DAB Radio Technical Problems

Crucial technical problems and disadvantages with the DAB system 

This overview is compiled 2018 by the Public Service Council experts desk in cooperation with broadcast engineers in Norway and Sweden. We will appreciate your feedback by email.

1. The efficiency of the DAB system is ridiculously low.

The inefficiency of a DAB multiplex depends most on the wider frequency bandwidth and the higher frequency range used. Also, the current weaker ERP output effect from the DAB transmitters, although it uses a very high input power for electricity consumption.

A DAB system is only economically efficient if you overbook and squeeze in more channels than the system is capable of, and then it still takes a lot of dB to handle the RF power and headroom.

You must distinguish between economic efficiency and the technical.

Compared with FM stereo, however, the DAB system has some advantages but only with a maximum of three stereo channels per mux.

2. Poor efficiency of the transmitter


The poor efficiency of the DAB transmitters will require installation of super transmitters but with expensive operating costs. You must therefore compare standard DAB to a good FM or good DRM system.

There is a lack of documentation and in pure dB between broadcast power (ERP) and electricity consumption per transmitter (not per radio channel that economists prefer to compare with). Between FM-mono DRM+ and with DAB+.

3. Locked flexibility reduces full sound quality capability

The locked flexibility of the DAB+ multiplex (mux) structure reduces the number of radio channels in each mux automatically if full sound quality is required.

4. Lack of transmission technology


There is a lack of transmission technology - transmit diversity - which will reduce power demand. Other developed digital systems with more modern transmission features could therefore significantly improve coverage.

Especially DVB-T2 lite but also DRM30/DRM+ has a number of features that will enhance the robustness of transmission which DAB+ today is missing.

5. Limit of maximum bitrate

Limit of maximum bitrate in audio standard AAC punctuates the ability to provide full audio quality in AAC/He-AAC V2 audio encoding. Also VBR (variable bitrate) cannot be used in a DAB mux.

Referring to the internationally accepted listening tests on the subject under AES:
http://www.aes.org/e-lib/browse.cfm?elib=16969

6. PAD will limit sound quality

PAD (program associated data) with its extra data included in the audio stream, which is used for additional information is still allowed to take dynamic audio bitrate from the audio encoding, which further will limit the sound quality but this is beyond the listening test results.

Any upper limit for databits rate in PAD is not in the DAB standard and can therefore be easily misused by for example news editors that quickly need to get data to listeners.

When the audio coding dynamically changes over time it deteriorates in resolution than the current listening tests have been able to show. The more radio channels broadcast in a DAB mux the greater the impact on the sound quality, PAD gets in the system.

7. Quantity will kill quality

Therefore, the limited capacity of each DAB mux automatically prioritizes a quantitative culture in comparison to a quality culture. The quality of sound and also for design are the losers today. This will go in the opposite direction to what the music services like Spotify and Tidal are aspiring for.

8. Hybrid DAB-FM also an alternative

Hybrid FM and DAB are not mentioned at all in the document, rather hybrid between DAB and Internet data.

A hybrid solution between an updated FM network and the other digital radio systems solves both sound quality dilemma and reception dilemma in practice in the receivers

9. DAB increases equipment costs for listeners

There is no mention of the gigantically high costs for the listeners being forced to purchase new DAB-able receivers versus the cost of expanding the FM networks. Or versus relying on a developed combined FM and Internet structure based mainly on mobile/smartphone reception (Example: Finland, Sweden and Latvia).

10. Absence of the EBU standard R128 and DRC


No mention of Loudness War and the absence of the EBU standard
R128 which in practice further destroys the sound in DAB+

No mention of the major loss of the important DRC (Dynamic Range Compression) feature in DAB+ previously implemented in old DAB.
If the DRC function had been maintained also in DAB+, it would have been easier to introduce the EBU R128.

11. No software updates

Software update is also missing in DAB+ networks.

12. Problems with the DAB stickers in cars

There are a lot of reception problems with the DAB sticker (converter) in particular, the incorrectly mounted receiver antennas inside the car compartment. Additionally, almost all of these DAB stickers works poorly for type of regional DAB+ broadcast. This, as fewer transmitters are used as normal, assist the reception within a SFN system broadcast area.

In particular, the lack of input in dB to the receiver is particularly noticeable of the reception problems with the receiving antenna on the front panel.

13. All channels in same basket is a security problem.

This is a major dilemma in the event of major crises and disasters, and even in the case of major technical faults in the networks as out of sync but also in the case of rough weather conditions.

14. Not enough base stations will limit SFN.

SFN (Single Frequency Network) cannot be utilized in a larger transmission area in full because there are too few base stations. With more established base stations, these time problems will be reduced, but at the expense of the economy.

15. Power supply structure is complicated and expensive.

Alternative power supply will be difficult and expensive to install because a DAB network consists of more transmitter stations than for FM. Too short masts with fewer antenna elements mean poorer radio signal. And with weaker output effect. This together with the fact that the system itself is ineffective.

A crisis mode also reduces the amount of "man made noice”, thus making it possible to utilize the effective radio broadcasting of the FM -Mono system in a better way.

Also you cannot shut down various radio channels in order to gain in electricity power during a major crisis.

At a general crisis diesel supply for so many base stations in a general crisis will be problematic and alternative power becomes extra expensive to install. Often, the roads involved in the transport of diesel to the sites are damaged in a crisis situation.

16. Sound quality and antennas

The sound quality has been tested in detail in AES and 3 channels have almost space in DAB+ and no more. Old DAB was able to deliver a good sound but the risk was great that you had problems if you as a listener did not install your own roof antenna. Since the great demand to cover mobile reception with DAB, the transmitter antennas have been vertical. Therefore, for a good result old VHF3 television antennas have not been usable.

