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 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 more than 20 minutes. Only the microgroove standard was new, as both vinyl and the 33 1⁄3 rpm speed had been used for special purposes for many years, as well as in one unsuccessful earlier attempt to introduce a long-playing record for home use by RCA Victor.Although the LP was suited to classical music because of its extended continuous playing time, it also allowed a collection of ten or more pop music recordings to be put on a single disc. Previously, such collections, as well as longer classical music broken up into several parts, had been sold as sets of 78 rpm records in a specially imprinted "record album" consisting of individual record sleeves bound together in book form. The use of the word "album" persisted for the one-disc LP equivalent.The prototype of the LP was the soundtrack disc used by the Vitaphone motion picture sound system, developed by Western Electric and introduced in 1926. For soundtrack purposes, the less than five minutes of playing time of each side of a conventional 12-inch 78 rpm disc was not acceptable. The sound had to play continuously for at least 11 minutes, long enough to accompany a full 1,000-foot (300 m) reel of 35 mm film projected at 24 frames per second. The disc diameter was increased to 16 inches (40 cm) and the speed was reduced to 33 1⁄3 revolutions per minute. Unlike their smaller LP descendants, they were made with the same large "standard groove" used by 78s.Unlike conventional records, the groove started at the inside of the recorded area near the label and proceeded outward toward the edge. Like 78s, early soundtrack discs were pressed in an abrasive shellac compound and played with a single-use steel needle held in a massive electromagnetic pickup with a tracking force of five ounces (1.4 N).
Longer pieces recorded live, which extended over the course of several discs, pioneered the system of recording odd-numbered sides inside-out and even-numbered sides outside-in so that the fidelity would match when changing sides or discs. Since no changers were present in radio broadcasting, the sides had to be pressed in a hybrid of manual and automatic sequencing, arranged in such a manner that no single disc had to be turned over to play its other half, i.e., instead of a three-disc set having 1–2, 3–4 and 5–6 for manual or 1–6, 2–5 and 3–4 for automatic, broadcast sequences would have 1–4, 2–5 and 3–6.Some transcriptions were recorded with a vertically modulated "hill and dale" groove, as this was found to allow not only a deeper bass due to the fact that turntable rumble was laterally-modulated in early radio station turntables, but also an extension of the high-end frequency response, neither of which was necessarily a great advantage in practice because of the limitations of AM broadcasting. However, today we can enjoy the benefits of those higher-fidelity recordings, even if the original radio audiences could not.Beginning in the mid-1930s, one-off 16-inch 33 1⁄3 rpm lacquer discs were used by radio networks to archive recordings of their live broadcasts, and by local stations to delay the broadcast of network programming or to prerecord their own productions. In the late 1940s, magnetic tape recorders were adopted by the networks to prerecord shows or repeat them for airing in different time zones, but 16-inch vinyl pressings continued to be used into the early 1960s for non-network distribution of prerecorded programming. The LP's microgroove standard began in the late 1950s, and in the 1960s the discs were reduced to 12 inches, becoming physically indistinguishable from ordinary LPs.RCA Victor introduced an early version of a long-playing record for home use in September 1931. 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 78s. 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 normally pressed in Victor's new vinyl-based Victrolac compound, which provided a much quieter playing surface. They 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. The New York Times wrote, "What we were not prepared for was the quality of reproduction...incomparably fuller.
Longer pieces recorded live, which extended over the course of several discs, pioneered the system of recording odd-numbered sides inside-out and even-numbered sides outside-in so that the fidelity would match when changing sides or discs. Since no changers were present in radio broadcasting, the sides had to be pressed in a hybrid of manual and automatic sequencing, arranged in such a manner that no single disc had to be turned over to play its other half, i.e., instead of a three-disc set having 1–2, 3–4 and 5–6 for manual or 1–6, 2–5 and 3–4 for automatic, broadcast sequences would have 1–4, 2–5 and 3–6.Some transcriptions were recorded with a vertically modulated "hill and dale" groove, as this was found to allow not only a deeper bass due to the fact that turntable rumble was laterally-modulated in early radio station turntables, but also an extension of the high-end frequency response, neither of which was necessarily a great advantage in practice because of the limitations of AM broadcasting. However, today we can enjoy the benefits of those higher-fidelity recordings, even if the original radio audiences could not.Beginning in the mid-1930s, one-off 16-inch 33 1⁄3 rpm lacquer discs were used by radio networks to archive recordings of their live broadcasts, and by local stations to delay the broadcast of network programming or to prerecord their own productions. In the late 1940s, magnetic tape recorders were adopted by the networks to prerecord shows or repeat them for airing in different time zones, but 16-inch vinyl pressings continued to be used into the early 1960s for non-network distribution of prerecorded programming. The LP's microgroove standard began in the late 1950s, and in the 1960s the discs were reduced to 12 inches, becoming physically indistinguishable from ordinary LPs.RCA Victor introduced an early version of a long-playing record for home use in September 1931. 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 78s. 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 normally pressed in Victor's new vinyl-based Victrolac compound, which provided a much quieter playing surface. They 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. The New York Times wrote, "What we were not prepared for was the quality of reproduction...incomparably fuller.
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