Hi there-
This might be a ridiculous question, but I’m wondering if there’s a module for simply cutting the brightness of video in response to a CV or MIDI signal. Preferably for CVBS video, but LZX video could be useful as well. Also, if there’s a way to sync this to the framerate of the video signal (i.e., cut brightness every other frame) this would also be useful.
I think you could use a Swatch and VCA combo.
The “Y” value controls the Luminance. So if you take the Y output from Swatch and run it through a VCA. Take the VCA out and patch it to the Y input of Swatch.
Some VCAs behave better than others for video. My Doepfer A-130-2 works well but the Intellijel Quad VCA distorts quite a bit.
The LZX Factors is three video-rate VCAs so you could treat a red, green, and blue LZX signal signal between the three channels (or if just B&W, use just one channel) and use the same CV to modulate all three channels thanks to normalization. Though like the stuff @Boneoh suggested, it’s not synced to framerate so not a perfect answer.
If this is a specific example of what you want to do, you might not need to worry about syncing it to the frame, since (with frames being 1/30th or 1/25th of a second) it’ll likely be perceived as an overall reduced brightness across all the frames.
If you’re looking for slower timing than every other frame, it will probably be more perceptible. In that case, you’re going to want something that outputs a frame clock. The LZX Cadet 1 Sync Gen can do that, though it’s out of production and I think some of the parts to build a new DIY one are hard to find now, so you best bet is to find a used one if this is what you want. The LZX Visual Cortex can do that too (and do a lot more neat stuff), but it’s out of production now too (and pricey if the frame clock is the only thing you want it for).
Some people (including myself) were discussing making a module that would work with the LZX Gen3 line (and as a result, would also work with normal CVBS) to output a frame clock and some other clocks from the signal, but I don’t know if any of us actually completed the project. (I unfortunately got waylaid by a lot of things, and shifted my focus to some other projects. I may yet revisit it one day, but it’s not high on my list right now.)
Thanks for your replies. These are interesting ideas.
There are many video modules that will act as triple VCAs… Factors, Proc, Crossfade, FKG3
For frame sync, to avoid horizontal “tearing”, my method is this.
Vertical ramp (or video sync’d vertical sawtooth) →
Comparator (any audio rate comparator will work, or you can use a single channel of Keychain) →
Sample and Hold trigger (any audio rate S&H will work)
Modulation signal → S&H signal input
S&H output → whatever you wish to modulate (in this case, the VCA CV input)
If you have Cadet 1 or Visual Cortex, the Vsync output can go directly into the S&H trigger. But since A) those are not in production, and B) I’m working in high definition, those aren’t options for me.