LPs) in a certain sequence enabled them to be stacked and played on record changers. After the discs were stacked and one side of each disc had played, the entire stack would be turned over and replaced on the changer shelf. Thus, to be heard in the proper sequence, each disc of a four-disc set would contain, respectively, "sides" 1&8, 2&7, 3&6 and 4&5a practice known as "automatic sequencing", "changer sequencing" or "auto-coupling". In pre-LP days, classical symphonies and concertos, and later, original cast albums, would be recorded using this format. This "drop-automatic sequence" was designed for record changers which simply dropped records rather than reversing the stack as it was played in sequence. Other record changers, including some made as far back as the 1930s by RCA and GE in addition to the much later Thorens TD-224, were capable of reversing the stack automatically. The RCA and GE units kept the records stacked on the turntable and slid the top record to the side after playing it. A separate sequence, the "slide-automatic sequence," was made for these changers, with sides coupled 1&5, 2&6, 3&7 and 4&8. Some record changers could play both sides of each record. Manual sequence (sides coupled 1&2, 3&4, 5&6 and 7&8) worked with these. Examples were the Markel 75, Capehart turnover, Fisher/Lincoln, Garrard RC-100, and Thorens Symphony CD50/CD53 changers. During the late 1930s and early 1940s, Victor released 78 rpm record sets in all three sequences (with set numbers preceded by M for manual, DM for drop-automatic or AM for slide-automatic sequencing), for players of each of the three kinds it manufactured. Columbia used MM for drop-automatic sets of three or more records, X for manual and MX for two-record drop-automatic sets. Some radio station copies were produced in "relay sequence" to be played by a DJ on two turntables with no break between sides, which were coupled as 1&3, 2&4, 5&7 and 6&8. The slide-automatic sequence also allowed uninterrupted play with two turntables. See also CD changer References External links Stack-O-Matic Turntables, a retro-style record player with the changer feature manufactured by Crosley Radio Corporation , an article about a predecessor of the record changer V-M Audio Enthusiasts – a 1999 company that took over after Voice of Music was liquidated Australian inventions Turntables