how to make mad professor dub bass effect that sweeps and growls

[Roman]

King Tubby used to get a similar effect.
There is an effect Mad Professor gets where the bass is momentarily sent to some effect that adds a sweeping growly sound.
It sounds like a resonant filter sweep on a synth bass sound. Like if you had a saw tooth bass sound filtered down to a deep sine wave tone and then opened the LPF a bit to let some growly tone through with a resonant sweeping sound.
Like the resonance is up a bit.
I seem to remember him saying he uses a Line 6 box for that. And when I check his studio kit list he has two Line 6 Filter Pros.
I am confident enough with these clues to buy one and try it.

How is this effect created? Is it as simple as sending to a LPF with resonance up or something. I thought the sweeping effect might be independant of the send level to the effect.
Maybe King Tubby did the same thing with an analogue filter.
I can't imagine the specifics of how this would result in a growly sweeping bass effect. Especially when the bass sound sent to the effect is often a smooth bass sound.
Just thought I'd get some opinions. But this may be too specific or specialist a question for this board.

[Kiwi]

I'm interested in these sort of sounds too. Line6 have an effect based on the Mu-tron III envelope follower which was used by Stevie Wonder, Bootsy Collins etc. It was designed to get synthy sounds out of real instruments. Its useful, and it's made me wish for the real thing - or a good analog equivalent.

If your bass doesn't have enough harmonics, add a distortion pedal. A Big Muff can be good.

[joeq]

if it is a synth, one thing to try is to duplicate the instrument, sending the same midi to both, then play around with some modulating stuff on ONE of the copies

if it's a bass guitar, still make a duplicate and distress the duplicate so it 'rubs' against the original