Jay Yeary / Inside Audio
05.05.2014 06:00 AM
The Difficulties of Getting a Great Mix to Air

Jay Yeary
I started mixing for television in the late 1970s, during the good old analog days when TV audio was more of an afterthought than it is now. At the time, we were mixing daily two-hour variety shows live to satellite, with a full band, vocal ensemble and guest artists. We worked very hard to translate the live music into a decent experience for the home listener and it wasn’t easy.

That was when I discovered on-air processing chains and the damage they can inflict on a mix, no matter how carefully crafted it is. Back then broadcast television was all analog, so dynamic range was non-existent and most air chains were set to keep the signal legal, even if it meant crushing the audio to do so. It turned out that the best course of action was to precondition the mix for the air chain by carefully managing dynamics, limiting the dynamic range, and not pushing frequencies that were never going to make it home anyway.

This process mitigated the damage, but mixes still didn’t match the way they sounded in the control room. Then along came digital television, and with it came the promise of finally delivering mixes that sounded the same in the home as they did in the control room. Unfortunately, that promise has turned out to be difficult to realize in practice because of the complexity of the digital delivery chain (Fig. 1). In this column we’ll look at that complexity and what mix engineers can do to get their intended mix to the listener.

PROCESSING IN THE PATH

Fig. 1: The complicated path of television mixes

Creating a great mix can be a challenge, but creating the content is easier than getting it the consumer. As soon as the content enters the broadcast chain, things start to get sticky. Some chains may be set to pass the audio through unaltered, but more than likely there is still processing in the path. It’s there to insure that audio destined for broadcast meets the channel’s delivery specifications, to reformat it if it doesn’t, and to make sure that what goes out is legal.

Some HD networks want all audio to be in 5.1 when it is received, which means that any stereo content will be upmixed to surround. If the upmix device is set up correctly, the newly created surround will sound pretty good in the home. Unfortunately, for viewers listening in stereo or those watching SD channels, the upmixed audio will be downmixed back to stereo, the format it originally started in, but it will not sound the same as the original mix because its soundfield has been altered twice. In this instance, the downmix is inevitable but the initial upmix could have been avoided by delivering the material in 5.1 to start with.

There are some networks that perform gentle air-chain processing, which will still alter the original mix of the content, though not drastically, as it makes its way to the AC-3 encoder (in the U.S.) for its final encode prior to air. Other broadcasters have their air-chain processing set to aggressively control loudness and dynamics of content and commercials to avoid complaints from viewers. Oddly, complaints still come their way, but they’re from content creators who pay attention to how their programs sound.

The trickiest and least controllable part of the process is at the listening end. The best possible world is when viewers subscribe to HD services and have their televisions, cable boxes, receivers, and other devices properly connected to their home audio systems. The reality is that the majority of viewers are not watching HD, even if they subscribe to it, and most aren’t listening through high-quality audio systems. In fact, a lot of home viewers—along with people in airports, waiting rooms, and hotel rooms—end up listening, in stereo or mono, through the speakers in the television itself. That means they will hear the mix through underpowered speakers and may also be listening to processing that has been engaged inside the set. Television manufacturers now include an array of audio processing options, from surround emulation, to sound modes meant to emulate different environments, to automatic volume controls. If any of these processing options are engaged, the audio will be transformed into something new.

MOBILE DEVICES
Content also ends up in a greater variety of places than ever before. Mobile phones and tablets are convenient devices, but they typically have terrible speakers, some only have a (mono speaker), with tiny amplifiers that aren’t capable of much volume. Personal computers don’t sound any better unless decent external speakers are connected, and even then the content is likely to be a limited bandwidth stereo stream. This means that most mobile and streaming television will be heard through headphones or speaker docks, on devices that may also have onboard audio processing engaged.

There are however, a number of things a mix engineer can do to insure that content makes it to the viewer as intact as possible. First and foremost, deliver content in its intended playback format if at all possible. If it will play out in stereo, then deliver in stereo, and if it is meant to be 5.1, then deliver it in 5.1. Delivering in the final format should help avoid unnecessary up or down mixing.

Next, mix to the target loudness of the channel using a CALM-compliant loudness meter (currently BS.1770-3) without abusing the ± 2 dB to either side since that could cause rejection of the content or trigger an air-chain processor looking for this type of variation. Try to limit the dynamic range of the material somewhat, not enough to drastically change the content, but enough to rein in the loudest and softest parts. This will minimize drastic loudness differences between content and advertising.

Finally, it is more important than ever to listen to the mix in every format it will be heard in—surround, stereo, mono—than it is to try and listen to e0p4.032very device it may be heard on. Create a great mix, deliver in the playout format, at the correct loudness level, and pray for a Blu-ray release.

Jay Yeary is a television audio engineer who spends his days working for a large media corporation. He can be reached through TV Technology or via Twitter at @TVTechJay



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