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Resolution!

Cutting Edge
By Dave Shapton

Pinnacle's Showcenter: a good idea that will be even better when uncompressed  audio playback is supported.Pinnacle's Showcenter: a good idea that will be even better when uncompressed audio playback is supported.

At a time when audio quality is supposedly getting better, compressed formats are dominating consumer digital devices and services. Cutting Edge takes issue with the trend away from full-resolution playback.

16-bit At Its Best

If you want to hear just how good 16-bit recordings can be, try almost anything on the DMP record label (www.dmprecords.com /technology.htm). They've specialised in digital recording from the earliest days and always seem to come up with recordings that make the best of the available headroom. The very first DAT machine I had (an Aiwa Excilia) came with a DMP demo tape of a big band. It blew me away — and this was in 1988!

Technological progress is supposed to mean that things keep getting better. But there are still times when progress seems to make them worse. History is littered with examples — mainly, it seems to me, concerning the ability of one nation to threaten the well-being of another. And sometimes scientific breakthroughs expose us to dangers we couldn't even have conceived of before.

What I'm going to talk about this month is quite trivial compared to any of this stuff, but it's a worry to us, in our speciality, which happens to be making music and delivering it to the ears of the people we want to listen to it.

Hearing Is Believing

I'm a great fan of quality in audio. When I listen to a recording, I like to think what I'm hearing is as close as you can get to the original performance. With some reservations that I won't go into here, I think this is a pretty good definition of quality in a recording.

Even with a track that has either been heavily processed in a studio or completely artificially created, I want to hear it the way the artists, producers and engineers heard it. If a hip-hop producer chose to use a vintage sampler because the D-A converters sounded grungy, I want to hear what he or she heard, as much as I'd want to hear what makes a Stradivarius sound different and better than a cheaper instrument that a student might use.

There's actually no problem at all with the recording process these days. All it takes is some good A-D converters and a 24-bit, high-sample-rate recording device (a computer, probably) and we can record at a resolution and quality that would have been unthinkable at almost any price ten years ago. No, what's really winding me up is that we can't always get to hear these recordings properly. And, at the same time, people are getting 'normalised' to listening to what is actually pretty poor quality, for a number of reasons — which I'll come to shortly.

A Bit Important

But first of all, you may be surprised that some of the best recordings I've ever heard have been recorded at a resolution of 16 bits, with a mere 44.1kHz sample rate. It's quite fashionable to dismiss 'mere' CD quality as being so low-fi that it's almost offensive to listen to, but this is a tad unfair because, with a dynamic range of 96dB (a rule of thumb is that you get 6dB of dynamic range for each bit) and frequency response in excess of 20kHz, a well-recorded CD can sound fantastic.

Bear in mind, though, that this dynamic range is only available if all of the bits are used. If you're worried about headroom (and you probably should be) while you're recording, you'll probably do what most people do and only use, say, 12 of the available 16 bits for the majority of the recording. And extended quiet passages are a real problem. Not only will they be perhaps using less than eight of the available bits, but you might also be tempted to increase the volume, and then you'll hear all sorts of unpleasant things going on.

So, of course, 24-bit is better. And high sample rates help because even if we can't hear the extended upper frequencies, they probably interact and create effects that we can hear lower down in the spectrum. At the very least, real-world objects, including musical instruments, don't have a brick-wall filter that prevents them from making sounds above the human limits of hearing, so it seems sensible to record and reproduce them faithfully, however they produce their characteristic timbres.

It's a pity, then, that there is a distinct trend for consumer audio products to move away from delivering the full audio potential of even the humble CD. A significant factor in the 'dumbing down' of audio quality is MP3 files and players. On the one hand I'm really pleased to see these products selling in big numbers, and that you can actually download and pay for music — which is what most of us have been willing to do all the time. But I also feel, if I'm going to commit to paying for a track or an album, that I'd want to have the right to use the full-quality version of the track as well, and not just its 11:1 compressed lesser-ego. And here's the crux of the problem: MP3 files at low bit rates (and that includes 128kBit/s, in my opinion) just don't sound very good. Despite the miracle that is perceptual coding and compression, the quality is just not good enough for serious listening.

MP3 Conquers The World

DAB radios may be digital, but that doesn't mean they can always deliver the best audio quality.DAB radios may be digital, but that doesn't mean they can always deliver the best audio quality.This is a problem we just can't ignore if we're going to protect and preserve the integrity of the music we spend so much time and money creating. Here's a case in point. I've just received a new device from Pinnacle, whom we mostly know as the new owners of Steinberg. It's called the Showcenter, and is designed to live near your TV and hi-fi while it plays MP3 files and MPEG-4 video from your computer. The idea is that your computer (or 'media server') sits in another room, where it can be as noisy as it likes, as the Showcenter silently draws the material across the network and lets you choose what you hear, or see on your TV screen.

What a great way to listen to CDs, I thought: rip them as WAVs to my 250GB Firewire drive (it'll store over 300 uncompressed albums!) and play them across the network into my stereo. The Showcenter even has electrical and optical S/PDIF outputs, so there's no reason why quality shouldn't be brilliant. Except that it doesn't play WAVs — only MP3. What a missed opportunity! I mentioned this to Pinnacle, and they quickly responded, saying that they were working to add PCM (ie. uncompressed) playback. Meanwhile they also support playback of MP3 files encoded at up to 320kbit/s, which should sound pretty good. It would be even better if the Showcenter could play 24-bit files. We'll have to wait and see what Pinnacle come up with.

