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Working CD-4 (software) Demodulator!

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quattro64

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Jan 22, 2009
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Ok, I will be working more on hifi projects this winter, So hopefully I will have those projects finished and working soon so I can get you some files to work with.
 

Brice

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Jun 13, 2018
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All,

I'm not sure this is the right place to post this, but my hope is that CD-4 enthusiasts will know more about this than most....

Someone has very kindly provided me with a UD-4 needle-drop. Our recommendation with these discs is to use a BMX decode which we already have:


However, I have discovered that it's easy to decode the UD-4 subcarrier signals in the pre-existing CD-4 demodulators, so a full QMX decoder is within reach.

The problem I have is not knowing what to do with these subcarrier signals. I have the classic UD-4 references (for example, Discrete-Matrix Multichannel Stereo. D.H. Cooper & T. Shiga, Journal of the Audio Engineering Society JUNE 1972, VOLUME 20, NUMBER 5) and have read them all. But they don't answer the practical questions concerning: noise-reduction; de-emphasis; matrixing; etc...

Does anyone have anything PRACTICAL on UD-4 decoding? Ideally a manual on a commercial product. I can't find anything. Was there even a practical decoder for UD-4?

Many thanks,

Richard
 

fredblue

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All,

I'm not sure this is the right place to post this, but my hope is that CD-4 enthusiasts will know more about this than most....

Someone has very kindly provided me with a UD-4 needle-drop. Our recommendation with these discs is to use a BMX decode which we already have:


However, I have discovered that it's easy to decode the UD-4 subcarrier signals in the pre-existing CD-4 demodulators, so a full QMX decoder is within reach.

The problem I have is not knowing what to do with these subcarrier signals. I have the classic UD-4 references (for example, Discrete-Matrix Multichannel Stereo. D.H. Cooper & T. Shiga, Journal of the Audio Engineering Society JUNE 1972, VOLUME 20, NUMBER 5) and have read them all. But they don't answer the practical questions concerning: noise-reduction; de-emphasis; matrixing; etc...

Does anyone have anything PRACTICAL on UD-4 decoding? Ideally a manual on a commercial product. I can't find anything. Was there even a practical decoder for UD-4?

Many thanks,

Richard
 

Brice

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Jun 13, 2018
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France
Hi Fredblue,

Thanks for the jpeg. Does this mean you have the manual for this machine? Can you send it to me? (Use the support email for Stereo Lab if you wish.)

Best,

Richard
 

fredblue

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Hi Fredblue,

Thanks for the jpeg. Does this mean you have the manual for this machine? Can you send it to me? (Use the support email for Stereo Lab if you wish.)

Best,

Richard
hi Richard,

you're welcome!
i don't have the manual i'm afraid, or the demodulator itself, just passing on the info. it is a scarce piece of equipment but i have seen a couple of examples pop up for sale in the last few years so its not beyond the realms of possiblity somebody here may have one and can help out.

all the best,
Adam
 

Circular Vibes

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I do not know if this will help. I can not find the post now but in the last month I saw an old post where a veteran QQ member offered the manual or schematic by email. I am on my phone and search sux big tine on it. I might be wrong but I think it might have been Quadtrade. Don't blast me if I remembered wrong. If anyone finds that post I need it too as I have a UDA100 on a slow boat from Japan.
 

Brice

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Messages
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Location
France
Dear fredblue and Circular Vibes,

Thanks so much for the replies.

Understood Adam. Your post at least confirmed that there was a commercial UD-4 demodulator: that's helpful.

Circular Vibes, if you do manage to get hold of a manual, it would be wonderful to see it too.

I have been listening to the demodulated signals from a UD-4 needle-drop. They are quite clean (albeit narrow-band and sounding like AM radio!) They are certainly useable, but it's difficult to tell exactly how.

Best,

Richard
 

quad4all

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User Clemens from the Netherlands offered the UD4 manual in another post. You might want to contact him.
 

