Depending on where and when you rifle to high school , you may retrieve the instructor wheeling in the 16 mm moving-picture show projector to play plastic film in family . If you ever pick up a strip of the film and looked at it along the sprocket holes , you would have consider a dark strip with a wavy blank pipeline down the middle . This striptease holds anoptical soundtrackfor the film .
The idea behind optical soundtrack is attractively simple . The white-hot line running down the dark strip varies in width . A lamp shines through one side of the slip and hits a photodetector on the other side . The photodetector ’s output signal runs through an amplifier and drives a speaker . The vibrations of the sound are translate into changes in the white strip ’s width . The photodetector sees and variations in light saturation and reproduces the audio ( seethis pagefor details ) . The optical auditory sensation organization is easy to summate to the plastic film and honest over the life of the film .
This same optical organization was used in theaters playing 35 millimetre film when talking pic were first released . In the 1950s optical soundtracks were replaced by magnetic transcription – magnetic strips just like those on acassette tapewere applied to the film and sound was commemorate on them ( seeHow Cassette Tape Worksfor details ) . magnetized recording allowed for stereophonic sound and surround auditory sensation , and also improved the sound timbre . But there were problems with magnetic strip lifespan . Also , the magnetised strip show made the movie a flock more expensive .
In the 1970s , stereo sound using two optical cartroad was made potential by Dolby . This system permit for two-channel playback and surround sound , and offered Dolby noise reduction as well . Dolby has been improve the system for many old age – see the radio link for details .
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