Frequence of the signal

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fatimah
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 :"(
  4 件のコメント
fatimah
fatimah 2011 年 12 月 13 日
I am trying to find the frequency spectrum of signal.
Thank you for help
Jan
Jan 2011 年 12 月 13 日
Who is plazzzzzze ?

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回答 (1 件)

Paulo Silva
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)
  6 件のコメント
Paulo Silva
Paulo Silva 2011 年 12 月 13 日
1- Find the peaks (findpeaks function from S.P. toolbox or similar code)
2- Find the time T between two of those peaks
3- F=1/T
fatimah
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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