Editing Vocoder (section)

==History==
[[Image:Homer Dudley (October 1940). "The Carrier Nature of Speech". Bell System Technical Journal, XIX(4);495-515. -- Fig.7 Schematic circuit of the vocoder (derived from Fig.8).jpg|thumb|upright=1.35|Schematic circuit of Dudley's Vocoder<br />(based on: {{harvnb|Dudley|1940|p=[https://archive.org/stream/bellsystemtechni19amerrich/bellsystemtechni19amerrich#page/508/mode/1up 508]|loc=Fig.7<!-- Schematic circuit of the vocoder -->}}<ref>
  {{cite journal
   | first     = Homer | last = Dudley
   | date      = October 1940
   | title     = The Carrier Nature of Speech
   | url       = https://archive.org/stream/bellsystemtechni19amerrich/bellsystemtechni19amerrich#page/495/mode/1up
   | journal   = Bell System Technical Journal
   | volume    = XIX | issue = 4
  }}</ref>)]]
{{multiple image
| align             = right
| direction         = horizontal
| total_width       = 310
| image1            = SIGSALY.jpg
| caption1          = SIGSALY (1943–1946) speech encipherment system
| image2            = HY-2 VOCODER.jpg
| caption2          = HY-2 Vocoder (designed in 1961) was the last generation of channel vocoder in the [[US]].<ref name="cryptomuseum">{{cite web|url=https://www.cryptomuseum.com/crypto/usa/hy2/index.htm |title=HY-2 |publisher=Cryptomuseum.com |access-date=2019-07-31}}</ref><ref name="jproc">
  {{cite web
   | title     = HY-2 Vocoder
   | url       = http://jproc.ca/crypto/hy02.html
   | publisher = Crypto Machines
  }}</ref>
}}

The development of a vocoder was started in 1928 by [[Bell Labs]] engineer [[Homer Dudley]],<ref name=autogenerated>{{cite journal|author=Mills, Mara|year=2012|title=Media and Prosthesis: the Vocoder, the Artificial Larynx, and the History of Signal Processing|journal=Qui Parle |volume=21|issue=1|pages= 107–149|url=https://muse.jhu.edu/article/491050/summary|doi=10.5250/quiparle.21.1.0107|s2cid=143012886|url-access=subscription}}
</ref> who was granted patents for it on March 21, 1939,<ref name="USpatentapplication2151019">
{{cite patent
 | country = US
 | number = 2151091
 | status = application
 | title = [https://patents.google.com/patent/US2151091 Signal Transmission]
 | pubdate = May 21, 1939
 | gdate =
 | fdate = October 30, 1935
 | pridate =
 | inventor = Dudley, Homer W.
 | invent1 =
 | invent2 =
 | assign1 = [[Bell Telephone Laboratories]], Inc.
 | assign2 =
 | class =
}} (filed October 30, 1935)
</ref> and Nov 16, 1937.<ref name="USpatentapplication2098956">
{{cite patent
 | country = US
 | number = 2098956
 | status = application
 | title = [https://patents.google.com/patent/US2098956 Signaling system]
 | pubdate = 1937-11-16
 | gdate =
 | fdate = 1936-12-03
 | pridate =
 | inventor = Dudley, Homer W.
 | invent1 =
 | invent2 =
 | assign1 = [[Bell Telephone Laboratories]], Inc.
 | assign2 =
 | class =
}}
</ref>

