What does that even mean? 

When people hear pitch it is an exponential relationship. That means every octave you go up, you double the frequency. We hear volume in a similar way. Electronics don’t hear in that way, so on an oscilloscope the signal that is 3dB quieter is half as big. When you have an “audio taper” pot, the mid point is actually 15% of the resistance. So one rule of thumb is that if the VCA is controlling an audio signal the response should be exponential and if it is controlling control voltages, the response should be linear. That’s the rule Buchla followed.

In almost all cases, we have exponential control of an Oscillator and the cutoff of a filter. Baked in with that theory is that however we hear a parameter is how the CV should respond. But VCAs have a more complicated history.

It stands to reason that if the CV inputs track the way we hear a parameter, then our CV generators should put out linear ramps. But, very likely if you make an envelope generator without voltage control of the times you are sending the level signals through the pots on the way to a capacitor to ground. This kind of circuit creates what is called an RC curve. The decay and release phases of the envelope will have a gentle exponential curve. When paired with a linear VCA, the decay will sound natural and smooth. The thing is, the attack on an RC curve type envelope is convex. That is it starts rising fast and slows down as it gets close to the peak. When paired with a linear VCA this isn’t at all like linear ramp into an exponential VCA. 

I believe that whenever you hear someone talk about “punchy bass” they are talking about an RC envelope-linear VCA combination. Exhibit A Minimoog. Research has shown that punchiness is our brain’s way of interpreting sounds that rise fast and hang out at max level a little while before decaying. The convex attack on an RC envelope paired with a linear VCA gives that punchy attack and smooth exponential decay. But, what about slow attack sounds? All the synths that were branded as being good for pads but terrible for “punchy bass” have linear envelopes. Some even have exponential VCAs, which are cursed with the anti-punch attack. The best they can hope for is a very fast envelope attack that skips over that phase, lest they be accused of having slow attacks.

The best solution is a VCA with both inputs. The ARP 2600 has both and an envelope normalled to each one. Oddly, the RC curved ADSR is normalled to the exponential in, but I believe this hyper-exponential decay and semi punchy but fast attack is what makes Vince Clarke say the 2600 makes the best drums. 

So what do you want? I don’t know. I just carry around all these examples in my mind and lean this way or that depending on the situation. The Verbos Amp & Tone has both inputs available at the same time. You could try using one for the envelope and one for amplitude mod or accents.