This is an interesting one. The instrumental riff is 3 bars long, and there's a competing tension between the feeling of it being 3 bars of 4/4 or 2 bars of 6/4. Harmony says one thing, then drums and words say other:
This dichotomy gives it that crucial ingredient for a great loop - tension. The third bar of the cycle seems to 'hang', with the lyrics and the drums propelling it on whilst the harmony has been frozen in an unusual place. Imagine the loop with the Ab major chord coming on beat one of bar 3. Boring eh?
2. Frank Zappa, Eat That Question
This song introduced me to the magic of the Fender Rhodes and George Duke. It's just what some people call a 'monster riff'. No syncopation, no rests, no wonkiness, no harmony exactly...but it's just so tasty.
One thing I realised was common to all of the tracks I was shortlisting for this post was that the riffs never implied chord V very strongly. Chord V is a bit of a party-pooper when it comes to repeating riffs I think - it's definitely used, but a clear V-I cadence opens the window for the tension being built up to just fly out of. The cooler plagal sound of IV, and its hip friends biii and bVII bear repetition a lot more easily.
Mr Day is a based around a riff on a 12 bar blues form, but instead of a last 4 bars using chord V (either as ii-V-I or V-IV-I) , it descends through IV and iii. Rhythmically we're propelled along this bit by the crotchets too. It's simple but clever little alteration to the blues that makes the riff endlessly listenable and fun to play:
On the face of it these are all fairly simple pieces of music. The compositions could all be written down on one page of A4, if indeed any of them were ever written down in the first place. They all take something familiar - a beat, a mode, the blues form - and subtly sculpt it into a musical idea that has character and vibe when taken up by the musicians. Getting that mix of familiarity, simplicity and individuality right is what makes writing a killer riff so hard. I think it's a challenge that remains for everyone that composes, whether for their school funk band, a professional jazz orchestra or as an electronic musician; the bits that sound the simplest are sometimes the hardest to get right!