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Radio Gaga

From Hi-Fi World - October 2005 issue

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Radio Gaga

With its arcane politics, risible bitrates and poor sound, Steve Green pronounces Digital Radio to be well and truly dysfunctional...

 

frontier_chorus_chip

venice-fs2020-band-iii-dab

Frontier Silicon’s basic Venice DAB module offers Band III reception in a compact,

highly integrated module. At its heart lies the Frontier Silicon Chorus chip. Whilst

other Venice modules additionally offer L band reception, there are no plans

for L Band transmissions in the UK (those in Germany have been unsuccessful)

so budget radios are Band III only.

 

When DAB started in the UK we were promised CD-quality audio and a wide choice of stations. Since then the bean counters and marketing people have taken over and quality has been traded-off for quantity, with the result being that the UK – once  a proud bastion of broadcast quality – now has the dubious honour of being the country with the worst sounding DAB in the whole world.

 

The UK was also the first country to seriously promote DAB. And now that sales have taken off we’re beyond the point of no return, while other countries are free to adopt systems that use more advanced technology..

 

The concept of DAB originated in 1986 in the form of a European research project titled Eureka 147, following breakthroughs in audio data compression algorithms. The original intention was to provide radio in CD-quality to fixed and mobile receivers with excellent reception even when travelling at high speed. And by 1990 all the main technologies to enable this had been successfully chosen, and have never been replaced to this day.

 

One of the most – if not the most – important technologies that make up a digital radio system is the audio codec (COder/DECoder), and the codec chosen to be used on DAB later became standardised by the Moving Pictures Expert Group as MPEG-1 Layer II, or MP2 for short. This codec requires a bit rate of 192 kbps (kilobits per second – ‘kilo’ signifies ‘thousand’) or higher to provide FM-like audio quality – for a given audio codec, the higher the bit rate the higher the audio quality will be, and vice versa.

 

Originally, it was widely expected that stereo radio stations on DAB would use bit rate levels between 192 kbps and 256 kbps, and the BBC did indeed use 192 kbps for Radios 1, 2, 3 and 4 until December 2001. Now, however, 98% of all stereo radio stations on DAB in the UK use a bit rate of 128 kbps and these stations sound significantly worse than their FM versions. In the UK, DAB cannot be considered an alternative to FM for anyone who cares about audio quality.

 

So how did UK DAB get into this sorry state? No single institution or individual is uniquely culpable. The broadcasters and regulators have made a series of decisions, some merely misguided, some motivated by political expediency, and some motivated, frankly, by naked greed. These decisions have brought about the present situation.

 

In 1988, in the early days of DAB, there were only 119 analogue radio stations transmitting in the UK, and fitting digital versions of all of these stations into the spectrum available for DAB would not have been a problem. But in 1991 the Radio Authority replaced the IBA as the regulator of commercial radio and was given a remit to ‘broaden choice’. And broaden choice it did, with the total number of analogue radio stations standing last year at a whopping 325. Of course, this meant that the amount of spectrum required for DAB was far higher than that originally envisaged – a point that I will return to in a moment.

 

The BBC had been experimenting with DAB since 1990, and began transmitting Radios 1—5 on DAB in 1995 with the expectation that the receiver manufacturers would produce receivers for the system. Unfortunately they didn’t, and the first receiver to hit the shelves was the Arcam Alpha 10 in 1999, a snip at £800. In the same year the Digital One national commercial multiplex was launched, and still the manufacturers didn’t produce reasonably-priced receivers. Worried that their investment was showing no signs of a return, Digital One decided in early-2001 to enter into a joint venture with the chip designers, Imagination Technologies – who are also the owners of Pure Digital – to get the firm to design a DAB receiver chip. By integrating as many components into the chip as possible, this would reduce the manufacturing cost of receivers, and enable the production of a portable radio that would sell for the “magic” price of £100. The chip was manufactured by licensed partner Frontier Silicon. The result of this was the Pure Evoke-1, which lit the touch paper for DAB sales.


worldwide_bit_rates

So Digital One’s bold investment got reasonably-priced receivers in the shops, and thus undoubtedly got the DAB ball rolling. But the decisions culminating in the Evoke-1 locked the UK into decade-old technology, as well as drastically limiting the amount of spectrum that the UK could use for DAB. This bit of history is the main reason we now have sub-standard DAB in the UK.