One objection to using uncompressed PCM files instead of compressed formats such as MP3, AAC and ATRAC, is that they take up 10 or more times the space. True. But how many people use the whole capacity of their 40GB iPod? That's still enough space for around 60 uncompressed CDs! Plenty for the average bus ride, I'd say. Tell me if I'm missing something, but I'd have thought it pretty simple to implement uncompressed playback on just about every platform, storage issues aside.

The Digital Airwaves

But the biggest issue of all at the moment, for me, is digital radio. If I worked for the tabloid press I'd be considering using the word 'scandal' in my banner headline, but this is Sound On Sound, so you're going to get a more reasoned account of all that's wrong with DAB, and why it matters so much to us.

DAB, or Digital Audio Broadcasting, is supposed to be the next stage in the evolution of radio broadcasting, and in some ways it is. But in one very important sense it isn't: quality. If you were to ask, say, 20 people in the street what makes digital radio better than analogue, I reckon that 20 of them would say that it was quality. I think it's fair to assume that most people associate digital with better quality, and even if they've never heard digital radio it's a fair assumption to make — which is exactly what I did, in fact.

So I was shocked to find, when I bought my first digital radio a couple of weeks ago, that in a comparison of the digital version of Radio 1 with the FM (analogue) one, the FM station won hands down. Surprising, to say the least. A bit of poking around with the radio's menus revealed a display of the current bit rate for a given station. In the case of Radio 1 it was 128kbit/second — around the same bit-rate as a typical MP3 file, in fact. So not exactly CD-quality sound, then! Quite possibly not the 'Crystal Clear' sound claimed on the box, either. And in practice it didn't even sound as good as an MP3 file. That's because digital radio in this country doesn't use MP3. It uses what would be called MP2 but is actually MPEG-1 Layer 2 audio. As you might imagine, this earlier version of the perceptual encoding algorithm used with MPEG-1 video is quite a lot less efficient than MPEG-1 Layer 3. So the painful conclusion is that supposedly 'near CD-quality' DAB can and does typically sound worse than an average MP3 file. To my ears, a bit-rate of around 160kbit/s is necessary to match the quality of a 128kbit/s MP3 file. To their credit, some DAB stations transmit at this rate or even higher.

Digital Radio Via Freeview

There's good news for you if you want to listen to digital radio and don't need a portable solution. It's Freeview, the free-to-air terrestrial digital TV system that has risen from the smouldering wreck of ITV Digital. Buy a Freeview box, plug it into your TV and hi-fi, and, hidden among all the shopping channels, you'll find most of the radio stations that also appear on DAB. Best of all, they tend to use a higher bit rate. Some Freeview boxes even come with S/PDIF outputs, so you can bypass what must inevitably be the rather dodgy analogue audio stages in such remarkably cheap devices. You'll need a good aerial, though, because audio dropout on Freeview is very nasty indeed.

To be perfectly fair, I don't think anyone is deliberately misleading anyone else, and I also think that the majority of DAB users are very happy with their radios. DAB is certainly easy to use, gives less interference, offers a great choice of stations, and has the potential to sound very good. Most people won't make direct comparisons with FM, and almost certainly won't listen though a high-quality speaker system. In fact, the bit rates chosen are probably a pretty good compromise, given that most people are listening to DAB on portable radios with 3-inch speakers.

The problem is caused by the limited number of frequencies available for DAB, and the expense of creating a national infrastructure which is at least partially duplicating the existing radio setup. Digital radio stations are grouped together on a single frequency in an arrangement called a multiplex. If there was only one station per multiplex, DAB could probably work with uncompressed audio, but the commercial reality is that there are a lot of stations. This means that the audio must be compressed. The more stations you have, the lower the quality, and there are too many stations per multiplex. Simple as that.

That's why the whole situation is so frustrating. DAB could sound superb. It was designed by people who really know what they're doing. The best tool to hand when they were devising the system was MPEG-1 Layer 2, and this was fine if they were able to use an appropriate bit rate. It's not their fault that the system is being compromised by a rash of stations.

It's a pity, too, that the compression format is hard-wired into the receivers. If they could all be upgraded, the broadcasters could use a more efficient codec, giving better quality at the same time as allowing even more stations to use the same multiplex — and all using the same 'transport stream' to deliver the data. I know this is possible, because Microsoft and Imagination Technologies, who make the 'Pure' DAB receivers, have done tests with surround sound over DAB using Windows Media 9 audio codecs.

For now, my advice is still to go ahead and buy DAB radios. I've tried radios from Pure and Bush, and I really like them. If you don't listen too critically, they don't sound too bad through their small speakers, and I love the way they 'just work'. But don't expect hi-fi performance. What you'll get though a quality sound system is muddy, warbling sound, with a poor stereo image, unless you listen to, say, Radio 3, which has a higher transmitted bit-rate.

How do you feel about a digital transmission system that messes around so much with carefully-crafted musical works? Let me know what you think about the DAB issue. Let the BBC and the independent broadcasters know too.

Published April 2004