Homer Dudley

We’re all mad here. I’m mad. You’re mad.
Alice’s Adventures in Wonderland

The VOCODER at a demonstration
The VOCODER at a demonstration

Homer Walter Dudley (1896-1980), B.S. in electrical engineering, 1921, Pennsylvania State College; M.A. in mathematics, 1924, Columbia University, was a member of the research staff of Bell Telephone Laboratories from 1921 to 1961. His work focused on improving the transmission of speech by wire, cable, and radio telephony systems. He received 37 patents for inventions in the fields of telephony and speech synthesis, and in 1965 was awarded the Franklin Institute’s Stuart Ballantine Medal for his work on the VOCODER, the first Electronic Speech Synthesizer.

It seems in 1926 Dudley began experimenting with electromechanical devices to produce analogs of human speech. A key to this process was the development of a parallel band-pass filter, which allowed sounds to be filtered down to a fairly specific portion of the audio spectrum by attenuating the sounds that fall above or below a certain band. This led in October 1928 to the idea of the “Vocoder” (for “VOice” and “enCODER”), first demonstrated at Harvard in 1936—a method of reproducing speech through electronic means and allowing it to be transmitted over distances, such as through telephone lines. By reproducing human speech electronically, the elements of speech could be filtered into ten specific audio spectrum bands, rendering it more easily transmitted over telephone lines with greater clarity and legibility. The speech could also be compressed down to a very narrow frequency band, to allow multiple transmissions simultaneously on different bands. This enabled many telephone conversations to be transmitted at the same time over one line.

A diagram of Voder
A diagram of Voder

With the assistance of fellow Bell Labs engineer Robert R. Riesz (a specialist in the physics of speech and hearing), in 1937 Dudley created the “VODER” (for “Voice Operation DEmonstratoR”), a console from which an operator could create phrases of speech controlling a VOCODER with a keyboard and foot pedals. Although it was considered difficult to operate, VODER was demonstrated at Bell Laboratory exhibits in 1939 at New York World’s Fair and Golden Gate International Exposition. With a woman operator sitting behind the console, phrases resembling human speech could be demonstrated to the audience, although the produced sounds were often difficult to understand. Whereas the VOCODER analyzes speech, transforms it into electronically transmitted information, and recreates it, the VODER generates synthesized speech by means of a console with fifteen touch-sensitive keys and a pedal. It basically consists of the “second half” of the vocoder, but with manual filter controls, and requires a highly trained operator.

On 21 June 1938 Dudley and Bell Labs were granted a patent (see US pat. Nr. 2121142) for a “System for the artificial production of vocal or other sounds”.

Biography of Homer Dudley

Homer Walter Dudley (1896-1980)
Homer Walter Dudley (1896-1980)

Homer Walter Dudley was born on 14 November 1896 in Oranda, Virginia, USA. He was the son of Reverend Walter Lee Dudley (1866-1944), and Sarah Catherine (Showalter) Dudley (1861–1919). Homer had a brother—Virgil Showalter (1895–1982), and two sisters—Katharine Louise (1898-1985), and Esther Virginia (1900–1974).

Walter Dudley was a pastor of Walnut Springs Church of Christ and principal of Oranda Institute (a church schoolhouse), and together with his wife also gave lessons to students, in classical and religious subjects. Dudley’s family moved to Pennsylvania when Homer was a schoolboy in 1907. Having been trained to be a grade school and high school teacher, Homer found it difficult to keep discipline in the classroom and soon gave up teaching. After taking part in WWI, Homer intended a change in career and enrolled in Pennsylvania State University, where he developed an interest in the nascent science of electronic engineering. After taking some college courses in electronic engineering, Dudley found employment with Bell Laboratories, which was at that time a division of Western Electric Company. His career with Bell Labs spanned 40 years, most of it in the Telephone Transmission Division. Dudley was one of the most productive inventors of Bell Labs, together with William Shockley and Claude Shannon.

During World War II Dudley worked with Alan Turing on the SIGSALY project for the US Military. SIGSALY was a method of transmitting speech in a secure manner, rendering it unable to be understood by unauthorized listeners. It utilized technology developed in the VOCODER and VODER projects and added a random noise source as a method of encrypting speech. SIGSALY was successfully used by the US military for transmitting the highest level of classified messages.

One of Dudley’s final projects was an electronic kit distributed by Bell Labs for home hobbyists and students. It was called “Speech Synthesis: an Experiment in Electronic Speech Production”, and contained the components with which to create an electronic circuit that could produce three different speech formants. The kit entered production in 1963 and was produced until the late 1960s.

In 1924 Dudley married Leta Marie Fairbairn (1899–1965) and they had three children. Homer Dudley died on 18 September 1980 (aged 83) in Maplewood, New Jersey.