Broadcasting Audio Science

Everyone is talking about the Commercial Advertisement Loudness Mitigation (CALM) Act and the ATSC A/85 specification.

The goal is to resolve the perceived loudness discrepancy between programs and commercials (the latter a.k.a ‘interstitials‘). There is some humor in this – on multiple levels.

If you mix sound for picture, the North American standard for Program Loudness is -24 LKFS (-23 in the EU) – the voltage difference from there to 0dBFS is more than 10 times!!! This makes logical sense because that type of programming requires enough headroom to allow for a wider dynamic range – the sound of a truck, siren or explosion being enough to drown out a conversation and have impact. Logical, right?

By contrast, the people responsible for commercials ‘build’ them like pop records, with the goal of getting as close to kissing 0dBFS as possible. There’s almost no dynamic range in commercials in part because they are emulating current pop music – engineers are simply having too much fun abusing dynamics processing tools.

To reconcile the differences, the first question might be ‘whose job is it?’ Obviously it’s not happening at the source although the easiest thing would be to require -20dBFS to be the new 0dbFS at jingle houses… Next would be to have a dedicated audio person at the helm of every national and local broadcast facility. We all know that is not going to happen, for all sorts of reasons. Bottom line is that A/85 establishes standards by which program material can be measured, as defined by ITU-R Recommendation BS.1770. Having a target – combined with analysis tools – is part of the process.

The ATSC is about to adopt BS.1770-3, which will clarify and define the following:

1) It introduces the concept of “gating”; think noise gate in that the measurement ignores quiet passages, making for better alignment with subjective loudness

2) It also intros a strict definition of True Peak measurement, which is of lesser value in the grand scheme of things but is nonetheless yet another step in the right direction.


No matter what percentage of broadcast programming is pre-recorded, the ‘final assembly process’ is essentially LIVE, 24/7, either under human control / intervention, or automated. Now that all audio is digitized, there is also an opportunity to take advantage of metadata so that each audio stream can be ‘stamped’ with ‘loudness analysis’ so that the last device in the distribution chain can automatically change levels without altering the intended dynamics.

Since LPCM is not delivered to the consumer, it’s Dolby Digital that we’re talking about here. The metadata value – dialnorm or Dialog Normalization – has been around ever since AC-3 has existed. Trouble is, that approach of relying on accurate metadata has not worked since Dolby Digital became the mandated codec for DTV some 8 years ago…Hence, the CALM Act! :-(

Yes, you can still game the system (not saying how!) but, that just means that something in the air chain will sit on your mix and make it sound like shite (again). As a wise man recently said, now that loudness should no longer be a differentiating factor, mixers can finally/once again gain audience share by using their ears and skills to make great mixes that stand above the rest in terms of all the metrics other than loudness.


Now that managing audio broadcast levels has become a ‘law,’ the process is much more complicated, i.e., when between-program breaks become ‘interstitials.’ Can you tell I am still LOLZ about that new vocabulary word?

It is never too late to have an increased awareness of how your piece of audio fits into the larger sonic puzzle. And yes, there is software to assist in the process. This is not an endorsement, but someone has to do it. Batch processing will assist in this monumental task.

Even public radio has great difficulty getting a consistent balance between presence / intelligibility and proximity effect from its many human sources – and we generally think of this institution as having higher audio standards. This tangent was a column topic in past years.

Mastering any of the audio arts requires a higher understanding of Loudness, Proximity Effect and the ability to monitor – aurally and visually – the full audio spectrum, from the harder to hear frequencies below 160 Hz to the potentially painful octave from 2.5kHz to 5kHz. It applies to all audio disciplines.

My thanks to OMas for the audio standards enlightenment!

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