Delusional DAB arguments page
Brian Butterworth published on UK Free TV If you post a rant about DAB, the post gets moved to this archive page.
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Friday, 18 February 2011
Saturday, 19 February 2011
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electronic_engineer1:06 PM
Briantist: perhaps Terry has 'acclimatised' to all FM stations transmitting in stereo, whereas many on DAB - including Radio 4 at times - broadcast in poor quality mono.
The scientific evidence proves that with good reception for both, all DAB transmissions (with the possible exception of Radio 3) have inferior sound quality to their FM equivalents. This is because far more DAB stations have been squeezed in than the system was designed for, so amount of data available for each is far too low.
Repeatable double-blind scientific tests show high frequencies are absent or distorted on DAB stations, and the stereo image is very poor. And even in areas supposedly covered by DAB, the signal level is lower than that defined as being necessary for reliable indoor listening.
Your opinions are, of course, welcome and interesting, but your comment that you have a 'small cheap DAB radio' says it all. With respect, perhaps you should try listening on a good-quality stereo system and considering the scientific evidence before posting the next of your many uncritical celebrations of the UK's obsolete DAB system.
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Tuesday, 22 February 2011
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Terry12:01 AM
Briantist... what broadcast format do you listen to on your car radio? Is DAB a reliable listen on the move? Does DAB radio guzzle batteries?
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Kev9:30 AM
Poole
Well I have a mixture of DAB and FM radios in my house - and DAB sounds way too compressed - although it is very clear (if you can live with the delay if you have an FM radio playing in one room and DAB in another(!).
But.. virtually everyone has FM radios in their houses, cars, garages and the government's plan to switch it off is dictatorial to say the least; many people just cannot afford to replace radios at the whim of MPs. It's just another money-making exercise - trying to use the technology before it's ready - Digital-TV being another one...
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Kev's: mapK's Freeview map terrainK's terrain plot wavesK's frequency data K's Freeview Detailed Coverage
Thursday, 24 February 2011
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Steve Brian4:54 PM
I for one can't see the benefit of DAB, especially as it's field strength on band 3 will always be inferior to the same power levels on band 2.
I have been in the professional broadcast industry as a transmitter engineer, service technician and presenter on various stations for 40 years now and I can certainly tell the difference in audio quality between a nice well modulated VHF FM carrier wave and a highly digitaly compressed FSK DAB broadcast.
I am not against digital transmission, but the way it has been implemented around the world really a bugs me. There is plenty of RF spectrum in the universe to let a digital broadcast breath and spread its wings and not use as much, or hardly any digital compression. After all, the NICAM 728 digital system used on the PAL TV system and also for a time as a recording medium, as well as for linking outside broadcasts back to racks rooms, etc. was and indeed still is a much more natural sounding digital system. So why didn't the broadcasters of the world unite and put together a trully great digital system that doesn't throw away great chunks of audio information due to the psycho-acoustic algorythms that are employed in the audio codecs of the DAB syatem? As it stands, the system that is used in the UK was designed for 256 kbits per second, but over the years has been squashed so much to squeeze too many broadcasts into a small part of the RF spectrum. The result is stations broadcasting in 64 kbps mono, 128 kbps stereo and I believe on a few in 192 kbps stereo.
These low bit rates do produce audible artifacts and the reason most people don't hear them, is that a lot of people have lost the art of enjoying real hi-fi sound; they tend to listen to cheaply made imported audio products with tiny speakers with tuned ports to simulate reall bass notes and treble boost circuts to try and add some color to the flat lifeless and clinical sounding DAB audio sound.
If you listen to an FM broadcast, the sound is more natural and OK it's audio bandwidth is limited to a brickwalled 15 KHz, it does not really affect the sound to that extent as most people over the age of 30 years would not really detect 15 KHz to any great level, and infact as we age the Higher frequencies do tail off rapidly. Ayway, there is not that much in the way of audio information above 15KHz that would really add much to any program material. The use of pre-emphasis is to overcome the triangular noise relationship that FM produces and the 50uSec curve is well controlled by HF limiters and overshoot clippers at the transmitters and should not impart hardly any distortion to the audio reception. So the argument about pre-emphasis and de-mphasis is no-goer in my opinion, as a good quality FM system will knock any bit rate starved DAB signal for 6 any day of the week. The only downside to FM is that it uses the Zenith GE pilot tone system for stereo. It works well, but is a suppressed carrier AM system which is transmitted at a really low power ratio on the FM carrier wave as opposed to the mono part of the signal. This does mean that at least 10 dB of signal to noise ratio is lost with a stereo FM signal, where as a DAB signal will sound slightly better in terms of noise due to there being no analog chain for it to pass through.
