In simple terms. Key = Gmin (blues). Chords are parallel inverted 5ths. Or, in other words - 4ths. A perfect 5th inverted becomes a perfect 4th - always. So G D is the 5th. Inverted becomes D G (perfect 4th). So the chords in 4ths are D G, F Bb, G C. There are always variations such as adding the low G for more bass. Adding the Ab Db accidental works fine because it stays within the 4ths structure the song is built on. And playing fewer notes is better - the bass player needs a job too. I hope I am not confusing thinga more. BTW. In the recording and live as well, the organ is piped through a distortion and sounds like a second guitar. Confuses a lot of peoplw.

In simple terms. Key = Gmin (blues). Chords are parallel inverted 5ths. Or, in other words - 4ths. A perfect 5th inverted becomes a perfect 4th - always. So G D is the 5th. Inverted becomes D G (perfect 4th). So the chords in 4ths are D G, F Bb, G C. There are always variations such as adding the low G for more bass. Adding the Ab Db accidental works fine because it stays within the 4ths structure the song is built on. And playing fewer notes is better - the bass player needs a job too. I hope I am not confusing things more. BTW. In the recording and live as well, the organ is piped through a distortion and sounds like a second guitar. Confuses a lot of people.