The signals are combined, and the result is much cleaner sound. Each signal then travels through a compander, where the signal is compressed to further eliminate low-level noise and is then expanded again. A technique called pre-emphasis boosts the signal of each band above 10 decibels, the level of ambient noise.
MOVIE AUDIO TRACKS MOVIE
But when Dolby Laboratories introduced Dolby A in 1965, a noise reduction method originally developed for professional recording studios, the movie industry saw an opportunity to reinvent the optical track.ĭolby A breaks the incoming audio signal into four discrete bands. There had been experiments with stereo optical tracks, but there was too much noise to make that sound system worthwhile. Magnetic sound-on-film had a couple of advantages over optical at the time:Įven though magnetic recording provided as many as six discrete tracks of sound on a film, the expense was simply too much. In the 1950s, magnetic recording became popular. The biggest problem with this method is that the natural graininess of the film can create a lot of background noise. The more transparent the strip is, the more light shines through. It uses a strip that varies in transparency instead of width. The pre-amplifier boosts the signal and sends it to the amplifier, which distributes the signal to the speakers.Ī variation of this method is known as variable-density soundtrack. Since the width of the transparent strip changes the amount of light, this results in a variable electric current that can be sent to a pre-amplifier. The wider parts of the strip allow more light, which causes the photocell to produce more current. The amount of current is determined by the amount of light received by the photocell. The light is changed to electrical current by the photocell. The light that passes through the film shines on a photocell. As the film passes the audio pickup, an exciter lamp provides a bright source of light, focused by a lens through the transparent line. For this reason, it is known as a variable-area soundtrack. This strip varies in width according to the frequency of the sound. The most common method is an optical process whereby a transparent line is recorded along one side of the film. Once this calibration is done, projectionists can splice film together knowing that the sound will synchronize properly.
A test film is run to calibrate the sound to the picture. Most analog pickups are in the basement (below the lens), while digital pickups are normally in the penthouse (fastened to the top of the projector). This is because the audio pickup, or reader, is set either above or below the lens assembly of the projector. An interesting thing about sound-on-film is that the sound is several frames away from the corresponding images. In the early 1930s, sound-on-film began to supplant sound-on-disc as the technology of choice for adding a soundtrack to a movie. It was a simple but very effective way to add audio to a movie. The record was played on a turntable that synchronized sound to the film by controlling the speed of the projector. The sound recording was usually done after the movie was filmed. Vitaphone, used in "The Jazz Singer," consisted of a record player playing a wax record. The mechanism for delivering sound in the early days of cinema was incredibly simple.