EBU • UER - Technical Review

A first comprehensive compendium on Digital Audio Broadcasting (DAB) in English has finally been published!

The whole DAB community has been waiting for this marvellous event since 1995, when the first regular DAB transmissions started in the UK and Scandinavian countries. As someone who was deeply involved for more than a decade in R & D work for the Eureka-147 DAB system and was promoting the system worldwide, I am extremely pleased to see the publication of such an excellent summary of the Eureka-147 DAB Project results, during the years 1987 to 1999.

The book is actually much more than a collection of technical information contained in the ETSI standards and the various Eureka publications. It really is a very useful “one-stop” handbook that includes a lot of practical examples of DAB services; some useful guidance on how to use correctly the particular system parameters, and useful tables and lists at the end of the book. It is quite a useful complement to the existing standardization texts, and may save the development engineer – who previously would have had to search for this information in too many different sources – a lot of time.

The book seems to be intended for “professional users such as developers and manufacturers of professional devices, and the planning engineers and operational staff working for broadcasters, network providers, service and content providers”. Being written by engineers for engineers, the book is probably too narrowly technical for non-specialists. It is probably too detailed and specialized to be of interest to the general public, or even programming, commercial, legal and political people who would like to learn more about DAB. It may however be useful to the students of technology high schools, or practising engineers who have not been involved in DAB and wish to catch up quickly.

The two editors were successful in attracting the collaboration of many – mostly German – authors for the various sections. It is however a pity that the palette of authors is not more international in flavour, in order to reflect the fact that the Eureka-147 Project was truly international. It is well known that the Project represented the collaborative efforts of many French, UK, Swedish and other European engineers as well. As an example, the COFDM modulation scheme was brought into the DAB system by our French colleagues working at the CCETT institute in Rennes (now part of France Telecom R&D). It would have been appropriate to ask one of their research staff to report on the experimental evidence and their experiences in using this system.

Recent technical developments in the Internet (IP technology, streaming media, copyright management, security, etc), mobile communications (GPRS, UMTS) and interactive broadcasting (MHP, TV Anytime) have had a strong influence on DAB developments during the last two years or so. The Eureka-147 Project ended in December 1999 and any further developments on DAB are now taking place under the auspices of the WorldDAB Forum. Of course, this book could not take into account all these latest developments. But the developments now taking place within the Technical and Commercial Module of WorldDAB – such as Java Virtual Machine and DAB/Mobile convergence – are extremely important, provided that they will soon be translated from the laboratory to the shelves of consumer electronics shops.

IP tunnelling, another interesting approach to deliver multimedia streams and files to PCs via DAB, is not covered in the book, nor is the use of MPEG-4 in DAB. The receiving of DAB signals via computing devices – using PC (and PCMCIA) cards or devices such as Psion’s Wavefinder – is not dealt with either. Not surprisingly, conditional access is only covered very superficially, yet it is becoming increasingly important for the commercial success of multimedia services carried by the DAB transport mechanisms.

Practising broadcasters will probably need more detailed information about the planning and frequency management parameters, and the results of the Wiesbaden 1995 planning meeting. Also, it may have been useful to include at least some BER vs. C/N curves and the protection ratio curves, as these are essential technical parameters required to understand the performance of the system. The EBU document, BPN 011 – “Collated Performance Evaluations of the Eureka 147 DAB systems”, which covers these points in detail – should have been mentioned in the bibliography (along with the other included BPNs). Perhaps a second edition of the book could embrace these important missing bits.

All in all, the book is a useful compendium to provide general background information on the Eureka-147 broadcast system. As the system grows and more experience about its usage is gained, it may be appropriate to adopt a less technology-prone approach and focus more on how the user could use DAB to access attractive new interactive services and applications.

It should be pointed out that the EBU members remain committed to DAB, as it is an excellent and well-proven technology. The EU-147 system is still the only system that is capable of replacing the old analogue FM system. During the last 5 to 10 years, EBU members have been investing heavily in large DAB transmitter network infrastructures in their countries: DAB signals are now available to more than 60% of the population in most European countries. These broadcasters certainly hope that their huge investments in DAB infrastuctures will one day be paid off. The lack of a substantial receiver base has significantly reduced the motivation for operators and broadcasters to further invest in DAB, at least in the short term. Consequently, DAB is not moving as fast at the moment as we would all like.

