About JSM Loudness — Built in Montreal
Accurate, offline loudness measurement. 100% browser-based, no upload, exact ITU-R BS.1770-4 coefficients.
Why I built it
I'm Sehmus, a Montreal-based audio developer and musician (memolimusic). Existing online LUFS meters either upload your audio, use approximated filters, or get the gating wrong by 0.5-1 LUFS. For Spotify, YouTube, TikTok mastering, that error matters.
JSM Loudness implements exact EBU R128 gating, K-weighting, and 4x oversampled true-peak with verified reference: -14.05 LUFS on EBU reference, -17.5 RMS equivalent, 3.4 dB offset handled correctly. All processing runs via Web Audio API + WebAssembly in your browser.
What makes it accurate
- ITU-R BS.1770-4 coefficients exact — not approximated biquad
- EBU R128 S1 gating: -70 LUFS absolute, -10 LUFS relative, 400ms blocks, 75% overlap
- True-peak: 4x oversampling per ITU, reports dBTP and inter-sample peaks
- LRA, PLR, PSR: for dynamic range assessment for TikTok, podcasts
- No upload: File stays on device, zero server cost, private for unreleased music
Transparency
Built in Montreal, QC. Privacy-first under Quebec Law 25. No account required. Free analyzer, optional one-click fix to -14 LUFS integrated with true-peak safety.
Contact: contact page or via memolimusic on Instagram.