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Page:Popular Science Monthly Volume 89.djvu/84

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70

��Popular Science Monthly

��speech. It was the first time they had ever been caught and recorded. Man has been moldhig sound waves into speech with his mouth and Hps along lines represented by these curves for thousands of years; but he didn't know he was doing it. The chart on page 68 gives a complete set of these wave pat- terns. Just how a man molds sound waves into patterns such as these is shown graphically on page 69, the word "boat" serv'ing as an example. "Boat" was chosen because its various letters, as explained in the figure, make use in succession of the lips, tongue, and teeth — three of the principal agents in shaping sounds. It is, therefore, a representative example.

Splitting Up a Spoken Word for the Voice Typewriter

Having discovered that a set of natural letter-patterns exists, the next thing is to make use of them. Accord- ingly the machine shown on page 67 was designed, and has in part been made to operate. It has been named the "phonoscribe," and is intended to write down speech in natural letter- patterns automatically. As is described in the figure, it makes use of a selenium cell* and a set of special vibrating-mirror mechanisms. These latter are each arranged or "tuned," to care for vibra- tions only of a certain magnitude. This is necessary, for this machine is intended to deal with spoken siicech instead of whispers as did the recording machine shown on page 66. Since spoken speech, as has previously been outlined, is full of troublesome extra tones which ob- literate true wave forms, it becomes imperative to have such tuned mechan- isms as these to strain out the main or fundamental wave from its incumbran- ces. As shown in the figure on page 69 the main tone has a freciuency, or vibration-rate, of 100 per second. The incumbrances have rates respectively of 200 and 1,000 vibrations per second. The three mirror-mechanisms which li.indlc these rates are shown throwing their united liglit-bi'ams on to the selenium cell, iMilarging and diminisiiing the wid th (jf this light beam in unison,

•.S'lcnium iH .1 inrlal llic oliTtrtc:il rtindtictivity of which varies (lircctly with Ihe amnnm ol liitlil falHiiK on it at any itivon moment.

��and so cause the cell correspondingly to vary the electric current through the solenoid and recording apparatus shown in the center of the figure. The width of the light beams at any one instant of course depends on how much the mirrors happen to be vibrating, and this in turn is controlled b\- the amount of current coming from the telephone transmitter at the right. The trans- mitter naturally shapes this electric current to correspond with the varying sound waves reaching its diaphragm from the speaker's lips. The whole apparatus therefore works in harmony, and a string of natural characters appears on the paper, recording whatever the speaker at the right has said — in this case the word "boat."

This phonoscribe is interesting mainly as a forerunner of the actual voice- operated typewriter itself. It embodies some principles, notably that of the selenium cell and accompanying vibra- ting-mirror mechanisms, which will be used in the ultimate speech-recording machine itself. But in this latter case of the typewriter, a whole collection of selenium cells will be necessary — one for each key on the machine.

The selenium cells are so distributed that only one letter of the alphabet can affect them. Down inside the voice- operated part of the machine these cells will be erected to receive waves coming from the vibrating mirrors when a person speaks. The selenium cells within the machine are arranged to correspond to the characters of the natural alphabet (see chart of these, page 68). If an ordinary rotating mirror be placed in the path of the light beams coming from the vibrating mirrors, it will auto- matically "spread out" these beams from the straight line (such as is shown on the selenium tx-ll of the figure on page 67) to their natural wa\e shape (that shown on page 68) — this on the same principle that physics teachers of old used to "spread out" sound vibra- tions on a screen, using a revolving mirror. The "spread-out" \ibrations are intended to fall each on its own selenimn cell in the base of the machine, and because of this falling on the jiroper selenium cell, to alTect the correspt)niling t\ new ritcr ki'\'.

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