Advent of Computing Episode 29 - PCM, Origins of Digital Audio
May 3, 2020
The podcast dives into the fascinating history of Pulse Code Modulation (PCM) and its role in digital audio. Discover the groundbreaking work of Alec Reeves in 1937 that laid the groundwork for sound digitization. Explore the advantages and challenges of audio transmission from telegraphs to modern technology. Hear about the WWII-era SIGSALY system that used PCM for secure communication and its massive infrastructure demands. Finally, learn how early pioneers like Max Mathews pushed the boundaries of digital music synthesis.
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Telegraph Principles Inspired PCM
- Telegraph systems send information as discrete on/off pulses, making them resilient to noise.
- Reeves saw that treating audio as discrete data could combine telegraph reliability with audio fidelity.
Reeves' 1937 PCM Patent
- Alec Reeves patented pulse code modulation in 1937 to transmit audio like a telegraph.
- He described ADCs, DACs, sampling, and a full encode/decode system in his patent.
Digital Regeneration Prevents Noise
- Reeves proposed regenerative amplifiers that reconstruct digital pulses to avoid adding noise.
- Rebuilding the binary signal preserves fidelity across long cables unlike analog amplifiers.