Adapting the EuroRack audio world for video synthesis

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Fabong
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Re: Adapting the EuroRack audio world for video synthesis

Post by Fabong » Thu Oct 15, 2020 8:06 am

Why is it that you can't just plug oscillators into an RGB encoder without using a sync generator? Confused as to why this wouldn't produce a "valid" video signal. Couldn't a video system begin with an encoder only?
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Re: Adapting the EuroRack audio world for video synthesis

Post by FetidEye » Thu Oct 15, 2020 9:15 am

try it.
your signal will scroll . so you won't get a steady image (which you can call 'valid')
There will be images (such as in the video clip before this page). It depends on what type of image you like..
If you want to do shapes and more coordinated synthesis, you will find sync very useful!
If you like glitch and chaos... go for it!

the output of an audio OSC is also 'too hot' +-5v instead of 0-1v , so it will clip. (the Encoder has inbuild clipping)
the effect is that you will mostly see squarewaves.
you can attenuate it (passive) or use a LZX Scaler.

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Re: Adapting the EuroRack audio world for video synthesis

Post by Fabong » Thu Oct 15, 2020 10:43 am

FetidEye wrote:
Thu Oct 15, 2020 9:15 am
try it.
your signal will scroll . so you won't get a steady image (which you can call 'valid')
There will be images (such as in the video clip before this page). It depends on what type of image you like..
If you want to do shapes and more coordinated synthesis, you will find sync very useful!
If you like glitch and chaos... go for it!

the output of an audio OSC is also 'too hot' +-5v instead of 0-1v , so it will clip. (the Encoder has inbuild clipping)
the effect is that you will mostly see squarewaves.
you can attenuate it (passive) or use a LZX Scaler.
Thank you very much for your reply FetidEye, I understood that sync was useful but I thought without sync no video at all would be produced and I was wondering what the technical reason was! Now I understand better, that the output will not be a simple black screen, but perhaps "unstable"
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joem
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Re: Adapting the EuroRack audio world for video synthesis

Post by joem » Thu Oct 15, 2020 3:46 pm

Fabong wrote:
Thu Oct 15, 2020 10:43 am
Thank you very much for your reply FetidEye, I understood that sync was useful but I thought without sync no video at all would be produced and I was wondering what the technical reason was! Now I understand better, that the output will not be a simple black screen, but perhaps "unstable"
It also depends on what you're viewing your video on... For instance, on some old CRT monitors, you could plug an audio signal straight into the monitor (not recommended) and get some sort of image, but if you try that on pretty much any newer LCD/LED/OLED/whatever monitor, you'll almost certainly just see a blue or black screen because and no image (because the monitor doesn't think the input is a valid video signal). But if you use an encoder with a sync generator, any monitor should interpret it as a valid video signal.

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Re: Adapting the EuroRack audio world for video synthesis

Post by Fabong » Thu Oct 15, 2020 4:11 pm

joem wrote:
Thu Oct 15, 2020 3:46 pm

It also depends on what you're viewing your video on... For instance, on some old CRT monitors, you could plug an audio signal straight into the monitor (not recommended)
How come not recommended? Voltage levels too high?
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joem
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Re: Adapting the EuroRack audio world for video synthesis

Post by joem » Thu Oct 15, 2020 4:36 pm

Depending on the monitor and the audio signal, the monitor might not like the signal voltage and it might break something. Line-level audio probably won't be too risky since I think that's usually closer to video-level voltages, but modular-level audio is usually 5-10 times higher voltage than typical video signals. (As a youth I plugged lots of line-level audio into lots of CRT TVs and they all survived just fine... as far as I could tell.)

If you run a modular signal through an encoder like the LZX Cadet RGB encoder first, that will provide a safe output for whatever monitor you use. As FetidEye noted, the Cadet Encoder has built in clipping. (If you want to DIY just a clipping circuit, that should be fairly easy. I wouldn't be surprised if there's a circuit somewhere out there already for glitch-video people. Some of the Cadet modules have particularly simple clipping circuits that could also be adapted -- their schematics are freely available and super useful.)

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Re: Adapting the EuroRack audio world for video synthesis

Post by vrfats » Sat Nov 14, 2020 7:31 pm

Recently I've become more interested in video synthesis... I'm curious what a setup capable of doing voltage controlled cuts between input sources would look like. Could I use my Alyseum MATRIX two (A 16 in 16 out switching matrix) with several RGB encoders?

