Lou Dorren: A new CD-4 Demodulator!!! [ARCHIVE]

[ingresman]

Disclord: Do you have the patent number or a link to the Vector Cancellation decoder please? I'd be very interested to have a read of it
cheers

 

[JonUrban]

Well folks, I heard from Lou today!

He's been through some serious medical issues, but is on the rebound and sounded like he was ready to get back to his real job and other things, including the demodulator. Again, time will tell and this project is not his main focus, so we'll see. It's been a while, and it may be longer, but I just thought I'd let you all know that there is still a glimmer there somewhere.

 

[zabble]

I'm glad Lou is on the rebound. And a glimmer is better than nothing.

 

[bmoura]

Well folks, I heard from Lou today!

He's been through some serious medical issues, but is on the rebound and sounded like he was ready to get back to his real job and other things, including the demodulator. Again, time will tell and this project is not his main focus, so we'll see. It's been a while, and it may be longer, but I just thought I'd let you all know that there is still a glimmer there somewhere.

Lou is a great guy. Glad to hear he's back in good health !

 

[Disclord]

Disclord: Do you have the patent number or a link to the Vector Cancellation decoder please? I'd be very interested to have a read of it
cheers

It's US patent #3786193

 

[The Quadfather]

Well, I reckon by the time Lou gets these demodulators built, I hope to be out of this financial funk. Back in the game, so I can buy one.

The Quadfather

 

[ingresman]

It's US patent #3786193

thanks

 

[FM_Quad]

Because also I have now waited fruitless nealy 6 year of the often announced new demodulator, I have bought now the new QS/SQ Decoder from Australia. Thisitemm is now on the way to me.

By thinking again about the missing new Demodulator I have had the idea: Why not a development for such a CD-4 demodultor also with digital-technic? So I have asked now Chucky with PM, if there could be a possibility for building such a modern CD-4 demodulator.


Independent from the result I think, one of the fans in the USA, who is living in the area of San Francisco, should go self to Lou and see, which circumstances are around Lou Dorren. I have some time ago announced Lou such visite from me by him , when it was easier to do from Germany. Actual the situation is for me and most other fans here in my area some impossible.

Dietrich

As I mentioned on another thread, I would love to do a fully digital implementation, and may at some point. Alas like a lot of us, I have work and other commitments and have only devoted a little introductory time to it. My approach would probably start with a 192 KS/s stereo ADC at 24 bits followed by a DSP. One unknown would be the output format. Four analog outputs from DACs is certainly possible, but my preference would be to store it in digital form for reproduction. That would minimize the wear (and hassle) of playing the vinyl every time and also allow sharing these no-longer-in-production albums. In fact one option I had considered was digitizing to a PC and letting it do the decoding. I'm not sure it could do it in real time, but if not, it only has to do it once and you have a file to play. Again, the output format is a bit tricky, since four channel isn't a currently standard format.

Once I get past the house sale that has dragged on for six months and finish unpacking and the remodel, . . .

Just glad to hear rumblings of new life from Lou's new decoder. I was afraid health was the culprit again--sadly.

 

[Quadro-Action]

Hello FM-Quad,

I would wellcome also a new demodulator with digital working, but in the demodulator, not in the PC. I would also not bought the Aussi Invole decoder, when Iwould need some hours, before I could listen the result of a playing LP. Also a demodulator must work as standalone set with analog outputs for a right away listening by playing the quadradisc record. 4 channel is that, what CD-4 fans know and want. And it is even and further on modern concept. The CD-4 systems ist transmissing only 4 channels, but produce 5 listening channels together with the phantom center. The best economic way for a perfect surround-sound. And LP's in stereo, SQ or quadradusc has only very few distortions by a real careful handling. Better working with a record clean machine before playing, if needed.

No is further on Lou in the line of the completion of his long time announced demodulatoir. It is not acceptable to make fans hot and since 6 years later there is further on no a test protoype. How will have the fans a confidence in a real building, when he needs - may be one day - theire cash, before the demodulator is seen? Should we wait further on some years?

Dietrich

 

[FM_Quad]

Hello FM-Quad,

I would wellcome also a new demodulator with digital working, but in the demodulator, not in the PC. I would also not bought the Aussi Invole decoder, when Iwould need some hours, before I could listen the result of a playing LP. Also a demodulator must work as standalone set with analog outputs for a right away listening by playing the quadradisc record. 4 channel is that, what CD-4 fans know and want. And it is even and further on modern concept. The CD-4 systems ist transmissing only 4 channels, but produce 5 listening channels together with the phantom center. The best economic way for a perfect surround-sound. And LP's in stereo, SQ or quadradusc has only very few distortions by a real careful handling. Better working with a record clean machine before playing, if needed.

No is further on Lou in the line of the completion of his long time announced demodulatoir. It is not acceptable to make fans hot and since 6 years later there is further on no a test protoype. How will have the fans a confidence in a real building, when he needs - may be one day - theire cash, before the demodulator is seen? Should we wait further on some years?

Dietrich

Since I knew Lou personally at one time and have read from others that knew him better than I, the issue of trust is not a concern with me. If he is physically able, he will come through.
My personal preference would be a stand alone solution as you describe, but I would want both digital and analog outputs. I also agree that it should work for stereo, too. One of my original goals was to be able to do a high quality digitization of both stereo and CD-4 LPs. I have a collection of over 100 LPs and trying to keep working equipment (housekeepers are hazardous to styluses, for example, and I used to have an Empire belt driven TT who's belts would dry and crack almost as often as I used it--both of which are getting hard to find) not to mention cleaning the discs and properly storing them in a convenient location has been a problem. I'd like to digitize everything and know I at least had something to fall back on in case of either damaged media or equipment. Being both a musician and a digital engineer, I have no qualms about digital done right (although price pressures insure that it generally isn't done right).

