I did basic study of voltage controlled envelope generator based on analog circuit approach. However, I found the implementation quite complex, although its quality was good. So, I next tried another approach that has simpler circuit. This version calculates the EG curve using micro processor, and makes analog output using PWM with minimum external filtering circuit.
This version is inspired by Tom Wiltshire‘s Voltage Controlled ADSR Envelope Generator.
I’ve started studying voltage controlled envelope generator designs, since I have several use cases of it.
An envelope generator usually is implemented by an RC charging circuit with potentiometers as resistors. However, such design does not capable of quick parameters change. So voltage control (or digital control) functionality is necessary for better articulation. Also, non-potentiometer control is crucial to polyphonic voices.
There are several approaches to design voltage controlled envelope generators. This article describes about an analog approach which I tried first.
http://www.simonbramble.co.uk/techarticles/active_filters/active_filter_design.htm
I came across this page while I was looking for a page that gives comparison among various types of active filters.
Cool. You can compare by yourself using LTSpice.