Pulse-code modulation: Difference between revisions

Revision as of 04:13, 6 September 2023

Revision as of 18:59, 27 September 2023

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Early electrical communications started to [[Sampling (signal processing)|sample]] signals in order to [[Multiplexing|multiplex]] samples from multiple [[telegraphy]] sources and to convey them over a single telegraph cable. The American inventor [[Moses G. Farmer]] conceived telegraph [[time-division multiplexing]] (TDM) as early as 1853. Electrical engineer W. M. Miner, in 1903, used an electro-mechanical [[Commutator (electric)|commutator]] for time-division multiplexing multiple telegraph signals; he also applied this technology to [[telephony]]. He obtained intelligible speech from channels sampled at a rate above 3500–4300 Hz; lower rates proved unsatisfactory.

In 1920, the [[Bartlane cable picture transmission system]] used telegraph signaling of characters punched in paper tape to send samples of images [[Quantization (image processing)|quantized]] to 5 levels.<ref name="digicamhistory">{{cite web |url=http://www.digicamhistory.com/1906_1920.html |title=The Bartlane Transmission System |publisher=DigicamHistory.com |access-date=7 January 2010| archive-url = https://web.archive.org/web/20100210053055/http://www.digicamhistory.com/1906_1920.html| archive-date=February 10, 2010}}</ref> In 1926, Paul M. Rainey of [[Western Electric]] patented a [[facsimile machine]] whichthat transmitted its signal using 5-bit PCM, encoded by an opto-mechanical [[analog-to-digital converter]].<ref>U.S. patent number 1,608,527; also see p. 8, ''Data conversion handbook'', Walter Allan Kester, ed., Newnes, 2005, {{ISBN|0-7506-7841-0}}.</ref> The machine did not go into production.<ref name=Vardalas>{{citation |publisher=[[IEEE]] |title=Pulse Code Modulation: It all Started 75 Years Ago with Alec Reeves |url= https://insight.ieeeusa.org/articles/your-engineering-heritage-pulse-code-modulation-it-all-started-75-years-ago-with-alec-reeves/ |date= June 2013 |author=John Vardalas}}</ref>

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 its advantages, but no practical application resulted. Reeves filed for a French patent in 1938, and his US patent was granted in 1943.<ref>{{cite patent |country=US |number=2272070}}</ref> By this time Reeves had started working at the [[Telecommunications Research Establishment]].<ref name=Vardalas/>