For years music production lived through a loudness race: ever louder masters, compressed and limited, in the belief that "louder" meant "better". The spread of loudness normalization on listening platforms has changed the rules. To work well today you need to understand what loudness is, how it is measured and what happens to your file after upload.
Peak and loudness are not the same
A peak meter shows the highest value the signal reaches, but says little about how loud a track seems. Two files with the same peak at -1 dBFS can sound very different: one with lots of dynamics and isolated transients, the other compressed and dense, perceived as much louder.
Loudness is a measure designed to approximate human perception. It accounts for the ear being more sensitive to some frequencies and for the way energy is distributed over time.
The units: LUFS and LU
The most widespread standard for measuring loudness is described in the ITU-R BS.1770 recommendation and adopted in Europe by the EBU R128 recommendation. The unit is LUFS (Loudness Units relative to Full Scale), sometimes written as LKFS: a unit on the same scale as decibels, referenced to digital full scale.
LU (Loudness Unit) instead expresses a difference: going from -16 to -14 LUFS means raising by 2 LU.
The three main values
- Integrated loudness: the average loudness of the whole program, with a gate that excludes silences. It is the value used for normalization.
- Short-term: loudness over a 3-second window, useful for checking sections.
- Momentary: over a 400-millisecond window, for rapid changes.
On top of these there is LRA (Loudness Range), which describes how much loudness varies over the program.
True peak
Sample values do not always match the real peak of the reconstructed signal. Between two samples close to digital zero, the analog waveform can rise higher: this is the phenomenon of inter-sample peaks. A true peak meter, expressed in dBTP, estimates these values using oversampling.
It matters because lossy codecs and some converters can turn these hidden peaks into real distortion. That is why many specifications require a maximum true peak of -1 dBTP, or even lower.
What normalization does
When a platform normalizes, it measures the file's integrated loudness and turns it up or down to bring it to a reference value. The practical consequences:
- A master that is too loud gets turned down. If you sacrificed dynamics to gain volume, that volume disappears on playback, but the lost dynamics do not come back.
- A more dynamic master may sound better, because at equal loudness the transients have more room.
- A master quieter than the reference can only be raised as far as its peak allows; some platforms do not raise it at all.
Reference values differ between services and over time. For television in Europe the EBU R128 standard specifies -23 LUFS; for music streaming and podcasts higher values are used, often quoted between -16 and -14 LUFS. Before delivering work, check the current specification of the destination platform.
How to work in practice
For a podcast
- Aim for a consistent integrated loudness across all episodes, so listeners don't have to touch the volume.
- Keep true peak below -1 dBTP.
- Even out the voices before the final measurement: a guest much quieter than the host will stay that way even after normalization.
For music
- Decide the amount of compression for artistic reasons, not to win a volume contest.
- Measure integrated loudness and compare it to the reference: if you are far above it, you will be turned down.
- Compare your master with reference tracks at equal loudness, not by ear at different volumes.
A simple checking workflow
1. Finished mix, no limiter on the bus
2. Limiter with ceiling at -1 dBTP
3. Measure integrated loudness over the whole file
4. Adjust the input gain to the limiter
5. Measure again and export
In my work I find it useful to keep a loudness meter visible throughout the mix, not just at the end: it helps avoid pushing the volume without noticing.
In short
- Loudness measures perceived volume; peak only shows the maximum value.
- LUFS is the standard unit, defined by ITU-R BS.1770 and EBU R128.
- True peak catches peaks between samples: keep it below -1 dBTP.
- Platforms normalize: a master that is too loud gets turned down and only loses dynamics.
- Always check the platform's current specification before delivery.
