Science Finds Amazing New Uses for Sound (Jul, 1931)
Science Finds Amazing New Uses for Sound
by DR. SERGIUS P. GRACE
Assistant to Vice President, Bell Telephone Laboratories As told to J. EARLE MILLER Thanks to astounding discoveries made recently in the field of sound, you will soon be able to talk around the world, deaf mutes will hear, and communication in battle areas will be revolutionized. The amazing inventions which make such feats possible are described in this article.
IN A recent lecture on the new marvels being developed in the Bell Laboratories I placed my finger against the ear of one of the members of the audience, and he “heard” music and speech, though not a sound was audible on the stage.
That was electrostatic projection of speech directly into the human brain. The speech had been transformed into high voltage electric current, passed through my body, while the ear drum and surrounding tissue of the subject acted as one plate of a condenser receiver.
Just a laboratory experiment, so far, yet it is one of many new discoveries that are opening new leads into the field of hearing, helping improve devices for the transmission of sound, and bringing hearing back to the deaf. It is quite possible, as some research workers have suggested, that science may make it practical to “hear” without using the ear drum at all.
Hearing, it has been discovered, is partly an electrical manifestation in which a minute current is generated in the auditory nerve. At Princeton University not long ago electrical contacts were established to the audi- tory nerve and brain of a cat, the minute current in the nerve amplified through radio tubes, and words spoken into the ear of the living cat in one room were reproduced through loud speakers in another.
At Bell Laboratories we not only have developed special apparatus to make it easier for deaf people to use the telephone, but we have also created several portable outfits, known as audiphones, which help these unfortunate ones to join again in conversation with their friends. Few people realize that there is a definite upper limit to the loudness that the ear can stand, so that extreme cases of deafness are beyond the aid of even the most potent amplifier.
Under the guidance of Dr. Harvey Fletcher we have developed the audiometer, an instrument to measure hearing. It shows conclusively that no two cases of deafness are quite alike, and that hearing-aid that proves successful for one person may be quite unsuited for another. Dr. Fletcher has developed a simple method in which some one reads off lists of words, at a distance of three feet from the pick-up device. One list contains fifty words such as “bat, bite, boot, beat” in which the vowel is different for each; the other has fifty words in which the consonant differs such as “by, high, thy, guy, why”. After making this test with several hearing aids, and scoring errors in the consonants twice as heavily as in the vowels, the user can decide which device best suits his particular kind of deafness.
The projection of speech direct into the brain is only one of the fantastic marvels of recent years. Every day the air is filled with trans-oceanic radio telephone messages, winging their way between New York and Europe, South America, Australia and South Africa. From any telephone in the United States you can call any telephone subscriber in those far flung quarters of the globe, but when you talk no eavesdropper can listen in. Far down in lower New York your voice passes through a speech inverter mechanism which turns it into a new language, unintelligible to the ear. With patient practice one can learn some of the inverted words, but many are sounds which the human larynx cannot master.
The speech inverter is quite simple in theory. Normal telephone speech falls between vibrations of 100 cycles up to 2,900 cycles. When the speech is inverted, for every vibration is substituted a new one whose frequency is equal to some selected constant frequency, less the frequency of the original sound. We use 3,000 cycles for the constant frequency, and a deep bass note of 100 cycles is thus transformed into a high soprano of 2,900 cycles, while the high notes are inverted to deep bass. The result is much like passing light through a camera lens, which inverts the image, so the top of the picture is focused on the bottom of the film in the camera, and the bottom of the image appears at the top.
At the other end of the trans-oceanic radio phone circuits similar inverters reverse the process, and the party at the other end hears normal speech.
If there is another war the speech inverter may revolutionize the secrecy problem, not only in radio conversations, but on the telephone lines at the front. For, by simply changing the cycle according to a pre-determined arrangement, the enemy would be unable to pick up and translate the mes- sages, even with a similar machine.
Learning to speak a few words of the inverted language, so you can talk into a microphone and have them come out of the inverter changed into intelligible English, is an interesting experiment. If, for example, you can say “Cyaneon Playafeen Acecilofin” into the transmitter, the inverting apparatus will repeat back “Illinois Telephone Association”. There are always portions of the sounds that no human throat can master. Such a simple word as company, for example, becomes crink-a-nope.
Speaking of possible war uses of new sound apparatus, the “talking light”, one of the most interesting things still in the laboratory experimental stage, offers an opportunity to develop secret wireless communication from the front lines to the rear.
The talking light is an electric arc in which the flame acts as a loud speaker, and can be made to speak with almost the volume of a good dynamic speaker. The principle behind the phenomenon was discovered by the inventor of the telephone, Alexander Graham Bell, and Hammond V. Hayes, one of the early Bell System engineers. They found that speech could be transmitted by a beam of light, and also that when a telephone transmitter was connected across the terminals of an electric arc between carbon rods the flaming arc would reproduce the words spoken into the transmitter. At the same time beams of light were sent out which could be used to transmit speech several miles.
We have found that the light not only talks, but that it is modulated by the voice current just as the glow of a neon lamp is modulated by the signals reaching a television receiver. It is possible by using photoelectric cells to pick up the beam of modulated light to reproduce it directly at a distant point as spoken words. Such a system would be the last word in directional wireless, for no one could listen in save by inserting a photoelectric tube in the beam, and with the latter directed from the front lines toward the rear, the enemy could not eavesdrop.
Audiences listening to some of my talks on our work at the Bell Laboratories have been mystified by the fact that, though I am constantly walking about the stage, and no microphone is in sight, my voice reaches them, greatly amplified, through public address loud speakers. The secret is a tiny microphone, no larger than a quarter, hidden in the breast pocket of my coat, and connected to a trailing wire passing down to the floor inside my clothing. Originally a development of an improved transmitter for telephone operator, the device is now serving in a totally different field.
