The Filter is a voltage controlled, analog, state variable filter. The state variable topology was chosen because it allowed us to produce a very smooth and natural sounding filter, in addition to offering several other modes of operation, each with a unique sound and energy all their own.
There Is No Sweet Spot
The Filter defines the Jekyll and Hyde sound of Pittsburgh Modular. On the one hand, it offers a warm, organic sweep through the full frequency range. The lowpass filter is gummy and relaxed while the highpass is clean and defined. On the other hand, switching into oscillator mode turns theFilter into a howling beast capable of chunky walls of distortion and noise. The goal was to produce a filter that does not have a single sweet spot. We worked to make every turn of a knob or flip of a switch offer something new and musically engaging.
Multiple filter responses are available simultaneously including lowpass, highpass, and bandpass. The fourth filter response is a variable response that shifts between lowpass, notch, and highpass.
Switch It Up
Two switches, Gain and Mode, further expand the capabilities of the Filter. The Gain switch modifies the functionality of the Q while the Mode switch toggles between filter and oscillator modes.
Gain Switch (1-Q) Setting the Gain switch to "1" adds an inverted VCA response to the Q. Increasing the resonance (Q) decreases the output level of the Filter. An example patch would be to set the Gain switch to "1" and send a control voltage from an envelope generator to the QCV input. Switching the Gain switch to "Q" returns the standard filter Q response.
The Mode switch (F-O) switches between Filter and Oscillator modes. Set to (F)ilter, the Pittsburgh Modular Filter will not self oscillate, and operates as a clean, organic filter. Set to (O)scillator and without an incoming audio signal, the Filter produces a high quality voltage controlled sine wave. Adjusting the Q while in (O)scillator mode modifies the shape of the waveform. Add an incoming audio signal to the (O)scillator mode and the output changes dramatically. At normal settings the incoming signal modulates the self oscillating filter to produce complex sounds. At more extreme settings, where the Filter starts to struggle with self oscillation, the Q adds anything from ringing fuzz to heavy distortion to the incoming audio.