Passive LPG 1U by Intellijel

Without positive control voltage, the gate is completely closed and none of the LPG’s input signal is passed through to the output. Increasing amounts of positive CV open the gate, making the output signal both louder and brighter. At +5V, the gate is fully open and the input signal is passed through to the output.

This makes LPGs sound very different (and more “acoustic”) than the traditional complement of envelopes, VCFs and VCAs that are employed in most subtractive synthesizers. Exciting the vactrol (via the CV input) with a trigger, noise blast, or short envelope will result in a very natural sounding filtered envelope that’s reminiscent of the sonic characterics of struck objects, which are allowed to decay naturally.