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9954tony
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 25 Aug 2020, 22:58 |
Serious fan |
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Joined: 12 Sep 2015, 05:57 Posts: 210 Location: United States Has thanked: 5 times Been thanked: 54 times
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Titan91,
I was waiting for someone more knowledgeable to respond, and they can correct me if i am wrong.
While the spec says the highest frequency is 9.31Mhz (or whatever it is), happycube once told me you needed about ~12.5Mhz of bandwidth, minimum, for the captures. I don't know why that is the case, but that is what i recall (iirc).
Nyquist-Shannon states the minimum, but that is the minimum with the most quantization noise/error. You can't go with the 10 bit 14.4MSPS mode, because it isn't high enough. period. So that leaves you the 2 8 bit modes. The higher msps will get you less quantization noise/error, so i'd go for that.
Just make sure your disk is fast enough to save it.
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9954tony
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 28 Aug 2020, 01:53 |
Serious fan |
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Joined: 12 Sep 2015, 05:57 Posts: 210 Location: United States Has thanked: 5 times Been thanked: 54 times
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titan91 wrote: So I went ahead and installed the RF mod. I used part of an old VGA cable spliced to an arcade machine bill acceptor harness. This took me only an hour. The harness is well below the disc transport. Luckily I didn't have to remove the tray, just eject it. The karaoke Aux audio jacks are really handy to make this a clean 100% reversable mod. Wish I had heat shrink tubing though.
for the best signal to noise ratio, it would probably be better to use the cable shield as the ground, rather than the green wire. If you check out the domesday site, coax is recommended (i used an old piece of a wifi antenna cable). Additional, while convenient, the RCA connectors won't provide as good of S/N as BNC. It may not seem like it would matter, but the RF signal is very weak, and easily interfered with. I speak from experience, i tried to use SMA jacks and cables because i thought they would be "just as good" as BNC and they were easier to mount. When i switched to BNC, S/N improved.
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9954tony
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 09 Sep 2020, 03:56 |
Serious fan |
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Joined: 12 Sep 2015, 05:57 Posts: 210 Location: United States Has thanked: 5 times Been thanked: 54 times
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4 or so years ago, i did the TV card capture method, and i remember getting results that were better than what the player could display via composite out (although it was a PAL player). I did not even have to use an amplifier in between. I was using: 1. a CLD 1050 2. a panel mount BNC port installed on the back of the machine 3. no resistor with the coax soldered to the RF test point and panel mount BNC 4. an S-Video to BNC Y adapter for the input into the card. the 1050 may have had higher output??? If you read back far enough in this thread, i believe happycube said that after he started using the aforementioned BNC Y adapter, he no longer needed the amplifier either. As mentioned before, using the RCA jack is also poor quality: Quote: ^ from wikipedia. those are the only things i can say, but that is just based on my experiences. $20 on amazon for the parts (and a few extra BNC panel mounts for the future!)
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9954tony
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 09 Sep 2020, 18:03 |
Serious fan |
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Joined: 12 Sep 2015, 05:57 Posts: 210 Location: United States Has thanked: 5 times Been thanked: 54 times
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titan91 wrote: I agree, at this point the RCA connections and cables involved with the distribution amp I'm using are likely the issue. I thought about impedance and assumed this would be fine since the card's input is 75 ohms. However, the test point is likely not sending a signal that is matched to a 75 ohm input. Using a single 50 ohm BNC connector with 50 ohm mini coax would be best? Take whatever i say, with a grain of salt. I am no expert. I took a few DC electronics classes in high school, and have tinkered with things all my life. I never progressed into complex AC / RF though. Impedance in an AC circuit isn't a static value, it varies over the frequency spectrum. The rating given is Nominal impedance. So let's say an RCA connector, which was designed for audio frequencies, has a "nominal impedance" of 75ohms. That might only be for the 20hz-20khz frequency range for which it was designed, though. The impedance for frequencies higher could be significantly different. BNC connectors are rated up to several Ghz, so the nominal impedance rating of a BNC connector takes that into account. This is what i have been able to gather so far (this is my best interpretation, anyone with more succinct knowledge please correct me if i am wrong). All that being said, I was thinking about it last night, and i was wondering if maybe the LD-Decode "code" has evolved in such a way, in the direction of the DDD, that quality of the TV capture card method has diminished? This occurred to me because you said you had good results with the VHS captures with a similar setup? It may be the case, that in trying to get the best fidelity from the DDD, that fidelity from the TV card is compromised. It looks like your luma signal is pretty good, and that the noise is in the chroma signal?
