Optical Sound Examples

The major commercial use of optical sound on film started in the late 1920s. In its simplest form, optical sound is just flickering the light from a light bulb, similar to waving a hand in front of a flashlight. The light being modulated by the recording is turned into electrical sound signals via a phototube or photodiode. Although seemingly crude, optical sound is at the core of motion picture sound and saw decades of intense research and development. From the first optical sound feature in 1927 through the stereo prints of Star Wars, over a dozen different optical sound formats have been used with incredible results. Each optical format, though, has its own unique sound attributes and challenges.

Release Formats


Unilateral variable-area

Bilateral variable-area

Duplex variable-area

Duo-lateral variable-area 

Multi-area (35mm) / Mauer (16mm)

Mono dual-bilateral variable-area

Stereo dual-bilateral variable-area 


Studio Tracks

Wester Electric Licensed Equiptment

Push-pull variable-density 100mil

Push-pull variable-density 200mil

ERPI push-pull variable-area 200mil

Push-pull variable-density offset 200mil


RCA Photophone Licensed Equipment

Push-pull variable-area Class A

Push-pull variable-area
Class A

Push-pull variable-area
Class B

Push-pull variable-area
Class AB

Push-pull variable-area
Class A direct positive