The BBC distribute FM around the country in NICAM format, so assuming you can receive a relatively strong FM signal then you're basically hearing NICAM-encoded audio.

NICAM is 14-bit PCM companded to 10-bits using a sampling frequency of 32 kHz (see http://tallyho.bc.nu/~steve/nicam.html). So, not capable of CD-quality, but not too far off it. And although it might appear that its audio bandwidth will be narrower than MPEG audio because of the lower sampling frequency, all digital radio stations in the UK that I'm aware of lowpass filter with a cutoff frequency of about 15.5 KHz anyway, so there's really no difference in that respect.

Radio via DAB, DTT, digital satellite and cable uses MPEG Layer 2 at varying bit rates depending on which platform you're listening to. 98% of stereo stations on DAB in the UK use 128kbps, which sounds between poor and unbelievably dreadful, depending on which station you listen to. Radio 3 is the only station on DAB in the UK that uses 192kbps.

On DTT, the BBC's stations use higher bit rates, with Radios 1-4 all 192kbps, but the commercial radio stations use the same low bit rates as on DAB. There's a table of what bit rates which stations use on the different platforms here:

http://www.digitalradiotech.co.uk/index.htm#bit_rate_table

Since Radios 1-4 went on Freeview a couple of years ago I've usually been listening via Freeview, but I'd noticed that the BBC stations didn't sound as good as they used to on Freeview, and someone emailed me a couple of weeks ago saying that they thought that 192kbps MPEG Layer 2 probably wasn't up to the job of sounding better than FM. So the next day I listened to a load of FM stations and every one sounded better than the same station sounded on either DAB or DTT. Basically, I don't know why I persisted with DTT for so long. I think it's a case of the fact that the vast majority of the audience listens via FM, so they invest more effort into getting their FM stations to sound good. Some (but not all) of the broadcasters invest effort into getting their DAB stations to sound as good as they can, but the bit rates are just far too low to provide good audio quality.

The future of DAB in the UK is basically already decided, and the commercial broadcasters are dead set against increasing their bit rates and they're dead set against the BBC getting any more capacity to increase theirs, so it looks like DAB in the UK will never sound as good as FM does. The BBC has recently installed new MPEG encoders for DAB that were supposed to make a difference, and they did make a difference (they couldn't have sounded any worse than they did), but they still sound very poor because MPEG Layer 2 wasn't intended to be used at 128kbps.

Things might get better when some new technologies appear, such as the BBC iMP (interactive media player) that's going to use 128kbps WMA9, and all new set-top boxes for HDTV will have AAC and HE AAC decoders in them, so in years to come hopefully some radio stations will provide AAC streams. But until then I'm going back to listening via FM and monitor DTT to see if it gets any better.

I've listened to your samples and I can hear the reception faults on DAB, the different "sound" (probably due to different DRC, or maybe just your tuner) on FM, and the nasty rasping/gravel sound on DTT.

I used the ABX comparator in foobar2k (though the files weren't time aligned), enabled ReplayGain, and listened to the speech section. I didn't actually ABX, I just flicked between DAB vs DTT, and FM vs DTT. I listened through headphones. FM was clearly superior, though DAB would have been OK without reception faults.

The nasty sound on your DTT sample matches that from the start of this thread.

So, sadly, I think any fault is at the BBC, rather than in the original poster's set-up.

Time for an email to BBC reception advice!

Did anyone else try these samples, or compare their own? If so, what did you think?

Cheers,
David.

I'm adding my post to this thread in the hope that it helps get some attention to this issue. I've not heard the digital services, but there are plenty of obvious examples in relays that end up on FM. The 'listen again' archives the BBC retain for a few hours are especially poor. Even the wise move that Melvyn Bragg's In Our Time made in using MP3 instead of WMA doesn't help much, it's bitrate is so low the sound was awful. As I wanted to hear their discussion about heat and thermodynamics more than twice it's a good thing I decided to record it off FM... I hope this thread's discussion spreads and becomes something debated in newspapers and such. One encouraging point is that the thing is clear and unambiguous, you don't need to get into rigorous ABX for this stuff. Broadcasters ought to be aware that even for speech, intelligibility depends on a good HF response with good phase accuracy and low noise.

