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Topic: UK DAB digital radio sinks to a new low (Read 23914 times) previous topic - next topic
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UK DAB digital radio sinks to a new low

Many of you will know the sad and sorry story of DAB digital radio broadcasting in the UK. The main stations were simulcast at 192kbps mp2 from 1995, but in order to introduce new stations without using more radio spectrum, bitrates were cut to 128kbps or below for most stations by 2002. With mp2, and copious amounts of transcoding on the commercial stations, the result is a horrible mushy sound.

However, the BBC have plumbed new depths during the current "summer of sport". They have decided to keep their second (part time) sports channel "BBC Radio 5 live sports extra" broadcasting on DAB, even when the station itself is off air! This means there is a 32kbps repeating advert for the station playing in a continuous loop on DAB. To make way for this, their flagship classical station, "BBC Radio 3" has had its bitrate cut to 160kbps discrete stereo (previously 192kbps discrete stereo). Meanwhile, other BBC stations on the BBC national DAB multiplex remain at 64kbps - 128kbps mp2.

BBC Radio 3 listeners aren't too happy. Previously, they sometimes had the bitrate cut to 160kbps joint stereo during the day to make way for sporting events, but it was usually put back to 192kbps discrete stereo in the evening in time for live classical music concerts (in the evening, the bitrate was "borrowed" from BBC Radio 4, switched from 128kbps joint stereo to 80kbps mono). The current 160kbps discrete stereo, even during the important "Proms" live concert season, doesn't sound very good.

Here is a diagram of the BBC national DAB multiplex configuration...

http://www.wohnort.demon.co.uk/DAB/uknat.html

There are various threads on the BBC Radio 3 message boards, and on alt.radio.digital (Usenet / Google Groups).

If you care about audio quality, it might be worth complaining to the BBC, though be warned: they already have their pre-written response ready...

Quote
"Thank you for your e-mail regarding the changes made to the
DAB service recently.

We have rearranged our configuration to allow Five Live Sports
Extra to broadcast exclusively from a number of major sporting
events that we hold the rights to; World Cup coverage,
international cricket - Tests, ODIs and 20/20, tennis from
Wimbledon, Eastbourne and the French Open, Formula 1 racing
and international and domestic rugby.

We aim to balance the preferences of all our listeners -
giving them the best possible sports coverage (and fully
exploiting our rights to events as stated in Sports Extra's
remit) while maintaining good sound quality for Radio 3
performances.

(Five Live Sports Extra requires bit rate to broadcast and
this had to be found somewhere. It was decided that, as Radio
3 has the highest bit rate of BBC networks, it could
accommodate a small drop.)

Radio 3 still offers a bit rate of 160kbps - the highest of
the BBC services and significantly higher than non-BBC digital
radio broadcasts.

In addition, we have improved the DAB MPEG audio coding
algorithm at 160 kbps to maintain audio quality. We believe
that audio quality at 160kbps with the new encoding is almost
indistinguishable from 192kbps via the old encoding, and
internal testing supports this.

Research shows that choice is the key factor driving DAB
sales. To this end, it makes sense to ensure Five Live Sports
Extra is a compelling proposition.

In the meantime I appreciate your concerns and disappointment
with the changes made to Radio 3's output on the DAB network.
Please be assured your comments have been registered and made
available to our Reception Advice team.

Thank you again for contacting the BBC with your feedback.

Regards

Tony Brown
BBC Information"


Some factual inaccuracies, and some wishful thinking, but no mention of the broadcasts on DTT (Freeview) and DSat (Sky / FTA satellite) where the station can still be found at 192kbps.

It is a shame the BBC are so desperate to defend their indefensible DAB service!

Maybe if enough people complain, at least this latest change will be reversed.

Cheers,
David.

UK DAB digital radio sinks to a new low

Reply #1 –
I don't know much about MP2, but why do they sometimes use discrete stereo? Isn't Joint-Stereo better always? Or does that only apply to MP3?

