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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 24 Nov 2020, 20:10 
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I am still "fine tuning" my setup, but things are steadily improving. Currently, the setup is (all coax is rg174):

1. 4300D (uncalibrated, but supposedly "new in box" when i bought it, and appeared as such)
2. tapping RF off of pickup rather than internal RF test point (avoids 90s era amplification circuitry)
3. inline 50ohm (51 actually) resistor
4. pre made OPA657 amplifier board with manual gain adjustment: LINK mounted in a project box, SMA connectors removed, coax attached to board, and to BNC connectors. Powered with 6 "AA" batteries in 2 3x holders: LINK
5. an inline 20ohm resistor (should probably be higher ohm, the amp amplifies a lot, and is easy to overload the ADC)
6. 13+mhz low pass filter from mini circuits: link coax connected to BNC connectors so it is removable.
7. BNC "T" connector and 50ohm termination ( i like to have the option to remove it, but could be integrated into modified card)
7. Capture card, PCIe CXADC card: LINK which is modified, removing onboard LPF, onboard 75ohm termination, BNC port added where one of the RCA jacks was, wire connecting to the DC blocking cap on the circuit board for the S-Video input. 28.636mhz crystal replaced with 40mhz: LINK for 40msps capture without driver modification.

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EDIT: the above linked 40mhz crystal is tiny, and difficult to work with. I was unable to find a 40mhz crystal that was within the datasheet specs. However, it recently occurred to me that a 32mhz crystal in tenxfsc mode would also be 40msps. I believe this would work, and would be easier to install: 32Mhz crystal LINK



Things i am still investigating:
1. using alternate (10.7+) LPF
2. improved connection to PCIe board (get closer to chip pin to reduce exposed trace, which can pick up interference)
3. my short captures are better than long ones at same settings, indicating maybe a heat sink is needed?
4. update the driver to do 40msps without changing crystal (progress made, but S/N is poor).

For those that "only have a laptop" would be interesting to know if something like this works: mini pcie to pcie


Chapter 33 of ggv1069:
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 25 Nov 2020, 02:27 
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I was able to get my hands on a properly modified off the shelf PCI card thanks to 9954tony. In short, I wasn't able to get any good results with my modified ATI card. I kept encountering red herring circuit paths, dead end traces, and broken pads. Soldering directly to the input pins of the chip is quite an impossibility due to the size and fragility of the pins. The card I have on the way now is simpler than any of the cards I bought, with less components and clear to follow traces. This allows for an ideal tapping point to feed the signal to the chip directly.

Will report back next week when it comes in.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 10 Dec 2020, 02:44 
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The results with the properly modified card are marginally better. The noise floor at gain level 15 is excellent:

Image

They were much better for 9954tony on this same card, but he is using a proper amplifier and a player with a higher RF output. I have the same amplifier he is using on order. This one claims up to 89dB of gain, based on the OPA657 IC used in the Domesday Duplicator:

https://www.ebay.com/itm/OPA657-High-Sp ... r=1&_rdt=1

Currently, here's a result of the beginning of my CAV side:

Image

Getting better. Still low frequency luma noise in the image though in the form of wide bands. The chroma adjustments in ld-analyse have no effect on this. Next I tried further into the CAV side near frame 9,000 (5 minutes) which is where the "flip the disc" message ends. This gives me 3dB of additional gain, putting me at SNR of 30dB.

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Next, I opened up my player and adjusted a voltage regulator pot labeled "RF level" until my amplifier comes in. When I found out this is safe, I turned it up all the way. It was at about 50% from the factory and I can change this back later. This probably got me a whole decibel of additional SNR, barely measurable. The waveform is definitely higher, but SNR barely changes due to the weak signal.

