Modeled from the Doepfer A-124 hardware module, based on a vintage “Wasp” circuit using a non-linear 2-pole SVF (State Variable Filter) with OTA filter stages and CMOS buffers.
Solo bass with various cutoff and resonance:
Bass and lead with drum machine:
Doepfer A-124 for VCV Rack simulates a fully analog signal path including over 30 discrete components with over 60 component parameters. All 3 CMOS buffers are modeled using PMOS/NMOS complimentary pairs, allowing hardware-accurate saturation when driven at high levels.
Medium and high-quality DSP modes are available, using 1.5-3% and 2-4% CPU, depending on your machine.
To filter audio, patch an audio signal into the Audio In port, and listen to the BP Out (band-pass) or LP/HP Out (mixed low-pass / high-pass) output.
Adjust Lev. to set the input gain level, Frq. to set the filter cutoff frequency, and Res. to set the filter resonance. The Frq parameter tooltip displays the exact cutoff frequency in Hz.
To control the cutoff with CV, patch a CV signal into the CV1 or CV2 ports. The amplitude of the CV2 signal can be adjusted with the CV2 knob. The CV1 input tracks roughly 1V/octave, but due to the chaos of the analog circuit (especially with high resonance), the tuning does not perfectly match equal temperament. Both CV1 and CV2 inputs can be used simultaneously.
The Mix knob mixes the low-pass and high-pass signal for unique filtering effects. At intermediate values between the knob’s extremes, the LP/HP output functions as a variable shelf filter, with optional resonance. At the middle “5-5” position, the LP/HP output functions as a notch filter, creating interesting effects when resonance is used.
Right-click the panel to tweak module settings.