Envelope follower that I created a while back. The volume envelope of the drums controls the volume of the pad. Bass synth is not part of the demonstration; only there to sound pleasant.
How it works:
1) Split the drum signal into 2 parts: one untouched, and one with a waveshaper to set the value to 1 or -1 (i.e. the sign of the signal).
2) Multiply both drum signals using ring modulator. This results in the absolute value of the drum signal (product of two values with the same sign is positive).
3) Low-pass the result of step 2 to obtain the envelope. Step 2 is necessary to make the volume of the drums manifest as a low-frequency positive offset.
4) Multiply the result of step 3 with the pad using ring modulator.
Also, you can apply a waveshaper with a piece-wise linear function after the ring Modulator to achieve something akin to a compressor’s knee, ratio parameter. That’s my thought. Do you think that that’s correct?
No, I made this to avoid using the sidechained gate technique because it isn't sufficient for the goal of this demo. The gate is either on or off. In this demo, instead of controlling on/off, the sidechain controls the gain multiplier such that it is proportional to the volume of the sidechain.
That's very clever. I wish that there was a dedicated envelope follower device similar to the Autofilter. I think Attack, Release and Hold parameters would be a better way to control envelope shape and smoothness than filtering.