Frequency Finder UK - The future of DAB

With DAB receivers now available for less than Ł50 and the number sold in the UK approaching 1 million, DAB is finally starting to take off. The benefits of new station formats and better sound quality for AM stations are clear. However, for DAB to overtake FM as the dominant medium for radio listening in the UK, three main problems need to be solved.

Sound quality

With the current generation of MP2 audio coders used for DAB, a bit rate of at least 160 kbit/s is needed to give a sound quality comparable with a typical FM station. However, most DAB stations in the UK broadcast at only 128 kbit/s. When listening on a hi-fi or headphones, the difference is noticeable, with DAB sound flat and lacking at the high frequency end of the spectrum. New MP2 audio coders were installed on the BBC multiplex in Spring 2005, bringing a small improvement. However, this has not solved the audio quality problem. Ideally, a new national multiplex should be set up to take some of the national stations off the BBC, Digital One, local and regional multiplexes so that most music stations can broadcast at 160 kbit/s. Due to potential interference from France on channel 10 along the South Coast and the current use of channel 11A for radio microphones, it may be necessary to move the current 12A multiplexes over to 10A/B/C/D to make way for a the new national multiplex on channel 12A. DAB sound quality is discussed in more detail here and other solutions to the problem are discussed here. A long term solution is to change the audio coding standard. However, this would require new receivers, so would take many years to implement.

Reception

The two national DAB multiplexes now cover 85% of the population, giving better reception than FM in many places. However, not only is there another 15% of the population unserved, but a significant proportion of those officially covered have poor indoor reception. The capacity to increase transmitter powers is limited by the need to avoid adjacent channel interference and by international agreement. Clearly, a lot of investment in new transmitters is needed to give widespread robust coverage.

For the local multiplexes, reception is often poorer due to the use of lower power transmitters and potential interference from other multiplexes on the same channel. Spreading the local multiplexes over more channels would alleviate some of the co-channel interference and allow higher power in places. However, this would limit the space for introducing new national stations or improving sound quality. Therefore local multiplex operators should be encouraged to solve the problem by building new transmitters.

Programme choice

To appeal to the maximum number of listeners, DAB must offer all of the main programme formats. Many of the most popular formats, such as contemporary hits, oldie, dance and modern rock, are available only on local multiplexes. However, many parts of the UK, such as Derby, Gloucestershire, Herefordshire, Milton Keynes, Northamptonshire, Oxfordshire, Suffolk and Worcestershire have no local multiplex due to lack of frequencies. Priority should be given to extending the local multiplex network to wherever it is economically viable.

In the longer term, new formats will be developed and space will be needed for them on the DAB system. A further national multiplex would provide services for the maximum number of people with the minimum requirement for spectrum. The introduction of a national multiplex for improving choice (as opposed to sound quality) should be delayed until the turn of the decade, both to allow the current tranche of digital stations to establish themselves and to provide time for new formats to develop so that new stations genuinely extend listener choice, rather than simply copying existing stations.

DAB choice
DAB reception
DAB sound
DAB receivers
How DAB works
Digital index

Ofcom FM licensing 2004
Ofcom DAB and AM 2005
Future of FM
Future of AM
BBC music radio
Features index