Ofcom DAB switchover coverage planning proposals
Brian Butterworth published on UK Free TV The proposals cover the most pressing needs for the DAB network:
- provision of local radio DAB for those areas with no current coverage
- coverage of both homes and in-car use
- the addition of a new block (5A) that will allow the local radio blocks to expand to fill the "editorial" coverage areas to match the current FM areas
- the use of 99%/99% DAB prediction for indoor home reception, and normal car use.
Of particular interest are:
- FM current coverage maps and tables which show maps for the current BBC local radio and largest commercial local radio for each "editorial region".
- Local DAB build-out plans that show the expected coverage for each DAB area after various plans have been implemented.
Ofcom is asking for responses using this online form: Responding to the DAB Coverage Planning consultation by 5pm on 14 September 2011.
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Saturday, 2 July 2011
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Trevor Harris7:49 PM
I know my posts have been very negative so let me say something positive.
There are several alternatives to DAB and one I am particularly interested in is Digital Radio Mondial (DRM). This is not a multiplex system so is suited for local radio and can be used on AM and FM frequenies. Infact it can coexist with FM stations in Band II. The BBC has been heavily active in researching DRM but for obvious reasons has been very quiet about it.
It uses AAC and so is very efficient and can be used for surround sound.
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Jonathon Green8:13 PM
Briantist: "I have never, ever heard of "hissy" anything on DAB, it is simply impossible. As with all digital reception, it is perfect or nothing. Hiss is an analogue "feature".
Well, quite. And it's working very nicely for me which is why I have no desire to see my excellent DAB coverage "improved" to the match the appalling standards which the National FM network provides in my not-especially-rural corner of Essex... :-)
Lots of people (Trevor Harris in this thread for example) like to bang on about the poor quality of DAB relative to what a decent FM tuner with a clean aerial feed is capable but (trust me on this 128 Kbit/s of MPEG layer 2 wipes the floor in comparison with anything FM can deliver without the aid of a bigger aerial than I'm inclined to pay out.
There may well be arguments that the money spent on DAB might have been better spent on upgrading holes in FM coverage (both in terms of signal quality and program choice) or that we'd have been better off waiting for a better standard for digital radio to come along but DAB is what we got and (faults and all) it's given me several years of vastly enhanced listening pleasure over what FM was actually delivering to my home.
Internet radio is I feel something of a dead end in terms of broadcasting. I'm really not seeing anything remotely resembling universal mobile data coverage (3G or 4G) capable of delivering enough bandwidth to support a decent range of broadcast channels in the near future and I'm even more not seeing the network operators cutting the cost of mobile data to a level where it's a realistic alternative for the average user.
WiFi is fine assuming you've already got the infrastructure in place but I can't imagine (for instance) my 80-something year old mother paying out for a broadband internet connection, wireless router, and audio streaming device just to listen to the wireless for a couple of hours a day...
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Trevor Harris: Actually, with digital systems you can says "error free reception" as this is perfectly possible, as anyone who watches Freeview/digital satellite/digital cable knows. Or uses an internet connection, anything from ISDN to FTH.
For digital systems you define the BER (bit error rate) that is acceptable for the underlying transmission system, and the provide FEC (forward error correction) to deal with the BER issue. That's why Ofcom are saying that 99%/99% is the acceptable prediction level for the "calculation pixel". This is way, way above what FM delivers.
Your thinking is very analogue, if you don't mind me saying so.
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Sunday, 3 July 2011
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Trevor Harris12:49 AM
@ Johnathon Green
I am always carefull to say that most people don't want DAB. Some people are perfectly happy with DAB but my point is that the considerable expense of the system cannot be justified for such a small number of listeners.
Sound quality is subjective and some people are more sensitive to mpeg 2 artifacts than others so it might be acceptable to some people.
It is all rather complicated by the fact that the BBC uses Optimod digital sound processors on nearly all of its radio including FM. The manufactures claim that this filter will reduce the effect of mp2. The BBC does not use these horible devices on the 320 kb/s AAC streams.
Car radios with 3G are already available. I agree that coverage is not good enough yet and there are uncertainties about it's viability for radio. Again I think most people are happy with FM for thier car radios. Certainly the BBC will not be able to turn off the national FM stations for a very long time. Most mobile phones have an FM tuner as well.
I don't agree that 128k mp2 is better than FM. Infact the BBC's own research indicated that FM quality was about the same as MP2 at 225kb/s. Originally the BBC used 256kb/s.
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Trevor Harris1:00 PM
Dab radio uses convolutional coding for error correction which gives unequal error protection to different parts of the audio stream. This is considered a "weak" system because it causes audible "burbling" in poor reception conditions. There is no sharp cut-off but a gradual deteriation. This was fixed in DAB+ by using Read-Solomon as an inner layer of error correction. This is an "equal error protection" which gives a much sharper cut-off. Section 5.27 of the Ofcom report mentions this and that manufactures are trying to make this less noticable. Once a corrupt audio stream has passed through without the error being detected there is no way of knowing it is corrupt. They are trying to make a silk purse out of a pigs ear.
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Steve1:56 PM
Isn't the issue that even when as good as supposed to be DAB does not use enough bandwidth to match FM quality?
What I don't understand is what problem DAB is supposed to solve. FM seems entirely satisfatory. With DTB there is a clear gain over analogue. But not for radio.
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Iain Davies5:08 PM
DAB is a 1000 times better than FM!!!
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Jonathon Green5:13 PM
Trevor Harris:
"I don't agree that 128k mp2 is better than FM. Infact the BBC's own research indicated that FM quality was about the same as MP2 at 225kb/s. Originally the BBC used 256kb/s."
I'm not attempting to suggest that 128Kbit/S mp2 isn't better than FM *can* deliver but, where I live at least it's far, far better than FM *does* deliver under local conditions.
I don't doubt that FM is lovely for those who live in areas with good reception of a decent range of stations but here at least (and I'm not way out in the sticks, I'm in a not-particularly-rural bit of Essex) the arrival of DAB (flaws and all) totally transformed the listening experience - sure the same thing could have been achieved by re-engineering the local FM infrastructure (and somehow shoehorning BBC 6 Music and Planet Rock in) but that's not what they chose to do...
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michael5:28 PM
Nice to see a robust debate resurge! All make salient points. I would have been content with FM (and would welcome DRM on MW/LW one day...), but the theory of digital superiority will doubtless be imposed via DAB. As long as de-facto coverage and reception really is at least equal to FM now, at home on a portable and on the road, it will be worth it to receive the World Service and maybe one or two others! The sound-alike commercial stations may not all survive, so FM might have been good enough for the "survivors". Once implementation has been effected, lower running costs will comfort commercial operators. Should home reception not meet promises / expectations, I will relay the WS and local radio via micro-FM to save landfill from our many FM portables :-) Currently, there is a problem with "warbling" and cliff-edge silence when the DAB telescopic aerial is moved. I am not aware of plans to increase erp of existing DAB transmitters, without which "warbling" may be here to stay in less populated areas, as FM hiss and swish now. Maybe the DAB bird-song station was a discrete jibe... I will read the Ofcom online tome and sumit my comments in due time. Lets be positive and hope for the best!
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