The harmonic series is a sequence of frequencies that are whole-number multiples of a fundamental frequency. It begins with the fundamental (the 1st harmonic) and continues upward: the 2nd harmonic is twice the fundamental frequency, the 3rd is three times, and so on.
For example, with a fundamental of 100 Hz:
- 1st harmonic: 100 Hz
- 2nd harmonic: 200 Hz
- 3rd harmonic: 300 Hz
- 4th harmonic: 400 Hz
The relative amplitudes and phases of these frequencies determine the character of a sound, which makes the harmonic series the basis of timbre in most pitched instruments. Instruments and synthesis techniques use it to create rich, resonant tones or to imitate acoustic sounds.