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Old 18-11-2011, 17:46
first500
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I have a DAB radio factory-fitted in my car. One of its features is that it should automatically switch to the equivalent FM broadcast in the event of the loss of the DAB signal.

The benefits of this feature in a moving vehicle, with the current coverage of DAB are obvious, but sadly, this feature does not seem to work. I contacted the manufacturer (BMW) and was advised that automatic changeover is only possible “if the corresponding station’s signal is available in adequate quality and the IDs of the stations match.”

I have tested it a number of times on different stations in an area that I know suffers from poor DAB signal, but, at least in part, has a strong FM signal (Snake Pass between Glossop and Sheffield)

I believe it does not work because of the second part of BMW's response - different station idents on FM and DAB. For example on DAB, R4’s ident on the main radio display shows as “BBC Radio 4”, whereas on FM it is “BBC R4”. And similarly for other stations.

Does anyone know if this is the reason why it doesn't work?
Anyone got experience of it actually working?
If not, anyone know of plans by the broadcasters (particularly BBC) to make it work?
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Old 18-11-2011, 18:03
Mark C
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I have a DAB radio factory-fitted in my car. One of its features is that it should automatically switch to the equivalent FM broadcast in the event of the loss of the DAB signal.

The benefits of this feature in a moving vehicle, with the current coverage of DAB are obvious, but sadly, this feature does not seem to work. I contacted the manufacturer (BMW) and was advised that automatic changeover is only possible “if the corresponding station’s signal is available in adequate quality and the IDs of the stations match.”

I have tested it a number of times on different stations in an area that I know suffers from poor DAB signal, but, at least in part, has a strong FM signal (Snake Pass between Glossop and Sheffield)

I believe it does not work because of the second part of BMW's response - different station idents on FM and DAB. For example on DAB, R4’s ident on the main radio display shows as “BBC Radio 4”, whereas on FM it is “BBC R4”. And similarly for other stations.

Does anyone know if this is the reason why it doesn't work?
Anyone got experience of it actually working?
If not, anyone know of plans by the broadcasters (particularly BBC) to make it work?
Ignore what the display says, ie BBC R4, that's irrelevant as far as what decisions the receiver makes. What's important is the RDS PI code for FM, a four digit hexadecimal code, and the SID for DAB.

For Radio 4 the FM RDS PI is C204, on DAB the SID is C224.

As you can see they don't match.

Classic FM's do, they are C2A1 on both systems.

In my experience (limited) DAB radios do switch between the two formats on Classic.

I'm sure that a DAB service can point towards an alternative FM service with extra codes (similar to EON on RDS) but whether the broadcasters or manufacturers support that I don't know.

PI/SID codes can be obtained from this spreadsheet:-

http://stakeholders.ofcom.org.uk/bin...s/TxParams.xls
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Old 18-11-2011, 18:14
first500
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Ignore what the display says, ie BBC R4, that's irrelevant as far as what decisions the receiver makes. What's important is the RDS PI code for FM, a four digit hexadecimal code, and the SID for DAB.

For Radio 4 the FM RDS PI is C204, on DAB the SID is C224.

As you can see they don't match.

Classic FM's do, they are C2A1 on both systems.

In my experience (limited) DAB radios do switch between the two formats on Classic.

I'm sure that a DAB service can point towards an alternative FM service with extra codes (similar to EON on RDS) but whether the broadcasters or manufacturers support that I don't know.

PI/SID codes can be obtained from this spreadsheet:-

http://stakeholders.ofcom.org.uk/bin...s/TxParams.xls
Mark C - Brilliant! Thanks for this. So manufacturers create a feature that most broadcasters don't support!

I've tried to contact BBC reception support, but just get a bland auto-email back pointing me to their FAQ's.

Does anyone know a way of getting through to the BBC's technical team so that at least this issue can receive a raised profile?
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Old 18-11-2011, 18:19
tellytart1
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I think some other commercial stations have auto-switched on my DAB in-car receiver also.

BBC do not, for national or local radio.

