How to Mix 2 Video Signals

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Godphaser
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How to Mix 2 Video Signals

Post by Godphaser » Fri Feb 01, 2019 3:55 pm

Hi all,

Considering video synthesis as an extension of my audio eurorack rig.

Would love to mix 2 dvd players with some effects.

What would be the easiest/cheapest way to do so?

Basically like an LZX Visual Cortex but with an input for channel B.

Thanks!

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Post by FetidEye » Fri Feb 01, 2019 3:57 pm

the cheapest way would be a video mixer.

effects can be modular.

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joem
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Post by joem » Fri Feb 01, 2019 5:42 pm

FetidEye wrote:the cheapest way would be a video mixer.

effects can be modular.
Building on this, the reason why a standalone video mixer is going to be the cheapest option is because your two DVD players (or whatever you use) aren't actually sync'd with one another on a frame level, so you need to sync the signals before mixing. That sync'ing is called "time base correction" and video mixers have it built in. I'm pretty sure there aren't any eurorack time base correcters that are currently in production, though LZX used to make one that you might find used and LZX is currently developing a new one that's supposed to be released sometime this year I think. But either way, using the old LZX one or the new one, you'll need more equipment than just the TBC to mix the video and output it, so it'll cost more than a used standalone video mixer. (And most of the good mixers are only ever used now, since analog video isn't all that big of a thing anymore and a lot of things people used to do with video devices is now just done on computers.)

(If your two sources were already in sync, though, then you could mix them with a very simple DIY circuit, either properly using something like a LT1256 and a video opamp, or passably with a simple passive resistor mixer.)

Now, if you want glitchy mixing, you could use something like a Karl Klomp Dirty Mixer, which is very very easy to build, but since the two signals aren't in sync, it can be very glitchy, and one (or possibly both) of the signals will roll on the screen instead of staying still. I much prefer a clean mixer though.

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Godphaser
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Post by Godphaser » Tue Feb 05, 2019 5:28 pm

Thanks a lot for the answers!

Is something like a Panasonic WJ-AVE5 would be all I need besides 2 DVD players?

Def going for something clean but would love to make it glitch.

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Post by Agawell » Tue Feb 05, 2019 5:58 pm

looks like as long as the dvd players are composite or s-video out then you'll be ok

you could always stick something for glitch either between one of the dvd players and the mixer or after the mixer in the future

you could expand your search for this to include both big pauper and tachyons+, if you haven't already seen them

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Post by Godphaser » Tue Feb 05, 2019 8:14 pm

Agawell wrote:looks like as long as the dvd players are composite or s-video out then you'll be ok
Thanks! From my very little understanding of the idea of video mixing, syncing seems to be key. So I figured as long as it's the same format it should work.
Agawell wrote:you could always stick something for glitch either between one of the dvd players and the mixer or after the mixer in the future
Yes, that was the plan. But to be honest, all I know is the LZX modules.
Agawell wrote:you could expand your search for this to include both big pauper and tachyons+, if you haven't already seen them
Didn't know about these two and it looks amazing! Thanks a lot for sharing.

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Post by joem » Tue Feb 05, 2019 10:10 pm

If you can solder there are a couple of pretty easy to build video effect devices you can build that both make some neat glitchy output: AVE MOD V2 and Videffektor.

AVE MOD V2 is based on the Archer Video Enchancer and is basically a modded clone design. You can get that here: https://syntonie.fr/projects/video/archer-video-enhancer-mod/?lang=en
(I think he also sells built ones, too.)

Videffektor is an even easier build and is based on an original video effect design. There are a few different versions of PCBs out there, and here's one: http://fluxmonkey.com/video/videffektor.htm
(I'm not sure if he sells built ones.)

The benefit to using these devices instead of LZX modules is that they operate directly on the composite signal, so you can easily plug them in between the DVD player output and the mixer input. To do some effects with LZX modules, you need input and output module(s), like the Visual Cortex (or like a C1+C2+C3 from the Cadet series), AND you'll need whatever modules you want to make the effects.

The LZX stuff is really really great, by the way. Don't take any of this as being hard on it. It's just that it's easier and cheaper to get glitchy effects from other devices if you don't already have the base LZX modules for input and output. Plus with the video mixer you're planning, you can do quite a bit already... It has some built in effects, if you get a camera you can do some neat feedback, and you might even be able to do no-camera feedback. So add in a few cheap glitchy effects and you'll have quite a lot to explore. Think of the devices I linked to as being like guitar pedals and the LZX stuff as... well... a modular synth! If you want to go the modular route, you can and it can get VERY deep, of course, but you can also do quite a lot with just some guitar pedals.

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Post by Agawell » Wed Feb 06, 2019 1:38 pm

thanks for the links to the Videffektor and AVE, Joe

I must have missed these previously - will look at adding them to my LZX (mixed series rig) sometime this year

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Post by Godphaser » Tue Feb 12, 2019 10:01 am

Thanks a lot Joem, very edifying answers! :tu:

Now I have a way better grasp of the issue.

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Post by Marizu » Wed Feb 13, 2019 7:38 am

joem wrote: Now, if you want glitchy mixing, you could use something like a Karl Klomp Dirty Mixer, which is very very easy to build, but since the two signals aren't in sync, it can be very glitchy, and one (or possibly both) of the signals will roll on the screen instead of staying still. I much prefer a clean mixer though.
Just for the OP's information, the glitchy mixing is really cool, but it tends to work best on a CRT. Newer digital displays and projectors can give up trying to display a picture if the sync is out and they revert to a blank screen (usually blue) until they determine that they have a decent signal again.

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