Two filters adapted from the music-dsp collection:
Resonant Filter (low pass) and State Variable Filter (with output cross-faded from LP to HP).
Also added a text-book IIR algorithm, the Leaky Integrator, which works as a simple yet effective low pass filter.
All three are included with the latest OwlSim code, get an update from github -
and sound samples can be found on Soundcloud.