- Posts tagged BBC HD Audio
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Metadata: Getting it right, even when it's wrong.
Well, today is my last official day working on BBC HD audio. Somehow I don't think this project will leave me alone just yet, but after a week's leave, my main focus will be elsewhere. So I thought I'd take the opportunity to talk about something which has consumed a fair bit of my time, but which I haven't blogged much about: metadata. For the uninitiated, metadata is "data about data". A photo's metadata for example might tell you what camera it was taken with, where it was taken, what exposure was used and so on. In the case of BBC HD's audio, metadata is carried by the Dolby E and Dolby Digital streams we use, and has two main functions: it describes the audio being carried, and it controls the decoders in your homes. One parameter, often called dialnorm (for Dialogue Normalisation), tells your decoder how loud the programme is, so that it can attempt to smoothe out differences between programmes and channels to give you a more consistent loudness. Another set of parameters control what happens when your decoder downmixes the audio, meaning when it produces a stereo mix for your stereo speakers from the surround sound we may be sending. It's important stuff, so we have to make sure that metadata survives our distribution chain, and sometimes we even have to add metadata to a programme automatically, which can be tricky. Here's some of the work we've done...
That Syncing Feeling
It's been a long time since I've updated you, for which I apologise. However the good news is this will hopefully be my last post about lipsync issues on BBC HD. That's in part because I'm really running out of bad puns based on the word 'sync', but mostly because - and I realise I'm tempting fate here - we may have got to the bottom of it all. Let me elabourate...
Testing The Test
Last time I told you about the efforts we've been making at BBC HD to get an A/V sync test to your TV in order that you can measure the synchronisation between audio and video in your home TV setup. You'll be very pleased to know that we're done and the test has made it to air! Andy Quested has posted in his blog about how you can use the sync test - and its counterpart the test card - to line-up your equipment. I therefore won't repeat that here, but I wanted to give you a bit more detail about what we've achieved and how.
Don't Forget The Kitchen Sync
Monitoring
Last week was a bit of a busy one for me, dashing around between Kingswood Warren (the home of BBC R&I), Sky and a trip to the BBC's facility in Glasgow (as well as having just returned from a long weekend in Devon) but I just wanted to share with you some of what I got up to last Tuesday. I spent the afternoon and evening with the sound team of Later Live with Jools Holland at Television Centre. I was there to look at their surround sound production and the technology setup they have. It was an interesting insight into the programme maker's view on all this surround stuff, and while there is considerable enthusiasm from the team, it does add to their workload...
Down The Sync?
Last time, I told you a bit about my work looking into multichannel audio for BBC HD. I’m getting settled into this project now, and I’m starting to build a decent map of the Dolby E signal chain. I’ve met most of our technology partners and made contact with a few more. Here’s some of what I’ve found out so far…
It became clear pretty quickly that synchronisation is a big deal in the world of Dolby E. Really there’s 2 issues here:
- Traditional signal synchronisation, whereby video and audio signals' timing is adjusted to match a common reference, causes big problems in a Dolby E environment.
- Like any coding system, the encoding and decoding of Dolby E has latency involved. Therefore matching the delays between video and audio paths becomes critical to ensuring accurate lip sync.
So right now that's what I'm focussing on. Already I've discovered that we've got a number of gremlins in the system, but the folks at Red Bee and Siemens are working hard to make things better. In the mean time I'm getting under their feet asking for piles of information about their equipment setups, but hopefully also contributing in a helpful way too.
Welcome To BBC HD...