Given the use of compression, there's no reason for quality not to be great if done wisely, but I guess providers will do what they see fit, and we'll just have to accept it, or be prepared to unify in clear demand. At least, it should be better than the current pitiful quality in the online 'listen again' files the BBC uses. Either way, I don't think the quality will rise to better than the analog service, until they phase that out and demand reaches a peak from listeners who can't choose any more. In practice it might get better earlier, but if they're not pushed they won't do it early. Direct competition between broadcasters would accelerate the improvement when it happens, but even that won't force it it to happen early. That process must be triggered by demand.

I'll buy a digital receiver sometime, but I can wait.. That's probably the best single thing I can do to have my small influence, given extreme lack of money. Maybe if I was richer I could afford to subsidise development of digital receivers by buying each significant model that emerges, but that's not for me to do, and it doesn't do a thing to persuade the broadcasters anyway. If the broadcasters know that I and many others won't buy until they guarantee quality at least equal to high rate VBR MP3, they are going to find a small audience. They might think the mass of people are after convenience, and only the few and the highbrow will want more, but that is wrong. If masses of people can download files of at least 192 CBR on usenet and P2P systems, even the lowest mass expectations are going to be higher than are being met now. No wonder the industry wants us all to beleive that 128 CBR is 'CD quality'...

The_Doctor,

These things have already been discussed in newspapers...

http://www.david.robinson.org/papers/sundaytimes.html
(very slow to load)

Anything that is designed to be a replacement for FM and is initially advertised as sounding like a CD, but is then butchered to sound worse than most illegal internet downloads - such a service rightly deserves all the criticism it gets. Sadly, I think DAB may be stuck at low quality, for various reasons. That's why higher quality services elsewhere (e.g. DTT, DSat, internet etc) are so important - so the BBC need to be committed to provide high quality on at least one of those!

However, I don't think it's particularly fair to pick out BBC online's listen again service for criticism. It's a relatively new service - it doesn't replace anything (though it replaced last night's BBC Radio 4 FM repeat of Hitchikers guide to the galaxy for me because they cancelled it on FM to talk about this election thing - how inconsiderate!). As such, the fact we have it at all is good - and hopefully quality will improve as technology and bandwidths allow. I know for a fact that the BBC are looking at upgrading the service using multicast technology - a link to an internal test was leaked the other week, and it was rather good - though still not CD quality. Sadly that test has been taken down, but let me tell you: 132kbps was better than ~30kbps!

You're right to be worried about digital broadcasts though, and probably right to think that more of the general public would appreciate high quality broadcasts than the broadcasters give them credit for. Even if they wouldn't, this is the BBC - they're supposed to set standards, not drive them down!

Anyway, DAB rant over - let's hope they can get this issue on DTT fixed. The mux these stations are on isn't run by the BBC, but is a commercial mux on which the BBC rent space. It's possible something has changed without the BBC's knowledge or consent.

If anyone from the BBC is reading this (quite likely by now I'd guess) - please see what you can do, and see about convincing someone "upstairs" to commit to at least one radio delivery medium as a high quality one, and stick with it. Pick DSat if you like; you have so much bandwidth there may be the bean counters won't even notice!

Cheers,
David.

I time aligned the DAB and DTT samples and was easily able to ABX them. There seems to be a gravely sound to the presenter's voice on the DTT sample that is not present on DAB. The music sounded slightly different too but the difference was not big enough for me to say which one I think is best.

I have both DAB and Freeview and but since I mainly listen to Radio 1 Freeview always sounds better due to the higher bitrate (192kbps vs. 128kbps). I've attached some samples for anyone who wants to have a laugh at how inadequate 128kbps MP2 can be (and it's not because the 192kbps Freeview sample is of a high quality).

