7

Table Of Contents
15
191
15 Vocoder History
The vocoder is over 50 years old. This chapter discusses
its 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.
The Voder 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.