Nov 16, 1937. To demonstrate the speech synthesis ability of its decoder section, the voder (voice operating demonstrator) was introduced to the public at the AT&T building at the 1939–1940 New York World's Fair. The voder consisted of an electronic oscillator a sound source of pitched tone and noise generator for hiss, a 10-band resonator filters with variable-gain amplifiers as a vocal tract, and the manual controllers including a set of pressure-sensitive keys for filter control, and a foot pedal for pitch control of tone. The filters controlled by keys convert the tone and the hiss into vowels, consonants, and inflections. This was a complex machine to operate, but a skilled operator could produce recognizable speech. 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 II. The KO-6 voice coder was released in 1949 in limited quantities; it was a close approximation to the SIGSALY at 1200 bit/s. In 1953, KY-9 THESEUS 1650 bit/s voice coder used solid-state logic to reduce the weight to from SIGSALY's , and in 1961 the HY-2 voice coder, a 16-channel 2400 bit/s system, weighed and was the last implementation of a channel vocoder in a secure speech system. Later work in this field has since used digital speech coding. The most widely used speech coding technique is linear predictive coding (LPC). Another speech coding technique, adaptive differential pulse-code modulation (ADPCM), was developed by P. Cummiskey, Nikil S. Jayant and James L. Flanagan at Bell Labs in 1973. Applications Terminal equipment for systems based on digital mobile radio (DMR). Digital voice scrambling and encryption Cochlear implants: noise and tone vocoding is used to simulate the effects of cochlear implants. Musical and other artistic effects Modern implementations Even with the need to record several frequencies, and additional unvoiced sounds, the compression of vocoder systems is impressive. Standard speech-recording systems capture frequencies from about 500 to 3,400 Hz, where most of the frequencies used in speech lie, typically using a sampling rate of 8 kHz (slightly greater than the Nyquist rate). The sampling resolution is typically 8 or more bits per sample resolution, for a data rate in the range of 64 kbit/s, but a good vocoder can provide a reasonably good simulation of voice with as little as 5 kbit/s of data. Toll quality voice coders, such as