Lecture 1, Introduction | MIT RES.6.007 Signals and Systems, Spring 2011

[MUSIC PLAYING] PROFESSOR: I'm Al Oppenheim, and I'd like to welcome you to this videotape course on signals and systems. Signals, at least as an informal definition, are functions of one or more independent variables that typically carry some type of information. Systems, in our setting, would typically be used to process signals. One very common example of a signal might be, let's say, a

speech signal. And you might think of the air pressure as a function of time, or perhaps the electrical signal after it goes through the microphone transducer as a function of time, as representing the speech signal. And we might see a typical speech signal looking something like I've indicated here. It's a function of time, in this particular case.

And the independent variable, being time, is, in fact, continuous. And so a signal like this, we will typically be referring to as a continuous time signal. Now, it also, for this particular example, is a function of one independent variable. And that will be referred to as a one-dimensional signal corresponding to the fact that there's only one independent

variable instead of several independent variables. So the speech signal is an example of a continuous time, one-dimensional signal. Now, signals can, of course, be multi-dimensional. And they may not have, as their independent variables, time variables. One very common example are the examples represented by images. Images, as signals, we might think of as representing

brightness, as it varies in a horizontal and vertical direction. And so the brightness as a function of these two spatial variables is then a two-dimensional signal.