http://www.youtube.com/watch?v=TotbU952HNk&ob=av3n
The filter evolving bass sound.. it’s the main bass sound throughout the song, NOT the 808 kick.
It’s by itself at 1:37 if you’re confused.
Assign filter cutoff to the mod wheel, or just sweep the cutoff manually. Or are you looking for it to happen automatically? You’d need a digital synth with a big mod-matrix.
I’ve tried to replicate it on my Minimoog D. Not 100% identical but pretty close.
One OSC waveform square.
Filter envelope medium attack (1 sec.), medium decay (1 sec.), sustain level 50%, no release.
Volume envelope medium attack (.5sec), no decay, full sustain, no release.
LFO square waveform modulating pitch of OSC 1 one octave, modulation speed approx. 4 hertz.
Filter cutoff closed, resonance 50%, filter envelope amount 60%
I’ve included a link to a sample demo of that patch on my Minimoog D, first dry, then with panning reverb, and back to dry again.
The Little Phatty should be able to do that easily, although maybe not as “phat” as the Mini… 
http://soundcloud.com/thealien666/moog-bass-kirko-bangz/s-Gjs0Z