In the beginning of the Golden Age, American radio network programs were almost exclusively broadcast live, as the national networks prohibited the airing of recorded programs until the late 1940s because of the inferior sound quality of phonograph discs, the only practical recording medium. As a result, prime-time shows would be performed twice, once for each coast. However, "reference recordings" were made of many programs as they were being broadcast, for review by the sponsor and for the network's own archival purposes. With the development of high-fidelity magnetic wire and tape recording in the years following World War II, the networks became more open to airing recorded programs and the prerecording of shows became more common.
Local stations, however, had always been free to use recordings and sometimes made substantial use of prerecorded syndicated programs distributed on pressed (as opposed to individually recorded) transcription discs.
Recording was done using a cutting lathe and acetate discs. Programs were normally recorded at 33⅓ rpm on 16 inch discs, the standard format used for such "electrical transcriptions" from the early 1930s through the 1950s. Sometimes, the groove was cut starting at the inside of the disc and running to the outside. This was useful when the program to be recorded was longer than 15 minutes so required more than one disc side. By recording the first side outside in, the second inside out, and so on, the sound quality at the disc change-over points would match and result in a more seamless playback. An inside start also had the advantage that the thread of material cut from the disc's surface, which had to be kept out of the path of the cutting stylus, was naturally thrown toward the center of the disc so was automatically out of the way. When cutting an outside start disc, a brush could be used to keep it out of the way by sweeping it toward the middle of the disc. Well-equipped recording lathes used the vacuum from a water aspirator to pick it up as it was cut and deposit it in a water-filled bottle. In addition to convenience, this served a safety purpose, as the cellulose nitrate thread was highly flammable and a loose accumulation of it combusted violently if ignited.
Most recordings of radio broadcasts were made at a radio network's studios, or at the facilities of a network-owned or affiliated station, which might have four or more lathes. A small local station often had none. Two lathes were required to capture a program longer than 15 minutes without losing parts of it while discs were flipped over or changed, along with a trained technician to operate them and monitor the recording while it was being made. However, some surviving recordings were produced by local stations.[7][8]
When a substantial number of copies of an electrical transcription were required, as for the distribution of a syndicated program, they were produced by the same process used to make ordinary records. A master recording was cut, then electroplated to produce a stamper from which pressings in vinyl (or, in the case of transcription discs pressed before about 1935, shellac) were molded in a record press.
//en.wikipedia.org/wiki/Old_time_radio
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