The Serge Variable Bandwidth Filter (VCF2) is probably the rarest classic filter in the Serge system, offering a unique combination of 2 filters. According to the 1983 Serge catalogue, the “VARIABLE BANDWIDTH VCF (VCF2) has a band-pass output which can be varied manually or with voltage control. This is a standard response synthesizer VCF, typical to filters used in many studio systems. In the VCF2, two state-variable VCF's are connected in series to produce a total of five outputs. High pass, low pass, two fixed bandwidth outputs, and one variable bandwidth output are available. The outputs are all flat-response (no resonance) so the VCF2 is suitable for processing concrete sounds without introducing resonant coloration to the timbres. Under voltage or manual control, cut-off frequency of the high and low-pass outputs are affected, as well as the center frequency of the two band-pass outputs. Both center frequency and bandwidth are independently controllable on the variable bandwidth output."