For such a seemingly simple service, pushing out strings of text synchronous to our broadcasts can be a complicated process. LiveText, as it's commonly referred to, is available on FM, DAB, Freeview, FreeSat... and on the web.

The text itself is crafted by production staff in our systems and then we distribute it to these platforms. I specifically wanted to talk here about 'the web' - and our IP delivery mechanism for LiveText - what I call 'LiveText-via-IP'.

You may have noticed that LiveText appears on many of our national radio networks' web sites and we had it on the original Radio Player through a Flash client. When we started this a few years ago, it was an initial offering that would give us some feedback about how we should implement the service fully... and whether we should implement it at all!

Having collated all the feedback, and reviewed the delivery solution - we started to plan a new infrastructure.

Meanwhile - new services that also provide content synchronous to our broadcasts were being trialled - we have previously spoken about our Visualising Radio trials - you can see the parentage from the LiveText service. So delivering other media-types synchronously with our live streams is just as important.

What we needed was a way of implementing an infrastructure that could replace our existing LiveText-via-IP service, making sure we can deliver that and provide a system that is scalable and stable for new services.

Through a tendering process we eventually agreed on picking an open-source protocol and a company known for its expertise for server side implementations. We chose XMPP PubSub as the technology, and ProcessOne as the company. (XMPP used to be called Jabber, just in case you knew it by that name.)

Some of the considerations we had around this tender process:

• we wanted an open-source protocol, to allow anyone to be access it and where libraries for consuming the 'messages' were available in a variety of languages
• if we were going to use open-source, then any development should give back to the community - in the end with ProcessOne's ejabberd server nodes any extensions are fed back into the development of ejabberd and XMPP protocol
• picking anything requires us to investigate the 'pedigree' of such a system - so we wanted something that had evidence of widespread deployment and scale of delivery (how many concurrent users can connect at once) - XMPP hit the mark
• we also wanted some flexibility - so a protocol and server that would allow us to deliver what we need right now (simple text strings), and then grow with our ambitions - the XMPP protocol might seem a little bloated for delivering simple text strings, but as we develop the LiveText service over the next few years it allows us to, for example, mark up different languages, alternative messages for different clients/services. It also lets us provide new services using the same protocol - so the learning curve is lowered and hopefully reusability of code is improved.

So - where can you see this in action right now?

On the websites we have upgraded our Flash-based LiveText clients so they are consuming messages from our ejabberd services. Check it out on Asian Network's homepage.

Our Flash clients are built using the XIFF client library - an open source ActionScript library - we made some tweaks that we're feeding back to the XIFF developers.

There are currently two connection methods for our XMPP service - direct connection through sockets or via BOSH over port 80. If you are behind a firewall that blocks the XMPP ports then your client will connect using BOSH.

If you are using Firefox and have the FireBug addon installed - you can see some comms in the console. If you are behind a firewall which blocks our sockets you will also see activity in the network activity section in Firebug - showing the BOSH connection - just look for 'http-bind'.

We are now referring to our infrastructure solution as 'PushFeeds'. (We couldn't keep referring to them as 'a set of nodes of ejabberd that provides XMPP PubSub and BOSH' - just too lengthy to repeat all the time!)

Coming up - we are looking at other places to put LiveText-via-IP, whether on our websites or syndication locations. Also looking at devices on IP that could support this. And, of course, other services that could take advantage of push messaging like this - I'll take this opportunity to ask any BBC Staff interested to check out our internal wiki pages about the service.

Alan Ogilvie
Interactive Platform Producer, Audio & Music Interactive

Further information:

• XMPP website
• XEP-0060: Publish-Subscribe - the XMPP PubSub specification
• ProcessOne - the company we worked with to setup our service
• XEP-0124: Bidirectional-streams Over Synchronous HTTP - the XMPP BOSH specification
• XIFF Actionscript client library
• XMPP librariesare available in many common languages, if you don't want to write one from scratch.
• ejabberd - the open source server technology behind our service, supported by ProcessOne
• ejabberd developer community - find out how feed into ejabberd development, or make use of the technologies
• BBC Wiki page (Internal) - an internal page for BBC staff to find out about the service. (Link only works from within the BBC network)

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BBC iD is the new sign in system for BBC Online. It's currently being rolled out across all services that require a user to register or sign in. But Radio Labs is in the vanguard and has already switched systems. So if you want to comment on the blog you will need to use the new BBC iD system. If you have an existing BBC membership, you can use your existing membername and password to sign in to BBC iD. The first time that you do this you'll be prompted to upgrade to a BBC iD and update and confirm your personal details.

