The jackd enabled audio mastering software Jamin. The last version that uses Gtk2. With fixes for modern OSes.

You don't have to replace the gtk3 version if you already got it from the OS. This is a standalone executable, and it uses the same libraries and ladspa plugins and their location

Problems in the gtk3 versions include:

• single instance's Post EQ spectrum display drives X11 server CPU load to 50% of a core. gtk2 version is 2%.
• general spectrum display (tab 3) is entirely broken.
• somehow there is higher gain in the chain even with everything dialed to neutral.
• new UI makes it much harder to read what is going on.