I have a butterworth filter in MATLAB:
[B, A] = butter( 2, 3000/16000*2, 'high' );
I plot it in two ways:
[h,w] = freqz(B,A,8000); plot(w);
h = fvtool(B,A); h.Analysis = 'phase'; h.Fs = 16000; h.FrequencyRange='[-Fs/2, Fs/2)';
First plot gives me linear phase, and second one not.
Why do I get different plots?