Thanks for that Bob - I wonder why that chord isn't called C7b9 - maybe it is also referred to as that, as an alternative. For instance, I often see chords written as C7b5 but haven't come across C7-5......
As you say, it sounds just like a diminished(7th) chord and the KN7000 treats it as such, which is not surprising since the notes are actually a C#dim7. (or Edim7 or Gdim7 or A#dim7). Having had a play around with several different styles on my KN7000, the APC Bass notes just seem to play some or all of the notes within the diminished(7th) chord, as I would expect. The order in which they are played depends on the inversion of the chord. If I was composing a Bass track, I would normally do the same, since any other notes seem to be discordant.

Another peculiarity of the KN7000 is that if you just play a diminished triad - say C,D#,F# - the KN7000 treats this as Cmb5 (C minor flat5) - which I suppose it is - but if you add the 'A' on top, which technically makes it a C diminished 7th, the display then shows the chord as a C dim. Personally, if I see a chord sequence which includes a diminished chord, I always play a diminished 7th, since it sounds better to my ear............
In my experience, diminished chords on guitar always use the 4 notes and technically are Dim7th chords - any comments on that point John C. ?