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CLV content side with gain pot at 50%:

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CAV message side with the gain pot at 100%:

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I'll post an update when the amplifier comes in. Out of all the ones 9954tony has tested over the last few months, this is the best performing one. It appears to be designed for photodiodes and the characteristics of the type of RF signal generated by them. CD players, LaserDisc players, etc.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 16 Dec 2020, 19:36 
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So this is awesome. Here's an example of better-than-new preservation effort where someone takes a 90s era Japanese anime series on LaserDisc and captures it with the Domesday Duplicator. He then "remastered" the decoded material and re-released it on a standard definition Blu-ray disc (drop out correction plus advantages of ld-chroma-decoder maybe?). I came across this of all things while studying the D3D amplifier circuit.

https://dvdprime.com/g2/bbs/board.php?b ... id=2325321
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 22 Dec 2020, 03:55 
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Here's a pretty nice software defined QAM video decoding example, luma only.

https://www.youtube.com/watch?v=yvfZE28I75Y

Dirty FM video decoding has been done unofficially with the symbol decoder:

https://www.youtube.com/watch?v=rl8ACNnjPFA

Still waiting on my amplifier.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 26 Dec 2020, 04:33 
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Amplifier is in, but I have a needed SMA polarity adapter on order. Should come the first week of January and I should be set to test it out.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 06 Jan 2021, 02:06 
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The results with the OPA657 amplifier aren't good. The image is similar to what I was getting on my ATI cards, just garbage. I found a strong pulsing signal in the upper band, whose pattern resembles fields of video when comparing waveforms in Audacity. I was thinking maybe a ground loop or the ground I had tapped wasn't true ground. So I moved the ground to the official ground pin on the test point, with the same result. This noise is present with and without the LPF. Without and with the filter respectively:

Image
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Being my captured bandwith is 20MHz wide, the signal appears to be exactly at 75% on the band, or 15MHz. I immediately thought maybe this was from the RF modulator, and the video pulses were QAM modulated onto the carrier. Channel 3 is 61.25MHz, and its 4th lower harmonic is 15.3125MHz. This would make perfect sense, if this machine even had an RF output! It does not. I found a "VHF adapter" port, which is just audio, video, and a 12vDC power jack for an external modulator, which I don't have.

So I moved the player to the same power outlet as my capture PC, and even connected the composite output to input jacks on another device to rule that out. I don't have anything else turned on in the same room, especially near the OPA657. I'm also powering the amplifier with 100% clean DC +4.5v and -4.5V supplies from AA battery packs. But the noise is still there, and I have no explanation other than the CLD-V720's test point is simply poorly designed. Or, there's another issue with my particular player. Bad capacitors or something allowing noise from other circuits back through.

In the midst of this, I'll probably still use the modified card for vhs-decode with my VCR instead. The ultimate conclusion though is, just any LaserDisc player with an RF test point will NOT work.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 17 Jan 2021, 00:18 
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My hard drive died. After installing Linux Mint 20.1 (Ubuntu 20.04 base) with a new drive I can no longer build cxadc. I didn't have this issue before. Here's what I get following the GitHub instructions:

user@mintiplex:~/Downloads/cxadc-linux3-master$ make && sudo make modules_install
make -C /lib/modules/`uname -r`/build M=$PWD
make[1]: Entering directory '/usr/src/linux-headers-5.4.0-62-generic'
  Building modules, stage 2.
  MODPOST 1 modules
make[1]: Leaving directory '/usr/src/linux-headers-5.4.0-62-generic'
make -C /lib/modules/`uname -r`/build M=$PWD modules_install
make[1]: Entering directory '/usr/src/linux-headers-5.4.0-62-generic'
  INSTALL /home/user/Downloads/cxadc-linux3-master/cxadc.ko
At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:69
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:76
sign-file: certs/signing_key.pem: No such file or directory
  DEPMOD  5.4.0-62-generic
Warning: modules_install: missing 'System.map' file. Skipping depmod.
make[1]: Leaving directory '/usr/src/linux-headers-5.4.0-62-generic'
user@mintiplex:~/Downloads/cxadc-linux3-master$ sudo insmod cxadc.ko vmux=2 level=1
insmod: ERROR: could not insert module cxadc.ko: Invalid module format


dmesg log shows:

[   85.295496] cxadc: version magic '5.4.0-58-generic SMP mod_unload ' should be '5.4.0-62-generic SMP mod_unload '
[   91.645527] cxadc: version magic '5.4.0-58-generic SMP mod_unload ' should be '5.4.0-62-generic SMP mod_unload '


I did try a reboot, same issue. I built the module again and tried to insert and got the same error again. For some reason make wasn't building against the active kernel, it was building against another version of the kernel that was installed. I figured it out, what happened was I built the module then installed a kernel update. Following the reboot, it wouldn't insert because of the kernel version mismatch. Running make again should have worked, and it used to for me in the past when I installed kernel updates. But it did not this time.

