Drop this module (or a few of them) into your 1U row, patch in some sound sources, and then ping them with gates and CV to get some instantly pleasing results. So simple and fun!
In general, low pass gates (LPGs) control the amplitude and timbre of a signal by opening and closing a low pass filter. When the gate is closed, no frequencies are allowed to pass through (and no output is heard). As the gate begins to open, the lowest frequencies pass through to the output. As the gate opens further, the output grows louder and its high frequency content increases.
The Intellijel Passive Low Pass Gate 1U is a simple, vactrol based, 1-pole, passive low pass gate, which is controlled by an external CV input. 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.