What is Digital
Radio? What's wrong
with Analogue Radio?
How
does being digital get round this? What does the
digital receiver do?
What's the down
side? What's the up side?
Does it sound
better? How
much better? Any caveats?
What's
the best Digital Radio on the market? What's the competition?
How much do
they cost? When will they be
affordable?
Why
not have tuners that can receive analogue and digital?
Will I need
a new aerial?
What about the
future? Web
Resources?
This is to analogue FM/AM radio what the CD is to Vinyl.
A far more robust way of transferring information (audio or
data).
Actually a better analogy would be MiniDisc to cassette tapes,
since both digital radio and minidisc have some lossy compression
while CD does not.
What's wrong with Analogue Radio?
In ideal conditions, not much. With a good quality radio signal carrying a well-adjusted audio signal to a decent quality radio receiver, it sounds fine to most listeners. But the real world is not an ideal place. Radio signals bounce off obstacles like buildings, adding a delayed faint echo to the intended signal. You can often see this on analogue TV pictures as a faint "ghost" image to the right of main TV image. Radio signals usually suffer some degradation, and this affects the audio signals they carry. Radio signal strength isn't always adequate, and using a bigger aerial is not always practical. One does not want a roof-top high aerial on a portable or car radio!
How does being digital get round this?
In the very early days of radio, the radio signal could only be in one of two states: on or off. Samuel Morse invented the signalling system where information was sent as a series of radio pulses that where again in one of two types: long or short. All the receiving person had to do was to notice the difference between the two pulses, and write down the letters corresponding to groups of pulses. In this way, it did not matter if there was a lot of noise in the original signal, because that would be ignored and only the pulse lengths noted.
CD player technology replaces the analogue voltage from an LP phono cartridge with a series of on/off signals from a laser beam detector. This ignores minor errors in the signal. CD information also carries error-detection codes, so that if blocks of digital data are corrupted they can be corrected.
The primary aim of digital radio was to get CD-quality sound over the radio. A single radio carrier frequency would have to be switched on or off very rapidly. This gives less time for unwanted signal reflections to die away between pulses. This problem is solved by having a large number of carrier frequencies, each carrying fewer information pulses per second.
There are 1536 carrier frequencies in a digital radio service transmission. They are combined at the transmitter by Fast Fourier Transform.
What does the digital receiver do?
Step 1 is to receive the radio signal and
shift it to a lower and more manageable frequency range. This can
be done with silicon chip circuits instead of the many critical
components used in analogue receivers.
Step 2 is to seperate out the 1536 individual
carriers by the Inverse Fast Fourier Transform. There are
microprocessor architectures specialised for signal processing,
called Digital Signal Processors (DSP) . This step would normally
be a full-time job for a DSP chip.
Step 3 is to decode the messages from the
carriers. A reasonably fast microprocessor would be expected to
do this.
Step 4 is to decompress the digital message into
the decompressed audio signal desired for listening. The digital
audio is sent to a Digital-to-Analogue Converter (DAC) where it
can then be amplified to drive loudspeakers.
Cost - for now: A digital radio receiver is as expensive now as CD players where in their early days. As you can see, they are just as highly complicated. They require a considerable amount of computing power to work, comparable to a reasonable desktop PC. Obviously a PC is not convenient to use so to develop digital radios at realistic prices specialised chips have to be developed. Silicon chip development is very expensive, but once developed they can be produced in volume for very low costs.
There is some signal compression, but this is quite sophisticated. This is done to the MPEG 2 standard. You may have heard of the MPEG 3 standard used to agressively compress audio for transmission over the internet. MPEG 3 has higher compression ratios but relies on more computationally intensive techniques to compress and decompress the signal. MPEG 2 is the better choice for digital radio because it discards less information and requires less powerful (and therefore cheaper) processors to de-compress the data.
The cost should fall in the same way as they did for CD players. You can now get a portable CD player for a few tens of pounds. Digital radio is currently more expensive than analogue radios. Digital radio manufacturers are very motivated to push prices down to the same levels as analogue radios.
The broadcasting authorities have committed to switching off analogue transmissions by around 2010. So buying a digital radio will NOT be like buying a Betamax VCR (a.k.a. a bulky digital clock). And not because digital radios don't always have clocks! Analogue radio IS going to be replaced by Digital.
Buying an analogue radio isn't a silly idea - yet - because you could get a good 10 years service out of it. However, the amount of useful life will decrease, as will the analogue services you can receive. The gradual rampdown period is entirely intended, to make it a gentle transition for radio buyers and sellers.
Digital radio is far more flexible than analogue radio. For example, broadcasters can allocate more or less of the data stream to particular programmes, depending on their content. A non-stereo talk show uses less, a hi-quality live classical broadcast is allocated more.
