The Filter effect adjusts the tone of the audio signal by filtering out certain frequencies.
Effect Variation - The type of filter. Low pass filter (-24, -18, -12, -6 dB per octave ladder filter), high pass filter, band pass filter, notch filter and comb filter.
Frequency - The filter's cutoff frequency.
Resonance - The amount of filter resonance (feedback). For the notch filter, it controls the bandwidth.
Overload - The amount the filter is overdriven.