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

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Martins Jancevskis
回答： Urmila Rajpurohith 2019-9-11
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)')

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采纳的回答

Urmila Rajpurohith
Urmila Rajpurohith 2019-9-11
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.

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