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Analog vs. digital signals

Information can be stored and transmitted using an analog or digital signal. Analog signals reproduce real-world data, while digital signals convert this data into binary form. Interference can distort analog signals, making them unclear. Digital signals, however, remain clear despite interference because they only need to distinguish between ones and zeros. Created by Sal Khan.

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Video transcript

- [Narrator] In this video we're gonna think about analog versus digital signals. And 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 the 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. And as an example, let's say that you are trying to communicate the number 24 to someone. Well, one way to do it is as an analog signal. You could have, as time goes on, maybe this is some type of voltage across a wire. And 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. And so on the receiving end even though you transmit something that looks like this, that is a clear 24, the other person might get something like this. And so this isn't obvious that is a 24 anymore. It goes between 20 and 30, and 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 1 1 0 0 0. Now we have other videos on Khan Academy that explain how to convert back and forth between our decimal system that has 10 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 twos place. Instead of this being the hundreds place, this is the forth place. Instead of this being the thousands place, this is the eights place. And instead of that being the ten thousandths place, that's the sixteens place. So one way to think about it, 1 1 0 0 0 means 1/16 and 1/8. And if you add those together, you would get 24. 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, that tells you your first digit, that 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 1 1 0 0 0. 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 1 1 0 0 0. 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 0.9 or 1.1. It has to be either one or 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 zero. So they would be able to interpret it as 1 1 0 0 0, which is once again exactly 24.