What Is Harmonic Frequency?

Harmonics help you distinguish different musical instruments

A blocky, rainbow colored equalizer graph
A harmonic frequency is a regular and repeating multiple of an original wave pattern. franckreporter/Getty Images
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If you have studied any discipline of acoustics, radio signal technology, or electronics engineering, you might remember covering the topic of harmonic frequency. It is an integral part of how music is heard and perceived. The 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 same note.

Definition of Harmonic Frequency

A harmonic frequency is a regular and repeating multiple of an original wave pattern, known as a fundamental frequency.

If the original wave is set at 500 hertz, it experiences a first harmonic frequency at 1000 hertz, or double the fundamental frequency. The second harmonic frequency occurs at 1500 hertz,  which is triple the fundamental frequency, and the third harmonic frequency is 2000 hertz, which is quadruple the fundamental frequency, and so on. 

In another example, the first harmonic of the fundamental frequency 750 hertz is 1500 hertz, and the second harmonic of 750 hertz is 2250 hertz. All harmonics are periodic at the fundamental frequency and can be broken down into a series of nodes and antinodes.

Effects of Harmonic Frequency

Almost all musical instruments produce a characteristic standing wave pattern that contains both fundamental and harmonic frequencies. The exact composition of these frequencies 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 the same. Skilled musicians can instinctively tune instruments by listening to and comparing harmonic frequencies between adjustments.

Harmonics Versus Overtones

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 contribute to the overall quality or timbre of instrumental sound.