A walking bassline is the backbone of jazz music. It's used in many other genres besides jazz, but when people refer to walking basslines, jazz is usually the first thing thought of.
Hear, in your head, a tune where the bass is playing just straight quarter notes. Probably best to start by thinking of tune in 4/4. If you're playing in common time and the bassline is playing one quarter note every beat, you've got part of the bassline right there. The other idea in a walking bassline is to outline the harmony of a tune. This is to say that the bassline is playing notes that move. Contrast this with a rock tune where the bassist might simply play the root of the chord over and over and over and over and over and over and over and over. You get the idea. So, in a walking bassline the bassist is playing notes within the scale, the chord, and chromatic "approach" notes as well.
In this link:
Bass Line Construction: Target Approach, Chris Fitzgerald talks about building a bassline. The implication here is of a walking bassline.
A couple of things to add:
- the rhythm doesn't have to be constant straight quarter notes. Often, rhythmic embellishments are thrown in for variety. The theme, if you will, the overall feel, will always be that straight quarter note pulse, but many rhythmic variations can exist.
- the accent is usually on the 2 and 4, in 4/4 tunes, as opposed to the 1 and 3 common in rock music.
- these basslines usually don't play the same note repeatedly. Could you play the same note twice in a row? Sure, of course. But generally, these are like the rhythmic variations I spoke of before. Generally speaking, the notes move, usually in some pattern, (e.g. higher, lower, etc.).
- walking basslines are always improvised, (in jazz). One chorus is different from the next, or previous. One bar is different from the other. Static, ostinato figures are rarely done.
- walking basslines require a strong foundation in scales, chords, and overall music theory. One wants to have a strong understanding of their instrument, a good grasp of chords and scales, and big, big ears.
