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FFT help needed

Started by tanoli_hacker March 30, 2007
AOA
I am stuck with a problem sir n need your immediate help. I get an
EEG signal from net and try to process it.

Q. What is the result of taking FFT of a signal?

Q. What is on horizental and vertical axis when we plot result from
FFT?

I said that on x axis it is frequency in hertz but i was opposed and
said that we have to do something more to the result of FFT to get
frequency in hertz. What i have to do with this to get frequency in
hertz. And also tell me how to interpret the resultf of FFT and how
to visualize the frequencies.

These are some prolems which i have tried my best to solve but was
unable and i aslo asked from the people here in university but no
one exactly knows about it. Now you are requested to plzzzzzz check
these things and tell me about it.
Looking to hear from you ASAP.

Best Regards

Uzair Nazir Tanoli
close all;clear;clc

% Parameters---------------------------
N = 512; % number of points for FFT
dt = 0.005; % sampling time, 1/Fs where Fs is sampling frequency
T = 1; % final time

% Data---------------------------------
t = 0:dt:1; % time data
y = sin(2*pi*30*t)+4*sin(2*pi*70*t); % signal
Y = fft(y,N);

% Post processing----------------------
Pyy = 2*abs(Y) / min(N,T/dt);
f = 1/dt*(0:N/2)/N;
figure;
plot(f,Pyy(1:N/2+1))
title('Frequency content of signal')
xlabel('frequency (Hz)')
ylabel('amplitude of each mode')
grid on

% End----------------------------------