这段文字能够很好的解释这个公式:

To find the energy at a particular frequency, spin your signal around a circle at that frequency, and average a bunch of points along that path.

现在对这个傅立叶还不够理解,所以很难用中文表达:

将你的信号绕着频率旋转一周,平均分布在边缘上的点,便是该频率的能量。