Measure loudness (LUFS, true peak, LRA) · oneaudio cookbook

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 writes.

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.

To change a file’s loudness, see Normalize loudness.

A longer guide to EBU R 128 and streaming targets: Loudness normalization in C#.