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Ladder HPF Unit

A high-pass filter with resonance.
ladder-hpf.png

Overview

This is a digital simulation of the Moog ladder filter in a high-pass configuration with 4-poles (24dB/octave) and non-linear saturation in the feedback loop.

Frequencies below the cutoff are attenuated while leaving the frequencies above the cutoff (mostly) unchanged. The cutoff frequency is controlled by the combination of f0 and V/oct controls, while the bandwidth is controlled by the Q control.

This filter will resonate at high values of Q.

Common Filter Controls

  • V/oct: Transpose fundamental by an amount in cents.
  • f0: Set the fundamental (cutoff) frequency in Hz.

Special Controls

Q

Gain/Bias

This parameter controls the filter’s resonance. Resonance is the result of a soft-limited feedback path. This parameter sets the gain on that feedback. Higher values of Q (i.e. more feedback) yield a steeper roll-off but cause frequencies around the cut-off to be accentuated. The filter will resonate at Q-values exceeding 0.5 to 0.6.