The principle of operation of the Langevin Elop Stereo Electro-Optical Limiter is based around using a rectified sample of the audio to shine an LED (Light Emitting Diode) onto an LDR (Light Dependent Resistor). The photo-resistor in combination with a fixed resistor simply act as a changing voltage divider to attenuate the signal– like a smart volume control.
A similar principle was found in the older Teletronix & Urei LA-2A, LA-3, and LA-4 units which used a slower electro-luminescent panel-light on a conventional LDR encased in a light-tight enclosure.
The Langevin Elop Stereo Electro-Optical Limiter uses modern VACTROL technology (but with a trick!) for exact sample-to-sample tracking and no high frequency loss while digging deep into limiting– problems commonly associated with older LA-series limiters and other opto-based units.
The audio signal passes only through all-discrete Class A amplifiers in the Langevin version. Each channel can be run separately or switched to “stereo – link”. Due to their inherently quick attack, these Electro-Optical Limiters are skilled soldiers for tracking vocals or individual instruments.
