Philterkeyz is a resonant filter vst plugin with a difference.

Filter cutoff is controlled by midi notes and the cutoff frequency is calculated to match the frequency of each note.

Try inserting it after a vsti playing a riff. Feed that same riff to the plugin and the filter provides an added dimension.

Alternatively, try inserting it after a long sweeping pad sound, then routing your midi keyboard to philterkeyz. Raise the resonance and you can play a filter line over the top of the pad.