optocompressor

An optocompressor, also known as an optical compressor, is a type of audio dynamics processor that uses an optical circuit to control the gain reduction. This optical control is achieved through the interaction of a light source and a photosensitive resistor. When the audio signal exceeds a certain threshold, it triggers a light emitting diode (LED) or lamp, which in turn illuminates the photosensitive resistor. The increased light causes the resistance of the photoresistor to decrease, which then attenuates the audio signal.

The key characteristic of an optocompressor is its smooth and natural-sounding compression. The inherent soft-knee behavior and the gradual response of the optical components contribute to a less abrupt and more musical compression compared to other compressor types like VCA or FET compressors. This makes optocompressors particularly popular for vocal processing, bass guitar, and acoustic instruments where a transparent and unobtrusive level control is desired.

The attack and release times of an optocompressor are typically not independently controllable but are determined by the characteristics of the light source and the photosensitive element. Faster attack and release times are generally not achievable with standard optical components, leading to a more program-dependent and organic compression characteristic. Despite these limitations, the ease of use and the pleasing sonic quality of optocompressors have secured their place in recording studios and live sound applications for decades. Common examples include the Teletronix LA-2A and the UREI LA-3A.