Optical Sound Recording with a Silicon Carbide Electroluminescent Diode
A system has been designed for the optical recording of sound using the light from a silicon carbide electroluminescent diode and ordinary films such as Plus X Reversal or Kodachrome II A with no special processing. The soundtrack was dye or silver track according to the use of color or black-and-white film. Standard projectors with ordinary exciter lamps, slit and detector systems were used. During recording, the diode was held in close proximity to the film and required no intervening optics. Diode operating currents and voltages were modest. Frequency response of 100 to 6000 Hz has been obtained with equalization on 16mm film; this was primarily limited by diode dimensions. The diode itself imposes a limit of 50 kHz. The light is yellow and is produced by a forward biased p-n junction which was about 1 by 2 mm for 16mm recording. The recording is variable density. The operating point for black-and-white film is at 10% transmission and at 70% transmission for color film at 9000 Å. Signal-to-noise ratio is about 30 to 40 dB for black-and-white film and about 20 dB for color film. Noise is mostly film noise.
- Print ISSN
- 0361-4573
- Published
- 1967-12
- Content type
- Original Research
- DOI
- 10.5594/J09071