Ex. 9 shows a melody (measure one) that’s harmonized using only thirds (measure two). As you can see, the melody and harmony are relatively easy to play by themselves, but once you try playing them together (Ex. 10), it gets exponentially more difficult. I recommend you start very, very slowly—perhaps half the speed at which you’d play single notes. Also try using a hybrid picking technique, attacking the lowest notes with the flatpick and the higher notes with your middle finger. Not only does this let you pluck both notes simultaneously, but it also gives each line it’s own distinctive attack and tone, and this emphasizes the two-guitar sound we’re trying to emulate.
Our next example is also made up of diatonic thirds. Ex. 11 demonstrates the melody and harmony played one part at a time. Playing both parts at the same time presents its own special challenges, because the phrase contains several two-string hammer-ons and pull-offs (Ex. 12). Again play this very slowly at first. You might even want to tackle one group of notes at a time—the first four notes, for instance—before attempting to play the entire phrase. Notice how the repeated ascending phrase is played over a D chord the first time, but over a G chord on the second pass (measure three). This adds even more harmonic richness to the phrase.
Examples 13 and 14 cover some heavy metal-inspired tones using thirds and fourths. It’s the combination of the harmonies and the chromatic movement of the line that makes this melody so ominous. Note that on the recording, when I play with a clean tone I let the low 6th string ring out, adding to the harmony. But when I kick in the distortion, I mute the low E to prevent the line from being cluttered.
Finally, Ex. 15 is an Allman Brother-inspired phrase that also combines thirds and fourths. This line is particularly challenging due to the large interval leaps and syncopated rhythmic phrasing.
If you’re new to playing two melodic lines at the same time, be patient. It’s easy to give up and think “I’ll just get a harmonizer” or “I know someone who can play that low part.” But trust me: If you stick with it, the musical reward is worth the effort.