The De Gier/Vanderkley Fatboost is an active but subtle bass boost. It is designed to keep the sound as close as possible to the original passive sound. The boost is activated by a switch and gives you a maximum of 12dB boost of low frequencies. (We set it at about 4dB standard). It is ultra low noise. The result is as if your passive sound grew up intstantly. In the off position it is true bypass for a 100% passive sound.