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Tuner Choice

From Hi-Fi World - July 2005 issue

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Tuner Choice

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Noel Keywood offers sage advice to those wishing to buy a tuner…

 

If you want serious sound, then right now ye olde analogue VHF/FM is still the only choice. Digital Radio (nee DAB) was once touted as "CD quality", but this claim is becoming less common now that a sufficiently large chunk of the buying public has heard it!

 

Indeed, the cat’s now out of the bag on this subject; even in the European Broadcasting Union (EBU) DAB has strong critics and argument has broken out. DAB offers choice, having a swathe of stations not available on VHF/FM, and in fact sacrifices quality to do so; there is a direct trade-off between the two. DAB suits portable radios and cars (for which it was designed), but not good quality domestic hi-fi. All the same, you are likely to want both DAB and VHF, unless you prefer to use Freeview or Internet radio instead of DAB. Yes, with digital seeping in down your TV aerial, through the telephone lines and even drifting in on the ether, via broadband wireless and possibly your neighbour’s 802b, there’s no getting away from Digital Radio. These days you need a BSc just to sort out the options - and don’t worry, if you are confused, so is everyone else - including the broadcasters!

 

For hi-fi purposes though we’d all like decent quality and this always means ‘bandwidth’, as Claude Shannon usefully pointed out - for digital as well as analogue. At present that means VHF/FM alone; although bandwidth is available for digital broadcasts, it isn’t being allocated. Let’s look at the many digital radio options available today first.

THE DIGITAL DILEMMA

All digital broadcasts are compressed, as sufficient bandwidth for lossless compression isn’t available, so quality is always compromised to some degree. Internet radio usually uses mp3Pro, whilst DAB radio uses Stone Age mp2. Freeview and DSat use mp2 as well, but as both sometimes use higher data rates they can sound a little better than DAB. Generally, you will get best quality from mp3Pro internet radio at 128kbps, which can sound quite sweet and clean - unusual for digital. Try www.live-radio.net or the excellent www.digitalradiotech.co.uk for information on all this. And remember that internet stations can come with pop-ups, stomped on by Microsoft’s Service Pack 2 XP update, and an unwanted spyware payload as well, for which I recommend the free and excellent Ad-Aware SE cleaner from Lavasoft.

 

Mac OS Panther is getting recognised too, so Mac users shouldn’t be complacent. But then Apple iTunes plays radio that both Mac and Windows users can access for free. And of course there is the Windows Media Player. If you want quality, internet radio seems a poor choice, although www.tuner2.com picks pearls from the dross and is worth checking out. It’s a fast growing sector and if you can be bothered to find a station you like from the myriad available, then this form of extreme narrowcasting can be very interesting and even esoteric. Try www.techwebsound.com for example, for 1960s psychedelia that you never knew existed. Internet radio comes with playlists and info. Linked in with iTunes, you can even purchase some tracks online. Radio at this level has the power to revive an era, or a genre, by making it both accessible and available, something that sets it apart from one-way delivery systems, like transmitters on hills…


i-tunes


Get stations from around the world via the internet, using  Apple’s i-tunes player,

shown here. Alternatively, use Windows Media Player. Both are free.

 

Alternatively, if you have a wireless broadband router, check out the Slim Devices Squeezebox at www.multitask-computing.co.uk. It receives internet radio and has an audio output for the hi-fi. At present internet radio streams at 28-128kbps, giving mediocre sound quality except at the highest rate. However, internet radio solves a lot of broadcasting problems (no transmitters!) and could deliver really good quality if it could move to 192 or 256kbps data rates, and AAC encoding, or something equivalently good. This isn’t out of reach. It could well be the future of radio; many people think so.

