If playing C, he alternates to low G before playing a G chord, or alternates to high A before playing an F chord...
It is not really clear what you're describing. It mixes what I think are supposed to be bass tones with chord names and doesn't give octaves, but...
...the note nearest the root of the next chord...
...if it's any
G, low or high, before moving to a root of
G in any octave, it won't be the same interval as moving from any
A before going to a root
F in any octave. Categorically it won't be the same interval, so it doesn't make sense to think of these moves as "nearest."
I don't mean to pick apart your question. I'm just trying to show why I'm not following your description. Also, when you include the video of Jimmie Rodgers and mention Gene Autry, it kind of suggests you're interested in bass for their particular style, but your final sentence is more about bass generally.
I'm familiar with those musicians, but not an expert on them. I imagine they played bass with some flexibility, and approached the the first bass note of the next chord with more than one pattern which about be chosen ad lib. I wouldn't imagine they always play the approach by the smallest distance.
A common approach to bass is to play the chord root on beat 1, then play chord tones for the remaining beats. If the final beat of the measure is a step way from the root of the next chord, it makes an especially smooth bass part.
Approaching the next root by step can happen a few different ways. It depends on the distance between the two roots, whether you decide to use passing tones instead of chord tones, and the pattern you play. For example, between roots
F you could do...
...notice how the root is played twice in the second pattern to give a little time shift that switches the final approach tone from a half tone
HT below to a whole tone
My labelling of
WT is for chord tones that approach the next root by a step. But you can also have non-chord tones called passing tones
pt to make other step-wise patterns and sometimes chromatic color...
...notice that in the step-wise lines of the second and third pattern we also get the
HT approach tones.
When the root is a different distance that
F above, for example
A above, use the same principle of play root first, then chord tones, then an approach by step, but adjust the pattern for the difference in distance. If we stay with the pattern of going up the
C chord, the adjustments to the first two examples could be...
You can make similar adjustments to account for meter, for example...
...the basic movement up the
C chord remains, but we can either play a single or double root to shift the approach tone to the
When the two chord roots are separated by either a fourth or fifth (very, very common) you can also make the final approach by octave or fifth...
...the thing to notice is that the approach tone to the next root is playing with the fifth or root of the first chord "flipping" to the root or fifth of the second chord. In other words,
G2 fifth of the
C chord becomes
G3 root of the
G chord. And in the second example
C3 root of the
C chord becomes the (implied) fifth of the
F chord. I say "implied" because at beat 1 of the
F chord it hasn't actually been played, but it lingers in the memory, and of course if the bass continues and really does hit the
C3 it will indeed be the fifth of the
In the examples above the chromatic passing tones probably aren't in the style of Rodgers or Autry, they are more at home in jazz. If you want to avoid that, make a rhythmic adjustment to avoid the extra beat/tone. Swapping a single beat 1 of the root for two beats and vice versa is a simple way to make the adjustment. And if you want a really simple folk/county bass, just play alternating root and fifths.
You can find lot of tutorials and lesson for how to play bass lines with differing patterns and example, but for the most part they will be presenting the same principles as above.