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WPI Technical Theatre Handbook: Compact Disc (CD)
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Compact Disc (CD)

Another format familiar to most people is the compact disc. Until recently, this media was for all intents and purposes play-only. No consumer equipment existed to record CDs, so recording was an option only for the wealthy. Other folks were forced to use pre-recorded material, which wasn't a total loss, as several good sound effects libraries are available on compact disc.

A CD is a circular plastic disc just under 5 inches in diameter. Encased in the plastic is a thin layer of aluminum or gold. This aluminum has a series of pits and bumps that represent digitally encoded data. These pits and bumps are read by shining a low-powered laser at the disc and detecting the reflection. Compact discs, like DATs, store information digitally. They offer 16-bit resolution at a 44.1KHz sampling rate.

Compact discs and their associated players offer many advantages over any form of tape. First, CDs have no moving parts, and reading data off of a CD is largely a non-contact operation. This means that CDs have an extremely long life. Playing a CD does not appreciably affect the media, which is an incredible advantage over tape. Secondly, CDs have an effective indexing scheme so that up to 99 individual audio tracks may be called up almost instantly. The seek speed is a function of the actual CD player being used.

Recent advances in technology have made affordable, personal CD recording equipment possible. Recordable CDs are made of a metal alloy and a special organic dye. The recording process involves the use of a laser to heat the dye, and consequently deform the metal alloy layer. This creates pits and the bumps, just like those on mass-produced CDs, which are manufactured in an entirely different manner using a press. Recordable CDs can hold up to 74 minutes of audio, and as of this writing cost about $5 each. Recordable audio CDs can only be written once, they are not erasable.

For well under $1000, a CD burner can be purchased for a personal computer. With appropriate software, audio CDs can be created with relative ease. Several facilities on the WPI campus offer the capability to burn CDs, generally for only the cost of the blank CD.

next up previous contents index
Next: Mini-Disc (MD) Up: Input Previous: Digital Audio Tape (DAT)   Contents   Index
Steve Richardson 2000-07-06

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