Originally Posted by jaxstarke
What's the difference between a bass line that goes in this pattern-A, E, G, A, G, E (that one seems to be more prevalent in blues) and one that goes A, C#, E, F#, A, F#, E, C# (this one seems to be more prevalent in rockabilly)? I'm talking about the pattern on the fretboard. Is one called one thing and the other another? I'm just asking in case I'm ever in a position to play with a group and they tell me the key but not the pattern. If that makes any sense.
The first one is based on a dom7 idea as you have the G in there, but will work in many more situations and in better combinations if you see it as a minor Pentatonic of A C D E G A. As you see the choice is to use the C as a b3 not neglect it.
The second example is standard first part of any rock 'n' roll major based line, but can imply the dom7 aspect of the tonality if the A is changed for a G in the second run through. So it runs A, C#, E, F#, A, F#, E, C# A, C#, E, F#, G, F#, E, C#
If you carry it on to the next part from the IV then you play the D chord to imply the dom7 again so it becomes D F# A B C B A F# D now the C is the dom7.
The dom7 can be seen as a major traid with a flat 7 added on it, so making it a dom7 arpeggio, so it is not a major 7. But because it is build upon a major triad it wants to resolve to back where it came from (the tonic or root note).
If we accept a triad is 1-3 -5 then adding the b7 is building of the strong 5th note.
It is so called, or refered to because it occurs naturally in the seventh chord built upon the dominant (i.e. the fifth degree) of a given major diatonic scale.
Rather than go into any theory, just play it and hear it work, and just appreciate the fact that some call a dom7 a major/minor chord as it has elements of both in it.
Most Blues and rock 'n' roll can be seen as '7th implied' as the bass will play the b7 over a major triad or tonality of other instruments being used.