We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
32 MOTION PICTURE SOUND ENGINEERING
To date, standard methods of recording on film, both variable density and variable area methods, have given a volume range of approximately forty db, at the expense of considerable distortion. In the variable density system the principal limitation has been the small linear range of density between the toe and shoulder of the characteristic curve for positive stock, plus the distortion added by the noise reduction system because of its relatively slow operating time. Push-pull recording inherently reduces these limitations by the cancellation of the internal distortions.
When sound is recorded on film, either by the variable area or variable density method, certain harmonic and extraneous components appear in the reproduced signal which were not contained in the original signal.
For the variable density recording method these consist mainly of two distortion components; one introduced by the non-linear toe and shoulder portions of the film characteristic, and the second, signal components derived from the noise reduction apparatus. For variable area recording the distortion consists of shutter or bias signals and processing effects.
Push-pull recording, like the push-pull method of operating vacuum tube amplifiers, is a method of reducing certain of these distortion effects in the electrical signal to be reproduced. The similarity between film recording and vacuum tube circuits is quite complete, the one providing a means for cancelling out certain harmonics produced in vacuum tubes because of non-linear tube characteristics, the other accomplishing the same results for film recording in connection with the above mentioned distortion effects. In fact, the possibilities for push-pull recording had their inception in the success of the vacuum tube development.
This type of recording is secured by means of two sound tracks on the film which are reproduced by a double photo-electric cell arrange ment, which adds the signals from the two tracks in their proper phase relation. The two half-tracks are recorded out-of-phase on the film and the double photo-electric cell circuit is arranged to have a phase turnover, so that the signal will be reproduced in-phase (see Chapter XXII) . This phase turnover is accomplished in the same manner that the outputs of two push-pull vacuum tubes are joined together by a center tapped transformer. Thus, even order harmonic content introduced by the film is cancelled out because of an out-of-phase condition in the combining transformer. As in push-pull vacuum tube circuits, it is not possible to cancel out both even and odd order harmonics.