Filter Envelope Concepts (Super Basic Stupid Question)

Ok, apologies in advance. This is probably a stupid question, but I’m a bit confused as to how to approach envelope control of a filter in a basic subtractive-style synth.

I’d like a base filter cutoff freq, which tracks oscillator pitch, then an envelope will shift the cutoff freq up from the base by a peak amount set by a filter env. control.

What I’m not sure about is whether the amount the envelope offsets the base cutoff freq at its peak level should be constant, or a multiple of the base freq, in order to best emulate the behaviour of a traditional analogue subtractive synth.

Sorry this is really basic stuff (and something most forum members have long ago moved past).


You could try them both and see which one works better for you.

But… If the base frequency is 200 Hz and your envelope adds 600 Hz to that, this is two octaves. If the base frequency is 8000 Hz and the envelope adds 600, this is about one semitone. So addition is probably not what you want.

I always used multiplication (and don’t forget to .clip(20, 20000)!).


I think many analog synths make this configurable to some extent by providing controls like

  • env amount (how drastically should the filter frequency move over time?),
  • key amount (how much should the filter frequency change in function of the pressed note, e.g. higher notes can make the filter frequency open more), and
  • velocity (how should the filter frequency change based on how hard a key was pressed?).

It’s probably best to try out some things and use what you like most.

Cool, thanks both!

I’ll try multiplication first, then. That way, I can have the envelope add a musically-meaningful offset to the cutoff frequency.

Thanks guys. I’ll let you know how I get on!