That sounds like a real bass guitar played with some basic slap technique...would be tough to capture the subtlety with a synth patch. It's going to sound mechanical, unless you have a really good bass sampler instrument (if you wanna capture the sound of this song more precisely) or a synth patch that's got good performance control (at the very least, velocity sensitivity that's perhaps mapped to more than volume, for example filter freq). Also...if you listen to the first 4 notes, he cuts the note off a tiny bit sooner each time...even though it's a simple bass part, don't underestimate the value of those little intentional performance nuances.