Your answer gave me hope and I decided to take a look inside the “midifilter” folder. Here’s what I’ve got.
This is the content of the .tar file available on the website, Linux 64bit option.
In the same website there are these installation instructions:
Unzip the .tar file, move the lv2 plugin to $HOME/.lv2/ and the application to $HOME/bin. A Linux installer is in the making.
Well, the contents in that folder are getting me a bit confused. It doesn’t seems to me that there’s either an app or plugin file there.
And I’ve rechecked in Ardour for the MIDI Key-Range Filter plugin and there was nothing to be found.
I didn’t give up hope, nonetheless. After all, I believe in this way of making things and I love working with Ardour.
OBS: Just in case someone asks I’ve created the .lv2 folder in my home directory as well as I did all the other steps in the installation instructions.