4638 is a voltage-controlled oscillator (VCO) module for the Eurorack modular synthesizer. It is capable of producing audio frequency oscillations, as well as control voltage signals. It features an intuitive and user-friendly design, including four voltage-controlled parameters: Frequency, Pulse Width, Slave Waveform, and Hard Sync. Additionally, it includes controls for octave and fine tuning, as well as a glide control for smooth transitions between oscillations. With its versatile capabilities and accessible user interface, 4638 is an ideal choice for any modular system.