DAB - Digital Audio Broadcasting

DAB stands for Digital Audio Broadcasting and is a method for the digital transmission of radio signals. DAB is the transmission technology of the future and will replace FM radio in the medium to long term.
The DAB method was developed in Europe within the framework of EUREKA project 147 and is currently being introduced in a large number of countries. The DAB standard has been adopted by all European countries, Australia, a number of Asian countries (Singapore, Taiwan, South Korea, China and India) and some countries in the New World (Canada, Mexico, Paraguay).

 
The only exception among leading nations is the USA, which has launched a digital-radio standard of its own called IBOC (In Band On Channel). Information on the IBOC situation in the USA is available from the Federal Communications Division FCC; technical details are available from the iBiquity Digital Corporation.
The country with the widest availability of DAB is the UK. About 85% of UK households can receive DAB, and the number of DAB radio stations is now more than 400. A recent survey shows that more than a third of the UK population knows about DAB technology.

How DAB Works

First, the analogue acoustic signals must be digitised, i.e. converted to series of zeros and ones, and then processed in the following three steps for optimal transmission:
Any sounds that are out of the range of human hearing are filtered out before transmission. The method used to achieve this is called MUSICAM (Masking Pattern Adapted Universal Subband Integrated Coding And Multiplexing) and results in a significant reduction of the transmitted data without impairing the listening experience.
Next, a so-called multiplexer attaches supplementary data to the signal. Since transmission is digital, it is irrelevant whether it is sound, text or images that are broadcast, so with DAB it is possible to relay not only audio signals, but also to forward to the receivers' displays useful supplementary information (e.g., song titles and interpreters) in dynamic text form, so called Programme Asscociated Data (PAD). One example of PAD are Dynamic Labels (information like song titles etc. that is transmitted in dynamic text form to the display of the DAB receiver). MOT (Multimedia Object Transfer) even makes it possible to transmit multimedia data (e.g., images from CD booklets).
Another option is to provide data services that are independent of radio broadcasting, so-called NPAD (Non Programme Associated Data), e.g., information on the arrivals and departures at an airport.
In the multiplexer, the signal can be combined with the digitised signals of other radio studios and converted to a uniform data stream (also called "package" or "ensemble").
In a final step, the digital data stream is split into small units and chronologically nested. At the same time, error protection is added, which ensures that erroneous and missing packages can be reconstructed or extrapolated. This erro protection level is assigned a specific value (usually 3 or 4). The lower the value, the better the protection level.
From the broadcasting locations, these small units can be transmitted in the form of a single frequency block at 1.5 MHz. The individual packages are distributed across up to 1,536 "sub-frequencies" or carrier frequencies. This modulation procedure (which is called COFDM - Coded Orthogonal Frequency Division Multiplex) greatly reduces interference.
The receivers are equipped with built-in Viterbi decoders which put the digital signal in the correct chronological order and check the signal for transmission errors. Finally, the digital data is converted back into analogue sound that can be heard by the user.


Advantages of DAB
DAB offers great advantages over today's VHF, medium-wave, long-wave and short-wave transmission:
With DAB, ten radio programmes can be broadcast on a single frequency.
As long as a given DAB receiver can pick up the signal sent out by a broadcasting station (even if the signal is very weak), sound reproduction is ensured. There is none of the fading (weakening of the sound) that is typical of VHF reception; the DAB signal is reproduced at a constant volume. If the signal is too vague to be interpreted by the receiver, reception is interrupted completely or the device switches over to the appropriate VHF frequency (if possible).
Interference such as that which can be caused by power lines are filtered out by the DAB receiver. Such noises should simply not occur; as indicated above, reception is either excellent or not available.
Interference caused by stations that are on close frequencies – a phenomenon that is typical of VHF – does not occur in connection with DAB.
If the signal is reflected by natural obstacles or buildings, the reception quality of DAB is improved due to the multiplication of the signal, whereas VHF reception is considerably worsened in such cases.
In addition to audio signals, DAB offers a wide range of supplementary services, including the transmission of song titles, interpreters, images, CD booklets, etc.
Many newer receivers have attractive auxiliary features that offer a completely new radio experience: a pause button that allows the user to stop the programme a nd restart it at the same place, the possibility to record favourite programmes and a programming function that allows specific programmes to be flagged for recording before they are broadcast.

What You Should Know Before Buying a DAB Receiver
First check and see if you can receive DAB where you live or drive.
If possible, buy a receiver that can pick up both DAB and VHF/FM. Many devices have other attractive features such as built-in MP3 players, a record/rewind function, etc.
Due to the relative weakness of today's DAB signals, in-house reception is not yet completely satisfactory; the quality may vary significantly depending on the position of the receiver within a building. If possible, first try and see if you have adequate reception.
An additional antenna installed on the outside of your home may give you better reception provided you are in an area that has reception at all. Installing such an antenna is expensive and should not really be necessary.
If you are interested in buying a car radio, you should note the following:
In addition to a DAB car radio, you will need a DAB antenna and a connector cable.
There are two kinds of antennas available: roof antennas and windscreen antennas. A windscreen antenna is usually sufficient, but a roof antenna offers better reception, especially when the DAB signal is not very strong.
The connector cable should be as short as possible; a long one may impair reception.
Depending on the model of your car, installation of the antenna and cable may be awkward (for example, DAB reception may interfere with the car's electronics). It is advisable to find out in advance which devices are suitable for your needs.

DAB Links

International
World DAB Source of information on DAB around the world.

Danish DAB
DAB Danmark DAB Danmark is an organisation consisting of manufacturers, distributers, dealers and radio stations. There aim is to increase public awarness of DAB in Denmark.
DR Radio DR's radio section.
DR netradio DR radio channels available through live Internet streams.

Swedish DAB
DAB Ensembles Worldwide Sweden
Sveriges Radio (SR) Swedens Public Service radio broadcaster.
Swedish Educational Broadcasting Company Utbildningsradion (UR) UR is one of three companies within the Swedish public broadcasting system. As part of public service operations, UR provides a wide range of educational programs on TV and radio.

UK DAB
BBC Digital Radio BBC Digital Radio Information.
Digital One Website of the national commercial digital radio operator, full of useful information about national DAB stations.
Digital Radio Now A one-stop guide to DAB in the U.K., coverage, stations equipment and information on in car DAB.
Digital Radio Development Bureau The Digital Radio Development Bureau (DRDB) is a trade body funded and supported by the BBC and commercial radio multiplex operators.
uk-dab.info Website for DAB digital radio enthusiasts.
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