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right direction even though they do not fill the need as completely as the Armed Forces would like.
The intermodulation method described in American War Standard Z52. 15-1944 is used for measuring wave-form distortion on variable-density sound records which is due principally to incorrect photographic processing, including both exposure and development of negative and positive. A suitable adjustment of one of these variables, the positive exposure or density, usually is sufficient to reduce this form of distortion to a satisfactory amount.
In general, the intermodulation method of measuring distortion employs a complex wave consisting of a low frequency and a high frequency at one-fourth the amplitude of the low frequency, the combination being recorded on the sound negative and processed in a specified manner. Any wave-form distortion in the overall process causes a change in high-frequency amplitude in some portion of the low-frequency cycle. The ratio of the average variation in amplitude of the higher frequency in the reproduced wave to its original amplitude is called the intermodulation. Intermodulation test results are not directly proportional to harmonic measurements but in most cases an intermodulation figure of 10 per cent corresponds to a harmonic reading of about 2^4 per cent.
The cross-modulation test is mainly for the purpose of measuring a form of distortion in variable area sound records which is caused by the spreading of the image in either positive or negative. In order to obtain proper wave form, output level, and noise reduction, it is necessary for variable area prints to have high-density contrast between the clear and exposed portions of the track.
At satisfactoritly high track densities an appreciable amount of image spread occurs, producing partial rectification of high frequencies. To compensate for this, an equal and opposite amount of image spread is introduced into the negative. Therefore, to establish the correct negative and print density combination, amplitude-modulated high frequencies are recorded and printed over a suitable density range. By measuring the rectified component from the prints, the correct density combinations are indicated.
These standards are intended to supplement the American War Standard Specification for 16-mm Motion Picture Release Prints, Z52.3-1944.
DeVRY EXECUTIVE ON TRIP
H. B. Engel, sales manager of the DeVry Corporation, is on a tour of the Southern States for the purpose of conferring with theatre equipment dealers regarding new DeVry theatre projectors and sound equipment.
he helped you take a shower
The engineers and maintenance men of our reservoirs and water systems are at their appointed posts day and night, guarding the flow of water that eventually reaches your home. When you turn the tap for a drink of cool water or a refreshing shower, you never stop to think of the men who make this miracle possible.
Nor do motion picture audiences stop to think of the projectionist who is responsible for the picture on the screen. His is an important job — and his teammate, the Altec Service Engineer understands its complexities. Together they work well in the public service.
LTEC
250 WEST 57TH ST. NEW YORK 19, N. Y.
PARTNERS IN PUBLIC SERVICE
APRIL 1945
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