What Is Harmonic Frequency? (Definition)

A blocky, rainbow colored equalizer graph
A harmonic frequency is a regular and repeating multiple of an original wave pattern. franckreporter/Getty Images

If you have studied any discipline of acoustics, radio signal technology, or electronics engineering (to name a few), you might remember covering the topic of harmonic frequency. It happens to be an integral part of how music is heard and perceived. Harmonic frequency is one component that helps us accurately determine the unique quality of sound made by different instruments, even when they are playing the exact same note.

Definition: A harmonic frequency is a regular and repeating multiple of an original wave pattern, known as a fundamental frequency. So if the original wave is set at 500 Hz, it would experience a first harmonic frequency at 1000 Hz, or double the fundamental frequency. The second harmonic frequency would be at 1500 Hz (triple the fundamental frequency), the third harmonic frequency would be 2000 Hz (quadruple the fundamental frequency), and so on. All harmonics are periodic at the fundamental frequency and can be broken down into a series of nodes and anti-nodes.

Pronunciation: hahr•mon•ik free•kwuhn•see

Example: The first harmonic of 750 Hz is 1500 Hz, and the second harmonic of 750 Hz is 2250 Hz.

Discussion: Most all musical instruments produce a characteristic standing wave pattern that contains both fundamental and harmonic frequencies. The exact composition of these frequencies is what allows the human ear to discern the differences between two vocalists singing notes in unison at the same pitch (frequency) and volume (amplitude) level.

This is also how we know that a guitar sounds like a guitar and not an oboe or a trumpet or a piano or a drum. Otherwise, everyone and everything would sound exactly the same. Skilled musicians can instinctively tune instruments by listening to and comparing harmonic frequencies between adjustments.

The term 'overtones' is often used in discussions relating to harmonic frequencies. Although similar – the second harmonic is the first overtone, the third harmonic is the second overtone, and so on – the two terms are in fact separate and unique. Overtones help contribute to the overall quality or timbre of instrumental sound.