What is the relationship between the fs (sampling frequency) and the amplitude of the FFT-function output in matlab? As the amplitude of the FFT output changes as the sampling frequency is changed.
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There is a relationship between length of the input signal and the FFT output, not the sampling rate.
Fs = 1000; t1 = 0:0.001:1-0.001; % 1000 samples t2 = 0:0.001:0.1-0.001; % 100 samples x1 = cos(2*pi*100*t1); x2 = cos(2*pi*100*t2); xdft1 = fft(x1); xdft2 = fft(x2); subplot(211) plot(abs(xdft1)) subplot(212) plot(abs(xdft2))
However, if you compute the power spectral density, using something like periodogram(), then the sampling frequency will come into play in scaling the PSD estimate.
Of course, depending on how you sampled the signal (the length and sampling frequency), you may have situations where the frequency does not fall directly on a DFT bin, and the can affect the amplitude.