Because it’s not. I don’t know why but 440Hz is at 59.17 and 880Hz is 70.74 – which would imply a semitone every… 0.96 knob steps or so.
But this probably varies on the device. My Track 3 voice for example is noticeably flatter than this – 70.74 on Track 3 is more like 860Hz. And yeah that sucks if you’re trying to get it to track to the keyboard.
I made that chart before Overbridge as well. Now that we have precise two-decimal values for the filter I can probably tighten that curve up a bit.