Government consultation proposes to allow more mono stations on DAB

28th April 2006

The Department for Culture, Media & Sport (DCMS) have launched a public consultation that proposes to increase the amount of DAB multiplex capacity used for non-audio services from 20% to 30%, primarily in order to allow BT to launch their BT Movio mobile TV service on the Digital One national commercial DAB multiplex later this year, but the 30% limit will apply to all multiplexes.

As the sub-sections of the consultation paper below show, BT's planned mobile TV service will require two stereo radio stations to be reduced to mono to fit the new service in.

The consultation paper fails to mention, however, that the Primetime radio station will cease transmitting on the Digital One multiplex in May, because Digital One refused to renew their licence, which can only have been to make way for the forthcoming launch of the BT Movio mobile TV service.

Here's the pertinent sub-sections from pages 3 & 4 of the DCMS consultation paper (308 KB):

"8. For instance, BT Wholesale have begun to develop a service, known as BT Movio, which uses the data capacity on the national commercial multiplex to provide TV services to a hand-held device which can also be used for telephony and to listen to DAB radio. BT research, from the trial with Virgin Mobile, indicates that, to be a compelling proposition to consumers, the service needs at least five TV channels as opposed to the current three. This could be achieved if the data limit were increased to 30%.
9. We are concerned that any increase in the data limit should not lead to a reduction in the number of services offered on the national multiplex. In order to increase the amount of spectrum available for data, we understand that Digital One, the multiplex operator, is proposing to broadcast one of its current services in mono (as permitted by its licence), and to ask Ofcom to allow it to broadcast a second service in mono. The second service will revert to stereo in 18 months time when technical changes introduced by BT will mean that its service can be carried on less multiplex capacity than is required at the outset. It is on the understanding that Ofcom will not agree to any reduction in the number of services broadcast on the multiplex, and will time-limit the reduction to mono, that we are proposing to increase the data limit to 30% of the multiplex capacity."

So, Ofcom and the government think it's a good idea to reduced two stereo radio stations to mono to squeeze mobile TV onto a DAB multiplex. And they say that one of the two stereo stations that will change to mono will revert back to stereo after 18 months, but anyone that knows anything about the way that Ofcom and the commercial radio groups work will know that even if the station does revert back to stereo it will do so at a lower bit rate, and hence at a lower audio quality than it currently uses.

If you are against allowing more mono radio stations on DAB then you should respond to this consultation.

To be honest, though, there's already lots and lots of music stations that are transmitted in mono on DAB, and DAB became a system that is only suitable for small portable radios a few years ago, so a couple of radio stations changing to mono is just an extension of the dreadful audio quality already broadcast.

Another interesting thing about the above plans are that they want to squeeze five mobile TV channels into 30% of a DAB multiplex. But BT Movio's DAB-IP service has to use stronger error correction than the DAB system uses (the DAB-IP system will use an "outer layer" of error correction coding, called Reed-Solomon coding, on top of the inner layer of coding that the DAB system provides) to make transmission of video possible. So taking the additional error correction into account, the 30% capacity of the DAB multiplex allows the five mobile TV channels to be transmitted at just 64 kbps! This is an utterly laughable bit rate to use for a channel that includes both video and audio and the picture quality and audio quality of these mobile TV channels can only be utterly appalling.

But hey, the UK is already the sewer of the world when it comes to digital broadcasting – we use the worst digital radio system, the worst mode (2K whereas everywhere else uses 8K) on our digital terrestrial TV system, the DAB bit rates are the lowest anywhere in the world and the bit rates on digital TV have been falling over the last year or two.