If you wanted to know how to do sidechian compression in Ardour - now you do.
I'm demonstrating the process with 4 different open-source plug-ins, starting with a sock Ardour compressor, which does a suprisingly good job!
Also: here's a teaser-song for that video in case you missed it:
https://www.youtube.com/watch?v=51518m3AATM
Enjoy!