 

Listening to radio via Freeview TV receivers is another option (see p22). In the UK, Freeview TV is attracting more attention than DAB and a wide range of set-top boxes are available, from a bewildering range of manufacturers, including the Sony VTX-D800 and Philips DTR500, both of which are quality units. Also, you may be interested in SetPal and newer Novapal technology, as used by Daewoo, Labgear and others: go to www.novapal.com for a fascinating if a little technical look at a UK technology little recognised. This will interest those living far from transmitters, or experiencing other reception problems. Nokia also make well regarded Freeview receivers.


radioscape-module


The anatomy of a digital tuner, in this case the RS200 module from Radioscape,

found inside both the Arcam DT-91 and Cambridge 640T we review this month.

Signal from the aerial is amplified and downconverted in frequency, processed

digitally in the Texas DSP chip, then converted to analogue. A form of Software

Defined Radio, this is the future of tuners.

 

At around £100 or less, Freeview receivers make a lot of sense for audio use; as well as radio you get digital TV too. They are easy to use: just connect the audio outputs to the hi-fi and you have access to DAB stations, transmitted via digital television. That Freeview commonly offers higher data rate and better quality than DAB is something that undermines DAB’s position as a source of radio in the home. It also complicates the picture generally; for example, shouldn’t hi-fi tuners have VHF and Freeview audio, rather than DAB? Or perhaps they should offer the full Monty, with TV output too? Instead, we have DAB tuners that offer VHF/FM, a by no means logical pairing for domestic audio…

 

An interesting and arguably more appropriate alternative to this arrangement is to use a good analogue VHF/FM tuner connected to your amplifier’s Tuner input - see our reviews - and a Freeview tuner connected to Aux (or better still, via a digital input), to get DAB stations via Freeview. Of course, if you have satellite TV then again you can get many DAB stations at higher data rate than via DAB broadcasts, so connect up your satellite box instead. Satellite radio is Free To Air, so you do not need a Sky package.

 

It’s pretty much accepted now that the mp2 encoding of DAB, known as Musicam, desperately needs improvement if sound quality of DAB is to be brought into the modern world and this is being discussed in the background, with AAC a future possibility. Meanwhile DAB struggles on, promoted hard in the UK by the BBC which has invested heavily in it. DAB offers hiss-free reception and has the potential to sound good. However, it has been hampered both by an archaic compression system that is difficult to upgrade or replace, and by broadcasting policy that favours variety above quality, without reasonable compromise. As a result data rates are low and quality poor. This makes DAB best for portable radios and car tuners, providing they can actually pull in a clean signal, of course!

 

Other developments in broadcast transmission, such as DVB-H (Digital Video Broadcasting - Handheld) are now threatening DAB. Open dissension has broken out on the future of broadcasting as a result - and I haven’t mentioned mobile phones, the cellular network and 3G! In the meantime, whilst debate builds in the background, VHF/FM remains a clear leader if you want to enjoy good sound quality. And no it won’t be switched off tomorrow; Ofcom now say they cannot predict when this will be possible whilst there’s so much disagreement and turmoil on the future of broadcasting.

THE ANALOGUE OPTION

VHF/FM tuner choice has narrowed, high-end designs from Japan becoming rare. Long gone are 1970s super-tuners like Pioneer’s TX-9500 MkII, Yamaha CT-7000 and Sansui’s TU-9900. Analogue tuners like these were replaced by synthesiser tuners, like Hitachi’s FT-5500 MkII from the mid-1980s, which eliminated tune errors (remember AFC?), as well as mechanical tuning. Since then companies like Philips have managed to cram very high performance VHF tuner blocks onto chips, rendering discrete analogue tuners obsolete. Nowadays this is exclusively what you get when you buy a hi-fi tuner, manufacturers in effect packaging chipsets. If you are interested in a very high quality analogue tuner, then Marantz offer the ST-6000, Naim the NAT03 and Linn the complex and advanced Pekin at the top end of the market. Further down, price wise, exist less complex conventional designs from NAD, Denon and Creek (and Pure’s DAB tuner, which has a normal analogue VHF section).

