On Thu, Apr 22, 2010 at 12:19:27AM +0200, Arnold Krille wrote:
> Attached is a small python script that generates some sinus data at 0.5, 0.49
Well done !! This is how you learn and understand things.
> Sounds strange, especially when you see the perceived amplitude-modulation for
The 'amplitude modulation' is an artefact of looking at a
graphical interpretation that doesn't do antialising. It's
the sum of f=0.49 and f=0.51. When the latter is removed,
the 'amplitude modulation' disappears.
> It is also clear, why f=0.5, phase=0 shows an amplitude of 2: All the
For f=FS/2 the alias and the original are the same except
that the alias has the imaginary 'sine' part inverted (by
symmetry). So the 'cosine' part (the one where the peaks
of the waveform coincide with the samples) is doubled, while
the 'sine' part (samples at zero crossings) gets cancelled.
O tu, che porte, correndo si ?
E guerra e morte !
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