No aliasing occurs due to use of anti-aliasing
filter. However, the time-axis waveform does not appear as
a complete rectangular wave because the filter does not pass high
frequency components and thus distorts the waveform.
Fig. 3-9a
Without an anti-aliasing filter, the time-axis waveform
appears to be the original rectangular wave. However, aliasing
appears on a result of FFT processing showing frequency components
that actually do not exist.
