Ideally what we like to see is a transmission system that is universal in the same way that AM and FM are all round the world at the moment but that also used spectrum efficiently, provided excellent technical quality and was allied with excellent content.

The problem we see is that there are so many conflicts, driven by a combination of differing interests that this is unlikely to come about in technical terms and we're not that impressed with the content likely to be offered in many places.

We still think the idea of using additional spectrum, as is done with DAB, beats the idea of cramming digital into existing analogue signals for a number of reasons albeit we are conscious that the UK DAB transmissions use the inferior (in terms of getting quality for the same bandwidth) MP2 coding rather than more advanced codecs that have been developed and are being used in other systems.

The DAB system can of course adapt to the more advanced coding - it has to when it is used for DMB (Digital Multimedia Broadcasts) - and both the Digital Radio Mondiale (DRM) and iBiquity HD systems use more advanced codecs for their terrestrial transmissions as do the two satellite services. The problem is that you can't get all the signals on one receiver albeit combined DAB/DRM receivers are beginning to be developed and this raised the question of whether this could be made possible in future and if so how best to approach future developments.

At the moment as happened with original video recording systems, consumers are stuck with having to wait or buy equipment that will almost certainly be inferior - and more costly - to what is going to be possible and there is no clear inter-compatible way forward.

In the US, we believe the Federal Communications Commission has double-ducked the issue - allowing the satellite companies to supply proprietary receivers that are good for only one service and also in taking a route with HD that protects existing companies at the expense of potential new entrants albeit the development of broadband - and specifically broadband wireless - services or of new forms of software-defined systems could provide workable and economically viable options for such new entrants.

If they do, our view is that the result will be a more significant weakening of terrestrial radio than would have happened had a different approach been adopted using additional spectrum.

Looking at the digital future, we now split our consideration into areas of technical and content issues.

The whole point going digital relies on a combination of audio and spectrum use benefits and these in our view should be indissolubly linked with a consideration of universality and receiver costs: If the audio is not up to standard, we can't really see justification for the move and unless it is significantly better a move can only be justified in terms of using spectrum more efficiently since, other things being equal, there is a benefit if audio is the same in being able to provide more services.

So how does digital fare in these terms. We've already made our point about universality - something that would also reduce unit costs as mass manufacture got under way. What about audio quality and efficient use of spectrum?

Audio quality:

This splits into two main elements, the quality as perceived by a listener and the robustness of the transmission-reception combination. On the latter we can only speak from our experience which is effectively limited to Eureka DAB as broadcast in the UK since to test such things one needs to both have a variety of similar chosen listening environments, similar material, and the ability to test in the home, on the move and in various locations.

That being so we can only comment in terms of the general qualities of digital namely that the signal remains clear in terms of interference until nearly our of range when there is some degradation - one UK comment describes it as like putting the speakers in "Bubbling mud" - and then suddenly no signal. That was something we observed dramatically displayed during a BBC digital audio demonstration (not DAB) some years ago in the early days of digital when a signal put down around 301 metres of cable was perfect, at around 301.5 started experiencing problems and at 302 died completely (We also recall that using only a short length of the wrong cable destroyed the signal that had been carried successfully over the 301 metres of properly chosen cable).

In other words for listeners in an area where the signal is strong, digital audio broadcasts are certainly "cleaner" than analogue signals unless a high-end properly set up tuner is being used for the analogue reception.

Of quality as perceived by the listener, we see nothing but benefit in all the digital systems in use when it comes to speech and for music the problems are generally a matter of how good a signal the broadcaster chooses to transmit - broadly speaking in MP2 (the codec used by the UK DAB system - it is inferior to MP3 and those used in HD, DRM and DMB) we have found BBC Radio 3 fine, albeit not CD quality, at 192KBPS, the normal transmission quality, but not not quite as good when listened to on quality speakers when, because of sports broadcasts on Radio Five Live Extra, this is reduced to 160KBPS.

