Here is an easy explanation, before computers the Fourier transform of sound was computed using a bank of filters. Each filter was tuned to detect a certain fre

Here is an easy explanation, before computers the Fourier transform of sound was computed using a bank of filters. Each filter was tuned to detect a certain frequency. To go back from frequency to the original sound you have to replace the filters by sound generators (generating the same frequency the filter was tuned to) In my interactive sample below I have a filter tuned for each note of the piano (you'll need a microphone) https://htmlpreview.github.io/?https://github.com/aguaviva/GuitarTuner/blob/master/GuitarTuner.html https://htmlpreview.github.io/?https://github.com/aguaviva/G... It also works with guitars, in fact each string played openly should match each of the vertical lines. This is how I tune my guitar. There is more to it, but still it is a great start :)