rowan.depomerai

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…

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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…

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It’s been about 3 weeks since I’ve posted anything on this blog other than links to other sites. I just wanted to let you all know that this is down to the immutable law of diaries, journals and blogs:

The amount of time available to write in a diary/blog is inversely proportional to the amount of things worth writing in it.

In other words, I’ve been really busy. I have all sorts of news about BBC HD Audio, and lots of ideas buzzing around for personal posts too. I promise I’ll update as soon as I can, and that I’ll do my best to make it worth the wait!

Thanks.

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. Read the rest of this entry »

A couple of weeks ago I told you about the work we’ve been doing on the synchronisation of audio and video (lipsync) in our surround sound signal chain. However, no matter how much work we do, there’s one thing we can’t control, and that’s the equipment in your front room. You might not know this, but your shiny new flat-screen TV (LCD or plasma) introduces somewhere in the region of 40 to 100 milliseconds of delay, which means that if your audio isn’t delayed to match, the sync between the two is quite considerably wrong. Worse still, the audio is ahead of the video, which is much more noticeable than the sound being late.

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