In numbers 3 and 13 of this series I mention Variable Intensity Sound-on-Film recording. From my reading on the subject, VISOF appears to have been invented by three German researchers who called themselves the Tri-Ergon Company.
The Fox Motion Picture Studios in Hollywood developed their own version of VISOF and used it for a few years, but they abandoned VISOF in favor of another sound-on-film technology when they merged with a company that used the other system.
I first became attracted to VISOF because it seemed to illustrate an alternative way for music to be amplified, or to clarify how music can be amplified.
Consider the record of a music performance on film, consisting of a sequence of varying shades of transparency and opacity. (Film lingo calls these varying 'densities.') As a vinyl record has impressions of the varying travel of a needle, VISOF has impressions of the varying brightness of a bulb.
When this film record is played back, a bulb called the exciter lamp shines through the film and its light, modulated by the varying densities, impinges on a photoelectric transducer.
What initially struck me about this process years ago is that by varying the brightness of the exciter lamp, you can clearly visualize how the playback sound can be made louder or softer.
This was something of a revelation for me, inasmuch as I had initally started my research in audio electronics for the purpose of learning exactly how it was possible to take a given piece of music or musical signal and make it louder.
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