FFT of white noise with different sampling rate

1. How does sample rate affect FFT?
2. Does sampling rate affect SNR?
3. How do you choose a sampling frequency in FFT?
4. Does sample rate affect noise?

How does sample rate affect FFT?

The amplitude of the DFT (FFT) is proportional to the number of samples. Therefore, if you sample for twice as long at the same sampling frequency, or if you sample for the same duraiton but twice as fast, you will have twice as many data points, and the DFT amplitude will be twice as large. See examples below.

Does sampling rate affect SNR?

Noise bandwidth decrease, the output noise energy reduce and the output SNR increase with the sampling rate increasing. So, we can obtain high SNR by increasing the sampling rate.

How do you choose a sampling frequency in FFT?

The frequency resolution is equal to the sampling frequency divided by FFT size. For example, an FFT of size 256 of a signal sampled at 8000Hz will have a frequency resolution of 31.25Hz. If the signal is a sine wave of 110 Hz, the ideal FFT would show a sharp peak at 110Hz.

Does sample rate affect noise?

There are several situations where an increased sampling rate does indeed increase the noise level, due to increased bandwidth of the sampling system or increase of sampling noise from the sampling system for example.