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joem
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Re: Adapting the EuroRack audio world for video synthesis

Post by joem » Sun Nov 15, 2020 6:48 pm

vrfats wrote:
Sat Nov 14, 2020 7:31 pm
Recently I've become more interested in video synthesis... I'm curious what a setup capable of doing voltage controlled cuts between input sources would look like. Could I use my Alyseum MATRIX two (A 16 in 16 out switching matrix) with several RGB encoders?
I don't think the Alyseum MATRIX two is going to work very well with video signals. The product page says "Analog Bandwidth: 0Hz to 20KHz" and also "Inputs & Outputs buffered with unity gain/low offset Op-Amp." The bandwidth range sounds like it's audio/CV range, and the op-amps they use to buffer the input/output are most likely contributing to that bandwidth limit. You could try running video through it and see how much it blurs it, and maybe it's acceptable to you.

I've used my Doepfer A-151 Quad Sequential Switch to switch between video sources before and it seems to have decent bandwidth for video. Some modular switches can handle video rate input/output, some can't. Usually it's ones that don't buffer their input/output that can handle it the best.

Bear in mind that switching between sources usually requires all the sources to be in sync (gen-locked) with each other. If they're not, then you're going to get glitches during each transition when whatever you're outputting to has to figure out what the sync is for each video source. If you're going into something digital this could mean a no-signal of blue screen for a moment, and if you're going into something analog it'll mean a moment where the screen scrolls or shows some sort of glitch. Again, this might be acceptable to you, or it might not.

To that end, some sources can sync with each other. Some video cameras (like old security cameras or old pro tv cameras) or other old pro tv gear (that a tv station might have used) might have a genlock input/output, and that's what that's for. If you're using gear that can't sync with each other but you want it synced, you need a Time Base Corrector (TBC). LZX have a really neat TBC module coming out soon, but it's not out just yet (hopefully by end of year). Another common option for TBC is to use an old video mixer that has TBC built in. Or you can get an old standalone pro TBC device that a tv studio might have used.

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Re: Adapting the EuroRack audio world for video synthesis

Post by vrfats » Thu Nov 19, 2020 4:49 pm

joem wrote:
Sun Nov 15, 2020 6:48 pm
vrfats wrote:
Sat Nov 14, 2020 7:31 pm
Recently I've become more interested in video synthesis... I'm curious what a setup capable of doing voltage controlled cuts between input sources would look like. Could I use my Alyseum MATRIX two (A 16 in 16 out switching matrix) with several RGB encoders?
I don't think the Alyseum MATRIX two is going to work very well with video signals. The product page says "Analog Bandwidth: 0Hz to 20KHz" and also "Inputs & Outputs buffered with unity gain/low offset Op-Amp." The bandwidth range sounds like it's audio/CV range, and the op-amps they use to buffer the input/output are most likely contributing to that bandwidth limit. You could try running video through it and see how much it blurs it, and maybe it's acceptable to you.

I've used my Doepfer A-151 Quad Sequential Switch to switch between video sources before and it seems to have decent bandwidth for video. Some modular switches can handle video rate input/output, some can't. Usually it's ones that don't buffer their input/output that can handle it the best.

Bear in mind that switching between sources usually requires all the sources to be in sync (gen-locked) with each other. If they're not, then you're going to get glitches during each transition when whatever you're outputting to has to figure out what the sync is for each video source. If you're going into something digital this could mean a no-signal of blue screen for a moment, and if you're going into something analog it'll mean a moment where the screen scrolls or shows some sort of glitch. Again, this might be acceptable to you, or it might not.

To that end, some sources can sync with each other. Some video cameras (like old security cameras or old pro tv cameras) or other old pro tv gear (that a tv station might have used) might have a genlock input/output, and that's what that's for. If you're using gear that can't sync with each other but you want it synced, you need a Time Base Corrector (TBC). LZX have a really neat TBC module coming out soon, but it's not out just yet (hopefully by end of year). Another common option for TBC is to use an old video mixer that has TBC built in. Or you can get an old standalone pro TBC device that a tv studio might have used.
Thanks for all of this info. I have a fuzzy understanding of sync signals but frequency ranges on op amps is new to me...

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nangu
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Re: Adapting the EuroRack audio world for video synthesis

Post by nangu » Thu Nov 19, 2020 5:19 pm

vrfats wrote:
Sat Nov 14, 2020 7:31 pm
I'm curious what a setup capable of doing voltage controlled cuts between input sources would look like.
If you’re ok with using MIDI instead of CV, the Edirol mixers would be worth a look. V4, V8, V440HD, and V4EX..

I haven’t used a V4EX, and haven’t done very much with MIDI yet on the other 3. But I’m willing to look into it and report back if you’re interested- let me know...

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