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.
280 IX. SOUND-RECORDING EQUIPMENT AND ARRANGEMENT
stereophonic demonstration). Still later, nnmerons patents were issued in different countries of the world ; some of those filed in the United States gave rise to much expensive litigation in which the fate of many millions of dollars depended upon the outcome.
Today all modern recording equipment utilizes the noise reduction principle ; in all arrangements the average transmittance of the positive film is made approximately equal to the modulation. This is accomplished by automatically "blacking-in" the sound track area not used for modulation in a variable-area film. Thus, on a positive, the sound track is almost entirely opaque when there is no modulation as only a small portion of the width is needed for the modulation ; when full modulation occurs, the sound track has maximum transmittance as full width is needed for the modulation. At modulation levels between these two limits, the average transmittance is kept approximately proportional to the modulation by means of the noise-reduction amplifier (often called a bias amplifier) and its adjuncts.
If the signal-recording and noise-reduction functions are thought of as two separate functions, one means is used to record the signal and the other to record the noise-reduction current. The wave form of the signal should be undistorted; the wave form of the noise-reduction current is altered by rectification. The rectifier is connected to a filter circuit, with the charging characteristics of the filter determining the attack time of the noise-reduction system, and the discharge characteristics of the filter determining the decay time. Mathematically, the bias current provided at the output of the bias amplifier is a rectified envelope of the signal current. In the design of practical equipment, the input to the bias amplifier "bridges" the signal circuit, being connected in such manner that it does not appreciably alter the transmission characteristics of the circuit, and draws a negligible amount of energy from it, e.g., 5% or less.
A typical commercial design would include: (1) an amplifier portion to increase the audio frequency energy level to a convenient point, {2) an audio rectifier, (3) a filter circuit for the control of charge and discharge times, and (4) an output d.-c. amplifier tube. In such a commercial design it is customary to provide maximum d.-c. output from the bias amplifier when no signal is present, and minimum d.-c. output when maximum signal is present. In this manner, failure of the bias amplifier will cause merely the omission of bias but will not distort the recorded signal.
The bias amplifier is usually actuated by the signal being recorded. The unidirectional current output of the noise-reduction amplifier may