Getting an FFT signal into a for loop.

%% Q1

clc;

clear;

n=0:1000;

fs=8000; % Sampling frequency, Hz

nfft=1024; % Number of samples

nf=fs*(-nfft/2:nfft/2-1)./nfft; % establishing frequency points (x-axis), figure 2

time=(1:length(n))./fs; % establishing time points (x-axis), figure 1

x1=5*cos(2*pi*500*time);

x2=5*cos(2*pi*1200*time+0.25*pi);

x3=5*cos(2*pi*1800*time+0.5*pi);

x=x1+x2+x3; % Sum of three signals

plot(time,x)

xlabel('Time (s)') % x-axis label

ylabel('Amplitude') % y-axis label

title('Sum of Sampled Signals') % title

figure;

X=fftshift(fft(x,nfft)); % FFT of sum of 3 signals

plot(nf,abs(X))

xlabel('frequency(Hz)') % x-axis label

ylabel('Magnitude') % y-axis label

title('Frequency Response') % title

I need help getting this last section into a for loop, i can not figure it out and need help. The graph labeled "frequency response" is the correct graph I need however i need the means of getting that graph to be from a for loop.

Answer 1

[VBBV]

clc;
clear;
n=0:1000;
fs=8000; % Sampling frequency, Hz
nfft=1024; % Number of samples
nf=fs*(-nfft/2:nfft/2-1)./nfft; % establishing frequency points (x-axis), figure 2
time=(1:length(n))./fs ;% establishing time points (x-axis), figure 1
% x1=5*cos(2*pi*500*time);
% x2=5*cos(2*pi*1200*time+0.25*pi);
% x3=5*cos(2*pi*1800*time+0.5*pi);
% x=x1+x2+x3; % Sum of three signals
 
%plot(time,x)
% xlabel('Time (s)') % x-axis label
% ylabel('Amplitude') % y-axis label
% title('Sum of Sampled Signals') % title
for i = 1:length(n)
%figure;
x1(i)=5*cos(2*pi*500*time(i));
x2(i)=5*cos(2*pi*1200*time(i)+0.25*pi);
x3(i)=5*cos(2*pi*1800*time(i)+0.5*pi);
x(i)=x1(i)+x2(i)+x3(i); % Sum of three signals
X=fftshift(fft(x(1:i),nfft)); % FFT of sum of 3 signals
plot(nf,abs(X))
end 
xlabel('frequency(Hz)') % x-axis label
ylabel('Magnitude') % y-axis label
title('Frequency Response') % title 

[Connor Roche]

is there any way to not use "fft" or "fftshift" in this code?