 

First, however, the technology decisions that led to the Evoke-1 have to be considered within the context of how much spectrum was available for DAB to use at the time, and how much was expected to become available in the future – all expectations have come to fruition: seven Band III (174 – 239 MHz) channels already available by 2001; sixteen L-band (1452 – 1490 MHz) channels available by 2007; four or five additional Band III channels expected to become available after an international frequency-planning conference in 2006.

 

The first of the technology decisions limited the new receivers to Band III reception only instead of enabling them to receive both DAB bands. Now, with over 95% of the 1.5 million DAB receivers in use in the UK being Band III-only devices, this pretty much rules-out L-band being used to carry radio stations. In any case, broadcasters have no plans to use this spectrum. Working at a very high frequency, it is short range only, being easily obstructed by buildings and hills. Band III DAB already suffers reception black spots; L Band DAB would be more of a problem.

 

One of the main attractions of DAB for the commercial radio groups is that it allows them to transmit more radio stations, and thus make more money. And with only twelve Band III channels available – seven available now plus five awaiting international clearance – it is impossible to carry all the radio stations that want to transmit while at the same time providing these stations at a good level of audio quality. So, there was a classic quantity versus quality trade-off, and quality lost out, with the result being that 98% of all stereo music stations now use 128 kbps and sound very poor. Moreover, Ofcom recently announced that even with the five additional channels they cannot find room for 31% of all analogue radio stations!

 

However, because so few DAB receivers had been sold by early-2001, Digital One and the chip designers effectively had a clean slate to work on. So the opportunity was there to replace the outdated MP2 audio codec with a modern codec such as AAC (Advanced Audio Coding), which requires a lower bit rate to achieve a given level of audio quality, as well as bring the error correction scheme up to date. These two changes would have allowed the number of radio stations transmitting at any given audio quality to be tripled! This would have solved the capacity problem at a stroke, and therefore there would have been absolutely no reason to reduce the audio quality to today’s pitiful levels.

 

Improved error correction has, in fact, recently been added to the DAB specification, and it is very likely that a new audio codec will also be added. And while other countries will be able to take advantage of these improvements, it’s now too late for the poor old UK.

 

The downside of replacing the audio codec and error correction scheme would have been that the few thousand receivers sold up to that point would become obsolete once transmissions changed to the new format. But if it was explained to the early-adopters – most of whom were audiophiles – that the changes were being made to preserve the audio quality, and that the status quo would result in poor audio quality, then most would have accepted it.

However, it would be wrong to single out poor technology decisions as the cause of poor DAB audio quality in the UK. There are other reasons. The Radio Authority should simply not have allowed the broadcasters to use 128 kbps for stereo music stations in the first place. And of course no-one forced the commercial radio groups to use insufficient bit rate levels – it is simply their greed that has led them to do so.

 

And the BBC is far from innocent in all of this. For instance, in the public consultation for their five new digital radio stations, the BBC considered mentioning that adding the new stations would degrade the audio quality of existing stations, but then decided to withhold this information from the general public. And despite a lukewarm response from license-fee payers to three of the five proposed digital radio stations all were launched anyway. And now, Radio 1, Radio 2, Radio 4, 6 Music and 1Xtra all use 128 kbps; BBC7 only uses mono even though the vast majority of the content was recorded in stereo; the Asian Network uses mono yet carries music and drama; and whenever Radio 5 Sports Extra is on air – typically about 30 hours per week – either Radio 3 has its bit rate reduced if this occurs in the daytime, or Radio 4 is reduced to mono if it happens in the evening.

However, the bit rates of the BBC’s radio stations – and many of the commercial stations as well – are higher on Freeview, digital satellite and cable, so audio quality is better via those platforms than via DAB. But FM with good reception still beats the lot…

 

So, to recap on the story of DAB in the UK so far - as BlackAdder would have it - ‘it started badly,  tailed off a little in the middle and the less said about the end the better’ – but apart from that it was excellent...

 

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