Electro-Harmonix White Finger XO Analog Optical CompressorLet There Be White! Just like its cousin the Black Finger, the White Finger yields transparent, long sustain that preserves attack. Two optocouplers (LED and lamp) offer distinctly different readings and uniquely varied compressions. The White Finger features multiple FETs instead of vacuum tubes, making it the affordable alternative. Specifications True Bypass LED optocoupler for a faster attack compression Lamp optocoupler for softer blooming