As DAB has taken far too long to come to market fruition (is it already at the end of the tunnel?), it is no longer the only digital system that is capable of delivering digital radio to the general public. Other systems are increasingly being considered to deliver some forms of digital radio and music. These may be technically less perfect than DAB, but technical quality is sometimes less important than the cost, convenience and choices on offer. The main competitors that DAB will have to face in the market are many and their ranks are becoming more and more numerous. DVB, DRM, cable, satellite, audio webcasting and music delivery over the Internet (as well as audio over GPRS and UMTS). As this competition is vigorous, it will be necessary to reposition the role of DAB technology and analyse which comparative advantages – in terms of technical, cost, user friendliness and other parameters – it can still offer from the user point of view.

The book is a good account of the past engineering efforts that went into the development of DAB, but it lacks the vision of how radio in general and DAB in particular will look like in the future. Such a vision of DAB’s future prospects is not given by the authors or editors. Nevertheless, I am sure that the authors are aware of the fact that radio broadcasting is on the verge of radical changes. These are being driven mainly by the strong advances in Internet technologies. From the user’s standpoint, the biggest change will probably occur in terms of the radio receiving sets. Conventional, stand-alone radio sets will progressively be replaced by PDAs, mobile phones, hand-held computers, set-top boxes and various Internet-connected appliances. Expressed another way, DAB chip sets could be included in all these various devices, together with a DAB-specific front end to capture the terrestrial DAB transmissions. To this end, efforts should be made to further reduce the power consumption of DAB chips. If not, the battery life of a common DAB/GSM device would be much shorter than that of GSM alone. Furthermore, it would be advantageous to develop a common chip set for DAB and DRM. Technically, the difference between the two systems is not big and the overhead should be reasonably small. In the car dashboard, DAB could be integrated in a common control centre, comprising a mobile phone, navigation unit, car computer, media receiver and recorder, in conjunction with a relatively large display. It seems that Ford and General Motors Canada plan to market such a centre as a standard line fitment, from 2004.

The second major change will be at the level of the delivery mechanisms and transmission systems. Radio broadcasts will be conveyed to the end user not only through dedicated DAB networks but also through the Internet, telecom networks, wireless LAN, satellite, cable etc. Dedicated DAB networks will no longer be the only system to carry digital radio. The user will not really be interested in how the signals travel from the content source to his/her receiver. Broadcasters are increasingly agnostic about which networks will be used to bring their programmes to the general public. Any network will do, provided it is cost efficient and reliable. DAB networks will become a very useful transport mechanism, not only to carry radio but also unrelated multimedia applications to computers and other IP-based devices.

The third, and perhaps the biggest, change to come in radio broadcasting will be a radical departure from today’s real-time linear broadcasting. Currently, you select a TV channel. Tomorrow you will select a programme, according to your preferences, and will “consume” it at your convenience – wherever and whenever you wish. You will be able to compose your own channel. The user, not the broadcaster, will decide what he/she would like to listen to.

To conclude, the DAB transmission system is certainly an important stepping-stone in the migration process from analogue to digital broadcasting. This book gives a fairly complete picture of how the underlying technology works. The EBU should be proud of having taken part in these important developments and having contributed to them so positively.

Of course, no book can cover everything and some priorities have to be decided. In this book, priority has been given to the system aspects while the frequency management and propagation aspects are not covered in depth. Another book on DAB will have to be written to cover these points, and also to show how this brilliant technology is able to interoperate with other delivery technologies. A new book, written from the end user perspective, will have to give a broad picture of all the technologies that can bring digital radio services and future multimedia streams to the general public.

Digital Audio Broadcasting: Principles and Applications
W. Hoeg and T. Lauterbach (Eds)
Hardbound volume of 265 pages
Ref: ISBN 0-471-85894-3. Price £50.00.
John Wiley & Sons, Chichester, UK, 2001.
http://www.wiley.co.uk

This book is aimed at advanced webmasters who want to embellish their websites with some animations and interactivity. As webcasting is becoming an attractive complementary service offered by practically all EBU members, this book could represent an excellent guide. Many books and manuals on Flash design are available on the shelves today but most are of little practical use, especially if you want to “wow” the world with an award-winning website. There is a huge gap between being able to create basic animations and being able to produce an effective and absorbing website. To this end, animations should be used with care.

