Technical
Information
Optical Sound Tracks are made of on an extremely high-contrast, light-sensitive
photographic film that has been exposed using a pizeo-electric effect
which converts the electro-magnetic signal on a magnetic sound track into
a light beam that exposes the film. After exposure, the film has to be
developed as any other photographic film. What is produced is a clear,
light-blue piece of film with a 1/4" black silver sound track on
one side.
Since Optical Tracks are film and cannot be resynced once made, precautions
should be taken before making the track to insure that the source track
is in sync with the picture.
Sometime sync problems can result from importing and exporting tracks
to and from editorial systems. The exported track source should be checked
with the picture after it has been exported from the editorial system
and before the Optical Track is made.
The black edge of the modulation viewed under a microscope is not completely sharp. It appears to be a mini fade to white (clear). This lack of edge sharpness can be minimized with the proper use of an effect called cross-modulation.
Cross-modulations works this way. If the mini fade of the optical track can be blended in a complementary (opposite) way with the mini fade of the print film the result is a sharper edge to the print image.
Sound companies send cross-modulation tests to every film laboratory where their optical tracks will be developed. Two decisions are made as a result of these tests. One is the exposure level at which the track will be "shot" and the second is the gamma level (contrast) at which the optical track will be developed. These two factors are complementary, in that within a limited range, less exposure with more developing or more exposure with less developing will both yeild good optical tracks.
