Media UK

DAB digital radio

While technically DAB means 'Digital Audio Broadcast', in the UK this term is generally used to refer to the Eureka 147 standard of terrestrial digital audio broadcasting, or 'T-DAB'. A multimedia version, T-DMB, also exists in some areas of the world.

One of a number of analogue and digital radio platforms in the UK, DAB Digital Radio offers a number of claimed benefits for listeners over analogue:

• Improved choice. Many digital-only channels are available, from the BBC and commercial broadcasters.
• Easy tuning. Stations are identified, on-screen, by name. You don’t have to remember what frequency they’re on.
• Same frequency, same quality, wherever you are. Once you’ve chosen your station, it will stay tuned to it all the time within the transmission area.
• Better sound quality than AM broadcasters, and interference-free from pirate broadcasters on FM.
• On-screen info, including information on currently broadcasting shows and songs.
• Mobile reception. You can get DAB digital radio in the car, in the kitchen, on your PC, on personal stereos and mobile phones.

Sound quality

While DAB digital radio sounds excellent at the originally-envisaged audio quality of 320k or more, a lack of available frequencies combined with a general explosion of media choice has resulted in a reduction of bitrate per station to add more choice, therefore reducing the quality of the transmissions.

For a system that was first sold on its 'CD-quality sound', the audio quality of DAB Digital Radio has come under intense scrutiny in some quarters. Some audiophiles report sound quality "worse than FM". In the main, this is true: a perfect FM signal will always sound better than a perfect DAB Digital Radio signal. However, perfect reception for FM is difficult, and normally requires an external antenna and an absence of interference from buildings or pirate broadcasters, neither of which is particularly possible in most urban areas.

Definitions of 'quality' are difficult, particularly with audio, which can only be subjective. DAB offers a much higher signal-to-noise ratio than FM (there's no hiss), and is more tolerant of less-than-perfect reception; however, all digital audio suffers, to a greater or lesser degree, from artifacts introduced in the encoding process. Because of the generally low bitrates used, DAB suffers a little more than other radio platforms.

Because DAB is a digital medium, audio problems caused by low signal strengths are more obvious: from 'bubbling mud', caused when the inbuilt error-protection is beginning to break down, to complete loss of programmes.

Certainly most agree that DAB Digital Radio gives a user more local choice than any other format, in what most listeners see in independent tests as better than average sound quality; and DAB is almost universally acknowledged to sound far superior to an AM analogue transmission.

Reception

DAB's digital signals are, in general, "either there or they're not" - that is to say, a sufficiently strong signal should generate perfect reception, while a weak signal will generate either unpleasant audio or silence.

While in-car reception, for users with a suitable antenna, is surprisingly good, Digital One are currently increasing the number of transmitters with a view to achieving improved portable reception. This work was completed within the M25 in July 2005.