What is digital radio?

AM and FM radio signals produce 'analogue' radio - a frequency is assigned to a broadcaster and receivers tune in on it with mixed results that are usually influenced by atmospheric factors. Because analogue signals are basically copies of the original sounds, the music can be recreated inside a receiver. Digital signals, on the other hand, are computerised and have to be decoded to be played.

What's the advantage of digital radio?

The sound is CD quality, free of interference. Because the signal is computerised, it can contain other kinds of data such as images and text - even moving images. Typically, a digital radio broadcast contains cover art and descriptions of the music.

Digital signals can also be stored on receivers for later replay or downloaded as MP3s into portable players. Listeners have control over the music once it's received and can usually skip back in a playstream and get all the information about a song as well as listen to it again.

How is it broadcast?

Digital radio signals can be sent out alongside regular AM/FM radio signals, by satellite, via the internet, or by cable. How you listen depends on how the signal is broadcast and there are even portable digital radios - and digital car radios - making their way onto the market. Watch for a big international push after January's International Consumer Electronics Show in Las Vegas, at which many new digital radio models will be launched.

While there are still a number of competing standards, the most popular globally is called Digital Audio Broadcasting. DAB allows signals from a group of stations and services to be bundled together and transmitted as a single data stream - a 'multiplex' or 'ensemble'.

In the UK, where the BBC is taking all its stations digital, there will be seven multiplexes. Digital radio signals are free and already available to more than 80 per cent of the country.