The root cause was make was re-using one or more files in the cxadc source folder. I had to delete the folder and re-extract it clean from the GitHub zip file. Ran the same command again and cxadc built, inserted, and is working now no problem.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 30 Jan 2021, 21:05 
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I and others have seen constant issues where cxadc doesn't want to work when loading the kernel module. The errors in the terminal state the device doesn't exist, yet the /dev/cxadc0 special device file is there. I think I found out why this is constantly happening with Ubuntu and Mint. It seems to be driver signature enforcement in the kernel. When building, I get this:

make && sudo make modules_install
make -C /lib/modules/`uname -r`/build M=$PWD
make[1]: Entering directory '/usr/src/linux-headers-5.4.0-62-generic'
  AR      /home/user/Downloads/cxadc-linux3-master/built-in.a
  CC [M]  /home/user/Downloads/cxadc-linux3-master/cxadc.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC [M]  /home/user/Downloads/cxadc-linux3-master/cxadc.mod.o
  LD [M]  /home/user/Downloads/cxadc-linux3-master/cxadc.ko
make[1]: Leaving directory '/usr/src/linux-headers-5.4.0-62-generic'
[sudo] password for user:           
make -C /lib/modules/`uname -r`/build M=$PWD modules_install
make[1]: Entering directory '/usr/src/linux-headers-5.4.0-62-generic'
  INSTALL /home/user/Downloads/cxadc-linux3-master/cxadc.ko
At main.c:160:
- SSL error:02001002:system library:fopen:No such file or directory: ../crypto/bio/bss_file.c:69
- SSL error:2006D080:BIO routines:BIO_new_file:no such file: ../crypto/bio/bss_file.c:76
sign-file: certs/signing_key.pem: No such file or directory
  DEPMOD  5.4.0-62-generic
Warning: modules_install: missing 'System.map' file. Skipping depmod.
make[1]: Leaving directory '/usr/src/linux-headers-5.4.0-62-generic'


And when checking the dmesg logs, I get this:

13:48:10 kernel: cxadc driver loaded
13:48:10 kernel: cxadc: module verification failed: signature and/or required key missing - tainting kernel
13:48:10 kernel: cxadc: module verification failed: signature and/or required key missing - tainting kernel
13:48:10 kernel: cxadc: loading out-of-tree module taints kernel.
13:48:10 sudo:   user : TTY=pts/0 ; PWD=/home/user/Downloads/cxadc-linux3-master ; USER=root ; COMMAND=/usr/sbin/insmod cxadc.ko vmux=2 level=1


What's weird is I never had this issue for months at a time, then started having the problem. Maybe there was an update that changed the driver signature enforcement or something. It's not the first problem where the module wouldn't insert due to kernel version being incompatible. I get no errors in the terminal when inserting it but when I run rmmod, I get a message saying the module isn't even loaded. The device file creates fine, but the module doesn't load for that reason. I removed that folder and re-extracted/re-built the module. Tried inserting again, it says the file exists. Yet, I can't access cxadc0 and using rmmod says it's still not loaded.

I read somewhere there are two solutions, one is signing the kernel module so the kernel will load it. Another is re-building the kernel with an enforcement flag disabled (lol). I still don't understand why so many people seem to not have this issue, but one of the Discord guys and I do. I also read secure boot in the UEFI settings could cause this, and the CMOS battery did die and clear my settings about a month ago. However, I checked today and secure boot is turned off.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 30 Jan 2021, 23:55 
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I was told those are simply warning messages and the module isn't being blocked by the kernel. The issue was a conflict with existing kernel modules loaded on boot. My setup is working again. I opened the below issue on GitHub for happycube to take a look at.

https://github.com/happycube/cxadc-linux3/issues/8
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 27 Mar 2021, 22:13 
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I took a hiatus from this to work on my vhs-decode workflow, which allowed me to get a very nice 46dB SNR from those captures. In that case, my OPA657 amplifier screwed up the captures. To get an SNR number that high I tapped the VCR using a BNC connector and mini coax going directly to my CX card with another 1ft mini coax to s-video pigtail adapter cable and 13MHz filter, with the external amp out of the picture entirely.