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9954tony
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 12 Sep 2020, 02:20 |
Serious fan |
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Joined: 12 Sep 2015, 05:57 Posts: 210 Location: United States Has thanked: 5 times Been thanked: 54 times
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@titan91 I set up my old tv capture card to test. this isn't great, and definitely not as good as i got before with the tv card, but it isn't as bad as yours. Of note, when i did this a long time ago, it was the CLD-1050 straight from RF test point. This is 4300 and a 47ohm resister inline. Also, my card is cx8802. Also, my card isn't honoring the sample rate setting, i meant to capture at 35.8, but it ended up being 28.6
Last edited by 9954tony on 12 Sep 2020, 22:54, edited 1 time in total.
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9954tony
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 14 Sep 2020, 20:16 |
Serious fan |
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Joined: 12 Sep 2015, 05:57 Posts: 210 Location: United States Has thanked: 5 times Been thanked: 54 times
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@titan, the RF gain pot also effects everything downstream, because you can see a difference on the screen when you have the composite/svideo hooked up. I think in my previous cxadc capture, i still had my physical low pass filter hooked up (that i use with the lime) which eats some of the signal. I did a new one today without it. This is 4300>47ohm resister>BNC>svideo bnc y adapter: Then, i hooked up this $12 RF amp i bought on ebay years ago (i removed the SMA connectors and soldered leads to the board, i power it with a 9 volt battery). ebay amp. This was so powerful, i had to put another resister inline (20ohm) because 'leveladj' clipped at level 0. This bumped me up 5/6db in the S/N ratio: My card still won't honor the settings in the config file, it just does 8bit@28msps. Not sure if 35msps would help there?
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9954tony
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 16 Sep 2020, 01:31 |
Serious fan |
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Joined: 12 Sep 2015, 05:57 Posts: 210 Location: United States Has thanked: 5 times Been thanked: 54 times
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It's just a regular resistor, yeah. You would only want to add a resistor if you get a more powerful amp and experience clipping i think, your signal is already weak. I added the resistor to the 4300 because i needed it for testing with the LimeSDR setup. I don't have a resistor at all on the 1050. The little amp i have adds more gain depending on voltage applied, up to 12 volts. Attaching a 9v battery was easy, so that is what i did.
Maybe that player you have just outputs low RF?
You mentioned before you had an SDR. While you probably can't use it to capture, you might be able to use it to monitor the RF signal in real time using gnuradio companion. I've done that quite a bit, testing out which things improve or degrade the signal strength.
you could turn up the RF gain too, just mark where it is before you turn it, in case it has a negative effect, then you can set it right back to where it is if it doesn't help, while checking the test point signal strength.
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9954tony
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 17 Sep 2020, 17:40 |
Serious fan |
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Joined: 12 Sep 2015, 05:57 Posts: 210 Location: United States Has thanked: 5 times Been thanked: 54 times
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titan91 wrote: Chad, would it be possible to add a feature to ld-analyse to export the frames of a TBC file as a series of PNGs? There's already a single frame export feature, hopefully it wouldn't be hard to add this in as another option. Ld-chroma-decoder does the job, but it outputs raw bitmap files that must be further muxed and processed by ffmpeg. This extra option would really help with the learning curve and speed of conversion I feel. This would probably be "really" low priority from them, because, as you said, you can already do this with a longer tool chain command line. I wrote a perl script that basically does this, download that. or here is the direct code: #!/usr/bin/perl $staticdiv = 1500000; #very crude aproximation of frame size if (!$ARGV[0]){ print 'Must provide file name, number of pics, pal/ntsc as input\n'; exit 0; } chomp($ARGV[1]); $filesize = `ls -ail $ARGV[0]|awk '{print \$6}'`; $frames = int($filesize / $staticdiv); #rough count of number of frames for ($x=5; $x < $frames; $x=$x + int($frames / $ARGV[1])) { print "FRAME:$x\n"; if ($ARGV[2] =~ /pal/ ) { $command = qq(ld-chroma-decoder -s $x -l 1 $ARGV[0] -|ffmpeg -f rawvideo -r 25 -pix_fmt rgb48 -s 928x576 -i - -an -vf "yadif,scale=768:576" -y $ARGV[0]$x.png); $output=`$command`; }else{ $command = qq(ld-chroma-decoder -s $x -l 1 $ARGV[0] -|ffmpeg -f rawvideo -r 30000/1001 -pix_fmt rgb48 -s 760x488 -i - -an -vf "yadif" -y $ARGV[0]$x.png); $output=`$command`; } }
USAGE: getpics.pl input.tbc 6 ntsc That would output 6 .png files from input.tbc spaced equally throughout the capture. ntsc is default, so you could technically leave that off.
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