In the Spectra Analysis Processing Block
the Critical Frequency is being normalized (Wn = cut_off_freq * 2 / freq_hz) before executing the Butterworth filter.
Is this because the Data is also being Normalized (to the mean)?
Hello @MMarcial,
I am definitely no the most confident in DSP here 
@AlexE / @yanedge could you have a look please?
Best,
Louis
Hello,
The critical frequency is normalized because the filter design library we use requires it, please see this for more information. This is unrelated to normalizing the amplitude of the data. The Spectra Analysis Processing Block does not normalize the amplitude.
Hope this answers your question.
Best,
Yan
1 Like
Yes, that answers my question.
…and indeed the amplitude is not normalized but is offset via:
# offset by the mean
fx = np.array(fx) - np.mean(fx)
Thank you