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An Intrstng Exprmnt in Spch
January 1957 Radio & Television News

January 1957 Radio & Television News
January 1957 Radio & Television News Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio & Television News, published 1919-1959. All copyrights hereby acknowledged.

Here is a little insight into early speech processing research by the Bell Telephone Laboratories. 1957 was the early era of real-time digital processing where the need to cram more calls into less signal space (bandwidth) led to sampled systems - 1:6 in the case of this advertisement from Bell that appeared in Radio & Television News. Engineers of the day would be amazed at how the state of the art has advanced since then, both in mathematical techniques and in miniaturized hardware. Waaaaay back in the early 1990s while working at Comsat Laboratories, in Germantown, Maryland, one of the Intelsat earth station modem transceivers I worked on used groundbreaking software algorithms to reduce call bandwidth by replacing certain parts of spoken word sounds with shorter segments of code that would then be reassembled at the receiver end. I specifically remember the software guys have a hard time getting the "s" sound, "ess," working properly. That issue and many others were conquered long ago. 

An Intrstng Exprmnt in Spch

Vibrations of the sound "or" in the word "four" - RF Cafe

Vibrations of the sound "or" in the word "four." Pattern represents nine of the "pitch periods" which originate in puffs of air from the larynx when a word is spoken.

An electronic sampling of the "or" sound - RF Cafe

An electronic sampling of the "or" sound. One "pitch period" in three has been selected for transmission. This permits great naturalness when voice is rebuilt. Intelligible speech could be sent through a 1 in 6 sampling.

The selected samples are "stretched" for transmission - RF Cafe

The selected samples are "stretched" for transmission. They travel in a narrower frequency band than complete sound.

Using the stretched sample as a model - RF Cafe

Using the stretched sample as a model, the receiver restores original frequency. In all speech, sounds are intoned much longer than is needed for recognition - even by the human ear. Electronic machines perform recognition far faster than the ear.

The receiver fills in gaps between samples - RF Cafe

The receiver fills in gaps between samples, recreating total original sound. Under new system, three or four voices could travel at once over a pair of wires which now carries only one - and come out clearly at the end!

Some day your voice may travel by a sort of electronic "shorthand" when you telephone. Bell Laboratories scientists are experimenting with a technique in which a sample is snipped off a speech sound - just enough to identify it - and sent by wire to a receiver which rebuilds the original sound. Thus voices can be sent by means of fewer signals. More voices may economically share the wires.

This is but one of many transmission techniques that Laboratories scientists are exploring in their search for ways to make Bell System wire and radio channels serve you more efficiently. It is another example of the Bell Telephone Laboratories research that keeps your telephone the most advanced on earth. The oscilloscope traces at right show how the shorthand technique works.

Bell Telephone Laboratories Logo - RF Cafe

World center of communications research

Largest industrial laboratory in the United States

     Original full-page Bell Telephone Laboratories advertisement - RF Cafe

Original full-page Bell Telephone Laboratories advertisement



Posted April 25, 2023
(updated from original post on 6/20/2013)

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Kirt Blattenberger - RF Cafe Webmaster

1996 - 2024


Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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