Sorry, I forgot to report back after speaking with Sequential's support team.
Here is the description I was provided about how the filter Drive works:
Drive simply increases the gain of the oscillators as they enter the filter circuit. It is, as you note, a fairly subtle effect and quite dependent on the oscillator levels set in the mixer.
To best hear the Drive effect, oscillator levels should be set to halfway or less. Then turning up Drive will provide the gain makeup and increase the overall levels into the filter. Setting oscillator levels near or at max will make the effect somewhat difficult to discern. The amount of resonance set at the filter will also have an effect on the Drive sound qualities.
I noticed that modulating filter Drive using the mod matrix allows for more significant range than what can be achieved using the knob on the front panel. This is the response I got when I asked about this behavior specifically:
Checking a Take 5 here, I do find that I can a bit more extreme of a gain effect by driving the Drive param with the Global LFO in the Mod Matrix. This is expected behavior. [...]
The Mod Matrix parameter allows for pushing the parameter a bit beyond what the panel control can accomplish.
I still wasn't completely satisfied because something still didn't make sense:
I've noticed that when FM 2->1 is enabled, the Drive knob doesn't appear to have any significant impact on the tone of the patch... But modulating Drive using the mod matrix appears to have a SIGNIFICANT impact on the tone. In fact, you can continue stacking modulation routes against the Drive parameter and even past 5 separate routes, you can still keep hearing new range from the Drive circuit.
What didn't make sense is that the effect you get when modulating Drive in an FM patch is TOTALLY different than the range of sounds you get when modulating Osc FM Lvl in an FM patch.
To help verify what I found, I sent over a sysex patch (attached to this post) and these test steps:
Okay, I've attached a sysex dump example. Let me know if it doesn't work.
The patch has ModWheel mapped to Drive. If the Drive destination is the same as the knob, moving ModWheel should sound the same (or at least close) to moving the Drive knob on the front panel.
Here's how to test it:
1. Load the patch
2. Play a note
3. Move Drive knob. Minimal affect on sound is heard
4. Move ModWheel. FM amount sounds like it's being changed
Please let me know if you hear a noticable difference between the mod wheel and the knob on this patch.
I also sent over an audio recording of the differences I was hearing (also attached to this post).
And after all that, Sequential support member seems to think everything is in order:
That is indeed what I'm hearing here. Your Take 5 is behaving as expected.
So, at this point, I'm personally going to use the Drive knob:
- As a subtle tone control when I'm careful about gain staging
- When I want full resonance but need to knock self resonance off the filter
- When I want to have more tone control over wild FM patches using the modulation matrix
- When I've got an audio-rate modulation routes targeting the filter or harmonic content in the oscilator/mixer sections, and the subtle nature of the Drive control can appear to have more impact on the final tone of the patch
While it sure would be nice to see a signal path diagram for this instrument, I'm happy enough knowing a little more about how to use the Drive control.
For giggles and some closure on this, I created a patch named Aashi Noo to explore how much Drive can impact the sound when Take 5 is pushed out to it's limits in terms of feedback, noise, and aggression. It's attached as well (Zensynth is me). Feel free to use it, if you think it's useful, just let me know if you release anything commercial with it so I can feel good.
Be careful; it's friggin' loud. Think, Blade Runner fog horn.
That's all I've got on Drive at this point.