A very curious problem I think, and I'm really looking for any thoughts no matter how bizarre as to what might be going on here. It is an interesting read in itself.
A new Rotel tuner, the T14 DAB/FM/Streamer has thrown up a weird issue with its coax SPDIF feed when used to feed Sony Minidisc recorders. A minority of DAB stations give a 'Din Unlock' (Digital Unlock) error on the MD recorders (I have tried two very different era recorders that use different technology and chip sets and both behave the same). Din Unlock means either the data is missing altogether but can also mean the data is just not recognised.
It is weird because the error occurs only on a few DAB stations which throws suspicion on the data content. Classic FM (curious name for a DAB station I know) is one and there are several others including a few BBC ones.
Sample rate as such doesn't seem to be a factor because there are some stations at 48kHz that are OK and some that are not. The MD recorders have a built in sample rate convertor and accept 32kHz, 44.1kHz and 48kHz.
The coax SPDIF feed from the Rotel works correctly when fed into stand alone DAC's. I have tried a FiOO portable DAC and a Marantz Pearl Lite SA-CD player which can be used as a DAC. Both work correctly with all content.
The SPDIF feed can also be 'daisy chained', first into the Marantz and then re outputted again as SPDIF by the Marantz and fed to the recorders. The same error occurs with the same received stations. So we now have a different SPDIF 'output stage' (the Marantz rather than the Rotel) feeding the recorders and yet with the same Din Unlock error.
Coax to optical convertors have also been tried and give the same result. The MD recorders can accept coax or optical.
An old first generation DAB tuner (Pure DRX-701ES) does not give these errors on any DAB station.
So the big question is where and what might be going on.
I approached Rotel who have been extremely helpful but ultimately they have been unable to find any really plausible explanation. The BBC are also very interested in this and asked me to try some specific stations as a test but like Rotel can not really come up with anything definite although Rotel did put forward the theory that perhaps the Sony's reconstitute the clock from the Bi-Phase transitions in the SPDIF data whereas the Marantz and other DAC might use a locally generated clock. Could that be a reason? I really don't know.
One theory that got mentioned elsewhere was whether 'copy bits' were present in the affected stations data but I have been assured that no stations do this. Classic FM were also contacted and did say the same. Sony unfortunately appear not to want to get involved beyond saying to take the recorders for repair at an authorised centre... but they are not faulty...
So is it something in the broadcast data that throws up some compatibility issue, or is it the Rotel's processing of the data that is upsetting the MD recorders or perhaps it is adding something. Then there is the old first generation Pure tuner that does not give these errors with its SPDIF feed.
Ultimately it may just be one of those unexplained 'compatibility' issues with no real resolution I suppose.
The recorder is currently using both digital and analogue inputs (via its A/D convertor) and so I can record all content if needed.
So there we are, and thanks for reading.
A new Rotel tuner, the T14 DAB/FM/Streamer has thrown up a weird issue with its coax SPDIF feed when used to feed Sony Minidisc recorders. A minority of DAB stations give a 'Din Unlock' (Digital Unlock) error on the MD recorders (I have tried two very different era recorders that use different technology and chip sets and both behave the same). Din Unlock means either the data is missing altogether but can also mean the data is just not recognised.
It is weird because the error occurs only on a few DAB stations which throws suspicion on the data content. Classic FM (curious name for a DAB station I know) is one and there are several others including a few BBC ones.
Sample rate as such doesn't seem to be a factor because there are some stations at 48kHz that are OK and some that are not. The MD recorders have a built in sample rate convertor and accept 32kHz, 44.1kHz and 48kHz.
The coax SPDIF feed from the Rotel works correctly when fed into stand alone DAC's. I have tried a FiOO portable DAC and a Marantz Pearl Lite SA-CD player which can be used as a DAC. Both work correctly with all content.
The SPDIF feed can also be 'daisy chained', first into the Marantz and then re outputted again as SPDIF by the Marantz and fed to the recorders. The same error occurs with the same received stations. So we now have a different SPDIF 'output stage' (the Marantz rather than the Rotel) feeding the recorders and yet with the same Din Unlock error.
Coax to optical convertors have also been tried and give the same result. The MD recorders can accept coax or optical.
An old first generation DAB tuner (Pure DRX-701ES) does not give these errors on any DAB station.
So the big question is where and what might be going on.
I approached Rotel who have been extremely helpful but ultimately they have been unable to find any really plausible explanation. The BBC are also very interested in this and asked me to try some specific stations as a test but like Rotel can not really come up with anything definite although Rotel did put forward the theory that perhaps the Sony's reconstitute the clock from the Bi-Phase transitions in the SPDIF data whereas the Marantz and other DAC might use a locally generated clock. Could that be a reason? I really don't know.
One theory that got mentioned elsewhere was whether 'copy bits' were present in the affected stations data but I have been assured that no stations do this. Classic FM were also contacted and did say the same. Sony unfortunately appear not to want to get involved beyond saying to take the recorders for repair at an authorised centre... but they are not faulty...
So is it something in the broadcast data that throws up some compatibility issue, or is it the Rotel's processing of the data that is upsetting the MD recorders or perhaps it is adding something. Then there is the old first generation Pure tuner that does not give these errors with its SPDIF feed.
Ultimately it may just be one of those unexplained 'compatibility' issues with no real resolution I suppose.
The recorder is currently using both digital and analogue inputs (via its A/D convertor) and so I can record all content if needed.
So there we are, and thanks for reading.
You mentioned sample rate, but what about bit depth? I doubt a DAB radio would output anything a Minidisc recorder couldn't handle, but you never know, so it might be worth verifying what the radio actually outputs (if you maybe have an oscilloscope or something that can decode SPDIF).