Digital has another advantage: analogue FM stations often use a circuit that boosts the more quiet parts of the sound ("Dynamic Range Compression" or "Automatic Gain Control"), which can be desirable for low-fi radios. It raises the desired sound above the undesired noise. Making quieter sounds louder can improve listening in non-quiet environments such as factory floors, shops or cars. However, music lovers normally wish to enjoy sound in natural full dynamic range, in living rooms where unwanted noise has been minimised. I've never seen an analogue radio with the ability to reverse DRC. Digital Radio can't do this either, but specification allows for receivers to add the level of DRC desired. Competent broadcast studios now omit DRC from digital broadcast material because it isn't necessary or desirable. Digitally received material is thus more faithful to the original.
I'm told that Radio 3 and Classic FM are now uncompressed on digital, so listen to these stations to compare the sound with and without compression. There's some doubt as to whether people want DRC in or not, so rather than the radio manufacturer decide for you, you can set this yourself. The kind of people buying digital radio today tend to be reasonably well off, therefore more mature and more likely to want to listen to live classical music in concert hall clarity. They're also more likely to ask "what the heck is dynamic range compression?!". So by default, the unit should give you the unmodified signal. If you want some DRC, then you can go to a sub-menu and add DRC until it is as similar to FM as you prefer. The Arcam tuner has this DRC feature - the Technics ST GT 1000 does not.
Hmm, it depends. Back in 1999, I said Yes, in my opinion as a ordinary bloke. Since then it seems that the DAB providers have lowered the bit rates (and hence the quality) to cram more stations in. This is like watering down the beer to fill more mugs. And we are the mugs for not complaining. See Digital Radio Tech for more details. The technology isn't the problem: DAB can provide bit-rates as appropriate (e.g. less for mono talk shows, more for audiophile music). It's just that the best technology can be mismanged by some pointy-haired bosses.
I'm not an audiophile so I didn't tell much difference between mint condition vinyl or tape and a CD. I did however easily notice the irritating noises when I didn't spend begrudged time picking off the dust with a sticky roller, cleaning the tape heads, the occasionally tape being chewed up, and clicks due to scratches. Library records were noticably worn.
Likewise with radio. I'm happy with the few stations with a strong signal. Any noise tends to be noticed in the silences between words or sounds. But the weaker signals are not pleasant to listen to. With digital radio, one transmitter carries many broadcast services, so each service has the same radio signal strength. There's no more fiddling about for stations and finding your favourites have weak reception while others are strong.
Classical music buffs are among the most enthusiastic about digital radio. The silences are completely silent: any noise picked up by the carrier is ignored. So in that brief anticipatory hush waiting for a piece to begin, you can feel part of the audience, including those who go to performances with the express purpose of having a good cough and a fidget!
Analogue vs. digital debates will no doubt arise for radio just as they did for CD and LP. Hi-fi magazines will probably publish a lot of letters and articles about this as they 'd have less to print if they did not! One magazine recently compared the Arcam Alpha 10 with a similarly priced analogue FM unit. Some preferred the familiar 'warmth' of FM, some preferred the clarity of digital. But this misses the point: both do well with a good signal, but digital is less sensitive to real-world problems. The analogue FM unit costs £800, which pays for the best quality components and engineering set-up time. The digital unit costs £800, but the bulk of the work is done by a few silicon chips. True they are expensive as any new technology is, but they fall in price over time. Analogue technology components are never as cheap to mass produce as silicon chips. Eventually you should get the sound quality of a top-end analogue radio for the cost of a low-end analogue radio!
Finally you should note that a single studio may feed many transmitters scattered around the country. The studio's audio signals are often transported on fibre optic links, as digital data. Non-live music usually comes from CDs which hold the music in digital form, and it was probably mixed on digital equipment.
Good question: digital data can be held to different degrees of accuracy. CDs store the music signal as 44 thousand 16-bit numbers (i.e. from zero to 65535) per second. Since CDs were invented, technology has progressed enough for silicon chips to do real-time compression and decompression of audio signals. Digital radio uses MPEG2 compression to get by with much lower data rates. It won't provide exactly CD quality sound, but it should be better than say MiniDisc which uses a fairly high 5 to 1 compression ratio. It is certainly a lot better than tape or your typical analogue radio service. It puts radio music in the same quality league as music from stored media.
Fidelity is in the ear of the listener, just as Beauty is in the eye of the beholder. Actually, everything is in the mind of the perceiver: the brain is a neural net that learns to get used to the way things sound. So making the signal more true to the original may not please all. If you're the type of person who thinks Vinyl records are warm and CDs are cold and clinical, you may find the same thing with Digital Radio. The transparency of digital transmission can expose deficiencies (of less-than-well-adjusted sound studios) that are muffle by analogue transmission. The BBC are aware of this, and are alerting studios to be aware of this.