UK DAB digital radio sinks to a new low

Reply #2 –
Absolutly terrible. I stopped listening to DAB a while back due to poor quality.

On another note, "The Chris Moyles Show" a few weeks back when in Germany, on one particular day, was very poor quality, and I'm talking over FM (97.9MHz) I can't prove the quality or provide ABX, but the broadcast was deffinatly lossy at some stage, I'd approximate the kind of quality you get with lame at 64 kbps!!!! I turned it off! The vocals were annoying and the music was even worse!!

Shame these standards take so long to ratify and adopt. Imagine what you  could do with more modern encoding approaches with that avaliable bandwidth!

Krsitian

UK DAB digital radio sinks to a new low

Reply #3 –
I'd say from limited experience that 128k mp2 is around 80k mp3 and should never be used. Worse case should be 160k, decent at 192k, optimal at 256k. I don't see much reason to use L/R over M/S coding , even if an mp2 encoder doesn't use adaptive m/s.

UK DAB digital radio sinks to a new low

Reply #4 –
Quote from: ShowsOn on
I don't know much about MP2, but why do they sometimes use discrete stereo? Isn't Joint-Stereo better always? Or does that only apply to MP3?


With mp2, Joint Stereo is "intensity stereo" only = frequency selective panned mono! As you might expect, it's audible. Sometimes it's preferable to the artefacts that would be heard if you used discrete stereo at low bitrates.

So, at a constant bitrate, it can make a bad situation (i.e. not enough bits) slightly better. Unlike mp3 (where mid-side joint stereo encoding and variable bitrate encoding can be manipulated to deliver exceptional results at the optimum bitrate), it cannot be a genuine positive benefit when aiming for transparent coding. You could argue that, when the source is near mono, intensity stereo will allow a more accurate encoding than discrete stereo at a given bitrate. This is true, but if you rely on this trick to deliver reasonable quality, then you probably haven't got enough bits to encode wide stereo sources properly at all.

Therefore, if the aim is transparent encoding, then with mp2 you need to have enough bits available to ensure that intensity stereo is never required.

EDIT: That said, if you're running at 160kbps mp2 (as Radio 3 is doing now), you really need intensity stereo. The reduced stereo sound stage is usually preferable to increased coding noise and lower bandwidth.

Cheers,
David.

UK DAB digital radio sinks to a new low

Reply #5 –
Quote from: kritip on
Absolutly terrible. I stopped listening to DAB a while back due to poor quality.

On another note, "The Chris Moyles Show" a few weeks back when in Germany, on one particular day, was very poor quality, and I'm talking over FM (97.9MHz) I can't prove the quality or provide ABX, but the broadcast was deffinatly lossy at some stage, I'd approximate the kind of quality you get with lame at 64 kbps!!!! I turned it off! The vocals were annoying and the music was even worse!!

Shame these standards take so long to ratify and adopt. Imagine what you  could do with more modern encoding approaches with that avaliable bandwidth!

Krsitian


As he was in germany, they most likely used a satellite or a secure low bandwidth wired connection to transmit the audio back. MAybe, they would of had to resort to an ISDN/POTS transmition codec which are below than your normal 128kbps MP3, especially in POTS. Its most likely the case that the low quality is down to the BBC not being able to use a high quality codec to transmit back to the BBC. This is probably not BBCs fault entirely. In most cases, quality is deceased when on an Outside Broadcast.  Nothing to do with the FM transmittion to your radio.

On the point of DAB, I have always refused to move over from FM / Internet Streams. Being an audiophile, I can't see how this is acceptable. But you think most of the country being the average joe, they probably wouldn't care or not notice the quality decrease. So this is why stations can get away with this.

All my fav stations are on the internet at reasonable quality (XFM/Virgin Radio/Captial) as 128kbps WMA streams. Nice to see it improving all the time and stations coming away from 32kbps Stereo WMA.

