1937 __ PCM, Pulse-Code Modulation
‣ Comment : Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a numeric (usually binary) code. PCM has been used in digital telephone systems and 1980s-era electronic musical keyboards. It is also the standard form for digital audio in computers and the compact disc "red book" format. British engineer Alec Reeves, unaware of previous work, conceived the use of PCM for voice communication in 1937 while working for International Telephone and Telegraph in France. He described the theory and advantages, but no practical use resulted. Reeves filed for a French patent in 1938, and his U.S. patent was granted in 1943. The first transmission of speech by digital techniques was the SIGSALY vocoder encryption equipment used for high-level Allied communications during World War II from 1943. In 1943, the Bell Labs researchers who designed the SIGSALY system, became aware of the use of PCM binary coding as already proposed by Alec Reeves. In 1949 for the Canadian Navy's DATAR system, Ferranti Canada built a working PCM radio system that was able to transmit digitized radar data over long distances. PCM is one of the many technologies important in communications and media that had their origins in the military. PCM, an important transitional technology, works digitally to transmit analog data uing binary signals. Before PCM, geographical distance was significant in electronic communication because in “conventional electrical systems of transmission, the distance of transmission still had played an extremely important part, since the noise produced by relays was cumulative”. PCM, like “penny postage” negated space. (Annmarie Chandler)
‣ French comment : Dès 1937, Reeves avait inventé la Modulation par Impulsion Codée, fondement de l’enregistrement numérique, mais il fallut attendre les progrès de l’informatique pour généraliser l’enregistrement numérique du son. Les premiers sont réalisés en 1979, conjointement par DECCA (”Concert du nouvel an” par Boskowsky) et Deutsche Grammophon (”Concerto de Tchaikovsky” par Gidon Kremer). En fait, l’apparition du CD audio est liée aux expérimentations effectuée dès les années 60 pour enregistrer l’image sur disque. En 1978, Philips invente un disque vidéo, le Vidéodisque, lu par un faisceau laser capté par une photodiode, et sort en 1982 le Compact Disc, utilisant la même technologie. (blog.bnf/fr/voix/)
‣ Source : Chandler, Annmarie (2005), “At a distance: precursors to art and activism on the Internet”, edited by Ann-Marie Chandler & Norie Neumark, Leonardo Books, MIT Press, Cambridge MA USA.
‣ Urls : http://www.quantium.plus.com/ahr/ (last visited )
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