17. High capacity shortage

Extension of type design and amount of audio channels has clearly been problematic in practice (higher bitrate is a must) because there is a high capacity shortage in the DAB system.

18. Full geographical coverage not possible

In reality, coverage with DAB is often poor where mobile networks today work perfectly. The difference is often dramatic and DAB coverage is missing in many places like:

- During airflighs
- On the trains
- On the ferries
- Inside cars
- At sea off coasts
- In railway tunnels
- In car tunnels
- In deep located parking garage
- Inside shopping malls
- Indoors and in climate-smart villas especially in rural areaa with extra efficient and climate-smart windows and also in house cellars.
In the sparsely populated area

Here the FM Mono generally works better than DAB+, but far from as good as the mobile networks/Wi-Fi networks, so the combination of several technical systems in symbiosis is preferred.

This will be a dramatic problem in a terrestrial radio network exclusively DAB depended (as in Norway)

19. Cross-border listening will not be possible for neigbouring countries

Because of limited transmitter reach reception will no be possible in cross border areas in neighboring countries. Therefore, national radio cannot be received internationally on DAB. As AM, FM and Internet would.

20. Surround sound is problematic

Surround sound is theoretically possible in DAB but falls out of practice due to the technical capacity deficiency in the DAB system and lack of receivers.

Receivability with a central speech channel in the center (3.0) is thus also impossible to put into practice in DAB+

21. DAB signals bouncing on aircraft.

The DAB SFN guard band is too short, which means direct excitation of the DAB signal in some difficult areas where odd terrain applies. (DRM and DVB-T2 Lite have great advantages here).

At airports, listening problems may occur if you install too few DAB transmitters in the network. This is because DAB signals from transmitters farther away from the network than the guardband is capable of are bouncing against the aircraft and down to the receiver while receiving a signal of a closer DAB transmitter. The long-range DAB signal acts via the aircraft as a local interference transmitter.

In Germany, there are problems just when you can receive long-distance DAB transmitters at some elevations, while a nearby DAB transmitter is shaded by a type of mountain mass. In Norway, 2-3 high-altitude transmitters could work together rather far out to sea in fishing waters and beyond the guardband's function. The transmitters function more and more as disturbance transmitters for each other. However at sea, you cannot establish additional DAB transmitters. 

On the coastline an FM transmitter is in general able to reach double the distance than a DAB transmitter.

22. The transmitter structure is not expanded.


The transmitter structure is also not expanded due to purely economic and practical reasons. Too expensive to install according to the Wiesbaden model.

If you botch here, you'll get more and more reception problems in time.
If you expand then it becomes more of an economic issue. Therefore, the digital system must be extra efficient as type DVB-T2 Lite or DRM+.
The quantity can be offered in urban areas and via mobile networks in an easier way.

23. Receiving capabilities for DAB in smartphones not in sight.

Because of lack of global demand there is no DAB reception capabilities in modern mobile or smartphones, but often for FM which becomes even more important in times of crisis and disaster.

24. Outdoor signal is weak, sensitive and deceptive

The level of reception with DAB outdoors is good as for other digital radio systems, but a generally the weak signal is sensitive and deceptive (the digital cutting edge).

25. Spectral band replication (SBR) problem.


In very difficult reflexes and at low bitrate on the sound, the DAB signal tends to drop the SBR pad (discovered by IRT Germany).

The sound then switches between full audio frequency range and a band-limited audio. The lower the bit rate used for the audio coding, the more cut-off of treble part (tweeter).

26. Problems with weak and uneven input.

F/S (full scale) click sounds. Big problems with weak and uneven input. The clicks are extremely strong and energy-efficient and can cause discomfort at high listening levels as in headphones.

With modern fault protection like in DVB-T2 Lite, DRM30/DRM+ and even mobile broadband, you can avoid these clips.

As with FM there is also no de-emphasis in the DAB listening that reduces the energy in the tweeter at reception disturbances.

27. Complicated reception adjustments

It's hard to receive DAB in some places if you do not have a great deal of antenna knowledge and are almost a hobby DX-er, which is not common.

28. High battery consumption is a security risk.

Battery consumption for DAB receivers are significant higher than for FM receivers. This will risk major security problems in case of crises. Crank powered or small solar cells are not enough here.

A single, portable FM radio can be 10 times more power-intensive than a DAB + receiver. An old FM radio with big batteries than more secure against power shutdown

29. Signal distribution f0r DAB transmitters not robust enough.

Alternative and secure signal distribution to the transmitters are missing for DAB but is already established for FM networks.

FM with a digital ballast (relay), the signal goes on longer and is safer due to the frequency bandwidth and transmission frequency. Therefore, it is also possible to change the reception frequency of FM to feed other transmitters, thus increasing safety. Operating these main transmitters is possible with alternative power as the above mentioned is possible.

Although even if the entire distribution system is down-and-out, FM will function smoothly with its relay-distributed transmission system. Tomorrow, even with full digital FM audio quality and the furthest out of the FM network.

30. Discussion about combining different radio systems is lacking.

 
There are no discussion about combining the different radio systems to one common system for the benefit of the radio listeners. Where the systems intersect and offer the listeners the best of several options.
Updated FM system with Internet and DVB-T2 Lite as well as DRM30/DRM+ integrated as a single radio system.

Additional  comments:


A radio system with a large coverage type FM or DRM+ can safely use the handover function between the transmitters. That's what the listeners do with FM, and as listeners today always do, and along with the diversity of antennas in the cars, it will give an extended and less disturbed reception in practice.

This feature is not reported in general documents regarding FM radio reception quality today. Also not reported is that all the digital FM enhancements that can be updated today in the system and thus provide better radio reception.