As mentioned above, Classic FM definitely does auto-switch.

Also, while DAB radios support it, no UK broadcaster that I know of use the traffic announcement flag on DAB.
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Old 18-11-2011, 18:23
chrisjr
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Mark C - Brilliant! Thanks for this. So manufacturers create a feature that most broadcasters don't support!

I've tried to contact BBC reception support, but just get a bland auto-email back pointing me to their FAQ's.

Does anyone know a way of getting through to the BBC's technical team so that at least this issue can receive a raised profile?
It's usually the radio manufacturers who don't follow the RDS spec or it's DAB equivalent. I've come across more than a few car radios in the past that didn't do what the RDS spec said they should be doing.

I seem to recall a Ford radio I think it was that just used the station name and ignored everything else, eg the AF feature that lets the radio auto-tune to alternate frequencies for the service.

Looks like the BBC haven't done the necessary to co-ordinate the DAB SID and RDS PI for their services (I suspect Radio 4 is not alone).

There may be reasons for this. If the DAB programme is significantly different to the FM service for example (which I have to say is unlikely). In that instance you might not want switching to occur.
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Old 18-11-2011, 19:35
Bangers
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The BBC have made a deliberate decision to keep the RDS PI and DAB SId seperate of their networks, they are well aware of the current situation.
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Old 18-11-2011, 19:58
hanssolo
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Also, while DAB radios support it, no UK broadcaster that I know of use the traffic announcement flag on DAB.
Looks like this will be tested soon!
http://forums.digitalspy.co.uk/showp...4&postcount=25
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Old 18-11-2011, 20:23
Nick_G
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The BBC have made a deliberate decision to keep the RDS PI and DAB SId seperate of their networks, they are well aware of the current situation.
Why would they keep them separate? Seems a bit odd to me. Unless it's because the delay with DAB would be distracting when the radio switches modes?
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Old 18-11-2011, 21:22
Mark C
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Why would they keep them separate? Seems a bit odd to me. Unless it's because the delay with DAB would be distracting when the radio switches modes?
Which I think is why Classic delay their FM output to match DAB
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Old 18-11-2011, 22:28
Nick_G
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Which I think is why Classic delay their FM output to match DAB
I read that Classic FM actually take the DAB feed and re-broadcast it on FM, which is why they are in sync.
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Old 18-11-2011, 23:08
Bandspread199
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I would imagine since it's a BMW that it works in Germany?
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Old 18-11-2011, 23:11
Sid Law
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I read that Classic FM actually take the DAB feed and re-broadcast it on FM, which is why they are in sync.
They are not in sync on my car radio!

When it switches between DAB and FM it is very obvious that DAB is about 1.5 seconds behind.

Both signals coming are coming from the same site (Angus).

I've never checked it when in other parts of the country.
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Old 18-11-2011, 23:28
Thine Wonk
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I read that Classic FM actually take the DAB feed and re-broadcast it on FM, which is why they are in sync.
I don't think that's right, not only would that reduce the quality of FM but also it would be a potential cause of dual failure and thirdly the compression seems different on DAB and FM.

I thought they just delayed the FM signal to be roughly in line with DAB delay.
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Old 18-11-2011, 23:47
Mark C
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They are not in sync on my car radio!

When it switches between DAB and FM it is very obvious that DAB is about 1.5 seconds behind.

Both signals coming are coming from the same site (Angus).

I've never checked it when in other parts of the country.
I've heard a stutter on Classic (a long time ago I admit) when the FM RDS switched between Sandale (Scotland ad region) and Holme Moss (N Eng ad region)

Of course don't forget that part of the delay a DAB receiver itself introduces is receiver specific, depending how much computing power it will have.
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Old 19-11-2011, 01:04
lundavra
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I've heard a stutter on Classic (a long time ago I admit) when the FM RDS switched between Sandale (Scotland ad region) and Holme Moss (N Eng ad region)

Of course don't forget that part of the delay a DAB receiver itself introduces is receiver specific, depending how much computing power it will have.
Do they have regional adverts? Decoding and re-encoding can add a delay.

