Frequently Asked Questions (FAQ)

• Quick Facts About DAB

  Over 500 million people around the world can now receive over 1000 different DAB/DMB services. Commercial DAB receivers have been on the market since summer 1998. There over 930 different DAB and over 180 different DMB receivers commercially available and the numbers continue to rise.

• Can you sum up DAB for me?

  DAB stands for Digital Audio Broadcasting. DAB is a digital radio system, which was developed by the Eureka 147 Project. It offers near CD-quality sound, more stations, additional radio and data services and therefore wider choice of programs, the ease of tuning and interference-free reception for the listener, plus the information potential of data, graphics and text. For the broadcaster, DAB provides a means of reaching listeners with sound quality on an equal footing with the CD player, and the ability to offer extra, potentially revenue-creating, services. Transmission will also be cheaper. For other areas of industry, there will be a new market for receivers and transmission equipment.

• Can you sum up DMB for me?

  DMB stands for Digital Multimedia Broadcasting. DMB uses the same infrastructure of a DAB network. This means that by simply adding a video encoder to an existing DAB network one can also transmit DMB. DMB offers new multimedia applications such as: mobile TV, picture radio, data services and new audio applications.

• Can you sum up DAB-IP for me?

  DAB-IP is based on the DAB system, however it allows new applications for the user, such as mobile TV. DAB-IP sends information via 'packet mode,' which is its main difference with DMB.

• What is wrong with FM and AM?

  We live in a digital world. Just about every communication process we engage in, from making a phone call to booking an airline flight, is in the digital domain. FM was invented in the 1940s, AM in the 1920s. So radio is using a delivery system that is anything up to 70 years old. DAB therefore is taking the oldest of broadcast media into the digital age. Furthermore DAB Digital Radio has many advantages and benefits for all concerned.

• Why does DAB sound better than today's conventional radio?

  Digital Audio Broadcasting provides crystal clear sound that is comparable to near CD quality - you can hear music as though you're in a first class concert hall, or listen to a discussion programme as though you're right in the studio. Remember what vinyl LPs sounded like compared to CDs? That's the difference between analogue radio (like AM and FM) and DAB. DAB is almost immune to the sort of interference that can make listening to today's conventional AM or FM radio less than satisfying. If you listen to FM in the car, you may have noticed hisses and plops as you drive along. That's caused by multipath interference when the FM signal bounces off buildings, trees and hills and arrives at your receiver out of phase with the main signal, confusing the transmission. But DAB is revolutionary because inside the receiver is a computer which sorts through the myriad multipath signals and other distortions to enhance the main signal. This means that even in the most difficult listening environments-like the centre of a city with high-rise apartment and office blocks-the DAB signal remains absolutely perfect. DAB receivers are intelligent.

• Are there other benefits for listeners?

  Absolutely! Because a digital receiver is a 'smart' set, it can do much more than simply pick up radio programmes. For a start, all radio programmes are identified by the station's name, rather than a difficult to remember frequency. The name appears on the digital display of the DAB receiver, and you can push a simple 'up' or 'down' button to scan through all the programmes that are on the air (with the name of each displayed), to find the one you want. More sophisticated sets will have large liquid crystal screens which can list all the stations that are on the air, making selection even easier. Once you have selected a station, your DAB receiver will stay tuned to it all the time, even if you are driving. You will not have to constantly retune to keep listening, because DAB radio uses a Single Frequency Network. National stations - like France Info in France or BBC Radio 4 in the UK - are transmitted on the same frequency in Bordeaux or Paris, London or Glasgow. It's another of the fantastic benefits of DAB and it means that less frequencies are used, which will allow more radio services to be transmitted.

• Can a DAB receiver find me types of programmes?

  DAB offers a special feature called Electronic Programme Guide (EPG). Some broadcasters will transmit extra data along with the radio programme, which identifies what sort of programme it is-for example, Classical Music or News. You can ask your DAB receiver to search for all the radio programmes which match your request- like Top 40. It will find the programmes that have that identification.

• Will there be other information too?

  All DAB receivers have digital displays (including some with large liquid crystal screens), and broadcasters will have the option to transmit additional programme-associated data (or PAD for short). This may include comprehensive information about a piece of music being played, such as the song title, composer, singer, album name and number and so on. The lyrics of an opera could be transmitted while it is in progress. And commercials could have accompanying text messages with more information about special offers, or contact phone numbers. Since DAB is digital, any information that can be digitised could be transmitted on DAB. Other services that are already being implemented include text-based traffic and weather information, emergency warnings, paging services, financial services like stock market reports and exchange rate news. DAB offers exciting new possibilities - let your imagination run free.

