SIRIUS
®
TECHNICAL REFERENCE MANUAL
Sampling and digital filter
Example
Legend for illustration “Sampling and digital filter”, from left to right:
● f
f
: Filter frequency: e.g. 800 Hz
● f
n
: Nyquist frequency: e.g. 1 kHz
● f
f2
: f
s
-f
f
= 1.2 kHz
● f
s
: Sampling frequency: e.g. 2 kHz
Sampled Signal: Since we have a sampling frequency of 2 kHz all signals over 1 kHz are folded back to
the Nyquist band (due to aliasing) when they are sampled by the AD converter (dashed lines in
Illustration “Sampling and Digital Filter”). Thus the Sampled Signal will already contain the wrong signal
components.
The digital filter will now attenuate all frequencies of the Sampled Signal (which already contains the
aliased signals) that are higher than 800 Hz.
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