My two DAB portables are near enough in sync but the Pure Evoke Flow always seems to lag behind my other radios when listening to VHF FM.
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Old 19-11-2011, 01:11
chrisjr
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Do they have regional adverts? Decoding and re-encoding can add a delay.
Don't think you can do that with DAB. The way a single frequency network works is that all transmitters in the network have to be carnying the same data and be time synched closely. Otherwise you get problems in the areas where two or more transmitters overlap.
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Old 19-11-2011, 02:31
lundavra
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Don't think you can do that with DAB. The way a single frequency network works is that all transmitters in the network have to be carnying the same data and be time synched closely. Otherwise you get problems in the areas where two or more transmitters overlap.
Sorry I meant VHF FM. Just wondered if they had different adverts in different regions. Only ever listened to them a couple of times at friends' places partly because of their limited coverage and also I don't like elevator music.
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Old 19-11-2011, 04:19
James Martin 2
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Pretty sure Classic FM have regional ads.
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Old 19-11-2011, 08:25
hanssolo
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Pretty sure Classic FM have regional ads.
Introduced 1996
http://www.campaignlive.co.uk/news/22377/
but
http://www.mds975.co.uk/txmaps/classic.html
For the purposes of commercials, Classic FM splits the country into five Regions giving its advertisers scope for slightly more targeted campaigns. This has the result that RDS radios, particularly in cars, may re-tune to a stronger signal whilst travelling across regional boundaries. If this happens during a commercial break it can sound as though the advertisements are being jumbled up. This is not the case but is an unfortunate side effect of the system.
http://www.thisisglobal.com/radio-sa...ds/classic-fm/
No mention now of regional sales so may have ended, they could expand the MXR and put Classic on it with regional opt outs, rather than D1, but seems have decided not to?
Also remember different programmes on FM and DAB which now have stopped?

Thought Global had a C and W/Thus MPLS network to link sites and transmitters?
http://thus2.net-genie.co.uk/_downlo...cs_weba400.pdf
Presumably Global would have main and backup links to main transmitters, the D1 DAB mux feed over satellite could be a backup, rather than main feed, for the FM sites?
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Old 19-11-2011, 09:03
Nick_G
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I don't think that's right, not only would that reduce the quality of FM but also it would be a potential cause of dual failure and thirdly the compression seems different on DAB and FM.

I thought they just delayed the FM signal to be roughly in line with DAB delay.
Here's the message where I read about the distribution using the DAB feed for FM:

http://uk.groups.yahoo.com/group/Sky...X/message/7786

This isn't the first time I've heard this, and I think I also remember hearing that there is more compression added for the FM signal, although I don't have DAB so can't do a comparison. What is clear to me though is that BBC Radio 3 on FM sounds much better than Classic FM to my ears.
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Old 19-11-2011, 09:52
hanssolo
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Here's the message where I read about the distribution using the DAB feed for FM:

http://uk.groups.yahoo.com/group/Sky...X/message/7786

This isn't the first time I've heard this, and I think I also remember hearing that there is more compression added for the FM signal, although I don't have DAB so can't do a comparison. What is clear to me though is that BBC Radio 3 on FM sounds much better than Classic FM to my ears.
Classic FM is distributed to the analogue tx by DAB, but with different adverts inserted somewhere in the chain. There is no time delay between FM & DAB
Can't quite see this as DAB gets to the main DAB transmitters by satellite from encoders at Arqiva for D1, so to insert regional ads would need a different feed for the FM transmitters, so why switch back to a feed for DAB after the regional ads (if they are still on air?). It could be done over the MPLS network if extended to the transmitter sites (which the PDF seems to say has not happened?) or a local playout server with preloaded ads interupting the D1 feed and some kind of box which adds delay?

Classic FM always has some compression, but might have different levels on the analogue and digital feeds as Optimod has different models for analogue and digital? Although may now be the same for Classic FM so auto switching in cars with DAB sounds similar with similar sound levels when switching to and from FM!

