Movietone Bulletin (November 1928)

light falls on a photo-electric cell. With proper developing and printing jthe light transmitted through the print is proportional to the exposure of the negative at the correspi nding point. The resistance of a btbio-clectric cell varies inversely proportionately to the light shining on it. Thus the current flowing through the cell is proportional to the light transmitted through the film. The voltage drop across a series resistance in the cell circuit is impressed on the grid of the first tube of an amplifier. After it has been amplified approximately 100,000 times, this voltage is impressed on a loud speaker and the diaphragm moves proportionately. As the amplificaticn is accomplished without appreciable distortion the movement of the diaphragm of the loud speaker is proporticnal to the movement of the diaphragm of the microphone and the sound which was recorded is reproduced. We are now in a position to analyze the sound track. If the source of the sound to be recorded has a frequency of 60 cycles, the Aeo light intensity will rise to a maximum, fall to a minimum and return to normal 60 times every second. The film moves 90 feet per minute or 18 inches per second. Therefore on every 18 inches of film there will be found 60 light and 60 dark striations, .15 inch wide. If the frequency were increased to 6000 cycles the width of the striations would decrease to .0015 inch. Thus the width of the band on the sound track is a measure of the frequency of the sound recorded. The difference in shade between the light and dark bands is a measure of the intensity of the sound. As most bodies vibrate or tend to vibrate in harmonic motion, the sound waves gradually increase and decrease. Therefore the striations usually are not sharp but gradually fade from one to another. This simple example of recording a single fixed frequency is seldom met in practice. The fundamental frequencies of the human _ voice vary from 60 to 1300 cycles and the overtones are as high as 10,009. Two musical tones from different instruments of equal intensity and frequency, but of different quality, will differ in the manner in which ene striation “fades into another. In orchestral recording many frequencies varying over the entire audible range of 20 to 10,000 cycles should be recorded at the same instant. The resulting sound track showing all of the varying frequencies is extremely complex and shows practically no uniformity or regularity. The accompanying picture is that of a strip cut from the center of a sound track and magnified to 30 times its original size. Plotted vertically under it are the approximate corresponding percentage transmissions of total light. As stated during the course of the text, this graph with a variable vertical scale could represent: (1) The vibration of the diaphragm of the microphone. (2) microphone current. (3) The Aeo light voltage. (4) The intensity of the Aeo light. (5) The exposure of the negative. (6) The transmission of the print. (7) The illumination of the photo-electric cell. (8) The photo-electric cell current. (9) The voltage impressed on the loud speaker. The vibration of the diaphragm of the loud speaker. Careful About Oil HEN oiling the projectors, WV nena a couple of extra minutes and do the job right. If you put more than one, or at most two drops of oil in any projector bearing, all over that amount will just run out, smear around, make a nasty mess and in all human probability get on the films. Flooding bearings with oil does not increase their life appreciably. It merely wastes oil, dirties things up and gets the films smeared more or less, to the damage of your own show and the show of those who must use the films after you are through with them. Another thing: Don’t use a toothin oil. Such oils run out of bearings quickly and are easily thrown off rotating parts. Use the oil recommended by the projector manufacturer by preference. If you can’t or you won’t do that, then consult your Bluebook of Projection, page 626, Vol. 2, and be guided by what you find there. If oil seeps out of the intermittent oil well through the shaft bearings, it is up to the projectionist to provide a wiper which will take up the seepage and carry it down to an absorbent pad placed in ins o (10) | FLICKERS | The children were eating animal crackers and naming the animals as they took them out of the box. Suddenly they took out a pretzel. They looked at it in amazement. Then one of them exclaimed: “TI know what it is. It is Lon Chaney!” | If it takes a ticket to get into heaven a lot of people will want a rain check. It’s nice to be an Eskimo husband. When he doesn’t come home for five or six months the family just think he is out to some night club. Did you hear about the absentminded bandit? He bound and gagged the safe and robbed the night watchman. Advertisements tell us that four people out of five have pyorrhea. The fifth, we take it, has false teeth. It used to be men wanted a wire who cooked like mother used to cook. Now they are content with a wife who knows a delicatessen store like mother used to patronize. Don’t get in the habit of guessing things are all right. Graveyards are full of guessers. Movietone is yet but an infant. But that is no reason why you should be careless with it and permit it to sound like one. the base of the mechanism to receive it. Don’t tell me you cannot do it, else I will lose respect for your ingenuity and ability. Oil gets on film because of (a): Seepage from the intermittent oil well which is not collected by a suitable wiper, and (b): By reason of over-oiling. There is no possible excuse for permitting oil to get on film. He who does permit such a thing has no right place in a projection room. We do not believe any movietone projectionist does permit it, and are glad to be able to say so.