User Manual

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21.3 Reference
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The aliasing artifacts are removed beautifully. The spectral
waveform in the graph is the actual spectrum.
Because of the rapid decay characteristic of the anti-aliasing
filter, the square wave edges exhibit ringing.
(2) When an anti-aliasing filter is used.
■ Window processing
Fourier transform is defined as the integration from negative infinity to
positive infinity, but in actual measurement this calculation is not possible.
Therefore only a limited segment of the continuous signal is taken for
processing. This is called window processing.
The FFT algorithm assumes that the data of that limited segment are
repeated and defines the input signal using a periodic function for determining
the frequency spectrum.
Depending on the phase at the start and end of the stored waveform, there
may be a difference between the waveform as calculated by FFT processing
and the actual input waveform.