For example, imagine a band is vamping on a dominant 7th chord for two measures, marking time until the next chord change. To spur harmonic momentum, a B-3 player might play a series of secondary chords that color the primary dominant 7th chord. Though the essential harmony is static during this two-bar section, we hear chordal movement. What’s going on?
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Walk the Line
These secondary voicings are often constructed around a melodic line that’s related to the chord of the moment. One classic line that shows up time and again in groovin’ music from New Orleans funk to Memphis soul derives from boogie-woogie piano and incorporates two chord tones—the 5 and b7—of whatever dominant 7th chord the band is playing at that time, plus the 6, which acts as a stepping stone between the 5 and b7 chord tones. Typically, the line ascends and descends in a 5–6–b7– 6 pattern and is harmonized with several other notes. As we’ll see in a moment, this harmony may be located above or below the 5–6–b7–6 line.
Fig. 1 shows three chord voicings we’ll use to start exploring line-based comping. As you fret these grips, notice how they each occur on the 5th, 4th, and 3rd strings. By staying on these strings, we keep the chords in the guitar’s middle register, an area that grants singers or soloists melodic elbow room.
In Fig. 2, we put these voicings to work to create an A7 comping pattern, which typically occurs over an A pedal tone established by the bassist. Cycle through this phrase several times at a moderate tempo, listening to the harmonic movement and feeling the syncopation in the middle of each measure.
There are several things to consider about this passage. For starters, the 5–6–b7–6 line— which, in this case, is E–F#–G–F#—ascends and descends on the 5th string. Another is that both the A7 and A9 grips are rootless. As long as the root—A—is implied by the bassist or another instrument, you won’t miss it. If you’re flying solo, with no one to pump out a pedal tone below you, you can keep these changes focused within the overarching A7 tonality by simply plucking a low A from time to time.
Unlike its companions, the D chord has a root (it’s located on the 3rd string). But in this context—sandwiched between A7 and A9—the D chord isn’t functioning as a full-on change. Rather, it simply provides momentary tension and release within the comping pattern. This quick, superimposed IV chord is a staple of gospel and blues piano.
One more thing: If you’re into music theory, you’ll notice that our A9 chord is also a first-inversion Em triad, as well as a partial G6. When comping, it’s often the case that you can name a particular cluster of notes several ways, depending on the context. Because we’re comping against an A7, we hear these three notes as a partial A9 chord. In another setting, we might identify them differently.
You can transpose this A7–D–A9–D comping pattern up and down the fretboard. For instance, shift the whole operation up to D7 in the 10th position, and you get a D7–G–D9–G phrase. Start two frets higher in the 12th position and you’ll have an E7–A–E9–A move that sounds great against E7. With a little imagination, you can create a soulful I–IV–V comping pattern to fill out an entire 12-bar blues progression in the key of A. Try it.