Ehlers 2-pole low-lag lowpass filter.
Cutoff as a cycle length in samples. Give this or cutoff, not both.
Cutoff as a fraction of Nyquist in (0, 1). Give this or period, not both.
https://screamer.readthedocs.io/en/latest/ for the Python reference and full details.
Ehlers 2-pole low-lag lowpass filter.