Here's my explanation: think of linear regression. Now ask yourself, what if I applied the idea of correlation/regression to a sine wave. An (audio) signal can

Here's my explanation: think of linear regression. Now ask yourself, what if I applied the idea of correlation/regression to a sine wave. An (audio) signal can be broken down into an addition of sine waves having different frequencies and phases. That, conceptually, is what we're trying to do with the Fourier Transform. What frequencies is the sound wave composed of, and of what amplitude. Phase angle is a consideration, but we are less interested in that. OK, that's a paragraph instead of a sentence, but it does motivate the whole raison d'etre of "why would I care anyway?"