In the SoundNotion interview, it was mentioned that Dorico supports altered unisons with up to five (!!) stems. The given example involved a “cherry stem” branching off the primary stem, which had its own notehead. In Messiaen (to name but one example), the primary stem doesn’t necessarily have its own notehead, but rather splits into two secondary stems. Will Dorico support this treatment of altered unisons, or will the primary stem be required to have a notehead?
Dorico’s handling of altered unisons is that one of the stems is always vertical, and the other stems branch off to the right and to the left.
It does not support the variant of having a partial straight stem with two stems branching off to the left and to the right, and I don’t expect us to support that convention any time soon.
At least with this excellent starting point, it sounds like the second variant could be rather easily achieved with a workaround, entering three altered unisons, and then hiding the notehead and shortening the stem of the middle one. This would depend, however, on the ability to manipulate stems as well as the order of the notes/accidentals.
We didn’t make the decision not to support the “all stems angled” variant arbitrarily, for what it’s worth. If you always have one note on the primary stem, then that stem is positioned horizontally at the same position as other coincident notes, and if you always have the first split stem branching off to the right, you do not disturb the rhythmic spacing at the start of the altered unison, and you may not need to disturb the rhythmic spacing at all if the space required to accommodate the additional accidental and its associated notehead falls within the existing ideal rhythmic space.
I appreciate that implementing the “all stems angled” variant presents difficulty with regard to automatic spacing. Nevertheless, it’s strength is exactly that the extra space it requires can be distributed on either side of coincident notes, which, especially in highly chromatic situations can be a great space saver.
It might be a space saver in some circumstances, but I think it introduces ambiguity where none would otherwise exist. The eye doesn’t really keep track of stems, but rather of noteheads (except in situations like beams between staves, of course), so making a note on a split stem always splay to the left, effectively appearing before other coincident notes, doesn’t seem like a good idea to me.
That is indeed a sound principle, although there are cases where ambiguity of note alignment is not an issue with this kind of notation. One example is Messiaen’s Apparition de l’Elise éternelle, where every altered unison is on the first beat of the bar:
Super excited that there will be any support for altered unisons!