How does one create a walking bassline over a guitar solo? Certain song tabs tell you what key the solo is in at certain moments, so I can follow along there, but when I try to improve over a solo, I end up making an out-of-tune droning bassline.
Stick to stuff in one key at a time. Know the appropriate scale notes for that key. A walking bass, in simple terms, is four in a bar, moving up and down in a sort of scalar manner. Think about it. Playing four notes in a bar in C, at least one, more likely two of the notes you play consecutively (up or down) from a C scale will contain a C, E and/or G. The best plan is to make sure one of these notes fits on the more important parts of a bar: beats 1 and 3.
Example - in C, for 2 bars - play C D E F G A B C. It works fine.Because 1st bar - C=1, E=3, 2nd bar - G=1. If the next bar is G, you can play the first note as the B below C, and go B A G F. If the next bar is F, then you may play F E D C, ending on the top C previously played.
All this is very basic walking bass, and you can sometimes merely get away with walking up and down the scale, with occasional jumps. However, it is probably a nice start point. Give it a try. There's a lot more, like chromatics, extra jump notes to stop the timing becoming staid, etc. etc.
It seems that you haven't figure the key the guitar solo is in, the most important thing is to find in what key you should be playing ,from their you should figure the scales , the notes and the chords you could use in your bassline.
knowing the theory behind the music you're trying to transcribe is crucial since it makes your job much easier.GOOD LUCK.