Saturday, May 20, 12:00 — 12:45
Jon D. Paul (Presenter)
This tutorial explores the history of digital audio technology, and the contributions of the great inventors that led to modern digital media. Signal analysis began in 1822 with Fourier’s trans- form. Audio compression started in 1938, with the VOCODER, Homer Dudley’s landmark speech encoder. Dudley invented electronic speech analysis and synthesis, and achieved ten times speech compression.
The onset of World War II created an urgent need for speech encryption of strategic conferences via short wave radio links. In just six months, an unbreakable top secret speech scrambler SIGSALY, was designed at Bell Telephone Laboratories (BTL). Brilliant engineers including Claude Shannon, Henry Nyquist, and Homer Dudley, invented and implemented eleven funda- mental breakthroughs, including PCM, flash A/D conversion and spread spectrum.
The VOCODER and SIGSALY block diagrams, construction and operation are discussed, with their close links to modern audio codecs.
We describe the interesting background of the engineers, inventors and mathematicians who laid the foundations of digital audio; Dudley and Shannon’s work on SIGSALY, Hedy Lamarr’s spread spectrum, and Turing’s Delilah scrambler. A reconstruction of the very first PCM codec ADC, using vintage tubes is described. This tutorial includes unusual photos, vintage music, early VOCODER speech and very rare SIGSALY decrypted speech.