Both of those points ought to be clear(er) in the manual. The manual pretty much dissuades you from home calibrating ! I’ve had to, but it always worried me I was undoing a better ‘factory’ fine calibration …
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Also @billywood, taking e.g. preset ‘BD 95’ you can see what happens when you interrupt the filter resonance. Put down some BD at 1 5 9 13 and 15, then plock the F2 resonance progressively lower on 15, listen as the drums disappear ! You may be experiencing a subtler version of this too !?