rncbc.org a.k.a. Rui Nuno Capela

Yes, you can insert LADSPA plugins into the mix. No sweat.

Each audio bus, either input or output, and each audio track can have one or several LADSPA plugins chained in arbitrary order, just like jack-rack :)

Plugins are accessible through the Mixer window. If you don't have it already, open the Mixer window from the respective toolbar button or through the View/Mixer menu.

Now that you take a closer look, on the Mixer widget, each audio bus or track strip you'll find an empty square, just below the bus or track strip title name. Left-click on it (with the mouse).

There appears the plugin context menu in its full glory :)

Choose Add Plugin...

OK. I'll leave the rest to you as an exercise ;) By this time I'm sure you can figure it out pretty nicely ...

Cheers
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rncbc aka Rui Nuno Capela