First some terminology: 'riff' does not stand for "Resource Interchange File Format" nor "Reykjavik International Film Festival" but for a short, often repeated phrase used as a refrain. A refrain is a section that is repeated such as the chorus in a song alternating verse, chorus, verse. Specifically the word 'riff' tends to refer to a short, energetic phrase on the guitar, especially in the low register. To my mind 'lick' is a pretty close equivalent, but Wikipedia makes a valiant effort to distinguish them here. The relevant section from the article is this:
A lick is different from the related concept of a riff in that riffs can also include repeated chord progressions. Licks are usually associated with single-note melodic lines rather than chord progressions.I'm going to let you make the momentous choice of whether to call the motto, theme or motif from "Layla" a riff or a lick. Here it is:
|Click to enlarge|
And here is the song itself:
This is the original version from 1970 with Eric Clapton and Duane Allman on guitars. There are a lot of layers, but the notation above is the basic material. Of course, some of the impact comes from the performance style with Clapton's unique vibrato in particular soaring over the accompaniment. About halfway through the original recording it turns into a long instrumental solo with piano and guitars in their highest register. Perhaps this was inspired by the Beatles "Hey Jude" which has a similarly long coda and goes on for seven minutes as well. But let's just look at that 'riff' as that is what is really memorable.
It starts with a very attention-getting turn ornament. I say "turn" because that is the name of the ornament it most closely resembles. A 'turn' is a main note decorated with the note above and the note below. Here are some typical ones:
The main note is C and the ornamental additions are D and B. In "Layla" the main note is D and it is preceded by A and C while the turn itself is atypically DFDCD. The ornament still focuses on the main note, D, but it extends the range of the turn from a third out to a sixth. The ornament lies extremely well on guitar. In the low version (you will note that the second line just transposes it up two octaves) it only requires one finger to execute in the left hand! The D is held while a second guitar plays the two-note chords in measure two--in this version they are condensed into one part. Then the turn is expanded by those long, syncopated notes in the second and third lines of the example. First it soars up from D to F and then back to E and D with C as a lower neighbor. The second time it soars up one note higher, to G, then repeats the descent. Hmmm, well, it turns out (sorry!) that the high passage that makes a beautiful contrast with the rhythmically energetic turn figure, is that same turn figure again, but this time without the A-C prefix. Do you see it? Take away that prefix and the opening notes are DFDCD. The high, contrasting passage has the notes DFECD. There is only one note different! Then it just repeats with G instead of F.
Now who else was able to get a lot of music out of one or two very simple ideas? Well, I can think of three at least: Bach, Haydn and Beethoven. And we see the same principles of unity and variation in Clapton's riff from "Layla".