Mainframe Experimentalism by Higgins Hannah

Author:Higgins, Hannah
Language: eng
Format: epub
Publisher: University of California Press

TELEPHONY, CRYPTOGRAPHY, MUSIC: A BRIEF HISTORY OF THE VOCODER

NATC is among the first musical applications of the Vocoder. But, in 1967, the device already had a rich history. Indeed, the Vocoder played a key role in the founding of digital technology and the inauguration of electronic and computer music. In 1928, Homer Dudley, a telephone engineer at Bell Labs, set to work to solve a major problem in long-distance telecommunication: how to compress broadband speech signals (with a frequency range exceeding 3,000 Hz) for transport across the very narrow (200 Hz) bandwidth of transatlantic telegraph cables. From the beginning, Dudley recognized that speech can be separated into two basic components: a sound source (produced by the vibrating vocal cords) and its modulation (by the nose, throat, tongue, and lips). Instead of compressing speech itself, Dudley surmised that the solution to the problem would involve transmitting an adequate description of the voice's two components and then using that description to reconstruct a version of the voice at the other end. He initially attempted to describe and transmit information about the movements of the speaker's vocal apparatus, but this proved to be far too difficult.5 He eventually hit on a purely electronic solution. Using a bank of narrow-band filters, Dudley sampled the energy levels of the speech signal at ten different frequency ranges (an eleventh sample registered the fundamental pitch of the voice), encoded these as a series of numbers, and then transmitted this coded description. At the receiving end, a synthesizer read the code and reconstructed the sound using an oscillator to recreate the fundamental frequency and a corresponding set of filters to shape it. Dudley named his device, patented in 1935, the Vocoder, a contraction of “voice coder” or “Voice Operated reCOrDER.” Four years later, at the 1939 World's Fair in New York, Dudley unveiled a related device, the Voder, which consisted of the synthesizer component of the Vocoder connected to a pair of keyboards, a set of foot pedals, and a variety of switches. Demonstrated hourly by a skilled operator, the Voder amazed and horrified visitors with its robotic pronouncements in several different languages.6

With its ability to translate speech into code, Dudley's Vocoder lent itself to encryption and hence received renewed interest during World War II. In early 1943, at the invitation of the White House, the English mathematician, logician, and cryptographer Alan Turing arrived at Bell Labs to aid the development of a speech encipherment system. Turing instantly recognized the possibilities of Dudley's Vocoder, which he and his American colleagues proceeded to modify and connect to a cryptographic system. The result was a pioneering piece of digital technology. Given a variety of enigmatic names—SIGSALY, Project X, Green Hornet—this top-secret collection of devices occupied forty equipment racks, weighed over fifty tons, and required its own air-conditioning system. SIGSALY was inaugurated on July 15, 1943, with a call between Franklin D. Roosevelt and Winston Churchill. By the end of the war, SIGSALY terminals had been installed at locations all over

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