A 4-pole (24 dB/oct) ladder filter modeled after the topology designed by Robert Moog in 1965. Four cascaded one-pole stages with tanh saturation at input and feedback produce warm analog-style distortion that scales with drive and resonance. Five filter modes (lowpass, highpass, bandpass, notch, and resonant) cover everything from classic subtractive sweeps to sharp self-oscillating leads. Resonance drives the filter to self-oscillation at high values, generating a sine tone at the cutoff frequency. A dry/wet control enables parallel filtering.