Nowadays, loudness management is everywhere: TV, iTunes, YouTube, Spotify, etc. If your music is too loud, it will be turned down. This creates a more consistent and enjoyable experience for the listener. To ensure that your music sounds its best wherever it’s played, it helps to have a solid understanding of loudness levels.
Luckily, it’s not that difficult! Let’s dive in…
What is ITU BS.1770-4?
Loudness measurements are taken using specialized loudness meters. These meters are standardized - they should all give the same measurement for the same piece of music. The standard is ITU-R BS.1770-4. What a mouthful! Let’s break it down. The “ITU” stands for “International Telecommunications Union,” the organization that developed the standard. The “-R” is the “Recommendation” sector of the ITU, and the “BS” is the “Broadcasting Service”.
The BS.1770-4 measurement does a few things:
- It uses “K” frequency weighting to de-emphasize the low-end
- It averages out brief high and low sample values
- It weights rear surround channels higher
- It uses gating to exclude low-level sections
The K-weighting step accounts for the fact that we do not perceive all frequencies as being equally loud. This is an important point. The BS.1770-4 measurement is designed to capture how we perceive loudness. This makes it difficult to “cheat” the algorithm to gain a competitive “loudness advantage” (if you even believe such a thing exists).
The BS.1770-4 measurement is an “integrated” or “overall” measurement. It computes a single loudness value for an entire song, CD, film, etc. It keeps measuring until you stop it. This has the effect of averaging out brief loud and quiet passages.
The rear channel weights are higher than the front channels because, according to ITU-R BS.1770-4, “…sounds arriving from behind a listener may be perceived to be louder than sounds arriving from in front of the listener.” They tested this stuff. I believe them.
The gating step filters out quiet parts of a program or song so that they do not contribute to the final loudness level. Two gates are applied: an absolute and relative gate. The effect of this is that only the loudest parts of a program are measured.
LUFS & LKFS
The final output is a single loudness value with units LKFS: “Loudness, K-weighted, relative to Full Scale”. You may come across another unit, LUFS, which stands for “Loudness Unit, relative to Full Scale”. LKFS and LUFS are the same. The “Loudness Unit” (LU) is used to specify loudness levels that are relative to something other than full-scale. This is analogous to using dB instead of dBFS. In fact, LKFS / LUFS are related to dB in that a 1 dB increase in a signal will result in the same increase in LKFS.
These new units are great for a few reasons:
- They give us a standard way to describe loudness
- A single number can describe an entire song or album
- They are based on how we perceive sound
Many DAWs are now ship with built-in loudness meters. If yours does not have one, many loudness meter plugins are available. I encourage you to try them out. In a future post we’ll discuss what levels you should be shooting for.