Click to view attachmentClick to view attachment

Earlier in this thread someone said that they were able to improve the sound quality of their Freeview (DVB-T) captures by running them though PVAStrumento. When I record radio stations with my DVB-T card they are saved as packetized elementary streams (PES) and they sometimes contains clicks and other artefacts when you try to play them. Running them through PVAStrumento or ProjectX converts it into a normal ES stream which removes the artefacts.

I wrote to BBC reception advice and received a helpful reply.

They are aware of an issue with the sound quality of Radio 3 via Freeview. This may be partly due to it being carried on a commercial multiplex. They are looking into the issue, but cannot give a date when it might be resolved.

They did point out that Peterborough, my nearest national BBC FM radio transmitter which "fell down" last year, would be back on full power soon - this has now happened.

One engineer at BBC reception advice has previously responded to complaints about digital radio by advising people to use FM instead. This engineer reportedly got into trouble for giving this advice, but it's still good advice, even if it isn't popular with the DAB/digital radio section in the BBC!

Cheers,
David.

Thank god for that. I thought I was cracking up - my recordings used to be great. Just to reassure people - I haven't gone off the case. I have some files from Dave Chapman and others (simultaneous DTT/DTS/DAB/FM comparisons) which I will be getting round to comparing and will post the results here shortly. Been a bit busy, plus problems with my own audio. But be prepared for the gravel effect.
Guy

I'm told that the BBC has changed something on DTT in an attempt to improve the sound quality, as of last week some time. Do we think it is now better or not?

For a start they could reduce the bitrate for Radio 4. 128kbps for speech?

Sounds promising. I'll give it a try tonight. It was just as bad as ever a week last Friday (29/7) when I last tried.
Guy

I just recorded this sample from Radio 3. It is only studio voices, but it displays the same gravel characteristics as before. I would say no change there.
Guy

Click to view attachment

I didn't think Just a Minute sounded any better last night (Monday 8th August) - I was listening to the comedy, not the sound quality, but the voices of some participants didn't sound right. It could have been the recording itself though - there has been some shoddy mic-ing/mixing on JAM recently, maybe due to difficult recording locations?

I'll try Radio 3 tonight if I get chance.

Cheers,
David.

Radio 4 is 192kbps on DTT and DSat, 80-128kbps on DAB (depending on what else is broadcasting at the same time).

192kbps is barely adequate - some of the plays are broadcast in matrix surround sound (sometimes something like Dolby prologic, sometimes an Ambisonic variant) - this is never advertised by the BBC, but producers trying to create "atmosphere" are free to use whatever techniques they like, so long as they're mono compatible!

Even the simplest round of applause can sound more like waves on the sea if encoded at less than 192kbps. As for "128kbps for speech" - if you just want intelligibility, then GSM at a few kbps is fine; but if you want it to sound like natural human speech, artefact free, not fatiguing, so that the technical quality of the audio doesn't distract from the content - then you need more than 128kbps mp2 (for stereo).

The BBC's tests (reproduced on Gabriel's site) showed that speech can be surprisingly challenging to encode transparently...

http://www.mp3-tech.org/programmer/docs/w2006.zip

Cheers,
David.

It won't play properly in my foobar - regular glitching and re-syncing.

Cheers,
David.

I listened to all the radio stations on Freeview last night, but didn't get the chance to catch any speech on Radio 3. I listened via headphones.

Results: quite depressing really!

Radio 1 - I must be getting old - I couldn't even beging to assess the sound quality, given the content they were playing!
1Xtra - distorted track, slight artefacting - but with both these problems fixed, it would sound excellent for what it is
Radio 2 - during desmond carrington (isn't he live from his front room in Scotland?) his voice has obvious artefacts, but the mono music did not. Later, Mark Radcliffe sounded better, though not perfect
Radio 3 - music sounded OK - pretty much like I remember radio 3 always sounding on DTT - OK, but the highs aren't as good as FM
Radio 4 - During both Front Row, and the late night comedy slot, there was obvious artefacting on the speech. Quite nasty. Could have been the source material
5 and 5 live - low pass filtered speech
6Music - OK
BBC7 - atefacted, both times I listened. The content was too old to have MPEG artefacts natively on it, and IIRC it's played out from lossless server, so these artefacts were part of the broadcast chain.
Asian network - terrible artefacts one show, clean but mono and low passed another
world service - low pass filtered speech

Commercial radio stations - all the stereo ones sound horrible, with obvious artefacts. The mono ones sounded duller, but with no obvious artefacts on 3C, some on Premier.

