TimDog73
New member
Not so long ago I discovered one of my friends had a collection of Quadradisc vinyl and a turntable equipped with a Shibata stylus but to my dismay I discovered that his demodulator had broken some years ago and he had not replaced it.
Due to the short supply of demodulators in the UK I set about investigating the possibility of using a PC to capture and demodulate the the signal. I do believe this is possible and we are getting some results although they sound a rough; however I am confident we should be able to improve on these if I can get some more detail on the CD-4 standard.
We have managed to find articles and manuals on on the subject including Lou Dorrens "New CD-4 Demodulator Project" and some patent documentation but so far there is not enough detail to enable us to get a result good enough to listen too. Unfortunately we don't have access to a CD-4 demodulator so bench testing at the moment is not possible for us; maybe someone out there would like to help with that? We are presently using some short clips from a test disc recorded before and after demodulation helpfully provided by someone in the US and some samples captured by my self with out CD-4 demodulation.
The development of a CD-4 modulator has also crossed my mind. We are already experimenting with software generated signals to test and calibrate our demodulator as they are devoid of interference and distortion inherent found in the analogue system; it's use could also be extended for calibrating the analogue ones still in existence and modulating signals to allow the cutting of new discs.
The sort of information I require is detailed filter characteristics for the PLL and ANRS circuits e.g. filter roll off rates, PLL Gain etc.
If there is anyone on this forum who has contacts in JVC who developed this technology or people from record companys who might have access to detailed documentation about the CD-4 standard. I would most appreciate it if you could put your hand up or get me in touch with them.
Many thanks in advance,
Tim
Due to the short supply of demodulators in the UK I set about investigating the possibility of using a PC to capture and demodulate the the signal. I do believe this is possible and we are getting some results although they sound a rough; however I am confident we should be able to improve on these if I can get some more detail on the CD-4 standard.
We have managed to find articles and manuals on on the subject including Lou Dorrens "New CD-4 Demodulator Project" and some patent documentation but so far there is not enough detail to enable us to get a result good enough to listen too. Unfortunately we don't have access to a CD-4 demodulator so bench testing at the moment is not possible for us; maybe someone out there would like to help with that? We are presently using some short clips from a test disc recorded before and after demodulation helpfully provided by someone in the US and some samples captured by my self with out CD-4 demodulation.
The development of a CD-4 modulator has also crossed my mind. We are already experimenting with software generated signals to test and calibrate our demodulator as they are devoid of interference and distortion inherent found in the analogue system; it's use could also be extended for calibrating the analogue ones still in existence and modulating signals to allow the cutting of new discs.
The sort of information I require is detailed filter characteristics for the PLL and ANRS circuits e.g. filter roll off rates, PLL Gain etc.
If there is anyone on this forum who has contacts in JVC who developed this technology or people from record companys who might have access to detailed documentation about the CD-4 standard. I would most appreciate it if you could put your hand up or get me in touch with them.
Many thanks in advance,
Tim
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