Now I really don't know on that, none of this is in my field of expertise at all. I do have a decent scope but nothing in the way of anything that could make sense of the SPDIF data.
So thinking more on what you say... I wonder if the Pure (which doesn't cause the problem) perhaps outputs everything at a resampled 44.1khz and standard 16 bit depth. Remember that MD is 'old' technology really. Or am I talking nonsense.
Good thinking 👍 though, you might be on to something.
I might be able to take the SPDIF of the Pure and feed it into the Marantz in DAC mode which should show me the sample rate at least. It would be interesting to see if a 48kHz station on the Rotel shows as 44.1kHz via the Pure and the Marantz. It might give a clue on why the Pure is OK and be a part of the puzzle.
Thanks 🙂
(This is from the user manuals of both MD's)
So thinking more on what you say... I wonder if the Pure (which doesn't cause the problem) perhaps outputs everything at a resampled 44.1khz and standard 16 bit depth. Remember that MD is 'old' technology really. Or am I talking nonsense.
Good thinking 👍 though, you might be on to something.
I might be able to take the SPDIF of the Pure and feed it into the Marantz in DAC mode which should show me the sample rate at least. It would be interesting to see if a 48kHz station on the Rotel shows as 44.1kHz via the Pure and the Marantz. It might give a clue on why the Pure is OK and be a part of the puzzle.
Thanks 🙂
(This is from the user manuals of both MD's)
If the minidisc players are old enough they may hail from the times when the IEC958 SPDIF standard was valid. The current standard is IEC60958 and there may have been changes to the consumer flags in the intervening years.
One is an MDS JE480 which was one of last I suppose being from the mid 2000's and the other, an MDS JB920 is from 1998.
Rotel mentioned something about IEC60958 in their investigations. The T14 uses the AK4104 DIT chip:
https://www.digikey.com/htmldatasheets/production/1746559/0/0/1/AK4104.pdf
They said:
There was also the talk of how the clock signal was derived in the MD recorders.
You know way more than myself on all this.
Rotel mentioned something about IEC60958 in their investigations. The T14 uses the AK4104 DIT chip:
https://www.digikey.com/htmldatasheets/production/1746559/0/0/1/AK4104.pdf
They said:
There was also the talk of how the clock signal was derived in the MD recorders.
I tried the Pure/Marantz combination to look at sampling rates and tbh was a bit surprised. It looks like the Pure resamples everything to 48kHz as that is what the Marantz (used as a DAC) shows for all DAB stations, the Rotel/Marantz set up gives 44.1kHz or 48kHz depending on DAB station tuned in.
I wasn't really expecting that and thought if anything the old Pure would output either the same as the Rotel or resample all to 44.1kHz.
Doesn't really help as far as I can see but an interesting observation all the same.
I wasn't really expecting that and thought if anything the old Pure would output either the same as the Rotel or resample all to 44.1kHz.
Doesn't really help as far as I can see but an interesting observation all the same.
My first guess would be that some DAB stations are broadcasting a flag which gets encoded into the auxiliary bits on the S/PDIF signal and the MD recorders are sensitive to that. I see the stations have
denied setting the copy bit but there are plenty of others they might tweak.
Is there such a device as an S/PDIF aux channel analyser that could be used to check?
https://en.wikipedia.org/wiki/S/PDIF#:~:text=The S/PDIF interface is,Dolby Digital or DTS decoding.
denied setting the copy bit but there are plenty of others they might tweak.
Is there such a device as an S/PDIF aux channel analyser that could be used to check?
https://en.wikipedia.org/wiki/S/PDIF#:~:text=The S/PDIF interface is,Dolby Digital or DTS decoding.
It seems likely that intent or not that copy bit is being set or not properly recognized. I wonder if interposing a WM8804 or WM8805 might allow you to manipulate the bit stream or somehow override the auxiliary bits? (Might need some fairly complex logic to do it?) Note I am pretty clueless about this stuff.
Indeed, the set of stations affected is a constant. There is no 'sometimes they work, sometimes they don't' in all of this.
This is really the only thing that makes sense to me. There has to be something in the data, something that the Rotel passes through unchanged (can't see the Rotel adding anything). I've no idea what variables can be tweaked in the code.
Anything like that is well above my paygrade I'm afraid. The analogue inputs are fine in practice for my needs but it would be good to know what is going on.
IMO the only way to find out is to analyze the stream. While there may be specialized SPDIF analyzers, a decent soundcard with SPDIF input and linux would show the details.
Linux drivers for AK4114/4117/4118 (and likely many other, but I have experience with these) read the SPDIF preamble registers, user-space tool iecset reports the values. Easy to check for any soundcard beforehand. Linux can be booted from from a live USB drive, no need to install anything.
Linux drivers for AK4114/4117/4118 (and likely many other, but I have experience with these) read the SPDIF preamble registers, user-space tool iecset reports the values. Easy to check for any soundcard beforehand. Linux can be booted from from a live USB drive, no need to install anything.
Thanks 🙂 That is really above my abilities but I suspect you are correct, it needs analysing in some way to see what is present that is upsetting the recorders. I can't really get why the old 1st generation tuner (the Pure) doesn't give this error and yet the new Rotel does. What could the Rotel do or add to the data that the Pure does not.
You could capture the data on an oscilloscope and then decode it by hand. It's a simple enough protocol that this is possible, though it would take significant time and effort. A quick search found an ST app note (AN5073) which I think contains enough information to work it out: https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.DM00431633.pdf