An overview of Digital Radio in 2010
Britain entered the age of digital radio as long ago as 1995, with a system called DAB Digital Audio Broadcasting which went on air using some of the 'Band III' frequencies vacated when 405 line TV was discontinued. DAB's technical format, known as Eureka 147, has since been adopted by broadcasters around the world, particularly in Europe but also in several other regions including Australia. A few use the much higher "L band" frequencies, but most DAB broadcasting is on similar Band III frequencies to those used by Britain. In some parts of the world, notably the USA and parts of south America, an alternative system known as HD digital radio, which operates "in band" and "on channel" alongside FM broadcasts has been adopted.
At a technical level DAB radio operates in a "multiplex" arrangement, delivering 'bouquets' or groups of stations, available in the UK within either a "national" or "local" multiplex. Whilst there is potential for high quality audio reproduction using the DAB transmission medium, there is also a compromise to be made over audio quality versus the number of stations available in each multiplex.
DAB technical parameters were originally defined using a then widely accepted and reliable data compression technique known as MPEG2. A typical fully utilised UK multiplex operating to the original standard might contain between 20 and 30 stations, each with a data channel, allowing a text display on suitably equipped receivers - in addition to the actual programme material. However, the more high audio quality (and stereo) stations there are, the fewer the total number of stations that can be accommodated within that particular multiplex. With regulatory, financial and spectrum efficiency pressures to incorporate as many stations as possible, resultant audio quality from DAB transmissions has been a longstanding matter of engineering and listener concern, and it continues to be the subject of technical debate.
Moreover the significant costs involved to broadcasters, noticeably patchy reception in some areas, and modest audiences delivered over an operational period of more than 10 years in the UK has shown many commercial services to be unsustainable in the long term. Reception limitations have been cited as an important factor: the nature of digital transmission systems in general means broadcast services tend to be either present or absent with no "grey areas" of weak signal where reception is still possible - if rather 'scratchy.'
The transmitter network is now being expanded, but in DAB's early years - and still today - low signal strengths can result in reception proving difficult in buildings and urban areas. This issue is felt by some engineers to have been one very significant factor which has impeded Digital Radio development in the UK. Some indeed have drawn parallels with the early years of what was then called Independent Local Radio, when a common complaint was inadequate field strengths, largely resulting from inexplicably modest radiated power levels on FM.
With a much higher number of transmitters - albeit sometimes still delivering doubtful field strengths, and large numbers of (relatively) modestly priced receivers now readily available, new digital services continue to appear. Meanwhile slow audience growth continues, and after many false starts, several digital-only stations have built up a loyal following. Many others have, however, already fallen by the wayside. In response to public pressure, British Government proposals to remove existing UK-wide network services from FM on a very tight timetable by 2015 (subject to certain DAB service criteria and listener penetration levels being met) have recently been relaxed, with no alternative date yet suggested.
In the wider arena, digital radio take-up by European broadcasters has been less than universal. Some indeed, have already closed DAB services, and debate has started about whether the system as originally specified should continue into the indefinite future, despite new and ever-improving technology becoming available. A further complication involves the likely arrival of significant numbers of high quality satellite-delivered digital radio services - expected across Europe by 2014.
Since the early 1990s the march of technology has been relentless, resulting in development of a newer, updated version of DAB called DAB+. This has been trialled and in one or two countries adopted as their digital radio standard, using a more recently developed and more efficient data compression system, known as AAC MPEG4. Depending on exact technical implementation, this has benefits in perceived audio quality and/or the actual numbers of channels broadcast in a given multiplex - or even both. However any attempt to introduce this newer DAB system in countries where the earlier system is on air and established will bring inevitable problems of 'backwards compatibility,' since many "old" DAB receivers currently in service will not necessarily be able to decode newer DAB+ transmissions.
Also, since the launch of the British DAB service in 1995, an entirely different digital radio system called Digital Radio Mondiale (DRM) has been developed and introduced. This was designed and intended for use in the long, medium and shortwave bands, at frequencies up to around 30 MHz. There are technical reasons why the first generation DRM system cannot be used beyond that approximate frequency, though experimental systems operating on DRM principles have been demonstrated as workable in the existing FM band and up to the same band III frequencies used by DAB. This system has been called DRM+, and some commentators are speculating that this 'non-multiplex' digital technology could one day entirely replace analogue FM broadcasting.
Though not without some known reception foibles at medium wave frequencies, especially at night, DRM allows generally more consistent reception than conventional AM over long distances when using the short waveband. Many international broadcasters are now radiating DRM services at high power on short wave, and various Long and Medium Wave services are also in operation. Quite apart from more consistent reception on a regional and national level, in general DRM delivers notably better audio quality than has ever been possible using the established international technical standards applied for many years to AM broadcasting.
To get round the compatibility problems resulting from use of all these possible formats in different locations, future digital radio receivers may well incorporate multi-band and possibly dual or triple digital format decoding algorithms - simply to allow reception of all expected formats in the regions where they are sold. This approach, whilst workable, seems likely to lead to quite expensive receivers.
Various websites provide information on digital radio news, product and technical information and background, DAB development and its reception, including:
www.ofcom.org.uk
www.getdigitalradio.com
www.radio-now.com
www.ukdigitalradio.com
www.digitalradiotech.co.uk
www.bbc.co.uk/digitalradio
www.localdigitalradio.co.uk
www.uk-dab.info
www.worlddab.org
www.dab-digital-radio.com.
Please note: Websites may be taken down at any time, and Moss Media accepts no responsibility for the existence or content of any site listed.
This is not an exhaustive list; to request that your digital radio website is added, please e-mail enquiries@mossmedia.co.uk 