SoundCheck

Level a DJ library to one loudness and make every track start exactly on the grid, without touching the sound or losing a single tag.

SoundCheck is a free, open-source desktop app for DJs and producers. Drop a folder, see what every track needs, fix the few grids that are wrong, and export files that rekordbox, Serato and Traktor agree with.

Status: in development, no usable release yet. What works today, from source:

• The app analyses a dropped library (loudness, BPM, meter and bar 1, with a Needs-review queue) and opens any track in a grid view to inspect and fix its grid while a click plays along, with live IN/OUT meters, an original/processed A/B and a volume control. It does not write files yet.
• sc-cli apply already changes WAV, AIFF and FLAC files: gain and an optional head trim (snapped back up to 1 ms to the quietest frame and faded in over 2 ms), every other chunk, block and tag carried byte for byte, verified, with a backup in ~/Music/SoundCheck Backups and sc-cli undo.
• sc-cli process <files> --batch-mode prepare|library exports: the planned gain, the Prepare cut and the tags written in place after a backup (or as copies with --out), verified against the planned length, with a sidecar recording the exported grid; grid edits and confirmations made in the app carry over to the exported file.
• sc-cli process also writes the batch's rekordbox XML (soundcheck-rekordbox.xml: each gridded track's location, tags and a 4/4 TEMPO with bar 1 where the export put it; importing a track overwrites its rekordbox grid and info, so try one first) and a grid-report.csv, into the --out folder or ~/Music/SoundCheck/exports/<date time>/; sc-cli xml <files> writes the XML for files already exported or only analysed.
• sc-cli plan --batch-mode prepare|library previews what an export will do to each file: the gain, the head cut (Cut 0.21 s, Starts on bar 1, Starts on a bar line (bar 1 at 8.00 s), Not cut: bar 1 1.00 s in, or Not cut: grid needs review until the grid is confirmed), the tags, or why a file is left to the rekordbox XML (MP3/AAC for now) or skipped.

Exporting from the app and MP3 output come next; sc-cli process already checks every exported file's grid against the written file's own analysis. The first pre-release, v0.1.0-alpha.1, follows once exported files pass rekordbox 7's own analysis; v0.1.0 is the first release for everyone. Watch the releases page or the changelog.

What v0.1 will do

• Same loudness: every track lands on one persisted DJ target (measured on the loud parts of the track, not the intro) or on a streaming target (integrated loudness). Gain only. When the true-peak ceiling would be hit, the row says "Short by X LU" instead of squashing the sound.
• Fits the grid: beats, downbeats and an exact two-decimal BPM, with a static grid you can inspect and fix in seconds (anchor, nudge, BPM, half/double, which beat is beat 1). Odd meters such as 9/8 and 6/8 are recognised and shown with their grouping. For tracks whose tempo changes, the grid can be fitted to the start. In Prepare mode (new tracks) lossless files are cut so bar 1 starts a few milliseconds after the start of the file, removing at most one beat (a file whose bar 1 lies further in is not cut); in Library mode (tracks already in a DJ app, with cue points) a file's length never changes. A per-batch rekordbox XML carries the grid.
• Nothing lost: every ID3, Vorbis, RIFF and AIFF block, cover art and DJ-app cue blob is carried byte for byte and verified after writing. Originals are backed up and every change can be reverted. Files are never renamed.
• Formats: WAV, AIFF, FLAC and MP3 in and out (MP3 loudness through the lossless global-gain patch, no re-encode); M4A, AAC, ALAC, Ogg and Opus are analysed only.
• A headless sc-cli that prints exactly the numbers the app shows.

What v0.1 does not do

No limiter or compression, no EQ, no "enhancement", no pitch correction, no warping or time-stretch, no key detection, no Windows or Linux build, no auto-updater, no writes to M4A/AAC/Opus, no direct writes into rekordbox or Engine databases, no filename suffixes. Some of these are planned for later versions; the changelog says which.

Building from source

Requires a stable Rust toolchain, Node 22+ and pnpm 11+. On macOS, Xcode command line tools.

git clone https://github.com/wow/SoundCheck && cd SoundCheck
./scripts/setup-dev.sh        # git hooks, sign-off, toolchain check
pnpm install
./scripts/fetch-models.sh     # beat-tracking model files (11 MB, checksum-verified) into models/
./scripts/verify.sh           # fmt, clippy, tests, typecheck, vitest
pnpm tauri dev                # run the app
pnpm dev:mock                 # the UI alone in a browser, with synthetic tracks (open /?demo=1)
cargo run --release -p sc-cli -- analyze <file>          # loudness, BPM, meter and bar 1
cargo run --release -p sc-cli -- plan <files>            # what processing would do to each file
cargo run --release -p sc-cli -- plan <files> --batch-mode prepare   # ... and what exporting would write
cargo run --release -p sc-cli -- process <files> --batch-mode prepare   # export (backup first; --out <dir> for copies)
cargo run --release -p sc-cli -- apply <files> --gain-db -3   # change files (backup first; --out <dir> for copies)
cargo run --release -p sc-cli -- undo <files>            # put the previous version back
cargo run --release -p sc-cli -- journal                 # recorded changes; `recover` finishes interrupted ones
cargo run --release -p sc-cli -- bench <file>            # speed of each analysis stage

Unsigned development builds show a Gatekeeper warning on first launch; release builds are signed and notarized. To run a development build you downloaded, remove the quarantine flag: xattr -dr com.apple.quarantine SoundCheck.app.

Contributing

See CONTRIBUTING.md for branches, commits (Conventional Commits with a DCO sign-off), tests and the review process, and docs/RELEASING.md for how versions and releases work. Product scope lives in docs/PRODUCT.md, the architecture in docs/ARCHITECTURE.md.

Licence

MIT OR Apache-2.0, at your option (LICENSE-MIT, LICENSE-APACHE). Every dependency in the shipped binary is under a permissive licence; the full list is generated into THIRD_PARTY.md for each release.