A compressor accomplishes it'sits task of reducing dynamic range by using a variable gain [[amplifier]] to reduce the [[gain]] of the signal. This is typically carried out in analog systems by using a [[voltage controlled amplifier]] which has its gain reduced as the power of the input signal increases. Optical compressors use a light sensitive diode to detect changes in signal gain, as expressed via a physical light. This vintage technique is believed by some to add smoother characteristics to the signal, because the response times of the light and the diode soften the attack and release.