| Technology - DAB Radio
As predicted in the last magazine Toshiba has discontinued its HD DVD products, handing victory to rival high definition disc format Blu-ray Disc. So is there another technology whose future is uncertain?
Recently in the media news there has been a lot of talk about DAB radio and its future, or lack of it. What does it mean for us in Northern Ireland?
Digital audio broadcasting (DAB) is meant to be the way forward for radio. How it works can wait until later, but the perceived benefits include:
- Very easy station location using a simple menu and station name display with no 'tuning'
- New stations not available on FM or AM are available on DAB: e.g. specialist music, news, sports, spoken word, comedy
- A fairly wide choice of radio stations, particularly in city areas
- Good reception is possible in areas of good signal strength
- No AM type crackling or buzzing and no FM type hiss and distortion
- Quite good sound quality is possible (but generally audio quality is poorer than FM)
The details of how the sound gets from the microphone in the studio to the loudspeaker in your receiver is too technical and complex for a parish magazine. The only difference to be concerned about with DAB, as compared to your standard AM and FM signals is due to the letter D – Digital.
As with CDs the level of the sound being recorded is sampled or measured very quickly and the value converted to a number that is then recorded. In play back the numbers are read and converted into the original sound. Because we are dealing with numbers we refer to it as digital. For a CD the sound is sampled 44,000 times a second.
Exactly the same principle is used with digital photography, but instead of sound the level of red, blue and green light at points in the picture are recorded. In your camera these values are usually immediately combined to reduce the size of the memory required to store the picture. This leads to some loss of quality and results in the JPG picture that you get. It is also easily observed that the more samples that have been taken, or the number of picture elements (pixels) the better the photograph.
DAB radio is no different. The sound is sampled and exploiting the characteristics of hearing the amount of information that has to be transmitted so that the sound can be recovered at the receiver, is drastically reduced. Once again the quality suffers due to this process.
There are different ways of compressing and reducing the information, identified by such terms as MP3 (really MPEG-1 Audio Layer 3), MPEG-4 and JPEG. At the moment DAB radio uses MP2 or MPEG-1 Audio Layer 2, and here is a problem waiting to happen.
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The other thing that is very different about DAB radio is that there are no stations to be tuned to. No longer will there be such memorable numbers as 208. The few broadcasters doing DAB, broadcast an ensemble or multiplex of stations all going out at the same place on the dial, to use the old term, or more correctly on the same channel. There could be up to 12 stations on each channel.
But each channel, like a water channel can only carry so much. If, to keep sound quality high, the original sound is sampled very quickly, it creates lots of information and so not as many stations can use the channel. This is just the same as the number of digital photographs that can be stored on your camera depends on the resolution that the pictures are taken at.
Better photographs means less pictures: better sound means less stations!
The broadcasters want to have as many stations as possible and so the quality of many of the stations is not very high. If the station is mainly speech, say a news station, then the quality can be reduced without being noticed. If it is classical music then is may not be adequate.
However there is a way forward. The amount of information that needs to be transmitted depends on the way in which the original sound has been compressed. If there is a better way of compressing the original, then better sound can be achieved for less information.
The better way is to use a form of MPEG-4 and create what is called DAB+. Unfortunately DAB and DAB+ are not compatible so yet again there are two competing standards. The Communications regulator Ofcom has no plans to allow broadcasters to adopt the new DAB+ standard in the UK at the moment, but this could change in the future. If the broadcasters and regulators do drop DAB in favour of DAB+ it's unlikely that current digital radio owners would be able to upgrade their model to receive the DAB+ signal. Make sure that any DAB receiver you purchase can be upgraded.
If you do want the latest technology and decide to acquire a DAB radio, make sure that it can be upgraded to DAB+ and if it is portable you have a large battery. Typically on a single charge, with DAB you get between one-sixth and one-twelfth of the time that you would have when in FM mode. This is due to all the processing it has to do.
From the two BBC multiplexes in our area you can expect to receive:
BBC Radio 1, BBC Radio 2, BBC Radio 3, BBC Radio 4, BBC Radio 5 Live,
BBC Radio FIVE LIVE Sports Extra, 6 Music from the BBC, BBC7,
BBC Asian Network, BBC World Service, 1Xtra from the BBC
and may be able to receive:
BBC Radio Ulster, City Beat 96.7, Classic FM, Cool FM, Downtown Radio,
Heat, Kiss, Q102.9, talkSPORT
The latest, but is it the greatest?
Alan
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