Surge XT's Vintage Ladder filter models the Moog ladder circuit via numerical integration of the differential equation

The Vintage Ladder filter in Surge XT offers four subtypes that model the Moog ladder resonant lowpass filter. Type 1 uses Runge-Kutta numerical integration of a differential equation approximating the analog circuit dynamics, giving the most physically accurate response. Type 1 Compensated adds gain compensation. Type 2 builds on Smith/Stilson and Antti Huovilainen’s work for a different analog character. Type 2 Compensated adds gain compensation. The Vintage Ladder is more CPU-intensive than the older Legacy Ladder but generally sounds better. Both support stable self-oscillation. The K35 filters model the Korg MS-20 topology: increasing resonance makes them sound progressively dirtier and more aggressive, with five saturation subtypes.

Examples

Use Vintage Ladder Type 1 for a classic Moog-style resonant lowpass sweep on bass. Use K35 with Heavy Saturation for an aggressive, gritty Korg-style filter on leads.

Assessment

Why does the Vintage Ladder require more CPU than the Legacy Ladder? What is the timbral difference between the K35 and Vintage Ladder filters at high resonance?