When dealing with a moveable grip, the simplest way to fret the static root against a 5-6-b7 line is to place the root in the highest voice, so it rings out above the line. (In our open-string boogie, the root was the lower note, so it sustained below the line.) Ex. 1 shows a piano-style boogie pattern with the root on the fourth string and the moving line on the fifth string. As you play this, listen to the 5 (D), 6 (E), and b7 (F) shifting beneath the droning root. These intervals imply a I-I6-I7-I6 progression (in this case, G-G6-G7-G6). You can move this figure up and down the fretboard, and thus play piano boogie in any key. The root for the progression’s chords is always the static note on the fourth string.
In Ex. 2, we flip the intervallic structure, putting the root in the bottom voice and the line above it. This creates a beefy rhythm sound, but is significantly harder to fret than the previous example’s version. The five-fret stretch to imply the G7 chord (beat three) is a doozie. Like the figure in Ex. 1, this I-I6-I7-I6 progression is moveable, which means it too works in any key. (You can also shift this pattern to the next higher string-set, so the root is on the fifth string and the 5-6-b7 line trucks along on the fourth string.) If you find the stretch is too hard as shown here in the third position, first learn this progression in the tenth position, where the frets are closer to each other, and then gradually slide down to lower positions as you master the moves.
The fun begins when we mix our “high root” and “low root” piano-boogie figures, as in Ex. 3. Sure, we could have simply shifted the G-G6-G7-G6 “low root” set down to the first position to play F-F6-F7-F6—and that sounds great. But by taking the less predictable route shown in this example, we expose the listener to both inversions of our piano-boogie intervals, thus increasing the riff’s harmonic complexity.