Rebuilding The First Vocal Encryption System

Back in the early days of radio, it was quickly apparent that the technology would revolutionize warfare, but only if some way could be found to prevent enemies from hearing what was said. During World War II, the Allies put a considerable amount of effort into securing vocal transmissions, resulting in a system called SIGSALY – 50 tons of gear developed by Bell Laboratories with the help of Alan Turing that successfully secured communications between the likes of Churchill and Roosevelt during the war.

Now, a small piece of the SIGSALY system lives again, in the form of a period-faithful reproduction of the vocal quantizer used in the system. It’s the work of [Jon D. Paul], who undertook the build to better understand how the SIGSALY system worked. [Jon] also wanted to honor the original builders, who developed a surprisingly sophisticated system given the technology of the day.

SIGSALY was seriously Top Secret in the day, and most of the documentation was destroyed when the system was decommissioned. Working from scant information, [Jon] was able to recreate the quantizer from period parts, including five vintage VT-109/2051 thyratrons scrounged from eBay. The vacuum tubes are similar in operation to silicon-controlled rectifiers (SCRs) and form the core of the ADC, along with a resistor divider ladder network. Almost every component is period correct, and everything is housed in a nice acrylic case. It’s a beautiful piece of work and a great homage to a nearly forgotten piece of cryptographic history.

Interestingly, Bell Labs had a bit of a head start on the technology that went into SIGSALY, by virtue of their work on the first voice synthesizer in the 1930s.

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A 38-Year-Old Vocoder Project

It is hard to remember that scant decades ago, electronic magazines — the pre-Internet equivalent of blogs — featured lots of audio circuits based on analog processing. Music synthesizers were popular for example, because microcontrollers were expensive and unable to perform digital signal processing tasks in the way you would use them today. [Julian] has been trying to build a vocoder from that era from ETI magazine. Along the way, he’s making videos documenting what he’s found and how’s he resolving issues.

The circuit generates levels for particular input frequencies. It does so with a two-op-amp bandpass filter, a two-op-amp rectifier, and then an op-amp lowpass filter. That’s five op-amps for each band (there are 14 bands) plus the support circuitry. And that’s just the input section! Today, you would simply sample the signal and do a fast Fourier transform (FFT) to get the same kind of data.

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Real Time Video Anonymizer

If you’re wondering, Cornell is just like every other university in one respect: the grad students are starving, and wherever there is free food, students circle like vultures. The engineering and CS departments have a mailing list alerting people to free food, but a more automated solution was desired. The first web cam ever was used to notify grad students if a coffee pot was full, but Cornell shot down this idea on the basis of privacy concerns.

It’s final project time for [Bruce Land]’s courses, and a project by [Ferian Chen] and [Sean Ogden] solved the privacy concerns of a webcam in a kitchen. It’s a real-time video anonymizer, that can also be used to livestream ransom demands if you’re so inclined.

There are actually two parts to this project. The first part pixellates faces and any other skin tone, just like you’d see on a true crime TV show. This part of the project was based on an FPGA-based face detection project. ‘Skin’ pixels are defined as having a difference between the red and green channels within a certain range. With the right lighting, it works very well.

You can identify someone with their voice, too, so [Ferian] and [Sean] also made efforts to disguise hungry student’s voices as well. This was done with a phase vocoder that changes the pitch of someone’s voice, but not the spectral characteristics. The result should have been an audio channel that can’t be pinned down to one person, but is still recognizable as speech. The audio processing didn’t work as intended, with noticeable artifacts in the output. There’s still some work to be done, and now that [Ferian] and [Sean] aren’t checking the kitchen every ten minutes, the might have the time to do it.

Retrotechtacular: The Voder from Bell Labs

voder

This is the under-the-hood view of the keyboard for the Voder (Voice Operating Demonstrator), the first electronic device capable of generating continuous human speech. It accomplishes this feat through a series of keys that generate the syllables, plosives, and affricatives normally produced by the human larynx and shaped by the throat and tongue. This week’s film is a picture montage paired with the audio from the demonstration of the Voder at the 1939 World’s Fair.

The Voder was created by one [Homer Dudley] at Bell Laboratories. He did so in conjunction with the Vocoder, which analyzes human-generated speech for encrypted transfer and re-synthesizes it on the other end. [Dudley] spent over 40 years researching speech at Bell Laboratories. His development of both the Voder and the Vocoder were instrumental in the SIGSALY project which aimed to deliver encrypted voice communication to the theatres of WWII.

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