LP

(Long Play) An analog audio recording pressed in vinyl that rotates at 33.3 RPM. Sound is literally "carved" into the platter in a spiral groove, starting at the outer edge of the platter. The undulations in the groove are an analog of the original acoustic waves. A needle (stylus) is placed in the groove which oscillates as the platter rotates. The oscillations are converted to electricity, amplified and sent to the speakers.

A Major Improvement
Mono LPs were introduced in the late 1940s, and stereo LPs in 1958. Two-channel stereo was accomplished by creating a V groove with left and right channels at 90 degree angles. The "long" play refers to the slower 33.3 RPM compared to 78 RPM records. The slower rotation increased the recording time per side from five minutes on a 78 to a half hour for the LP. Made of shellac resin, 78 records were brittle and easily breakable, but they were the primary music disc from the start of the 20th century until the late 1950s. The vinyl construction of the LP made it much more durable. Vinyl was also used for 45 RPM records, which were introduced in the late 1940s.

Still Hanging On
Although eclipsed by CDs in the 1980s, a small number of vinyl LPs have been pressed in the 21st century. LP phonograph turntables, typically high-end audiophile quality, are also being manufactured. See CD and turntable.