This might be totally unhelpful, because I’ve never used percussion notation in any notation software. However I tried a quick test (which became more complex).
Starting with a completely new file, and adding just a drum set player and instrument, and setting its percussion map to “General Midi”, I produced this:
I’m sure that I didn’t reproduce your setup correctly, because I found the notes for the bass drum on the F above middle C on my midi keyboard, and for the cymbal on F# a diminished 12th above middle C.
Bar 1: F, F#, both notes together. Looks ok.
But this looked suspiciously like putting the notes on a treble clef staff (which looking back on your original post is exactly what you don’t want).
So, bars 2-4: I played down and up the white keys and Dorico placed a note wherever a drum set instrument exists.
Bars 5 &6: Pressing and holding the F, then going up (or maybe down?) the white keys. This looked alright at the time.
Bars 7+8: Pressing and holding the F# and then playing down the white keys. Unexpected doubled notes do appear.
Because of the rhythm mess in bars 3 & 4, I decided to delete and re-enter everything. This time the result was as expected:
So then I checked playing notes simultaneously (extra note going up or down the white keys):
Bars 10-12: F played every whole note.
Bars 13-15: F# played every whole note.
Bars 16 & 17: I tested how closely together notes have to be played to appear at the same rhythmic position. It’s fairly timing critical .
In another recent post Daniel mentioned a fixed threshold of 100 msec. I’m not sure whether that’s relevant here but I’ll check that shortly.
In conclusion, there do seem to be cases where unexpected doubled notes can be generated in drum parts, but I can’t point to any specific causes.
In case it helps, here is my test file, so that you can see the settings I was using.
Drumkit-1.dorico (463.4 KB)
As I said, I’m a total novice in the percussion area of Dorico. If you can give me the settings I’d be happy to test this in something closer to your use case.
David.