Broadcast Advice for Audio Content Creators

Jay Yeary

The Society of Motion Picture Television Engineers recently announced it would merge with the Hollywood Post Alliance. It struck me as odd that these two seemingly dissimilar organizations would join forces, but in reality, both are in business together, creating and delivering content to appease the seemingly endless appetite of consumers.

Most episodic television shows are still created, shot and finished in Los Angeles, since a great many production companies and top-end talent live and work there. But without broadcasters, cable networks and their many avenues of distribution, much of this content would never make it to homes.

Delivering content that meets a broadcaster's criteria for air can often lead to contentious discussions between content creators and their broadcast partners, and these increasingly seem to revolve around why the audio mix sometimes sounds different in the home than it does in the mix suite. I deal with this regularly on the broadcast side of this relationship and offer some information here that might make things easier for both sides.

CONTENT DELIVERY SPECIFICATIONS

Delivering content that meets a broadcaster's criteria for air has lead to contentious discussions between content creators and their broadcast partners, particularly when it comes to audio mixing.

Production companies have been increasingly exercising their ability to deliver wide dynamic range audio programs that are mixed more like movies than traditional television shows.

Those of us working in broadcasting understand and appreciate the effort that goes into creating quality television, and we do our best to ensure that it reaches homes looking and sounding exactly the way the creators envisioned. Unfortunately this doesn't always happen and there are a number of reasons why.

The usual way things start to go off the rails occurs when a broadcaster's content delivery specifications are not followed, resulting in content that is delivered out of spec. Most networks spend a lot of time developing their delivery specifications to ensure that content gets through the broadcast chain unmodified to maintain the content creator's original intent.

CALM IS THE LAW

The reason LKFS and True Peak now appear in delivery specifications is because there were so many issues with loudness after the move to digital television that consumers complained profusely, prompting Congress to respond with the CALM Act.

The technical document referenced in the legislation is ATSC A/85, which specifies that audio be measured with an LKFS meter and that the dialnorm metadata parameter of the material be set to match this target. Commercials are measured for loudness across all audio channels while long-form content has its anchor element (typically voice) measured for the entire program with dialnorm set to match.

The majority of networks now have a defined loudness target that content must meet as well as a True Peak target, and some stray slightly from A/85 by measuring long-form content across all channels. The loudness of all content must match dialnorm or the specified value set by the network for loudness to be consistent across all programming.

Most broadcasters seek to preserve the original content by relying on proper measurement and delivery, but some have decided it is easier to install devices in the broadcast chain that limit and compress audio rather than worry about whether the audio is in spec.

Regardless, the best way to get unaltered content to air is to properly measure audio with an LKFS meter, using the version required by the network (the spec is updated periodically), and ensure dialnorm and content loudness meet the network's delivery specifications.

SOME THINGS ARE BEYOND OUR CONTROL

Even if a show makes it out of the broadcast chain unmodified, what happens next may be beyond the broadcaster's control. Television audio in the United States is usually broadcast as a Dolby AC-3 encoded signal, which is then often picked up by another provider for delivery to the home (some over-the-air broadcast networks retain end-to-end control).

Everything arrives at the home just fine in most cases, but there have been instances of content being decoded then re-encoded with significant changes including aggressive audio compression made to the original signal. Other issues lie in wait in the home itself where the viewer may be listening to the RF output from the cable box.

This output is a downmix containing 11 dB of gain along with severely limited dynamic range essentially the worst possible version of the audio. Fortunately, dynamic range control (DRC) is available so the home viewer can adjust the dynamic range without compromising the content creator's creative wishes. A DRC profile will need to be authored into metadata and end users must understand how to use this feature in their home system, but DRC has become increasingly important since most home viewers only occasionally want wide dynamic range audio in their home.

DISTRACTED LISTENERS

In a 2003 AES paper (Riedmiller, Lyman, Robinson. Intelligent Program Loudness Measurement and Control: What Satisfies Listeners? AES Convention Paper 5900, March 2003), Dolby introduced us to the concept of the comfort zone, when they presented data showing listeners will tolerate loudness variations of +5.6 dB and 10.2 dB before they reach for the volume control. At +10.8 dB and 19.1dB the loudness differences annoy the listener so much they will change the channel. This means that the average home viewer will only tolerate a maximum dynamic range of 30 dB.

Think about what television viewing is like in your own home and you'll realize that between background noises, other activities and interruptions, it is distracted viewing at its best, so it's no wonder that people prefer consistent au

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