OWON VDS Series - Manual (Page 26)

To select the FFT window
There are four FFT windows. Each one has trade-offs between frequency resolution and magnitude accuracy. What you want to measure and
your source signal characteristics help you to determine which window to use. Use the following guidelines to select the best window.
Type Characteristics Window
Hamming
Better solution for magnitude than Rectangle,
and good for frequency as well. It has slightly
better frequency resolution than Hanning.
Recommend to use for:
 Sine, periodic and narrow band random
noise.
 Transients or bursts where the signal levels
before and after the event are significantly
different.
Rectangle
Best solution for frequency, worst for magnitude.
Best type for measuring the frequency spectrum
of
non-repetitive signals and measuring
frequency components near DC.
Recommend to use for:
 Transients or bursts, the signal level before
and after the event are nearly equal.
 Equal-amplitude sine waves with
frequencies those are very close.
 Broadband random noise with a relatively
slow varying spectrum.
Blackman
Best solution for magnitude, worst for frequency.
Recommend to use for:
 Single frequency waveforms, to find higher
order harmonics.
Hanning
Good for magnitude, but poorer frequency
resolution than Hamming.
Recommend to use for:
 Sine, periodic and narrow band random
noise.
 Transients or bursts where the signal levels
before and after the event are significantly
different.
The figures below are examples for measuring sine wave with a frequency of 1kHz under the selection of four different windows for FFT:
Figure: Hamming window
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