 

[ndiamone]

See a related thread on
http://www.lathetrolls.net/viewtopic.php?f=15&t=4523

As you will see over there - in order to save the LP's from overuse back in the day - I myself have been FAIRLY successfull in disabling the audio-frequency modulation in an old Viking half inch instrumentation recorder which featured helical-scan heads similar to what they would later use in Beta HiFi consumer gear and BetacamSP.

Using Ampex 777 instrumentation tape - used reels of which were ubiquitous in the computer labs of the late 70's and early 80's - I was able to play the LP through the Shibata stylus and CD-4 capable cartridge (AT14S) without going through the RIAA curve - and record directly onto the instrumentation tape with the carrier wave intact - after which I was able to attenuate the resulting signal and pipe it through a standard CD-4 demodulator to recover the original quadraphonic sound.

 

[Quadro-Action]

Hello FM. Nothing against specilities, but a demodulator should work in first line for the most preferde handling. I think, Lou has also announced additional outputs for such special or digital working - like the computer generated picture of the item. But this is since 6 years only theory.
I will woder, when the demodultor will be sometime seen als reality.

Dietrich

 

[FM_Quad]

I understand, and if I get that far, I will have to consider the variations. The biggest difference is that I would be pursuing a digital implementation, so the output fundamentally would be digital. Providing analog outputs would not be a big deal, but definitely would be "the add in". An area I have little exposure to but would like to explore as well is putting out either coax or fiber sdif either quad (if that is a viable option) or 4.1, 5.1, etc with nothing in the center, subwoofer, etc. channels.

 

[TimDog73]

I am working with Robert on the Audacity forums to see I we can implement a software based CD4 demodulator. We have had some promising results with the audio captured at 192kHz 24bit at normal speed but we would like to try slowing down the capture to 1/2 or possibly 1/3 speed at the same sample and bit rate to increase resolution of the difference signal. Unfortunately we don't have the means to slow down playback to this extent, so to the question; is there anyone that would be willing to make us some recordings of a CD-4 disc before demodulation using a Shibata stylus at 1/2 and or 1/3 speed at 192kHz 24bit? Any help would be much appreciated.
Tim

 

[tektaff]

I am working with Robert on the Audacity forums to see I we can implement a software based CD4 demodulator. We have had some promising results with the audio captured at 192kHz 24bit at normal speed but we would like to try slowing down the capture to 1/2 or possibly 1/3 speed at the same sample and bit rate to increase resolution of the difference signal. Unfortunately we don't have the means to slow down playback to this extent, so to the question; is there anyone that would be willing to make us some recordings of a CD-4 disc before demodulation using a Shibata stylus at 1/2 and or 1/3 speed at 192kHz 24bit? Any help would be much appreciated.
Tim

It's an interesting idea, but one that presents a few problems. most phono cartridges are velocity types, so the frequency response at the low end will be out to lunch.
Wow and flutter become much bigger issues at low rotational speeds.
At slow speeds the carrier frequency will be within the RIAA "curve", so probably best recorded via a linear input, and then creating the right compensation curve in audacity.

Processing the signals in the digital domain makes a lot of sense, so you are on the right track.

I did think of creating a stand alone digital CD-4 decoder using an FPGA/DSP, but knew that once started i would never finish.

Hywel

 

[Owen Smith]

As I understand it the ANRSS noise reduction is going to be difficult to do in software, since it is dependent on the absolute levels of the signal. So there is a difficult calibration exercise to get the levels correct.

 

[tektaff]

As I understand it the ANRSS noise reduction is going to be difficult to do in software, since it is dependent on the absolute levels of the signal. So there is a difficult calibration exercise to get the levels correct.

If memory serves me correct, ANRS was a Dolby B type clone, so should be easy to calibrate from a CD-4 test record ( the ones with the bleeps and sweeps). Compression/expansion/gating algorithms are easy to configure in a software environment.
I've been led to believe most of the commercial audio software "plugin" development is done in MATLAB.
Hywel

 

[FM_Quad]

If memory serves me correct, ANRS was a Dolby B type clone, so should be easy to calibrate from a CD-4 test record ( the ones with the bleeps and sweeps). Compression/expansion/gating algorithms are easy to configure in a software environment.

ANRS morphed into a Dolby B clone when later applied to cassette tape. ANRS as used in CD-4 is a different animal, although based on the same principles. It is correct that calibration would be trivial with a CD-4 test record. Because the F-R subcarrier is FM modulated, the gain is predictable by design and not dependent on the sensitivity of the cartridge. The need for calibration is because the F+R baseband signal IS dependent on the sensitivity of the cartridge. The only way that (F+R) - (F - R) is going to yield just rear (and (F + R) + (F - R) is going to yield just front) is if the baseband sensitivity is equal to the subcarrier sensitivity. That's all calibration does. From a design standpoint, there are other issues, such as matched filter performance and channel delays that match what was used for recording, but those are all one time design issues.

I've been led to believe most of the commercial audio software "plugin" development is done in MATLAB.

Certainly MatLab can improve the productivity and the tools that work with it can generate C code for a DSP or FPGA equations. It's a fine tool if you have it or can afford to buy it. But it is far from necessary. There are still people who know how to write C code and understand DSP equations.

Wilton

 

[The Prof]

To Lou Dorren. Is your CD-4 demodulator still available for sale?
Regards - The Prof- Jake

 

[FM_Quad]

To Lou Dorren. Is your CD-4 demodulator still available for sale?
Regards - The Prof- Jake

See #1152 above. It hasn't yet been released. We're still hoping.