Resolution

FFT size:

Number of data point in each FFT block or subseries. The length must be a power of two and cannot exceed the total number of data points

Number of frequencies:

Is half of the FFT size

FFT duration:

Gives the length of the FFT analysis in seconds

Frequency interval:

The difference between two discrete adjacent frequencies. If manually changed, the value is automatically adjusted to the nearest possible value (function of time step and FFT size)