Brice

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Jun 13, 2018
Messages
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Location
France
Thanks for the suggestion of the manual. In fact, after much fiddling around, I got UD-4 to work and it works very well. Have a look (and listen) at:


The question now is whether it is worth encoding this in the main code branch. There seem to be so few records actually available, I'm not convinced it's worth the effort.

If others feel otherwise, please let me know.

Best, Richard
 

quattro64

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Jan 22, 2009
Messages
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I think you are correct about those records being rare. Though for hobbyist and professionals, collectors that might run across such record it would be great to have it covered in this product. Maybe charge a bit more for the pro version?
 

Brice

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I think you are correct about those records being rare. Though for hobbyist and professionals, collectors that might run across such record it would be great to have it covered in this product. Maybe charge a bit more for the pro version?
Hi Quattro,

Thanks, that's an interesting idea.

Richard
 

Brice

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Richard,
any indication on when the WOW feature might be ready for release?
Hi Banjo800,

The WOW! feature is now fully coded and operational. It is presently in testing. I can't give an absolutely firm date (it depends what the testing phase turns up). But we have got very good results in the lab' so I'm hopeful that it'll be worth waiting for.

(Apologies to Quadrophiles, this has noting to do wth quad!)

Richard
 

kfbkfb

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IIRC, CD-4 discs were pressed using the same equipment
as Stereo/Mono LPs, so a certain (hopefully very small
%) may have an off center center hole, I don't know if
this would have a major effect on CD-4 decoding or not.


Kirk Bayne
 

Circular Vibes

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IIRC, CD-4 discs were pressed using the same equipment
as Stereo/Mono LPs, so a certain (hopefully very small
%) may have an off center center hole, I don't know if
this would have a major effect on CD-4 decoding or not.


Kirk Bayne
Off center holes are caused by improper punching of the mother or stamper. In most cases it is hoped that quality checks would catch this. Holes are not punched after pressing, rather they are molded that way. I have never seen an off center CD4 disc yet but my Jethro Tull War Child has a serious warp from heat damage and the CD4 carrier and audio signal still seem to be fine. I just have to be careful which cartridge I play it on.
 

Brice

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Jun 13, 2018
Messages
54
Location
France
IIRC, CD-4 discs were pressed using the same equipment
as Stereo/Mono LPs, so a certain (hopefully very small
%) may have an off center center hole, I don't know if
this would have a major effect on CD-4 decoding or not.


Kirk Bayne
The software decoder in Stereo Lab will cope with standard levels of disc eccentricity (and worse). The demodulutor was designed to do that. In fact, it was one of the challenges in the software demodulator to cope with a wandering carrier. Most RF demod' code is based on digital radio applications with crystal-controlled carriers. By contrast even a standard disc (especially when replayed on a belt-drive turntable) has a surprising amount of carrier drift.
 

Mendemender

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Duffort, France
The question now is whether it is worth encoding this in the main code branch. There seem to be so few records actually available, I'm not convinced it's worth the effort.

If others feel otherwise, please let me know.

Best, Richard
Personally I would probably never use it. Then again, if you've done all the work of developing it, it would be a shame not to include it.
 

gvl_guy

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Off center holes are caused by improper punching of the mother or stamper. In most cases it is hoped that quality checks would catch this. Holes are not punched after pressing, rather they are molded that way. I have never seen an off center CD4 disc yet but my Jethro Tull War Child has a serious warp from heat damage and the CD4 carrier and audio signal still seem to be fine. I just have to be careful which cartridge I play it on.
Curious if you have a favorite cartridge for Quadradiscs. Especially one that seems to do well with any "defects."
 

dghan

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Joined
Feb 17, 2016
Messages
22
The software decoder in Stereo Lab will cope with standard levels of disc eccentricity (and worse). The demodulutor was designed to do that. In fact, it was one of the challenges in the software demodulator to cope with a wandering carrier. Most RF demod' code is based on digital radio applications with crystal-controlled carriers. By contrast even a standard disc (especially when replayed on a belt-drive turntable) has a surprising amount of carrier drift.
Do direct drive turntables have less carrier drift than belt drive?
 
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