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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 26 Jan 2014, 23:25 
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That is amazing to have software decoder for LD, LOVE IT.

I hope one day it will be fully usable to end user like me,

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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 27 Jan 2014, 23:15 
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happycube wrote:
Pre-emphasis is a birch. It's very hard to compensate for correctly...

... and almost every LD player fails to do it quite right. Maybe the X0 does. ;) (and possibly the player Laserdiscmodder re-capped etc - at least he claimed/showed it...) Perhaps when new the PR-7820 did as well, but if it used electrolytics they probably drifted by now.

Basically a sharp brightness change is exaggerated/pre-emphasized, and the player needs to de-emphasize it in return. When done properly, this reduces noise since the shifts are reduced. When not done properly, you see ringing once the signal returns to the proper level, and that shift gets de-emphasized as well, even though it shouldn't.

This is why you see ringing/ghosting on test patterns.


With Video Essentials the patterns show absolutely no ringing when played on my HLD-X0. The only other player(s) I own that came close to the X0 is the LX-900/Runco's - the TheaterVision, which is a CLD-99, has ringing and a pixelated, slightly smeared image due to the digital NR - here's the rub though, the X0 uses the same Y and C NR IC's as the 99, but the way the X0 is made, even with the NR set to the highest level and the 3D comb filter set to full on, there is absolutely NO smearing of chroma or lagging of chroma to luma - and the picture has a completely smooth, analog look without a strange pixelated look like the Pioneer's produce - as with the ringing, only the LX-900/Runco's come close to the XO.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 28 Jan 2014, 08:08 
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Thanks! I don't have anything new cooking yet... I think my next step will be looking into learning OpenCL and accelerating the FM decoder code. Dunno when I'll have something end-user-friendly, but that's probably my best shot at getting to real time, and I've got some other far-flung projects that probably need GPU help, too :)

It's interesting just how much better the X0 is at everything. (My WAG is the red laser and very picky component choices, layout, everything...)
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 28 Jan 2014, 19:37 
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OK, I do not mind command line, but what would I need to use, what "video capture card"

Also under what Linux flavour does it work?

And I need to figure out if any of my LD players even have RF out... (probably not...)
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 28 Jan 2014, 19:54 
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You need a video capture card with a CX2388x chip. The Hauppauge WinTV 34132 is what I've been using, IIRC. I use Ubuntu 64-bit, and I replace the regular capture card driver with my new version of the cxadc driver. It's the only low-cost high bandwidth ADC I know of.

A high-end SDR receiver that can pull in 28.636mhz at DC would also work.

I believe it's possible to build a cable between an AC3 RF out and the video capture card, i just haven't done it yet. Currently I use the raw/internal RF testpoint off a V8000 or V2800 wired up to a VGA amplifier/distributor after realizing it has enough bandwidth to be useful. I just need to order some 100uF capacitors and sacrifice an S-Video and RCA cable.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 28 Jan 2014, 20:30 
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Thanks, that would make it much easier (AC3 RF --> Hauppauge WinTV 34132)

Let us know if you manage to do it

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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 01 Feb 2014, 00:08 
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I second that request. Good luck!
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 03 Feb 2014, 07:46 
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Feeding the AC3 directly into the Hauppauge didn't seem to fry it, but the DVL-919 appears to be filtering out video RF. I'll try the CLD-D406 this week.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 07 Feb 2014, 14:21 
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Would this be a possible SDR? http://nuand.com/ 420$ is not cheap but a lot cheaper than USRP. Do you know of any other SDRs that would work?

Also how do you store the data captured, fileformat etc? Does it not take huge space?
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 07 Feb 2014, 19:49 
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12-bit IQ 28mhz capture would be quite awesome. That would even capture an X0's RF from MUSE disks. (If I was smart and got into Bitcoin early, I could afford such things ;) )

However, the frequency would need fixing (LD RF is DC-12ish mhz, the bladerf is 300mhz+), and you would have to be careful about the voltages (perhaps the upconverter could handle it)

There is quite a bit of data coming off it (28MB/sec), but nothing a modern desktop can't deal with.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 08 Feb 2014, 13:32 
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ADC 101 questions.
How do you calculate the data bandwidth?
How is the waveform stored?
I cant really get my head around the different mhz specs. The RFblade claims it is "capable of capturing 40MHz 12-bit full duplex quadrature samples in realtime" but at the same time it has a frequency range of 300MHz - 3.8GHz RF. How do they relate to each other?

