A few weeks ago, reports reached us that on a regional DAB MUX in Belgium and on some models of cars, there are problems with automatic switching between FM and DAB+: the car radio switches to a radio broadcaster on VRT’s DAB MUX, usually Radio 1, Radio2 or Studio Brussel. In some car models, it was even impossible to listen to the local\/regional broadcaster via FM if the FM frequency was set to a “preset”.<\/p>\n\n\n\n
Because we wanted to know the ins and outs of it and, above all, we were looking for a solution to the problem, we compared the FIC data<\/a><\/em><\/strong> of the small scale DAB+ pilot project in Flanders (Belgium) with the FIC data<\/a><\/em><\/strong> of the MUX of VRT (Broadcast Partners) and those of Norkring. The cause was soon found.<\/p>\n\n\n\n Apparently, some manufacturers’ car radio software does something wrong when a different code is used for the “SId<\/strong>” than the “PI code<\/strong>” (FM-RDS) used for the FM transmitter. But also adding the FM frequency(s) in the FIC data<\/a><\/em><\/strong> is something we don’t see in some pilot projects.<\/p>\n\n\n\n Theoretically, you could use different SId and PI and rectify this by explicitly <\/strong>linking both by transmitting additional information via DAB+.<\/p>\n\n\n\n Unfortunately, some car radios do not respond to this explicit link info. So overriding the implicit<\/strong> linking (SId simply equal <\/strong>to the PI) does not work. The phenomenon appears to be related to the price range of the radio (ditto car).<\/p>\n\n\n\n If one wants to make it work on ALL car radios, one should undoubtedly opt for the implicit linking: choose the same code for the DAB SId as the PI code for the FM-RDS.<\/strong><\/p>\n\n\n\n By the way, using explicit linking is only used if the two stations (DAB+ and FM) broadcast different program schemes for several hours a day. Then, by switching off explicit linking, one can decouple both stations (see ETSI document<\/strong><\/em><\/a>). This is a situation that never occurs in the local\/regional radio world.<\/p>\n\n\n\n Implicit linking is thus the best way to link your DAB+ broadcaster to your FM-RDS broadcaster, see also ETSI TS 103 176<\/a><\/strong><\/em>:<\/p>\n\n\n\n Our suspicion is that some radios work with limited FIC functionality and do not interpret certain instructions.<\/p>\n\n\n\n We therefore recommend checking (or having checked) whether the “PI code” is used as “SId” and that also the FM frequency(s) are added in the FIC data<\/strong><\/a><\/em>. The sysop or operator of the MUX should be able to answer that. In this way, you can ensure that the listener can continue to listen to his\/her favorite broadcaster without any problem regardless of which car he\/she is driving.<\/p>\n\n\n\n Important to remember:<\/p>\n\n\n\n A check of both parameters is therefore recommended to achieve maximum listener ship.<\/p>\n\n\n\n An example of what is broadcast in the FIC data<\/a><\/em><\/strong> can be found here<\/a><\/em><\/strong>.<\/p>\n\n\n\n The term “Service linking” is used for the action itself. For the system of switching, the term “service following” is used. The system is described in ETSI TS 103 176<\/a><\/em><\/strong>, chapter A.3.4 (Receiver Behaviour).<\/p>\n\n\n\n Finally, a word about audio volumes. So quality starts with lowering the FM audio level so that DAB+ can work qualitatively. Many countries have an agreement on this between “Broadcasters”. You can read how to do it in “Headroom in digital audio<\/a><\/em><\/strong>“.<\/p>\n\n\n\n <\/p>\n\n\n\n![\"\"](\"https:\/\/localdab.org\/wp-content\/uploads\/2023\/06\/ETSI-TS-103-176-A8.png\")
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The audio level of many FM stations is often FAR too high. Achieving a similar volume with DAB+ is technically IMPOSSIBLE<\/strong> without causing substantial distortion of the digital audio signal. This is because one has a finite number of bits at one’s disposal that CANNOT<\/strong> cope with these FM audio levels. This distortion will result in particularly poor audio quality in a digital system such as DAB+. <\/p>\n\n\n\n