What is the unit of frequency in a spectrogram- Hertz or frequency bins?
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Is it Frequency in hertz or in bins? If in bins, how do you convert it to Hertz?
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dpb
2014-3-8
The latter and by using your sampling frequency and sample time.
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dpb
2014-3-8
Again I reiterate -- fft "knows nuthink" about frequency, it's simply the two-sided DFT of the input in a vector of length N. If you want to plot against a real frequency, you have to create the frequency vector associated with your sampling frequency and sample length. See
doc fft % which shows an example of a PSD and a plot.
Note especially that the DC component is at point N/2+1. Also see
doc fftshift
OTOH, since you used the optional input Fs sample frequency to spectrogram, it normalized the plot to that and handles the display of the single-sided plot automagically for you as a convenience of being a higher-level routine than fft
Read the documentation more carefully and in full on the two specifically and the background information on the FFT in general as well as slowing down and really thinking about what it is that you're actually plotting and computing.
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