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pkg load signal
Fs = 10000;
t = 0:1/Fs:1-1/Fs;
x = cos(2*pi*1000*t) + cos(2*pi*1500*t) + cos(2*pi*2000*t) \
+ cos(2*pi*4000*t) + cos(2*pi*5000*t) + cos(2*pi*6000*t);
N = length(x);
xdft = fft(x);
xdft = xdft(1:N/2+1);
psdx = (1/(Fs*N)) * abs(xdft).^2;
psdx(2:end-1) = 2*psdx(2:end-1);
freq = 0:Fs/length(x):Fs/2;
figure("name","Figure 1: Periodogram Using FFT")
plot(freq,10*log10(psdx))
grid on
title('Periodogram Using FFT')
xlabel('Frequency (Hz)')
ylabel('Power/Frequency (dB/Hz)')
%filter
%sampling frequency
Fs = length(x);
Fnyq = Fs/2;
fc = 2000;
hc = fir1(41,fc/Fs)
f_filt = filter( hc, 1, x );
N = length(f_filt);
xdft = fft(f_filt);
xdft = xdft(1:N/2+1);
psdx = (1/(Fs*N)) * abs(xdft).^2;
psdx(2:end-1) = 2*psdx(2:end-1);
freq = 0:Fs/length(x):Fs/2;
figure("name","Figure 2: Octave fir1 filtering");
plot( freq,10*log10(psdx) );
title("filtered fft");
figure("name","Figure 3: Octave fir1 filter response diagram");
freqz(hc);
title("coef freqz");
%draw my own filter results
fir_coef =[
0.000000
-0.000310
-0.001913
-0.004532
-0.004058
0.008358
0.041693
0.095752
0.155110
0.194532
0.194532
0.155110
0.095752
0.041693
0.008358
-0.004058
-0.004532
-0.001913
-0.000310
0.000000
];
my_hw = fir_coef;
figure("name","Figure 4: Verify filter using custom coefficients");
my_filt = filter(my_hw,1,x);
N = length(my_filt);
xdft = fft(my_filt);
xdft = xdft(1:N/2+1);
psdx = (1/(Fs*N)) * abs(xdft).^2;
psdx(2:end-1) = 2*psdx(2:end-1);
freq = 0:Fs/length(x):Fs/2;
plot( freq,10*log10(psdx) );
title("my filtered coeficients fft");
figure("name","Figure 5: Show custom filter response diagram");
freqz(my_hw);
title("my coef freqz");
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