Hi T.C. My ear hears the same thing, Some strings sound out of tune, but according to the tuner it is bang on. I have tried to adjust the intonation, but it doesn't seem possible to get it exactly right.
I think another possibility is the track on Youtube could be slightly off. Some of these are old recordings, and come from different sources, and could be the player used to record it.
Yes, I have studied some theory, and do know the notes I am playing. But still at a beginning stage I would say. I was invited to play with some friends who play this genre, so that is why I am playing these tunes. When I first started, I really had little or no idea how to play along, other than just using the root notes of the chords. Then I started adding the fifth, and also the thirds. But was kind of stuck when trying to do walking bass. I found I needed to figure out what is the basic theory behind walking, and started to see how it is mostly a "traveling" from one chord to the next. You could do it with arpeggios, scale tones, or chromatically, or combinations of each.
Of course, the tune, and it's chord changes kind of dictate what you can/should do. How you should connect the changes. How is the chord progression moving around? Is it one chord per bar, two chords per bar, one chord over multiple bars? etc.
So far I have used the chromatic approach mostly, as I think it sounds most jazzy, most interesting. And also for the fact that it includes the major and the minor third, so works well over most chord changes.
Fly Me to the Moon was almost 100% walking up chromatically. When I walked down, I walked down the scale. This was a very fun tune, and lends itself perfectly for walking over.
Right now I am really working on my groove, or feel, and I feel that is the most important ingredient of the bass.
Nice to get the ear of someone who plays and studied bass... Thanks for the input.