Dictabelt

The Dictabelt, in early years and much less commonly also called a Memobelt, is an analog audio recording medium commercially introduced by the American Dictaphone company in 1947. Having been intended for recording dictation and other speech for later transcription, it is a write-once-read-many medium consisting of a 5-mil (0.13 mm) thick transparent vinyl (according to a 1960s Dictaphone user manual: cellulose acetate butyrate) plastic belt 3.5 inches (89 mm) wide and 12 inches (300 mm) around. The belt is loaded onto a pair of metal cylinders, put under tension, then rotated like a tank tread. It is inscribed with an audio-signal-modulated helical groove by a stylus which is slowly moved across the rotating belt. Unlike the stylus of a record cutter, the Dictabelt stylus is blunt and in recording mode it simply impresses a groove into the plastic rather than engraving it and throwing off a thread of waste material. The Dictabelt system was popular, and by 1952, made up 90% of Dictaphone's sales.