The groove may be simple, but its relationship to the song’s chord progression is not. To learn much more about chords and harmony and how they build the emotional structure of a song, you can check out our new course Unlocking the Emotional Power of Chords, but consider this a primer in case you’re ready.
In 12-TET, you don’t define your intervals by tidy ratios of whole numbers. Instead, you divide up the octave into twelve equally-sized semitones (the interval between two adjacent piano keys or guitar frets). You then add semitones together to make all the other intervals. To go up a semitone from any note, you multiply its frequency by the 12th root of two. To go down a semitone from any note, you divide its frequency by the 12th root of two. If you go up by an octave (12 semitones), you’re multiplying your frequency by the 12th root of two 12 times, which works out to two.