LADPSA Plugins are not native to LMMS, but are bundled with it; they are entirely controlled via knobs.
As these plugins are not maintained by LMMS, they are not documented here, but some reference links are provided below:
C* Plugins: http://quitte.de/dsp/caps.html
Calf Plugins: https://calf-studio-gear.org/
Steve Harris: http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html