close all, clear all, clc
N = 20;
fn = [0.3 0.4];
B = fir1(N, fn)
[H, w] = freqz(B, 1);
subplot(2,1,1)
stem(0:N, hamming(N + 1))
subplot(2,1,2) 
plot(w/(2*pi), 20*log10(abs(H))), grid