Digital audio broadcasting or DAB is the newest form of broadcasting
audio signals in digital form. Broadcast radio has now been in use
since the 1920s, and up until now has remained largely based on the
analogue "amplitude modulation" (AM) technology and the "frequency
modulation" (FM) technology introduced in the mid-20th Century. The aim
of converting to DAB radio is to result in higher fidelity, greater
noise immunity, the use of new services and the access of many more
radio stations throughout the world.
DAB radio works by using both MPEG and COFDM (Coded Orthogonal
Frequency Division Multiplex) technology to convert music and speech
from analogue signals into digital (binary) code. This greatly reduces
the potential for the broadcasted signal to be corrupted during
transmission by the effects of weather conditions or local sources of
interference.
DAB radio signals are broadcast in blocks called "multiplexes", each
carrying a multiple of services. One multiplex takes up approximately
the same amount of air space as one FM station. The way in which these
DAB radio “multiplexes” work means that the amount of stations locally,
regionally and nationally which you can receive is greatly increased
without any loss of quality.
Apart from the huge increase in choice of radio stations and the much
improved sound quality of DAB radio, “multiplex” technology can be run
through a single frequency. This means that if you’re listening to a
national station such as BBC Radio 4 and you drive from Lands End to
John O’Groats the radio never has to switch frequencies and therefore
you have a perfect signal all the way. With existing FM services BBC
Radio 4 has around 50 distinct FM frequencies, most of which are
recycled in different areas of the country. On DAB it has one, which it
shares with 10 others resulting in a seamless signal constantly without any sort of interference.
