NI-DSP Analysis VI Reference Overview Chapter 1
Part 3: NI-DSP Function Reference 1-8 NI-DSP SRM for LabVIEW for Windows
Window definitions used in National Instruments analysis libraries are designed in such a way that the window
operations in the time domain are exactly equivalent to the operations of the same window in the frequency domain.
To meet this requirement, the windows are not symmetrical in the time domain, that is:
w[0] ≠ w[N-1] (3)
where N is the window length. They are usually symmetrical in the frequency domain, however. For example, the
Hamming window definition uses the formula:
w[i] = 0.54 - 0.46 cos(2πi/N) (4)
Other manufacturers may use a slightly different definition, such as:
w[i] = 0.54 - 0.46 cos(2πi/N-1) (5)
The difference is small if N is large.
Formula 4 is not symmetrical in the time domain, but it ensures that the time domain windowing is equivalent to the
frequency domain windowing. If you want to have a perfectly symmetrical sequence in the time domain, you must
write your own windowing function using formula 5.
The choice of a window depends on the application. For most applications, the Hamming or Hanning windows
deliver good performance.