b = fir1(10,25/50);
a = [1];
[H,F] = freqz(b,a,128,10000);
magH = abs(H);
magDB = 20*log10(magH)
subplot(2,1,1);plot(F,magH);grid;
xlabel('Frequency  (Hz)');
ylabel('Magnitude'); 
subplot(2,1,2);plot(F,magDB);grid;
xlabel('Frequency  (Hz)');
ylabel('Magnitude in dB');