Optimal FIR Filter Design Procedure for the Parks–McClellan Algorithm

This code for calculating frequency/phase response works fs=8000;

f=[ 0 0.15 0.25 0.4 0.5 1]; % Edge frequencies

m=[ 0 0 1 1 0 0]; % Ideal magnitudes

w=[ 39 10 39 ]; % Error weight factors format long

b=remez(25,f,m,w) % (25+1) taps Parks-McClellan algorithm and Remez exchange

freqz(b,1,512,fs); % Plot the frequency response

axis([0 fs/2 -80 10])

But this doesn't work when i change the filter specification to:

fs=8000;

f=[ 0 0.01750 0.01875 0.06750 0.06755 0.1250]; % Edge frequencies

m=[ 0 0 1 1 0 0]; % Ideal magnitudes

w=[ 1220 1 1220 ]; % Error weight factors format long

b=remez(134,f,m,w) % (134+1) taps Parks-McClellan algorithm and Remez exchange

freqz(b,1,512,fs); % Plot the frequency response

axis([0 fs/2 -80 10])

Answer 1

[Satyajeet Sasmal]

Hi Zehaib

For your second filter specification, setting the axis limits to [0 fs/2 -80 10] forces your y-axis to be limited from -80 db to 10 db. Whereas, your Magnitude vs Frequency graph for the second case requires your magnitude to in the order of 2.4k db to 3k db (see image below)

Figure 1 is the second filter in your case.

Hope this answers your question.

-Satya