Sound Recording and Reproduction - Other Recording Formats

Other Recording Formats

In the 1920s, Phonofilm and other early motion picture sound systems employed optical recording technology, in which the audio signal was graphically recorded on photographic film. The amplitude variations comprising the signal were used to modulate a light source which was imaged onto the moving film through a narrow slit, allowing the signal to be photographed as variations in the density or width of a "sound track". The projector used a steady light and a photoelectric cell to convert these variations back into an electrical signal which was amplified and sent to loudspeakers behind the screen. Ironically, the introduction of "talkies" was spearheaded by The Jazz Singer (1927), which used the Vitaphone sound-on-disc system rather than an optical soundtrack. Optical sound became the standard motion picture audio system throughout the world and remains so for theatrical release prints despite attempts in the 1950s to substitute magnetic soundtracks. Currently, all release prints on 35 mm film include an analog optical soundtrack, usually stereo with Dolby SR noise reduction. In addition, an optically recorded digital soundtrack in Dolby Digital and/or Sony SDDS form is likely to be present. An optically recorded timecode is also commonly included in order to synchronise CDROMs containing a DTS soundtrack.

This period also saw several other historic developments including the introduction of the first practical magnetic sound recording system, the magnetic wire recorder, which was based on the work of Danish inventor Valdemar Poulsen. Magnetic wire recorders were effective, but the sound quality was poor, so between the wars they were primarily used for voice recording and marketed as business dictating machines. In the 1930s radio pioneer Guglielmo Marconi developed a system of magnetic sound recording using steel tape. This was the same material used to make razor blades, and not surprisingly the fearsome Marconi-Stille recorders were considered so dangerous that technicians had to operate them from another room for safety. Because of the high recording speeds required, they used enormous reels about one metre in diameter, and the thin tape frequently broke, sending jagged lengths of razor steel flying around the studio. The K1 Magnetophon was the first practical tape recorder, developed by AEG in Germany in 1935.