Analog vs. digital signals | Waves | Middle school physics | Khan Academy

In this video, we're going to think about analog versus digital signals. One way to think about the difference is an analog signal is trying to reproduce exactly, in some type of a signal, what is going on, while a digital signal is converting it usually to ones and zeros, which then can be converted back.

So the first thing to realize is that almost any type of information, it might be how intense a certain color is or how bright it is, or it might be a frequency of sound. All of that can be represented as numbers. So whether you're trying to transmit an analog signal or a digital signal, it really is about how do you communicate numbers using some type of signal.

As an example, let's say that you are trying to communicate the number 24 to someone. Well, one way to do it as an analog signal, you could have, as time goes on, maybe this is some type of voltage across a wire. If you put that voltage right at what the other person receiving it could interpret it as 24, well then you would transmit it, and they might, if they get this nice clean signal, see it as a 24.

Now, the problem with analog signals is what happens when you have interference. So let's say this is a really long wire that you're transmitting it over, or you're transmitting it using radio waves, and there's a lot of bad weather or other types of interference. So on the receiving end, even though you transmitted something that looks like this—that is a clear 24—the other person might get something like this.

This isn't obvious that it's a 24 anymore; it goes between 20 and 30. This could be interpreted as static or a garbled-up message, or just doesn't sound as clean, depending on what the 24 is trying to represent, or the image isn't as clear if this is representing, say, the lightness or the brightness of a pixel.

Now, the other option is to convert that 24 into binary. So, 24 can be represented in binary as one one zero zero zero. Now, we have other videos on Khan Academy that explain how to convert back and forth between our decimal system that has ten digits, zero through nine, and the binary system, which has two digits, zero and one.

But in case you're curious, and you don't have to understand this to know the difference between analog and digital signals and when they might be useful. This first place is the ones place, just as you're used to, but instead of this being the tens place, this is the two's place. Instead of this being the hundreds place, this is the fourth place. Instead of this being the thousands place, this is the eighths place, and instead of that being the ten thousand's place, that's the sixteens place.

So one way to think about it is one one zero zero zero means one sixteen and one eight. If you add those together, you would get twenty-four. What would that actually look like as a signal? Well, it could look something like this, where the person interpreting it knows that over this first time period, whatever voltage you're getting tells you your first digit. Then over the next time period, whatever voltage you're getting tells you the second digit and so on and so forth. So this would be one one zero zero zero.

Now, why is this useful? Well, let's think about the situation where all of a sudden there's interference again. Now, with the interference, you could still interpret this exactly as one one zero zero zero. Remember, the person receiving the signal, or the system receiving the signal, is just trying to determine whether it's getting a one or a zero.

So, even though this is being perturbed right over here, it's clear that we are at a one. We know that it would not be a point nine or one point one; it has to be either one or a zero. So it's clear that over this part right over here, you're getting a one, and then over here, you're getting three zeros. So they would be able to interpret it as one one zero zero zero, which is once again exactly twenty-four.