With that in mind, 9954tony has helped me find a Pioneer CLD-S250 machine that seems to work better for captures. I tried the amplifier on it and got nothing on the output at all. I connected the player directly to the same CX card using the 13MHz filter with a long 6ft mini coax cable (strike 1), with factory 5MHz low pass filtering on the card (strike 2), and a 75 ohm based impedance on the unmodified card (strike 3). Still, with all that, I'm probably getting the cleanest capture from LaserDisc as of yet. It's really weak and only 20dB black SNR so far, but the decode isn't bad for starters and the FM audio is flawless.

Next I'm going to swap my card to a modified one to bypass the stock low pass filter caps and 75 ohm terminating resistors and test again, with a 50 ohm terminator added which I have not tried before.

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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 06 Apr 2021, 00:42 
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Using the correct card, with player grounded to PC, termination, and gain brought down to 25 to avoid clipping, I'm getting black SNR of about 36dB and a good result. There's some constant noise in the red background of the program index screen, but this may just be the disc. The text is sharp and noise free. Still some 60Hz wavy pattern that is stationary in the image, likely due to mains hum in this room. I'll be moving my workflow at some point to try and isolate that.

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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 23 Apr 2021, 12:46 
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I moved my setup, but am still getting the noise. This is actually a warped disc. The scrolling wavy artifacts get worse as I play it. I can eyeball the side of the disc and tell it isn't flat. I'm flattening the disc using some heavy books and will try again in a couple weeks. Here's a couple videos covering this:



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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 12 May 2021, 01:32 
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I picked up a 1979 DiscoVision title, "Heroes." For DiscoVision, it's not bad video wise. However, there is some weird drop in SNR for one half of the disc that causes a lot of noise on every other field. This noise also obliterates the muffly and otherwise unimpressive mono audio track. I paid only $1.90 for this 3 disc title. I haven't look at the other discs yet, but what baffles me if I see absolutely no visual difference between the two halves of the disc. This is a CAV title, and the problem seems to get worse the longer I play it. There is no visible rot or tarnish that I can see, and am just going to chalk this up to a bad pressing.

I might try and de-interlace and throw away the bad fields just for the lols. That will still give me 30 frames per second which preserves all 24 film frames, but at the cost of half of the vertical resolution. Even if I did this and interpolated the resolution on the good fields it would probably still not be a bad result.

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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 26 May 2021, 17:22 
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I cleaned the problematic side of this disc with a medium strength plastic polish, followed by a low strength polish. There was some hazy speckling on about a quarter of the disc. I thought this would eliminate the poor reflectivity but the polishing made no difference. The disc itself must have cloud rot. Or it's a bad pressing. To my naked eye I don't see any cloudiness on the disc at all.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 26 May 2021, 17:27 
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Yeah, if that cloudy is under or inside the plastic then you are out of luck.
Novus is what I use and I've had good luck but its mostly if the disc is good to begin with, I've never been able to make a bad disc good
but have been able to make a good disc great.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 04 Jun 2021, 01:08 
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I've been squishing my warped Sony Take Five sampler disc with 70lbs of books for nearly 2 months. I'll try that again next week.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 13 Jun 2021, 19:04 
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After flattening my demo disc for several weeks I tried capturing again. This time the picture seems much improved and bend on the disc seems, at least to my eyes, to be not as bad. The disc also made less noise in my player. Still a little CLV crosstalk at the end but that's expected. I'll update again when it's done decoding.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 14 Jun 2021, 00:09 
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After another decode, it's hard to say if it's much better. I would assume so, as the SNR doesn't seem to drop as much as the disc goes on. SNR averages 35dB. A few screenshots after flattening from beginning to end:

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