Learn how to build an analog voltage-controlled filter (VCF) from scratch in this detailed tutorial video. Explore the intricacies of synthesizer circuit design, focusing on the challenging aspect of voltage control. Discover the principles of resonant high-pass filters, understand the basics of vactrols, and learn how to create DIY vactrols using FIMO clay. Dive into LED driving techniques, offset voltages, voltage mixing, and frequency range adjustment. Follow along with a comprehensive bill of materials and step-by-step instructions. Conclude the learning experience with a sound demonstration showcasing the finished VCF circuit.