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ig. 10. Brush penmotor charts of film before (below) and after (above) micropolishing. Sharp spike at right is a reference mark common to both curves.
Figure 9 is a reproduction of photolicrographs of areas of film which show 'here the little hills have been leveled. )riginally these had the globular apearance of the nodules shown in Fig. 5. "he polished area is always irregular, nd always very shiny as indicated by he glare areas. It will be noted there > no trace of shadow, showing good .atness.
Figure 10 shows some Brush •enmotor charts of a length of film before nd after Micropolishing. These charts vere made b'y recording a steady 1000ycles/sec tone, and then playing back nto the penmotor. Whenever there is a nomentary reduction in playback level t is indicated by the penmotor which esponds very rapidly and shows changes n level of very short duration. This ype of variation will not be shown by lormal volume indicators. To make the est a severe one, the bias current was djusted to give peak output. The ower part of Fig. 1 0 shows the dropouts resent before Micropolishing* and in the ipper part is shown the same film after Micropolishing. Although the process
This is the micropolishing process used by Beeves Soundcraft Corp. in making products bearing their trade-marks "Micro>olished Film" and "Micropolished Tape."
was developed primarily to combat nodules, it reduces the effect of other irregularities also.
This system has been in daily use for about six months and has resulted in a greatly improved product. Other benefits besides reduction of dropouts have resulted from the better head contact made possible. High-frequency response was improved by about 2 db at 10,000 cycles and there has been a marked reduction in intermodulation distortion.
Early in the work on combating dropouts a different approach to the problem was attempted. It was felt that for a time a softer coating should be less troublesome than a hard one, and that if a soft coating did have nodules they would be soft nodules. If the nodules were soft, they might wear off easily, hence there would be fewer dropouts. The first results were quite encouraging and an experimental program was laid out to determine how soft a coating could safely be. Before the program got very far, it was found that the softer coatings which had showed promise were no longer better than our regular material, and some actually were not even as good. It was then discovered that although they were kept in an airconditioned area these special coatings
Ernest W. Franck: Dropouts in Magnetic Film
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