Following on Hordijk’s fluctuation modulation, here’s a demo that I saw a while ago that’s been popping into my head, on how to program the lead sound for Vangelis’ Blade Runner theme. There’s a section on vibrato that starts around 4′23″.

I also took another look at the effects of uni and bipolar waveforms on linear FM in Robert Syrett’s Audulus Bahama oscillators – unipolar FM alters the perceived pitch (which makes sense for audible frequencies ¹ since the modulation is only in an upward direction) while bipolar waveforms keep it centered. I noticed that the Moog Model 15 App has AC and DC frequency modulation inputs as well. In that case it’s simply a question of how strong the (exponential) effect is.

I was also curious to take a look at how the Model 15 App handles sync. Hard sync is as one would expect, but the weak (soft) sync is quite sublte and beautiful in the way that it gradually matches up the phase of the waveform while attempting to preserve its shape.

And finally a look at the Make Noise DPO which very much takes both linear and exponential FM into timbral texture territory. Robert Syrett has made an Audulus version of that as well.

Having made a start on recreating Rob Hordijk’s fluctuation waveform I’ve now been trying to clarify for myself the sync aspect of this type of modulation – the way the modulated signal syncs with the modulating signal.

Hard sync is fairly easy to understand but soft sync, which is what is at play in Hordijk’s fluctuation can have many different forms. The Hordijk info site explains the fluctuation soft sync as follows:

The “fluctuation” modulation is a combination of AM and FM which soft syncs to the harmonics of the modulating signal.

Hordijk himself provides a little more detail in his Waveshaping & Fluctuation masterclass:

…when you come to the extreme points then it sort of forces it to zero again, but only if it is within a certain distance and that means that it basically tries to sync on harmonics, but traditional soft sync in an oscillator actually syncs on higher harmonics, but this actually syncs, soft syncs on subharmonics, so the modulating oscillator needs to be higher than the fluctuated modulator, oscillator, which with normal soft sync would be the other way around, so it’s not really soft sync, so I cannot call it soft sync, so I had to give it another name and I thought well maybe Fluctuation is a nice name, and so I call it Fluctuation…

Hordijk’s explanation brings up something else that I’ve had to clarify for myself – what exactly it is he means by subharmonics. The possible definition of subharmonics as “integral submultiples of the fundamental (driving) frequency” offered by the Wikipedia article seems to help here. I simply take it to mean that since the modulating oscillator is higher than the one it is causing to fluctuate, the modulated oscillator syncs at subdivisions of the modulating frequency, rather than multiples.

Now how does one do that in Audulus?