Between 1936 and 1939 electronic and acoustic engineer Homer Dudley and a team of engineers at Bell Labs produced the first electronic speech synthesizer, called the Voder ("Voice Operation DEmonstratoR").
The Voder was demonstrated at the 1939-1940 World's Fair in Flushing Meadows, New York and the 1939 Golden Gate International Exposition on Treasure Island, San Francisco Bay, by experts who used a keyboard and foot pedals to play the machine and emit speech.
♦ The Voder was a simplified version of the Vocoder (short for voice encoder) developed by Dudley from 1926 onward, and for which Dudley received US patent 2151091 A for Signal Transmission on March 21, 1939. Dudley's vocoder was used in the SIGSALY system built by Bell Labs engineers in 1943. SIGSALY was used for encrypted high-level voice communications during World War II. Since then the Vocoder has been widely applied in music, television production, filmmaking and games, usually for robots or talking computers.
On August 19, 2014 Nate Lavey and Jay Caspian Kang posted an outstanding video in NewYorker.com as Object of Interest: The Vocoder. The video, which is embedded here, can be slow to load.
On April 14, 2016 Episode 208, Vox Ex Machina of 99percentinvisible.org posted this outstanding page on Vocoder and SIGSALY: http://99percentinvisible.org/episode/vox-ex-machina/