Hi all (firstly sorry for the length of this post!
Im writing this because i recently replaced my Head Unit and decided to go for a DAB radio. I have been really disappointed in the DAB sound and thought I'd share my findings. DAB is getting a huge amount of marketing in the UK at present and imho a lot of it is misleading. The key sells are "Digital Sound Quality" which most people would assume to be CD like, and "Crystal Clear Reception"
First it'll helps to explain how DAB actually works, unlike FM where each individual station occupies it's own frequency on the spectrum, DAB broadcasts in several multiplexed feeds, these are called "Ensembles". Each Ensemble is a digital stream that contains several stations, your radio extracts only the part of the stream it needs for the station you want to hear and ignores the rest. The Ensemble is a fixed size (bitrate) of data, therefore broadcasters had to make a decision regarding how many stations to squeeze into each Ensemble, of course what they did was to maximize the number of stations, rather than having a reduced number at a higher bitrate and therefore sound quality (after all more stations=more revenue).
When DAB was introduced the recommended bitrate was 160kbps per station, however a few years on they are all down at 128kbps per station (even lower for the talk radio style and special interest stations). Even the BBC has had to drop its high-quality Radio3 from 190kbps to 160kbps and this drops further to 128kbps when they "borrow" some bandwidth when Radio 5 Live Extra is broadcasting.
Anyone into MP3 (iPods etc...) will be aware that 128kbps is considered as-low-as-you-want-to-go for music, and lots of people prefer to encode to a higher bitrate. The situation would probably be acceptable if DAB was delivering 128kbps MP3, however DAB broadcasts using the less efficient MP2 compression, this Is accepted as being around 25% less efficient than MP3, so to put DAB into perspective you should probably think of something around a 96kbps MP3.
At this low bitrate you'll certainly notice Sibilance in the treble leading to a slight lispy effect on DJ's voices, and if like me you're into Guitar based groups then you'll sometimes have trouble picking out instruments and even vocals from what becomes a frustratingly muddled sound.
"Crystal Clear Reception".
It is certainly true that you won't hear any Hiss on a DAB broadcast, but you almost certainly will experience drop-out, and the weird effects we've all heard on our mobile phones from time to time, I guess this should be called digital-noise.
Pros of DAB
Increased number of stations
Increased footprint of some stations
Cons of DAB
Sound quality not what it should be. (a strong FM station will sound better)
Certainly not without interference.
Will the situation get even worse as they add more stations?
So why did I get a DAB radio?, Radio 5 - even a 60kbps DAB feed sounds better than MW, and the London FM station XFM is a lousy FM signal in my area.
I'm not saying don't get a DAB radio, but don't go assuming it'll amaze you!