Bring on Digital Radio Mondial (DRM) and scrap DAB OFCOM, you silly buggers!

UK DAB digital radio sinks to a new low

Reply #6 –
The best stations (IMO) broadcast online anyway. Not at 192kbps, but still good enough for me.

UK DAB digital radio sinks to a new low

Reply #7 –
Quote from: ShowsOn on
I don't know much about MP2, but why do they sometimes use discrete stereo? Isn't Joint-Stereo better always? Or does that only apply to MP3?

MP2 joint-stereo is intensity stereo, which is a lossy coding method that ignores the phase difference between the channels. It is used for the higher frequency subbands only because humans don't usually notice phase differences at frequencies above some certain value (2 kHz?).

MP3 joint-stereo coding can be intensity stereo or mid/side-stereo, with the latter being a lossless transformation and therefore suitable for high quality encoding.

edit: OK, I'm too slow...

UK DAB digital radio sinks to a new low

Reply #8 –
Quote from: Tunster on
Bring on Digital Radio Mondial (DRM) and scrap DAB OFCOM, you silly buggers!


Sadly, it's all rather incestuous. Some of the people in charge at OfCom are the same people who developed and authorised DAB in the first place. They don't want to admit that they messed up.

DRM+ and DAB+ are both on the way, and will probably be used in other countries (not the UK). However, I know first-hand that people inside the BBC have slowed down DRM and DRM+ standardisation to allow DAB to get a hold first - they don't want to give DAB any serious competition until its irreversible entrenched in the UK. They were hoping to pull the same trick off across the whole of Europe, but some European broadcasters are too smart to fall for this - they know DAB v1 with mp2 is a daft choice when DAB+ / DAB v2 with AAC+ is just around the corner.

If only they'd stick everything at 256kbps mp2 on satellite (some stations are currently 192kbps, which is nearly good enough!), most people would be happy, and those who care about audio quality could just write off DAB as a bad joke.

Or we might see 128kbps AAC via the net for all BBC stations eventually.

Unfortunately, the person in charge of digital radio in the BBC sees DAB as the way forward, and isn't keen on letting anything else compete. Hence no DRM(+), no high bitrate satellite service, etc etc.

Cheers,
David.

UK DAB digital radio sinks to a new low

Reply #9 –
Quote from: 2Bdecided on
Quote from: ShowsOn on

I don't know much about MP2, but why do they sometimes use discrete stereo? Isn't Joint-Stereo better always? Or does that only apply to MP3?

With mp2, Joint Stereo is "intensity stereo" only = frequency selective panned mono! As you might expect, it's audible. Sometimes it's preferable to the artefacts that would be heard if you used discrete stereo at low bitrates.

It also depends on the "switch point" (the point at where the above spectrum is IS coded and the lower par is still L/R stereo). The theory that led to this design is the following: At high frequencies phase differences don't play the major role in determining a sound source's azimuth for us humans anymore. Thus IS (intensity stereo) solely concentrates on level differences (frequency selective panning).

Possible switch points (for MP2 IS) at 48 kHz are
3000 Hz, 6000 Hz, 9000 Hz and 12000 Hz.

I once read an article about this kind of azimuth perception that stated a switch point of above 10 kHz is "pretty safe" (not sure about its validity) -- you need to take special care while downmixing, though. BTW: Vorbis at -q5 does "point stereo" (aka IS) at above 10 kHz! <irony>someone please tell Monty "That's not how we do things for high bitrates."</irony> 

So, MP2 intensity stereo with a smart encoder could sound better (in most cases) than full stereo (given that the thing about "humanoid azimuth detection" is true)


Sebastian

UK DAB digital radio sinks to a new low

Reply #10 –
Quote from: SebastianG on
Quote from: 2Bdecided on

Quote from: ShowsOn on

I don't know much about MP2, but why do they sometimes use discrete stereo? Isn't Joint-Stereo better always? Or does that only apply to MP3?

