ACL - Dual State Variable VCF

The Dual State Variable VCF consists of two multimode filters with high-pass, band-pass, notch and low-pass outputs. The circuits feature an edge steepness of -12 dB per octave. Routing options allow serial or parallel connection. Thanks to normalizations and a total of three cutoff potentiometers, stereo material can be processed as comfortably as mono signals. Furthermore, a well-known feature from the Oberheim SEM synthesizer was implemented in the Dual State Variable VCF: The notch characteristic can be weighted more to the high-pass or low-pass side.
The basic character of the Dual State Variable VCF is rather soft, yet full-bodied. The resonance sounds extraordinarily rich and wet, even high values never sound all too harsh. While self-oscillating, the filters can be played like sine oscillators. By modulating both circuits in opposite direction, users are able to achieve interesting stereo effects.

The filters of the Dual State Variable VCF are identical in design. Per instance, there is an audio input with level control as well as potentiometers plus CV connectors for cutoff and resonance parameters. The modulation intensity of the control voltage channels can be adjusted via bipolar attenuators. In addition, each of the filters features a 1v / octave input, allowing the circuits to be played like sine oscillators while self-oscillating. On the output side, there are four sockets per VCF, which emit high-pass, band-pass, notch and low-pass signals. An extraordinary feature known from the Oberheim SEM: The notch characteristic can be blended into high-pass or low-pass.

The VCF’s signal flow is determined by two switches. With the first control element, users can wire both circuits in parallel or in series. The second switch decides whether the band-pass or notch output of filter A is fed to filter B.

Audio and CV inputs of both filters are normalized. The cutoff frequencies of the VCFs can be edited simultaneously via the Cutoff A/B potentiometer.