How do I connect ALSA sync out to MIDI control in?

I’m trying out Ardour 3. No trouble compiling, but I notice that Ardour’s MIDI control now shows up in the MIDI tab of qjackctl instead of ALSA, where it shows up in the version 2 series.

This is a deal-breaker for me. I use Openoctave, which shows up under ALSA.

How do I now connect the sync out of OO to the control in of Ardour?

I do not know if I correctly understood your question, but I think it is related to the difference between the ALSA MIDI used by OpenOctave and the Jack MIDI used by Ardour 3.

If this is the issue, you should use an ALSA-Jack MIDI bridge, like a2jmidid: