective spaces, again at 6 dB reduction with the tail decay tuned to the room.
3. Mouth De-click and De-plosive on dialogue-adjacent packs (Foley breath, vocal effort).
4. A 24 dB/octave high-pass at 30 Hz on every take to strip rumble below the lowest musical bin.

Fades are conventional. A 5 ms fade-in and a 20 ms fade-out on every clip head and tail. Hard cuts are not allowed; even a one-shot impact takes a 1 ms ramp at the head to suppress the DC step.

The naming convention

Filenames are not negotiable. Every WAV follows category_subject_descriptor_take_##.wav. A footstep on gravel, take 4, is footstep_gravel_medium-pace_take_04.wav. The category and the subject come from a fixed vocabulary; the descriptor is free text, kebab case, no spaces. Take numbers always pad to two digits.

Why so strict: a working sound editor searches a 10,000-clip library by substring. A loose convention fragments the search results across "Footstep_Gravel_01" and "footstep gravel medium 1.wav". The SONICHAOS search index relies on the convention to surface the right take inside two keystrokes.

Loudness, sample rate, bit depth

Every pack ships in two formats: 48 kHz / 24-bit for film and TV work, 44.1 kHz / 24-bit for music production. The conversion runs through SoX at the high-quality setting; we do not ship 16-bit. Storage is cheap; a re-dither down the chain is the editor's call.

The peak ceiling is -1.0 dBTP, measured per file. Integrated loudness is set per category, not per file, because an explosion and a key jingle should not sit at the same level. Categories carry a target band: ambience at -28 to -24 LUFS, Foley at -22 to -18, designed impacts at -16 to -12. The pack manifest lists the band each file falls into.

The signed manifest

A pack ships with a pack.json manifest that records every file's SHA-256, its loudness reading, its sample rate, and its take metadata. The manifest is signed with an ed25519 key tied to the pack ID. The public key is published on the pack's catalog page.

Two reasons for the signature. First, an editor who downloads a pack two years from now can verify the files match the originals; a corrupt WAV on a network share will fail the SHA check before it lands in a session. Second, an audit by a client's legal team can confirm the pack was sourced through SONICHAOS and not assembled from third-party material; the signature, the manifest, and the per-file receipts give a clean chain of custody.

What this means at the catalog page

Every SFX entry on /sfx exposes the same fields the manifest carries: the sample rate options, the bit depth, the loudness band, the file count, the total runtime, and the signing key fingerprint. None of those need to be guessed before download.

Browse the SFX catalog and the manifest is one click from every pack tile.