Unlike AM and FM frequencies (also called “analogue” radio frequencies) where one radio station is broadcast on one analogue frequency (such as 94.9 MHz used by BBC Radio London), DAB frequencies (such as 223.936 MHz used by the Greater London II multiplex) can carry multiple radio services on the same frequency. The process of combining the various separate radio services onto one DAB frequency is called multiplexing.

Licences to use DAB frequencies are awarded by Ofcom. Frequencies are allocated by Ofcom to cover various parts of the country according to an overall frequency plan, which ensures the efficient use of electro-magnetic spectrum whilst minimising interference.

Building and running each transmission network for each DAB frequency is the responsibility of the holder of each multiplex licence (in the case of the London II multiplex, Switchdigital (London) Limited). It is also the multiplex licensee’s responsibility to ensure that its network meets the technical codes set by Ofcom and that its dealings with each service provider are fair.

Each DAB frequency has a set amount of capacity it can use. Using an analogy of a pipe, the DAB frequency ‘pipe’ is a finite size and therefore the amount of ‘stuff’ (i.e. radio services) that can fit down one DAB frequency is also finite. The total number of radio services that can fit down any DAB frequency is determined by the ‘size’ of each radio service. And the size of each radio service is determined by the audio quality of each station. The higher the audio quality (i.e. stereo quality) the more DAB capacity that service needs, therefore the total number of stereo services that can fit down the pipe is fewer than the total number of mono services that could be carried on a mux. The sum of the audio quality characteristics of all the services on any given DAB multiplex will determine how many services can be carried on that multiplex frequency. Once the pipe is full, no more services can be added.

The audio quality of each service (subject to there being sufficient spare capacity on the multiplex) is selected by the radio service provider, though these must meet Ofcom’s minimum quality thresholds (which are 64kbits per second (“kbps”) for predominantly music radio services, and 48kbps for predominantly speech radio services). The table below sets out the audio quality levels available in DAB:

Audio Quality Level

Capacity Required

Coding rate

Mono (speech)

48kbps

24kHz

Mono (music)

64kbps

24kHz

High Quality Mono

80 – 96 kbps

48kHz

Stereo

112 – 128 kbps

48kHz

High Quality Stereo

160 – 192 kbps

48kHz

 

As mentioned above, the higher the audio quality selected, the more capacity required on the multiplex and therefore the higher the cost of transmission to the service provider.

The fees payable by service providers to the multiplex operator generally consist of three key elements:

  • Capacity Fee:  the fundamental element of the fees payable by service providers, which is proportionate to the amount of capacity the service uses on the multiplex.
  • Contribution Fee:  this fee element covers the cost of collecting your audio from your studio premises/racks room, encoding it and delivering it via broadcast quality telecoms circuits to our multiplex centre.
  • Deposit:  in cases where the service provider is a new company and/or does not have a long trading record, an advance fee will be payable upon signing of a contract before the service goes on air.  This advance is non-refundable and held by the multiplex operator for the duration of the contract, and used to offset fees payable in the final months of the contract.

Fees on the Switchdigital multiplexes are generally invoiced at the beginning of each month during the contract term.  Payment terms are thirty (30) days from the date of invoice.  Fees are also adjusted annually in line with increases in the Retail Price Index.

DAB+

DAB+ works essentially in exactly the same way as DAB, except that the audio compression and encoding technology used is more advanced, which means that a stereo service requires less capacity than a standard DAB channel (32kbps versus 112kbps).

In addition, given the coding is different to DAB, the chipsets in radio receivers themselves must be capable of decoding the broadcast signal.  Whilst virtually all new DAB radio receivers on the market today (including in-car stereos) are DAB+ compatible, a number of older DAB radios cannot receive DAB+ signals.

Current estimates indicate that the proportion of DAB+ compatible radio sets, on average throughout the UK, represent about one third of the total number of DAB capable radios.  This number is set to grow through the natural replacement cycle of radio sets and as more new cars are sold.

The positive flipside, however, for broadcasters using DAB+ at the moment is that the carriage fees are lower to reflect the lower capacity used on the mux and the lower DAB+ set penetration in the market.

OTHER FREQUENTLY ASKED QUESTIONS

Are there any other hidden charges?
No.  There may be some additional installation costs which some service provider may incur.  However, this is generally not the case, and in any event any such costs would always be agreed with the service provider prior to any costs being committed.  Other charges may be payable in the event a service provider moves its studio location, for instance, however these will also always be agreed first.

Who can broadcast?
Anyone who holds a current Digital Sound Programme Service (“DSPS”) licence from Ofcom is able to broadcast on a multiplex (subject to contract, Ofcom approval and enough capacity being available).  Switchdigital are keen to offer a wide range of distinctive services on its multiplexes that broaden listener choice and cater for a variety of tastes and interests.  Prospective service providers are asked to complete a short standard questionnaire, providing information on themselves, the proposed programming format and the financial sustainability of the service over the duration of the contact term.