Python2 and Gtk2 related dependencies are stable (no upstream breaking changes anymore). Python3 is new language dialect. Unfortunately there is hardly any backward compatibility for scripts written in the previous version 2 of the snake language.
The 2nd order resonant filters are implemented using a Mitra-Regalia style lattice filter, which has the nice property of being stable even while parameters are being changed.
All switches and controls are internally smoothed, so they can be used live whithout any clicks or zipper noises. This should make this plugin a good candidate for use in systems that allow automation of plugin control ports, such as Ardour, or for stage use.
The DSP code is written by Fons Adriaensen
The GUI provides knobs and toggle buttons for tweaking filter parameters. It also provides frequency response widget with differently coloured curve for each section and separate curve for total equalization effect.
The GUI uses the External UI extension. lv2rack (part of zynjacku) supports this extension. Ardour-2.8 needs patch to support the external UI extension.
The lv2fil GUI is written in python2 via py2gtk2.
The UI does not require OpenGL software stack nor GPU for operation.