Low Pass Gate
My initial attempt to model a low pass gate used a 2nd order biquad filter element, but I discovered it was unstable at low frequencies. I then tried creating a model based on the paper by J. Parker and S. D Angelo but I encountered overflow issues using their model with 32 bit calculations. In the end I decided to wing it and used a state variable filter design. Since the SVF has a 12 dB slope and the original Buchla unit is closer to 6 dB, it isn’t a particularly accurate model of the Buchla unit but I’m happy with the sound. Additionally the original Buchla design had a switch that allowed a selection of different modes, LP, VCA or both. Since we already have pretty good designs for stand-alone VCFs and VCAs I chose to implement the “both” mode only. The original design was only resonant when in LP mode and the resonance was fairly mild. This model is resonant in the combined mode and the resonance is adjustable. I initially chose the attack and decay times for the vactrol simulator based on the VTL5C3 vactrol data sheet but later doubled them based on the final sound. They can easily be adjusted if needed.
09/10/2019 @futureaztec mentioned that the MakeNoise LxD had a “strike” input allowing you to easily send a short pulse into the LPG control circuit. I thought it was a neat idea so I added one. The original model is still available.
||a gate on this input will generate a short pulse to the LPG control circuit (V2.1 only)|
||modulation input - attenuated by the mod knob|
||this value is added to the attenuated mod input|
||adjusts the filter resonance|
|2.1||LPG V2.1.audulus (42.4 KB)||09/10/2019||added a strike input.|
|2.0||LPG V2.0.audulus (41.4 KB)||08/09/2109||initial upload|