> "All the variable capacitors I know of are trimmable via mechanical steering, so this is news to me that this is now standard in audio electronics."
Of course! This is stuff I did when I was in high school years ago ! In college, I learned about active synthesis which is creating equivalent LC circuits out of OpAmps and RC elements -- using a potentiometer to modulate frequencies. And now everything of course is digitally synthesized. That is no longer audio electronics, it is more like programming,