Foxing Hour FELT - Voltage Controlled Video Filter

After more than two years of working on this one, I have finally optimized the filter core’s performance to a point that satisfies even my own excessive standards.

FELT is a filter for video with simultaneous High- and Low-Pass outputs for edge extraction and variable smearing respectively. The cutoff frequency is voltage controlled over a wide range.

Somewhat uncommonly, the High-Pass output is a bipolar signal meaning rising edges are provided above zero volts and falling edges are below zero. Accessing falling edges is as simple as inverting the output, or patching through an “absolute value” function to mix both rising- and falling-edges together.

The Low-Pass output delays the rise and fall time of provided luma signals to blur them from left to right as they appear on your display.

I will try to tag everyone who’s shared interest in the last two years…


FELT intro & demo by @rempesm

Single FELT w/supporting modules:

3x FELT w/supporting modules:


This is great, I wanted to confirm it supports HD timings too?

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Yep, no sync is required.
The screenshots above are 480i only because I wanted to use MemPal for stills. I’ll put it on the list to bring in some DVD footage for some new examples.


oh yes, the filter looks amazing! are there plans to do a tripple version with gen3 power? maybe smaller than 12hp?

also really like the demo by @rempesm :heart_eyes:
(btw it also helped to understand filtering more with my lzx contour)
you should list the video so people can find the demo via regular youtube search.


Yeah I didn’t realize it was possible to get HPF edge outlines/extraction on both the left + right sides of a figure - really useful tip

Totally appreciate wanting to confirm but unless you see a sync connection is required, you can reasonably assume any video module supports SD and HD timings. The wide bandwidth op-amps in an all analog circuit have no sense of video format–they just do the thing. I’ll pull some footage together with Fox but I’ve done 720p and 1080i patches before with it and it works the same as it does in SD.

Thanks! Edited to be public.

Awesome, glad this helped with understanding some quirks of video filtering!

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Yea it’s been most that will support HD timings, but there are some that won’t. Thanks for confirming @Fox and @rempesm this module and demo looks great. As far as I know, this maybe the first low pass video filter available in eurorack format?

Yep, it’s only the ones with sync connections that can potentially have a compatibility issue. If there’s no sync connection involved, no SD/HD compatibility problems are possible. It will just work.

The Visionary series Triple Multimode Video Filter had low pass, band pass and high pass outputs. Of course it’s not really possible to obtain one these days.

FELT shares some DNA with that design as they both are extensions of a circuit right out of the LT1228 datasheet. The devil is in the details of course and there’s quite a lot of fine tuning that @Fox did over the roughly two years of development. I may be biased but the cutoff range of this filter in one sweep is particularly impressive.


Nice, yea I was pretty sure due to lack of sync it should be good, but I’m not a module engineer. :rofl: Oooh I see, multimode I missed out on, but hoping band pass makes a return someday soon too. Definitely getting a Felt sometime this year. :heart_eyes:

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ReverseLandfill Blur is a lowpass filter.

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Ah, very true. I was thinking of ones where the cutoff is voltage controllable. Blur is definitely a low pass intended for video but does not give you continuous voltage control over the cutoff. It provides three distinct settings of blur with a fixed RC filter on a three way switch but the voltage control input is a dry / wet fader between the input and the blurred signal.

As I talk about in the demo video, getting a clean composite of a non-affected signal and a filtered signal requires a fader so Blur fills this need nicely in one module if you’re not so interested in direct control of the cutoff.


Nice work @Fox! This looks pretty great. And good demo @rempesm – that explained it perfectly!


yes, this looks like a really interesting module!
will this be offered as kit/ pcb set ?

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Thank you!
I have plans to put together some full diy kits at a later date if it works out.


I’m interested in panel/PCB set too, if that becomes an option (since I probably already have most of the through-hole parts).

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Id love 3x kits if they become available. :slight_smile:
Awesome module

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I’ve been patiently waiting for this one! I would be interested in kits but not fully assembled, mostly because of having a lot of parts in stock. Is it a mostly SMD circuit? Keep us informed if you go down the kit route

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I’d like pcb/panels… preferably via thonk, if possible!! possibly 3 of them!