Spectravox: Historic Inspiration; Homer Dudley And The Voder; Wendy Carlos And Bob Moog Begin To Experiment - Moog SPECTRAVOX User Manual

SPECTRAVOX: HISTORIC INSPIRATION

HOMER DUDLEY AND THE VODER

In 1928 Homer Dudley, a researcher at Bell Labs in Manhattan, had a revelation. Sending telephone
signals was costly—a wide bandwidth of data was needed to capture and transmit the fast fluctuations
of a speech waveform. That meant that the mammoth task of laying a cable under the Atlantic Ocean
for sending telephone calls between the United Kingdom and the United States would only be able to
carry 14 channels of telephone calls. But if the bandwidth of speech could be reduced somehow, that
cable could carry a lot more calls.
Dudley knew well the basic model of human speech. The vocal cords vibrate, and the shape of the
mouth and tongue filter the sound of the vocal cords into vowel and consonant sounds. The sound
generated by the vocal cords doesn't significantly change while speaking, however—all of the
important work done to articulate words is performed by the mouth and tongue. So, while playing
with the shape of his mouth and forming different words, Dudley realized that the motions of the lips
and the mouth were much, much slower than the very fast oscillations of the vocal cords. If you could
decouple the motions of the mouth from the vocal cords—if you could just send a signal that captured
the way the mouth shapes a sound—then you would drastically reduce the bandwidth required to send
a telephone call.
Dudley achieved this by running the speech signal through a bank of 10 bandpass filters. Each
bandpass filter captured how the mouth shapes a particular band of frequencies. This way, the voice
could be encoded into a handful of slow, low bandwidth signals, greatly reducing the bandwidth
required to transmit speech. The VOice enCODER—or VOCODER—was born. In order to demonstrate
how the principle of the VOCODER could be used to synthesize speech, Dudley came up with the
VODER—Voice Operating DEmonstratoR. The VODER, a device that was played by well-trained
telephone operators, took as its source signal either a sawtooth oscillator to mimic vocal cords (called
BUZZ) or a noise generator to mimic the unvoiced, sibilant sounds such as 's' or 'sh' (called HISS). A
switch bar on the operator's wrist switched between these two sources. 10 keys would then control the
10 bandpass filters, shaping the BUZZ and HISS into recognizable words and sentences. At the 1939
New York World's Fair the VODER was the star of the show—set up in the AT&T Pavilion right next to
the famous Trylon and Perisphere.

WENDY CARLOS AND BOB MOOG BEGIN TO EXPERIMENT

History may not repeat itself, but it often rhymes, and 25 years later at the 1964 New York World's
Fair a full vocoder (in place of the voder) was exhibited at the Bell Labs Pavilion. In the intervening
years Dudley's invention, having captured the public's imagination in 1939, had been put into service
during the outbreak of World War II as part of SIGSALY, the speech encryption system used for Allied
communication. Now it captured the imagination of a young composer named Wendy Carlos.
Carlos met Bob Moog a year later—birthing one of the most influential partnerships between an
engineer and an artist of the 20th century. Carlos acquired a large Moog modular synthesizer and
achieved worldwide acclaim with her 1968 landmark LP Switched-On Bach, but she never forgot about
the vocoder. Moog, too, had been fascinated by the vocoder and had tinkered with it in his spare time,
and in the late 1960s the two began working on vocoders together.
Intelligibility had been the name of the game in the intervening years for vocoding. Defense
departments and military contractors were interested in reproducing messages accurately and
securely, and that meant more and more filter bands (and thus a much more expensive vocoder).
Musicians, however, were more interested in a tool for creating interesting new sounds. Moog and
Carlos went back to Dudley's 1930s research which led them to the voder: a more affordable machine
that only had 10 filter bands and delighted people with its strange and futuristic sound.
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