Why does filtfilt function require a negative sign?

1. What is the purpose of the Filtfilt function in Matlab?
2. What is the difference between Filtfilt and filter?
3. What is zero phase digital filtering?

What is the purpose of the Filtfilt function in Matlab?

Description. y = filtfilt( b , a , x ) performs zero-phase digital filtering by processing the input data x in both the forward and reverse directions. After filtering the data in the forward direction, the function reverses the filtered sequence and runs it back through the filter.

What is the difference between Filtfilt and filter?

You can see that although filter() and filtfilt() both remove the high frequency noise, the use of filter() introduces significant phase delay. filtfilt() has zero phase delay. Further, at t=0, the output of filter() starts at 0, whereas the output of filtfilt() has matched the initial conditions exactly ².

What is zero phase digital filtering?

1. A filter for which the phase shift is zero for all frequencies. Zero-phase filters are anticipatory and hence are not physically realizable, i.e., half of the energy arrives before the time reference so that one gets output before the input arrives.