Problem in Designing Linear Phase (Zero Phase) FIR Filter!
3 views (last 30 days)
Show older comments
Minerva Bionic
on 15 Sep 2021
Commented: Star Strider
on 16 Sep 2021
Hi everyone,
I'am going to design a linear phse low pass FIR filter.
It seems that I'm defining something wrong.
lpf = designfilt('lowpassfir','FilterOrder',6,'CutoffFrequency',5000,'PassbandRipple',1,'DesignMethod','cls','ZeroPhase',true,'SampleRate',1e6);
IIR filter works fine but with considerable phase shift.
lpf = designfilt('lowpassiir','FilterOrder',3,'PassbandFrequency',5000,'PassbandRipple',1,'StopbandAttenuation',55,'DesignMethod','ellip','SampleRate',1e6);
I dont have any idea...
0 Comments
Accepted Answer
Star Strider
on 15 Sep 2021
I do not see that you are doing anything wrong.
However I made some changes that might improve things —
lpf1 = designfilt('lowpassfir','FilterOrder',46,'CutoffFrequency',5000,'PassbandRipple',1,'DesignMethod','cls','ZeroPhase',true,'SampleRate',1e6);
↑ ← CHANGED
figure
freqz(lpf1.Coefficients,1,2^16,1E6)
lpf2 = designfilt('lowpassiir','FilterOrder',3,'PassbandFrequency',5000,'PassbandRipple',1,'StopbandAttenuation',55,'DesignMethod','ellip','SampleRate',1e6);
figure
freqz(lpf2.Coefficients, 2^16, 1E6)
These are two different filters with different characteristics.
The phase delay/distortion will likely disappear with fitlfilt rather than filter to filter the signal. Tha is true for FIR and IIR filters in MATLAB.
In general, FIR filters require a much higher order (and so are llss computationally efficient) than IIR filters to get the same response. Here, I increased the IIR filter order from 6 to 46.
.
4 Comments
More Answers (0)
See Also
Categories
Find more on Filter Design and Analysis in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!