MATLAB: Finding time points/intervals when frequency of the signal is about exact value

frequencysignal processingSignal Processing Toolboxtime series

I would like to find at what time frequency of my signal is about 2 Hz. I know how to do fft of my signal but it does not let me find corresponding point in time. Do you have any idea how to do it?

Best Answer

http://www.mathworks.com/help/signal/ref/spectrogram.html

and look at Output Arguments.

Search the normalized frequencies output, w, for the one closest to your target frequency. That gives you a row offset into s. Search that row of s for the maximum absolute value. Index the column number into the time output, t, to get the time of the midpoint of that window.

At least that's what I figure from the documentation.

Related Solutions

MATLAB: Fft of a 2 simple cos functions

Replace the following line:

   f=(0:nfft/2-1)*Fs/nfft/2;

with:

   f=(0:nfft/2-1)*Fs/nfft;

MATLAB: Usinf fft shift i need only to display the positive part of the spectrum

Try this:

fs=1e5; %Sampling Frequency
t=0:1/(fs):0.001; %Time at which signal displays
%First,generating a signal
f=1e4;%Signal is 10kHz
Fn = f/2;                                                               % Nyquist Freqency (Added)
amp_signal=1;
signal=amp_signal*(sin(2*pi*f*t));
L = length(signal);                                                     % Added
%Frequency Domain of transmitted signal
transmited_signal_fft=fft(signal);
f_axis = linspace(0, 1, fix(L/2)+1)*Fn;                                 % Changed

Iv = 1:length(f_axis);                                                  % Index Vector (Added)
% % transmited_signal_fft=fftshift(transmited_signal_fft);              % (Commented-Out)
% % f_axis=linspace(-fs/2,fs/2,length(transmited_signal_fft));          % (Commented-Out)
%Plotting Signal
figure;
subplot(2,1,1);
plot(t,signal);
grid on;
title('Transmitted signal in time domain')
%Display transmitted signal in frequency domain
subplot(2,1,2);
plot(f_axis, 2*abs(transmited_signal_fft(Iv))/L);                       % Changed
grid on;
title('Transmitted signal in frequency domain')

See this version of the documentation for details: fft (link).

Best Answer

Related Solutions

MATLAB: Fft of a 2 simple cos functions

MATLAB: Usinf fft shift i need only to display the positive part of the spectrum

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