The ASM-1 VCF Module


The VCF is a tone-shaping module which processes the `raw' output of the VCOs to provide a wide variety of different tone colours and amplitude dynamics.

The VCF has four filter functions. A low-pass filter with a rolloff of -12dB per octave above the turnover point, a highpass filter with a rolloff of -12dB per octave below the the turnover point, a bandpass filter with variable Q and minimum slope of -6dB per octave on either side of the centre frequency, and a notch filter. The turnover point - or centre frequency in the case of the band filters - is the same for all four filter functions, and can be varied by the application of a control voltage.

The VCF is a state-variable design with an exponential voltage-to-frequency response set at 1Volt/Octave

The unit has the following features:-


  • CV Inputs (5 - 4 x +ve and 1 x ve)
  • Outputs for Highpass, Bandpass, Lowpass and Notch


Terry Mikulic
"Reader's Equipment, A VCF and an Envelope Generator"
Electronotes, Vol. 5, No. 33, Jan. 1, 1974, pg 5.

Bernie Hutchins
"The ENS-76 Home-Built Synthesizer System - Part 5"
Electronotes, Vol. 8, No. 71, Nov. 1976, pp 14-19

Copyright 2000. All rights reserved.     Revised: January 27, 2008