[mlyle]

Half a decibel per step is a reasonable chunk; average perceptible change is 1dB but sometimes it's better than that.

Figure maybe 65dB of useful dynamic range in a car + 10dB of range needed based on levels of the recording. That implies you want about 150 steps.

Go ahead and display a number between 1-30 if you want-- that's probably good for usability. I can find "13" and be close to what I typically want. Just, have the actual control surface move 5 steps per number so that I can fine tune.