Replicating Rob Hordijk’s Twin Peak filter with the 301

I own a Twin Peak Resonator made by Klangbau Köln based on Rob Hordijk’s Twin Peak filter. Such an excellent module, it’s more than a filter/resonator, it’s a fantastic sound source (wood percussions, sub basses, bass drum, fm clusters, etc) I could buy a second one but before I do, I’d like to know if it’s technically possible to emulate it in a custom unit made for the ER-301.

On top of that, Klangbau Köln’s version also has a very useful FM knob called XFM, Filter 2 modulates Filter 1, for FM

I’m reading about the custom units and middle layer SDK on this forum and I’m wondering: Do you think it’s possible to replicate this Twin Peak Resonator with the ER-301 ? I could try this as a first “custom-unit” project but before I try, according to the following schematic, do you think it’s technically possible to do this with the 301 ? Don’t you think it would be too CPU intensive ? (The module uses an analog path and a 301 version would probably not sound the same but that could be fun…)


I don’t know much about these modules but looked over the diagram you provided. I think the connections are possible, both in the middle layer and (probably) in the UI layer, and I don’t think it would be too CPU intensive at all.

The biggest limiting factor right now is going to be the filters. Right now the filters that are available are both 24db slope ladder filters (high and low pass versions). There is a BPF available in the middle layer but the neon isn’t done yet - you have to set the f0, Q factor, etc. at insert time and can’t put a control in to adjust it. So the filters available now don’t match your spec. Not sure how important that is.

You could probably build a 48dB filter flavor of it. Guessing there will be additional filter types available in the future so building something now could be like a phase 1 of your project. You can always get something working now and enhance it as the firmware advances.


Thanks! If you say that it won’t be too much CPU intensive, I will try. I didn’t want to end up with a unit using 80% of the CPU so it’s good to know. Yes you’re right the filters currently available don’t have the same slope. I think it’s worth trying with two 24db filters, the result might be interesting, who knows ? :slight_smile:

Yep, I don’t think you’ll end up anywhere near 80% CPU with this. Have a look at this handy list of approximate CPU usage per unit made by @a773.

Most of the units you’ll be using are pretty lightweight. I think it would be more efficient still if you built it in the middle layer, but this looks totally feasible as a UI layer build too.

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Thanks. Well, I’ve learned a bit of LUA and used it with Norns, I hope I can manage to build it with the middle layer, it will be a good first project :slight_smile:


Hi. I was wondering if you ever got anywhere with this idea. It is pretty ambitious to replicate those sounds but it would be interesting to see how a digital version might sound. I think some digital filters really are super nice. Eg stuff on the nord modulars really can add something to a mix.

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I wish I had but no, unfortunately I never had time to work on this.
I agree that the some digital filters are excellent. I don’t know how it would sound with the filters of the 301, a 48db/oct (two chained filters) slope, probably good too but the analog Twin Peaks can sound so weird sometimes and returns some unexpected results, I don’t think the digital version would make these cool sonic artefacts.

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Have you ever looked into this PDF?

There’s some Hordijk patches in here. Also, I think I remember reading or hearing somewhere that he used the Nord Modular to prototype some of his designs.

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Thanks for the link. Very interesting material indeed :wink: