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Overview

There are now numerous digital radio stations broadcasting in the UK. We explain how they work, and why you might want to tune in.

What is Digital Audio Broadcasting (DAB)?

Digital Audio Broadcasting is a transmission technology first designed in the ‘80s as a method of bringing the benefits of digital to traditional analogue radio broadcasts.

Put simply, it’s the current successor to the FM and AM radio broadcasts you’ve been listening to for years.

Considering that we’ve all been enjoying FM and AM broadcasts for decades, why is there a need to go digital? Well, as with all things in the technology world, gadgets evolve and DAB is seen as a natural progression as it brings numerous benefits to radio broadcasts – including, in theory, less interference, better sound and a greater choice of radio channels. All sounds good (excuse the pun), so let’s see how it works.

The magic behind DAB

As long as the sound is free of interference and of high quality, most users wouldn’t be interested in knowing exactly how those goals are achieved. For those who do want to know, however, here’s a brief breakdown of the steps involved in processing a DAB broadcast.

Firstly, the analogue signals are converted to digital (i.e. a string of zeros and ones). That digital information is then compressed to an audio format known as MPEG-1 Layer 2 (sometimes referred to as MP2 or MUSICAM). Compressing audio to MP2 involves removing sounds that are imperceivable to the human ear, doing so reduces the size of transmitted data whilst largely retaining sound quality.

With the use of a multiplexer, the digital audio is then supplemented with information such as Programme Associated Data (PAD). Information included in PAD can consist of useful data such as song titles, artist names and general radio station details. Think of it as similar to FM’s RDS and you’re on the right track.

The multiplexer then takes the digitised signal and combines it with the digital signals of other radio stations, creating a single group transmission called a DAB ensemble.

That ensemble is then modulated using Coded Orthogonal Frequency-Division Multiplexing (COFDM), which involves splitting the signal across 1,536 unique carrier frequencies. Using multiple carrier frequencies, or sub-frequencies, lessens the impact of interference. Should one carrier be disturbed by interference, the receiver is still able to retrieve the original sound using the numerous other carriers.

It all sounds very complicated – despite our gross simplification – but all that magic then ultimately finds its way back to the listener via DAB radios (such as the Pure Evoke Flow picture above). A DAB radio is equipped with a decoder that puts the digital signals in chronological order, checks them for errors and then converts them back to analogue sound for output to the user. That, essentially, is the magic.

What are the advantages?

Nationwide coverage
DAB broadcasts throughout the country – where available – use the same frequency and consequently do not require retuning. DAB radios automatically tune to all available stations, and they’re sorted by name as opposed to a frequency number – making it, in theory, easier to locate stations.

Added info
DAB stations also have the ability to display additional information courtesy of PAD. This can include real-time data such as the name of the track currently playing, or details of the radio station.

A greater choice of stations
Digital radio is more efficient than analogue, consequently allowing for more data to be sent in the same spectrum. This has enabled broadcasters to cram more stations into the same space, creating greater choice for the listener.

Less interference
Due to the method of transmission, including COFDM modulation, DAB broadcasts are far less susceptible to interference and reception quality should be of a high standard. As a digital transmission, DAB broadcasts should also be free of the hissing and crackling associated with FM.

Pause and rewind
Modern DAB radios include the ability to pause and rewind live radio broadcasts. Think of it like Sky+ TV, only, on the radio!

Are there any disadvantages?

It all sounds good thus far, but DAB isn’t without its faults.

Coverage
DAB isn’t yet available to everyone in the UK. Although coverage has increased rapidly in recent years, many areas still suffer from poor coverage or no coverage at all. To check reception in your area, visit ukdigitalradio.com.

Quality
One of the benefits of DAB broadcasts should be an increase in quality, but that doesn’t always prove to be the case. It is widely documented that many UK DAB stations broadcast in the MP2 format at a bit rate of just 128kbps, resulting on occasion in better sound from age-old FM. The MP2 format does support bit rates of up to 384kbps, so why such drastic compression? It’s done simply to create greater room for more stations; a case of quantity over quality, sadly.

Equipment
DAB broadcasts can’t be received by traditional FM/AM radios. Although DAB radios are now readily available, they are yet to become common place and their supremacy may not be realised until 2015 – that’s the year in which the UK government plans to cease analogue broadcasts. Today, many car manufacturers continue to use FM radios as standard.

Closing thoughts and the future of DAB

In closing, the numerous advantages of DAB outweigh the handful of disadvantages, but would-be buyers should be aware of another revision to digital radio known as DAB+.

DAB+, announced in 2006, is an upgraded version of DAB that makes use of improved error correction and the HE-AAC audio codec (commonly known as AAC+). HE-AAC is more efficient than MP2 and should result in higher-quality broadcasts.

Readers, however, should be aware that DAB+ is not backward compatible with the existing DAB standards. Consequently, current DAB radios may not support future DAB+ broadcasts, and those that do may require a firmware upgrade. We recommend readers check for DAB+ compatibility prior to making a purchase.

Exactly when DAB+ broadcasts will air in the UK remains unknown, but they're expected to be made available alongside existing DAB transmissions. Although firm time frames are currently unavailable, it is widely believed that standard DAB broadcasts will cease some time after the widespread adoption of DAB+.

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