EECS20N: Signals and Systems


This course is about signals and systems. Consider the following familiar sounds:

If you had a java-enabled browser, you would see an applet here.

These are the sounds of a modem dialing a telephone line, another modem answering, and the two modems negotiating to determine at what speed to communicate. Although you have almost certainly used one, do you know, really, what a modem is? It is a device that converts binary data (bit streams) into voice-like sounds for transmission over the telephone network. The telephone network is a system that carries voice-like sounds. What is a voice-like sound, really?

Why is there a sequence of sounds when the modem first connects? Generally the modems will try to communicate at the highest speed that is supported by both modems. The need to negotiate to determine what that speed is. You are hearing their negotiation. How do they really communicate? How does the negotiation converge to an agreement? What is the meaning of these sounds?

The modem that answers the phone answers with a tone that is plotted below:

If you had a java-enabled browser, you would see an applet here.

What does this plot really mean? What is its correspondence with the sound that we hear? We can show the sound in a very different way:

If you were able to run applets, you would have a display of sounds.

Here, the sound has been broken down into frequency components, and the amplitude of each component is plotted. It suggests that the answering modem is producing a tone at about 2100 Hertz. What does this mean? How does the originating modem recognize this tone?

These are the questions that this course answers. It is about the structure of signals (audio, video, images, events, and command sequences) and the systems that operate on these signals. It is particularly about signals in the real world and about how these signals are managed in the computational world. And it is about computational systems that engage the real world.