Where I could compare, FM sounded better. The artefacts on Radio 2 and 4 during the earlier shows were also present on FM (to a much lower degree). I didn't check the later shows.


None of this answers the original question - I'll try and catch some speech on Radio 3 tonight.

When I'm actually listening to the content (which I do sometimes!) I listen through speakers: Radio 4 has artefacts, and Radio 3 sounds a little duller than FM. The commercial stations are unlistenable.

The bitrates for these services are listed here:

http://www.digitalradiotech.co.uk/index.ht...tform_bit_rates

btw, doesn't the sound on interactive TV streams 701 and 702 sound awful now? IIRC they've dropped it to 128kbps. That'll be just great for the last night of the Proms!

The BBC really do need a bloody great big kick up the arse!

Cheers,
David.

I made a DTT recording from R3 last week (13/8/05) and just got round to checking it out, and the quality does seem to have improved. The graunching noise behind seems to have disappeared. Herewith a 1 minute sample, along with the mp3 equivalent after conversion to .wav, normalisation and conversion to .mp3.

Any thoughts? Looks to me like the beeb has fixed something.

As reported on here recently...

http://www.hydrogenaudio.org/forums/index....6371&hl=DAB

BBC Radio 3 via DAB was dropped to 160kbps mp2 discrete stereo.


The BBC have recognised their mistake, and changed to 160kbps mp2 joint stereo (!), which still isn't great for a flagship classical music station!


This has left many people seeking a high quality alternative.

Here is a page comparing DVB-T ("Freeview") with DVB-S (digital satellite - "Sky" if you like, though you don't need a Sky subscription to receive it, or even Sky branded equipment)

http://www.digitalradiotech.co.uk/samples/proms_2006/


The 192kbps streams from DVB-T sound far worse than the 192kbps streams from DVB-S.

Both have audible artefacts, but DVB-T is dramatically worse. To me, it sounds like it's been transcoded. The FM broadcasts (given good reception) sound better than any of the digital broadcasts.

It's one year since I wrote "The BBC really do need a bloody great big kick up the arse!" and little has changed!

Cheers,
David.

Since my original postings I have managed to make contact with BBC engineers who have been very sympathetic and agreed to receive and test mp2 samples from DVB-T. The result was an acknowledgment that the (192k) mp2 file was very bad quality, and much worse than the CD of the original broadcast which was retrieved from the BBC archive. Of course I can't prove that the mp2 sample file I provided is the same as the stream which was received by millons of listeners arond the country.

I am still trying to complete this dialogue which is difficult because it has to be conducted through a "contact us" web page which has disappeared!

More anon...

What an absolute bloody disgrace! The dropping of bitrate, that is.

...but it probably is.

How sad that no one within the BBC actually listens to these broadcasts for quality control!




There was a piece on BBC Radio 4's feedback programme about how difficult it is to contact the BBC! If you know the name of the engineer you were talking to, it should be fairly easy to figure out his email address - e.g. firstname.lastname@bbc.co.uk usually works, if they're really internal. R&D could be harder.



Let us know if you have any luck. Mind you, we'll hear if you have any luck!

Cheers,
David.

The DVB-S stream uses (adaptive) joint stereo where as the DVB-T stream is 100% discrete stereo. Perhaps that explains the quality difference?

I've noticed that the BBC use (adaptive) joint stereo for their radio stations on DVB-T multiplex B. Maybe they have more control over how things get encoded on their own multiplexes/transponders than they do for commercially ran ones like Multiplex A which carries BBC Radio 1-4 on DVB-T.

BBC R&D email addresses are usually: firstname.lastname@rd.bbc.co.uk