What difference will DAB+ make?

27th November 2006

DAB+, the unofficial name for DAB now that it's adopted the AAC+ codec, will provide the following improvements compared to what DAB offers at present:

1. Far more stations

DAB+ is four-times more efficient than the old DAB system is. This translates into either four-times as many stations being transmitted, or higher audio quality, or a combination of both. Ignoring the issue of audio quality for a moment, one thing is almost certain is that using AAC+ will result in far more radio stations transmitting on DAB, and thus the current, in my opinion, relatively poor breadth of choice available on DAB will be much improved, and hopefully we will see the smaller niches catered for, which currently there is no room for, as well as the fact that the transmission costs are prohibitive for smaller stations with the old DAB system.

2. The audio quality will be far better overall than it is today

The bit rate levels needed to provide good audio quaity using AAC+ are so low that it will be easy and cheap for radio stations to provide good audio quality. One of the main problems with using the old MP2 audio codec has been that the transmission costs required to provide high audio quality are ridiculously high, and this has militated against the broadcasters providing good audio quality.

For example, the BBC in particular is very likely to provide high audio quality with AAC+, because they are not expected to be able to launch any new stations, or if they are allowed to launch any new stations it will only be one or two at most, because the commercial radio groups would throw their toys out of the pram if they were allowed to launch any more stations than that.

Here's a possible BBC national multiplex configuration using the expected PL4A error protection level:

Station	Bit Rate kbps	Audio codec²	Audio mode	Audio quality	Capacity Units (CU)
Radio 1	132¹	AAC	Stereo + Surround	Almost CD-quality	72
Radio 2	132¹	AAC	Stereo + Surround	Almost CD-quality	72
Radio 3	132¹	AAC	Stereo + Surround	Almost CD-quality	72
Radio 4	102¹	AAC	Stereo + Surround	Almost CD-quality	56
Radio 5	64	HE-AAC	Stereo	Very good quality	36
Radio 5 Sports Extra	64	HE-AAC	Stereo	Very good quality	36
6 Music	132¹	AAC	Stereo + Surround	Almost CD-quality	72
BBC7	72¹	HE-AAC	Stereo + Surround	Very good quality	40
1Xtra	132¹	AAC	Stereo + Surround	Almost CD-quality	72
Asian Network	64	HE-AAC	Stereo	Very good quality	36
World Service	64	HE-AAC	Stereo	Very good quality	36
Data services	480	-	-	-	264
Total	1544				864

1 - the bit rate includes the bit rate for the MPEG Surround stream data, which is around 3 - 4 kbps

2 - AAC (LC-AAC), which is the audio codec used on iTunes and for the iPod, is used for higher bit rates and HE-AAC (High-Efficiency AAC) is used at lower bit rates, but is ideal for stereo speech

As you can see from the data services bit rate of 480 kbps, the BBC will be able to easily provide very good audio quality on all services, and provide MPEG Surround on all of the stations that would benefit from it, and provide all the currently mono stations in stereo with about a third of the capacity left over. Furthermore, the BBC has said in responses to public consultations that it would like to improve the audio quality of its stations on DAB, so I don't even consider it to be a realistic proposition that the BBC won't improve the audio quality of its stations.

I would also expect the more popular commercial radio stations to use bit rate levels that provide far better audio quality than they're currently provided at — using AAC+ they have to go down to ridiculously low bit rate levels like below 32 kbps before they provide the same level of audio quality as is currently provided on DAB where 98% of stereo stations use 128 kbps with the highly inefficient MP2 audio codec.

Overall, it is basically assured that the audio quality on DAB using AAC+ will be far better than it is at present.

3. Better reception quality

This is explained in the DAB vs DAB+ technology article, so I won't repeat it here, but suffice it to say that reception quality will be a lot more robust than it is now.

4. MPEG Surround

As well as DAB adopting the AAC+ audio codec, they have also adopted the MPEG Surround format, which, as the name suggests, allows surround sound to be transmitted.

MPEG Surround uses a very low bit rate stream (about 3 - 4 kbps) to carry the surround sound information, and tests have apparently shown that it performs well — it apparently performs in between the high quality discrete multi-channel and the lower quality matrix-based surround sound formats, which is pretty amazing if true given that the bit rate is only 3 - 4 kbps.