# Harmonic

If a signal (representing acceleration, displacement, sound pressure etc.) is composed of a number of components of frequencies which are all integer multiples of one (fundamental) frequency, these components are said to form a harmonic train. The component at twice the fundamental frequency would be known as the second harmonic, the component at three times the fundamental frequency the third harmonic, and so on. Harmonic response is the periodic response of a vibrating system exhibiting the characteristics of resonance at a frequency that is a multiple of the excitation frequency.

Fundamental, 2^{nd}, 3^{rd}, 4^{th}, 5^{th}, 6^{th} and 7^{th} harmonic.

The fundamental frequency of a harmonic tone is usually heard as its pitch, even when there is no energy at that frequency. This reflects the importance of harmonic tones in the experience of hearing, especially in the human voice.

- A harmonic series implies a fundamental whether or not one is present.
- In many cases, we will hear the fundamental of a harmonic series as its pitch even if there is no fundamental.

**See also: **Clipping, Frequency, Fundamental, Harmonic Analysis, Missing Fundamental, Overtone, Subharmonic, Subsynchronous.

**Subjects: ** Noise & Vibration