I stumbled onto a possible bug (or maybe working as intended, but in that case it maybe needs a rethink)
I sync Renoise to Ardour with Jack Transport, and was working on a song that has a part with where the 4/4 is broken up with 3/4 measures here and there. I edited in the time signature changes in Ardours time signature editor, but when I try to play it back in sync Renoise seems to get confused with the changing time signatures, every time the time signature changes in Ardour, the Renoise playback jumps to a different spot in the song, almost as if the time signature changes makes it recalculate position as if the entire song was in the new time signature.
My workaround was to remove the time signature changes in Ardour, but then it gets less convenient to edit the audio since measures in the editing grid doesn’t line up with actual measures in the audio.
Might there be some issues with the Jack Transport sync and changing time signatures?
Yes, this isn’t really covered by the Jack Sync protocol. Neither Tempo automation nor signature changes are shared between sync clients. Only the currently active value is transferred between clients, so a proper lookup simply isn’t possible.
So the only workaround is to avoid using signature changes with Jack Sync.
Automating tempo kinda works though, by syncing to the tempo free beat position provided by the transport master.