However, be aware that the phase may not be accurate when the magnitudes are extremely small.
Why am I unable to obtain a phase response plot using the FREQZ function?
I unable to obtain a phase response plot using the FREQZ function, but am able to get a phase plot when using the FREQZPLOT functionwith the same parameters. I would expect the plots to be the same using both functions. I use the following code to obtain the frequency response vector, but the phase response plot has nothing in it: freqz(num,den,4096,Fs); When I try to the following command: [h,f,s]=freqz(num,den,4096,Fs); freqzplot(h,f,s); I get a phase response plot. Note that my frequency response vector contains elements that have very small magnitudes.
Prashant Kumar answered .
2025-11-20
abs(h) <= eps^(2/3)
The elements with extremely small magnitudes are then set as having undefined phase. That is why you do not see a phase plot when you use the FREQZ function without any outputs using the following command:
freqz(num,den,4096,Fs);
[h,f,s]=freqz(num,den,4096,Fs); freqzplot(h1,f1,s);