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DIMENSIONS AND STANDARDS
sense, the initial bias setting of 0.005 in. would provide the approximate equivalent of the actuating delay time of the signal.
The best initial bias setting depends upon the character of the sound to be recorded. Experience has indicated that the setting of 0.005 in. is satisfactory for most kinds of recorded sound recorded upon most kinds of sound-recording equipments.
Checking the Initial Bias Setting of a Recording Machine. With the microphone and other input keys turned off, and with the gain controls and other signal controls set for zero signal, record a few feet of negative (3 to 5 ft.) at rated bias current as well as at several settings above and below rated current. (In the case of a Maurer Model D equipment, settings at 24, 26, 28, 30, 32, and 34 milliamperes are suit
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0002"
Fig. 16. Measuring the unmodulated . noise-reduction negative track widths obtained with various bias currents. Current values shown are typical of Maurer sound recording machines. A width of 0.005 in. is recommended.
able.) Keep a log sheet so that each test recording may be identified quickly. After having the film developed, indicate the width of each section of track so produced in the appropriate place on the log sheet. Select the AGN current that provides an initial bias track width of 0.005 in. See Figure 16. Widths are measured on the recommended microscope or equivalent measuring device. Initial bias track width is not critical ; if the initial bias setting is once measured and noted, there will be little need for change in the milliampere setting during the normal machine life. If the setting is maintained within plus or minus one milliampere, there should be little cause for concern about this adjustment.
Part 4A : Measuring the Scanning Beam of a Projector for Center Line and Width
General. The design of a good sound-translating system in a sound projector brings an engineer-designer face to face writh a dilemma. For