• I've heard that digital television is going to offer pay TV services; will DAB also have pay radio services and will DAB offer pay TV services?

  Because DAB receivers are intelligent, they can be configured to include Pay Radio services. Some broadcasters might offer special concerts available only on payment (because DAB is flexible, new services like Pay channels-or extra conventional free-to-air channels-can be added without having to switch off the ones already on the air) which you would subscribe to on an individual or long-term basis. Specialist financial services might also be available on subscription via DAB. -DMB services can also be free to air or pay services. For example, in Korea mobile TV, via DMB, is free to air. However, in Germany mobile TV, via DMB, is based on a subscription fee.

• Does DAB offer benefits for broadcasters?

  Broadcasters will accrue many benefits from DAB/DMB. Audiences will be able to enjoy better reception and find individual stations more easily-that means less complaints are likely to be received about these two topics! The near CD-quality sound that DAB offers means that radio will once again be able to directly compete against the perfect audio quality that the domestic CD or the very high quality cassette can reproduce. Unless broadcasters exploit this, they will lose listeners, particularly the younger generation, to these personal high-quality entertainment sources. Broadcasters will be able to offer more services, since DAB is flexible. Each package of radio stations (known as an ensemble) can be reconfigured at any time to allow new services to start and others to end. Extra sports commentaries can be added when matches start, or live classical music concerts can have extra digital capacity allocated to ensure that audiophiles receive the ultimate sound quality. Transmission will be cheaper, too. DAB can be transmitted at lower power than today's FM and AM signals yet with no loss in geographic coverage, which means less cost to the broadcaster (and less power consumption means DAB is more environmentally friendly than conventional FM and AM). Another advantage of digital radio transmission is that it is a cost-effective and powerful advertising medium.
  With the further multimedia applications, which can be placed into an exisiting DAB infrastructure, DMB offers broadcasters even more opportunities. These include: mobile TV, data applications, traffic and safety information, new advertising channels and many more.

• Does DAB use the same frequencies as today's radio broadcasting?

  DAB can be transmitted on frequencies from the FM band (88 MHz to 108 MHz), but the services that have been introduced in Europe, Canada and Australia, together with pilots in India, are using other frequencies. Many countries (including the UK) are using Band III (around 221 MHz), formerly used for black and white television signals. Others like Germany and Canada are using L-Band (1452-1492 MHz). DAB receivers currently on the market can receive both Band III and L-Band transmissions. A goal of industry and government is to see all radio broadcasting moved away from the existing FM band which could then be auctioned to commercial users of the radio spectrum (mobile phone operators, for example). In 2006, the World Administrative Radio Conference, which is the internationally recognised meeting that assigns all the world's radio spectrum usage, allocated the L-Band frequency range to digital broadcasting and also granted more frequencies throughout Europe for digital broadcasters. (Please click here to download frequency charts that display which channels are allocated to DAB technology).

• Who else benefits from DAB?

  Apart from listeners and broadcasters, key beneficiaries of this new technology are consumer electronic manufacturers and transmitter manufacturers. Listeners will have to buy new DAB receivers for the car, at home and mobile devices, which will provide a huge increase in sales for receiver manufacturers around the world. Electronic chip manufacturers also benefit because the chip forms the heart of the DAB receiver. In addition, broadcasters need new digital transmitters to send DAB to the consumer. DAB can help revitalise industries around the world.

• Where can I find DAB services on the air?

  DAB/DMB Services or pilot projects are running in many countries, including Australia, Belgium, Canada, China, Finland, Denmark, France, Germany, India, Italy, South Korea, Mexico, The Netherlands, Norway, Spain, Sweden, Switzerland. The BBC in the UK has a transmitter network that covers 90% of the population and the commercial coverage currently reaches 85%. New programmes and services are launched all the time. Visit the Country Updates section of our website for current details, or contact the WorldDAB Project office for more information.

• Why is there no interference on DAB, even in the case of mobile reception?

