In the harmonic series, the first harmonic is which interval above the fundamental?

• A. An octave
• B. A fifth
• C. A major third
• D. A minor second

Answer: (A)

In the harmonic series, pitches align at whole-number multiples of the fundamental frequency. The next partial after the fundamental is twice the frequency, which sounds as the same note higher—an octave above. That makes the first harmonic above the fundamental an octave. The other intervals come in later partials: the fifth appears after the octave in the series, while a major third or a minor second aren’t the earliest intervals produced by the initial partials. So the octave is the correct interval.