walking bass lines

how are they made?

Alot of passing tones. Say you have a dominant 7th chord

C
E
G
Bb

Bass players will play leading tones below that

B C
D# E
F# G
A Bb

Or sometimes even whole tones below

Bb C
D E
F G
Ab Bb

The way I look at walking bass lines is the following:

Given the progression:

C, D, Em

Let's use non inverted chords, so the bass is the name of the chord, a walking bass line would be developed by the following.

E|-0---2---0-|

B|-1---3---0-|

G|-0---2---0-|

D|-2---4-1-2-|

A|-3-4-5-----|

E|-----------|

As you can see, the bass line "walks" up to the next chord. It doesn't "have" to be single steps, but usually it is. Inverted chords makes this sound a lot better so experiment with it!