An elliptic (Cauer) IIR filter, realised as a cascade of 2nd-order biquad sections. Elliptic designs are equiripple in both the passband and the stopband, which gives the steepest transition of any classic filter for a given order — ideal when you need a sharp cutoff without a very high order. Choose a Response (lowpass or highpass), set the Order (2 to 8) for steepness, the corner Frequency, and the tolerated Passband dB ripple and Stopband dB attenuation. Like all IIR designs it trades linear phase for efficiency. The filter adapts automatically to the incoming signal's sample rate.
The elliptic analogue prototype for the chosen order and ripple/attenuation specification is transformed to the digital domain and factored into a cascade of 2nd-order biquad sections, each advancing one sample-frame per tick to stay inside WaveWarp's sample-per-sample engine. Every parameter change re-derives the cascade.