---
title: Loudness and mastering
order: 5
summary: Measure loudness the EBU R128 way and deliver to streaming, podcast or broadcast targets with a true-peak limiter.
---

Peak level tells you how close a file is to clipping. It does not tell you how loud it sounds. Streaming services, podcasts and broadcasters measure **loudness** instead, in LUFS (loudness units relative to full scale), and turn loud tracks down to a target. Deliver at the target and nothing is changed for you.

## Measure

<!-- run -->
```js
mix = audioGain( audioNoise( seconds=8, color="pink" ), -14 );
r = audioLoudness( mix );
println( "integrated " & r.integrated & " LUFS, range " & r.range & " LU, true peak " & r.truePeak & " dBFS" );
```

`audioLoudness` follows ITU-R BS.1770 and EBU R128 (K-weighting, gated 400 ms blocks, true peak from a 4 times oversampled signal) and returns:

| Key | Meaning |
|---|---|
| `integrated` | Loudness of the whole program in LUFS, with silence and very quiet passages gated out. The number services use |
| `range` | Loudness range (LRA) in LU: how much the loudness moves |
| `truePeak` | Highest peak between samples, dBFS |
| `samplePeak` | Highest sample, dBFS |
| `momentaryMax` / `shortTermMax` | Loudest 400 ms and loudest 3 s, LUFS |

Silence, or audio shorter than 400 ms, reads -120. This implementation agrees with FFmpeg's `ebur128` filter to within 0.1 LU on rendered music, and with the EBU reference tones (a stereo sine at -23 dBFS reads -23 LUFS).

## Master to a target

<!-- run -->
```js
mix = audioGain( audioNoise( seconds=8, color="pink" ), -22 );
final = audioMaster( audio=mix, target="streaming", truePeak=-1 );
println( audioLoudness( final ).integrated );   // -14
```

`audioMaster` sets the gain to reach the target, then a look-ahead limiter holds the peaks under the true-peak ceiling. The limiter lowers the loudness a little, so the gain is corrected and the pass repeated until the target is hit within 0.05 LU.

| Target | LUFS | Used for |
|---|---|---|
| `streaming` | -14 | Spotify, YouTube, Apple Music and most video platforms |
| `podcast` | -16 | Podcasts |
| `game` | -16 | Game audio |
| `broadcast` | -23 | EBU R128 television and radio |
| `cinema` | -24 | Film trailers and cinema |

Pass a number for any other level. `glue=true` compresses lightly first (2:1, slow) so a busy mix sounds more even. `audioNormalizeLoudness` does the same with a plain number of LUFS.

## The tools it is built from

You can use them directly:

<!-- run -->
```js
voice = audioNoise( seconds=4, color="pink", seed=3 );

voice = audioEq( voice, [
    { type: "highpass", freq: 90 },                       // no rumble
    { type: "peak", freq: 3000, gain: 3, q: 1 },          // presence
    { type: "highshelf", freq: 9000, gain: -2 }           // tame the hiss
] );
voice = audioCompress( audio=voice, thresholdDb=-20, ratio=3, attack=8, release=120 );
voice = audioLimit( audio=voice, ceilingDb=-1 );
```

| Function | Does |
|---|---|
| `audioCompress` | Turns loud parts down by `ratio` above `thresholdDb`, with attack, release and a soft knee. `makeupDb="auto"` matches the loudness of the input |
| `audioLimit` | A look-ahead limiter: no sample ends above `ceilingDb`, and the gain recovers over `release` |
| `audioEq` | Parametric bands: `peak`, `lowshelf`, `highshelf`, `lowpass`, `highpass`, `notch` |

## From the command line

```bash
bx-audio loudness mix.wav
bx-audio master mix.wav final.wav --target=podcast
bx-audio master mix.wav final.wav --target=-18 --truePeak=-2 --glue
```