The Vocoder and its Origins in World War 2

Kevin Koo

8 years ago

I listened to a podcast…

Recently, I tuned in to the 99% Invisible podcast on Tunein. That’s when I heard their very fascinating episode, Vox Ex Machina (Episode 208), which was about an invention from 1939 called the “voder”, called the “voice operating demonstrator”. It was like a piano for voices, because it was a keyboard which people could play with ten fingers. But as the podcasters noted, voder operators would train up to one year in order to learn how to operate the voder.

The inventor was a guy called Homer Dudley, who specialized in speech science. He worked at Bell Labs.

And then there was the Second World War

So, as the podcast noted, there was a war, called the Second World War. It was quite serious — my grandparents lived through it. I heard many horror stories about the Japanese soldiers in Malaya.

But at that time, the focus was on encrypted communications between the British Prime Minister and the American President. Encryption technology at the time was easily broken.

That’s when the President’s office contacted Bell Labs for a solution. Homer Dudley was called up.

Fortunately Homer had a solution. He had been working on speech technology for many years. That’s when he created SIGSALY, the “unbreakable speech encrypter”. SIGSALY used what is today known as a “vocoder”, which stands for “voice encoder”.

It was a very fascinating listen. Go, listen to the 99% Invisible podcast today.

An example of an early vocoder

The SIGSALY Patent

This one I found from the Wikipedia entry on SIGSALY.

US Patent No. 3967067 was filed on 24th September 1941, and was published on 29th June 1976. You might know that the lifespan of a patent is about 20 years…. so, its publication was probably more a matter of recognition, than exploitation of IP for profit. Which inventor doesn’t want to be identified with their invention? Most of them want recognition. Even if it’s 35 years after the patent was filed.

Man, I really hope that the inventor for US patent no. 3967067 made some money off his invention, somehow.

But I wonder why the patent stated the inventor as “Ralph K Potter” and not “Homer Dudley”? Maybe this isn’t the patent for the SIGSALY after all….

Some other patents from Homer Dudley

A Google Patents search reveals that Homer Dudley was a rather prolific inventor. Here are a few:

Privacy system – Patent No. US 2213320 A – Filed on 10th September, 1938. Published on 3rd September, 1940. “The present invention relates to systems and methods of transmission with privacy. It is appreciable to line wire or radio transmission, and to the sending of speechmessages or any other type of signals which comprise a band of frequency components such that the signal wave band can be subdivided into narrower subbands.” (This could be the SIGSALY patent.)
System for the artificial production of vocal or other sounds – Patent No. US 2121142 A – Filed on 7th April 1937, and published on 21st June 1938. “One of the objects of the present invention is to provide an arrangement for the synthetic production of speech or similar sounds and, particularly, to provide an arrangement of this type in which the desired vocal or other sounds may be produced by manual operation quite independent of any vocal control by the normal vocal mechanism of the human body.” (This should be the “voder” patent. It was demonstrated in 1939.)
Production of artificial speech – Patent No. US 2243526 A – Filed 16th March 1940, published 27th May 1941. “The present invention relates to the artificial production of speech or similar sound waves and to such artificial production in connection with a system for analyzing speech or similar waves.”

Final Thoughts

I must say that I owe quite a bit to Mr. Homer Dudley. Having read about the man and his inventions, I think:

VOIP, cheap international calls or free Internet-based calls owe their origins to his work on speech compression. I tend to call my family a lot using Viber / Line / Whatsapp whenever I go for holiday, just because I can.
Text-to-speech (TTS) technology also owes a lot to his work on text synthesis / artificial voice production. I tend to share webpages to “Voice Reading” on my Android phone. I then listen to the webpages being read aloud, while I do whatever I am doing.
Vocoders are being used today by musicians to distort their voices. I love music, and that guy made these robot-like voices possible.

So go, listen to that podcast already. Link is at the top of this blog post.

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