To introduce the State Variable Filter (S.V. Filter), we should first set up the oscillator section to produce a sawtooth waveform which is rich in overtones. This is a good input signal fodder to explore the State Variable Filter. First, please load the Init sound – this time, you do not need to crank up A on the Output Mixer!
Set Oscillator A’s PM Self to 90 % for a nice sounding saw-wave.
Set Envelope A’s Sustain to 60 % in order to produce a steady tone.
Now please proceed like this:
Enabling the S.V. Filter:
Press S.V. Filter (Output Mixer).
Set the Encoder to approx. [50.0 %].
The S.V. Filter input of the Output Mixer is fully open now and you can hear the signal passing the filter. Since input A is closed, all you are hearing is the plain S.V. Filter signal.
Press A – B (State Variable Filter).
This parameter determines the ratio between the Oscillator/Shaper signals A and B, fed into the S.V. Filter input. For now, keep it at its default setting A, i. e. [0.0 %].
The very basic Parameters:
Press Cutoff (State Variable Filter).
S.V. Filter (Output Mixer) is flashing to let you know that the S.V. Filter is part of the signal path.
Sweep the Encoder across the entire value range and dial in the default value [80.0 st].
You will hear the characteristic transition from bright to dull since overtones are gradually being eliminated from the signal. At very low settings, when the cutoff setting is below the frequency of the fundamental note, the output signal might become inaudible.
Press Reson (State Variable Filter).
Sweep the Encoder across the entire value range and dial in the default value [50.0 st].
When increasing resonance values, you will hear frequencies around the cutoff setting becoming increasingly edgier and more pronounced. Cutoff and resonance are the most effective filter parameters.
Excursion – Controlling the current Parameter using Ribbon 1
Sometimes, it can be more useful (or funnier) to control a parameter using a ribbon controller rather than an encoder. This is useful when performing with the parameter as well as adjusting values very accurately. To assign a Ribbon to a specific parameter (here the Cutoff of the S.V. Filter), simply:
Press Cutoff (State Variable Filter).
Press Mode (Base Unit Control Panel) until the Base Unit Display shows Cutoff. This mode is also called Edit Mode.
Slide your finger across RIBBON 1.
The parameter currently selected (Cutoff) is now controlled by RIBBON 1, or your finger tip
When using the C15’s Macro Controls, the Ribbons / Pedals can control various parameters at the same time. This very interesting topic will be covered in a later tutorial. Stay tuned.
Exploring some of the more advanced S.V. Filter parameters:
Our word of advice: No matter whether you are familiar with filters in general or not, please grab the user manual and take some time to study all those flashy S.V. Filter parameters in detail.
Excursion: The S.V. Filter functionality
The S.V. Filter is a combination of two resonating two-pole state-variable filters, each with a slope of 12 dB. Cutoff and Resonance can be controlled manually or modulated by Envelope C and Key Tracking.
The spacing between both cutoff-points is variable (Spread). The filter characteristics can be swept continuously from low through band to high-pass mode (L–B–H). Both filters work in series by default but can be continuously shifted to parallel operation (Parallel).
Setting Spread to 0.0 st creates a simple four-pole filter. At higher Spread values, the spacing between the two Cutoff frequencies increases.
Cutoff and Resonance always affect both filter sections in the same manner.
L–B–H determines the characteristics of both filter sections:
L – both filter sections work in lowpass mode. High frequencies are attenuated, producing a sound that can be described as round, soft, fat, dull etc.
H – both filter sections work in highpass mode. Low frequencies are attenuated, producing a sound that can be described as sharp, thin, bright etc.
B – the first filter section works as a highpass, the second as a lowpass. Low and high frequencies are both attenuated and a frequency band with variable width (Spread) passes the S.V. Filter. Particularly at higher Resonance settings, vowel/vocal-like sounds can be achieved.
FM provides a Cutoff modulation by the Oscillator/Shaper signals A and B. Very good for aggressive and distorted sounds.
Check out the parameters mentioned above and keep in mind that they all interact with each other in some way. Use the Default button to reset a parameter value.
Envelope / Key Tracking modulation of Cutoff and Resonance:
Press Cutoff (State Variable Filter) until Env C is highlighted in the display.
Set the Encoder to [70.00 st].
You will hear the sound becoming increasingly dull over time since the Cutoff is modulated by Envelope C. Vary the settings of Envelope C parameters and the modulation depth (Env C). For more dramatic filter sweeps set the Resonance of the S.V. Filter to higher values.
Press Cutoff (State Variable Filter) until Key Trk is highlighted in the display.
Sweep the Encoder across the entire range and dial in [50.0 %].
When set to 0.0 %, Cutoff has the same value across the entire keyboard range. When reducing the Key Tracking value, the Cutoff value will increase in higher keyboard ranges and the sound grows brighter – an effect you can find with many acoustic instruments. Please check Env C / Key Trk modulation of the Resonance as well.
Changing the Filter Characteristics:
The S.V. Filter is a four-pole filter composed of two two-pole filters. The Spread parameter determines the interval between the two cutoff frequencies of these two parts.
Set the Resonance to [80 %].
Press Spread (State Variable Filter).
By default, Spread is set to 12 semitones. Try settings between 0 and 60 semitones and also vary the Cutoff.
When reducing the Spread value, the two peaks will emphasize each other and the result will be a very intensely resonating, peaking sound.
Press Spread (State Variable Filter) again until L–B–H is highlighted in the display.
Sweep the Encoder across the entire value range and dial in the default value [0.0 %] (Lowpass).
Using the L–B–H parameter, you can morph continuously from lowpass through bandpass to highpass. 0.0 % is fully lowpass, 100.0 % fully highpass. The width of the bandpass is determined by the Spread parameter.
Cutoff FM:
Press FM (State Variable Filter).
Sweep the Encoder across the entire range.
Now the filter input signal is modulating the Cutoff frequency. Usually, the sound gets increasingly nasty and abrasive. Please note that positive and negative FM can produce quite different results.
Press FM (State Variable Filter) until A – B is highlighted in the display.
A – B blends between the Oscillator/Shaper signals A and B and determines the signal ratio which is modulating the Filter Cutoff. Depending on the waveshape and pitch of both Oscillator/Shaper signals, the results can differ considerably from each other.