"pretty" good

I looked into a dictionary and it says the adverb "pretty" means
1) to some extent; fairly
2) very.

When you say "How are you?" to your friend and he says "Pretty good," what does he mean,
he's so-so good,
or
he's very good?

Or does it depend on the way he says?
eg if he says "pretty" louder than "good", does it mean he's so-so good? And saying "good" louder can mean "he's very good"?

Thank you!