Harmonics or Overtones

Author: N.H. Crowhurst

We have described the two main properties of any single sound: frequency (which we recognize as pitch) and intensity (which we recognize as loudness). But there are other differences by which we can tell one sound from another, even if both are of the same frequency and intensity (pitch and loudness). For example, a violin and a flute do not sound the same, even when they play the same note equally loudly. The difference in sound quality or timbre arises from the fact that every note on any musical instrument consists of not just one frequency, but a combination of several frequencies.

A string vibrating in different ways produces different overtones.

These additional frequencies are multiples of the lowest frequency (called the fundamental), which is usually the one that determines the pitch of the note. If the fundamental is 440 cycles per second (A above middle C), the same instrument will produce a range of frequencies that are multiples of 440 cycles at the same time: 2 X 440, or 88° cycles, 3 X 440, or 1320 cycles, and so on up the scale. What makes the different instruments easily distinguishable is the fact that these overtones (or harmonics) may be present in different relative intensities; some may be absent entirely. Each instrument has its own characteristic "selection" of overtones in characteristic relative intensities.