To sum up this rather long missive, Digtal radio, OK, but let's have it properly thought out, let's have one worldwide standard and let's have some really hi-fi audio broadcast... After all, this is 2011 not the good old days of steam AM radio.
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Friday, 25 February 2011
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John1:37 PM
What the masses have yet to realise is just how switching off FM in faviour of DAB will effect them. Just take a look arround your home and car's to see just how many FM radio's most people own, from radio alarm clocks to car radios, what is everyone going to do about their car radio, particularly those built in systems which most are, such cars will still be on the road when FM is switched off, only a small percentage of cars on the road currently have DAB. Just think how much it is going to cost everyone to replace ALL their radio's, and for what exactly?
I think it is about time that the public was made more fully aware of this situation and the consequences and that a petition is set up to stop FM switch off, at least for another 10 years.
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Trevor Harris10:47 PM
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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Terry11:37 PM
... psycho-acoustic algorythms... highly digitaly compressed FSK DAB broadcasts... audible artifacts... flat lifeless and clinical sounding DAB audio sound... now that's what my ears tell me whenever I hear a DAB broadcast! Side by side and all things being equal I've no doubt that FM is a better quality listening experience!
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Saturday, 26 February 2011
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Steve Brian1:16 AM
The DAB situation that we are lumbered with in the UK and Norway (Who I believe also use the same DAB standard as the UK)is nothing short of a joke! To be told by polititians that it's all part of a Digital Ecconomy Act, is just laughable indeed for many reasons.
The first point I'd like to make is that DAB uses band 3; a terrible band to use for domestic broadcasting for many reasons mainly due to it's poor propagation and lack of field stregnth per metre; i.e: the ammount of voltage developed accross a 1 metre length of antenna rod in free space. This is measured in microVolts per metre, so for a frequency in band 3 of 200 MHz with a received field strength devloped across such an antenna of say, 50 microVolts per metre, the same antenna in band 2(FM)at 100 MHZ, would read 100 microVots, a 6 dB increase in level. Therefore to acheive the same punch as an FM band 1 transmission a DAB transmitter needs to put out a carrier wave of 4 times the effective radiated power to acheive the same level of building penetration. This is why DAB does not work at a moderate distance from a transmitter.
This is why we have people moaning that their brand new shiny DAB set only works if the set has been placed in a special spot on a window ledge, or with the antenna hangining out of a window of a tall building.
So to counteract this lack of field strength what do the idiots at OFCOM in charge of spectrum management do?... Yep!... they sanction the building of lots and lots of new DAB transmitter sites with even more power demand on the National Grid than the entire FM network of transmitters in the UK.
So, Digital Ecconomy Act, me arse! Oh, and then there's the power hungry DAB radios and the chargers that are needed to charge them up for portable use... Ever tried to operate a DAB radio on a battery of cells for more than 4 hours without them going almost flat anyone??! As I said before, digital radio, fine, but let's develop a worldwide compatible system that works and works well. The American IBOC digital system is on the right lines as it's backwards compatible with FM transmitter sites, using a digital sub carrier alongside of the FM carrier. Although IBOC is not perfect, it could be developed more and then the problem of poor propagation is then negated. After all, AM radio is a good univerally adopted broadcast medium and before anyone shoots me down in flames here, the sound quality on AM is restricted to a 4.5 KHz audio bandwidth in region 1 Europe by the broadcast regulators, not the broadcasters. A good quality AM signal with a 15 KHz bandwidth and using a properly designed wideband AM receiver sounds awsome! (As good as FM) Remember just how good the audio on Radio Caroline sounded with it's 50 KW transmitter and 10 KHz plus wideband transmissions using an Optimod AM processor.
If the RF spectrum was set up by broadcast engineers only and not politicians with their advizors then we would have more room to spread out and operate stations without all of the technical restrictions of reduced bandwith, too much digital compression and a money grabbing corporate industry who are only hell bent on making lots of cash, selling advertizing and pleasing their shareholders at the expense of higher technical standards for the listeners.
One final poit that also worries me about DAB is that it's a totalitarian medium... Think about it, right, if you don't get on to a multiplex, then your station can't broadcast; but with FM the ball game is in your court. In other words DAB is an exclusive club, right... in other words: "You pay us whatever we say or else we take you of the air"... Now that's hardly demorcratic is it?
It's not easy to broadcast as an independent operator on DAB it's either you join a multiplex or you have no future on the airwaves if they close down FM and AM as well. Maybe that's the Government's plan for even more ways in which to dumb down an already poor broadcasting system in the UK.
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