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?