Choosing the length of a signal when calculating the FFT

1. How do I choose my FFT size?
2. What is length of signal in FFT?
3. How does FFT length affect the spectrum?
4. What does signal length mean?

How do I choose my FFT size?

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.

What is length of signal in FFT?

The correct size of the FFT lengths for a linear convolution, is Nfft=Lx+Ly−1, where obviously those lengths correspond to the length of your signals x and y.

How does FFT length affect the spectrum?

The selected FFT size directly affects the resolution of the resulting spectra. The number of spectral lines is always 1/2 of the selected FFT size. Thus a 1024 point FFT produces 512 output spectral lines. The frequency resolution of each spectral line is equal to the Sampling Rate divided by the FFT size.

What does signal length mean?

Signal length is either the total number of points the vector containing it has, or if you also have a time points vector, the difference between the last and first time point.