Spectrogram of known frequency signal
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I need to generate a spectrogram for a frequency signal which I constructed by selecting only certain parts of diffrerent sine waves at different frequencies. In other words, I have a signal in the frequency domain but I do not have the time domain corrisponsent to input in
. Can I generate a spectrogram from an already known frequency domain signal?
Walter Roberson on 27 May 2021
If you have a list of frequencies and corresponding amplitudes, then:
If practical, find the greatest common divisor (GCD) between the frequencies. If you can do that, then each frequency will be an integer multiple of the GCD. Divide each frequency by the GCD to get its multiple; call that list of multiples M and the corresponding amplitudes A .
Now create a vector,
temp(M) = A;
So for example if the 7th frequency was 4 times the greatest common divisor, then temp(4) would be assigned the amplitude associated with the 7th frequency.
ix = [0, temp, fliplr(conj(temp))];
time_signal = ifft(ix);
And now you should be able to
spectrogram(time_signal, , , , GCD)