i have a question

[slapnpop]

i was watching my cousin makeup some crazy bass line off a drum beat and it was amazing. im just curious of what improvising like that is based off of or how do u learn to do that or sumthing?

[Deacon_Blues]

It's based on theory knowledge, scales/arpeggios knowledge and a sense of how to create a groove. It also helps a lot to listen to and play along to songs of various genres. It comes for free when you're getting comfortable with playing what you hear in your head.