Applying bandpass filter on a trace

[Vivek.G.Babu]

Hi all,
This is a trace I have which is symmetric from 0.0

This is the output trace I am getting when I am applying narrow bandpass filter

Clearly, after the filtering it is not symmetric in nature. It is suppose to be symmetric as the original trace, right? What I am missing here?
Please help

[trichter]

Hi,

the default filtering is causal, causing a phase shift of the trace. If you want to use a zero-phase filter which should preserve the symmetry you can use the zerophase=True option. See documentation of this option. Causality and zero phase shift are mutually exclusive.