What are the steps for making a 'fft filter'?
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Hi,
I am new to the fft filter and I want to know the steps of building a fft filter, e.g., what I need to know before I build this filter. In addition, my Matlab has Signal Processing Toolbox installed.
I am given a sequence with 131072 samples, the sampling rate is 500Hz. Also, I want to filter this sequence using low pass filter with cutoff frequency=20Hz.
My question is about the syntax of "fftfilt", how do I generate the coefficient vector b by providing the cutoff frequency(the freq range that i'm interested).
Thanks for your help, Kay
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Honglei Chen
am 23 Sep. 2011
Hi Kay,
You need to first design the filter to get coefficient b and then pass it into the fftfilt. For example, assume you need a 10th order filter with cutoff of 20 Hz and sampling frequency of 500 Hz, you can do
h = fdesign.lowpass('N,Fc',10,20,500);
hd = design(h);
x = rand(131072,1);
y = fftfilt(hd.Numerator,x);
HTH
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Arturo Moncada-Torres
am 23 Sep. 2011
Try checking this previous post. Although it is for a HPF, the main steps are practically the same ;-)
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