Question

please let me know reference of this MATLAB code.

please explain this code line by line.

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N=256; %% sampling number

n=linspace(0,1,N);

fs=1/(n(2)-n(1));

x=5*(sin((2*pi*10*n))); %% create signal

N=length(x);

f=[-fs/2:fs/N:fs/2-fs/N];

subplot(211)

plot(f,fftshift(abs(fft(x))));

title('|G(f)|');grid;

xlabel('frequency');

ylabel('|G(f)|');

%Zero padding

xx=[zeros(1,128) x zeros(1,128)];

N=length(xx);

f=[-fs/2:fs/N:fs/2-fs/N];

subplot(212)

plot(f,fftshift(abs(fft(xx))));

title('|Gz(f)|');grid;

xlabel('frequency');

ylabel('|Gz(f)|');

Answer 1

This code is see the effect of padding zeros in the signal. It increases the Resolution of the fft.

I have added comments to each line of code for your understanding

N=256; %The number of samples taken for x(n)

n=linspace(0,1,N); %creating the values of points @ where to sample the function x(n)

fs=1/(n(2)-n(1));   %sampling rate

x=5*(sin((2*pi*10*n))); %% create signal

N=length(x);    %length of the signal is equal to the number of samples taken

f=[-fs/2:fs/N:fs/2-fs/N];   %as we sample a signal with fs, We can only see the spectrum of it in the range -fs/2 to fs/2

subplot(211)    %making a plot of 2 images in one and usign the first image

plot(f,fftshift(abs(fft(x)))); %ploting the fft of the signal

title('|G(f)|');grid;

xlabel('frequency');

ylabel('|G(f)|');

%Zero padding

xx=[zeros(1,128) x zeros(1,128)];   %padding zeros at the front and back of the signal

N=length(xx);   %defining new lenghth of the signal

f=[-fs/2:fs/N:fs/2-fs/N];   %%as we sample a signal with fs, We can only see the spectrum of it in the range -fs/2 to fs/2

subplot(212) %making a plot of 2 images in one and usign the second image

plot(f,fftshift(abs(fft(xx)))); %ploting the fft of the padded signal

title('|Gz(f)|');grid;

xlabel('frequency');

ylabel('|Gz(f)|');

As can be seen, plot 2 has more details on the graph than plot 1. This shows the increases resolution of the fft