# How to determine cut off frequency for high pass filter using spectral density?

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

• First of all I can't see any high-pass filter... – jojek Jul 15 '15 at 8:16
• I can't really see a low-pass filter either. Maybe you just forgot to apply a window (if it's really a low-pass filter)? – user13706 Jul 15 '15 at 19:02