This document allows you to perform online Fourier filtering using an example of a signal consisting of two parts simulating pre-emergency and emergency modes. The pre-emergency mode is modeled by a sinusoidal signal, the emergency mode is modeled by a sinusoidal signal and an exponent. You can see the essence of the Fourier transform here. Instructions for using the Fourier filter are given here.

**Input signal:**

**Pre-emergency mode:**

Pre-emergency duration: ms

Signal: *i*(*t*) = · sin(2π··*t* + °)

**Emergency mode:**

Emergency duration: ms

Signal: *i*(*t*) = · sin(2π··*t* + °) + exp(-·*t*)

**Fourier filter options:**

Frequency of filter: Hz

Sampling frequency: Hz