With mp2, Joint Stereo is "intensity stereo" only = frequency selective panned mono! As you might expect, it's audible. Sometimes it's preferable to the artefacts that would be heard if you used discrete stereo at low bitrates.

It also depends on the "switch point" (the point at where the above spectrum is IS coded and the lower par is still L/R stereo). The theory that led to this design is the following: At high frequencies phase differences don't play the major role in determining a sound source's azimuth for us humans anymore. Thus IS (intensity stereo) solely concentrates on level differences (frequency selective panning).

Possible switch points (for MP2 IS) at 48 kHz are
3000 Hz, 6000 Hz, 9000 Hz and 12000 Hz.

I once read an article about this kind of azimuth perception that stated a switch point of above 10 kHz is "pretty safe" (not sure about its validity) -- you need to take special care while downmixing, though. BTW: Vorbis at -q5 does "point stereo" (aka IS) at above 10 kHz! <irony>someone please tell Monty "That's not how we do things for high bitrates."</irony> 

So, MP2 intensity stereo with a smart encoder could sound better (in most cases) than full stereo (given that the thing about "humanoid azimuth detection" is true)


Sebastian



Try this. Generate a pulse train of gaussian pulses, about 1/2 millisecond sigma, carrier at 10kHz.

Generate the pulse train at about 2 per second, starting with left preceeding right by about 25 milliseconds, and , and make the rep rate of the second such that it moves at about .5 millisecond per pulse until it's right preceeding left by the 25 milliseconds.

Put THAT through your intensity stereo coder. I dare you!
-----
J. D. (jj) Johnston

UK DAB digital radio sinks to a new low

Reply #11 –
Quote from: SebastianG on
It also depends on the "switch point" (the point at where the above spectrum is IS coded and the lower par is still L/R stereo). The theory that led to this design is the following: At high frequencies phase differences don't play the major role in determining a sound source's azimuth for us humans anymore. Thus IS (intensity stereo) solely concentrates on level differences (frequency selective panning).


Someone somewhere really misunderstood this stuff, and hard coded it into intensity stereo. Or else they knew full well it was a compromise, but the marketing people tried to pretend that it wasn't!

Here's the truth: if you have a high frequency sine wave (actually above 1.5-3kHz), it is perfectly true that humans simply cannot detect inter aural phase differences in the sine wave itself. It is impossible to detect, because the processing does not exist within the ear. There's a damn good reason for this: the size of the human head and the wavelength of sound at this frequency make it a pointless thing to try to detect - it won't help you to figure out where the sound is coming from.

However, if that sine wave is amplitude modulated in any way (e.g. it has a defined start and end point! or it gets louder/quieter/louder/quieter very quickly), and there is some time delay in this amplitude modulation between the two ears, then people will very easily detect this delay and use it to localise the sound.

So, while you can trash the phase of the fine structure (i.e. the time delay of the individual cycles of the high frequency waveform itself) and this is inaudible, the overall envelope of the high frequency waveform is important - if you have a signal where the envelope is different on each channel, and you make the two channels identical (or identical apart from an amplitude difference) then this is detectable and un.

Interestingly, Dolby understood this in the design of AC-3 - there's a mechanism for trashing the fine structure inter-channel delay, but maintaining the envelope inter-channel delay. With mp2 intensity stereo, both are trashed AFAIK.

Quote
Possible switch points (for MP2 IS) at 48 kHz are
3000 Hz, 6000 Hz, 9000 Hz and 12000 Hz.

