All posts by Trevor Harris
Below are all of Trevor Harris's postings, with the most recent are at the bottom of the page.
As far as I understand it is just the local multiplexes they are not alowed to own. The main purpose of the local multiplexes is to provide local commercial stations.
There is no reason why the BBC could take over the abandoned channel 4 national multiplex if ofcom allows. This would mean that the BBC could transmit all their radio at 256kb/s.
This solution still has a major problem in that DAB does not support surround sound. DAB+ does support AAC and so could support surround sound. If the BBC took on the spare multiplex thay could get all thier national stations on it if they adopted DAB+.
Unfortunatly this is politicaly difficult in that Channel 4 wanted to use DAB+ but ofcom turned them down. This was one of the reasons channel 4 handed the licence back.
Ofcom and the BBC have turned DAB into a pigs ear. The problem with DAB is that it has no advantages over FM with RDS so why switch.
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Actually David there is already an unused mutilplex available. This was originaly was bought by Channel 4 but was a commercial failure and so was handed back to Ofcom. I don't see any reason why the BBC could not use this as there is little chance that any one else will ever use it.
There are bigger issues though. Generally radio is going to need far higher bit rates. Itunes clearly believe there is a demand for 24bit downloads and is planning much higher quality sound. Even the BBC is using 320kb/s on radio 3 internet streams and also is considering surround sound radio. Some internet stations are steaming lossless flac.
Of course DAB does not support any of the future technologies. Ofcom used the "more choice" argument to justify low quality Dab. The very low DAB listening figures clearly demonstrate that people do not want more choice at the cost of quality.
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Actually Brianist I think you are wrong about MP3. Freeview uses MP2 audio and satellite uses MP2 or AC3 (stereo or 5.1). Freeview HD uses AAC (stereo or 5.1).
Actuall modern FM recievers handle mutipath and doppler rather well as is demostrated by many in car radios. As for premphasis this is nothing compared to the distortion added by the BBC using optimod signal processing. This processing is designed to disguise the artifacts produced by low bit rate MP2.
As I am sure you know DAB only has one level of error correction and so is much more vunerable to interference than FM.
Actually Steve I would favour DRM+ at the moment. This can be fitted on Band 2 between the existing FM stations. You are correct in about multiplex owners . They were the ones that lobbied Ofcom for lower bit rates. They could make more money from a larger number of low bit rate stations.
The BBC has been doing research into DRM+ but has been very quiet about it. Their papers always seen to sujest that it will be several years for DRM+ to be viable. This is just not true.
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Hi Brianist,
I would agree with others that we are all very grateful for your site which does give alot of information and help to others. I suspect you consider me as a "Digital Radio hater" but actually it is not true. I even bought my wife a digital radio for Christmas although she uses it with upnp, internet or usb stick and not DAB. I am how ever totally opposed to the enormouse amounts of money being spent on DAB just to service 15% of radio listening.
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@Brianist
I think you may be a bit optimistic for the BBC to move existing channels to HD. Danielle has already said there will not be any new channels till 2013.
I think it is more likley this is for the Wimbledon 3D experiment.
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Don't worry michael the FM stations will not close down in the foreseeble future. DAB uses higher frequencies than FM so to get even near identical coverage would require a large number of fill in transmitters.
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@Brianist
You may not have heared anything hissy but I certainly have heared the burbling sound sound many have reported. As we all know DAB only has one level of error correction and if this fails it can cause very odd audio effects. The fundemental error is making here is that coverage will mean interference free reception. Unfortunatly even with a strong signal if the error correction is inadequate you can still get poor reception. It is not a matter solely of signal strength it is the probability of not being able to correct the errors. With DAB this probability is quite high. You also see this with satellite reception. You can have a very strong signal but a very high error rate. I always align my satellite dish to give the minimum error rate.
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As for car radios Ofcom believes that cars may be converted to DAB with a simple convertor. If only they would do a bit of research. These devices simply do not work. Infact one manufacturer has abandoned production of these devices because they has a 40% return rate.
Many radios do not have an audio input and so these devices use a "spare" FM radio frequency to transmit to the radio. Unfortunatly in many areas there is no "spare" frequency to use. Certainly this is a problem where I live.
The other problem is that an external aerial is require to get a consistant signal. That will invalidate you warenty.
The plain fact is that most people are perfectly happy with thier FM car radios and do not need to change.
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Saturday 1 January 2011 11:45AM
I am listening to the concert on this link at 320kb/s:
http://www.bbc.co.uk/radi…html
The BBC seems to leave this stream on all the time.