Rooted interval
A rooted interval is in the context of octave equivalence a rational interval over an power of 2, i.e. of the form [math]\displaystyle{ x/2^n }[/math] for any positive integer x and nonnegative integer n.
Playing a rooted interval in a harmonic timbre, the virtual fundamental is of the same pitch as the bass, or whole octaves below the bass. In other words, the virtual fundamental is in the same pitch class as the bass. This gives rooted intervals the distinct characteristic of securing its own bass than suggesting other pitch classes.