Arranging the Bass Line

[JDMEK5]

I don't know if anyone else picked up, but I'm no good at arranging a bass line.
Sure, I can hear it, and tell where it goes up and down; but when it comes to notes, I got nothing.

So I was wondering if someone (some people) could help me a little; show me some tricks of the trade.
Is there a method of some kind? Do you just listen? If I don't have it now, will I ever?

[Bespinben]

What you can do is slow the tempo of the song down with Audacity and then apply bass boost, assuming the bass line is fairly agile.

[JDMEK5]

Ok thanks! There's no way to lower the treble volume though, is there?