# Find Magnitude Responce at $\omega=\dfrac{\pi}{2M}$ where $M$ is the number of channel in QMF

I have frequency response of low pass filter

    M=8  %%%channel
x=8*512
d1=fir1(N-1,wc/pi,w);
% L=length(d1);
% for k=1:L
%     b2(k)=((-1)^k)*d1(k);
% end
%%%%%%Frequency response
h1=fft(d1,x);
a1=max(abs(h1));
m1=20*log10(abs(h1/ a1));
c=0:x-1
plot(f1/x,m1)


I have to find magnitude responce at $\omega=\dfrac{\pi}{2M}$ i.e., $h_1$ at $\omega=\dfrac{\pi}{2M}$

• So what's your problem with finding the magnitude at $\omega=\pi/2M$? – Matt L. Aug 23 '15 at 19:44

• if i use freqz instead of fft then what is magnitude responce at ω = π/2M.Code Given is d1=fir1(N-1,wc/pi,w);  [h1,fre1]=freqz(d1,1,x)  a1=max(abs(h1));  plot(fre1/pi,a1)  – Rajat Sharma Aug 24 '15 at 19:11