The Middle Ground
Illawarra Mercury
Saturday January 18, 2003
It's sort of in the middle. Least I think it is.
Normally, when faced with researching anything technical my brain starts to hurt. Even trying to read my video's instruction manual creates an immediate ache inside my skull.
But, in the name of answering this question, I persevered and here's what I figure is the right answer.
Your average CD is a bit of plastic, about 1.2mm thick. Most of it is something called an ``injection-moulded piece of clear polycarbonate plastic" (and even that phrase hurts).
When they're making the CD, that part has all these microscopic bits of data impressed into it. That data is in one long spiral of bumps and troughs. That spiral runs from the centre of the disc to the edge rather than starting from the outside. (That's why you can have those really small discs the size of business cards).
Next a thin layer of reflective aluminium is whacked over the top of those bumps. Then you get an acrylic layer on the top of that, on which the label is printed.
Now, if you put the CD in a player it will sit over the laser. What it does is pass through that polycarbonate thingo at the bottom, reflect off the aluminium layer and then something called an ``opto-electronic device" reads the changes in light. The bumps reflect light differently to the troughs and somehow the mechanical trickery of the machine allows it to transfer that into music.
I know that last bit doesn't sound very authoritative but my head started hurting too much to keep researching.
© 2003 Illawarra Mercury