The Future Is Now

What’s really exciting about it, and a little scary, is that it’s actually here. All of those modern surround-capable receivers, and all of those new-fangled “digital” set-top boxes that come from cable or satellite service providers, any receiving box that includes Dolby Digital decoding also has metadata control capability. And it’s kind of interesting, educational even, to hear it work.

But first, you should go to Dolby’s website and download a really pretty comprehensive PDF called A Guide To Dolby Metadata. This guide describes in substantial detail how Dolby’s version of metadata works. It’s pretty wild. There are about twenty different metadata control parameters (plus a bunch of about fifteen sort of mysterious “informational” parameters), about two-thirds of them concerned with issues of surround downmixing (which is the not inconsiderable problem of mixing surround program down to stereo for the vast majority of end-users). In addition, there is the fairly famous “level adjustment” parameter called dialnorm (formally labeled “Dialogue Level,” which is confusing, because it’s neither about dialogue nor is it a level) and a pretty cool compressor parameter called “Dynamic Range Control,” which offers a bunch of different compressor settings for a pretty interesting looking compressor.

The hard part to keep in mind is, all this DSP is running in parallel in the end-user gear – not in the control room or post suite. Producers now have immense amounts of distributed media power, as in “Hey, lets turn up the level on 30 million TVs by 15 dB for this commercial! Whoa, dude!” or “Whaddaya think? Film Standard or Music Light on the Dynamic Range Control? I kinda dig Music Light myself.” As Dolby graciously puts it, “This control . . . requires the producer to correctly set the metadata parameters because they affect important aspects of the audio – and can seriously compromise the final product if set improperly.”

In the guide, Dolby suggests a series of possible metadata setting templates or arrays, called “Combinations.” There’s one for action films in surround, one for drama, one for mono newscast, a surround music combination, and a combination for Live Sporting Events. I suspect these combinations are being used as default settings in many production houses across the land.

Now, you’d think that the end-users would have the right to over-ride these control settings, and to a limited extent they (uh, that’s us) do. We have volume and mute controls of last resort, for instance. But I was startled to discover that I couldn’t turn off the compressor. Massive compression is often obvious – I had figured it was ham-handed audio somewhere in the production line, but now I have to wonder if it isn’t my set-top box. More investigation is called for.

In any case, it seems pretty benign right now. In a direct comparison between a set-top feed using digital audio with metadata and a parallel feed using analog cable (I think), there are distinct differences in audio, and the set-top box really seems to deliver a nicer, more uniform audio signal.

But the system is really hard to suss out. Explanations in the manual supplied by the cable service provider barely mention Dolby, do not mention metadata, have terminology that is different than that in the Dolby Guide for the various settings that ARE available, and generally treat the issue of signal processing as non-existent. In fact, there are no explanations even of the input and output jacks on the set-top box.

This makes it practically impossible for the end-user, of course. It also defeats one of Dolby’s goals for metadata, which is, according to the Guide, to provide “unprecedented capability for content producers to deliver the highest quality audio to consumers in a range of listening environments. It also provides choices that allow consumers to adjust their settings to best suit their listening environments.” Now that’s interesting. And bold!

Thanks for listening.

Dave Moulton is still trying to program his VCR. You can complain to him about anything at his website, moultonlabs.com.

Post a Comment