Introduction To Film

Introduction To Film
Maya Deren

Saturday, February 2, 2013

Handmade Films and Analog Sound

Handmade Films and Analog Optical Sound

Optical sound constitutes the recording and reading of amplitude based on the amount of light that is projected through a soundtrack area on a film using an illuminating light or laser and a photocell or photodiode. As the photocell picks up the light in varying intensities, the electricity produced is intensified by anamplifier, which in turn powers a loudspeaker, where the electrical impulses are turned into air vibrations and thus, sound waves. In 16 mm, this optical soundtrack is a single mono track placed on the right side of the projected image, and the sound head is 26 frames after the picture gate.  Consequently, in editing the sound should be 26 frames ahead of the picture. In 35 mm, this can be mono or stereo, on the left side of the projected image, with the sound head 21 frames after the gate .[2]
The first form of optical sound was represented by horizontal bands of clear (white) and solid (black) area. The space between solid points represented amplitude and was picked up by the photo-electric cell on the other side of a steady, thin beam of light being shined through it. This variable density form of sound was eventually phased out because of its incompatibility with color stocks. The alternative and ultimately the successor of variable density has been the variable area track, in which a clear, vertical waveform against black represents the sound, and the width of the waveform is equivalent to the amplitude. Variable area does have slightly less frequency response than variable density, but because of the grain and variable infrared absorption of various film stocks, variable density has a lower signal-to-noise ratio.
Optical stereo is recorded and read through a bilateral variable area track, recorded using Dolby Stereo matrix encoding and Dolby noise reduction. Left, center, right and surround channels are matrix-encoded into these two tracks.
In the 1970s and early 1980s, optical sound Super-8 mm copies were produced mainly for airline in-flight movies. Even though technology was soon made obsolete by video equipment, the majority of small-gauge films used magnetic sound rather than optical sound for a higher frequency range.

Check out this handmade film workshop in Dublin Ireland. Or go to the "HOW TO" videos on the lower right side of this blog.

No comments:

Post a Comment