CD Players
CD players operate according to the same principles that DVDs and laser discs do. They're somewhat simpler than those devices because they only carry audio information, not video information, but otherwise they're pretty much the same. To understand how the laser of the CD player reads the music, it helps to understand how the CDs themselves are constructed.
Construction
CDs consist of a thin layer of aluminum sandwiched between a clear piece of plastic on the bottom and a piece of acrylic on top. The aluminum contains a series of bumps and divots, which extend outward in a long, continuous spiral. The bumps are so tiny as to be invisible to the naked eye. They form an elaborate binary code: a series of 1s and 0s, much the same as the information stored in a computer. That code contains the music of the CD. It then becomes a question of translating it as such.
Laser
The laser in the CD player moves along the string of code when it plays the CD. It starts on the innermost part of the CD and slowly spirals outward--much like an old record player, only in reverse. As it reflects off the aluminum, it bounces back into an optical reader. However, when it strikes one of the bumps, it changes directions slightly and the receiver doesn't pick it up. Those two states form the basis of the binary code--on/off or 1/0--which creates the digital signal. The hardware in the CD player then translates that into sound and amplifies it to play out of your speakers.
Tracking
The laser has to move at a steady pace across the CD into order to pick up the signals properly. The bumps on the outside of the CD move past it more quickly than the inside of the CD, which can disrupt the signal. So a tracking system within the CD player makes sure that the laser stays pointed where it's supposed to and a spindle motor varies the speed of the disc so that the bumps pass over the laser at the same rate throughout the playing time.
Subcode Data
In addition to the bumps themselves, most CDs contain subcode data, which help divide the information into specific sections. That allows you to skip ahead on the CD to a new track automatically. It can also tell more sophisticated CD players the title of the song, the title of the album and the artist.
Tags: laser player, much same