  DAB combines a number of processes to achieve this:

  • Most interference during mobile reception is caused by multipath reception and the Doppler effect. Multipath reception means that at the receiving antenna the directly received signal and portions of signals reflected from buildings and hills overlap each other, thus causing frequency-dependent interference. The Doppler effect occurs with vehicles in movement and causes slight frequency shifts, and this can lead to time-dependent interference. DAB uses up to 1536 carrier frequencies distributed over a 1.5 MHz-wide band rather than just one carrier frequency (as in the case of VHF-FM). This means interference only affects some of the carriers, and the majority are always received noise-free (OFDM).
  • Another consequence of multipath reception is that direct and reflected signal components reach the receiver at different times. The bits for transmission are transmitted in groups, known as 'symbols'. In multipath reception intersymbol interference occurs, i.e. symbols adjacent in time overlap each other due to the signal components arriving at different times. To prevent this disruptive intersymbol interference, the symbol duration is lengthened by a guard interval at the DAB transmitter. This provides the receiver with a clean symbol since it delays using the signal until the interference caused by overlaps has ended.
  • For each useful bit, 1 1/3 ... 4 bits are transmitted. This extensive redundancy makes it possible to reconstruct the transmitted bit sequence in the receiver, even if part of it is disrupted during transmission (FEC - forward error correction).
  • In the receiver, error concealment can be carried out at the audio reproduction stage, so that residual transmission errors which could not be corrected do not always cause disruptive noise.
  • DAB transmission networks are usually common frequency networks, i.e. all the transmitters in the network are operated on the same frequency. If the guard interval is long enough, the receiver cannot tell whether time-delayed incoming signal components are reflections or from another transmitter. On the margin of a transmitter's service area, the neighbouring transmitters may fill the reception gaps and a more uniform pattern of received field strength may be achieved than with VHF-FM (network gain). In places where problems would nevertheless arise, e.g. in a valley or the radio shadow of a high-rise building, additional gap fillers can be installed. Common frequency networks make DAB more frequency-effective than VHF-FM.

• It's claimed that DAB provides near CD-quality audio. However, I have read that 80% of the data stored on a CD is not transmitted at all with Musican audio coding. Is there really no audible difference?

  It is correct that a stereo signal which needs 1.4 Mbit/s on a CD requires only about 200 kbit/s through Musicam (or, better, MPEG Audio Layer 2) data reduction (reduction by a factor of 7). This technique underwent the most stringent testing in the international standardisation procedure, including numerous listening tests involving hundreds of people. The respondents first hear the original and then two other versions of a spoken/musical item, of which one is coded and the other is the original version again (they do not know which is the original). Respondents then rank each of the two pieces on a scale from 1 to 5 (1= very poor quality, 5 = indistinguishable from the original). The results are analysed statistically. These tests have consistently shown that for nearly all types of speech and music, at a data rate of 192 kbit/s and over, on a stereo channel, scarcely any difference between original and coded version was observable (ranking of coded item >4.5). One advantage of the MPEG Audio technique is that future findings regarding psychoacoustic effects can be incorporated later, so it can be expected that today's quality level using 192 kbit's will be achievable at lower data rates in the future.

• What are 'additional services'?

  DAB was developed with the aim of improving radio reception. This is why audio transmission was at the forefront of the development process. But DAB, as a digital transmission system, can transmit other data as well as audio. In principle any type of information can be transmitted by DAB, provided simply that it is available in digital form and does not exceed the maximum available DAB data rate (approx. 1.7 Mbit's). Examples of such additional services are still pictures accompanying radio programmes, digitalised traffic messages (Traffic Message Channel), electronic newspapers, software updates and even animated video. This process leads to 'multimedia broadcasting' (DMB) in which all forms of information can be conveyed via the common transmission medium DAB. In this context DAB could be described as the 'cordless information highway'. In contrast to multimedia applications via TV/cable, DMB additional services can also be received in-car and with portable equipment such as mobile phones, USB devices, and other handheld devices.

• Six radio programme channels (for example) will be transmitted jointly in a DAB multiplex. Is this always the case?

  No. The DAB multiplex is flexible. But it is true that six stereo programme channels, for example, can be transmitted (e.g. all 192 kbit's-data rate programme channels and adequate error correction for in-car reception). Some programme channels make do with a lower audio data rate (e.g. during a news programme) while others need less error correction but a higher data rate (e.g. a classical music channel mainly aimed at home listeners). The number of channels in a DAB ensemble can even depend on the time of day; for instance, on Saturday afternoon a stereo channel could be divided into a special sports channel and a further mono channel. The overall data rate available in DAB can thus be flexibly distributed over various programme channels, and the number of programme channels per DAB ensemble is flexible.

• Do I need a new radio set to receive DAB and what about receiving DAB?

