What causes overtones to be heard?
Overtones are often called harmonics. this happens when an oscillator is excited. and most of the time the harmonics are not constant and thus different overtones decay at different times
most oscillators such as the string of the guitar will vibrate at normal frequencies.
these normal frequencies at their lowest are called fundamental frequency. But, when an oscillator is not tuned and is excited, it oscillates at different frequencies.
thus the higher tones are called overtones. And since they oscillate at such different frequencies they also decay at different rates.
thus enabling our ear to hear them.
a trained ear can hear these changes and overtones in a single note!