LP record

The LP (from long playing or long play) is an analog sound storage medium, specifically a phonograph record format characterized by: a speed of 33+1⁄3 rpm; a 12- or 10-inch (30- or 25-cm) diameter; use of the "microgroove" groove specification; and a vinyl (a copolymer of vinyl chloride acetate) composition disk. Introduced by Columbia Records in 1948, it was soon adopted as a new standard by the entire US record industry and, apart from a few relatively minor refinements and the important later addition of stereophonic sound in 1957, it remained the standard format for record albums during a period in popular music known as the album era. LP was originally a trademark of Columbia and competed against the smaller 7-inch sized "45" or "single" format by RCA Victor, eventually ending up on top. Today in the vinyl revival era, a large majority of records are based on the LP format and hence the LP name continues to be in use today to refer to new records.

At the time the LP was introduced, nearly all phonograph records for home use were made of an abrasive (and therefore noisy) shellac compound, employed a much larger groove, and played at approximately 78 revolutions per minute (rpm), limiting the playing time of a 12-inch diameter record to less than five minutes per side. The new product was a 12- or 10-inch (30 or 25 cm) fine-grooved disc made of PVC ("vinyl") and played with a smaller-tipped "microgroove" stylus at a speed of 33+1⁄3 rpm. Each side of a 12-inch LP could play for about 25 minutes, allowing for a total runtime of approximately 50 minutes.

Despite some earlier experiments and attempts at commercial marketing, the Long Play format did not begin to enjoy commercial popularity until the early 1950s.

Starting in 1926, the Edison Records company experimented with issuing Edison Disc Records in long play format of 24 minutes per side. The system and playback system (still mostly wind-up phonographs) proved unreliable and was a commercial failure.

By mid-1931 all motion picture studios were recording on optical soundtracks, but sets of soundtrack discs, mastered by dubbing from the optical tracks and scaled down to 12 inches to cut costs, were made as late as 1936 for distribution to theaters still equipped with disc-only sound projectors.

Unless the quantity required was very small, pressed discs were a more economical medium for distributing high-quality audio than tape, and CD mastering was, in the early years of that technology, very expensive, so the use of LP-format transcription discs continued into the 1990s. The King Biscuit Flower Hour is a late example, as are Westwood One's The Beatle Years and Doctor Demento programs, which were sent to stations on LP at least through 1992.

In September 1931, RCA Victor launched the first commercially available vinyl long-playing record, marketed as "Program-Transcription" records. These revolutionary discs were designed for playback at 33+1⁄3 rpm and pressed on a 30 cm diameter flexible plastic disc, with a duration of about ten minutes playing time per side. Victor's early introduction of a long-playing record was a commercial failure for several reasons including the lack of affordable, consumer playback equipment and consumer rejection during the Great Depression.

These "Program Transcription" discs, as Victor called them, played at 33+1⁄3 rpm and used a somewhat finer and more closely spaced groove than typical 78 rpm records. They were to be played with a special "Chromium Orange" chrome-plated steel needle. The 10-inch discs, mostly used for popular and light classical music, were normally pressed in shellac, but the 12-inch discs, mostly used for "serious" classical music, were pressed in Victor's new vinyl-based "Victrolac" compound, which provided a much quieter playing surface. These records could hold up to 15 minutes per side. Beethoven's Fifth Symphony, performed by the Philadelphia Orchestra under Leopold Stokowski, was the first 12-inch recording issued. Compton Pakensham, reviewing the event in The New York Times, wrote, "What we were not prepared for was the quality of reproduction ... incomparably fuller."