Another use for small and extremely sensitive microphones is in guarding the vaults of the Federal Reserve and many other banks. Tiny microphones are set in the vault walls, and they are so sensitive that a hand tapping against the vault will set them off, while they are so adjusted that they remain insensitive to footsetps passing near, to trucks in the street, and to the rumbling subway trains.
A very clever electrical engineer might possibly locate one of the circuits, and, after study, determine just the right amount of resistance to put into the line and so circumvent the microphones while bank robbers could work. So, to guard against that bare chance, the watch service officers are provided, with a device by which, at frequent intervals, they can sweep through a whole cycle of resistance changes and determine whether any one has been tampering with the circuit. The cleverest bank robber doesn’t have a chance with this system.
Another laboratory experiment which always fascinates the public is the speech delay mechanism, which, in one form, is just a clever amusement device, and, in another, is an important part of the trans-oceanic radio telephone system. With a long coil spring connected to a telephone transmitter at one side of the stage it is possible to so delay the movement of the voice vibrations along the wire that you can speak in one end and hear the words come out the other quite a bit later. That’s more or less a me- chanical affair, the shape of the coiled spring actually delaying the movement of the waves.
But down in lower New York every message passing through on the radio-telephone circuits is delayed for a couple of hundredths of a second by electrical means. The trans-Atlantic wireless-telephone service can work in only one direction at a time, because the sending and receiving stations are tuned to the same wave-length. A voice current going to Europe is picked up also by the American receiver, and unless the wire line between receiver and transmitter is blocked, the signal would “loop the loop”, causing the circuit to howl. If you are talking from New York to London you control the circuit so long as your voice continues. When you stop, relays must work to reverse the channel, so the person at the other end can answer. Your voice, as electrical impulses, travels with the speed of light, while the relays, being mechanical, must have a fraction of a second to work. That’s where the speech-delay apparatus comes in. The man in London may start talking instantly, but the apparatus will store up his voice in London for an instant while the relays are doing their work.
While primarily concerned with the development of the telephone, we are constantly contributing to many other fields. One of the most recent developments was the eliminating of the last disturbing sound from talking picture films. In the early days of sound recording on movie film there were many outside noises. Eventually they were eliminated one by one, until finally only a swishing sound remained. By changing the mechanism of the light valve at the recording end it is now possible to eliminate this last noise, and a remarkable change in talking pictures was the result.
Research in the recording of talking picture sounds on wax discs also has resulted in a marked improvement in reproduction. We have gone back to Edison’s original method, as used on the old-time cylinder records. He utilized what is known as “hill and dale” recording, the cutting stylus engraving a line of varying depth, instead of the waving, side to side method which Berliner developed with the first disc records. The hill and dale method was not a success because of the limitations of the acoustical method of recording.
In following the wavy line on present day records, the reproducing needle is thrown back and forth from side to side of the groove, and does not follow accurately the path traced by the cutting stylus. By reverting to the hill and dale method, and using a permanent needle in the form of a sapphire point, our engineers have attained practically perfect reproduction.
The reproducing mechanism itself is a marvel of lightness, weighing so little that the playing life of records is extended indefinitely. We have records which have been played a thousand times without appreciable wear.
Besides contributing to such widely separate fields as better hearing and the talking pictures, our staff also is assisting in the research designed to isolate the cause of cancer, and in other biological fields. This is an offshoot of our investigation into the crystalline structure of metals and alloys, a subject of great importance in the manufacture of telephone apparatus. Francis F. Lucas, with his photo-micrographic equipment which utilizes ultra-violet light and magnifies as much as 5,000 diameters, has been able to explain many obscure things about why metals harden under heat treatment, and why they crack in service.
Applying his technique in the field of biology, he has been able to take pictures of living cells without the use of stains, which might damage or change their structure. He is able to take photographs of successive layers right through the cell, at intervals of one one-hundred thousandth of an inch. In other words, if the cell is one-thousandth of an inch thick he can get one hundred photographs showing its structure at as many layers. Pictures taken of the surface of brain tissue have shown such startling things that plans are being considered for improved apparatus by which a “map” of a section of brain may be made, just as aerial photographic maps are made by assembling large numbers of photographs taken at appropriate intervals. If the full power of Dr. Lucas’ equipment were utilized, a map of a section of brain only one-fourth of an inch square could be made with an enlargement to more than 104 feet square. Of course, a larger area would first be photographed in smaller detail, and then special sections selected for further magnification and study.
There is no apparent connection between our work and study of cells, but the photo-micrographic equipment has already contributed toward one of the major improvements in telephonic communication, an improvement which is saving at least $10,000,000 worth of lead per year in making telephone cables. Lead hardened with antimony has been been used for cable sheaths, but they had an annoying habit of breaking down after a few years of use. Dr. Lucas discovered by micro-photographs that the antimony after a certain period disassociated itself from the lead. As a result of that discovery a new mixture was found, one so much stronger that a thinner, lighter lead covering could be used, and the result was an enormous saving in lead. His studies of all the metals and alloys which go into telephone equipment manufacture also have contributed to general improvements in many lines.
Another field to which the telephone industry has contributed, is the improvement of radio broacasting. Crystals to control the frequency of a broadcasting station and keep it on its exact wave length .have been developed, and so successfully that two stations in Iowa, under the same management, are broadcasting all the time on the same wave length, instead of giving only half time service as would be necessary if they shared the wave.