So I was watching this (https://www.youtube.com/watch?v=WkIR23emsWY) by technology connections and I just realized that I have no idea how CDs work. The video is about how some CD players can read audio of a CD where the data is just copied directly onto a CD with a computer whereas older players only had hardware compatible with CDs formatted as …. digital audio?
I was trying to figure it out on wikipedia, how is a commercial CD you’d buy in a store different from a CD with files copies onto it?
I remember my dad used to use a burning tool to make images. Why are they called images? How is an image different from a CD?
Why are some CDs readable and writable but some aren’t?
In: Technology
Since you’re already watching Technology Connections, I highly recommend going through his series on all the different ways we’ve recorded audio and video.
Let’s start with how digital audio works in general.
Imagine a [suspension bridge](https://cdn.britannica.com/76/22076-050-4F3391DC/suspension-bridge-forces-lines-tension-compression.jpg) and you wanted to record the shape of that top cable. One way to do that is to sketch the same shape on paper. The paper version is an analog of the shape, rising and falling in the same way. You can recreate the bridge by reversing the process and making the cable take the same shape as your drawing.
Digital audio is different. Instead, look at the vertical cables and pretend you measured each one and wrote down the length. What you wrote down is no longer an analog of the top cable, but you can still recreate that shape by cutting new vertical cables and laying a top cable down so it matches those. That’s how digital audio works.
Once you have that list of numbers there’s all sorts of ways to store them. A standard CD is very simple, with all the numbers for each song just written down one after another. There’s a directory that says where to find the tracks, and that’s basically it.
For an MP3 CD, the numbers aren’t just a simple list. They’ve been compressed. Basically, an algorithm finds ways of storing the numbers in ways that use less space. This can get very complicated, but imagine only writing down the difference between the heights of each cable, rather than the total height. That’s a smaller number that needs fewer bits to write down. The player decompresses this data back to the original number list before it reconstructs the audio. This makes a file like you have on a computer and can include metadata like artist, album, title, etc.
How this MP3 file is stored on the CD is different, too. This is a data CD, with an actual file system, file names, folders, etc. It’s far more complicated and capable. Which means it also needs a more capable computer to access and use the data.
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