People always come up to me and ask "How do you do that, you must be ambidextrous, you must be able to split your brain." Split my brain? What does that mean? I guess what fascinates listeners the most is two-part independence playing. Sections 1,2,3 and 4 are examples of a simple left hand ostinato. I use it on my CD "Doubleguitar 2," as an introduction and segue to the tune "Beautiful Love." I see it as a D minor bass groove with a tempo anywhere between half note equals 60 to 120. I put in notes for the right hand, but feel free to play anything you like over it (C major, D minor, chromatics,etc). The rhythm is most important part of the exercise.
Examples 1, 2 and 3 illustrate how to play half, quarter and eighth notes over the left hand vamp. If you have trouble at a particular spot play the left hand alone then bring in the right hand at that spot. You should be able to start your right hand at any point in the bass groove. Don't be afraid to begin very slow. Remember, you have to be able to play the hands separate before you can put them together. Practicing one hand at a time is essential!
In example 4 the dotted quarter note rhythm in the right hand can be very challenging, especially when playing over ostinatos like this one here. Notice how the notes in both hands start out together, then they begin to separate on the last beat of the second bar. The rhythmic pattern repeats itself after six bars. If you have trouble spots, be able to isolate them, then keep the left hand going and start the right hand at that spot. I spend a lot of time working on bars 3 thru 6 of example 4. Try these right hand rhythms over other tunes and vamps. Notice how hairy it gets when playing through different chord changes.
Working on "over the bar line" rhythmic figures like this is essential in
freeing up your improvisations. Small errors that appear in two-part independence playing are usually the result of bad fingering or not being able to blend the hands together rhythmically. Putting the microscope on these small trouble areas is the only way to be able to really nail them consistently. Note for note, rhythm for rhythm, this kind of knowledge is what separates people who are really doing it from those who are faking it, or as Jaco said "just wiggling there fingers." I suggest you start the exercise with the metronome at 96 equals a quarter note or slower. The metronome should click four beats per measure and accent the first beat. Gradually bring the tempo up to a half-note equals 104 with the metronome clicking on beat 2 and 4.