 

No matter how sophisticated, all conventional tuners need a strong signal from the aerial to render hiss inaudible - around 1mV. When buying a hi-fi tuner, bear this in mind. Buying a more expensive model with better sensitivity figures affects this requirement little. In most areas of Britain you need an outdoor aerial to get a signal as strong as this. Which is why VHF is thought by some, if you believe DAB hype, to be ‘hissy’. With sufficient signal it is in truth very quiet. For example, I tested a 1980s Hitachi FT-5500 MkII alongside the tuners this month (I use this tuner as a ‘control’ since it gives stable and advanced performance) and it manages -80dB hiss, which is extremely quiet. Sadly, for some reason I do not know, but likely to do with cost, modern VHF/FM tuners rarely give better than -73dB hiss. In use this is sufficiently low for them to seem pretty quiet, but it is close to the limit of audibility. You won’t hear hiss in normal use, except when silences exist in a programme, not uncommon on Radios 3 and 4.

 

DAB overcomes this drawback, but ironically both the Arcam and Cambridge tuners tested this month challenge this ability, using an ultra-sensitive and quiet DAB front-end, together with digital signal processing to achieve radically low VHF/FM "full quieting" figures that approach DAB performance. This was a surprise to me; I had to re-check many times before believing what the test equipment was telling me. These tuners need very, very little signal - 27uV (millionths of a volt) - to give minimum hiss. That’s around thirty times less than other vhf/fm rivals. You’ll get this from most indoor wire aerials. The bad news is that, at present, the minimum level of hiss is painfully high, at -63dB (Arcam) 10dB worse than conventional immediate rivals in the group, meaning you will hear hiss no matter how good an aerial you use!


dtr500_05_webimagefullsize

Philips DTR500 Freeview receiver - higher quality radio than DAB with the high

data rate stations. In future though, radio via TV channels will be the norm if

DVB-H takes off.

 

How do Arcam and Cambridge achieve such a performance? This brings me onto future tuner developments, being driven by the big semiconductor manufacturers like Texas Instruments. The big word here is Software Defined Radio, or SDR, which in curtailed form exists within the Cambridge and Arcam tuners; SDR has arrived in high fidelity already. Both are radical under the hood, but there’s far more to come. Imagine connecting an analogue-to-digital convertor (ADC) up to an aerial to turn its tiny signal into digital straight away. It’s then processed by a computer. This is the basic idea behind SDR, all processing being carried out by a computer. At present the upper limit for direct A-to-D conversion is 80MHz or so, the start of the VHF/FM band, albeit at limited resolution. Higher speed ADCs are coming though; quality is likely to be well below hi-fi standards for some time yet all the same.

 

Both the Arcam and Cambridge tuners have a powerful Digital Signal Processor inside, the Texas DRE200, to number crunch the radio signal into audio. These are not tuners as we know them. The block diagram published by Radioscape shows the quiet and sensitive front-end of their receiver module is used by both DAB and VHF/FM sections, which partly explains why the vhf section has exceptional performance figures. As direct conversion to digital from VHF frequencies is currently not practicable, a frequency downconvertor (divider) is used. An ADC is then used to digitise the r.f signal before it is number crunched by the DSP to extract VHF/FM data and turn it into digital audio for conversion by a DAC into analogue audio. This is a form of Software Defined Radio, meaning the Arcam and Cambridge tuners are a step up again in technology from all that has gone before - and I am talking vhf/fm here, not DAB.

 

It isn’t all good news, as our tests show. Both produce the extended distortion spectra that characterise digital systems and, viewed on a spectrum analyser, this alone told me straight away I was dealing with digital processing, so pronounced is it. Distortion like this is readily audible and generally unpleasant. The all-analogue tuners, by way of contrast, have relatively mild distortion spectra, dominated by second and third harmonics which, subjectively, are relatively innocuous.

 

Then there’s the noise problem, curable by the use of a better ADC I would guess. What you have to remember here is that Radioscape are DAB specialists. The module in both tuners is a DAB tuner onto which has been bolted a semi-digital vhf/fm section, about which they say little. A quieter, dedicated VHF solution may well be possible in the near future, using refined SDR techniques. It looks a very promising way to get quality VHF/FM radio, which will be available to us in the UK for a long time yet.


 

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