We would note here that a lot depends upon an individual's hearing - ours is now not as good as it was (a degradation probably less than that which will be experienced in a few years by any youngster who overdoes the headphone levels on a personal audio player), the listening environment and the quality of the audio equipment and we doubt that we'd notice the differences had we been listening on standard computer speakers or in a noisy environment).

For those who want to check in further detail on the comparisons between analogue and digital and various systems we'd suggest the following sites:

1 - Sam C Lin's site for comparisons of CD quality and that of MP3 - he provides diagrams of analysis of audio from CD and in MP3 up to 320 KBPS and concludes in essence that, even with excellent hearing (up to 20KHZ in his case - and we'd add that lower bit rates cut the higher frequencies), 192Kbps MP3 is more than adequate for listening with a computer or in a car and 256Kbps and 320Kbps MP3 were virtually indistinguishable from the CD. He added that non-critical listeners really don't notice (nor do they care about) the difference in audio quality between CD's and 128Kbps MP3's.

2- Steven Green's site - A UK site that compares various digital audio standards, severely criticises current UK DAB standards and also provides some very useful comparative samples.

They are in the MP2 format UK that DAB transmissions use (which you can play on a computer or save as MP3 and burn to CD) plus some BBC comparisons from FM (in MP3 format), Classic FM in MP2 and from FM (in AAC/MPEG-4 format) , and also some BBC Radio 3 classical music samples from FM as AAC (MPEG4 - this will play in Real Player or WinAmp but you will have to download the 3ivx MPEG-4 toolkit to play this in WMP), MP3 (320KBPS) and lossless FLAC format (with a link to download FLAC and WinAmp - the 15.7 MB FLAC file, by the way, became 7.2 MB when converted to 320kbps MP3).

3: iBiquity's comparison samples -these are 160 KBPS MP3 promos rather than real samples, meant to show the improvement HD brings, disappointing in their choice and variety and also quality. If these are the best it can do it's a system best scrapped unless it has tremendous other advantages. In addition if it's a real demonstration of the quality of some US analogue transmissions (listen to the FM Jazz samples - there is no classical music sample from FM, only from AM - then compare to Green's FM samples of BBC Radio 3) it scores to a considerable degree because US analogue radio is so poor.

4: Coding Technologies site for information on various codecs.

We regret we have been unable to find any reasonable comparisons between XM's standards (it uses CT-aacPlus encoding) and those of Sirius (it uses PAC- Perceptual Audio Coder and the latest information we have been able to find on Lucent's site simply says this delivers "CD-like quality audio at 96 Kilobits per second") nor a reasonable assessment of their quality compared to CD, DAB and HD. Because they are proprietary systems, details do not seem to be public and we have found no sites offering audio samples.

Efficient Use of Spectrum:
This is an area where time has brought considerable improvements in codecs that allow the same quality to be achieved at lower bit rates - see the links above for more - and should the broadcasters wish to provide the technical quality would certainly enable audio to be transmitted at CD quality as opposed to near-CD (The latter term an exaggeration for HD if the samples they provide are anything to go by).

The best technical quality in will never make interesting audio of someone who can't sing singing caterwauling, can't use a bow scraping a violin, or with nothing to say droning on in a monotone and we remember nearly 20 years ago now being involved in a discussion on what would fill a 750 or 1,000 channel TV world. At that time our views were that, like specialist magazine publishing that was beginning to take off thanks to the development of desktop publishing technology, the only way in which that number of channels could be filled - we were thinking in terms of one-language area - would be with a combination of a fairly small number of mass audience services plus specialist channels, some of which would be pay channels. Had we been asked the same about radio, our response would have been the same.

We have seen little to change this perspective since except that the internet has changed the nature of advertising to a degree that in our view exacerbates the problems for mass audience services and also allowed on-demand services that can considerably expand the range of pay services, something that is also being boosted by mobile technologies.

