How can I plot 'period' by using fft functoin??

How can I plot 'period' by using fft functoin??

[Mathieu NOE]

hello

maybe you should show what you have tried so far... and then we will help you

tx

Answer 1

[Chunru]

Fs = 1000;            % Sampling frequency                    
T = 1/Fs;             % Sampling period       
L = 1500;             % Length of signal
t = (0:L-1)*T;        % Time vector

S = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t);

X = S + 2*randn(size(t));

Y = fft(X);

% Compute the two-sided spectrum P2. Then compute the single-sided spectrum P1 
% based on P2 and the even-valued signal length L.

P2 = abs(Y/L);
P1 = P2(1:L/2+1);
P1(2:end-1) = 2*P1(2:end-1);

% Define the frequency domain f and plot the single-sided amplitude spectrum P1. 
% The amplitudes are not exactly at 0.7 and 1, as expected, because of the added 
% noise. On average, longer signals produce better frequency approximations.

figure
f = Fs*(0:(L/2))/L;
plot(f,P1) 
title('Single-Sided Amplitude Spectrum of X(t)')
xlabel('f (Hz)')
ylabel('|P1(f)|')

%% Plot the spectrum vs period (this can be done but rarely used)
figure
f = Fs*(0:(L/2))/L;
plot(1./f,P1) 
title('Single-Sided Amplitude Spectrum of X(t)')
xlabel('T - period (sec)')
ylabel('|P1(T)|')
xlim([0 0.2])