State Variable Filter

Overview

State Variable Filter is a Zavalishin filter which implements, in addition to state-variable second-order low-pass, band-pass, high-pass, and band-stop filters, first-order low-pass, high-pass, and all-pass filters. Its cutoff frequency and resonance can both be CV-modulated, with controls for both level and depth, and there are button-selectable options to enable gain compensation, self-oscillation, matched analog Nyquist frequency, and soft-saturation clipping.

Controls

• The Freq knob adjusts the filter's cutoff frequency over the range from 20 Hz to 10 KHz, with logarithmic response.

• The Res knob adjusts the filter's resonance, or Q, over the range from 0.707 to 20. Note that the optional gain compensation (see below) reduces low-frequency response with increasing Q to prevent overload.

• The frequency CV input jack, along with its associated Depth (D) and Level (L) knobs, enables CV modulation of the filter's cutoff frequency.

• The resonance CV input jack, along with its associated Depth (D) and Level (L) knobs, enables CV modulation of the filter's resonance amount. Note that with the self-oscillation option active this can result in some very loud squeals, so approach tweaking starting from the low end of the range, and carefully.

• The Filter Type Toggle is a multistate toggle with seven positions, letting you select which type of filter you want. Note that holding down Ctrl (W) / Cmd (Mac) while left-clicking on this toggle will bring up a quick-select menu containing all the choices, to ameliorate your incipient carpal-tunnel syndrome, while holding down Alt (W) / Opt(Mac) while left clicking cycles through the choices backwards.

• The S Osc Toggle switches the filter's ability to self-oscillate on and off. Use this with care and lowered volume, as it can very quickly put you in mind of a four-engine turboprop bomber.

• The Gain Toggle enables gain compensation, which reduces low-frequency response with increasing resonance, so as to help prevent overloading of the signal.

• The Match Toggle puts the filter in a mode where it attempts to behave like a comparable analog filter, with finite, non-zero gain at the Nyquist frequency, which, for Voltage Modular, is half of its internal sample frequency of 48 KHz. You might find this more musically interesting, although it's basically a matter of taste.

• The Clip Toggle engages both a soft-saturation clipper and, since the clipper is inherently non-linear and can alias at high enough frequencies, 4X oversampling.

• The In and Out Vu Meters display the input and output levels in logarithmic scale.

• The In and Out Jacks, with their associated level knobs, are the main input and output points for the filter.