DAB - a revolution in radio quality?

A layman's guide to the new digital radio technology, its audience benefits...and implications

Grae Allen

'DAB' (Digital Audio Broadcasting) is still little-known outside the radio industry. But it will set broadcasting standards for the next 50 years, and for instance deliver 'CD' sound quality - more or less anywhere, any time of day - along with many other benefits. Essential briefing for everyone involved with the radio medium, this paper also explains DAB's pluses over AM anf FM; the likely European standard EU147); and the huge investment already in place. To bridge the 15-year gap while DAB-only sets become the norm, current analogue service will be 'simulcast', requiring additional frequencies. But eventually there will be more radio as well as far greater convenience. The first BBC services may begin in 1996, commercial stations shortly afterwrads. The completion date is less clear.

Digital technologies are, of course, making themselves felt everywhere in business and domestic life. `Digital' has brought us the Compact Disc (CD), NICAM Stereo sound for television, and increasingly sophisticated PC and Mac computers on our desktops and laptops. The telephone network is now largely digital, bringing ISDN and other sophisticated communication services to companies of all sizes. But unlike all these, DAB is scarcely known yet, outside the radio industry itself.

FORMIDABLY BETTER QUALITY

DAB offers the possibility for radio to provide consistent `CD' quality, no matter where or when one listens. The receivers will be self- tuning, with all stations available at the press of a button; all with equal quality and coverage (within obvious limits). In short, DAB will be a transparent radio medium from which listeners will choose services purely on the basis of the programme content and the quality of their production.

THE HISTORICAL PERSPECTIVE

Through all the recent technological advances, radio has remained virtually unchanged. Since the 1930s, broadcast radio has used AM (Amplitude Modulation) on both the Medium Wave and Long Wave bands. Only the receivers have become smaller as the technologies have allowed.

In the 1950s, FM (Frequency Modulation) broadcasting began on the VHF Band, providing much better quality. However, it was not until the early 1970s, with the advent of commercial radio, that FM became well established. By this time, Stereo was also a feature of FM. It was only as receiver designs improved and satisfactory FM could be received in cars and on hand portables that the real benefits of the enhanced quality available on FM began to be perceived by the audience.

CHANGING CONSUMER EXPECTATIONS

The introduction of consumer digital audio equipment, particularly the CD, has driven a continuing move for popular radio music services to be made available on FM and in stereo. This has been true of services targeted at all age groups - not only those for the young. Increasingly, it is the middle and older age groups that are complaining that the services to which they listen are not available on FM.

For every radio transmitter there are tens of thousands of receivers. This demands that changes in radio technology must be implemented gradually and that any new scheme must have adequate longevity. There is simply no quick way to update the installed base of receivers from one technology to another. This was part of the reason for the delay in the success of FM. However, changes in radio technology must meet the increasing expectations of the consumer.

Many radio listeners are also users of CD, both at home and on the move, and two recent product launches - the DCC (Digital Compact Cassette) from Philips; and the Mini Disc from Sony - will further expose consumers of recorded audio material to digital quality. Radio must keep up. In an increasingly consumer-led market the consumer expects the supplier to overcome any `delivery' problems and this applies equally to radio.

SHORTCOMINGS OF EXISTING SERVICES

The technical shortcomings of existing radio services are well known and there is a limit to how much individual listeners can do (or be expected to do) to overcome these. AM radio services are subject to interference, particularly during the hours of darkness, when it is often easier to receive a station hundreds of miles away rather than one in one's local area.

The absolute quality of AM services is also limited. Broadcasters have pushed `processing' techniques to their limit, particularly in the last five years, to make the best of what is possible on AM. This processing

is aimed at making the services easy to listen to in the average listening environment, which often has a substantial level of background noise. This can be caused by the car or truck engine while on the move, or the noise of children or the Hoover at home. Processing allows the signal to `cut through' background noise and improve both the quality and the intelligibility, and this has been important in maintaining audiences on AM.

Whilst FM does not suffer from interference in quite the same way as AM and generally provides much better quality, including stereo, it brings its own problems.

  • It can be difficult to receive effectively on the move and on portables inside buildings.

  • It suffers what is known as `multipath' caused by reflections from local obstacles or even people moving around a room.

  • Under good conditions FM will provide very high quality - however, it is not consistent.

When the parameters of the FM system were established in the 1950s it was envisaged that users would have rooftop aerials linked to fixed receivers. Today such arrangements represent only a very small proportion of listening. The planning criteria have not changed and the broadcasters have relied on improvements in receiver technology. These have now been stretched to the limit to provide the portable and mobile facilities that most listeners today want and expect.

Any new technology for radio must tackle all of these problems. The technology of broadcasting must become transparent to the consumer. This is the role of DAB services which, once established, will set the parameters for radio for perhaps 50 years or more.

