Modular Diary

A little over a year ago I set about recreating Rob Hordijk’s modular system in @Audulus. You can follow that journey in podcast form here:, or here:

Modular Diary

A background project that I’ve been busy with during the course of the last few months has been making recordings of the demo patches that I’d put together for my series of Audulus Hordijk Modules. After adding those to the respective posts on my site it occurred to me that it might be fun to record the texts and combine them with the examples, creating audio versions of the posts that could then be made available via a podcast feed.

As is often the case, it took a little longer than anticipated to get everything in place, but it’s finally done – hopefully useful as a little review of the project.

Here’s the link should you be interested in listening to them in a podcast player:, or check it out on HuffDuffer where there are also links to open the feed directly in various podcast apps (should you be on a mobile device of some kind):

It’s also possible to follow through all the entries on my site, which also includes the individual audio examples, starting here:


17/ The Sound of Cybernetics: Roland Kayn And the Voice of Electricity


12/ Freeform / Modular / DAW-less


10/ Eliane Radigue: IMA Portrait Documentary


7/ Inside: Erica Synths


2/ Meng Qi: One-offs

Modular Diary

Following on my post on bipolar VCAs: Since there are some similarities between what’s going on with bipolar amplitude modulation and through-zero frequency modulation I thought I’d take another look at these topics in a little more detail.

Learning Modular has a nice post on Understanding the Differences Between Exponential, Linear, and Through-Zero FM, and from there I revisited @RobertSyrett’s Know your Nodes video on Comparing different types of FM.

One aspect that through-zero FM and bipolar AM modulations have in common is that they don’t freeze (or shut-off) output when the modulation signal falls below zero. Both do this by inverting the waveform in question. In the case of TZFM it is not the amplitude that is inverted but the phase of the waveform: In the Learning Modular video Chris Meyer describes this inversion as the oscillator ‘running backwards’ while @RobertSyrett in his Audulus demonstration talks of a reversal of the direction in which the waveform is being read. This means that there can be sudden changes in the direction of the waveform (in addition to it being sped-up/slowed-down) but without the potential jumps at the point of inversion that can occur with bipolar AM.

With both types of modulation sidebands are generated and this results in a change in the harmonic content of the waveform. In my previous post I noted Chris Meyer’s demonstration of the way in which the fundamental of the carrier falls away as bipolar AM (ring) modulation is increased, but remains present with amplitude modulation. Similar processes are at play in FM (of all kinds) and I came across a series of old Sound on Sound articles, one of which includes an good explanation of how the Bessel function can be used to describe the amplitude of each pair of side bands, and how they relate to the strength of the other partials and affect the relative strength of the fundamental.

@RobertSyrett demonstrates in his video how with TZFM sweeping the frequency also changes the character of the Bessel function (i.e. the timbre of the sound), while with PM the character of the Bessel function is uniform across the frequency range since the phase is not calculated in relation to the hertz value of the modulator – i.e. the timbre/harmonic structure of the waveform stays the same across the frequency range.

Phase modulation differs from TZFM in that the modulating waveform also changes the starting point of the carrier waveform. With TZFM the carrier remains in phase with modulating signal (through a continuously morphing Bessel function).

(I’ve also posted this on the Audulus forum.)


Beautiful, subtle performance by @Jespertralala Pedersen with his @MakeNoiseMusic and self built Serge systems at Sonic Festival CPH.

Modular Diary

Rob Hordijk includes bipolar VCAs1 as part of both the Mini Matrix Node Processors and the Dual Fader and has demonstrated, in his various tutorials on these modules, the ring modulation effects that this makes possible.

Via a recent Reaktorplayer tweet I came across a nice Learning Modular tutorial demonstrating the difference between amplitude and balanced (ring) modulation.

Towards the end of the tutorial there’s also a nice demonstration of the way in which the fundamental of the carrier falls away with ring modulation but remains present with amplitude modulation.

I’ve uploaded some simple demonstrations using my Audulus versions of both the Mini Matrix - Node Proc and the Dual Fader to the Audulus forum.

audio version of this post

  1. A bipolar VCA is like a normal VCA when operated with positive control voltage. But when using a negative control voltage, the output will swing back through zero amplitude and the output will be inverted.—Londonmodular