Audiobook chapter loudness checker
Choose all your chapter files at once. Each one is measured in your browser, and you see which chapters are louder or quieter than the rest and by how much.
How it works
Chapters recorded on different days, re-recorded pickups and TTS batches almost never come out at the same level. Listeners notice a 2 LU jump straight away, and audiobook retailers reject files whose RMS, peak or noise floor is outside their limits, or that start and end without room tone.
How to use it: choose your chapter files (MP3, WAV, M4A or FLAC — whatever your browser can play), pick what to match them to, and press Compare loudness. Loudness is measured with the ITU-R BS.1770 method (K-weighting, 400 ms gated blocks), the same one EBU R128 and streaming services use. Nothing is uploaded.
The table shows integrated LUFS, RMS, sample peak, noise floor (quietest half second), silence at the start and end, and the gain in dB to reach your target. Chapters more than 1 LU from the median are flagged, as are files outside the common audiobook spec: RMS −23 to −18 dB, peak at or below −3 dBFS, noise floor at or below −60 dB, 0.5–1 s of room tone at the start and 1–5 s at the end. Copy the table as CSV for your editor.
FAQ
Are my files uploaded?
No. They are decoded and measured in your browser only.
How accurate is it?
LUFS follows BS.1770 and matches ffmpeg’s ebur128 filter within about 0.1 LU in our tests. Peak is sample peak, so true peak can be up to about 0.5 dB higher — leave a little headroom.
A long file fails or the tab freezes?
Hour-long WAVs need a lot of memory in the browser. Split very long chapters or use MP3.
Does passing here mean my audiobook will be accepted?
No. It checks the measurable numbers only. Retailers also listen for noise, breaths, edits and pronunciation.