Block - Low-Pass Gate 1.0
Combination VCA and LPF for West-Coast Percussive goodness
This is the 11th Block in Michael Hetrick's "Euro Reakt" series. A Low-Pass Gate is an effect that combines a low-pass filter with a voltage controlled amplifier (VCA). This effect is frequently used to make physical sounding percussion tones.
Low-Pass Gates play an extremely important role in West-coast style synthesis. These were originally made popular in Buchla synthesizers, and have been explored by modern module makers like Make Noise, Wiard/Malekko, SSF, Mutable Instruments, and more.
Most analog low-pass gates are based on opto-isolators, also known as "vactrols". A vactrol is an LED and a light sensor wrapped in a light-proof case. The vactrol effectively acts as an interpolator for modulation inputs, imparting a fast attack time and slow, rubbery decay. In typical usage, a low-pass gate will be modulated using a gate or trigger. The "vactrol" for this digital low-pass gate is implemented from research found in this paper: http://dafx13.nuim.ie/papers/44.dafx2013_submission_56.pdf For builders, it has been conveniently packaged as a reusable macro.
The vactrol's output controls the amplitude of the VCA and/or the cutoff of the low-pass filter (determined by setting the LPG's mode to VCA, LP, or BOTH). If you would like to hear some sound examples, check out the included ensemble for patching ideas!
OFFSET - Adds bias to the vactrol, leaving it partially open.
DAMP - Controls the decay time of the vactrol.
RES - The resonance of the low-pass filter. Only audible in LP or BOTH mode.
MODE - Choose between VCA (amplifier only), LP (filter only), or BOTH.
LIN/EXP - Controls the modulation curve for the VCA and filter cutoff.
ENV - Controls the depth of modulation that the vactrol imparts on the VCA and filter.
IN - Audio Input
VAC - Vactrol Input. Typically, you would hit this with a gate or trigger, but you can place any modulation source in here. The source will be modified to have a rapid attack and slow, rubbery decay.
PING - Converts a modulation source to a trigger.
DIRECT - Modulation input. Skips the vactrol and modifies the VCA/Filter directly without interpolation.
OUT - Main Output, post-filter and VCA.
ENV - Output's the vactrol's control signal.