Macromedia Flash is more than just an authoring application that brings animations and interactivity to your HTML pages. It is also a web-optimized vector-based technology which makes use of the SWF (Shockwave for Flash) file format and the ActionScript scripting language. Vector formats describe shapes and formatting more efficiently than bitmap images which describe the colour of every pixel. The SWF format efficiently describes the difference between image frames to enable smooth animations which require low bit-rates, so that they can be streamed over ordinary modem connections.

Flash 5 replaces the primitive collection of actions available in Flash 4 with a fully-fledged scripting language called ActionScript which shares common roots with JavaScript. This makes it possible to react to user input, allows for adding conventional user interface elements such as text entry fields and menus, and allows the fetching of documents identified by URLs. With the help of an additional server technology called “Generator”, Flash movies can be generated dynamically at the server side, with content tailored not only for different users, but also for different computing devices, geographical areas or times of the day. The term Flash movie is commonly used to designate the output animation, constructed and edited within the Flash authoring environment, which is stored in a movie file with the extension .fla. If a movie is to be played within a web page, suitable tags such as <object> or <embed> must be included in the HTML source code for the page.

The book explains also how to make lip-synching cartoons or to connect Flash to a WebCam using Macromedia Generator.

The book is intended for advanced users of Flash technology who are able and willing to perform some programming using the Flash ActionScript language. In order to allow as many potential readers as possible to benefit from the book, some fundamentals are well explained: for example, how the timeline works, and what are key frames and “tweening” ^[1], symbols and instances, events etc. Some elementary material on programming and simple language constructs, such as conditional statements and loops, are also included. There is good coverage of sound as well as graphics, and a full explanation is given of how to build interactive movies with actions and event handlers.

An important part of the book is a chapter about abstractions. This is where computational processes or data objects are given a name in order to be able to manipulate the named object. Creating a movie clip is an example of abstraction: having edited the symbol once and added it to the library, you can create instances of it in a movie or within other clips, without worrying how it was put together. Every instance of a clip symbol is identical or not. In the latter case, clips include some parameters and are called “smart clips”. A large portion of the book is devoted to this central concept.

At the end of each chapter the reader will find some exercises and experiments. A strong emphasis is given to the practical work in actually creating animations and experimenting with the Flash scripts and with the visual elements of the Flash movies. As Flash technology is advancing fast, some refinements are often necessary. In order to help the reader to cope with these changes, a website is available to accompany the book: http://www.wiley.co.uk/flash/.

One of the reasons that Flash is so popular is that Macromedia made the SWF format open (in 1998) and provided an SDK (System Development Kit) for third-party developers. This has helped to establish SWF as a de facto industry standard. But it has also opened up the competition – graphic design programmes such as Adobe Illustrator (Adobe LiveMotion) and CorelDraw (RAVE – Real Animated Vector Effects) are now offering SWF export capabilities. There is also an interesting package called SWiSH 1.5 (www.swishzone.com) which uses pre-supplied animation effects, primarily applicable to text.

It should be pointed out that the open-standards body, Worldwide Web Consortium (www.w3.org), is developing a different standard called SVG (Scalable Vector Graphics). Like SWF, the SVG format capitalises on the efficiency of vector representation, as opposed to pixels. However, while SWF is a self-contained, binary, streaming, frame-based format, SVG is an integrated, XML, object-based format. SVG is currently less spectrum-efficient but is more future-proof. It fits well with the future XML-based structure of the web, enabling interoperability with other XML-based applications and attractive features such as searchable text, repurposing and automatic production. The SVG code can be fully integrated into the web page, enabling CSS-based (Cascaded Style Sheet) formatting and Java-script-based control across the page as a whole. SVG also works fine with XML-based SMIL (Synchronized Multimedia Integration Language – see the article published in this issue). By moving the processing demands to the player and the client, SVG can support advanced formatting features such as 3D and bitmap-based filters.

The present commercial implementations of SVG are disappointingly slow. While it is almost certain that Macromedia will have to move and embrace XML, the speed and bandwidth efficiency of Flash should not be compromised if possible.

