I have 2 simultaneous signals that both are designed to measure eye movements.
They are sampled at 250 Hz.
We have 12 subject recordings.
For 3 stable periods in each subject, we choose 256 points and did an FFT.
Prior to the FFT, the data were mean-centered and detrended with a 2nd
order polynomial. They were also windowed with a Hann window.
We are focused on the magnitude spectra plots.
We have a total of 12 X 3 = 36 magnitude spectra, which we average. These averages are shown in the attached figure.
My hypothesis is that the second signal is a low-pass filtered version of the first. The filter has ringing in the passband.
I want to design a digital filter that I would apply to signal 1 that, after fft, analyses would produce a magnitude spectra like that of signal 2.
How would I go about this?