Thanks in advance for enlighten a RF noob!
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 09 Feb 2014, 01:29 
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The bandwidth calculation is quite straightforward. In the case of 12-bit 40mhz IQ samples, it's 1.5 bytes per sample * 40 million samples/second * 2 (I and Q). So it's 120MB/sec.

My current capture device setup is at 8x FSC (28.636mhz), 8-bit, so only 28.6MB/sec. It can also do 10x FSC (~35MB/sec)

The waveform is basically stored as captured. I haven't bothered to do any sort of compression on it.

The RFblade has a tuner, which captures a 28mhz range of that 300-3.8ghz RF. The actual ADC is at 40mhz off the tuned signal. Look at some SDR groups for a better overview than I can give.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 09 Feb 2014, 21:00 
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The D406 also low-pass filters the RF. :(

I posted a Python version of the RF decoding code. Still hard to read, but much shorter (and slower) than the C++ version. Mostly did it to learn a bit more about numpy, and as a testbed for other developments (OpenCL experiments)
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 09 Feb 2014, 22:25 
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Ah that is a shame about your player, do they all lowpassfilter?

I am by no measure knowledgable in how a laserdisc works, if I have understood it correctly there is pits of variable length that a laser reads. Through some magic DAC this is made into a RF signal and further amplified and filtered? And this is the signal you capture? Why going this route instead of reading the laser itself? Is it much harder to do or why did you choose this way of doing it? Just curious, also what card you recommend me to buy if I would like to experiment with this, I would like to test it on tapebased(betam umatic etc)?

Keep up the good work!
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 09 Feb 2014, 23:28 
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luuude wrote:
Ah that is a shame about your player, do they all lowpassfilter?

I am by no measure knowledgable in how a laserdisc works, if I have understood it correctly there is pits of variable length that a laser reads. Through some magic DAC this is made into a RF signal and further amplified and filtered? And this is the signal you capture? Why going this route instead of reading the laser itself? Is it much harder to do or why did you choose this way of doing it? Just curious, also what card you recommend me to buy if I would like to experiment with this, I would like to test it on tapebased(betam umatic etc)?

Keep up the good work!


The laser reads the pits which creates a Pulse Width Modulation FM RF analog signal containing al the information encoded on the disc -from there the RF is filtered and directed to the video demodulator, analog FM audio and EFM PCM digital audio, etc.... No digital processing of the signal takes place in standard players and didn't until the early 90's.

In players with a Dolby AC-3 RF output, the output is the full RF signal from the disc -the external demodulator isolates the right FM audio channel to extract the Dolby Digital signal.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 10 Feb 2014, 00:35 
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Thanks!

I'm using the WinTV 34132. There's one listing with 3 available on eBay US for $14+$5 shipping each.

I've looked at my D406 schematics and there's an RLC filter in front of the RF line going to audio and AC3 RF. My calculations have the video RF at a very small fraction of the audio signal. The decoder basically can tell sync areas apart from non-sync, with a good helping of fuzz.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 19 Feb 2014, 08:47 
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I've made some good progress on Python versions of the RF and color decoding phases. They're not commented enough to be comprehensible yet, but are a lot shorter (and slower!)

They're rather useful for trying quick changes. I cleaned up the de-emphasis quite a bit, and reduced decoder-specific chroma noise.

I've got an actual application idea for this - a lot of museums etc had disks of images made, and at least the Smithsonian had very low quality digitizations made. (i.e. http://si-siris.blogspot.com/2013/12/up ... links.html) I just happened to find at the uni junkyard a while ago a demo disk from a company that did this, and I ran my latest code and got images like (http://i.imgur.com/JgfXfmM.png)

Know anyone who needs some nice .png's?
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 19 Feb 2014, 10:34 
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AWESOME!

Hope to test it myself one day in the near future - maybe without using Python, but *only* a simple .exe windows software... (^^,)
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 02 Mar 2014, 06:47 
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Probably not going to do a Windows version any time soon, myself. (If someone else wants to do it, though...)

Added some 2D-ness to my comb filter today. It doesn't do much for diagonals, but it cleans up the vertical lines nicely. :) (and there's a little bit of code to deal with horizontal lines etc)

A shot from the Pioneer ref disk and S&W (a bit fuzzy, VE's always been a problematic disk for me) here:

http://imgur.com/a/UY6Na
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 02 Mar 2014, 09:26 
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Very nice results, good job!
Hope at least to have a linux (non command-line) software... ;)
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