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Low pass filter design

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Toygar Ozel
Toygar Ozel on 16 Jun 2020
Commented: Robert U on 17 Jun 2020
Hi, i designed a low pass filter but it is not working to 0.05 sec. After this point filter work normally. How to i can fix it thank you.
Fs=10000;
Ts=1/Fs;
signalLength=1000;
t=(0:signalLength-1)*Ts;
filtLP= designfilt('lowpassfir','FilterOrder',50,'CutoffFrequency',250,...
'SampleRate',Fs);
outputAfterFilterLPFourier = fft(outputAfterFilterLP,NFFT)/signalLength;

Accepted Answer

Robert U
Robert U on 17 Jun 2020
Hi Toygar Ozel,
have a look at the step response of your filter, e.g. using filter designer. You can determine easily that the group delay of your filter is around 0.05 s. You would have to use another filter design in order to reduce the group delay.
Kind regards,
Robert
  2 Comments
Robert U
Robert U on 17 Jun 2020
All filters have delays. The question is rather how much delay is still ok for the application, and how phase should look like in order to not distort the signal too much. Finding a working filter within these requirements is part of the filter design work.
Kind regards,
Robert

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