Variable resonance filter

https://www.modulargrid.net/e/random-source-variable-q-vcf

The Serge Extended Variable Resonance filter (VCFQ) is probably the most famous filter of the Serge system and one of the essential Serge modules. It is an excellent, extremely versatile general-purpose VCF that provides simultaneous low-pass, high-pass, band-pass and notch (band-reject) outputs combined with unique flexibility. Its trigger in, LOW mode and self osciallation allow a variety of uses from Oscillator to VC processing.

http://randomsource.net/docs/RandomSource_Serge_VCFQ_Euro.pdf