Owner’s Manual
Page 11
Optical Compression
There are many ways to create a circuit that controls the gain
reduction of a compressor. Each method has its own character-
istics and all have produced popular compressors over the years.
One of the most popular types is the optical compressor.
An optical compressor is created from the combination of a light
sensitive resistor called a photocell, and a light source such as a
small bulb or LED. Devices called optocouplers combine a pho-
tocell and light source inside a light-proof package. The photo-
cell increases its resistance when input level increases the intensity
of the light - that increased resistance provides the compression.
While attack is the time it takes for compression to occur,
“release” is the time it takes for the signal to return to normal.
Photocells have a characteristic called “memory” that makes
such a compressor interactive. When just a few brief attacks have
been experienced, the photocell recovers quite fast, bringing back
the level more quickly. However, after repeated and constant
attacking, the photocell builds up a memory of the light pulses
and recovers more gradually. This helps to smooth out the com-
pression and preserve the character of the sound.
The optocoupler used in the Punch Factory is designed especial-
lyfor audio and is produced exclusively for Aphex. It has special
characteristics unusually well suited to musical instrument com-
pression, making the Punch Factory unique in the world of com-
pression.
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