Hans is, of course, the authority on this, and others may have played with it, but I might be able to be of some help, if you can give me a day or so...
As some already know (and this is a good opportunity for a special shout-out with thanks to Larry Serra N6NC for loaning me his QCX+ to be the Guinea pig and first article), I'm working on a digital AGC circuit which, in one configuration, will replace the analog volume pot with a handwheel encoder, Having got the basic limiter working nicely last night (like most things, it was a bit more complex that it promised to be at first), I'm just about to code up an encoder interface for volume and threshold adjustment to run on an ARM processor. To test that interface I'm going to code up an encoder simulator that will provide a programmable sequence of simulated encoder transitions at a programmable rate. If it would be any help, I can shift my task list and do that first. Just let me know if you want that information.
Darn it, Jens, now you've got me thinking about it ;-)
So I totally get the idea of setting the tuning step to 1Hz or 10Hz and spinning a nice heavy tuning knob with the gusto you've give to a roulette wheel, or starting a lawnmower, so...
Given than an ARM running as a peripheral is going to be a lot more responsive than the already heavily burned 328, and given that I'm building in one encoder interface already, I could add an additional interface and some code to the digital AGC mod to store up the counts from the external encoder and send them through to the QCX at close to the maximum rate, whatever that turns out to be. That way you can spin the dial to your hearts content, and know you'll get there. Latency for sub-max spin rates would be negligible, so you wouldn't even notice its presence.
It won't be tomorrow, or even next week, but if I'm going to propose that somebody blow the cash on a Teensy and bits around it on a board to get fancy-schmancy digital AGC, then it makes sense to use the beast to to something else useful at the same time, in order to get the maximum value from the hardware.
As always, suggestions and comments of encouragement and hearty ridicule and derision all warmly invited.
p.s. You're QCX+ is about to go under the knife/soldering iron, Larry, but fear not!
pps. The more I keep talking about these mods the more I get the urge to do a full CAT interface with touch screen for in-shack operation, and WiFi interface with full audio streaming for working from anywhere on the back forty... one thing at a time; maybe I should have retired at 65 after all...