[sdiy] Modulation question

[Tom Wiltshire]

Hi All,

I've been thinking about modulation sources on synths. Basically you  
get envelope generators of some sort, and LFOs.

One of these generates aperiodic changes, and the other produces  
periodic changes. I had thought that that pretty much covers it,  
since every kind of change is either periodic or aperiodic.

However, there is something else which I'd been missing which is that  
some changes are predictable and some are not. Envelope generators  
are a source of predicable aperiodic changes, and LFOs are obviously  
predictable, since they're periodic.

Consequently, I'm currently working on an unpredictable aperiodic  
modulation source, done digitally. The basis is a 64-bit LFSR noise  
source. The source (I'm calling it a random modulation generator,  
RMG) can either interpolate linearly between noise values to produce  
random slopes, or interpolate quadratically to produce random curves.  
I've been having an absolute bitch getting sufficient accuracy out of  
16-bits to allow really slow modulation waves.

That's the background, but what I'd like to know is whether there are  
other important types of modulation that I'm still missing.

What's your favourite modulation?!