Hi, What I have been trying to achieve is learn about signal processing ,particularly filters. Newbie to DSP,so far! I have 2 signals with me.Voltage and current signals. Both are unfiltered. I have managed to filter out these two signals to remove most of the noise. Now,I want to find the impedance in the signals before the fault occurs and after the fault occurs. This is the algorithm that I have used (Link to the image has been attached) http://s1284.photobucket.com/user/sandycook9211/media/Screenshot101_zpse9cf445d.png.html While I have managed to get peak current and peak voltage values correctly,(I verified by finding maxima of data signals) the trend of resistance and reactance values is bothering me. For starters, can someone confirm the above algorithm to calculte Ipeak,Vpeak,R and X for "before fault" (input is filtered V and I signals) and "after fault" (unfiltered V and I raw signals) ? My data window is 60 and I run through 60 samples for each iteration. Ie,1st iteration from 1 to 61st, 2nd iteration ,from 2 to 62nd etc until I traverse the entire data. Moreover, I just assumed "before fault" to mean filtered signal and "after fault" to mean unfiltered input signal. Is this correct? Any help will be appreciated,thanks in advance!