I once read an article about this kind of azimuth perception that stated a switch point of above 10 kHz is "pretty safe" (not sure about its validity) -- you need to take special care while downmixing, though. BTW: Vorbis at -q5 does "point stereo" (aka IS) at above 10 kHz! <irony>someone please tell Monty "That's not how we do things for high bitrates."</irony> 

So, MP2 intensity stereo with a smart encoder could sound better (in most cases) than full stereo (given that the thing about "humanoid azimuth detection" is true)


I can't remember how sensitive we are to envelope phase at 12kHz. It almost certainly depends on the characteristics of the signal, and how you listen. If we're sensitive to it at all, then it's a problem. However, I agree that there must be a point, or situations, where use selectively it isn't a problem.

The point I was making is that, with CBR mp2, if you have to rely heavily on IS, then you probably don't have enough bits for transparency most of the time.

Which brings me back to UK DAB: have you heard 128kbps mp2 JS?     

Cheers,
David.

UK DAB digital radio sinks to a new low

Reply #12 –
I may be able to grab a Freeview radio brodcast direct form my TV card, and upload an mp2 sample from that, no transcoding etc. Thats if anyone is interested

Would it be similar to DAB broadcast? It also is mp2 and has some low bitrates!

Kristian

UK DAB digital radio sinks to a new low

Reply #13 –
Can someone let me know where I should complain about this? Is there an email address I can write to, or an online complaints form anywhere?

It's a real shame that people abuse technology like this... like my freeview box - some channels are really poor quality, and I even get blocky pictures on the main channels sometimes.  "Digital" used to be synonymous with high quality, but the overuse of compression in MP3s, Freeview and DAB mean this just isn't the case any more. 

Ed

UK DAB digital radio sinks to a new low

Reply #14 –
Quote from: 2Bdecided on
Interestingly, Dolby understood this in the design of AC-3 - there's a mechanism for trashing the fine structure inter-channel delay, but maintaining the envelope inter-channel delay. With mp2 intensity stereo, both are trashed AFAIK.

The only difference I see is the ability to invert the signal (180° phase shift) on selected channels for the "coupling channel" (which is also possible for AAC's IS).

Quote from: 2Bdecided on
Which brings me back to UK DAB: have you heard 128kbps mp2 JS?     

Not that I remember. I encoded a movie soundtrack once in 160 kbps JS MP2 for an SVCD via tooLame. Quality was "okay" IIRC. (tooLame used to dynamically switch between 5 variants in its JS mode: 32/32 stereo bands (full stereo), 16/32 stereo bands, 12/32 stereo bands, 8/32 stereo bands, 4/32 stereo bands) -- Dunno how bad 128 kbps JS gets.

Sebastian

UK DAB digital radio sinks to a new low

Reply #16 –
Quote from: edwardar on
Can someone let me know where I should complain about this? Is there an email address I can write to, or an online complaints form anywhere?

It's a real shame that people abuse technology like this... like my freeview box - some channels are really poor quality, and I even get blocky pictures on the main channels sometimes.  "Digital" used to be synonymous with high quality, but the overuse of compression in MP3s, Freeview and DAB mean this just isn't the case any more. 

Ed


It's even worse on Sky Digital believe it or not - ITV1 for example is reduced in resolution to about 580 x560 iirc. Pointless.

UK DAB digital radio sinks to a new low

Reply #17 –
Quote from: seanyseansean on
It's even worse on Sky Digital believe it or not - ITV1 for example is reduced in resolution to about 580 x560 iirc. Pointless.


They do this on Freeview also, generally on repeated stuff on channels like ITV3. I noticed this when recording stuff on my Freeview card then burning to DVD and noticing it had to be reencoded because it's not a DVD standard resolution

UK DAB digital radio sinks to a new low

Reply #18 –
Quote from: Woodinville on
Try this. Generate a pulse train of gaussian pulses, about 1/2 millisecond sigma, carrier at 10kHz.

Generate the pulse train at about 2 per second, starting with left preceeding right by about 25 milliseconds, and , and make the rep rate of the second such that it moves at about .5 millisecond per pulse until it's right preceeding left by the 25 milliseconds.

Put THAT through your intensity stereo coder. I dare you!


