The frequency domain

The author aims to give you some idea of what a pole is and why it is a significant concept. To do this, he gives a tour of the mysterious world that control engineers call the frequency domain. The article is intended as a conceptual preview for undergraduate students and assumes minimal technical background. The frequency domain is a kind of hidden companion to our everyday world of time. We describe what happens in the time domain as temporal and in the frequency domain as spectral. Roughly speaking, in the time domain we measure how long something takes, whereas in the frequency domain we measure how fast or slow it is. Why do control engineers like the frequency domain so much? In a nutshell, the reason is this: most signals and processes involve both fast and slow components happening at the same time. Frequency domain analysis separates these components and helps to keep track of them.