The system samples analog input and then conduct FFT on the samples and then display the spectrum. Currently, the issue is the displayed spectrum line position is keeping shift between each scan. After examining the whole system, I found all the components in the system are consistency except the sample rate which varies between 9B~10B, but it always satisfies the Nyquist sampling rate(2B). My question is whether the unstable sample rate may lead to the frequency shift?
My question is whether the unstable sample rate may lead to the frequency shift?
Since the frequency bins in the FFT are proportional to the sampling rate, if you change the sampling rate, you change the frequency of those bins. If you know what the sampling rate is on every particular data set, you can resample it to be consistent between all of them.
That 9bandwidth to 10bandwidth variation will cause 10% spreading of the spectral lines.
If you have 100,000 Hz Nyquist, and you expect a clean frequency line at 25,000 Hz, expect the 25,000 Hz to be 2,500 Hz wide.
If you gather 0.1 second of samples, you can expect 10 Hz frequency bins.
Thus 2,500 Hz line spreading should be very observable.