I'm new to DSP so the question might seem a little bit stupid: When using a low pass filter (say Butterworth filter) with Python, I came across an algorithm with which I can reconstruct my signal after filtering (from scipy.lfilter). I'm just wondering how the signal is reconstructed. I thought they used Fourier transform but it's not mentioned. Thank you!
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I agree with A_A. Just take deeper in Butterworth filter design and this article may help you to understand better.