Eli5:When one speaker is playing two (or more) frequencies of sound, think harmony in music) the resulting sine wave is an average of those two frequencies. How does the brain interpret it as two different notes when one speaker is playing the average of two frequencies?

Question

Eli5:When one speaker is playing two (or more) frequencies of sound, think harmony in music) the resulting sine wave is an average of those two frequencies. How does the brain interpret it as two different notes when one speaker is playing the average of two frequencies?

In: 11

Answer 1

The average of two sine waves is **not** a sine wave: [this is how it looks](https://www.desmos.com/calculator/yciw4ps3tm). While it looks “siney”, it also clearly has unequal peaks. It is also possible to “decompose” it back into original sines. Our ears have mechanical “sine decompositors” inside: they have parts that can only vibrate at some specific frequency, so each only picks up one sine wave. The brain gets sines already decomposed.