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172 Chapter 14 EVOC 20 PolySynth
Vocoder History
You may be surprised you to learn that the voder and vocoder date back to 1939 and
1940, respectively.
Homer Dudley, a research physicist at Bell Laboratories, New Jersey (USA) developed
the Voice Operated reCOrDER as a research machine. It was originally designed to test
compression schemes for the secure transmission of voice signals over copper phone
lines.
It was a composite device consisting of an analyzer and an artificial voice synthesizer.
These were the:
 Parallel bandpass vocoder: A speech analyzer and resynthesizer, invented in 1940.
 Vocoder speech synthesizer: A voice model played by a human operator, invented in
1939. This valve-driven machine had two keyboards, buttons to recreate consonants,
a pedal for oscillator frequency control, and a wrist-bar to switch vowel sounds on
and off.
The analyzer detected the energy levels of successive sound samples, measured over
the entire audio frequency spectrum via a series of narrow band filters. The results of
this analysis could be viewed graphically as functions of frequency against time.
The synthesizer reversed the process by scanning the data from the analyzer and
supplying the results to a number of analytical filters, hooked up to a noise generator.
This combination produced sounds.
The Voder was demonstrated at the 1939 World Fair, where it caused quite a stir. In
World War II, the vocoder (now called VOice enCODER) proved to be of crucial
importance, scrambling the transoceanic conversations between Winston Churchill and
Franklin Delanore Roosevelt.
Werner Meyer-Eppler, the director of Phonetics at Bonn University, recognized the
relevance of the machines to electronic music after Dudley visited the University in
1948. Meyer-Eppler used the vocoder as a basis for his future writings which, in turn,
became the inspiration for the German “Elektronische Musik” movement.
In the 1950s, a handful of recordings ensued.
In 1960, the Siemens Synthesizer was developed in Munich. Among its many oscillators
and filters, it included a valve-based vocoding circuit.
In 1967, a company called Sylvania created a number of digital machines that used
time-based analysis of input signals, rather than bandpass filter analysis.
In 1971, after studying Dudley’s unit, Bob Moog and Wendy Carlos modified a number of
synthesizer modules to create their own vocoder for the Clockwork Orange sound track.