---
title: "Measure loudness (LUFS, true peak, LRA)"
url: https://recursiveai.org/oneaudio/cookbook/measure-loudness/
description: "Measure integrated loudness in LUFS, loudness range and true peak in C# with oneaudio’s ITU-R BS.1770-5 and EBU R 128 meter, for a whole file or live…"
version: "1.2.1"
---

# Measure loudness (LUFS, true peak, LRA)

Measure integrated loudness in LUFS, loudness range and true peak in C# with oneaudio’s ITU-R BS.1770-5 and EBU R 128 meter, for a whole file or live, block by block.

The input is `game-mix.wav`, the file [Mix audio files](https://recursiveai.org/oneaudio/cookbook/mix-audio/) writes.

```csharp
using OneAudio;
using OneAudio.Loudness;

// One call: integrated loudness, loudness range and true peak.
LoudnessResult r = Audio.Measure("game-mix.wav");
Console.WriteLine($"game-mix.wav: {r.IntegratedLufs:F1} LUFS, LRA {r.LoudnessRange:F1} LU, " +
                  $"true peak {r.TruePeakDbtp:F1} dBTP");
Console.WriteLine($"max momentary {r.MaxMomentaryLufs:F1}, max short-term {r.MaxShortTermLufs:F1}");

// Skip true peak (4x oversampling) when you only need LUFS: it's the costly part.
double lufs = Audio.Measure("game-mix.wav", truePeak: false).IntegratedLufs;
Console.WriteLine($"without true peak: {lufs:F1} LUFS");

// A live meter: feed blocks as they come, and read momentary (400 ms) and
// short-term (3 s) loudness at any time.
using IAudioDecoder decoder = Audio.Open("game-mix.wav");
var meter = new LoudnessMeter(decoder.Format, truePeak: true, loudnessRange: true);
int channels = decoder.Format.Channels;
float[] block = new float[4800 * channels];         // 100 ms
int read, n = 0;
while ((read = decoder.Read(block)) > 0)
{
    meter.Process(block.AsSpan(0, read * channels));
    if (++n % 20 == 0)                              // every 2 s
        Console.WriteLine($"{n / 10,3} s  momentary {meter.MomentaryLufs,6:F1}" +
                          $"  short-term {meter.ShortTermLufs,6:F1}");
}
Console.WriteLine($"integrated {meter.IntegratedLufs:F1} LUFS, range {meter.LoudnessRange:F1} LU, " +
                  $"true peak {meter.TruePeakDbtp:F1} dBTP");
```

```text
game-mix.wav: -18.7 LUFS, LRA 2.6 LU, true peak -1.8 dBTP
max momentary -14.1, max short-term -16.7
without true peak: -18.7 LUFS
  2 s  momentary  -20.7  short-term  -21.1
  4 s  momentary  -20.8  short-term  -19.4
  6 s  momentary  -16.6  short-term  -17.3
  8 s  momentary  -18.3  short-term  -17.6
 10 s  momentary  -23.6  short-term  -19.1
 12 s  momentary  -20.8  short-term  -19.9
 14 s  momentary  -22.0  short-term  -19.1
 16 s  momentary  -21.0  short-term  -20.2
integrated -18.7 LUFS, range 2.6 LU, true peak -1.8 dBTP
```

ffmpeg’s `ebur128` filter gives the same integrated loudness (−18.7 LUFS) and true peak (−1.8 dBTP) for this file.

## The readings

| Reading | What it is |
|---|---|
| `IntegratedLufs` | The loudness of the whole program, gated: blocks below −70 LUFS, and blocks 10 LU below the ungated level, are left out |
| `MomentaryLufs`, `MaxMomentaryLufs` | Over the last 400 ms |
| `ShortTermLufs`, `MaxShortTermLufs` | Over the last 3 s |
| `LoudnessRange` | The spread of short-term loudness in LU, per EBU Tech 3342 |
| `TruePeakDbtp` | The highest peak between samples as well as on them, found by 4× oversampling, across all channels |

Before any audio, the readings are negative infinity and the range is 0.

## Good to know

- The meter passes EBU Tech 3341 cases 1 to 23 and Tech 3342 cases 1 to 6 within their tolerances.
- It works at any sample rate from 4 kHz up, and the K-weighting filters are designed for the actual rate.
- Channels are weighted from the channel mask: 1.41 for surround and side channels, and the LFE channel is left out of the loudness but not the true peak.
- The results don’t depend on how the audio is split into blocks. Everything is allocated in the constructor, so a meter can run on a real-time thread.
- True peak is the expensive part. Pass `truePeak: false` when you only need LUFS.
- The true-peak filter lags by 12 samples, so a peak in the last 12 frames shows only after more audio arrives.
- The mixer has the same meters built in, per bus. See [Mix audio files](https://recursiveai.org/oneaudio/cookbook/mix-audio/).

To change a file’s loudness, see [Normalize loudness](https://recursiveai.org/oneaudio/cookbook/normalize-loudness/).

A longer guide to EBU R 128 and streaming targets: [Loudness normalization in C#](https://recursiveai.org/oneaudio/articles/loudness-normalization-csharp/).