WHAT IS DAB?

As mentioned earlier there are several approaches to DAB. The most advanced is one developed in Europe by a group known as Eureka 147. Broadcasters in the USA have so far firmly rejected EU147 in favour of one or perhaps several alternative technologies. However, none of these are yet proven in practice, though extensive US field trials, including EU147, are planned for late 1993/early 1994. EU147 DAB has been widely demonstrated as an effective, if expensive, scheme. It looks likely to be adopted in the UK, Germany and France and elsewhere throughout Europe and Scandinavia, and also in Canada and Mexico - where it is likely to be delivered by satellite.

The members of EU147 are a combination of European national broadcasters and manufacturers of both transmission equipment and radio receivers, including BBC, Grundig, Bosch, Telefunken, Philips and Daimler-Benz. The project was formed around 1987 with a brief to develop a worldwide digital broadcast standard to take radio into the 21st century. An immense amount of development, effort and money has gone into the project (360 man years and 80 million Deutschmarks between 1987 and 1991). The European Commission is funding the standards work to create a definitive technical standard document, against which the DAB system will be established.

The work of EU147 has come much more into the public domain in the last 18 months and the standard is about to enter a public comment phase with an expectation of its formal adoption during 1994.

THE HURDLES TO MAKING DAB A REALITY

However, several hurdles lie in the path of DAB: some are technical, others financial. Many of these arise through the need to simulcast, ie to maintain existing analogue services alongside DAB. This period must be long enough to enable reasonably priced receivers to become widely available. (It is likely that the first sets will be multi-standard, ie covering AM, FM and DAB.) It is hoped that car manufacturers may act as a catalyst by fitting DAB sets in new cars.

This need for simulcasting, which is envisaged to run for 15 years or more, requires additional (temporary) radio frequencies, or `Parking-Spectrum', in order that during this period DAB can co-exist with AM and FM. Beyond the simulcast period it is envisaged that DAB will largely, but not exclusively, replace AM and FM broadcasting. (When DAB finally replaces FM, DAB sets will automatically take account of any frequency change. Consumers will not be expected to change sets again.)

Aside from the technical and engineering hurdles, the cost of implementing DAB represents a major challenge to all broadcasters, particularly local independents. DAB will not expand the number of listeners available, though it will defend radio against other audio media. If the BBC implement DAB, it seems likely that the independent sector will soon follow. The timing may vary, with larger markets in a stronger position to carry the additional overheads of operating a DAB network alongside existing AM and FM services.

BENEFITS TO THE CONSUMER

The benefits of DAB to the consumer will be manifold:

  • DAB offers consistent high quality comparable with CD.

  • Such quality would be available on all types of DAB receivers, whether these are fixed as part of a hi-fi system, or are hand portables used around the home or in the open air, or are fitted in-car, or are Walkmans.

  • The quality will be consistent, independent of the time of day, or location, or whether fixed or on the move.

  • Receivers would be much more `user friendly'. They would be virtually entirely push button operated, without any fiddly tuning controls and would have a display giving details about the station and perhaps even about the music or other programme content. They might also display a list of other stations available.

  • The receivers are expected to be self-seeking, ie they will tune themselves to all available DAB broadcasts, and listeners can simply flick between the channels in much the same way as they currently do with television.

In the longer term, ie after the simulcast period ends, DAB will enable more radio than would be possible with AM or FM. DAB is `spectrum efficient', particularly for national services. That is, it uses fewer frequencies for the same number of services compared to AM and FM. Indeed a common block of frequencies will provide service throughout the country, something which is simple impossible with the existing AM or FM schemes.

Also, in the longer term, direct satellite based radio will be possible, though it is not envisaged that such services will operate in Europe until around 2010.

TIMESCALES

The timescales for the introduction of the first phase of DAB are still under debate. I believe the BBC are enthusiastic to establish a credible national service which might begin around 1996. Commercial broadcasters, both local and national, will build DAB services shortly thereafter, in order that consumers continue to have a broad range of services.

DAB will permanently change the radio broadcasting environment, bringing consistent high quality to the vast majority of programmes. The only remaining question is exactly when?

NOTES & EXHIBITS


Grae Allen

Grae Allen

After graduating in electronic engineering, Grae Allen joined Radio Clyde's engineering department in 1978 before spending two years as a development engineer with Clyde Electronics. He became chief engineer at Radio Clyde in 1992, where he is presently director of engineering. Grae was one of the technical consultants involved in establishing Satellite Media Services (distributing audio by satellite to the independent radio network) of which he is now a director. He is also deputy chairman of the AIRC technical committee, and chairman of the independent radio industry's committee on Direct Audio Broadcasting.