Then, to show the speech synthesis ability of its decoder part, the Voder (Voice Operating Demonstrator, US application 2,121,142 [8]), was introduced to the public at the AT&T building at the 1939–1940 New York World's Fair.[9] The Voder consisted of a switchable pair of electronic oscillator and noise generator as a sound source of pitched tone and hiss, 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.[10] 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.[9][media 1]