Greetings: There is so much good stuff on RF Cafe that there is no way to list or
link to all of it here. Please use the Search box or the Site
Map to find what you want - there is a good chance I have it. Thanks!
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.
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. 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. They
travel in a narrower frequency band than complete sound.
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, 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.
World center of communications research Largest industrial laboratory
in the United States
Original full-page Bell Telephone Laboratories