- Time Response: In designing an anti-aliasing filter, there is a temptation to have it's
attenuation roll-off extremely quickly. The way to achieve this is to increase the order
of the filter (see the previous discussion of filter order). A so-called brick-wall filter
(one with infinitely high order), however, causes a sinc function time response that
decays proportionally to 1/t. What this means is that an extremely high order filter that
eliminates all signals above the cutoff frequency will cause signals that change rapidly
to ring on for a long time. A very undesirable effect.
- Phase Distortion / Time delay: Most analog filters have a non-linear phase response.
This a problem since non-linear phase causes an unequal time (group) delay as a
function of frequency. The higher frequency signals will arrive later than low frequency
signals. This can especially be a problem when multiple sensor outputs are compared
such as when using a microphone array.
- Amplitude Distortion: By definition, the filter will modify the frequency structure of
the sensor signal which is usually not desired
Thu Oct 17 11:25:23 PDT 1996