Re: They need to stop
"DAB fills a need that doesn't exist, and never did exist."
The issue is the FM band (if one is talking about receiving good quality, non-fading radio broadcasts. (hence discounting AM, inc MW, LW and DW).
The problem with FM is that there is a limited bandwidth (88-98 MHz originally and it was widened to 88-108 MHz when the emergency services were moved off FM to a higher frequency (which also solved the issues of prisoners in jail only being allowed to use AM-only radios which became increasingly difficult to buy in the late 1980s).
And so trying to fit multiple FM broadcasts into a 20 Mhz bandwidth is tricky esp given that the BBC (as a national broadcaster) has mutliple frequencies allocated to it (hence Radio 2 is broadcast on 88-92 Mhz and depending on where you live - ditto with Radios 1, 3 and 4). These alone swallow up lots of frequencies and hence local stations have to somehow "fit in" between the BBC allocations.
Allocating the same (or very similar frequencies) to competing broadcasts causes "beating" and you get unsatisfactory covereage of both...esp if the "selectivity" of cheap FM radios is quite poor.
So, DAB was invented as a way to help solve the issue of having a limited bandwidth (and hence limited range of stations), plus the way the DAB signal is transmitted is that "beating" does not occur and instead DAB radios are designed to work by receiving different signals from different transmitters operating on the SAME frequency, as the combined signal gives you better reception.
DAB thus solved the issues of:
1) Better sound and no "hiss" (if they all broadcast at CD quality, which they don't in practice due to transmission costs)
2) More choice of stations (but limited by Arqiva charging very high rates) and limited by OFCOM for not awarding licences freely)
3) Better use of available frequencies as not only was Band 3 VHF set aside for DAB but also L band was available too - ideal for local DAB stations due to the limited transmission range of broadcasts and therefore Band 3 could be kept for National broadcasters and L-band just for local use.
4) DAB can also carry other types of information on the carrier - some DAB tuners actually have a digital output socket that could have been used to carry visual information, such as subtitles, travel information for those on the move, or graphical information about the station or even the lyrics to the music being played....but this has not been championed by anyone.
FM is still plagued by the same issues as it was back in 1992 when DAB launched...hissy broadcasts, and limited range of station choice and interference due to beating or from pirate FM radio stations in many cities (London, Birmingham and Manchester for instance).