Difficult to explain. let me draw:
C5 is a note
C5 _ _ _ _ _ _ _
A 3/16 would create this kind of echo:
C5 _ _ c5 _ _ c5 _
None of the LADSPA ones I tried just give you a normal 3/16 delay.
What exactly do you mean with this? Are you talking about triplets? Just use the calculator to find out how long a triplet is regarding to the BPM and round the result to the available ms. Or is 3 for left to center to right, for semiquavers?