White Finger Pedal
Optical compressors work by treating an incoming signal with optically controlled attenuator (a type of volume control) comprised of a fixed resistor and a shunt opto-coupled photocell. Because this attenuator is passive, as opposed to the more common active AGC (Automatic Gain Control) compressor circuits, it doesn't add an electronic signature to the signal, thus preserving the tone and character of the original sound.
The White finger is a fixed threshold compressor, meaning the threshold remains constant while you have the ability to change the amount of signal that goes to the compressor circuitry. The signal level sent to the compressor is controlled by both the Pre-Gain and Compress knobs. Some gain is needed to adjust the output level so that it matches the original level, and this is accomplished with a FET fixed gain pre-amp circuit. In general, compressors are used to sustain melody lines, minimize changes in signal level, or add a forward percussive effect to instruments or drums.
The proof is in the pedal...
Just like its cousin the Black Finger, the White Finger uses two optocouplers (LED and lamp) to offer uniquely varied compressions - without all the pumping or breathing of other models.
The only difference is that the White Finger has more sustain and utilizes multiple FETs instead of vacuum tubes - making it a more affordable alternative. Let there be "White!"