look at songster as well, they have a pretty good database of midi files and have tab and notation. http://www.songsterr.com/
you can remove the basslines or listen to just the basslines. If you pay for the subscription you can speed and slow down the music
as needed. I play in 2 bands that do alot of covers. I was able to quicky enter the name of the song or artist. Liten to the bassline after removing all instruments to et a general idea of fills, melodys,ect. Nice program for a quick musical breakdown.
you can use the database for free as well but do not have some of the paid functions.