# Frequence of the signal

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fatimah 2011 年 12 月 13 日
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 :"(
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Jan 2011 年 12 月 13 日
Who is plazzzzzze ?

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### 回答 (1 件)

Paulo Silva 2011 年 12 月 13 日
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)
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fatimah 2011 年 12 月 15 日
Elige Grant
&&
Paulo Silva
Thank you for cooperation :)
I am trying to do my best to finish my job

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