You can read more and comment on the Internet blog and there is more help on BBC iD here.

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Planet B is a science fiction series on BBC 7, the second series starts on the 29th November. You can read more about series two of Planet B on the Radio 4 blog.

Before you read on, you should put your headphones on and listen to this...

With any luck you should have just had an interesting if not mildly disturbing sonic experience. And - by the way we don't really have your brain on a database; it was all just a sonic illusion..... As with all great Sci Fi special FX techniques it was done using a technique that was created a very long time ago and then re hashed in the 70s. The technique is called Binaural and has more or less been around since the dawn of broadcasting, when the French used it to broadcast operas though the telephone network to paying customers. It was originally patented in 1931 by Alan Blumlein as part of his pioneering research into Stereo for EMI.

Now if your not really interested in recording techniques you can stop reading now, as the rest of this blog will be as painful as sitting next to the really boring guy at a dinner party who talks about how the ABS in your car works...for hours. For those of you who are interested, you can read this and laugh at me, saying 'no, no, no - you so called BBC so called expert, you clearly have done it all wrong!'

Anyway, Binaural is a stereo recording and playback technique that tries to recreate sound in a three dimensional way. Surround sound for headphones. For true modern binaural recordings a 'dummy head' should be used with microphones placed inside replica ears, but there are a few variations on that theme. The basic idea is that two omni-directional microphones are placed a heads-width apart and are separated by a head-like object. So when listened to on headphones the sound appears as it would if you where really there. The drawback is that it only works on headphones and is in no way compatible with summed mono, i.e. the single speaker DAB radio in your kitchen. Also, as it is still just an illusion that tricks your brain, people can experience dummy head binaural in different ways. A common complaint being that all the sound seems to be coming from behind the listener.

A clever person has already written this wikipedia page on Binaural if you are interested in finding out more. And there's more on Dummy Head recording here. And a clear demonstration by a very nice chap on YouTube here. And there are other binaural shorts on You Tube including a virtual haircut which is fun;

BBC Radio Drama did an excellent play using binaural called The Revenge in the 70s with no dialogue. It's totally gripping and well worth a listen if you can find it. There are also many music recordings using binaural including some tracks on Pearl Jam's 'Binaural' album.

For the Planet B Immersive trail you just heard we actually used three different types of stereo. Those being 2 track Mono, L and R stereo and Quasi Binaural stereo.

The Quasi Binaural elements were captured in a few different ways. For the opening scene the voice of planet B says 'Thank you for choosing to upload your brain' while the probe moves around your head - we used two different techniques. For the vocal element I recorded the actress in a standard voiceover way with a Mono cardioid large diaphragm condenser mic; in this case a Neumann U87. This was then played back through speakers in the studio's live area positioned at opposite poles around a Jecklin Disk microphone array. (The disk was chosen over the dummy head for its better compatibility with data compression techniques).

The probe effect in the first scene was achieved by playing back the probe sound FX through a Fostex self powered speaker which was moved around the mic array manually. In the end it took three very quiet people to move the speaker, and my Phillips Shaver for extra intensity.

For the three scenes Spy world, Jurassic Adventure and Operation Extreme Glory, all the vocal elements were recorded using the Jecklin Disk, including the background voices in Spy World and the screaming soldiers in Extreme Glory.

The final binaural elements are the brain removal sequence. We again used the three person Fostex speaker dance for the sawing of the skull. The disk was then replaced by a melon and a coconut. These were operated upon with various implements and much fun was had by those of us listening on headphones to the squishing and scraping.

The rest of the sound design was done in L and R Stereo, and panned Mono using some spatial plugin's. It was all recorded, designed and mixed within the excellent Pro Tools HD. The in-studio SFX playback was done using Spot On play out software. We monitored using Sennheiser HD25-1s and Beyerdynamic DT250s. The recording console was a Studer Vista 6.

For me it was an interesting experiment in sound, combining different stereo techniques to create a unique listening experience. But really it was all down to the BBC Radio Drama Development team in coming up with such an excellent idea, and a brilliantly imaginative script!

Caleb Knightley is a Senior Studio Manager and Sound Designer for BBC Radio Drama.

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