I am simply sending a signal from a function generator, split it into two signals, and then send it into two inputs of an oscilloscope which can interface with my PC. I take the FFT of these two signal inputs and see a noise floor around 1e-7 V, but how can I know if this is the right noise floor value?
If I was to send this same signal, duplicate it again, and input it into this oscilloscope. Cross-correlate these two signals in the frequency domain (multiply with a conjugate), then I should observe a lower noise floor as the noise of the systems (function generator, oscilloscope, wires) should cancel out. But I observe a noise floor of around 1e-14 V which is really low... so I am not sure how to validate this, if it works or not.
edit: reworded my question better with right terminologies