The EBU Project Groups B/BMW (Broadcasting of Multimedia on the Web) and P/AMM (Authoring of Multimedia) are paying due attention to the progress of Flash and other authoring tools and technologies for the Web.

^[1] Frames lying between two adjacent keyframes are interpolated or tweened. Several properties can be used for the tweening process; for example, the position of objects in the frame, their brightness, transparency, size, rotation or shape. Scripting actions and interactivity can only be attached to keyframes and not to tweened frames.

Flash 5: Interactivity and Scripting
N. Chapman
Bound volume of 251 pages
Ref: ISBN 0-471-49781-9. Price £24.95.
John Wiley & Sons, Chichester, UK, 2000.
http://www.wiley.co.uk

Peter Symes’ book “Video Compression Demystified” is a well balanced survey of the contemporary techniques and tools of video and audio compression. It is a revision and expansion of Peter’s earlier book “Video Compression”, published in 1988. Much has evolved since then, although basic principles such as lossless and lossy compression remain.

Peter covers the material in a non-mathematical way, and the text will be useful to those engineers who need to know how compression works, and to discuss and compare the different systems, without delving into the more advanced mathematics that a university students’ text would give. The book is probably best suited to the practising engineer who needs a topup of the latest information about compression technology, but has neither the time nor the inclination to become an equipment designer.

The book begins with an introduction to compression, and the characteristics of digital coding. The basic types of entropy coding, predictive coding and transform coding are covered, as well as quantization principles. The book goes on to discuss the JPEG system – the father of modern video coding. After this comes a description of Motion Compensation – which was the main tool which took video compression forward beyond JPEG. MPEG-1 tools are explained, and the characteristic macro blocks, etc. The book then moves closer to the present day with information on MPEG-2, now the mainstay of digital television broadcasting throughout the world.

Armed with this knowledge, some elements of the quite complex MPEG-4 compression tools are explained. These will be the mainstay of video delivery on the web, and may also be used for digital broadcasting. The book also includes a chapter on MPEG-7 and MPEG-21, which covers the metadata needed for MPEG-4, and overall system issues.

The book then deals with the DV compression system. Some consideration is also given to technologies not yet used, such as Wavelets and Fractals, and the goals of JPG-2000 are also outlined.

The book has a chapter on Audio Compression, and includes the essential features of the masking systems used for MPEG audio compression, but this is not primarily a text book for audio engineers.

Finally the book outlines some elements of streaming media, which is the way in which real-time video and audio are delivered over the Internet.

The book includes a glossary of terms, a bibliography and a list of Internet resources (though sadly the EBU website is not listed, although the DVB site is). Accompany the book is a CD-ROM which includes a number of freeware or demonstration versions of software applications for the compression of still images, video and audio (although this is not the most essential feature of the book – probably more up-to-date versions could be downloaded straight from the Web).

Overall, the book is a welcome tool in the armoury of those engineers who need to stay on top of the core technologies used in broadcasting.

Video Compression Demystified
P. Symes
Bound volume of 346 pages
Ref: ISBN 0-07-136324-6. Price £36.99.
McGraw-Hill International (UK) Ltd., 2001.
http://www.mcgraw-hill.co.uk/

The NLE Buyers Guide – which we've reviewed here previously, when new printed editions have been published – is now available on-line from a dedicated website: http://www.nleguide.com/.

The new online guide includes every type of nonlinear editing system – including turnkey systems, card/hardware unit and software packages, software-only packages, and disk recorders / servers. Aimed at video editors from the "prosumer" upwards, the NLE Buyers Guide website has a database of just over 200 NLE systems which is searchable by application, system type, host platform, video input/output and cost range, as well as by manufacturer and system name.

At the NLE Buyers Guide website, you will also find links to a pilot online version of Sypha's sister publication – The DAW Buyers Guide which, of course, is dedicted to digital audio workstations.

Digital Audio Broadcasting: Principles and Applications W. Hoeg and T. Lauterbach (Eds)	John Wiley & Sons
Flash 5: Interactivity and Scripting N. Chapman	John Wiley & Sons
Video Compression Demystified P. Symes	McGraw-Hill
NLE Buyers Guide Y. Hashmi and S. Plumbridge (Eds)	Sypha Publications