2. Signal filter (pt1 and pt1pt1:  non-causal, in MATLAB called filtfilt)

To explain the difference between normal pt1-filter and a non causal pt1-filter, two copies are made from signal 3 >> signal 4 and 5

1. Signal 4 ist filtered with pt1 filter of 200ms (like a RC filter, resistor and capacitor)
2. Signal 5 ist filtered twice (200ms); from start to end of protocol and from end to start; it is a non-causal filter!
   Advantage: there is no phase shift to the original signal; ideal for subsequent documentation or a better view of noisy signals

In the example you will see at point 894s, that the signal 4 has a phase shift of 200ms and signal 5 is congruent at this point.