The AutoFilter is a versatile filter effect with several unique features. You can use it to create classic, analog-style synthesizer effects, or as a tool for creative sound design.

The effect works by analyzing incoming signal levels through use of a threshold parameter. Any signal level that exceeds the threshold is used as a trigger for a synthesizer-style ADSR envelope or an LFO (low frequency oscillator). These control sources are used to dynamically modulate the filter cutoff.

The AutoFilter allows you to choose between different filter types and slopes, control the amount of resonance, add distortion for more aggressive sounds, and mix the original, dry signal with the processed signal.

Getting to Know the AutoFilter Interface

The main areas of the AutoFilter window are the Threshold, Envelope, LFO, Filter, Distortion, and Output parameter sections.

Figure. AutoFilter window.

AutoFilter Threshold Parameter

The Threshold parameter analyzes the level of the input signal. If the input signal level exceeds the set threshold level, the envelope and LFO are retriggered—this applies only if the Retrigger button is active.

Figure. Threshold parameter.

The envelope and LFO can be used to modulate the filter cutoff frequency.

AutoFilter Envelope Parameters

The envelope is used to shape the filter cutoff over time. When the input signal exceeds the set threshold level, the envelope is triggered.

Figure. Envelope parameters.
  • Attack knob and field: Sets the attack time for the envelope.
  • Decay knob and field: Sets the decay time for the envelope.
  • Sustain knob and field: Sets the sustain time for the envelope. If the input signal falls below the threshold level before the envelope sustain phase, the release phase is triggered.
  • Release knob and field: Sets the release time for the envelope (this is triggered as soon as the input signal falls below the threshold).
  • Dynamic knob and field: Determines the input signal modulation amount. You can modulate the peak value of the envelope section by varying this control.
  • Cutoff Mod. slider and field: Determines the impact of the envelope on the cutoff frequency.

AutoFilter LFO Parameters

The LFO is used as a modulation source for filter cutoff.

Figure. LFO parameters.
  • Coarse Rate knob, Fine Rate slider and field: Used to set the speed of LFO modulation. Drag the Coarse Rate knob to set the LFO frequency in Hertz. Drag the Fine Rate slider (the semicircular slider above the Coarse Rate knob) to fine-tune the frequency.

    Note: The labels shown for the Rate knob, slider, and field change when you activate Beat Sync. Only the Rate knob (and field) is available.

  • Beat Sync button: Activate to synchronize the LFO to the host application tempo. You can choose from bar values, triplet values, and more. These are determined by the Rate knob or field.
  • Phase knob and field: Shifts the phase relationship between the LFO rate and the host application tempo—when Beat Sync is active. This parameter is dimmed when Beat Sync is disabled.
  • Decay/Delay knob and field: Sets the amount of time it takes for the LFO to go from 0 to its maximum value.
  • Rate Mod. knob and field: Sets the rate of modulation for the LFO frequency, independent of the input signal level. Typically, when the input signal exceeds the threshold, the modulation width of the LFO increases from 0 to the Rate Mod. value. This parameter allows you to override this behavior.
  • Stereo Phase knob and field: In stereo instances of the AutoFilter, sets the phase relationship of the LFO modulations between the two channels.
  • Cutoff Mod. slider and field: Determines the impact of the LFO on the cutoff frequency.
  • Retrigger button: When the Retrigger button is active, the waveform starts at 0 each time the threshold is exceeded.
  • Waveform buttons: Click one of the following buttons to set the shape of the LFO waveform:  descending sawtooth, ascending sawtooth, triangle, pulse wave, or random.
  • Pulse Width slider and field: Shapes the curve of the selected waveform.

AutoFilter Filter Parameters

The Filter parameters allow you to precisely tailor the tonal color.

Figure. Filter parameters.
  • Cutoff knob and field: Sets the cutoff frequency for the filter. Higher frequencies are attenuated, whereas lower frequencies are allowed to pass through in a lowpass filter. The reverse is true in a highpass filter. When the State Variable Filter is set to bandpass (BP) mode, the filter cutoff determines the center frequency of the frequency band that is allowed to pass.
  • Resonance knob and field: Boosts or cuts the signals in the frequency band that surrounds the cutoff frequency. Use of very high Resonance values causes the filter to begin oscillating at the cutoff frequency. This self-oscillation occurs before you reach the maximum Resonance value.
  • Fatness slider and field: Boosts the level of low frequency content. When you set Fatness to its maximum value, adjusting Resonance has no effect on frequencies below the cutoff frequency. This parameter is used to compensate for a weak or “brittle” sound caused by high resonance values, when in the lowpass filter mode.
  • State Variable Filter buttons: Switch the filter between highpass (HP), bandpass (BP), or lowpass (LP) modes.
  • 4-Pole Lowpass Filter buttons: Set the slope of the filter to 6, 12, 18, or 24 dB per octave—when the lowpass (LP) filter is chosen as the State Variable Filter.

AutoFilter Distortion Parameters

The Distortion parameters can be used to overdrive the filter input or filter output. The distortion input and output modules are identical, but their respective positions in the signal chain—before and after the filter, respectively—result in remarkably different sounds.

Figure. Distortion parameters.
  • Input knob and field: Sets the amount of distortion applied before the filter section.
  • Output knob and field: Sets the amount of distortion applied after the filter section.

AutoFilter Output Parameters

The Output parameters are used to set the wet/dry balance and overall level.

Figure. Output parameters.
  • Dry Signal slider and field: Sets the amount of the original dry signal added to the filtered signal.
  • Main Out slider and field: Sets the overall output level of the AutoFilter, allowing you to compensate for higher levels caused by adding distortion—or by the filtering process itself.