Digital vs. Analog Stuff

Digital vs. Analog Stuff

Before we had DVD, or CD for that matter, most of us only knew the Analog world. When I think of Analog, I am reminded of the real world around us. There is no pure black or white, no exact absolutes. Video was the same way in the analog world. Let me start with some over simplication ok? In fact, in most of my articles here, I'm going to do my best to keep things simple. There is no shortage of extremely technical information on the internet already, so if you want more information, after you read this, feel free to Google any of my terms here, ok?

Ok, lets start by taking a step back. Think of a dial, like the speedometer in your car. Say it goes from 0 to 100 miles per hour, for example. If you look at it very careful while you're driving (which I don't recommend!) you will notice it move around a little, it might be somewhere between 54 and 55 mph, lets say. In fact, if you were to hold a magifiying glass over the needle, you could maybe even decide it was between 54 1/2 and 54 3/4. Then if you looked even closer, you could get more percise even. Now, follow with me a little bit, because this will be the base for the rest of the descussion, ok?

Lets say you look at it, and decide to just call it 54 1/2 mph. But someone else looks at it and says its more like 54 3/4. A third person might look really close and call it 54 5/8. Who cares, right?

Now lets look at the same thing on a Digital speedometer. Glowing green segments clearly show 54 mph. Anyone who looks can see that. Genius, right? But is it actually correct? Or is it rounding the number to the nearest whole number? Hmmm...

This is the good thing about something Digital, not just video, but music, or data, or anything else we care to count. 54 is always 54. There's no "static" or snow or bouncing needles, its just 54. If I make a digital copy of 54, then you copy 54, and on down the line for 1000 people, the end answer should still be 54. Compare this to the old school game, where you whisper a secret to someone next to you, then the next person passes it on, and by the end of the line, its not even close to what you said!

If I have a digital video clip, and I post it on the internet, and you copy it, you could repost it, and it would be exactly identical. That is why the Recording Industry is so worried about people who post videos or songs online. The copy is so perfect, there is no practical reason to buy the song, when the copy is just as good.

So, with that covered, here's a little brain teaser for you... Digital isn't exactly Better than Analog. But Digital is easier to make copies of an have the same quality from start to finish. If you start analog, and then make copies of the copies, you quickly go through "generation loss" and the finished product is not as good as the original.

Digital Compression
I'm sure you know about MP3 audio, at least you've heard of it, right? Apple's iPod brought MP3 into the main stream, but the MP3 audios have been around for a few years before then.

Let's start with a quick over view again, and then we'll have something useful to build on. The specific numbers aren't really important, but it gives you some theory. Lets start with a normal Music CD. Normally a CD can hold 80 minutes of audio (a 700 MB CD... the original 650 MB CD could hold 74 minutes, but we're trying to keep it simple right?)

Ok, lets say we buy a CD and want to listen to it on our iPod or other portable player. Until recently, the iPods and other players didn't have enough storage space to hold a whole CD, so we needed to find a different way. Enter the world of Compression.

In video, movies and animations, there is a phrase called Frames per Second. Normally video is 30 Frames per Second (fps). Movies are shot at 24 fps. Some animations are drawn at 12 fps. What does this mean, and what does it have to do with my MP3 audio? Wow, we're sure jumping around here! Hang on, we'll get there, I promise! There is a phrase "persistance of vision", maybe you've heard of it? It is loosely related to the phrase "the hand is quicker than the eye". If you were to look at a strip of movie film, you'd see the pictures, or frames. If you looked closely, you could see that some things moved from one frame to the next. But when we watch the movie, its just fast enough, and smooth enough, that we ignore the "jumps" between one frame and the next, and we see a smooth motion.

Ok, that's great, but we are talking about audio... I think :) Let me see if I can show you how a lossy compression scheme can work to save space in an audio file, and still make it sound pretty good. Imagine a series of values, from 1 to 10... 1, 2, 3, 4, 5... 10. Now if we were in analog, there would be an infinite number of fractional values between 1 and 2, right? Because we're in digital we could say that anything beyond .001 would be ignored. So we could have 1.001, 1.002, 1.003. or 1000 segments between 1 and 2. Now lets say we didn't need it to be that perfect, we're just going to listen to this song for entertainment while we're jogging, we're not trying to fool someone into believing we're actually at the symphony, ok? Well in that case, maybe we could cut down to 10 segments between 1 and 2... like 1.1, 1.2, 1.3, 1.4, etc... Wow, we've gone from 1000 down to 10. Because we don't need that percision, we've saved a lot of work and storage space. You could do the same thing in your check register, too! Say you know you'll never have more than $9,999.99 dollars in your account, you could narrow that last column, or write a little bit bigger. By slightly reducing your precision, you've saved some space. That's kind of how compression works. Or one way it works.

There's other ways as well. I alluded to the frames per second of video earlier. In Audio, or any other data for that matter, you can choose to sample at different intervals. I'm not going to go into quantum physics here ok? But it does make sense, if you measure something less often, you would need less room to write it down, right? CD audio is sampled at 44,100 times per second. If you drop that to 22,000 times a second, it still sounds pretty good, some people can tell there is a reduction in quality, but its not to bad. 11,000 times a second is a bit worse again. But 44 to 22 saves you half the space.

A few things to keep in mind there, once you eliminate the precision, you can't get it back. So from our 1.1, 1.2, 1.3 example, even if you add the zero back on, you only get 1.10, 1.20, 1.30, and there are no steps between. That's why a camera that can record directly to DVD can't make a movie as nice as a camera that shoots to a lower compressed format, even if everything else is equal.

If you really want to get into some details, places like Wikipedia.org are good places to start. Heres a link to their page about MP3, for example: http://en.wikipedia.org/wiki/MP3

Theres so much more, but this will give you some things to think about! Or not, right?

This article ©2000 - 2008 BlueStar Productions

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Article by Carlin Comm
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