I am smitten by this song by the seatbelts called adieu. link below.
its mostly a vocal and piano song but the double bass is there and fills in the chords nicely.
I'm having a problem understanding how to play it. I used an app to roughly map out the chords and can play the root notes easily with the song but there are many notes I just can't seem to grasp.
How do I learn this?
You should be able to learn that song note for note without understanding the underlying theory.
My last two years of high school I was asked to play in a university big band. I could read standard music notation, but had almost no understanding of music theory. Also I had no idea how to read and interpret jazz chord notation, and the bass parts for at least half of the tunes were written primarily with chord notation.
The band director provide music and also recordings of the actual arrangement. I learned the recording note for note at first. Then I learned patterns well enough that I could use them freely over the changes. This is possible because in the form of a song, the changes tend to be organized into sections that repeat over and over again. For example you might have a form like AABA or ABAA. There are of course also sections were the form might be broken, so I had to play those sections note for note.
Later when I went to college I took three semester of classical music theory. These semesters covered harmonization of diatonic 7 chords in the major and minor keys, and how to write smooth voice leading with four part harmony. Diatonic means only the notes that belong to a key signature are involved, so there are no chromatic or altered tones. Knowing what notes to consider diatonic in jazz chord progressions can be tricky...but you don't need to delve too far into that right now.
My foundation in classical theory gave me what I needed to learn how to read and interpret jazz chord notation. One of the young jazz guitar instructors on staff mentored me on how to read jazz chord notation, answered my questions, and jammed after hours once a week, so I had a chance to learn and grown.
In it simplest form, a walking bass line is just the root note played in quarter notes. As you get more complicated you start adding chord tones. First add the 5th 1,5,1,5 |CGCG|. Then try using the notes of the triad 1,3,5,1 |CEGC|...or |CCEG|...or |CEGG|. The ideas is you should explore all the possibilities...however, One rule to start with, usually you start the downbeat of a measure on the root of a chord, but this is a rule you can learn to break later. Continue developing by integrating all four notes of the 7th chord 1,3,5,7 |CEGB|. Are you might want to try a major 6th chord. |1,3,5,6|1,6,5,3,|1 |CEGA|CAGE|C You should recognize this as the bass line to Glenn Millers' "In the Mood"...also many 50 era songs use this bass line.
The next step can be adding diatonic none chord tones. For example if you are playing I to V, you might play something like |1,2,3,4|5...| |CDEF|G...|Note the 5 is actually the 1 (root) of the V chord. Essentially you are walking up from the I chord to the V chord. Note that 1,2,3,4 is what I call a linear line; when you play 1,3,5,7 it is what I call an arpeggiated line.
You can also throw in chromatic notes that are not diatonic. For example if you were play I to IV you could play |1,3,5,b5|4...| |CEGGb|F...| Note the 4 is actually the 1 (root) of the IV chord. Some might think of this as |1,3,5,#4|4...| |CEGF#|F...| The #4 and b5 are the same tone, but have a different name. When different notes are actually the same pitch, we call them enharmonic.
If you want to to learn how to improvise this sort of bass line, you need to know the major and minor keys; the diatonic 7th chords and the major and minor 6th chords; and how to read jazz chord notation. I also suggest learning harmonization of the major and minor keys up to at least the 7th chords.
Harmonization in this context basically means you know the shape of the seven diatonic 7th chords in major, natural minor, harmonic minor, and jazz/melodic minor. Having this knowledge helps determine how each chord functions within the progression. The idea is to analyze a chord progression and decide which notes are diatonic. Jazz tends to wander around instead of staying firmly in one key center, so it tends to get pretty complicated.
The hardest part about reading jazz chord notation is there are multiple ways to write out most chords and you have to be able to instantaneously recognize and interpret all of them. For example D minor7 can be written D-7.
Here's an online resource that you may find useful:
[Bob magnusson] the_art_of_walking_bass_a_method_(book_za.org)