Digital and analog information | Information Technologies | High School Physics | Khan Academy

In this video, we're going to talk about analog versus digital. Something that's analog can be any value within a given range, while something digital is represented by a number of discrete or separate levels.

To distinguish these two ideas, I like to think about clocks. An analog clock has the numbers and the hands, and it's analog because the motion of those hands is continuous. They can sweep across the circle, representing any of infinite times on that clock. For example, between 3:06 and 3:07, the minute hand is actually going to be at some point between those marks on the clock, showing one of the infinitely possible times that the clock can represent.

Compare that to a digital clock. A digital clock is only going to show you 3:06 or 3:07; it will never display any of the many fractional seconds between those two times. Digital only takes on certain discrete values, and it has a finite number of those values. So, an analog waveform signal will smoothly sweep across the infinitely many possible values it has, while a digital waveform signal will only be at one of a number of discrete values. So, the shape of the wave will be more square or step-like.

Let's check out an example so this makes a little more sense. I like music, so we're going to talk about sound. Sound is an analog signal or wave. So, if we look at a graph of sound volume over time, it's going to have a smooth, continuous analog waveform. Both the amplitude, or the volume, and the frequency, what we hear as pitch, are changing continuously between infinite possible values.

Alright, and that's because sound waves, the vibration of particles propagating through the air, actually change continuously. The very first sound recording and reproduction technology imprinted that analog wave directly onto a material. For example, records imprint that sound wave into vinyl, and cassettes print the sound wave onto tape. A major drawback of this technology is that for the sound to play back exactly as it was recorded, that waveform needs to stay untouched.

Right? So think about scratching vinyl or stretching or smudging a cassette tape. That's directly deforming the wave, so you'll never be able to reproduce the sound exactly as it was recorded. So, technology advanced, and sound waves became digitized. Here's how.

Alright, so recall our analog sound wave. We have a smooth analog wave that's taking on any number of infinitely possible values within this range. In order to digitize this wave, we're going to describe numbers to the amplitude at different points. Alright, watch as magic! So we go over here and make a scale.

So, we're breaking up the amplitudes into discrete possibilities. Then we can go through the wave and at specific points of the wave, measure what is the amplitude based on that scale. So, over here we're at the first point of the scale, at this peak. We're at the second point of our scale, then the first, the third, the second, the fourth, back down to the first. Now that we have this wave broken up into discrete levels, right, we can ascribe the numbers, and we effectively turn this analog wave into a set of numbers: one, two, one, three, two, four, one.

Our wave has been digitized. Now that the digitized wave can be played back through a speaker to recreate the analog wave, as long as a sampling happens at a quick enough rate, humans can't tell the difference.

Alright, so the digitization of waves is all about ascribing specific numbers to some of those mechanical properties of the wave. The important thing here is that now that the wave has been digitized, the digitized sound wave can be reliably stored, processed, and communicated with computers.

So, some information is lost in translation, but once the wave is digitized, its quality will never degrade. Okay, and that allows for a lot more reliable technology because the wave is represented with numbers instead of it being physically imprinted on some material.

So, humans prefer to store information like sound digitally, and there are ways to turn analog signals, which can represent any of infinite possible values, into digital information, which is useful because information is stored only at a number of discrete or separate levels.