I just noticed that A-Compressor doesn’t show me any frequency movement when I hit any key on my midi / or have something recorded already on that track. Also any parameter (ratio, attack, release, threshold…) doesn’t do anything. Except if I click on Side-chain button then the frequency starts to move (visually) when I press on my midi, but even then…it doesn’t modify the actual sound. This isn’t a problem with the other plugins. (like for example A-Expander works just fine)
Maybe it’s something to do with the Pin section (inputs/outputs) I really don’t know…
Because I have Ardour 5 also ( and Ardour 6 compiled in usr/local ) I copy the plugin from Ardour 6 and replace it with the other one from Ardour 5 in usr/lib/lv2 folder. And now it’s working