Has anyone found a demodulator for CD4 (Quadraphonic) Vinyl

[jaffa225man]

Sorry to dredge up such an old post, but I thought I could help out a bit, as I just got into 70s cd-4 in a small, but expensive, way. I've recorded the JVC calibration/test record 4DE-205-A for anyone still wishing to continue this audacity plugin. My recording equipment includes an Audio Technica AT14Sa phono cartridge, a Fisher MT-6320 turntable, a MIX MX750 mixer (used purely as a phono preamp), an M-Audio Delta 1010LT, and a Samson S-Direct Plus direct box. The recordings were done with the Delta 1010LT at 96000Hz, and 24-bit (as they're the max for the Delta 1010LT). I've created two recordings, as I am unsure my first method has the necessary impedance bridging:
1. Turntable->Mixer (Preamp)->2 RCA line inputs on the Delta 1010LT
2. Turntable->Mixer (Preamp)->Direct Box (in Guitar Mode)->2 microphone inputs on the Delta 1010LT

The volume levels are slightly different for each recording. Also, the second recording has a higher right channel volume for some reason, although the levels were set equally in envy24control, etc.
I didn't amplify the recordings to 0 dBFS, or delete the lead-ins or lead-outs. They are exactly as they were initially input, unedited but compressed to flac (from 96kHz, 24-bit wav).

In audacity, with Analyze->Plot Spectrum, I do see the "30Khz" tone in each recording, so although I'm not sure the frequency response is flat that high, there seems to be no equipment in either setup with a limiter for lowpass, etc. I was worried about the Samson S-Direct Plus (which states "10Hz - 20kHz"), and the MIX MX750 (which I can't seem to find any manual or specs for).

Please excuse the clicking due to my not cleaning the record yet.

Here they are:
1. https://drive.google.com/open?id=0B2uOb ... 1FOZ0J2eTQ
2. https://drive.google.com/open?id=0B2uOb ... Ug0dVZJOUk

I probably won't have google host these forever so don't hesitate to download them as soon as you can. If someone (TimDog73?) would like, I approve of them being re-hosted for the long-term. By the way, I'm not that same "chap in the USA", but I am one, and have also been an advocate for Free Software's Four Freedoms as long as I can remember, and hope to help make CD-4 less expensive and more reliable for everyone.

[Robert J. H.]

Sorry to dredge up such an old post, but I thought I could help out a bit, as I just got into 70s cd-4 in a small, but expensive, way. I've recorded the JVC calibration/test record 4DE-205-A for anyone still wishing to continue this audacity plugin. My recording equipment includes an Audio Technica AT14Sa phono cartridge, a Fisher MT-6320 turntable, a MIX MX750 mixer (used purely as a phono preamp), an M-Audio Delta 1010LT, and a Samson S-Direct Plus direct box. The recordings were done with the Delta 1010LT at 96000Hz, and 24-bit (as they're the max for the Delta 1010LT). I've created two recordings, as I am unsure my first method has the necessary impedance bridging:
1. Turntable->Mixer (Preamp)->2 RCA line inputs on the Delta 1010LT
2. Turntable->Mixer (Preamp)->Direct Box (in Guitar Mode)->2 microphone inputs on the Delta 1010LT

The volume levels are slightly different for each recording. Also, the second recording has a higher right channel volume for some reason, although the levels were set equally in envy24control, etc.
I didn't amplify the recordings to 0 dBFS, or delete the lead-ins or lead-outs. They are exactly as they were initially input, unedited but compressed to flac (from 96kHz, 24-bit wav).

In audacity, with Analyze->Plot Spectrum, I do see the "30Khz" tone in each recording, so although I'm not sure the frequency response is flat that high, there seems to be no equipment in either setup with a limiter for lowpass, etc. I was worried about the Samson S-Direct Plus (which states "10Hz - 20kHz"), and the MIX MX750 (which I can't seem to find any manual or specs for).

Please excuse the clicking due to my not cleaning the record yet.

Here they are:
1. https://drive.google.com/open?id=0B2uOb ... 1FOZ0J2eTQ
2. https://drive.google.com/open?id=0B2uOb ... Ug0dVZJOUk

I probably won't have google host these forever so don't hesitate to download them as soon as you can. If someone (TimDog73?) would like, I approve of them being re-hosted for the long-term. By the way, I'm not that same "chap in the USA", but I am one, and have also been an advocate for Free Software's Four Freedoms as long as I can remember, and hope to help make CD-4 less expensive and more reliable for everyone.

Thanks a lot.
I'm curious how the demodulation will work for these files.
I have to analyse the plug-in as it doesn't seem to be loadable in the newest Audacity version.
Robert

[cyrano]

Thanks for your efforts, Robert.

I had no idea you could do this with Nyquist. I'm following this thread!

[Robert J. H.]

Thanks for your efforts, Robert.

I had no idea you could do this with Nyquist. I'm following this thread!

You can actually do everything in Nyquist.
It's just a question of the time it takes to process.
The FM demodulation works pretty good but it has to be done sample by sample because of the usage of "Atan2" which works with numbers only.
I'm trying to replace it with a trigonometric identity that works with sounds or with a fast approximation (e.g. lookup table).

[jaffa225man]

Yes, thanks very much for continuing this Robert! I'm glad to see there's still an interest, and hope the recordings will be useful and of sufficient quality to test your work.

[jaffa225man]

I know it probably won't make a difference, but I had been intending to clean the record and needle and rerecord. I finally did that, so here's the latest recording. If memory serves, the sound is not that improved from before, but the LP is now pristine. I also equalized the left/right levels of an independent source through the same chain (although a line input on the MIX MX750 - not through it's phono preamp). I used setup number two from before: Turntable->Mixer (Preamp)->Direct Box (in Guitar Mode)->2 microphone inputs on the Delta 1010LT.

The recording is still louder on the right channel, but the only possibilities for that (if it is indeed not pressed into the record that way) are differences in the MIX MX750's line and phono preamp, or perhaps the needle is weighted wrong or misaligned. It's easy enough to match each channel's levels in software (audacity, anyone? ), if you feel the need. It's still an unedited, uncut 24-bit recording at 96kHz, merely converted from wav to flac.

Anyway, I hope you're well, and here's my latest try: https://drive.google.com/file/d/0B2uObE ... sp=sharing