While taking a look at the difference between the Epoch Modular TwinPeak filter and the one that Rob Hordijk uses in his own system, I got curious about his Dual Fader module. At first I thought that it might not be all that relevant in the Audulus context, but the closer I looked, the more compelling I began to find it.

The NOVARS Research Centre has fortunately posted an extensive series of Hordijk tutorials (presented by the man himself) and I found it very useful to take a look at the two videos (#12 and #12a) in which he presents the Dual Fader.

My first take-away was the simple idea of using one half of a cross-fader as a VCA with an RMS curve, and so I put together a little Audulus VCA and a comparison patch with exponential and logarithmic curves.

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.

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.

Download: epochTWIN.audulus
Download: epochTWIN Demo.audulus

I made a little more progress on my Audulus Blippoo today, with a pulse-width signal generated from a comparator between the two oscillators and, perhaps most importantly, a form of Twinpeak filter.

Once again I found it very useful to take a look at James Cigler’s demo and overview of the Epoch Modular TwinPeak (despite its somewhat shaky start).

The filter adds a lot of character to the chaotic core of the Blippoo, and its ingenious (again cross-modulating) design makes it a lot of fun to play with. I can imagine it being well worthwhile putting together a standalone version of it for use in other contexts.

A standalone Audulus (µ)module would require a little more thought into how the controls are linked up and presented – for the moment I’ve simply kept everything loosely connected since I’m still in a process of learning and discovering how the different parts affect the whole.

The next step is to implement the sample and hold.