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3.2.6Music To the Brain: Your Brain’s Automatic Overtone-processing Skill
Although you think you only hear Middle C, (the fundamental, at 261.6 Hz), your brain sort outs all the overtones. Automatically. Without the slightest conscious effort on your part. A miraculous feat of naturally-selected engineering.
Any note you play on any musical instrument is named for the fundamental, even though each note comes with a bunch of overtones.
Your brain has evolved mechanisms to identify harmonic relations. It breaks a tone into its various harmonics or overtones, analyses them, then puts them back together to identify the sound as a specific tone (as opposed to random noise).
Because the separate harmonics are related to each other in simple frequency multiples (Table 4 above), the brain understands that a single soundmaker must be producing them. The necessity of identifying soundmakers probably drove the evolution of the brain’s naturally-selected ability to parse a tone into its overtones. In Palaeolithic times, having the capacity to tell the difference between an owl’s hoot and a lethal predator’s growl would have saved you from getting eaten.
The harmonic series is sometimes known as the chord of nature, because it’s not cultural in origin; it’s a phenomenon of nature. Any tone, whether coming from a musical instrument or not (e.g., pinging a wine glass), consists of a fundamental plus a batch of overtones that are always related to the frequency of the fundamental as integer multiples of the fundamental.