To demonstrate the [[speech synthesis]] ability of its decoder section, the [[voder]] (voice operating demonstrator)<ref name=USpatentapplication2121142>
{{cite patent
 | country = US
 | number = 2121142
 | status = apprication
 | title = [https://patents.google.com/patent/US2121142 Signal Transmission]
 | pubdate = 1938-06-21
 | gdate =
 | fdate = 1937-04-07
 | pridate =
 | inventor = Dudley, Homer
 | invent1 =
 | invent2 =
 | assign1 = [[Bell Telephone Laboratories]], Inc.
 | assign2 =
 | class =
}}
</ref> was introduced to the public at the AT&T building at the 1939–1940 New York World's Fair.<ref name="120years-HomerDudley">{{cite web|url=http://120years.net/the-voder-vocoderhomer-dudleyusa1940/|title=The 'Voder' & 'Vocoder' Homer Dudley, USA, 1940|date=2013-09-21|work=120 Years of Electronic Music (120years.net)|quote=The Vocoder (Voice Operated reCorDER) and Voder (Voice Operation DEmonstratoR) developed by the research physicist Homer Dudley, ... The Voder was first unveiled in 1939 at the New York World Fair (where it was demonstrated at hourly intervals) and later in 1940 in San Francisco. There were twenty trained operators known as the 'girls' who handled the machine much like a musical instrument such as a piano or an organ, ... This was done by manipulating fourteen keys with the fingers, a bar with the left wrist and a foot pedal with the right foot.}}</ref> The voder consisted of an [[electronic oscillator]]{{snd}} a sound source of [[pitch (sound)|pitched]] tone{{snd}} and [[noise generator]] for [[noise (audio)|hiss]], a 10-band [[band-pass filter|resonator filters]] with [[variable-gain amplifier]]s as a [[vocal tract]], and the manual controllers including a set of pressure-sensitive keys for filter control, and a [[Expression pedal|foot pedal]] for [[pitch control]] of tone.<ref name=haskinsLabs>
{{cite web
 | title     = The Voder (1939)
 | url       = http://www.haskins.yale.edu/featured/heads/SIMULACRA/voder.html
 | work      = Talking Heads: Simulacra
 | publisher = [[Haskins Laboratories]]
}} Based on {{cite book
 | author    = James L. Flanagan
 | chapter   = Speech Synthesis
 | title     = Speech Analysis, Synthesis and Perception
 | publisher = Springer-Verlag
 | date      = 1965
 | pages     = 172–173
}} (See [http://www.haskins.yale.edu/featured/heads/SIMULACRA/graphics/voder.gif schematic diagram of the Voder synthesizer].)</ref> The filters controlled by keys convert the tone and the hiss into [[vowel]]s, [[consonant]]s, and [[inflection]]s. This was a complex machine to operate, but a skilled operator could produce recognizable speech.<ref name="120years-HomerDudley"/><ref group=media>
{{cite AV media
 | title     = One Of The First Vocoder Machine [sic]
 | url       = https://www.youtube.com/watch?v=mSdFu1xdoZk
 | medium    = Motion picture
 | date      = c. 1939
}} A demonstration of the [[voder]] (not the vocoder).
</ref>

Dudley's vocoder was used in the [[SIGSALY]] system, which was built by Bell Labs engineers in 1943. SIGSALY was used for encrypted voice communications during [[World War&nbsp;II]]. The KO-6 voice coder was released in 1949 in limited quantities; it was a close approximation to the SIGSALY at {{nowrap|1200 bit/s}}. In 1953, KY-9 THESEUS<ref>{{cite web |url=https://www.cryptomuseum.com/crypto/usa/ky9/index.htm |title=KY-9 |publisher=Cryptomuseum.com |access-date=2019-07-31}}</ref> {{nowrap|1650 bit/s}} voice coder used solid-state logic to reduce the weight to {{convert|565|lbs|kg}} from SIGSALY's {{convert|55|ST|kg}}, and in 1961 the HY-2 voice coder, a 16-channel {{nowrap|2400 bit/s}} system, weighed {{convert|100|lbs|kg}} and was the last implementation of a channel vocoder in a secure speech system.<ref>{{cite web |url=https://www.nsa.gov/Portals/70/documents/about/cryptologic-heritage/historical-figures-publications/publications/wwii/sigsaly_history.pdf |title=Campbell.qxd |access-date=2019-07-31}}</ref>

Later work in this field has since used digital [[speech coding]]. The most widely used speech coding technique is [[linear predictive coding]] (LPC).<ref>{{cite journal |last1=Gupta |first1=Shipra |title=Application of MFCC in Text Independent Speaker Recognition |journal=International Journal of Advanced Research in Computer Science and Software Engineering |date=May 2016 |volume=6 |issue=5 |pages=805–810 (806) |s2cid=212485331 |issn=2277-128X |url=https://pdfs.semanticscholar.org/2aa9/c2971342e8b0b1a0714938f39c406f258477.pdf |archive-url=https://web.archive.org/web/20191018231621/https://pdfs.semanticscholar.org/2aa9/c2971342e8b0b1a0714938f39c406f258477.pdf |url-status=dead |archive-date=2019-10-18 |access-date=18 October 2019 |quote=LPC methods are the most widely used in speech coding}}</ref> Another speech coding technique, [[adaptive differential pulse-code modulation]] (ADPCM), was developed by P.&nbsp;Cummiskey, [[Nikil Jayant|Nikil S.&nbsp;Jayant]] and [[James L.&nbsp;Flanagan]] at Bell Labs in 1973.<ref>{{cite journal |last1=Cummiskey |first1=P. |last2=Jayant |first2=Nikil S. |author2-link=Nikil Jayant |last3=Flanagan |first3=James L. |author3-link=James L. Flanagan |title=Adaptive quantization in differential PCM coding of speech |journal=[[The Bell System Technical Journal]] |date=1973 |volume=52 |issue=7 |pages=1105–1118 |doi=10.1002/j.1538-7305.1973.tb02007.x}}</ref>