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sound-track area is a narrow strip carrying recorded soundsignals. If the exciter-beam is correctly located at dead centre, no sound will be heard from the loudspeaker, but if it is offset, the sound then heard will indicate on which side of the soundtrack the scanning beam is overlapping, and adjustments to the sound-optics can then be made accordingly.
If the sound heard from the buzz track is low pitched (300 cycles) the beam is overlapping on the picture side of the track ; if high pitched (1,000 cycles) it is overlapping on the outer-edge side.
The adjustment which has to be made to align the soundtrack directly under the scanning-beam entails, usually, the tightening or slackening of a screw holding a guide-roller (in some cases the sound-drum) so that the film is then moved bodily into the correct position.
Constant Frequency Test-Films
These are used to test accuracy of focus of the scanning beam and are a great help to the technician in locating and correcting the causes of flutter and wow. When in use they provide a long steady note of certain frequencies, and any variation in the speed of the film through the sound-head is at once made obvious to the listener.
The projectionist usually has to rely on his sense of hearing alone when lining-up the sound optics, but the technician, besides using such test-films as the constant-frequency type, also makes use of a number of instruments whereby to measure the sound and its quality. The gliding-frequency test-film, for instance, produces a steady note which slowly rises in scale until the point is reached when the amplifier is no longer able to reproduce it without distortion; the technician then looks at one of his meters and discovers, perhaps, that the amplifier isn't so hot on sound above 8,000 cycles, and other meters will tell him why and where to look for a possible fault.
But are these films of any use to the operator who is not a technician? Yes, they can be very useful indeed, and almost anyone using them for the first time will find them of value and simple to use.
Frequency test-films are available as single, multi or gliding frequency test-films in the 16-mm. gauge.
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