Why does filtfilt provide me wrong results?

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pietro
pietro 2015-2-8
评论： pietro 2015-3-19
Hi all,
I'm using filtfilt function to filter some signals since i would like to minimize the phase lag between the original signal and the filtered one.
Here my code:
LPsig= designfilt('lowpassiir','FilterOrder',10,'PassbandFrequency',1,'PassbandRipple',0.2, ...
'SampleRate',Fs);
dfCoeff=double(LPsig);
FilteredSignalP=filtfilt(dfCoeff.Coefficients,1,Signal);
In this plot the filtered and non filtered signal are compared: http://s9.postimg.org/46qlzkz67/Immagine.jpg
There is the edge effect with a huge ripple. I found out that both effect are increased with the filter order, with a filter order of 10 both of them are negligeble. Could someone explain to me why? Anytime I have to filter data, I change almost randomly the filter parameter (filter order, filter type, passband ripple, etc) until I get a good result. How may I select the filter parameters?
Thanks
Regards
Pietro

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回答（1 个）

Erik S.
Erik S. 2015-2-8
Why do you write dfCoeff = double(LPsig);
Everything is double precision already.
Call the filter function like
FilteredSignal = filtfilt(LPsig,Signal);
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Erik S.
Erik S. 2015-2-9
Can you send the data you want to filter? Do you know which answer to get from the filter?
pietro
pietro 2015-3-19
Hi Erik, I'm sorry for the delayed reply, I was convinced I had the email notification turned on. I will send you the data this evening, because I have limited internet connection at my workplace.

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