runs 100% locally · Web Audio API
Audio mastering — LUFS normalizer
Drop in a raw recording and master it to a standard loudness target using ITU-R BS.1770 (the same measurement Spotify, Apple, and YouTube use) — no upload, no per-minute charge.
Your audio is decoded and processed by the Web Audio API in this tab. It never leaves your device.
Drop an audio file here, or click to browse
MP3, WAV, M4A, and most common formats. Up to 300MB.
No file yet — drop an audio file above to master it.
How the measurement works
K-weighting
Your audio is filtered to match human loudness perception before measurement — the exact filter defined in ITU-R BS.1770-4.
Gated blocks
Loudness is measured in 400ms windows, with silence and outlier-quiet sections excluded — the same "gating" broadcasters use, not a simple average.
Safety limiter
If hitting your target would clip the loudest peaks, we scale back slightly instead — you'll see a note when that happens, rather than a distorted file.