Knobs shouldn't be hard to use - hold down the knob that needs the adjustment and then drag in either of two directions to set the value. Maybe have a pop-up over the knob that displays the value as it's in use.
I also played with the idea of letting users slide their finger off a knob (tap and slide away from the center). This allows for moving the finger over a longer circumference, hence enabling a great degree of precision. The problems with this approach are that it takes longer to operate such knobs, you need to communicate to the user what the max allowable distance from the knob is, it can interfere with scrolling, and it doesn't work for knobs close to the edge of the screen. (Your idea works well for knobs at the edges.)
And this is just knobs! There are many other components, interactions between them, as well as associated accessibility challenges, haptics, etc. Instead of reinventing the wheel, I was hoping that human factors people had developed relevant guidelines, but perhaps it simply is not a prevalent enough problem.
Here's a section from the manual that loosely explains the concept[1]:
> Adjust a slider or dial’s value by dragging up and down, or left and right for horizontal sliders. For finer control, move your finger away from the dial.
My only Apple product is also an iPad, and I mostly use it to make music with Auxy Studio:)
Do you use any fun apps on Android? Currently, my favorite apps are Digitron and Nanoloop. (No affiliation, but Digitron's upgrade was gifted to me.)