Frequence of the signal

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fatimah
fatimah on 13 Dec 2011
Hi , How I can calculate frequence of the signal in the matlab ?? Is there any function do that in matlab ?? can you give me sample example to do that .. Help me plazzzzze :"(
  4 Comments
Jan
Jan on 13 Dec 2011
Who is plazzzzzze ?

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Answers (1)

Paulo Silva
Paulo Silva on 13 Dec 2011
From the MATLAB documentation of the fft function:
Fs = 1000; % Sampling frequency
T = 1/Fs; % Sample time
L = 1000; % Length of signal
t = (0:L-1)*T; % Time vector
% Sum of a 50 Hz sinusoid and a 120 Hz sinusoid
x = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t);
y = x + 2*randn(size(t)); % Sinusoids plus noise
plot(Fs*t(1:50),y(1:50))
title('Signal Corrupted with Zero-Mean Random Noise')
xlabel('time (milliseconds)')
NFFT = 2^nextpow2(L); % Next power of 2 from length of y
Y = fft(y,NFFT)/L;
f = Fs/2*linspace(0,1,NFFT/2+1);
% Plot single-sided amplitude spectrum.
plot(f,2*abs(Y(1:NFFT/2+1)))
title('Single-Sided Amplitude Spectrum of y(t)')
xlabel('Frequency (Hz)')
ylabel('|Y(f)|')
%I added the next lines to find the value
%find maximum value, it should be the fundamental frequency (approximated)
[C,I]=max(2*abs(Y(1:NFFT/2+1)))
f(I)
  6 Comments
fatimah
fatimah on 15 Dec 2011
Elige Grant
&&
Paulo Silva
Thank you for cooperation :)
I am trying to do my best to finish my job

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