Hordijk TwinPeak Filter

(This is a repost of part of a thread on the old forum – the thread, in fact, that kicked-off a wave of activity around clones of (Eurorack) modules and general activity on the Audulus forum last year. )

Looking through, organizing, and reviewing the many Audulus patches that I’ve accumulated and worked on over the last year, I was reminded of the Hordijk TwinPeak filter. A simplifed version of it was included in the Blippoo Box that I’d put together, and I remembered that I’d meant to make a standalone version of it at the time – only to realize that that had already been tackled on the forum.

Here’s my fresh take on the Epoch Modular version demonstrated in the James Cigler video at the top of the forum thread, building on the updated modules and approaches that have been introduced over the course of the last year.

RH-RM epochTWIN.audulus (105.2 KB)
RH-RM epochTWIN Demo.audulus (184.1 KB)

I’ve also put together a version of the TwinPeak filter following the layout and design Rob Hordijk created for his own modular system. It doesn’t have the cross-fader that is a handy feature of the Epoch Modular version, but that’s not necessarily needed in the context of Hordijk’s system since it includes a Dual Fader module. There’s a directness and clarity in the pure symmetry of his design that I find very satisfying.

The hordijk-synths.info site appears to no longer be online, but can fortunately still be accessed via the Internet Archive’s Wayback Machine. I also discovered the recently established Hordijk Modular Blog, which has an enthusiastic entry on the TwinPeak filter that includes an informative video in which Hordijk himself explains how the design enables not only a bandpass filter, but one with two peaks.

RH-RM TwinPeak.audulus (104.4 KB)
RH-RM TwinPeak Demo.audulus (173.2 KB)

I’ve also put together a simplified, single input, micro version of the TwinPeak filter. The modulation input is set to only alter peak 2 by default, but this can easily be changed by opening up the hood and changing it to peak 1 or adding it to both.

The Hordijk Modular Blog suggests using multiple TwinPeak filters in order to achieve a complex filter with multiple resonant peaks, so I’ve tried something of that out in a little demo with the filters being triggered at sub-audio rates.

RH-RM uTWIN.audulus (90.2 KB)
RH-RM uTWINS Demo.audulus (292.2 KB)


Thanks for posting this!

When you have some time to create a rundown of the controls for this, it would be great if you reposted it over at the VCF subcategory.

I’m working on a template for posts so you don’t have to make all the tables from scratch.

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“When I have some time” :slight_smile:

I’ll concentrate on getting some of the older posts up first.

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I created a default post for those categories that might make it easier!