K9 Dynamic Filter

K9 // Dynamic Filter

Kilpatrick Format Multi-mode Filter and Envelope Follower - 1 Space

The K9 filter offers a wide variety of filter sounds through its multi-mode design. With a clean and precise character, K9 is not designed to have a highly characteristic sound but instead to be a useful building block in the exploration all kinds of timbres. To add even more capabilities to the Kilpatrick Format system the K9 also includes a highly versatile envelope follower section which can be used to track an audio signal and provide useful outputs.


The K9 filter is completely analog and based on a four-stage low-pass filter architecture. Through the use of a computer-controlled pole-mixing system, nine different filter modes can be selected:

  • PHASER - A useful phasing effect for adding animated quality to any patch.
  • LPF1 - Single-pole low-pass filter.
  • LPF2 - Two-pole low-pass filter.
  • LPF3 - Three-pole low-pass filter.
  • LPF4 - Four-pole low-pass filter.
  • HPF1 - One-pole high-pass filter.
  • HPF2 - Two-pole high-pass filter.
  • BPF1 - One-pole band-pass filter.
  • BPF2 - Two-pole band-pass filter.

The cutoff frequency can be controlled manually or via CV by using the V/OCT IN control which is calibrated for a V/octave response for proper key tracking in a patch. The FM control allows exponential FM control with an adjustment input level. The resonance control can be adjusted manually or changed by voltage control.

In addition to the filter functions, the filter also has a built-in VCA, making it great for starter systems. The AM LEVEL and AM CV IN allow voltage control, and the VCA GAIN adjusts the level manually.

Envelope Follower

The envelope follower section allows the average amplitude of an audio signal to be tracked and used as a control voltage. Either a banana (high level) signal or a minijack (low level) signal can be used as the input. The FOLLOW IN LEVEL adjusts the input sensitivity and the SMOOTHING control affects how fast the signal is tracked.

Four simultaneous outputs are offered:

  • Normal (+) envelope output
  • Inverted (-) envelope output
  • Gate signal - enabled when the envelope signal is about a preset threshold
  • Pulse signal - pulses when the envelope signal exceeds a preset threshold


No longer available.