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The five waveshapes produced by the VCO, the description of which was concluded last month, can further be processed to produce a wide range of tone colours using the tone-shaping modules, which consist of the voltage- controlled filter (VCF), voltage- controlled amplifier (VCA) and the Attack, Decay, Sustain, Release (ADSR) envelope shaper. This month`s article describes the VCF, which is the module that tailors the spectrum of the VCO signal. A somewhat unusual circuit is employed for the VCF, and four filter functions are available: lowpass, highpass, bandpass with variable a, and notch. Despite this versatility the VCF circuit is simple to construct, easy to adjust and reliable.