Like any technology that uses scarce radio spectrum, digital radio is subject to regulation. In the commercial sector, digital radio is regulated by the Radio Authority, who will implement policy set out in the Broadcasting Act 1996. Both the Act and the Radio Authority guidelines are comprehensive and complex. However, it can be broken down into these main areas:

Regulation of frequency spectrum

In the UK, seven blocks of frequencies in Band III have been assigned for use by digital radio. They lie between 217.5 and 230 MHz, but are more generally known by as 11B, 11C, 11D, 12A, 12B, 12C and 12D.

Each frequency block can carry one digital radio multiplex. A multiplex is just a fancy word for a number of radio services mixed up together. Each multiplex can carry up to six or more services, and this is one of the key differences between analogue and digital radio. In analogue radio, one frequency means one service; but in digital, one frequency block can carry many services, thus making more efficient use of the radio spectrum.

Regulation of multiplex capacity

Although digital radio multiplexes make clever use of digital compression techniques, there is still a capacity limit on any given multiplex. There’s a direct correlation between how much capacity a given service uses and the audio quality: the higher the capacity, the better the quality - a lower capacity reduces the quality but more services can be broadcast. It’s a question of making the best judgement about how many services you have on the multiplex, and how good they sound. The Radio Authority are specifying minimum capacity rates and leave it to the broadcaster to use more if they want to.

Regulation of data services

What exactly do we mean by data? Broadly, data services are divided into those services which support or enhance the sound programme and those which have nothing to do with the audio, but which could be commercial data services.

Regulation of content

As digital radio is able to carry many services simultaneously, it requires a new model for the regulation of content. The Radio Authority will license multiplex operators, who will pledge to carry a certain range of programmes and services on their multiplex. Each individual sound service will be licensed as a Digital Sound Programme licence, and these may be ‘portable’ between multiplexes. The Radio Authority has a set of guidelines for potential multiplex operators and programme providers.