The outcome could have been worse

By Jeffrey KraussAn interesting thing happened on the way to Congress. A badly written law was drafted to deal with an admitted problem. Hearings were held. The industry, perhaps out of fear, put together a committee of experts that designed a practical approach to solving the problem. And the draft of the law was changed to require compliance with the work of the industry experts. Although in our industry we prefer voluntary industry standards to mandatory laws and regulations, in this case the outcome could have been much worse.

Loud commercials have always been an annoyance to TV viewers, but this is the first time a concerted industry effort has led to a positive outcome.

The work of the experts has been published as “ATSC Recommended Practice A/85: Techniques for Establishing and Maintaining Audio Loudness for Digital Television.” You can download this document for free at

It is based on a particular feature of the Dolby Digital (AC-3) audio system used in the U.S. Digital AC-3 audio contains not only a digital representation of the sound, but also “metadata” elements that provide instructions to the decoder for recreating the sound at the receiver. The key metadata element in dealing with loudness is “dialog normalization” – or “dialnorm.”

In concept, it’s simple. Measure the loudness of a typical segment of dialogue in a program and assign that value as the dialnorm of the program. Measure the average loudness across an entire commercial and assign that as the dialnorm value of the commercial. When you insert the commercial (which is now a digital file) into the program, if the dialnorm value of the commercial is not equal to the dialnorm of the program, apply an overall gain correction to modify the commercial’s dialnorm value to make it equal to that of the program.

Of course, it isn’t quite that simple. The A/85 document is 70 pages long. A good part of it explains how to make loudness measurements. For example, you have to use a meter that follows the requirements specified in ITU-R Recommendation BS.1770.

But the last five pages are a quick reference guide for TV station and cable MSO engineers, and they contain some key ideas:

  • The goal is to present to the viewer consistent audio loudness across commercials, programs and channel changes.
  • Measure the program loudness when dialogue is present.
  • Measure the commercial loudness over the duration of the commercial.
  • Ensure that all program and commercial audio content matches the dialnorm value of the station’s AC-3 encoder; use a BS.1770 meter to verify the loudness of the dialogue.

So as a cable MSO or TV station, you have to know the correct value of dialnorm for each program. Maybe you tell the program supplier what value you want, or maybe they tell you what value they supply. Maybe you don’t trust them, so you use your BS.1770 meter to check that the dialnorm value they supply is actually the loudness of typical dialogue.

Similarly, you need to know the correct value of dialnorm for each commercial you insert. Maybe you need to check that the ad agency is supplying the correct value of dialnorm in the digital file that contains the commercial. If you don’t trust the ad agency, then you need to make the measurements yourself. And at insertion time, you need to apply an overall gain correction to the commercial so that its dialnorm matches the dialnorm value of the program.

By the way, there is already an FCC rule that incorporates an ATSC requirement that mandates both that dialnorm metadata be carried in the audio for digital TV, and that the value be set correctly. But until now, ad agencies may have paid less attention to supplying the correct value. Or maybe some have knowingly set the value incorrectly to cause the audio output to be louder than it should. And there will always be some ads that have the correct value when averaged over the whole commercial, but that have some periods of silence and some periods of very loud audio.

And until now, TV station and cable MSO engineers may have paid less attention to dialnorm than they should have. That will have to change.

In mid-November, the House Energy and Commerce Committee passed H.R. 1084, the Commercial Advertisement Loudness Mitigation (CALM) Act. It is expected to pass the full House of Representatives. It requires the FCC to “prescribe” a regulation that incorporates by reference that ATSC A/85 Recommended Practice. Any broadcaster that demonstrates that compliance would result in severe financial hardship could get a one-year waiver.

It could have been worse. The original language required that “the average maximum loudness of advertisements shall not be substantially higher than the average maximum loudness of the program material that such advertisements accompany.” But the term “average maximum loudness” is undefined and self-contradictory, and who knows how the FCC might have defined it.

At least this way we have a document created by industry, using proper terminology, and specifying procedures that should actually solve the loud commercial problem.