Using FFT, I want to plot a Magnitude Frequency Characteristic of a Digital FIR filter.

my filter is defined by y(n)=x(n)+0.75x(n-1)+0.5x(n-2)+0.25x(n-3). This filter should have 256 points. IBased on this characteristic, is it a low pass filter?

I am trying to plot a magnitude/frequency graph but I get a bad plot.

clc;
clear all;

b0 = 0.25;
b1 = [4 3 2 1];

b = conv(b1,b0);

[h,w]=freqz(b,256);

plot(w/pi, 20*log10(abs(h)))
ax = gca;
ax.YLim = [-100 20];
ax.XTick = 0:0.1:10;
xlabel('Normalized Frequency')
ylabel('Magnitude (dB)')

Answer 1

[Urmila Rajpurohith]

You can get Magnitude plot by running the below code

clc;
clear all;
b0 = 0.25;
b1 = [4 3 2 1];
b = conv(b1,b0);
freqz(b,256);

And from magnitude plot it is observed that the filter is a Low pass filter.