What LUFS means
LUFS (loudness units relative to full scale; LKFS is the same thing under another name) measures how loud audio sounds to people over its whole length, not just its peaks. Platforms use it to play everything at a similar volume: if you deliver louder than their target, they turn you down; quieter, and you sound weak next to everything else, or they turn you up and risk distortion. True peak (dBTP) is the highest point the waveform reaches, including between samples; keeping it below the limit avoids clipping when the file is converted to MP3 or AAC.
Targets by platform
| Where it's going | Integrated loudness | True peak |
|---|---|---|
| Podcasts (Apple Podcasts guidance) | -16 LUFS, give or take 1 | -1 dBTP |
| Spotify and other streaming | About -14 LUFS (playback normalization) | -1 to -2 dBTP |
| YouTube | About -14 LUFS (playback normalization) | -1 dBTP |
| European TV and radio (EBU R 128) | -23 LUFS | -1 dBTP |
| US TV (ATSC A/85) | -24 LKFS | -2 dBTP |
| E-learning and internal video | No standard; -16 to -19 LUFS is common | -1 dBTP |
Platforms revise their figures from time to time, and broadcasters and streaming services publish delivery specs of their own. Always check the current specification for the place you're delivering to.
Audiobooks
ACX, which supplies Audible, measures differently. Its published requirements include each file's RMS level between -23 and -18 dB, peaks no higher than -3 dB, and a noise floor no higher than -60 dB RMS, with one chapter per file and a little room tone at the start and end. Other audiobook distributors have their own specs. Audiobook platforms also have rules about AI narration, and some don't accept it, so check before you produce a whole book. See AI narration for audiobooks.
How to measure and hit a target
- Audacity: Effect › Volume and Compression › Loudness Normalization sets a file to a LUFS target in one step. See editing in Audacity.
- ffmpeg: measure with
ffmpeg -i mix.wav -af ebur128 -f null -, or normalize withffmpeg -i mix.wav -af loudnorm=I=-16:TP=-1.5:LRA=11 out.wav. - Video editors: Premiere Pro, DaVinci Resolve and Final Cut Pro all have loudness meters, and most can normalize on export.
- Free meters: standalone loudness meter plugins work in any audio workstation.
Order of operations
- Assemble the voice lines and set the gaps.
- Add music and effects, and balance them against the voice.
- Mix down to one file.
- Normalize the whole mix to the target, with a true-peak limit.
- Export in the platform's format, then measure the exported file once more.
Normalize the final mix, not each line separately: normalizing lines individually to the same LUFS can make quiet, intimate lines as loud as shouted ones.
Why AI voiceover is easy to master
Takes from abcVoiceover are clean and consistent from line to line, with true silence between files, so they need little compression or noise reduction. Most of the work is balancing voices against each other and the music, then one normalization pass at the end.