LKFS, LUFS, dB Oh MY!
If you produce audio for broadcast, then you know there are standards. In this article we will discuss at a high level the differences between LKFS, LUFS, dB and ITU-R-BS.1770 and the standards for mixing for TV and Commercials in the United States.
Lets start with what the difference is between LKFS, LUFS and dB. Despite the different names, LFKS and LUFS are identical. Both terms describe the same phenomenon and just like LKFS, one unit of LUFS is equal to one dB. LKFS/LUFS are absolute measures, and depending on which broadcast standard is in use, the loudness target level could be e.g. -24 LKFS or -23 LUFS.
LKFS, LUFS & LU
When measuring loudness, three terms are essential to be aware of: LKFS, LUFS and LU. What tends to create confusion is that these terms are very similar and basically aims at describing the exact same thing.
LKFS is an abbreviation of: Loudness K-weighted Full Scale, and one unit of LKFS is equal to one dB.The LKFS term is used in the ITU BS.1770 standard and the ATSC A/85 standard also operates with this term. Other organizations, such as The European Broadcast Union (EBU), uses the term LUFS, which is an abbreviation ofLoudness Units Full Scale. Despite the different names, LF KS and LUFS are identical. Both terms describe the same phenomenon and just like LKFS, one unit of LUFS is equal to one dB.
LKFS/LUFS are absolute measures, and depending on which broadcast standard is in use, the loudness target level could be e.g. -24 LKFS or -23 LUFS. However, in order to aim for a more 'traditional number, a relative measure has been defined: Loudness Units (LU). Now, the broadcaster can set the target level (regardless of whether it is -23 or -24) to 0 LU, and again, one LU is equal to one dB.
There is a great article by TC Electronic here that gives a ton more technical information.
Why does this matter to mixing for broadcast? Well there has to be standards for loudness, etc. in order to ensure sonic continuity on TV, advertising, etc. Ever notice that commercials can be louder the the show? Poor mixing.There is even agreed upon guidelines, a paper called ATSC A85 that documents firm loudness recommendations. It’s practices are even mandated in an act of Congress called the Commercial Advertising Loudness Mitigation (CALM Act).”
What is the CALM act? The Commercial Advertisement Loudness Mitigation (CALM) Act was passed on September 29, 2010. The bill was proposed in the house of representatives by congresswoman Anna Eshoo from California. Legend has it she was inspired to write the bill after disproportionately loud television commercials interrupted a holiday dinner she was hosting.
Conceived as a solution to the loud commercial problem, the CALM act references something called the Advanced Television Systems Committee (ATSC)’s Recommended Practice A/85. The full document is available at atsc.org, but we’ll attempt to convey the highlights.
As ATSC A85 gets updated, the CALM act is automatically updated to reflect any new recommendations, so in essence the CALM act is bound directly to A/85.
From the FCC website:
“Specifically, the CALM Act directs the Commission to establish rules that require TV stations, cable operators, satellite TV providers or other multichannel video program distributors to apply the ATSC A/85 Recommended Practice to commercial advertisements they transmit to Viewers.”
While the scope of this bill is directly focused on commercials, if you mix episodic television, be it long form or half hour, by association you must mix within the guidelines of this act. The intent is that when watching TV, viewers can go from program to commercial and back to program without any apparent change in loudness, and as you change channels you can go from one to the next with the same experience.
It’s worth mentioning that prior to the creation of this legislation, the number one complaint to the FCC with regards to broadcast television was the unpleasant loudness of commercials. Since the time the act took effect on December 13, 2012, it’s worth noting that the number one complaint to the FCC in regards to broadcast television is... still the loudness of commercials. OK, so apparently the passage of the act didn’t work out exactly as planned.
Want to know more about this and mixing check out the Mixer's Guide to Loudness for Broadcast here from our friends at Izotope
Now what is ITU-R-BS.1770? ITU-R BS.1770 Loudness and True-peak level standard. It specifies anchor based normalization for regular programs, but all-source loudness normalization for commercials and interstitials, both at a default Target loudness of -24 LKFS. Put differently, regular programs are under a liberal, rubber-band rule around -23LKFS, while the level of commercials is defined precisely and transparently. So....if you are mastering for Broadcast TV it can be -23LKFs/LUFS/dB but IF you are mixing for commercials is must be mastered at -24. But hold on!
Now as with all things FCC and the U.S. Government, they decided to screw around with the CALM act and add some revisions. In 2011, to give the CALM Act a chance of becoming effective, two revision were published, calling for the inclusion of all sources when measuring commercials, i.e. measuring loudness rather than speech. In the original version of A/85, only the 'anchor method was recognized. Even though the 2011 revisions were published after ITU had defined BS.1770-2, the ATSC standards ambiguously pointed to BS.I 770-1, which was then no longer in effect.
From March 2013, this ambiguity has gone, because the A/85 recommended practice now prescribes ITU BS.1770-3 for all programming. So this means that for TV AND Commercials, they must comply to ITU-R BS.1770 Loudness and True-peak level standard.As stated above.... both at a default Target loudness of -24 LKFS/LUFS.dB.
So there you have it! Hope that helps if you are mixing and mastering for TV and Commercials. Lastly, there are also standards for other countries, Spotify, iTunes, etc. but we will save that for another day. Here are a couple of other links to some great articles on this topic