Before Siri . . .
Pedro, the Voder is the name for the first computer that could produce speech. Bell Telephone brought out Pedro to the Franklin institute to show the new option off.
The Voder (from Voice Operating Demonstrator) synthesized human speech by imitating the effects of the human vocal tract. The operator could select one of two basic sounds by using a wrist bar. A buzz tone generated by a relaxation oscillator produced the voiced vowels and nasal sounds, with the pitch controlled by a foot pedal.
A hissing noise produced by a gas discharge tube created the sibilants (voiceless fricative sounds). These initial sounds were passed through a bank of 10 band pass filters that were selected by keys; their outputs were combined, amplified and fed to a loudspeaker. The filters were controlled by a set of keys and a foot pedal to convert the hisses and tones into vowels, consonants, and inflections. Additional special keys were provided to make the plosive sounds such as “p” or “d”, and the affricative sounds of the “j” in “jaw” and the “ch” in “cheese”.
Unfortunately, as is often the case, what was simple in theory was extremely difficult in practice. To get the machine to actually speak required an operator to manipulate a set of keys and a foot pedal to convert the hisses and tones into vowels, consonants, stops, and inflections. And the operator needed a year’s practice just to master the keys. Even then, how to get a robot to do proper talking instead of recreating pre-programmed patterns or voice from text without an operator was another level of aggravation that we’re still trying to sort out. This was a complex machine to operate. After months of practice, a trained operator could produce recognizable speech.
Performances on the Voder were featured at the 1939 New York World’s Fair and in San Francisco. Twenty operators were trained, with Mrs. Helen Harper particularly noted for her skill with the machine.
The Bell Telephone Laboratory’s Voder was invented by Homer Dudley in 1937‒1938 and developed on his earlier work on the vocoder. The Voder actually produced only two basic sounds: a tone generated by a radio valve to produce the vocal sounds and a hissing noise produced by a gas discharge tube to create the sibilants. These basic sounds were passed through a set of filters and an amplifier that mixed and modulated them until what came out of the loudspeaker.
The quality of the speech was limited of course; however, it demonstrated the synthesis of the human voice, which became one component of the vocoder used in voice communications for security and to save bandwidth.