The mass audience services - on radio or TV - will therefore in our view find it increasingly difficult to fund themselves from advertising as agencies move to more targeted approaches but will always fulfil some advertising needs but specialist and pay services will grow in comparison.

So in practical terms what does this mean for digital radio? Where it is advertising-funded, we see online continuing to make inroads into local advertising but additional services could tap some of the revenues that would otherwise have been lost as indeed can web sites. The net effect in our view will however not be as positive as some of the promotional material for HD in the US suggests.

When it comes to music, other forms of listening will continue to take some of the share (and when it comes to pop it would seem that the video is considered essential -- it doesn't seem to be irrelevant to sales in the classical world either as Vanessa Mae's wet clothing would indicate) but there will still be a demand for a simple and cheap way to sample new songs. HD channels will help this albeit satellite radio is always going to provide more in this area and we suspect that in the long run a large percentage of those who have tried satellite will stick with it.

For news or programming that has a news content, however, downloads and podcasts will always be behind radio so we suspect that these formats are likely to retain their strength albeit not expand that much using additional channels.

For public broadcasters and indeed for material on commercial channels that sponsors want to be associated with we think digital will enable expansion and potential additional use of archived comedy and drama and documentary services. We could also at one time have seen broadcast as a way round some of the limitations of online but as broadband proliferates this may be less of a benefit albeit the internet is still a less efficient way of distributing on a one-to-many basis.

Overall therefore we think extra digital channels will be good for radio as they allow additional services but that this is only up to a point since listening time won't expand that much and the extra services all involve some cost, however small. We certainly wouldn't be tempted to increase valuations of radio stocks that significantly on the back of digital.

Overall we think digital can be of considerable benefit but are concerned about two major issues - that of broadcasters trying to cram too much into available spectrum with consequent technical quality degradation and of the loss of a worldwide universal standard that currently benefits analogue consumers because it has brought the cost of transmitters and receivers down to a very low level and allowed equipment to be used round the world.

We know technology will continue to advance but within limits as far as compression technologies go - once you've got most of the compression right there's a limit to how much further reductions in requirements can be achieved.

What we'd like to see therefore is planning ahead and international agreement on standards for a DAB-based system using the best codec available; on an open-standard for encoding digital within existing signals - DRM is already open, of course, and we'd like to see HD presented with the option of competing to win an open-standard contest or killed off but admit we may be biased by the fact that on the samples it provides, it's best is considerably inferior to the FM sample on Steven Green's site - and surely iBiquity SHOULD be showing off the best it can do!; and on a universal standard for satellite audio (currently represented by WorldSpace, Sirius, XM and audio channels on digital TV platforms). Such agreement ideally should be reached within 3-4 years with the aim of putting all systems worldwide on the same standards say ten years hence, with agreement also on spectrum use to allow a gradual move to the new platforms in the meantime until the old digital systems are switched off.

As far as equipment is concerned, we'd like to see the development of chip technology that would allow receivers sold to be upgraded to new standards - either by software upgrades or chips that be changed simply by a user.

Such a system would we think be to the overall benefit of listeners and manufacturers, would bring the cost of receivers down dramatically, and be of tremendous advantage in maintaining open broadcast standards for travellers and international broadcasts (think how much some governments would love to have a proprietary system that prevents people being able to receive information from outside.).

We see some problems with this scenario - iBiquity and existing US radio players who benefit from the current proprietary systems would fight tooth and nail to keep their dominance and exclude other players from the market - but they're problems of the few not the many.

Perhaps the best compromise in the US would be to introduce a new open system (such as DRM if iBiquity isn't prepared to move and can't win the contest on technical grounds) for encoding in current signals and require broadcasters to use it as a condition of licence (Yes, it would mean fewer HD signals in the meantime) and a universal system for satellite transmissions and require XM, Sirius and other players to use that) thus giving US listeners the benefits of reduced receiver prices from a worldwide market and allowing the proprietary signals to lapse into disuse.