I am asking this here, because it is something which you bold europeans are experimenting with (and which Norway seems about to make official and exclusive by 2017), but which is totally unknown to radio listeners in North America. WHAT is this "Digital Radio"?
America has been experimenting with the proprietary IBOC ("HD Radio") system as a bridging technology (a digital stream on a sub carrier of a regular FM station) in some regions, but as far as I know that never really took off. So basically, the situation in the US is traditional FM (VHF) and AM (MW) stations for local and regional broadcast, and country-wide pay radio stations via satellite (Sirius XM). Satellite radio is virtually unknown in Europe, basically due to the fragmented market with a large number of languages to support and only few Pan-European stations. AM radio on medium wave has been almost completely shut down, it's successor Digital Radio Mondiale (DRM) wasn't successful. FM radio is still going strong. Since the 3m broadcast radio band is rather crowded in densely populated areas, and more and more stations asking for bandwidth, a decision has been made by the European Broadcasting Union (EBU) to migrate to digital radio. The first iteration was DAB ("Digital Audio Broadcasting"), a bunch of multiplexed MPEG1 MP2 encoded audio streams, modulated as COFDM, which allows single-frequency networks and reliable mobile reception. It has been phased out recently and replaced with DAB+, which uses the MPEG4 HE AAC v2 audio codec and adds Forward Error Correction. Due to the more efficient compression a DAB+ multiplex can have up to twice the number of DAB streams. Needless to say a DAB+ signal cannot be decoded by a DAB receiver, it requires new equipment. The frequencies used are in the VHF III band (a former analogue TV area) and for local stations in the L band, so it doesn't clash with traditional FM radio. IBOC, in contrast, requires the double bandwidth on the already crowded FM band for each multiplex.
Is it likely to officially replace traditional Frequency Modulation ("FM") radio for broadcast media across Europe? Does this mean that everyone will have to either buy convertors or new radio equipment (like home stereos, iPod radios, and car radios) in order to listen to music/news/weather/sports?
If the EBU has it their way, FM radio would be switched off everywhere in Europe in 2017. This is not likely to happen, not even 2021 (politicians love that number for some unknown reason...) to which it has been postponed by Germany. The problem is that nobody buys a receiver as long as FM radio is still around, but the FM signal can't be turned off before a certain ratio of DAB+ receivers has been reached. So manufacturers had been waiting for the programs to start broadcasting in DAB/DAB+, and the radio stations were waiting for receivers becoming available. At least there are now relatively inexpensive DAB+ radios to buy, but still it's a rather small market, and the only reason there are programs to listen to in Germany is a) the strong public radio landscape and b) massive subsidies by the German states. DAB+ receivers for cars, which is the most important use of broadcast radio, are quite rare, though. Also, many areas of Germany are still not covered, see the map at
http://digitalradio.de/index.php/de/empfangneu — the map is overly optimistic, of course.
The whole thing is probably going to fail like the DVB-T (our equivalent of ATSC) disaster. They replaced analogue TV with it here, but almost everyone is on cable or satellite anyway, and except for some metropolitan areas only public television is available, as the commercial broadcasters plainly refuse to pay for distribution unless they can go pay TV (which will be DVB-T2, rendering all DVB-T receivers worthless...)
In the meantime, Internet access via mobile phone has become affordable and available almost anywhere, G4/LTE is stable even at fast Autobahn speeds, so Internet radio will likely render DAB+ obsolete before it becomes available everywhere. Traffic information is the main reason why drivers in Germany (and other European countries) listen to broadcast radio. You can get traffic information from Google Maps or as a subscription service from other vendors via Internet now. This will obsolete broadcast radio before DAB+ covers the same area as FM radio nowadays.
The only problem nobody thinks about: how to inform the public in case of a major disaster. Mobile Internet is rather complicated and fragile, structure-wise. Feeding or deploying an AM or FM transmitter during some catastrophic event is trivial. We'll lose that venue, and only few people even realize that this might become a big issue eventually.
My prediction: DAB+ is not going anywhere, FM radio will stay (though likely with less stations) for at least another 10 years, nobody will give a damn in the end because Internet radio or streaming services is going to be ubiquitous and affordable for everyone. And we're all gonna die because nobody can tell us about the big meteorite about to hit the earth.