When you listen to most singers who are riffing—which is improvisation, especially in R&B and blues styles—as well as pop styles that incorporate those genres—you'll hear lots of Minor Pentatonic runs. While this may sound complicated, it's actually the opposite. Getting the Minor Pentatonic mode into your ear and voice means you can sing any combination of just five notes to improvise. It's a great short cut! You'll also hear Major Pentatonic runs, though less often.
What is a Minor Pentatonic scale (or mode)? In a minor key, the notes are 1, m3, 4, 5, m7. In the example below in the key of A minor, that's A, C, D, E and G. Notice we leave out the 2 and 6. (In most music theory these scale tones are written in Roman numerals, capitalized for major and small case for minor.)
The Major Pentatonic mode is 1, 2, 3, 5, 6 (which is the black keys on a piano). In our example here that's A, B, C#, E, and F#. Notice for Major Pentatonic we leave out the 4 and the 7.
When you're riffing the order of the notes doesn't matter so much. What's more important are the feel, the soul, and your agility. Common tones that singers land on for dramatic effect—the same as other instruments do, such as guitar and keys—are the 1, m3, and 5. You'll hear a lot of melisma—which means sliding between notes on one vowel; bent notes; growls and grunts; and varied dynamics used within one riff. Rhythm matters, too. For example, try holding out a note then run quickly down to a lower tone in the mode.
Sometimes a singer will draw from the blues scale, which is a Minor Pentatonic with an added #4 (same as b5). In our example of the key A minor that's adding a D#.
Let's look at some examples from famous singers. First, in the iconic song "Pride and Joy" by Stevie Ray Vaughan (which incidentally I recorded on my second album, Must Be Love), the melody itself is sung in the minor pentatonic mode. Vaughan's guitar solos are primarily using the blues mode. He begins singing at 0:54.
From the world of pop, this example is Christina Aguilera singing "Candyman," harkening back to the group The Andrew Sisters from the 1940s. But her riffs are't nothing like how the Andrew Sisters sang. She's using primariily the Minor Pentatonic mode.
Here are two examples of riffs drawing from the Major Pentatonic mode. The first is Oleta Adams, one of my favorite and lesser-known singers who has a gorgeous instrument and very soulful style. This is her version of "Everything Must Change." At 5:15 you'll here a few notes of the Major pPentatonic mode in her improvisations. The second example is by Stevie Wonder singing his iconic song "Sir Duke" from his album Songs in the Key of Life.
See what you can find in recordings by the singers you admire!
Minor Pentatonic Riffing Practice
The exercise below is from the improvisation page in this Series, where there's also musical accompaniment. Notice that in the exercise, the rhythms are all even. This is so you can become familiar with this pattern smoothly and easily. An actual riff wouldn't tend to be this neat and tidy though.
Have fun trying this out, and don't worry if you don't get is sounding amazing right away! Remember, everything worthwhile takes time to master.