How it Works
CD vs. Cassette
Applications
DVD Future
Computers
Television
DVD Central
Charting "the next big thing" in the consumer electronics
market. By E-Town.
How
Things Work: CD's
Answers to common questions by University of Virginia
Physics Professor Louis A. Bloomfield.
Eastman-Kodak
Developers of the PhotoCD standard.
|
How
it Works
The compact disc is essentially a small plastic-coated aluminium disk
on which tiny holes are pitted on one side, creating spiralling rows of
hills and valleys. When inserted in a CD player, or drive, the disc is
turned, and a low-powered laser beam is directed
at the pits. The drive interprets the hills and valleys as on and off,
which are converted by a photodiode into varying electrical signals. Where
there is a pit, the laser is not reflected on the photodiode, but when
there isn’t a pit, the light bounces into the photodiode,
producing a signal. This process creates a digital audio format, which
at the time was remarkably superior to existing technologies.
CD vs. Cassette
CD’s were considered superior to magnetic recording tape because of
its ability to produce over 65 000 levels of voltage  ,
resulting in better dynamic range and the elimination of noise, or "hiss".
As well, the CD is highly reliable, with no moving parts on the media (the
disc itself), and nothing but light touches it. Unfortunately, costs are
still relatively prohibitive - they cost slightly more to produce, the
players are more expensive than basic cassette players, and until recently
it was impossible to record on them. Even today, recordable CD’s are very
expensive. But despite these setbacks, the CD was slowly adopted, and music
stores are seeing cassette sales dwindle.
Applications
The Compact Disc technology has been adopted for several other recording
technologies. CD-ROM (Compact Disc - Read Only Memory) drives, which store
digital information for computers, have become a standard feature on multimedia
computers, with most commercial software now distributed on this technology.
Also, Eastman-Kodak developed the PhotoCD standard, which can store 100
high resolution digital images on a single disc. For video recording, the
relatively expensive LaserDisc format uses oversized discs to deliver high
resolution digital images in home-theatre set-ups.
DVD Future
Despite these many advantages, the current Compact Disc standard is
doomed to be replaced by the even better Digital Versatile Disc, or DVD.
Current CD’s can hold 74 minutes of audio, or 650MB of computer data, and
even the larger LaserDiscs don’t hold as much as DVD, which can "stack"
two layers of data on one side. This technology is currently available
as a LaserDisc replacement, delivering high quality compressed MPEG video
and Dolby 3-D audio, but will also soon replace CD-ROM drives in computers,
eliminating the need for several discs to complete sophisticated computer
games. When the prohibitive price drops, they will also replace audio CD’s. |