  Yes, since the DAB transmission mode differs fundamentally from VHF-FM. The advantages of DAB, especially interference-free reception in near CD-comparable quality and transmission of numerous digital additional services, would be impossible without a completely new technology. Since DMB uses the existing DAB infrastructure, all DMB receivers are also DAB audio receivers. Unlike DAB only receivers, DMB devices allows the viewer to watch mobile TV and other available applications.

• Do you need a special antenna for DAB reception?

  DAB can be received with a telescopic or disk antenna on a car and with a whip or throw-out antenna on a portable radio. The antennae are smaller than what was used for FM, since it is planned to use shorter wavelengths for DAB than for VHF-FM. In principle, however, DAB antennae look like present-day car or portable radio antennae.

• Who invented/developed DAB?

  DAB has been under development since 1981 at the Institut für Rundfunktechnik (IRT) and since 1987 as part of a European research project (Eureka 147). Broadcasters, research institutes, network providers/operators and consumer electronics firms have contributed.

• What happens when I leave a DAB network's service area?

  The range of a DAB transmission network is of course limited. Since the DAB receiver sees for itself that too many transmission errors have occurred, on leaving the service area there is no static and background noise but the receiver switches to muting. Then, if desired, one can switch over to FM radio (if available, to the same programme channel). Automatic switching will be possible in future.

• How does DAB stand with regard to 'electrosmog'? Will it mean building more new transmission towers and what happens if I also want DAB?

  Regardless of the controversy surrounding 'electrosmog', the following can be said. The DAB system has been devised so that existing transmission towers can be used and scarcely any new transmitter sites are needed. A DAB transmitter requires a capacity which is only a fraction of that of a present-day FM transmitter in the same service area. This will not only save power and make service provision more economical, but also reduce the electromagnetic field strength in the transmitter vicinity. This 'economy effect' is more marked in the VHF range than in the L-band.
  In order to be able to send DMB signals, you must add a video encoder onto an existing DAB infrastructure.

• What is the difference between DSR (digital satellite radio), ADR (Astra digital radio), RDS (Radio Data System), digital mobile telephone, digital television (DVB) etc and DAB?

  • DSR/ADR: These are also radio transmission systems providing near CD-quality radio (DSR without audio data reduction, ADR like DAB with Musicam). They do however have limitations compared with DAB, in two respects:
    • they are broadcast via satellite and thus receivable only on a fixed basis, i.e. with cable connection or satellite dish, while DAB is also receivable in-car and by portable receiver etc. This is a big advantage, since car and portable receivers account for some 85% of radio reception. Moreover, satellite systems are, unlike DAB, ill-adapted to local radio with its strong audience appeal;
    • practically speaking they offer only audio transmission and only limited additional services, and possess limited flexibility with regard to future multimedia applications.
  • RDS: This is an add-on system to FM radio. Although it simplifies operation (display of station names etc) and reception quality is improved (it tunes to the best transmitter), it does not eliminate the ever-recurrent reception disturbances due to multipath propagation in in-car FM reception. DAB will offer all the functions RDS provides, but in a better and more extended form. The data rate available for transmission of RDS information is only very low (approx. 730 bit's net, DAB's comparable Fast Information Channel - FIC - offers 32 kbit's).
  • Mobile telephone: Unlike DAB, this is a two-way communication system (point-to-point). It can also transmit numerous functions that DAB provides (especially digital additional services), although with limitations regarding data rate (usually < 9.6 kbit's). DAB is especially suited to addressing a large number of subscribers in a wide distribution area (typical example: electronic newspaper), the mobile telephone is better for addressing individual subscribers (e.g. fax, e-mail). The two systems can also be combined: R&D projects are working on this
  • Digital television (DVB): This system was developed chiefly for use in television, although as a digital transmission system it can, like DAB, also transmit audio and data. There are a variety of standards for satellite transmission, cable distribution and terrestrial broadcasting. The latter, like DAB, uses the OFDM transmission system, though with a bandwidth of 8MHz. Since mobile reception was not a development goal, the system parameters were optimised according to other criteria (hence, for example, no time-interleaving, small subcarrier separation, less rugged synchronization system). For this reason mobile reception of DVB-T transmissions is only possible with limitations on reception quality or service area. For radio and data broadcasting applications the data rate is, inter alia, far too high (several tens of Mbit's) and frequency planning too inflexible in view of the large bandwidth.

• Can I pick up DAB broadcasts from other countries?

  DAB is terrestrial, which means one can only receive DAB transmissions, via a DAB receiver/radio, from the country in which they are currently based.