Tuning is slightly different. Instead of dialling through an AM or FM band searching for islands of reception in a sea of noise, digital receivers scan for services and present the user with a menu of services to dial through. Aquiring a particular service takes a second or two so digital receivers don't start to change service until you press a button to confirm your choice. You can still assign services to preset service buttons, just as many analogue radios do.
Timing may have occasionally odd effects. As mentioned above, the transport of signals digitally is not as near-instantaneous as analogue radio - digital takes a second or two to compress and decompress. Dialling a phone-in show and hearing a delayed version of your phone converstation on the radio might be disconcerting. So time pips and the chimes of Big Ben will be delayed! Since these are very predicatable events, the BBC might be able to record them and transmit them a little early. I can't tell one day' chimes from another.
Reception is significantly different. Everyone is aware that aerials need to be placed for the best signal. With analogue radio, this is easy to judge because you can hear the audio quality gradually getting worse as the radio signal strength goes down. For very weak signals, you can tell you need a good external arial. With digital radio, this is not so easy because the technology maintains the audio quality until the signal is so poor that it just has to give up (this is just like CD players correcting errors due to scratches until there are so many scratch errors they turn the sound off). For this reason, a signal quality meter is a very useful feature on a digital radio, not a gimmick. If your digital radio seems to be having problems, don't panic! On the Arcam Alpha 10 system you can monitor the amount of errors per second it is having to correct. Less than ten is quite normal. Several tens is still reasonable. If you have hundreds or more then your reception is quite poor, and you may need a bigger or higher arial. It might be wise to check your location before you buy a digital radio for your home: the BBC have a map of digital radio coverage on their website. Most of the population of the UK is covered. Most of the main motorways are covered, as digital radio tackles the car radio reception problems (fading, poor reception, limited arials, etc). I did once buy an analogue tuner only to immediately find I could only pick up a couple of local stations well. The dealer would have been quite entitled to refuse to take it back, as there was nothing wrong with the radio itself. It would have been my job to get an adequate arial. Happily the dealer and I agreed to part exchange it for a CD player instead. The same thing applies to TVs, mobile phones and digital radios. Reception is not the dealers problem, but a good dealer should warn you they don't want the hassle of returning money any more than you want to return products.
What's the best Digital Radio on the market?
It's very early days yet, so it's hard to say. Digital offers the most noticable benefits to those with the poorest reception conditions: cars. So most Digital Radios on the market are for cars. I can't imagine paying £1000 for a car radio, but then again I can't imagine buying a car! However if you spend a lot of time on the road in a company car, then digital radio may well be good value. Right now, the only way to get good quality audio in a car is to have a CD player. These are hundreds of pounds themselves, plus you have expensive CDs sitting in your car.
For home use, the market is even smaller. The Arcam Alpha 10 Digital Radio Tuner was the first digital tuner for home audiophile use in the UK. I should declare a bias here: I helped develop it. I don't get any benefit from praising it as I no longer work for Arcam. On the contrary, I was made redundant so you might expect me to be disgruntled and anti-Arcam. I can't blame Arcam for a tough economic climate, it was nothing personal (others went also), and I had no financial commitments so no hard feelings at all. Anyway, having helped develop it I do have enough insider knowledge to say that it is a decent product for a variety of reasons:
Firstly, Arcam chose the best digital tuner module available. This was designed by Roke Manor Research, who have a lot of experience in some very advanced technology so they are no novices. There were other modules around but they were not quite as good or bug-free as the Roke Manor Research module. None of these modules are cheap, unless you consider how expensive it is to have custom silicon chips made. The module contains lots of RF circuitry (good RF engineers are so scarce they can virtually name their price) and a custom silicon chip combining a digital signal processing and a fast microcontroller. The custom chip is based on Hitachi technology. Hitachi command a major share of the market for digital radio technology for mobile phones, so they are no novices either.
Secondly, the rest of the unit is very well developed in terms of quality and cost. Arcam had previously developed their flagship Alpha 10 amplifier in such a way that the front panel could be taken over by processors in expansion boards such as a home cinema surround sound processor. I know this because I developed the code for the front panel! It didn't take a genius to realise that the same front panel could be used by a digital radio processor. By re-using existing parts, the development cost was significantly reduced. For example, it costs about £50,000 to develop tooling for a plastic front panel. Expensive, but cheaper than drilling and machining lots of metal front panels. On top of that, there is the saving in time and money for developing a front panel. All this money that Arcam didn't have to pay is money they don't have to extract out of customers.
So there you have the story. The Arcam unit is the best value for money that Arcam could make it. It's not a case of kludging things to work, the re-usability of the front panel is an entirely valid consequence of it's design. Arcam could only sell it for less if the bought-in module became cheaper (which will happen over time) or they subsidised it (which would be cheating).
