Analog and Digital Signals

The real world doesn't come in neat little chunks. Sound, light, and motion all change smoothly and endlessly, that's what we call analog. Sing a note and your voice wobbles up and down every tiny fraction of a second; there's no limit to how much detail is really there.

Computers can't store an endless stream of detail, so they turn analog information into digital information: a long list of numbers written as 1s and 0s. To do this, a computer samples the analog signal, meaning it takes a quick snapshot of the wave's value many times every second, then rounds each snapshot to the closest number it can store.

The more snapshots the computer takes per second, the closer the digital copy sounds or looks to the original analog signal. That's why digitizing something always loses a tiny bit of detail, but it also means the result can be copied, saved, and sent around the world without wearing out.

Every computer and phone that talks to another device is really just sending patterns of 1s and 0s back and forth. Even a plain number gets turned into bits first. The number 5 is 101 in binary, so a computer could send it using three wires: one wire turned on, one turned off, one turned on.

Real networks send those same 1s and 0s as electric or radio pulses racing down a cable or through the air. Each pulse is either high (a 1) or low (a 0), so a receiver only has to tell which one it got, not measure some wobbly in-between value the way it would with an analog wave.

That's the whole trick behind digitizing a message: turn it into numbers, turn the numbers into a stream of pulses, send the pulses, and let the receiving device read the pattern back and rebuild the original message.

Once a signal has been digitized into numbers, those numbers have to be stored or sent somewhere, and that takes up space. The more detail a digital file keeps, the bigger it gets.

Compression is a trick for shrinking a digital file without losing the information that actually matters. There are two kinds. Lossless compression squeezes a file down while keeping every single bit of the original data, so you can rebuild it perfectly. Lossy compression throws away some detail people won't really notice, like tiny changes in sound or color, so the file can shrink even more.

This is one of the big reasons digital signals beat analog ones for sending and storing information: once something is a list of numbers, you can compress it, copy it exactly, and send it again and again without it wearing out or picking up extra noise.

Some digital files, like photos, videos, and songs, try to capture an enormous amount of real-world detail. Keeping every bit of that detail would make the file huge, and our eyes and ears can't even notice all of it anyway.

Lossy compression shrinks a file by throwing away the least important information first, the details people are least likely to miss. A photo might lose some subtle color differences, or a song might drop sounds too quiet to hear over louder ones.

Because lossy compression permanently deletes some of the original data, you can't get the exact original file back afterward. But the file becomes much smaller, which makes it faster to send and easier to store, one more reason digitized signals travel so well compared to analog ones.

Pictures on a screen are just huge grids of numbers, one number for the color of every tiny dot, or pixel. Storing every single pixel's number takes a lot of space, so computers look for shortcuts.

One simple shortcut is called run-length encoding. Imagine a row of pixels that's white, white, white, white, then black, black, black. Instead of writing white four separate times, the computer just writes four whites, then three blacks. That's a much shorter way to say the exact same thing.

This is lossless compression: the file gets smaller, but when you unpack it again, you get back the exact original picture, pixel for pixel. No detail is lost, which is exactly why digital copies of pictures, sounds, and other signals can be stored and shared again and again without decay.