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Music Technician: Matthew McIntire

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What Makes Up a CD

"A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of an injection-molded piece of clear polycarbonate plastic. During manufacturing, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. We'll return to the bumps in a moment. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic."   The CD is made of polycarbonate plastic.  Aluminum is sprayed over to protect the plastic and the spiral.  Aluminum is an element with an atomic symbol of Al.
Cross-section of a CD

How do the structures play a role in how a CD player work.

The structure of the polycarbonate plastic is moldable when the first make it.  The polycarbonate plastic has a molded spiral or rigid bumps, that a laser reads as music.  The Aluminum on the CD is used as reflective material for the laser to read.  The acrylic is used to protect the aluminum so that it doesn't get scratched off, and the CD player's laser will still be able to read it.

What's Inside the CD Player

"The CD player has the job of finding and reading the data stored as bumps on the CD. Considering how small the bumps are, the CD player is an exceptionally precise piece of equipment. The drive consists of three fundamental components:
A drive motor spins the disc. This drive motor is precisely controlled to rotate between 200 and 500 rpm depending on which track is being read.
A laser and a lens system focus in on and read the bumps.
A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track. The tracking system has to be able to move the laser at micron resolutions."
 

How It Works

"What the CD Player Does: Laser Focus
Inside the CD player, there is a good bit of computer technology involved in forming the data into understandable data blocks and sending them either to the DAC (in the case of an audio CD) or to the computer (in the case of a CD-ROM drive).
The fundamental job of the CD player is to focus the laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light. The bumps reflect light differently than the "lands" (the rest of the aluminum layer), and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes."
 

How An MP3 Player Works

An MP3 player works about the same way a CD player works, except that the songs are compressed down to a smaller size.  A CD that has a 32 MB song on it, would be compressed to about 2 MB on an MP3 player.  All of them are digital recordings.

RESOURCES

Most of the information from this webpage was taken from Howstuffworks.com.  All of the pictures are taken from Howstuffworks.com also, except for the Lynard Skynard picture which was taken from Yahoo.com

"This page is not that of a real company but is for a chemistry assignment for General Chemistry 140 at Monmouth College."