I assume by "gaussian pulses" at "carrier 10 kHz" you are referring to amplitude modulation.
Woudn't a bad outcome just indicate that the temporal resolution of the "panning side infos" is too low?

I think it'd be fun to check how current Vorbis coders perform at -q5 (usually transparent, usage of IS at above 10 kHz) in this situation

Sebastian

UK DAB digital radio sinks to a new low

Reply #20 –
Quote
BBC plans digital radio boost


John Plunkett
Friday February 9, 2007
MediaGuardian.co.uk

The BBC is to expand its digital radio coverage by building 10 new transmitters and is to trial a new digital transmission technology, digital radio mondiale.

The plans will take the BBC closer to its target of making its digital radio broadcasts available to 90% of the population, up from its current level of 85%, according to the corporation.

DRM is a new digital service that can be broadcast from existing medium wave transmitters and will be trialled in the Plymouth area, broadcasting BBC Radio Devon.

The BBC director of radio, Jenny Abramsky, said the new transmitters "represent a real and worthwhile improvement to the coverage of our DAB digital radio network. It shows the BBC's continuing commitment to making our services available on DAB digital radio."

Two of the new transmitters, which are being built by Arqiva, are already broadcasting to Newport and Gwent and south-west Glasgow and Dunbarton.

Seven transmitters will broadcast to Bury St Edmunds, Norwich and parts of east Norfolk, Arundel and the south downs, Alnwick and east Northumberland, Newhaven, Mansfield and York and East Riding of Yorkshire.

Most of the new transmitters will be broadcasting by the end of April. A further transmitter is planned for the Isle of Man.

The DRM trial will begin in April and will last a year.

http://media.guardian.co.uk/radio/story/0,,2009790,00.html?


This looks like good news. It was argued the BBC was too deep into this DAB stuff to make the switch to DRM but apparently not. AAC instead of MP2 as a codec would be a great improvement.
Every night with my star friends / We eat caviar and drink champagne
Sniffing in the VIP area / We talk about Frank Sinatra
Do you know Frank Sinatra? / He's dead

UK DAB digital radio sinks to a new low

Reply #21 –
BBC R&D have already carried out lots of DRM test broadcasts, but this looks quite interesting.

That article quite unhelpfully mixes up the new DAB tx sites (where the BBC is playing catch-up with Digital1 - the national commercial DAB mux) with the DRM test from one tx site.

Maybe they're sick of waiting to simulcast existing BBC local FM stations on many as yet nonexistent local commercial DAB muxes which they are forced to use.

Cheers,
David.

UK DAB digital radio sinks to a new low

Reply #22 –
Quote from: probedb on
They do this on Freeview also, generally on repeated stuff on channels like ITV3. I noticed this when recording stuff on my Freeview card then burning to DVD and noticing it had to be reencoded because it's not a DVD standard resolution
Yes, on channels such as ITV3 or More4 resolution will change to 544x576 - I think for ad breaks.  You can use DVDPatcher to fool apps into treating the stream as valid DVD format.

Are stations still broadcast at 192kbps on Freeview?  I have a card in my PC and a Humax PVR9200T downstairs, but I've only used them for video so far.  I have the demuxed streams of Gangster No.1 on my laptop at the moment and the audio is 160kbps CBR MP2.  I'll have to try recording some radio.
I'm on a horse.

UK DAB digital radio sinks to a new low

Reply #23 –
I think I'd rather take 128kbps IS MP2 over the ultra low bitrate HE-AAC (gotta be less than 32!) that XM radio is using.

UK DAB digital radio sinks to a new low

Reply #24 –
Quote from: Firon on
I think I'd rather take 128kbps IS MP2 over the ultra low bitrate HE-AAC (gotta be less than 32!) that XM radio is using.


Actually I think its 64kbps.  In any case its not that great I agree.  And sounds even worse if you don't have your XM hooked up by your aux input in your vehicle.