Editing Vitaphone (section)

==Vitaphone soundtrack discs==

[[File:VitaphoneDemo.jpg|thumb|A Vitaphone projection system was demonstrated in 1926. Engineer E. B. Craft holds a soundtrack disc. The turntable, on a massive tripod base, is at lower center.]]

In 1924–1925, when Western Electric established the format of the system which would eventually be named Vitaphone, they settled on a {{convert|16|in|cm|adj=on}} diameter disc rotating at {{frac|33|1|3}}&nbsp;[[Revolutions per minute|rpm]] as a good practical compromise of disc size and speed. The slow speed permitted the 11-minute playing time needed to match the maximum running time of a then-standard 1000 foot (300 meter) reel of film projected at 24&nbsp;[[frame rate|fps]], yet the increased diameter preserved the average effective groove velocity, and therefore the sound quality, of a smaller, shorter-playing record rotating at the then-standard speed of about 78&nbsp;rpm.<ref>Grayson, Eric. "Grayson on Film: Sounds and Silences", ''[[Classic Images]]''. September 2022</ref>

Like ordinary pre-[[Polyvinyl chloride|vinyl]] records, Vitaphone discs were made of a [[shellac]] compound rendered lightly abrasive by its major constituent, finely pulverized rock. Such records were played with a very inexpensive, imprecisely mass-produced steel needle with a point that quickly wore to fit the contour of the groove, but then went on to wear out in the course of playing one disc side, after which it was meant to be discarded and replaced. Unlike ordinary records, Vitaphone discs were recorded inside out, so that the groove started near the synchronization arrow scribed in the blank area around the label and proceeded outward. During playback, the needle would therefore be fresh where the groove's undulations were most closely packed and needed the most accurate tracing, and suffering from wear only as the much more widely spaced and easily traced undulations toward the edge of the disc were encountered.

Initially, Vitaphone discs had a recording on one side only, each reel of film having its own disc. As the sound-on-disc method was slowly relegated to second-class status, cost-cutting changes were instituted, first by making use of both sides of each disc for non-consecutive reels of film, then by reducing the discs to {{convert|14|or|12|in|cm}} in diameter. The use of RCA Victor's new "Vitrolac", a lightweight, flexible and less abrasive vinyl-based compound, made it possible to downsize the discs while actually improving their sound quality.<ref>Barton, F.C. (1932 [1931]). ''Victrolac Motion Picture Records''. Journal of the Society of Motion Picture Engineers, April 1932 '''18'''(4):452–460 (accessed at archive.org on August 5, 2011)</ref>

There were exceptions to the {{convert|16|in|cm|adj=on}} standard size of 1920s Vitaphone discs. In the case of very short films, such as [[Trailer (promotion)|trailers]] and some of the earliest musical shorts, the recording, still cut at {{frac|33|1|3}}&nbsp;[[Revolutions per minute|rpm]] and working outward from a minimum diameter of about {{convert|7+1/2|in|cm}}, was pressed on a {{convert|12|or|10|in|cm|adj=on}} disc when the smaller size sufficed.