I think I might have ran into a bug - either that or I’m losing my mind. I regularly use Shift+I to transpose notes. So I just tried to transpose a couple of bars down an augmented unison by entering Shift+I, t-a1, Enter. As a result, the notes were transposed up. This is reproducible, I could add a file but I get the same result in any project. I’m on the latest version of Dorico Pro (actually I get the same result in Dorico 5 as well). As far as I can tell it works fine for all other intervals. It also works when using the Transpose tool to transpose down an augmented unison. I haven’t been very active on the forum over the last couple of weeks so please forgive me if this has already been reported (I can’t find it in a forum search).
It seems to be true: in @Zalde’s example (to transpose from C# to C), t-d1 works.
But interestingly, the interval calculator in the Transpose Dialog gives Augmented Unison for C# to C♮ (and down transposition works, as Zalde points out).
Ah, I can see the logic behind that. For some reason (let’s blame it on the flu) it never occurred to me to try transposing by a diminished unison, which indeed only leads to notes being transposed downward. Now that I know that I won’t forget it.
But, as @charles_piano shows, when I ask the transpose tool to calculate the interval between a C# and C natural it tells me to transpose down by an augmented unison. Also, diminished is not a quality I can select in the Transpose tool for a unison interval, only Perfect, Augmented or Diatonic. Ah, well.
