I have filtered out the low frequency noise from the signal. For further analysis, I want to compare it with FIR filters (for which I require cut off frequency). Hence, I took the power density spectrum of noise using Welch method and found its peak and used the same as cut off frequency. The PSD looks like this .
What would be the cut off frequency? The peak occurs at $0.0031$ Hz or should I take a value between $0-0.5$Hz.
Note: The frequency range of my signal is $0-2$ Hz