2.1.1 Recording principle
Mechanical carriers constitute the oldest, commonly used type of carrier used for recording and reproducing audio. The first true recording system was the cylinder phonograph, invented by Thomas A. Edison in 18774, improved and marketed from 1888 onwards. Originally intended as an office device for dictation purposes, it became popular for scholarly recording of language and ethnic music from the 1890s until the 1950s. Cylinders were also used by the phonographic industries for pre-recorded music. This format, however, was less successful as a commercial product than the gramophone disc and, though it was still used for recording, replicated carriers vanished from the market in the late 1920s. Mechanical disc formats governed the pre-recorded music market from the early 20th century until the 1980s, when they were superseded by the Compact Disc.
In recording a mechanical carrier, the sound, which is a function of the variation of air pressure, is transformed into movements of a cutting stylus and engraved into the surface of a rotating medium. This was originally done by purely mechanical methods: the sound was captured by a horn and moved a membrane at the closed end of the horn. The membrane was connected directly or by levers to a cutting stylus, which engraved the movement of the membrane into the surface of a rotating wax cylinder or disc. The reproduction of the sound reverses the process: a stylus is moved by the modulated groove and drives a membrane, the vibrations of which are amplified by the horn.
By the mid-1920s this acousto-mechanical process was superseded by a magneto-electrical system in which the sound is transformed by a microphone into an electrical signal that moves an electrically driven cutting stylus. The reproduction was also improved by electrical pick-up systems, the amplified signals of which are converted to mechanical movement by a membrane in a loudspeaker or headphones. Recently optical, contact-less replay of mechanical carriers has been developed which, however, for various reasons, has not achieved wider acceptance. (For signal retrieval from mechanical carriers see IASA-TC 04, sections 5.2 and 5.3.)
4. This first “tinfoil phonograph” of 1877–78, which recorded by indenting a tinfoil sheet wrapped temporarily around a cylinder, is typically distinguished from the later “cylinder phonograph” which recorded by cutting a groove in a permanently cylindrical carrier.
