Butterworth filter: Number of coefficients?
7 views (last 30 days)
Show older comments
Hello
I am trying to create a low pass filter. My device has a sample rate of 100 and the cutoff value should be 10 Hz.
But according to the manual the filter should also have a setting "number of coefficients". And this should be 40 in my case...
How can I implement the number of coefficients into the filter?
Thanks.
My Code:
Fs = 100;
Fco = 10;
Fn = Fs/2;
Wn = Fco/Fn;
[b,a]=butter(1,Wn,'low')
m_filtered=filter(b,a,m)
0 Comments
Accepted Answer
Star Strider
on 19 May 2020
The first argument to butter is the filter order, and the number of coefficients in the transfer function vectors will be 1 less than that, so:
Fs = 100;
Fco = 10;
Fn = Fs/2;
Wn = Fco/Fn;
n = 40;
[b,a]=butter(n-1,Wn,'low');
figure
freqz(b,a,2^14,Fs)
should do what you want.
Note that this creates an unstable filter.
Are you absolutely certain that you want to use a IIR filter here? A filter order of 40 is more typical of a FIR filter, especially for a lowpass application such as this. (If you want a FIR filter instead, use the kaiserord and fir1 functions to create it.)
8 Comments
More Answers (0)
See Also
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!