The Pulverisateur’s filter block consists of two Butterworth filters, one low-pass and one low-pass or hi-pass, with a roll-off of 12 dB per octave each, connected in series or in parallel. The filter section provides controls to set its mode of operation, cutoff frequency, resonance, keyboard tracking and filter spacing.

Pulverisateur filter section
Figure 7.6.2: The Pulverisateur's filter section.

  1. Mode: These radio buttons set the frequency response of both filters and the way in which they are connected. The “LP/LP” radio button sets both filters to low-pass and connects them in series. The “LP/HP” sets one filter to low-pass and the other to high-pass. In this mode, their connection blends from serial when spacing is negative to parallel when spacing is positive.
  2. Frequency: This knob sets the cutoff frequency of both filters as a percentage of a range going from 18 Hz at minimum to 15,5 KHz at maximum.
  3. Resonance: This knob sets the amount of resonance of both filters from no resonance at minimum to full resonance at maximum.
  4. Keyboard track: This knob sets the amount by which the pitch of incoming notes modulates the cutoff frequency of both filters from approximately 33% of the filter’s frequency range per octave below the cutoff at minimum through no modulation at center to 33% of the filter’s frequency range per octave above the cutoff at maximum. Note: A C4 note produces no modulation and is the reference pitch from which the modulation produced by other notes is measured.
  5. Spacing: This knob sets the amount by which the cutoff frequency of each filter is shifted away from the value set by the frequency knob as a percentage of the filter’s frequency range. Both filters’ cutoff-frequencies are shifted away in opposite directions. Its range goes from full negative shift at minimum through no shift at center to full positive shift at maximum. Note: When the filter mode is set to “LP/HP”, this knob also blends the connection between the filters from serial in the negative range to parallel in the positive range.

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