R3 only has compression during daytime for listeners in cars to ensure quiet passages of music can be heard above the road noise!
When it switches between DAB and FM it is very obvious that DAB is about 1.5 seconds behind.
edit just did a test near London
Classic on FM is about half a second before DAB
Classic on FM is about quarter of a second before Freesat.
delay might depend on the design of the set's decoder
in a car a DAB/FM switch with half a second delay may not be too disturbing?
Why would they keep them separate? Seems a bit odd to me. Unless it's because the delay with DAB would be distracting when the radio switches modes?
Maybe as the BBC are now rolling out national DAB quicker to match FM coverage they don't see the need to auto switch, which also means audio processor settings can be optimised for either digital or analogue characteristics?
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Old 19-11-2011, 10:54
Mark C
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For the purposes of commercials, Classic FM splits the country into five Regions giving its advertisers scope for slightly more targeted campaigns. This has the result that RDS radios, particularly in cars, may re-tune to a stronger signal whilst travelling across regional boundaries. If this happens during a commercial break it can sound as though the advertisements are being jumbled up. This is not the case but is an unfortunate side effect of the system.
Although in recent years Classic FM have toggled the RDS PI code during ad breaks, to prevent receivers switching transmitters during the breaks. Heart operate the same system where a local station has spilt ads. You can see the secondary PI in the Ofcom tables. I'm not sure the practice is compliant to the RDS spec though !
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Old 22-11-2011, 15:24
first500
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The BBC have made a deliberate decision to keep the RDS PI and DAB SId seperate of their networks, they are well aware of the current situation.
Hi Bangers,

If you have any inside knowledge of this I would appreciate to know why they've deliberately done this?

Could the decision have been taken before the spec for auto switching of in-car receivers was formulated?

If so, how does one go about influencing them to reconsider?

As I said at the start, I think this should be regarded as a great safety feature, and therefore not one that should just be ignored by a body like the BBC, just because they can!
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Old 22-11-2011, 15:56
Jim_AFCB
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To answer the OP, it works on my Ford/Sony DAB radio in that when I lose Wave 105 temporarily while driving across the New Forest, the FM signal kicks in.
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Old 01-12-2011, 18:35
first500
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Update:
I have received the following responses from various bodies on this issue - basically it's all "not my problem, guv" buck-passing. Let me know what you think.

From Ofcom

I have liaised with an Broadcast Licensing engineer and his response is as follows:
The BBC have implemented their linkage in a manner that is in accordance with the ETSI (European Telecommunication Standards Institute) specification. They use linkage set numbers and ODA147 (open data application) within the FM RDS to achieve switching. Unfortunately not all receive manufacturers respect the ETSI specification in full.
Broadcasters, manufacturers, transmission providers, the car industry, Ofcom and Government are working together to define a minimum specification for receivers. Once this minimum specification is complete it is hoped that new receivers will implement switching correctly.
The BBC implements its own RDS PI codes and DAB SIDs and, providing they implement them in accordance with the ETSI specification, Ofcom cannot intervene.

From BMW (Car Radio ”maker”)

In relation to the DAB radio issue, as a result of your enquiry I have been advised that we have undertaken testing using the BBC Digital channels and find that the BBC does not currently support this function. At this present time the BBC have not announced any plans to update their systems to include this function. It may be possible that there are local network stations that can support the ident change; however, we do not have any confirmed details that I can provide you.


From “BBC Audience Services”

We understand you've encountered problems with your DAB reception recently in your car with regards to the ID codes not being transmitted.
The BBC uses an industry standard for DAB/FM linking, however we believe that some in car radios are not utilising these signals for correct switching.
Further information should be available on the BBC's R&D website at:
BBC RD - Homepage
We hope this information helps to resolve your difficulties but nevertheless please be assured that your submission has been made available to the personnel responsible for monitoring BBC Reception issues. These reports are reviewed regularly to highlight any ongoing reception issues
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