The VCF is a tone-shaping module which processes the `raw' output of the VCOs to provide a wide variety of different tone colours and amplitude dynamics.
The VCF has four filter functions. A low-pass filter with a rolloff of -12dB per octave above the turnover point, a highpass filter with a rolloff of -12dB per octave below the the turnover point, a bandpass filter with variable Q and minimum slope of -6dB per octave on either side of the centre frequency, and a notch filter. The turnover point - or centre frequency in the case of the band filters - is the same for all four filter functions, and can be varied by the application of a control voltage.
The VCF is a state-variable design with an exponential voltage-to-frequency response set at 1Volt/Octave.
The unit has the following features:-
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