Yesterday we whetted your appetite for Digital Audio Broadcasting (DAB), and the advent of CD quality, feature-rich radio. Today we examine the nuts and bolts that bring the music to your ears.
Think of the difference in quality between a DAB signal and the current AM/FM signal as like comparing an 8-track cassette chassis to a MiniDisc player. DAB will almost completely eliminate the familiar pop and whistle interference of a conventional radio, caused by multipath interference of FM signals ricocheting off buildings and pylons. These bouncing signals arrive at your receiver out of sync with the main signal, resulting in a "ghosting" distortion.
DAB receivers, on the other hand, are intelligent. A processing engine within each digital receiver handles broadcasts from central digital multiplexes -- the BBC owns one that hits sixty percent of the UK population -- and sorts through the tangle of multipath signals, enhancing the main signal. A DAB receiver is therefore a "smart set", in other words, it doesn't just receive, it acts on the information it is sent.
With the introduction of DAB, transmission costs should be greatly reduced -- savings that broadcasters could pass on to consumers. DAB transmits at greatly reduced power, with no reduction in coverage. Although it can be transmitted over the 88MHz to 108MHz FM band, European services are being rolled out over other frequencies. The UK is currently using Band III, the old 221MHz black and white television band.
To receive these new signals, consumers will need new hardware; that means an extra cost to Joe Public, and greater sales for chip developers and receiver manufacturers around the globe, such as Hitachi, JVC or Panasonic.
Whether your receiver is a stand-alone device or built into home hi-fi equipment, radio reception is just the beginning. Second generation, and hopefully more affordable devices, will all feature large LCD screens displaying every available station and service in a browsable format. Equally, program types will be separated out into subject areas, as will more abstract services such as meteorological information, advertising spiel, subtitles, GPS information and so on. The only limitations with DAB are the imaginations of receiver manufacturers and broadcasters. BBC's blue-sky visionaries are already getting busy with their design packages, conjuring up receivers shaped like wrist watches, or even shower gel bottles for a bathroom DAB.
Exponents of the ultimate In-Car Entertainment (ICE) will also benefit from DAB's use of a Single Frequency Network, which will negate the need for constant retuning in a far more sophisticated manner than current Radio Data System (RDS) stereos.
As with Digital TV, DAB will be a perfect medium for "pay-per-listen" services, such as operas, far-flung concerts, exclusive DJ sets, Top Ten charts-on-demand or even financial services, served to your exact location through correlation with global positioning satellites.
In a nutshell:
- DAB has been knocking around since 1981, when it began development at the Instut fur Rundfunktechnik (IRT), and also since 1987 as part of a European research project -- Eureka 147.
- The UK is on the cutting edge of infrastructure development.
- Services and pilot projects are up and running in the majority of European countries. It's now down to the consumer to set a level of demand and drive down prices.
DAB -- Not to be confused with:
- RDS: This is the natty addition to modern in-car stereos that displays FM radio station names. It does nothing for reception quality.
- Internet radio streaming: Ordinary analogue radio broadcasts spun over the Web. Fun, but full of interference.
- Internet digital radio: Digital radio over the Internet is a great idea for the future but our homes are not equipped with the necessary broadband links today.
- DSR/ADR (Digital Radio by Satellite/Astra Digital Radio): CD-quality radio transmissions broadcast via satellite, and thus only receivable from stationary sets.
- Mobile telephones: An obvious one you'd think, but today's handsets can chuck some quite sophisticated audio services around. However, these are usually limited to around 9.6kbit/s, which isn't good enough for digital radio broadcast.
- DVB: This is your digital telly. It can be used for digital audio, and can utilise OFDM, but mobile reception isn't up to scratch because, well, a TV was never designed to be a radio...