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Constant angular velocity
From Wikipedia, the free encyclopedia
Constant angular velocity (CAV) describes the motion of a body rotating at a constant angular velocity, because as it rotates it moves through a constant angle per unit time. CAV is one method of writing or reading information from a rotating data disc.
An LP record spins at an angular rate (CAV) of 33⅓ rpm. Because the linear distance travelled by the phonograph stylus per revolution of the record decreases as it moves closer to the center of the disc, the data rate decreases. When LPs were introduced in 1948, motor speed control was not nearly as accurate as it is today, and the more desirable constant linear velocity (CLV) would have been more difficult to achieve. Thus a record cut and replayed with CLV would have suffered increased wow and flutter distortions.
When playing back music, a compact disc (CD) employs CLV to maintain a constant data rate. The motor speed decreases from 495 to 212 rpm as the read head moves away from the center to keep the disc moving past the read head at a constant linear velocity.
- Constant linear velocity (CLV)