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What Is DAB Digital Radio?
Once upon a time radio was just plain old radio but now it can include
satellite radio, Internet and DAB. DAB digital radio is a new way
of broadcasting radio via a network of terrestrial transmitters.
It provides listeners with more choice, better sound quality and
more information. DAB digital radio is like analogue radio, only
much better. In the UK, the BBC was the pioneer of digital radio
beginning transmission in September 1995. Digital One, the national
commercial radio multiplex operator began broadcasting in November
1999.
DAB is similar to analogue radio but provides high quality listening,
many new stations and no frequencies, making it easier to tune to
stations. There's no interference and no retuning in the car. In
addition there are new features such as text, data and even pictures.
Tomorrow’s DAB digital radios will do more. 'Rewind radio',
record programmes in real time or set a timer, download audio and
data - the technology for all these functions already exits. You
can use an EPG (electronic programme guide) to organise your listening
preferences, save a programme for later, or dig down for more information
on news, finance and sports stories. Each multiplex operator can
allocate 20% of their capacity for data (see below).
If you live in a poor signal area where the FM signal is barely
audible, then DAB may offer you better reception. About 80% of the
UK population (2003 figures) can already receive digital radio.
How Does Digital Radio Work?
Digital radio works by combining two digital technologies to produce
an efficient and reliable radio broadcast system:
An audio compression system, called MPEG, reduces the vast amount
of digital information required to be broadcast. It does this by
discarding sounds that will not be perceived by the listener - for
example, very quiet sounds that are masked by other, louder sounds
- and hence not required to be broadcast, and efficiently packages
together the remaining information COFDM technology, (Coded Orthogonal
Frequency Division Multiplex) ensures that signals are received
reliably and robustly, even in environments normally prone to interference.
Using a precise mathematical relationship, the digital data signal
is split across 1 536 different carrier frequencies, and also across
time. This process ensures that even if some of the carrier frequencies
are affected by interference, or the signal disturbed for a short
period of time, the receiver is still able to recover the original
sound.
The interference which disturbs FM reception, caused by radio
signals 'bouncing' off buildings and hills (multi-path) is eliminated
by COFDM technology. It also means that the same frequency can be
used across the entire country, so no re-tuning of sets is necessary
when travelling, or taking a portable receiver to a different area.
Instead of having a different frequency for each radio station,
digital radio combines several services together in what is called
a multiplex.
The multiplex is able to carry stereo and mono radio channels
as well as services such as text and data. The UK has been allocated
seven multiplexes by the Radio Authority - in the spectrum 217.5
- 230.0 MHz. It is possible to carry more services on this one frequency
allowing the spectrum to be used more efficiently.
The multiplex has a gross capacity of 2,300,000 bits which are
used for carrying audio, data and an in-built protection system
against transmission errors. Of these about half the bits are used
for the audio and data services. Throughout the day, the data capacity
allocated to each service can be varied by the broadcaster.
Each multiplex can carry a mixture of stereo and mono audio services
and data services too; the number of each dependent on the quality
required. A multiplex is a technical term used for "a number
of stations sharing just one frequency to transmit its services".
It is a digital transmitter located within a region broadcasting
stations operated by a company or group (e.g. BBC, Digital One,
Switch Digital etc).
A multiplex can broadcast data as well as sound. An example of
a receiver is a product available for desktop PC's - the Wavefinder
from Psion. There are two channels available on DAB currently broadcasting
data. These are Digizone and BBC Vision Radio. Digizone is an interactive
service where users can play games and interact with radio stations
broadcasting on the Digital One commercial multiplex. BBC Vision
Radio is a data station broadcasting world news, weather updates,
sport and business news, travel updates and also programme details
of all BBC Radio stations. These services can only be received via
a Wavefinder or Digital Radio PC card.
So what are DAB's benefits?
Quite simply... more choice! Listeners in most major towns and cities
in the UK can receive between 30 and 50 radio stations with digital
radio, in many cases that's more than double what's available on
analogue. And it's not just more of the same - the content within
that choice of stations is unique and exciting, delivering station
formats that just don't exist on analogue. The FM spectrum is so
clogged right now that there's no room for new stations that would
expand listeners' choice with, for example, soul music, or country
music, or big band swing, or any of the other 100+ brands that are
available uniquely to DAB.
More Information! Digital radio receivers have a screen on which
stations can transmit information via Dynamic Label Segments (DLS).
Some stations already transmit the latest news, travel, and weather,
what's on now and next, Web site addresses and phone numbers. Tomorrow's
radios will offer much more sophisticated data. The potential for
advertisers to use the DLS facility on DAB for targeted advertising
is an exciting prospect, and in the future, advertisers can use
DAB to deliver Internet-type commercials.
Because digital radio uses the spectrum more efficiently than
analogue, it is possible to broadcast more channels using the same
frequency, making room for broadcasters to expand their station
portfolios.
It also offers less noise. DAB digital radio delivers improved
sound quality. The technology allows the receiver to lock on to
the strongest signal it can find and ignore everything else. This
eliminates the hiss, crackle and fade so familiar on analogue radio.
With DAB digital radio there are no frequencies to remember and
sets are tuned by station name. National stations stay put, so there's
no retuning on the move.
DAB Is Gaining Strength
The BBC turned on the UK's first digital services eight years ago
and four years ago Britain's first new commercial digital radio
stations took to the airwaves. In addition, 2002 saw the arrival
of the first sub-£100 pound digital radios. This is a far
cry from only two years ago when prices were high and interest and
awareness among the general public was low. At that time there were
only 24 digital radio stations in the UK. Now there are more than
100 and 80% of the country can receive digital radio stations.
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