I haven't disclosed any information about the Arcam Alpha 10 Digital Radio that a competitor could not have found out by buying a unit and opening it. You can bet your boots they have done so already. Nor can competitors make the same savings Arcam did, because they don't have the parts specifically designed for re-use.
Cymbol are a smaller company, selling a unit with a metal finish which some may prefer. This is completely button operated, so you can't quickly dial through services as you can with the Arcam unit. It's more expensive than the Arcam unit, and even more so with the higher-resolution DAC option. Personally I think a higher-resolution DAC is only warranted for CD players were there is an uncompressed 16-bit digital data to interpolate. Digital radio sound has already been compressed and decompressed, so there is no point in trying to "fill in" samples in addition to those "filled in" by the decompression process. The DAC chosen by Arcam is more than adequate for the job. Anything more doesn't pay its way.
Technics are selling a digital radio for less, I hear. They're a bigger company so I guess they can sholder more initial development costs. I can see they have a custom VFD display, which is certainly an extra expense eventually paid for out of the customer's pocket.
RadioScape
sell digital radio boards for the PC. They're quite a different
market than audiophile hi-fi, but still very interesting if you
want to expand your PC instead of having another hi-fi box to
cart around from place to place. I don't know how much burden
they add to your PC's processor. Being in a PC, there is scope
for storing the MPEG2 data on hard disk for later playing.
Software could be upgraded from the net too.
See my RadioScape notes.
Arcam Alpha 10 Digital Radio: £800
Cymbol:
Technics ST1000: I heard this was circa £500 (UK), £590 (Sweden
7995 SEK).
Tag Maclaren T32R: £1300 for Analogue, plus £900 extra to have
digital as well.
See my DAB Tuner Comparison
page to find what you get for your money.
There's a bit of a chicken and egg situation: prices won't start to lower until enough have been sold to pay for the development costs. And fewer people buy radios at £800 than they do at analogue radio prices. Hi-fi buffs are a minority market, so when a manufacturer comes along and says "we want big numbers of digital tuner modules to fit in expensive cars as standard" then that will drive the costs down a lot. It's expected they will come down in price in similar speed as CD players - slowly but surely. When you buy depends on how long you're prepared to spend your finite listening hours without one. Don't take anyone's word for it - go and listen to one yourself, and you decide. I reckon you'll probably decide you want one sooner rather than later.
Why not have tuners that can receive analogue and digital?
It's certainly possible - if I bought a new tuner today I would want one that is analogue now and could be upgraded to digital when I felt the module was affordable to my pocket. However, almost all of the people who enjoy radio enough to pay £800 for a digital radio already have a good radio. So a combination radio would just add expense and there's plenty of that already.
The best aerials are carefully designed to match the radio frequency they are meant to pick up (typically a quarter of the wavelength), and the input impedance of the receiver (so the radio energy is absorbed by the receiver instead of reflected back to the aerial). Analogue FM is centred around 99 MHz. Digital is over twice that, around 230 MHz, nearer the frequencies used for mobile phones. So aerials for digital radios are more like the short ones used by mobile phones. If you live in a strong signal area, you could try your existing FM aerial just to get things up and running. But that's like having an expensive telly and using a coathanger or set-top aerial - more prone to unsatisfactory reception. Digital radio is designed to work well even with a modest aerial, but there is a lower limit! If you really are straining to pick up radio, height is usually more important than location - that's why TV aerials are put above the roof. Radio broadcasts primarily travel horizontally to receivers, and signal strength plummets as buildings block the line of sight, typically halving every metre below roof top level.
Quite exciting: We've seen an inkling of what's possible from data broadcasting: teletext on TV signals, and radiotext on RDS radio signals. Digital radio could be used to broadcast pictures (though not in real-time, that job belongs to the telly!) or text or software. LCD screens suitable for showing pictures are very expensive, so only portable PCs merit the cost for now. Portable TVs can only merit screens a few inches in size. But for those with computers it may be possible to receive broadcast web pages (e.g. the BBC's web site?) and newspapers without running up huge phone bills. You might even be able to record particular radio programmes on hard disk for listening at a more convenient time.
The newsgroup alt.radio.digital has a small but growing band of digital radio users at where you can listen to and discuss digital radio. The best people to ask about the quality of digital radio are the listeners themselves. Check out the websites of The BBC, Arcam, Technics, Cymbol, Technics and so on for latest information. The Canadian authorities have been doing a lot of research and have put the results on the web. This covers much of the non-technical issues as well, such as politics, who's doing what, announcements, etc.
The BBC's engineering
information pages
The BBC have information
about digital radio and a map of reception in the UK. See the 33K
pdf file:
A Technical
Overview of Digital Radio by Stephen Baily, of BBC
Research and Development,
Philips make DAB decoder chips.