Runciter. Filter with parallel lowpass, bandpass and highpass outputs, resonance, controllable input overdrive and brick-wall fuzz.
Filters were always dramatic sound-shaping tools, one reason why they’re still so popular. But users today expect more than a simple resonant lowpass, so here's RUNCITER! For classic wah-wah, add low- and highpass together then control cutoff from a MIDI pedal. Or max out the resonance and drive the input from -48db to 48dB for a vast range of effects... instant glittering sweeps or absolute filter mayhem!
Filters are very dramatic sound-shaping tools, one reason why they’re still popular after so many years. Technically related to equalizers, filters are often used much more radically and creatively.
There are several classic designs with different characteristics. The most familiar are the so-called cascade and state variable filters. Both these types offer multiple modes (lowpass, bandpass and highpass) as well as a feedback circuit for resonance. Like in equalizers, feedback intensifies frequencies around the cutoff point, but unlike EQ, the ability to emphasize frequencies to the point of self-oscillation is considered desirable. Runciter follows the state variable principle, and can deliver lowpass, bandpass and highpass forms simultaneously, with variable resonance.
Especially lowpass filters are found in practically all analog synthesizers and digital emulations. Modulating cutoff frequency via an envelope generator is such standard practice that most synths include a dedicated envelope for this purpose. Cutoff modulation via envelope generator is also suitable for filter-based effects, so Runciter offers several envelope options.
Another interesting characteristic of filters is overdrive. Depending on the circuit design, some components can be easily pushed beyond their natural limits, resulting in a strangely pleasing distortion. Filters were soon designed with post-distortion in mind e.g. the wah-wah pedal. Runciter follows the very same principle: It not only emulates the overdriven components, but also includes a powerful distortion stage.
Cutoff and Resonance
The cutoff knob controls filter frequency, with a logarithmic range of 20 Hz to 20 kHz. The rim of the knob shows the frequency, while the central display shows the same information as octaves (from 0 to 10). 1 unit corresponds to 1 octave.
The resonance (feedback) in Runciter goes from very mild to a point very close to self-oscillation.
￼Drive and Output
The drive parameter adjusts the input gain by a generous +/- 48 dB, and has a significant impact on the amount of distortion the filter circuit delivers. The output level may also be affected - use the output knob to compensate whenever necessary.
Note: The lower the input level, the louder the resonance can become in comparison. Conversely, higher input levels reduce the relative amount of resonance, and distortion takes center stage.
Lowpass, Bandpass and Highpass
These knobs mix the output of all three filter types. You can e.g. emphasize the cutoff frequency of the lowpass (without using resonance) by adding a little bandpass. If the lowpass and highpass are set to the same value, the result is a so-called peak filter. The height of the peak can be controlled via the resonance knob.
The Mix knob cross-fades the output from 100% dry to 100% filtered.
Fuzz and Colour
The fuzz knob adds strong distortion, and its tone is controlled via the colour knob. Of course the distortion sound is highly dependent upon the audio being processed!
Technical note: The fuzz parameter is actually a level-dependent offset which forces the signal against a ‘brick wall’ within the non-linear filter circuitry. This method creates even-numbered harmonics like tube distortion. It is usually considered pleasant, but this type of distortion often means a loss of bass. You normally wouldn’t need much fuzz for a crunchy sound, but response to more extreme values is surely a plus!
Envelope, Env Rate, Env Sense
Runciter has a built-in envelope generator, or more precisely an envelope follower: The input signal is analysed, the data is turned into a control signal that modulates the cutoff frequency. Cutoff can rise and fall in parallel with peaks and troughs in the input signal, resulting in a sound similar to an ‘auto-wah’ stomp box.
The large envelope knob controls the modulation amount, either negative or positive. The smaller env rate knob affects modulation speed by smoothing the envelope. The env sense parameter determines the threshold of the analysis (like the threshold in compressors).
Envelope movement is displayed in a green bar below the env mode knob. The best strategy is usually to set a medium env rate, find the env sense value that delivers maximum movement in the indicator, then adjust cutoff and envelope to taste.
This is a menu/switch with a choice of six different envelope generator modes:
fast - a very short attack time paired with a slow release time. This envelope mode is particularly good for percussive filter effects.
ride - medium attack and decay times. This mode is suitable for smoothly ‘riding’ the input.
slow - reacts rather slowly to jumps in volume, but falls fairly rapidly during quiet passages. Suitable for adding motion to long static tones.
transient - the input signal is analyzed for transients (steep flanks in the wave) instead of jumps in volume. As soon as a transient is found, it triggers the envelope with a short attack and an exponential decay. Transient mode is particularly good for percussive material such as drums or dynamic guitar.
note trig - use MIDI Notes to trigger the envelope.