What Is LUFS? Jargon-busting answer:
When artists ask “How loud should my master be”, what they probably mean (technically speaking) is “What LUFS should my master be?”. But understanding the concept behind integrated LUFS vs dB (decibels) is essential, and can be confusing.
What are LUFS in audio? = LUFS stands for Loudness Units relative to Full Scale (or just “Loudness Units/LU”). They are a way of measuring the intrinsic volume of a piece of audio, relative to 0dB which is the absolute loudest signal possible in digital audio – in the same way that a cup can only ever be filled up to 100% full, and no more. You cannot push digital audio beyond 0dB without clipping (like overflowing in our cup example).
A cup with 100ml capacity can only ever hold a maximum of 100ml. The same theory holds in digital audio, where 0dB is the audio measurement equivalent of the maximum capacity of the cup to hold water.
Practically speaking, a LUFS measurement tells you the perceived loudness of a piece of music across a sustained measure of time, and this LUFS measurement is the most accurate reflection of how “fat”, “full” or “hefty” the track will sound compared to similar tracks, when played through the same Soundsystem, at the same volume (without any automatic volume levelling system).
LUFS are very similar to the more famous dB/decibel. Actually, in practical terms 1dB is the same amount as 1LU. So if you lower the volume of something by -3LUFS, you could also say you reduced it by -3dB.
So what’s the difference between dB and LUFS? Both LUFS and dB can be used to express a measurement of difference between 2 things e.g. “take the vocals down -2dB” (from where they are now), or a fixed volume reference (e.g. “the neighbours registered a noise complaint of 80dB” (compared to the base reading 0dB of the meter at measurement location).
The most important dB vs LUFS difference from a professional audio work perspective is that the dB scale represents how much air pressure a sound will produce over a very short time, and needs to be referenced to another point (which is standard air pressure) to get a measurement.
In contrast, LUFS is a unit of measurement measured from within the audio, relative to the loudest it could possibly be, and measured over a longer time.
So the LUFS measurement is more similar to measuring how much water we have in our cup with 100ml capacity. LUFS is measured backwards from full-scale (full capacity), so using our 100ml cup analogy again, if we had 90ml of water in the cup, you could also say you had the capacity of 10ml left, or -10ml to full capacity. If you only measured from an empty cup (with 100ml capacity available), through to to 0ml capacity left (a full cup), then if you had 50ml water in the cup, there would be -50ml capacity available… If you had 60ml water in there, the spare capacity measurement would be -40ml… If you had 20ml of water in there, the spare capacity would be -80ml etc.
Same idea for digital audio measurement: digital audio can only ever go to a maximum point before clipping (the cup overflowing), which is always referenced at 0dB (our full capacity). Both dB and LUFS are measured like this. So a measurement of -5dB means you can raise the volume up another 5dB before the audio clips (the cup runneth over). A measurement of -10LUFS means there’s a limit of another 10LUFS before the audio is the loudest it could ever possibly be (the full cup again). So if dB and LUFS are so similar, where does the difference lie?
Measuring audio using LUFS gives a more accurate picture of the track volume over a longer time (often the entire track is measured and represented). So a whole tracks LUFS measurement takes into account all the quiet sections and loud sections too, rather than just being measured at one specific point like with dB.
LUFS are the best unit we have to measure audio loudness at the moment, but when finishing a master you still need to use your ears rather than trust the numbers blindly, as so many other factors come in to play in perception of the listener, like genre, tempo, instrumentation and vocal styles. Especially if considering tracks across an album.
For some heavy music styles, the published target LUFS for Spotify may not actually reflect your musical intention perfectly either, and you will probably find your music lacks a certain “oomph” if you stick rigidly to the published targets!
If you want to read more about why LUFS standard for streaming may not give the results you want in all situations, and more info about LUFS when mastering check out this deeper dive article: How Loud Should My Master Be In 2022? Which covers questions like how many lufs should my master be, Spotify lufs, lufs for Soundcloud, lufs and true peak for Spotify and more.