A favorite “West Coast” module that synthesists of all tastes should check out is the LPG: the low-pass gate, which acts like a VCA but with a filter element that also dampens the high frequencies. The classic application of an LPG is to tame the harmonics created by an FM oscillator pair to create the infamous “Buchla Bongos” sound; I also find LPGs to be useful for arpeggiated or sequenced musical lines.

A new “hybrid” application I’ve found LPGs to be useful for is to process the output of dedicated percussion modules. An LPG naturally damps both the amplitude and harmonics of the input to mold most sounds into a typical percussive shape, freeing you up to dial in the initial noise and harmonic mix you like without worrying about the original sound ringing out too long or taking up too much room frequency-wise in a mix.

I’ve become particularly fond of the sound and controllability of the Pittsburgh Modular Lifeforms Dynamic Impulse Filter (DIF for short), which replaces the traditional vactrol circuitry with a new “impulse” circuit that has a wider range of user-tunable decay which does not vary from module to module (normally an artifact of using vactrols). Either your own envelope or just this impulse circuit may be used to control the DIF’s Sallen-Key two-pole low pass filter circuit, which has a good sound: smooth in LPG mode; aggressive in resonate filter mode.

In the video below, I pair up the DIF with a Noise Engineering Basimilus Iteritas to create some very tough yet very well-controlled percussion sounds:


This is the 4th of four movies on the Dynamic Impulse Filter that is in my course Learning Modular Synthesis: Eurorack Expansion. The first movie provides an overview of the DIF, with the other three cover melodic, “Buchla Bongo” (an update on the movie linked to up top), and hybrid percussive uses. I’ll be covering other LPGs in the Eurorack Expansion Weekly series; if you don’t have an LPG of your own yet, the DIF makes an excellent starting point.